Dissertations / Theses on the topic 'Baryons – Mesons'

The purpose of this thesis has been to study the S=-1 meson-baryon interaction in S-wave employing an effective chiral SU(3) lagrangian up to NLO and implementing unitarization in coupled channels. Such a study requires fixing the NLO coefficients of the lagrangian which are not well established yet. In general, the low energy constants of an effective lagrangian are obtained from fitting procedures to the experimental available data. These parameters have been constrained to a large set of experimental K^- p scattering data into πΣ,K ̅N, πΛ channels, to γ, R_n and R_c branching ratios, and to the precise SIDDHARTA value of the energy shift and width of kaonic hydrogen. The novelty of our work is the inclusion of the scattering data from K^- p⟶K^+ Ξ^-,K^0 Ξ^0 reactions in the fitting procedure, since they become especially sensitive to higher order terms, as they cannot proceed with the WT term of the lagrangian, except indirectly via unitarization contributions. We have paid a special attention to the effects that a systematic inclusion in the lagrangian of the NLO and Born terms has on the low energy constants, particularly on the NLO coefficients. The main difference among the models we get from the fits is reflected in the isospin components of the total cross sections of the reactions we study. To check the reliavility of these models, we have performed new fits which take into account data from isospin filtering reactions. The stability and accuracy of the parameters have been tested by including phenomenological resonant contributions to the scattering amplitudes of the reactions that are especially sensitive to the NLO corrections. These resonant terms have been useful to reach better agreement with the experimental data. In order to explore other processes that take place at higher energies and can provide more information of the NLO parameters, we have studied the Λ_b decay into states containing a J/ψ and meson-baryon pairs. Furthermore, the Λ_b⟶J/ψ ηΛ process has allowed us to study the implications of observing a possible strange partner of the hidden charm pentaquark state P_c (4450). The conclusions and analysis of each chapter are summarized below. The second chapter is devoted to study the role played by NLO and Born terms, as well as the relevance of certain reactions in obtaining a more reliable parametrization for the NLO coefficients. We started by comparing different fitting procedures consisting of unitarized calculations employing a kernel in which we include or not the NLO term and which take into account or not the scattering data of the K^- p⟶KΞ reactions. From the results of all these combinations, and particularly from the successful reproduction of the experimental data reached by the WT+NLO model, we have shown for the first time that the NLO order terms of the chiral Lagrangian are absolutely necessary to reproduce the K^- p⟶KΞ reaction data. In this way, the sensitivity of the NLO lagrangian to such reactions has been clearly established. Given this sensitivity and the fact that the existing K^- p⟶KΞ scattering data are limited and suffer from large uncertainty, more accurate data are required before giving a more definitive answer about the values of the NLO coefficients. Next, contrary to the assumption we made about the little effect of the Born terms in the earlier stage, we have proved that they become non-negligible in the K^- p⟶KΞ reactions. The parametrization of the new fit (WT+NLO+Born) has confirmed the expectations of obtaining significant changes in the NLO coefficients compared to those of the WT+NLO model. Despite this, we do not get any improvement neither in accuracy of the parameters nor in the χ_(d.o.f)^2. This fact has led us to an interesting finding that allows us to understand how such different parametrization could give so similar agreement with the experimental data: the inclusion or non inclusion of the Born terms can seriously modify the isospin decomposition of the K^- p⟶KΞ cross sections due to their sensitivity to the higher order terms. Such differences in the isospin components point to the need of constraining the models with experimental data from reactions that proceed through I=0 or I=1, thus providing more reliable parameters of the meson-baryon lagrangian. Most of the data employed in our fits are coming from antikaon-proton scattering and therefore contain contributions from both isospin I=0 and I=1 components; being the only exceptions the π^0 Σ^0,πΛ channels, which select I=0 and I=1 respectively. We then have widened the number of experimental observables used in the fits including scattering data from K^- p⟶ηΛ,ηΣ^0 reactions, which are of pure isospin 0 and 1 respectively. These efforts culminated in the WT+NLO+Born (η chan) model that, as far as we know, is the only chiral model in the literature which reproduces K^- p scattering data into all possible S=-1 channels with good agreement. Regarding the parametrization related to this model, the inclusion of these new experimental data has been crucial for obtaining a very homogeneous and accurate set of NLO coefficients, as well as natural sized values for all the subtraction constants. This leads us to think that the inclusion of more experimental data from isospin filtering processes could favor more reliable values for the low energy constants. The proposed measurement of the K_L^0 p⟶K^+ Ξ^0 reactions in I=1 with a secondary K_L^0 beam at Jlab would complement the information one can obtain from K^- p scattering data to constrain the theoretical models. We have presented our prediction for this reaction employing some of our models, concluding that, as more contributions are taken into account in the interaction kernel and more data are included in the fit, the predicted values are closer to the only two available experimental points of this reaction. None of these two data points have been used in any fitting procedure. This prediction seems to point out towards the reliability of our parametrizations, particularly the WT+NLO+Born (η chan) one, which we consider our best pure chiral model. In order to improve the description of the experimental K^- p⟶KΞ and K^- p⟶ηΛ scattering data, it is also possible to considerate the inclusion of high-spin resonances in such processes. Since they are the most sensitive reactions to the NLO terms, this could also lead to modifications of the NLO parameters. In this way, we can study the stability and accuracy of the parameters present in the models. This is performed in the third chapter of this thesis. We first allowed for the explicit contribution of the high spin hyperon resonances Σ(2030) and Σ(2250) to the K^- p⟶KΞ amplitudes, aiming at establishing an appropriate amount for the background, which in this work is associated to the chiral contributions, and, hence, obtaining more reliable values of the associated low energy constants. The resonant amplitude has been calculated by applying the Rarita-Schwinger method while the chiral amplitude has been obtained employing a lagrangian with a WT and NLO contribution giving rise to the NLO+RES model. Since the resonant terms introduce an angular dependence in the amplitudes, we also attempt the description of the KΞ differential cross sections. We find the resonant terms to have a double benefit. On the one hand, they allow for a reasonable overall description of the scattering data, including the total and the differential cross sections of the KΞ production reactions. On the other hand, by absorbing certain structures of the cross section, the inclusion of resonant contributions permit finding a more stable solution and therefore more precise values of the low energy constants of the chiral unitary model. Then, we have performed a similar study for WT+NLO+Born (η chan) model, which we consider our best chiral model. In contrast to the study carried out previously, this model has been constrained with additional data (K^- p⟶ηΣ^0,ηΛ cross-section data), meaning that, since the K^- p⟶ηΛ reaction is also very senstive to the NLO terms, the corresponding NLO coefficients are more reliable. This makes the analysis of stability acquire a more decisive character. Aiming for this, we have extended the resonant contributions to the K^- p⟶ηΛ process, particularly we have taken into account the contribution of the Λ(1890) resonance which has also been incorporated to the K^- p⟶KΞ amplitudes, in addition to the Σ(2030) and Σ(2250) resonances. The results obtained confirm the previous findings: there is a notable improvement of the agreement with the experimental data and the parameters take similar values to the ones corresponding to the model without resonances. This stability is specially marked for most of the NLO coefficients. Having proved the effects of the isospin filtering processes on the NLO coefficients, in Chapter 4 we have shown that the Λ_b⟶J/ψ ηΛ decay and, particularly, the Λ_b⟶J/ψ KΞ one provide very valuable information concerning the meson-baryon interaction in the S=-1 and isospin I=0 sector. The dynamics of the reaction, where the light quarks of the Λ_b play a spectator role, is such that it filters I=0 in the final state. This is so because the "u" and "d" quarks in the Λ_b baryon necessarily couple to I=0 and the weak decay favors the b⟶cc ̅s transition, so there is an s-quark at the end of the weak process, which together with the "ud" pair in I=0 gives a total isospin I=0. Thus, these decays may offer complementary information to that obtained from K^- p⟶KΞ scattering data, where both isospin 0 and 1 contributions combine to give the final results. Our study is based on the models WT+NLO (Model 1) and WT+NLO+Born (η chan) (Model 2) developed in this thesis to describe the K^- p scattering. Both models produce quite different invariant mass distributions for the decay of the Λ_b into KΞ and ηΛ states, which are in turn quite different also from phase space, indicating the sensitivity of these processes to the strong internal dynamics. The differences between models are more visible in the Λ_b⟶J/ψ KΞ decay process. The reason stems from the fact that the decay into ηΛ can proceed at tree level, while the selectivity of the Λ_b decay processes producing the J/ψ does not allow the formation of a KΞ pair in a primary step. This is only produced through rescattering of the K ̅N and ηΛ primary components. Thus the Λ_b⟶J/ψ KΞ reaction is directly proportional to the meson-baryon scattering amplitude, concretely to the ηΛ⟶KΞ and K ̅N⟶KΞ components in I=0, which can lead to a marked pattern of interferences. These models also predict sizable differences for the Λ_b decay in the energy region of KΞ and ηΛ production, reflecting that the I=0 component of the meson-baryon interaction, which is the one playing a role in the Λ_b decay processes studied here, is not very well constrained by the fitting to K^- p⟶KΞ data. The recent finding of two structures in the J/ψ p invariant mass distribution of the Λ_b⟶J/ψ K^- p decay, associated to two pentaquark states, together with its plausible explanation in terms of a previously predicted hidden charm baryon molecular state, prompted us to study the decay of the Λ_b into J/ψ ηΛ final states. The Λ_b⟶J/ψ ηΛ decay, being a coupled channel of the Λ_b⟶J/ψ K^- p one, will occur with similar strength and one could observe, in the J/ψ Λ invariant mass spectrum, possible strange partners of the two non-strange pentaquark states reported by LHCb collaboration. We recall that when the hidden charm N^* resonances were theoretically predicted as molecular states in several unitary approaches, some partner hidden charm strange Λ^* states were also found. We have taken advantage of this finding and have predicted what signal should one of these states leave in the ηΛ and J/ψ Λ invariant mass distributions of the Λ_b⟶J/ψ ηΛ reaction. We have found that, taking the values of the couplings of the hidden charm Λ^* state to the D ̅^(0*) Ξ_c^' and J/ψ Λ channels obtained in the unitary approaches, one should observe clear and sizable peaks in the J/ψ Λ mass distribution of the Λ_b⟶J/ψ ηΛ decay. We have studied the dependence of our results on reasonable changes in the parameters of the models involved in our description of the process, as well as on the unknown properties of the speculated hidden charm strange pentaquark. We have observed that, while there appear changes in the position of the peak and in the shapes of the distributions, a resonance signal in the J/ψ Λ invariant mass spectrum is clearly seen in all the cases. This gives us confidence that such an experiment should result into a successful proof of the existence of this new state and we encourage the experimental analysis of this decay channel, for which our theoretical study predicts a similar strength than for the Λ_b⟶J/ψ K^- p reaction already analyzed by LHCb. The present work is our first step toward building a more complete chiral model in S=-1 sector to help analyze the forthcoming more precise data in the KΞ production. In addition, the findings and the features observed in this study indicate that the actual measurement of the complementary observables analyzed here would provide valuable information, novel so far, that would enrich our knowledge of the meson-baryon interaction and help us make progress in our understanding of hadron dynamics.
En esta tesis se ha estudiado la interacción mesón-barión en onda S en el sector de extrañeza -1 empleando un lagrangiano de SU(3) hasta segundo orden, implementando la unitarización en canales acoplados. La condición indispensable para llevar a cabo un estudio de este tipo, forzosamente, pasa por fijar el valor de los coeficientes presentes en los términos de segundo orden, los cuales no poseen un valor bien determinado. Generalmente, las constantes de baja energía de los lagrangianos efectivos se obtienen mediante procesos de ajuste a los datos experimentales disponibles. Tradicionalmente, en este sector de extrañeza, dichos parámetros se ajustaban a los datos experimentales de la dispersión K^- p a los canales πΣ, K ̅N, πΛ, así como a las razones entre secciones eficaces en el umbral de producción K^- p: γ, R_n y R_c; y a los precisos valores del corrimiento y la anchura parcial del estado 1s del hidrógeno kaónico obtenido por la colaboración SIDDHARTA. Lo novedoso en nuestra tesis es la inclusión de datos experimentales procedentes de la reacción de dispersión K^- p⟶K^+ Ξ^-,K^0 Ξ^0 en los procesos de ajuste. La motivación para ello se debe a la especial sensibilidad de estas reacciones a los términos de órdenes superiores, ya que estas reacciones no proceden de manera directa mediante el término WT que es el dominante a primer orden. A esto se le suma el hecho que las contribuciones que provienen de la redispersión de los canales acoplados no son capaces de reproducir adecuadamente los datos experimentales. Dado lo anterior, nos centramos en estudiar los efectos producidos por la inclusión sistemática en el lagrangiano de los términos de segundo orden ("NLO") y los de Born sobre las constantes de baja energía, particularmente sobre los coeficientes de "NLO". La principal diferencia entre los modelos que se obtienen de los ajustes se refleja en las componentes de isospín de la sección eficaz total de las reacciones que aquí se estudian. Así pues, para comprobar la fiabilidad de estos modelos, se llevaron a cabo nuevos ajustes teniendo en cuenta datos experimentales procedentes de reacciones de filtrado de isospín. Adicionalmente, se han estudiado la estabilidad y la precisión de los parámetros obtenidos de los ajustes añadiendo contribuciones resonantes de manera fenomenológica a aquellas amplitudes de dispersión asociadas a las reacciones que son especialmente sensibles a las correcciones de segundo orden. Debe destacarse que las contribuciones resonantes han proporcionado una mejora del acuerdo entre los modelos teóricos y los datos experimentales. La desintegración de Λ_b dando lugar a estados que contienen una partícula J/ψ junto con un par mesón-barión resulta ser un proceso muy interesante para extraer información sobre los parámetros de "NLO" a energías más altas. Además, el proceso Λ_b⟶J/ψ ηΛ nos ha permitido estudiar las implicaciones que tendría la posible existencia de un homólogo extraño del pentaquark con encanto escondido P_c (4450). Las conclusiones y el análisis de cada capítulo están descritos en los párrafos siguientes. El Capítulo 2 está dedicado al estudio del papel que juegan los términos de "NLO" y los de Born, así como la relevancia de ciertas reacciones para obtener parametrizaciones más fiables de los coeficientes de "NLO". Al principio, comparamos diferentes ajustes que se basaban en cálculos unitarizados empleando núcleos de interacción que incluían o no los términos de "NLO" y para los cuales se tenían en cuenta o no los datos experimentales de la reacción de dispersión K^- p⟶KΞ. Fruto de los resultados obtenidos de todas estas posibles combinaciones, y más particularmente de la excelente reproducción de los datos experimentales lograda por el modelo WT+NLO, se mostró por vez primera que los términos de "NLO" del lagrangiano quiral son absolutamente necesarios para reproducir los datos experimentales de las reacciones K^- p⟶KΞ. De este modo, se evidenció la sensibilidad del segundo orden del lagrangiano a dichas reacciones. Dada esta sensibilidad junto con el hecho que los datos existentes de la reacción de dispersión K^- p⟶KΞ son limitados y que tienen asociada una gran incertidumbre, para poder dar una respuesta definitiva sobre los valores de los parámetros de "NLO" se requerirían datos experimentales más precisos. Después, contrariamente a lo que se asumió a cerca del efecto negligible de los términos de Born, demostramos que estas contribuciones no pueden menospreciarse en las reacciones K^- p⟶KΞ. Las significativas diferencias en los coeficientes de "NLO" entre la nueva parametrización obtenida para el modelo WT+NLO+Born y la que se obtuvo para el modelo WT+NLO confirmaron el hecho anterior. A pesar de esto, no se apreció ninguna mejora en la precisión de los parámetros ni en el χ_(d.o.f)^2. Este resultado nos permitió entender cómo dos parametrizaciones tan diferentes pueden tener una bondad del ajuste tan similar: la inclusión o no de los términos de Born puede modificar notablemente la descomposición en componentes de isospín de la sección eficaz total de la reacción K^- p⟶KΞ debido a su sensibilidad a los términos de orden superior. Tales diferencias entre las componentes de isospín nos llevan a pensar que si nuestros modelos se ajustan a datos experimentales procedentes de reacciones que actúan como selectores de isospín podremos extraer valores más realistas para los parámetros presentes en el lagrangiano. La mayoría de los datos experimentales empleados en nuestros ajustes vienen de la dispersión protón-antikaón y, consecuentemente, contienen contribuciones tanto de componentes de isospín I=0 como de I=1 siendo las únicas excepciones los canales π^0 Σ^0,πΛ, que filtra isospín 0 y 1 respectivamente. Así pues, se decidió ampliar el número de observables empleados en los ajustes añadiendo datos experimentales de las reacciones de dispersión K^- p⟶ηΛ,ηΣ^0, las cuales tienen solamente una única componente de isospín para sus secciones eficaces, i. e., isospín 0 y 1 respectivamente. Todos estos esfuerzos culminaron con la obtención del modelo WT+NLO+Born (η chan) que, hasta donde sabemos, es el único capaz de reproducir razonablemente bien los datos de la dispersión K^- p a todos los posibles canales del sector S=-1. Respecto a los parámetros de este modelo, se puede destacar el papel relevante de estos nuevos datos experimentales a la hora de obtener unos valores muy homogéneos y precisos para las constantes de "NLO" junto con unas constantes de substracción cuyos valores se acercan más a los valores naturales. A la vista de estos resultados, la inclusión en los ajustes de nuevas reacciones donde se filtre el isospín podría favorecer la obtención de valores más realistas para las constantes de baja energía. La propuesta para medir la reacción K_L^0 p⟶K^+ Ξ^0 en I=1 empleando el haz secundario de K_L^0 en Jlab podría suponer una fuente de información complementaria a la dispersión K^- p. Se ha presentado una predicción para esta reacción empleando algunos de nuestros modelos de la cual se concluye que, cuantas más contribuciones se tienen en cuenta en el núcleo de interacción y más datos experimentales se incluyen en los ajustes, más cerca estamos de reproducir los dos únicos puntos disponibles para esta reacción. Hay que remarcar que ninguno de estos puntos se ha utilizado en los ajustes. A la luz de estos resultados, parece que nuestros parámetros toman cada vez valores más confiables, particularmente los del modelo WT+NLO+Born (η chan), al cual consideramos nuestro mejor modelo quiral puro. Con la intención de mejorar la descripción de los datos experimentales de las reacciones K^- p⟶KΞ y K^- p⟶ηΛ, se incluyeron resonancias de spin alto en estos procesos. Como estas reacciones son las más sensibles a los términos de "NLO", este hecho podría inducir modificaciones en los valores de los coeficientes de "NLO". De este modo, podemos estudiar la estabilidad y precisión de los parámetros presentes en los modelos. Este estudio se llevó a cabo en el Capítulo 3. La primera parte de este estudio consistió en la inclusión explícita de los hyperones de spin alto Σ(2030) y Σ(2250) en la amplitud de dispersión K^- p⟶KΞ, con la intención de fijar una contribución quiral con la cual los términos resonantes puedan interferir para reproducir adecuadamente las estructuras mostradas por los datos experimentales sin tener que forzar a los parámetros de "NLO" a tomar valores sobrestimados. Para calcular la amplitud resonante, hemos utilizado el método de Rarita-Schwinger, mientras que la amplitud quiral se ha calculado empleando un lagrangiano con los términos WT y NLO dando lugar a un nuevo modelo, NLO+RES. Como los términos resonantes introducen una dependencia angular en las amplitudes, se decidió aprovechar este hecho para reproducir los datos experimentales de la sección eficaz diferencial con un acuerdo razonable dadas las limitaciones del modelo para ello. De aquí se puede concluir que la inclusión de términos resonantes cumple una doble función. Por un lado, nos permite obtener una mejora global en la descripción de los datos de dispersión, tanto los de las secciones eficaces totales como los de las diferenciales en las reacciones de producción KΞ. Por otro lado, absorbiendo ciertas estructuras de las secciones eficaces, la inclusión de términos resonantes permite encontrar mínimos más estables y, por consiguiente, valores más precisos de las constantes de baja energía del modelo quiral unitario. Seguidamente, realizamos un estudio similar para el modelo WT+NLO+Born (η chan). Comparado con el anterior, este modelo ha sido ajustado a datos experimentales adicionales (datos de las secciones eficaces K^- p⟶ηΣ^0,ηΛ). Como esta última reacción también es sensible a las contribuciones de "NLO", sus correspondientes coeficientes serán más confiables. Esto hace que el estudio de la estabilidad adquiera un carácter más decisivo. Con esta motivación, se han extendido las contribuciones resonantes a los procesos K^- p⟶ηΛ, teniendo en cuenta para este caso particular solo la contribución de la resonancia Λ(1890). Esta última resonancia ha sido también incorporada, junto con las ya empleadas Σ(2030) y Σ(2250), a las amplitudes de dispersión K^- p⟶KΞ. Los resultados obtenidos confirman lo que ya se había observado con anterioridad: hay una notable mejora en la reproducción de los datos experimentales y los parámetros adquieren valores similares a los del correspondiente modelo sin resonancias. Esta estabilidad es especialmente remarcable para la mayoría de los coeficientes de "NLO". Habiendo demostrado los efectos de los procesos que filtran isospín sobre los coeficientes de "NLO", en el Capítulo 4 se muestra que la desintegración Λ_b⟶J/ψ ηΛ y, particularmente, la Λ_b⟶J/ψ KΞ proporcionan una información interesante relativa a la interacción mesón-barión en el sector S=-1 y I=0. La dinámica de esta reacción, en la cual los quarks ligeros que conforman la Λ_b actúan como espectadores, es tal que filtra el I=0 en los estados finales. Esto es así, ya que los quarks "u" y "d" en el barión Λ_b se acoplan necesariamente a isospín 0 y la desintegración débil favorece la transición b⟶cc ̅s; quedando, por lo tanto, un quark "s" al final del proceso débil, el cual tiene isospín 0 que junto al anterior par "ud" darán un isospín total I=0. Así pues, estas desintegraciones podrían ofrecer información complementaria a la que se obtiene de los datos de la reacción de dispersión K^- p⟶KΞ cuyas componentes de isospín I=0 y I=1 se combinan para dar los resultados finales. Basamos nuestro estudio en los modelos WT+NLO (Model 1) y WT+NLO+Born (η chan) (Model 2) que han sido desarrollados en esta tesis para describir la dispersión K^- p. Las distribuciones de masa invariante producidas por ambos modelos son diferentes para las desintegraciones de Λ_b a los estados KΞ y ηΛ, siendo a su vez bastante diferentes respecto al espacio fásico, indicando la sensibilidad de estos procesos a la dinámica interna de la interacción fuerte en los estados finales. La diferencia entre modelos es mucho más apreciable en el proceso de desintegración Λ_b⟶J/ψ KΞ. La razón se deriva del hecho que la desintegración en ηΛ puede proceder de manera directa ("tree level"), mientras que para la desintegración de Λ_b que da lugar a una J/ψ no permite una formación del par KΞ directamente, a no ser que este se produzca vía la redispersión de los componentes primarios K ̅N y ηΛ. Por tanto, la reacción Λ_b⟶J/ψ KΞ es directamente proporcional a la amplitud de dispersión mesón-barión, concretamente a las componentes de I=0 correspondientes a ηΛ⟶KΞ y K ̅N⟶KΞ cuya interferencia puede dar lugar a patrones muy marcados. Estos modelos también predicen diferencias notables para las desintegraciones Λ_b en las regiones de energía donde se producen los pares KΞ y ηΛ, poniendo de manifiesto que la componente de I=0 de la interacción mesón-barión, que es la única posible por provenir de la desintegración Λ_b, no está bien fijada por los ajustes a los datos experimentales de las reacciones K^- p⟶KΞ. Las dos estructuras halladas recientemente en la distribución de masa invariante J/ψ p de la desintegración Λ_b⟶J/ψ K^- p que han sido asociadas a dos estados de pentaquark, con su plausible explicación en términos de un estado molecular con un barión y un par cc ̅, nos llevaron a estudiar la desintegración de la Λ_b en los estados finales J/ψ ηΛ. La desintegración Λ_b⟶J/ψ ηΛ, que puede conectarse en canales acoplados a la desintegración Λ_b⟶J/ψ K^- p, podría tener lugar con la misma intensidad y sería posible observar, en su distribución de masa invariante J/ψ Λ, un posible compañero extraño de los dos estados de pentaquarks observados por la colaboración LHCb. Conviene tener presente que cuando las resonancias N^* de encanto escondido fueron teóricamente predichas como estados moleculares utilizando varios métodos basados en la unitarización, algunos compañeros extraños como los estados Λ_b fueron encontrados. Aprovechando esta información, hemos predicho qué tipo de señal dejarían estos estados en las distribuciones de masa invariante ηΛ y J/ψ Λ de la reacción Λ_b⟶J/ψ ηΛ. Hemos visto que tomando los valores de las constantes de acoplamiento del estado Λ^* de encanto escondido a los canales D ̅^(0*) Ξ_c^' y J/ψ Λ obtenidos por los métodos basados en la unitarización, uno observaría una señal clara y con un apreciable pico en la distribución de masa invariante J/ψ Λ de la desintegración Λ_b⟶J/ψ ηΛ. También se estudió la dependencia de nuestros resultados a cambios razonables en los parámetros que caracterizaban los modelos involucrados en nuestra descripción del proceso, así como la dependencia en las posibles propiedades de dicho pentaquark. En todos los tests que se realizaron, la señal resonante seguía siendo claramente visible en la distribución de masa invariante J/ψ Λ. Esto nos hace pensar que en el caso que se llevara a cabo tal experimento podría dar prueba de la existencia de este nuevo estado. Este trabajo ha sido un primer paso hacia la construcción de un modelo quiral más completo en el sector S=-1 que nos será útil para analizar los venideros datos más precisos de la producción KΞ. Además, los hallazgos y características observados en este estudio indican que la medida de observables analizados aquí proporcionaría una información valiosa, hasta ahora novedosa, que enriquecería nuestro conocimiento de la interacción mesón-barión y nos ayudaría a progresar en la comprensión de la dinámica de los hadrones.

Le but de nos etudes est de construire une theorie unifiee des mesons et des baryons, qui est sensee modeliser la chromodynamique quantique (qcd) dans son regime non-perturbatif. Dans cette these, les mesons sont les champs elementaires et les baryons leurs excitations de type soliton topologique. Le degre d'arbitraire dans la determination du lagrangien effectif peut etre elimine si l'on tient compte de la phenomenologie bien connue du secteur des mesons. Cette derniere nous amene naturellement a considerer un lagrangien effectif contenant les mesons les plus legers , , , a#1, (chapitre i). Les parametres du modele sont determines en ajustant les observables du secteur mesonique. Nous construisons les solutions de type soliton dans le secteur a charge baryonique unite, et nous etudions les proprietes statiques des baryons. Nous avons etudie les interactions statiques entre ces solitons, et montre que des forces attractives ayant la bonne portee apparaissent dans le canal central de l'interaction nn. Ceci est a opposer a tous les calculs precedents effectues a partir du modele de skyrme, qui n'aboutissent qu'a des forces repulsives. Dans le but d'eclaircir le probleme de la masse des baryons dans les modeles ou ces derniers sont consideres comme des solitons topologiques, nous avons evalue la premiere correction quantique a la masse du soliton. Dans le chapitre ii, nous avons montre que cette correction est tres grande dans le cas du modele de skyrme original. Nous avons ensuite montre que les effets quantiques sont moins importants si l'on inclut des termes d'ordre superieur, par exemple un terme d'ordre six dans les derivees du champ du pion. Dans le chapitre iii nous avons etudie la stabilite des solitons topologiques, dans le cadre du systeme. Nous avons montre que les ambiguites existantes dans la litterature concernant ce probleme, disparaissent si le meson est suppose se transformer d'une facon homogene par une rotation du groupe chiral non lineaire. Ainsi nous avons montre que les mesons et jouent un role similaire dans le mecanisme de stabilisation du soliton

We use the nonperturbative techniques of current algebra and PCAC (partial conservation of axial-vector currents) to compute the nonleptonic weak decays K → 2π and 3π, as well as the two-body and nonresonant three-body decays of the charmed D and F(D(s)) mesons. In the case of two-body decays, the constituent quark model is employed to calculate the resulting unphysical meson-meson reduced matrix elements. Using an analogous current algebra - PCAC prescription, the three-body meson decays are expressed in terms of the previously determined two-body amplitudes. We utilize the pole model to extract baryon-baryon reduced matrix elements from the B → B' π and B'γ weak decays, which are then also computed in the constituent quark model. We make predictions for more than sixty decays with essentially no free parameters and, in most cases, find reasonable agreement with the data.

Cette thèse a utilisé la méthode des règles de somme de QCD pour étudier la nature des résonances du charmonium suivantes: Y(3930), Y(4140), X(4350), Y(4260), Y(4360) et Y(4660). Il y a des fortes indications que ces états ont des structures hadroniques non conventionnelles (ou exotiques) lorsque leurs masses respectives et les modes de désintégration observés expérimentalement sont incompatibles avec ce qui est attendu pour l'état conventionnel du charmonium.Le même phénomène se produit dans le secteur du bottomonium, où les nouveaux états Yb(10890) et Yb(11020), observeés récemment pourraient indiquer l'existence de nouveaux états exotiques du bottomonium. De cette façon, on vérifie que l'état Y(4140) peut être décrit soit par une structure moléculaire D*s D*s (0++) ou par une mélange entre les états moléculaires D*s D*s (0++) et D*D* (0++). Les états Y(3930) et X(4350) ne peuvent pas être décrites par les courants moléculaires D*D* (0++) et D*s D*so (1-+), respectivement. On vérifie également que la structure moléculaire psi' f0(980) (1--) réproduit très bien la masse de l'état Y(4660). Une extension naturelle au secteur du bottomonium indique que l'état moléculaire Y' f0(980) est un bon candidat pour l'état Yb(10890). On a également fait une estimation pour les états moléculaires possibles formées par des mésons D et B, ce qui pourra être observé dans des expériences futures au LHC.Une vaste étude, en utilisant le formalisme habituel des règles de somme et aussi le Double Rapport des règles de somme, est fait pour calculer les masses des baryons lourds en QCD. Les estimations pour les masses des baryons avec un (Qqq) et deux (QQq) quarks lourds sont un excellent test pour la capacité de la méthode de règles de somme à prédire les masses des baryons qui n'ont pas encore été observés
The QCD sum rules approach was used to study the nature of the following charmonium resonances: Y(3930), Y(4140), X(4350), Y(4260), Y(4360) and Y(4660). There is strong evidence that these states have a non-conventional (or exotic) hadronic structures since their respective masses and decay channels observed experimentally are inconsistent with expected for a conventional charmonium state. The same phenomenon occurs on the bottomonium sector, where new states like Yb(10890) and Yb(11020) observed recently could indicate the existence of new bottomonium exotic states. In this way, one verifies that the state Y(4140) could be described as a D*s D*s (0++) molecular state or even as a mixture of D*s D*s (0++) and D*D* (0++) molecular states. For the Y(3930) and X(4350) states, both cannot be described as a D*D* (0++) and D*s D*s0 (1−+), respectively. From the sum rule point of view, the Y(4660) state could be described as a ψ' f0(980) (1−−) molecular state. The extension to the bottomonium sector is done in a straightforward way to demonstrate that the Y' f0(980) molecular state is a good candidate for describing the structure of the Yb(10890) state. In the following, one estimates the mass of the exotic Bc-like molecular states using QCD sum rules - these exotic states would correspond to a bound states of D(*) and B(*) mesons. All of these mass predictions could (or not) be checked in a near future experiments at LHC.A large study using the Double Ratio of sum rules approach has been evaluated for the study of the heavy baryon masses in QCD. The obtained results for the baryons with one (Qqq) and two (QQq) heavy quarks will be an excellent test for the capability of the sum rule approach in predicting mass of the baryons which have not yet been observed

Afin de mesurer les durees de vie separees des hadrons beaux neutres et charges, les donnees enregistrees en 1991 et 1992 par le detecteur delphi du lep ont ete analysees. Les hadrons b sont identifies par leur desintegration en j psi, suivi de la desintegration de celui-ci en une paire de muons. Les performances du detecteur permettent de reconstruire avec precision les longueurs de vol des b dans le plan r phi, de meme que leur impulsion par une technique de regroupement de particules en jet, dont le j psi constitue le noyau. Le temps propre est ainsi determine evenement par evenement. L'estimation de la charge des hadrons b repose sur une methode de discrimination entre les particules qu'ils ont generees et celles provenant du processus de fragmentation. Apres selection, 80 evenements permettent de mesurer une duree de vie de 1,20 ps pour les hadrons b neutres et de 1,80 ps pour les b charges, avec une erreur de 0,40 ps dans les deux cas

In this thesis we have studied baryon resonances generated from the dynamical interaction of two hadrons. We are interested on this study as an alternative approach to explain the increasing number of observed charmed states which apparently do not fit into the traditional three quark picture of a baryon. In particular, we study baryon molecules with JP = ½ - which can be formed from the attractive interaction of a pseudoscalar meson (0-) and a ground state baryon (1/2+) in s-wave (L = 0). Therefore our aim is to contribute to the understanding of the observed charm baryon spectra by checking if the dynamical origin can explain those states which are candidates to be a baryon resonance with JP =1/2-. The important feature of our model is the description of the meson-baryon interaction in terms of the t-channel vector meson exchange which is fully solved without any approximation. The first part of the thesis is devoted to study these sort of baryon molecules in free space. In order to learn about the nature of a baryon it is important to study its different types of decays. For this reason, we will calculate the strong decays of dynamically generated resonances into meson-baryon components, as well as the electromagnetic transition of such hadron molecules into the lowest-lying ground states. In the second part of the thesis we have included medium and temperature effects on the formalism to study the properties of the charmed baryon resonant states in hot and dense matter. This will allow us as well to study the properties of charmed mesons (D, D, Ds and Ds) in the nuclear medium which will be simultaneously dressed in the self-consistent calculation for the first time. The behaviour of these mesons will influence the charmonium production whose suppression is connected with the possible formation of quark-gluon plasma at a dense matter and high temperature scenario.
En esta tesis se han estudiado las resonancias bariónicas generadas a partir de la interacción dinámica de dos hadrones. Estamos interesados en este estudio como un enfoque alternativo para explicar el creciente número de estados observados con quark encanto y que aparentemente no encajan en la imagen tradicional de tres quarks de un barión. En particular, se estudian las moléculas de bariones con JP = ½ - que pueden formarse a partir de la interacción atractiva de un mesón pseudoescalar (0-) y un barión del estado fundamental ( 1/2+) en onda s (L = 0). Por tanto, nuestro objetivo es comprobar si el origen dinámico puede explicar aquellos estados que son candidatos a ser una resonancia bariónica con JP =1/2-. La característica importante del modelo es la descripción de la interacción mesón-barión en términos del canal t de intercambio de mesones vectoriales, que está resuelto sin ningún tipo de aproximación.La primera parte de la tesis está dedicada a estudiar este tipo de moléculas en el espacio libre. Con el fin de aprender sobre la naturaleza de un barión es importante estudiar sus diferentes tipos de desintegración. Por esta razón, calculamos las desintegraciones fuertes de las resonancias en canales mesón-barión, así como la transición electromagnética a bariones de estado fundamental.En la segunda parte de la tesis se ha incluido en el formalismo los efectos del medio y de la temperatura para estudiar las propiedades de los estados de bariones encantados en materia caliente y densa. Esto nos permitirá también estudiar las propiedades de los mesones encantados (D, D, Ds y Ds) en el medio nuclear, que serán vestidos autoconsistentemente en el cálculo por primera vez. El comportamiento de estos mesones influirá en la producción de “charmonium”, cuya supresión está relacionada con la posible formación de plasma de quark-gluón en materia densa y caliente.

L'objet de cette these est l'etude de la production des mesons charmes a partir du faisceau de sigma moins a 330 gev/c de l'experience wa89 du cern. Le debut de ce manuscrit est consacre a la presentation du contexte theorique et experimental actuel. Suit une description de l'ensemble du dispositif instrumental de wa89. La recherche et l'obtention des mesons d plus, d moins, d zero, anti d zero, d(2010) plus et d(2010) moins font l'objet de la suite de ce travail. Dans chacun des cas sont detaillees les coupures conduisant aux signaux ainsi que les distributions en xf (variable de feynman) et pt (impulsion transverse). Les sections efficaces de production ont ete estimees grace a un monte-carlo. Les resultats sont en accord avec les predictions de qcd et de pythia. Enfin une tentative prometteuse a ete faite en vue d'observer la production de charme associe

xxvi, 199 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
The abundance of B mesons at B factories opens the door to the search in rare decays for physics outside of the Standard Model. Flavor-changing neutral current transitions proceed only via higher order in the Standard Model, resulting in a b [arrow right] s³y branching fraction of about 3 x 10 -4 , but hypothesized particles could alter the rate significantly. Decays of B mesons that proceed via this electroweak penguin diagram are an interesting example of flavor-changing neutral currents, due to the large number of accessible final states with observables that are sensitive to new processes. This dissertation describes the analyses of such decays B - [arrow right] p ³, B - [arrow right] £ 0 p ³, B - [arrow right] p and B - [arrow right] p using about 350 million B meson pairs recorded by the BABAR detector in the years 2001 through 2006. In addition to the decay rate, the distribution of the invariant mass of the baryon pair is presented, using a method for statistical unfolding. The analysis is the first of these decays at the BABAR experiment and lays the groundwork for future analyses of the branching fractions and angular correlations of b [arrow right] s decays containing A hyperons and other baryons at BABAR or higher luminosity B factories.
Adviser: James E. Brau

Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xv, 133 p.: ill. Includes abstract and vita. Advisor: Richard D. Kass, Dept. of Physics. Includes bibliographical references (p. 132-133).

L'experience graal est consacree a la comprehension de la structure dynamique du nucleon et de ses etats excites, les resonances baryoniques. L'etude experimentale des reactions de photoproduction de mesons sur le nucleon est accomplie a l'aide d'un faisceau de photons polarises et d'un multi-detecteur 4. Le faisceau est produit par retrodiffusion compton de photons laser sur les electrons de 6 gev du synchrotron europeen a grenoble (l'esrf). Cette these porte sur l'analyse des premieres donnees acquises par la collaboration graal. Apres la caracterisation du faisceau et le calcul de la dose de photons etiquetes, l'analyse decrit les techniques d'identification des reactions de photoproduction des mesons 0 et. Les performances du systeme de detection, resolutions et efficacites, sont determinees a partir des mesures experimentales et des simulations. Les prises de donnees realisees en 1997 ont permis d'etudier les reactions p 0p et p p dans une gamme d'energie des photons allant de 550 a 1100 mev. L'analyse complete de ces deux canaux a ete effectuee et des resultats finaux pour la section efficace d/d et l'observable de polarisation ont ete obtenus. L'ensemble des corrections aux donnees ainsi que l'evaluation des erreurs systematiques sont presentes en detail. L'asymetrie faisceau obtenue avec une polarisation lineaire des photons, a ainsi ete mesuree pour la premiere fois dans la production du. La section efficace du meme processus et les mesures obtenues pour la production de 0 ameliorent grandement la precision et la couverture cinematique de la base de donnees existante. Les observables de polarisation sont sensibles a des contributions tres petites, difficiles a discerner dans les mesures de section efficace. Ainsi, le rapport de branchement de la resonance n*(1520) dans le canal a pu etre determine avec une bonne precision: b = / t o t = (0,08 0,01)%. Ces resultats sont selectifs pour les modeles des hadrons et contribuent ainsi a l'amelioration de notre connaissance des baryons et des mesons.

Charmed hadron production has been studied in 225 pb^-1 of data collected with the ZEUS detector in the HERA-II runnning period. Studies were made in the D* → D⁰π → Kππ decay channel to determine the potential for the microvertex detector to improve charm signals. Integrated cross sections were measured for the decays D⁰ → K⁰_sπ⁺ π⁻, D^± → K⁰_s π^±, D^±_s → K⁰s K^± and Lambda^±_c → Lambda⁰π^± in the kinematic region 5< Q² < 1000 GeV², 0.02 < y < 0.7, 1.5 < pT(D,Lambda_c) < 20.0 GeV, -1.6 < pseudorapidity(D, Lambda_c) < 1.6. The D⁰ cross section was additionally measured down to pT(D⁰) > 1.0 GeV. Differential cross sections as a function of Q², x, pT(D) and pseudorapidity(D) were measured for the D⁰, D^±, and D_s^± channels. The measurements were compared to next-to-leading order (NLO) QCD calculations, and good agreement found for all variables in all channels over the measured kinematic region. The strangeness-suppression factor, gamma_s = D_s^±/(D^± + D⁰), was measured and found to be in good agreement with values previously measured at HERA and elsewhere, and with the DJANGOH and RAPGAP Monte Carlo. The ratio of charmed baryons to mesons, Lambda_c^±/(D^± + D⁰), was measured and also found to be in good agreement with Monte Carlo.

O Método do Grupo Ressonante (RGM) é um método utilizado no estudo da interação hádron-hádron, na qual não são desprezados os graus de liberdade internos destas partículas. Nesta dissertação estudaremos os efeitos associados `a interação entre um quark pesado Q com outro leve q no potencial de troca de um gluón chamado de One Gluon Exchange Potencial (OGEP), tradicionalmente obtido a partir de um potencial relativístico de interação do modelos de quarks, fazendo uma expansão em potências de momentos nos espinores constituintes (potencial de Fermi-Breit). Faremos uma aproximação semi-relativística para o quark leve q, enquanto que o quark pesado Q será considerado não-relativístico. Este potencial semi-relativístico será usado no RGM para estudar a interação entre charmônios e nucleons como no caso da interação J/ψ-nucleon.
The Resonating Group Method (RGM) is used in hadron-hadron interactions, when internal degrees of freedom of composite particles can’t be neglected. In this dissertation we shall study the effects associated with the interaction between a heavy quark Q with a light quark q, using the the One Gluon Exchange Potential (OGEP) traditionally obtained from a relativistic interaction potential in the quark model, by an expansion in powers of momentum of the constituent spinors (potential Fermi-Breit). We will make a semi-relativistic approach for light quark q, while the heavy quark Q will be considered non-relativistic. This semi-relativistic potential will be used in the RGM to study the interaction between charmonia and nucleons as the case J/ψ-nucleon interaction.

The first-time measurement of the angular dependence of the beam-helicity asymmetry for $\gamma p \rightarrow pK^{+}K^{-}$ is shown and compared to $\gamma p \rightarrow p\pi^{+}\pi^{-}$. The data obtained were from the CLAS g12 experiment at Jefferson Lab. The experiment utilized a beam of circularly polarized photons with energies between 1.1 and 5.4 GeV incident on an unpolarized liquid hydrogen target, which produced an unprecedented number of strange hadrons in photoproduction. The production mechanism for strange hadrons is not well understood. The beam-helicity asymmetry is a polarization observable that provides information on interfering production mechanisms in the reaction. It is shown that the asymmetry is sensitive to several kinematic variables that are key in modeling the reaction dynamics. Furthermore, the comparison of the beam-helicity asymmetry between the kaon and pion channels serves as a platform for the investigation of flavor dependence. A partial wave analysis on the $pK^{-}$ system is also performed in a search for missing hyperon excitations.

Le plasma de quarks et de gluons est un état de matière obtenu lors de températures et de densités d’énergie extrêmes où les quarks et les gluons sont libres. Cette matière chaude et dense peut être créée dans les collisions d’ions lourds ultra-relativistes. Les mesures des spectres des particules identifiées produites dans des jets représentent un outil majeur permettant d'étudier les propriétés du plasma créé dans les collisions et d'ainsi comprendre les relations entre divers mécanismes contribuant à la production de particules dans ce milieu. Cette thèse présente une analyse des spectres en impulsion transverse des baryons Λ et mésons K0S produits dans des jets chargés lors de collisions Pb–Pb centrales à l'énergie sqrt(sNN) = 2.76 TeV mesurées avec ALICE au LHC. Les résultats sont utilisés pour discuter l'origine de l'augmentation du rapport entre baryons et mésons observée pour la production inclusive des particules dans les collisions d’ions lourds ultra-relativistes
Quark–gluon plasma is a state of matter existing under extreme energy densities and temperatures where quarks and gluons are deconfined. This hot and dense strongly interacting matter can be created in ultra-relativistic heavy-ion collisions. Measurements of spectra of identified particles produced in jets represent a major tool for studying properties of the plasma created in the collisions and for understanding the interplay of various mechanisms which contribute to the particle production in this medium. In this thesis, we present the measurement of the transverse-momentum spectra of Λ baryons and K0S mesons produced in charged jets in central Pb–Pb collisions at the centre-of-mass energy sqrt(sNN) = 2.76 TeV, measured with ALICE at the LHC. The results of the analysis are used to discuss the origin of the enhancement of the baryon-to-meson ratio observed for the inclusive production of light-flavour particles in ultra-relativistic heavy-ion collisions

Dans les collisions d'ions lourds ultra-relativistes (A-A), la matière se trouve dans des conditions extrêmes de densité d'énergie; elle forme un plasma de quarks et de gluons déconfinés. Aux énergies du RHIC et du LHC, le rapport baryon sur méson, tel Λ/K0S, prend des valeurs élevées sur une plage d'impulsions transverses intermédiaires pour les collisions centrales A-A. L'objectif de ce travail est de vérifier si la production accrue de baryons est seulement due à des effets collectifs au cœur du système formé ou s'il existe aussi un impact lié à une fragmentation des partons modifiée par le milieu. À l'aide de corrélations angulaires à deux hadrons, les K0S et Λ produits en association avec un hadron de haut pT (processus durs) sont séparés de ceux issus du milieu thermalisé (processus softs). Les rapports Λ/K0S à relier aux mécanismes durs et softs sont établis; les résultats sont obtenus pour les collisions Pb-Pb à √sNN = 2.76 TeV enregistrées en 2011 avec l'expérience ALICE
In ultrarelativistic heavy-ion collisions, the QCD matter is under extreme conditions of energy density, forming a quark-gluon plasma (QGP), in which quarks and gluons are deconfined. At RHIC and LHC energies, a large baryon-to-meson ratio, like Λ/K0S, was observed within the transverse momentum range 2 < pT < 6 GeV/c for central heavy-ion collisions. The goal of this dissertation is to verify if the baryon-to-meson enhancement is only due to collective effects of the bulk of matter, and if there is also a contribution related to in-medium modifications of parton fragmentation.With two-hadron angular correlations, the K0S and Λ produced in association to an energetic hadron (hard processes) are separated from those originated from the thermalised medium (soft processes). The differential Λ/K0S ratios related to the soft or hard production processes are extracted. The results are obtained for the Pb-Pb collisions at √sNN = 2.76 TeV recorded in 2011 with the ALICE experiment

CBM, une des expériences majeures du nouvel accélérateur FAIR en cours de construction au GSI (Darmstadt), a pour objectif d'explorer le diagramme des phases de la matière nucléaire dans la région des hautes densités baryoniques nettes. Un de ses principaux thèmes de physique est l'étude de la production des particules à charme ouvert dans les collisions d'ions lourds. La mesure directe de ces particules nécessite l'utilisation d'un détecteur de vertex très précis. La présente thèse est une contribution à la conception et au développement de ce détecteur, appelé MVD. Une première partie de la thèse concerne l'évaluation, à l'aide de simulations réalistes, des flots de données à transmettre par les capteurs qui équiperont la première génération du MVD. Les résultats obtenus montrent que les performances attendues des capteurs permettront de mener à bien le programme de physique de CBM. Une deuxième partie porte sur les performances attendues pour la reconstruction des particules à charme ouvert, à travers leur désintégration hadronique, dans les collisions Au+Au. Des simulations détaillées ont permis de démontrer que la reconstruction du méson D+ → π+ π+ K-, par exemple, est faisable avec une efficacité de reconstruction de 2% et un rapport signal/bruit de 1.5. La statistique attendue en deux mois de prises de données a été évaluée à environ 6.9 x 104 mésons D. Dans la dernière partie, il a été montré que cette statistique permettrait d'effectuer des études détaillées du flot elliptique intégré des mésons D. La mesure du flot elliptique différentiel de ces particules requerrait, cependant, des statistiques plus élevées, et donc l'utilisation de capteurs plus performants.

The parity violating weak decay of hyperons offers a valuable means of measuring their polarization, providing insight into the production of strange quarks and the matter they compose. Jefferson Lab’s CLAS collaboration has utilized this property of hyperons, publishing the most precise polarization measurements for the Λ and Σ in both photoproduction and electroproduction to date. In contrast, cascades, which contain two strange quarks, can only be produced through indirect processes and as a result, exhibit low cross sections thus remaining experimentally elusive. At present, there are two aspects in cascade physics where progress has been minimal: characterizing their production mechanism, which lacks theoretical and experimental developments, and observation of the numerous excited cascade resonances that are required to exist by flavor SU(3)F symmetry. However, CLAS data were collected in 2008 with a luminosity of 68 pb−1 using a circularly polarized photon beam with energies up to 5.45 GeV, incident on a liquid hydrogen target. This dataset is, at present, the world’s largest for meson photoproduction in its energy range and provides a unique opportunity to study cascade physics with polarization measurements. The current analysis explores hyperon production through the γp → K+K+Ξ− reaction by providing the first ever determination of spin observables P, Cx and Cz for the cascade. Three of our primary goals are to test the only cascade photoproduction model in existence, examine the underlying processes that give rise to hyperon polarization, and to stimulate future theoretical developments while providing constraints for their parameters. Our research is part of a broader program to understand the production of strange quarks and hadrons with strangeness. The remainder of this document discusses the motivation behind such research, the method of data collection, details of their analysis, and the significance of our results.

This thesis calculates and compares the pion nucleon sigma term with and without the contributions arising from processes that involve decuplet baryons.
Thesis (M.Sc.) -- University of Adelaide, Dept. of Physics and Mathematical Physics, 1996?

Thesis (Ph. D.)--University of Wisconsin--Madison, 1993.
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The distribution of the gluon action density in mesonic systems is investigated at finite temperature. The simulations are performed in pure SU(3) Yang-Mills gauge theory for two temperatures below the deconfinement phase. The action-density isosurfaces display a prolate-spheroid-like shape. The curved width profile of the flux tube is found to be consistent with the prediction of the free bosonic string model at large distances. In the intermediate source separation distance, where the free string picture poorly describes the flux tube width profile, we find the topological characteristics of the flux tube converge and compare favourably with the predictions of the free bosonic string upon reducing the vacuum action towards the classical instanton vacuum. As a byproduct of these calculations, we find the broadening of the QCD flux tube to be independent of the UV filtering at large distances. Our results exhibit a linearly divergent pattern in agreement with the string picture predictions. We investigate the overlap of the ground state meson potential with sets of mesonic-trial wave functions. We construct trial states with non-uniform smearing profiles in the Wilson loop operator at T = 0. The non-uniformly UV-regulated flux-tube operators are found to optimize the overlap with the ground state. The gluon flux distribution of a static three quark system has been revealed at temperatures near the end of the QCD plateau, T/Tc ≈ 0.8, and another just before the deconfinement point, T/Tc ≈ 0.9. The flux distributions at short distance separations between the quarks display an action-density profile consistent with a rounded filled Δ shape iso-surface. However the Δ shape action iso-surface distributions are found to persist even at large inter-quark separations. The action density distribution in the quark plane exhibits a nonuniform pattern for all quark separations considered. We systematically measure and compare the main aspects of the profile of the flux distribution at the two considered temperature scales for three sets of isosceles triangle quark configurations. The radii, amplitudes and rate of change of the width of the flux distribution are found to reverse their behavior as the temperature increases from the end of the QCD plateau towards the deconfinement point. Remarkably, we find the mean square width of the flux distribution shrinks and localizes for quark separations larger than 1.0 fm at T/Tc ≈ 0.8 which results in an identifiable Y-shaped radius profile. Near the deconfinement point, the action-density delocalizes and the width broadens linearly with the quark separation at large quark separations. We present a method to include the thermal effects into the junction width of the baryonic string model. The profile of the baryonic gluonic distribution is compared with the width of the string picture’s junction fluctuations. The comparison reveals that the best fits to the junction fluctuations of the baryonic string are near the Fermat point of the triangle made up by the quarks. This result supports the underlying picture of Y-shaped string-like flux tubes connected at a junction.
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2011

We examined strong interactions in the low-energy regime in terms of two complementary non-perturbative approaches: the interplay of large-N_c QCD and chiral perturbation theory was studied. While the expansion in the parameter 1/N_c is based on quark and gluon degrees of freedom, chiral perturbation theory uses hadrons as effective degrees of freedom. The focus of our work was the investigation of mesons and baryons composed from up-, down- and strange quarks. We used the chiral SU(3) Lagrangian with (J^P = 1/2^+)- and (J^P = 3/2^+)-baryon ground states as building blocks. In the SU(3)-flavour limit the latter form an octet and a decuplet, respectively. Studies in chiral perturbation theory hold a challenge: the chiral Lagrangian consists of an infinite number of terms. The treatment of low-energy QCD physics via a perturbation theory requires the ordering of these terms according to their relevance. We used the interplay between large-N_c QCD and chiral perturbation theory to shed light on the structure of the chiral Lagrangian. In the limit of large-N_c the low-energy parameters of the chiral Lagrangian are correlated. For instance the masses of the two baryon multiplets turn degenerate in the SU(3)-flavour limit. This serves as the starting point of our investigations. In this work we analysed the time-ordered product of two scalar and two vector currents in the baryon ground state. The examination of these matrix elements at large-N_c was compared to corresponding results derived in chiral perturbation theory. From this we obtained sum rules for some low-energy parameters of the chiral Lagrangian. The results for the vector correlation function were used to constrain a phenomenological interaction of light vector mesons with the baryon ground states. In the second part of this thesis we addressed a formal problem which arises in a partial wave decomposition of reaction amplitudes for particles with non-vanishing spin. In particular we considered the vector meson photoproduction off the nucleon as it is currently studied by e.g. Jude (2015), Wilson (2015) or Sokhoyan (2015). A decomposition of on-shell production amplitudes into covariant partial wave amplitudes which are both free from kinematical constraints and compatible with the microcausality condition was achieved. A Mathematica code using the FeynCalc package was written and applied to some tree-level contact terms and s-, u- and t-channel processes.

M.Sc. (Physics)
The differential cross-section for p(e, e¡ä¦Ø)p has been studied at Q2 ¡« 5.5 (GeV/c)2. Here Q2 represents the four momentum squared of the virtual photon in the excitation of baryonic resonances by an electron projectile. The excitation cross-section for the baryonic resonances and their de-excitation rates and channels provides information on the underlying structure of QCD. The selection of the ¦Ø decay channel constrains the particular baryonic resonances that contribute to the measured cross-section. A significant aspect of the data presented from W = 1.72 GeV to W = 1.92 GeV is that the Q2 falls in the region where the transition from non-pertubative processes characterised by constituent quarks dominate to the regime where the hard processes are expected to play an increasing important role. This is therefore an interesting region to acquire further data. In order to extract the ¦Ø-meson differential cross section from the JLAB data, the data was compared to a full Monte Carlo simulation of the detector based on events generated for omega production in a way that the production cross section was varied to achieve a match to the data. The binning selected for this procedure takes into account the measure of robustness of the stripping of the ¦Ø peak from the multi-pion background as well as the statistics in the measured data and the Monte Carlo simulation of the signal and background physics [1]. An error estimation technique for the cross section was based on determining the dependence via the Monte Carlo simulation of the extracted cross section parameters on the experimental set-up (including parameters for the spectrometer, target beam geometries and performance). We compare our results with a Regge-based model for hadronic content in the t-channel exchange of a photon in Q2 region of overlap. There is an extension of this data into a completely new region, which is the highest yet measured. The result from the study of baryonic excitation via the ¦Ø channel gives a good correlation between theory and experiment in the overlapped kinematic regime of the used theoretical simulation.

The predictions of the SU(3) flavor symmetry of the strong interactions for the weak decay of charmed baryons and B-mesons are detailed. It is hoped that comparison between these predictions and experiment will shed some light on the underlying dynamics involved in these weak decays. Although only a few decay modes of the charmed baryons and B-mesons have been studied experimentally it is hoped that the next generation of B-factories and even Z-decays at LEP will provide enough events to test these predictions.

The study of matter at extreme densities has been a major focus in theoretical physics in the last half-century. The wide spectrum of information that the field produces provides an invaluable contribution to our knowledge of the world in which we live. Most fascinatingly, the insight into the world around us is provided from knowledge of the intangible, at both the smallest and largest scales in existence. Through the study of nuclear physics we are able to investigate the fundamental construction of individual particles forming nuclei, and with further physics we can extrapolate to neutron stars. The models and concepts put forward by the study of nuclear matter help to solve the mystery of the most powerful interaction in the universe; the strong force. In this study we have investigated a particular state-of-the-art model which is currently used to refine our knowledge of the workings of the strong interaction and the way that it is manifested in both neutron stars and heavy nuclei, although we have placed emphasis on the former for reasons of personal interest. The main body of this work has surrounded an effective field theory known as Quantum Hadrodynamics (QHD) and its variations, as well as an extension to this known as the Quark-Meson Coupling (QMC) model, and variations thereof. We further extend these frameworks to include the possibility of a phase transition from hadronic matter to deconfined quark matter to produce hybrid stars, using various models. We have investigated these pre-existing models to deeply understand how they are justified, and given this information, we have expanded them to incorporate a modern understanding of how the strong interaction is manifest.
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Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2010

The study of matter at extreme densities has been a major focus in theoretical physics in the last half-century. The wide spectrum of information that the field produces provides an invaluable contribution to our knowledge of the world in which we live. Most fascinatingly, the insight into the world around us is provided from knowledge of the intangible, at both the smallest and largest scales in existence. Through the study of nuclear physics we are able to investigate the fundamental construction of individual particles forming nuclei, and with further physics we can extrapolate to neutron stars. The models and concepts put forward by the study of nuclear matter help to solve the mystery of the most powerful interaction in the universe; the strong force. In this study we have investigated a particular state-of-the-art model which is currently used to refine our knowledge of the workings of the strong interaction and the way that it is manifested in both neutron stars and heavy nuclei, although we have placed emphasis on the former for reasons of personal interest. The main body of this work has surrounded an effective field theory known as Quantum Hadrodynamics (QHD) and its variations, as well as an extension to this known as the Quark-Meson Coupling (QMC) model, and variations thereof. We further extend these frameworks to include the possibility of a phase transition from hadronic matter to deconfined quark matter to produce hybrid stars, using various models. We have investigated these pre-existing models to deeply understand how they are justified, and given this information, we have expanded them to incorporate a modern understanding of how the strong interaction is manifest.
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2010

Title: Study of strange particle production in jets with the ALICE experiment at the LHC Author: Vít Kučera Institute: Institute of Particle and Nuclear Physics Supervisors: RNDr. Jana Bielčíková, Ph.D., Nuclear Physics Institute of the CAS; Dr. Christian Kuhn, Institut Pluridisciplinaire Hubert CURIEN Abstract: Quark-gluon plasma is a state of matter existing under extreme energy densities and temperatures where quarks and gluons are deconfined. Complex phenomena occurring in the plasma emerge from the strong interaction of its constituents. This hot and dense strongly interacting matter can be created in ultra-relativistic heavy-ion collisions and its properties can be studied by measuring particles produced in the collisions. Partons produced in hard scatterings interact with the medium which modifies the production of particles in jets. Measurements of spectra of identified particles produced in jets represent an important tool for understanding the interplay of various hadronization mechanisms which contribute to the particle production in the medium created in heavy-ion collisions. In this thesis, we present the measurement of the pT spectra of Λ baryons and K0 S mesons produced in charged jets in central Pb-Pb collisions at the energy √ sNN = 2.76 TeV, measured in the ALICE experiment at the LHC. The...

Lattice QCD affords us the unique opportunity to study the quark structure of hadrons non-perturbatively, through the couplings of quark- field operators to hadron mass-eigenstates. In this thesis, we study cases of flavour wavefunction mixing which are induced by broken flavour-symmetry, with particular consideration for the effects of isospin-breaking and electromagnetism. Namely, we investigate mixing between the octet baryons 0 and , and the pseudoscalar mesons 0, and 0, respectively. The latter scenario introduces the computational challenge of calculating disconnected quark-loop diagrams on the lattice, and we have investigated various techniques for improving the calculation. Additionally, we calculate the masses of the pseudoscalar mesons in lattice QCD+QED simulations, and investigate their behaviour with respect to the flavour-symmetry features observed through the state mixing. Finally, we detail and present lattice determinations of the weak decay constants of the pseudoscalar mesons, with the investigation being informed by the aforementioned state mixing. The results obtained from lattice simulations in each investigation are used to t quark mass and charge extrapolations for the relevant quantities.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2022