Dissertations / Theses: 'Electron-positron annihilation'

1

Moscoso, Michael Douglas. "Electron-positron pair winds /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Avalos, Victor P. "Positron annihilation investigation of electron irradiated silicon." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23204.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Turnock, Graham. "Applications of resummation techniques to electron-positron annihilation." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259591.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Nahn, Steven C. (Steven Christopher) 1968. "Pair production of W bosons in electron positron annihilation." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50334.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Michopoulos, Yanos. "Perturbative QCD studies of multijet structures in electron-positron annihilation." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6702/.

Full text

Abstract:

To investigate the effect in perturbative QCD of multigluon emissions on the transverse momentum distributions of multijet final states in electron-positron annihilation, we use a simplified model based on the approximation that gluons are emitted independently. As a guide to these multigluon emissions, we study the two-gluon contribution in some detail and calculate the Q(_T)-distribution for four-jet events in e(^+)e̅(^-)annihilation, using suitable jet-defining cuts, needed both theoretically, to regularize the soft- and collinear-gluon singularities, as well as experimentally, to group the final-state particles into distinct jets. To ascertain the accuracy of our approximate model, we compare our results with the exact ones, obtained by a Monte Carlo generation of events using the full matrix elements. We find that, for realistic values of the cuts, there is a significant kinematic region of agreement. This agreement and the validity of our model are further elaborated by taking its Abelian QCD limit, calculating distributions in other event shape variables and studying the jet broadening phenomenon. The applicability of our model is also delineated by finding it to be in remarkable structural and numerical agreement with the more exact algorithm of Altarelli et al. Finally, to investigate the effect of higher order and virtual graphs corrections to low order tree-level results, we use our model to calculate the O(a(^2)(_s)) Or-distribution for three-jet events in e(^+)e(^-) annihilation with virtual contributions included. We study the dependence of these corrections on the resolution parameters used to perform the (analytic) cancellation of infrared and collinear singularities between real and virtual graphs and discuss their physical consequences.

APA, Harvard, Vancouver, ISO, and other styles

6

Kwan, Pui-ying Rebecca, and 關珮瑩. "The focusing of the HKU positron beam, and an extended design for incorporating secondary electron-positron annihilation lifetimespectroscopy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36837192.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Kwan, Pui-ying Rebecca. "The focusing of the HKU positron beam, and an extended design for incorporating secondary electron-positron annihilation lifetime spectroscopy." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36837192.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Hawkes, C. M. "A study of the reaction esup(+)esup(-)-musup(+)musup(-)(gamma) at centre of mass energies up to 46.78GeV." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355754.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Ng, Cheuk-kwong, and 吳卓光. "Implementing variable energy positron lifetime spectroscopy based on secondary electron timing from thin carbon foil in transmission geometry." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/207171.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Sterner, Kevin L. "Electron-positron annihilation into photons at √s = 50 to 64 GeV." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40450.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Pu, Anle. "Positron annihilation investigation of vacancies in as-grown and electron irradiated diamonds." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ53210.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Lerner, Leonid. "Tests of quantum chromodynamics in 4-jet production in electron positron annihilation." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306436.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Wechakama, Maneenate. "Multi-messenger constraints and pressure from dark matter annihilation into electron-positron pairs." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2013/6740/.

Full text

Abstract:

Despite striking evidence for the existence of dark matter from astrophysical observations, dark matter has still escaped any direct or indirect detection until today. Therefore a proof for its existence and the revelation of its nature belongs to one of the most intriguing challenges of nowadays cosmology and particle physics. The present work tries to investigate the nature of dark matter through indirect signatures from dark matter annihilation into electron-positron pairs in two different ways, pressure from dark matter annihilation and multi-messenger constraints on the dark matter annihilation cross-section. We focus on dark matter annihilation into electron-positron pairs and adopt a model-independent approach, where all the electrons and positrons are injected with the same initial energy E_0 ~ m_dm*c^2. The propagation of these particles is determined by solving the diffusion-loss equation, considering inverse Compton scattering, synchrotron radiation, Coulomb collisions, bremsstrahlung, and ionization. The first part of this work, focusing on pressure from dark matter annihilation, demonstrates that dark matter annihilation into electron-positron pairs may affect the observed rotation curve by a significant amount. The injection rate of this calculation is constrained by INTEGRAL, Fermi, and H.E.S.S. data. The pressure of the relativistic electron-positron gas is computed from the energy spectrum predicted by the diffusion-loss equation. For values of the gas density and magnetic field that are representative of the Milky Way, it is estimated that the pressure gradients are strong enough to balance gravity in the central parts if E_0 < 1 GeV. The exact value depends somewhat on the astrophysical parameters, and it changes dramatically with the slope of the dark matter density profile. For very steep slopes, as those expected from adiabatic contraction, the rotation curves of spiral galaxies would be affected on kiloparsec scales for most values of E_0. By comparing the predicted rotation curves with observations of dwarf and low surface brightness galaxies, we show that the pressure from dark matter annihilation may improve the agreement between theory and observations in some cases, but it also imposes severe constraints on the model parameters (most notably, the inner slope of the halo density profile, as well as the mass and the annihilation cross-section of dark matter particles into electron-positron pairs). In the second part, upper limits on the dark matter annihilation cross-section into electron-positron pairs are obtained by combining observed data at different wavelengths (from Haslam, WMAP, and Fermi all-sky intensity maps) with recent measurements of the electron and positron spectra in the solar neighbourhood by PAMELA, Fermi, and H.E.S.S.. We consider synchrotron emission in the radio and microwave bands, as well as inverse Compton scattering and final-state radiation at gamma-ray energies. For most values of the model parameters, the tightest constraints are imposed by the local positron spectrum and synchrotron emission from the central regions of the Galaxy. According to our results, the annihilation cross-section should not be higher than the canonical value for a thermal relic if the mass of the dark matter candidate is smaller than a few GeV. In addition, we also derive a stringent upper limit on the inner logarithmic slope α of the density profile of the Milky Way dark matter halo (α < 1 if m_dm < 5 GeV, α < 1.3 if m_dm < 100 GeV and α < 1.5 if m_dm < 2 TeV) assuming a dark matter annihilation cross-section into electron-positron pairs (σv) = 3*10^−26 cm^3 s^−1, as predicted for thermal relics from the big bang.
Trotz vieler Hinweise auf die Existenz von dunkler Materie durch astrophysikalische Beobachtungen hat sich die dunkle Materie bis heute einem direkten oder indirekten Nachweis entzogen. Daher gehrt der Nachweis ihrer Existenz und die Enthüllung ihrer Natur zu einem der faszinierensten Herausforderungen der heutigen Kosmologie und Teilchenphysik. Diese Arbeit versucht die Natur von dunkler Materie durch indirekte Signaturen von der Paarzerstrahlung dunkler Materie in Elektron-Positronpaare auf zwei verschiedene Weisen zu untersuchen, nämlich anhand des Drucks durch die Paarzerstrahlung dunkler Materie und durch Grenzen des Wirkungsquerschnitts für die Paarzerstrahlung dunkler Materie aus verschiedenen Beobachtungsbereichen. Wir konzentrieren uns dabei auf die Zerstrahlung dunkler Materie in Elektron-Positron-Paare und betrachten einen modellunabhängigen Fall, bei dem alle Elektronen und Positronen mit der gleichen Anfangsenergie E_0 ~ m_dm*c^2 injiziert werden. Die Fortbewegung dieser Teilchen wird dabei bestimmt durch die Lösung der Diffusions-Verlust-Gleichung unter Berücksichtigung von inverser Compton-Streuung, Synchrotronstrahlung, Coulomb-Streuung, Bremsstrahlung und Ionisation. Der erste Teil dieser Arbeit zeigt, dass die Zerstrahlung dunkler Materie in Elektron-Positron-Paare die gemessene Rotationskurve signifikant beeinflussen kann. Die Produktionsrate ist dabei durch Daten von INTEGRAL, Fermi und H.E.S.S. begrenzt. Der Druck des relativistischen Elektron-Positron Gases wird aus dem Energiespektrum errechnet, welches durch die Diffusions-Verlust-Gleichung bestimmt ist. Für Werte der Gasdichte und des magnetischen Feldes, welche für unsere Galaxie repräsentativ sind, lässt sich abschätzen, dass für E_0 < 1 GeV die Druckgradienten stark genug sind, um Gravitationskräfte auszugleichen. Die genauen Werte hängen von den verwendeten astrophysikalischen Parametern ab, und sie ändern sich stark mit dem Anstieg des dunklen Materie-Profils. Für sehr große Anstiege, wie sie für adiabatische Kontraktion erwartet werden, werden die Rotationskurven von Spiralgalaxien auf Skalen von einegen Kiloparsek für die meisten Werte von E_0 beeinflusst. Durch Vergleich der erwarteten Rotationskurven mit Beobachtungen von Zwerggalaxien und Galaxien geringer Oberflächentemperatur zeigen wir, dass der Druck von Zerstrahlung dunkler Materie die Übereinstimmung von Theorie und Beobachtung in einigen Fällen verbessern kann. Aber daraus resultieren auch starke Grenzen für die Modellparameter - vor allem für den inneren Anstieg des Halo-Dichteprofils, sowie die Masse und den Wirkungsquerschnitt der dunklen Materie-Teilchen. Im zweiten Teil werden obere Grenzen für die Wirkungsquerschnitte der Zerstrahlung der dunkler Materie in Elektron-Positron-Paare erhalten, indem die beobachteten Daten bei unterschiedlichen Wellenlängen (von Haslam, WMAP und Fermi) mit aktuellen Messungen von Elektron-Positron Spektren in der solaren Nachbarschaft durch PAMELA, Fermi und H.E.S.S. kombiniert werden. Wir betrachten Synchrotronemission bei Radiound Mikrowellenfrequenzen, sowie inverse Compton-Streuung und Final-State-Strahlung bei Energien im Bereich der Gamma-Strahlung. Für die meisten Werte der Modellparameter werden die stärksten Schranken durch das lokale Positron-Spektrum und die Synchrotronemission im Zentrum unser Galaxie bestimmt. Nach diesen Ergebnissen sollte der Wirkungsquerschnitt für die Paarzerstrahlung nicht größer als der kanonische Wert für thermische Relikte sein, wenn die Masse der dunklen Materie-Kandidaten kleiner als einige GeV ist. Zusätzlich leiten wir eine obere Grenze für den inneren logarithmische Anstieg α des Dichteprofiles des dunklen Materie Halos unserer Galaxie ab.

APA, Harvard, Vancouver, ISO, and other styles

14

Greenshaw, T. J. "A measurement of the c and b quark assymetries in electron positron annihilation." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370415.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Ho, King-fung, and 何競豐. "Some positron annihilation studies on highly doped and supersaturated N-type silicon." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30287108.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Zhang, Yu, and 張毓. "Investigation of the lifetime spectrum of monoenergetic positrons in silicon involving secondary electrons emission from a carbon foil as start signal, and positron annihilation spectroscopy studies of strontium titante." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/197507.

Full text

Abstract:

A proposed design of the variable energy positron annihilation spectroscopy (VEPALS) system based on secondary electron (SE) emission from a thin carbon foil has been investigated practically. The SE yield and the positron transmission coefficient were investigated as a function of the positron beam energy, the annular electrode potentials, and the column lengths of the annular electrode. The positron lifetime spectra of single crystal p-type silicon(Si) sample under different annular electrode potentials were analyzed. The result gives a supposed annular electrode potential of 1.5 kV. In view of this, the positron lifetime spectra were measured under different positron beam energy by fixing the annular electrode potential. It can be seen that all the spectra have the main p-type Si bulk lifetime component of 234 ps occupying more than 60% intensities. The intensity of the 234 ps component reaches up to 84.5 ±1.3 % when the positron beam energy is 15 keV. Further, the origin of the satellite peaks in the positron lifetime spectra are also investigated. It has been shown that the satellite peaks is attributed to the overflowing positrons on the MCP detector. The single crystal strontium titanate (STO) substrates after vacuum annealing treatment have been investigated in detail by several experimental techniques. The crystallization changes induced by the vacuum annealing were investigated by X-ray diffraction(XRD). Secondary phases were occurred after annealing treatment. The measured X-ray photoelectron spectroscopy (XPS) at O1s and C1s core levels were analyzed. The additional peaks after annealing are attributed to hydroxyl species, C-OH compounds, and carbonates. The variable energy Doppler broadening spectroscopy (VEDBS) and the traditional coincidence positron annihilation lifetime spectroscopy (PALS) were used to probe defects in STO samples. For long annealing time samples, the S parameters decrease below the reference level. The S-Wplot suggests that almost the same type of vacancy defects were induced during the annealing treatment. The positron lifetime results suggest that the main defects in annealed samples are oxygen monovacancies or divacancies and Sr-O vacancy complexes. The sample with annealing time of 110h has minimum positron effective diffusion length and maximum average lifetime, which is attributed to the increase of the vacancy-type defects during the long annealing treatment.
published_or_final_version
Physics
Master
Master of Philosophy

APA, Harvard, Vancouver, ISO, and other styles

17

Zhou, Taojun, and 周濤俊. "All-electron and full-potential positron annihilation calculations forintrinsic and defective zinc and zinc oxide." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39634164.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Zhou, Taojun. "All-electron and full-potential positron annihilation calculations for intrinsic and defective zinc and zinc oxide." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39634164.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Lam, Chi-hung. "Positron annihilation spectroscopy studies of 6H N-type silicon carbide and Zn-doped P-type gallium antimonide." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36299996.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Pouladdej, Ali Carleton University Dissertation Physics. "A study of hadronisation in e[positive]e[negative] annihilation at the Z[superscript degree] using K[superscript degree] mesons." Ottawa, 1992.

Find full text

APA, Harvard, Vancouver, ISO, and other styles

21

Glendinning, I. "A study of inclusive lepton pairs in multihadronic events from electron positron annihilation at PETRA." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377472.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Lam, Tat-wang. "Construction of a positron-lifetime spectrometer and its application to studying electron irradiation induced defects in 6H silicon carbide." Click to view the E-thesis via HKUTO, 2003. http://sunzi.lib.hku.hk/hkuto/record/B31549913.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

To, Chun-kit, and 杜俊傑. "Defect studies of single crystal and thin film zinc oxide by positron annihilation spectroscopy and cathodoluminescence." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B4608955X.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Alam, S. (Sher) Carleton University Dissertation Physics. "The one loop radiative corrections to W pair production in electron positron annihilation in the supersymmetric extension of the Salam-Weinberg model of the electroweak interactions." Ottawa, 1992.

Find full text

APA, Harvard, Vancouver, ISO, and other styles

25

Lam, Chi-hung, and 林志雄. "Positron annihilation spectroscopy studies of 6H N-type silicon carbide and Zn-doped P-type gallium antimonide." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36299996.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Bull, P. S. "A study of specific hadronic final states in electron-positron annihilation at 34GeV centre of mass energy." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375226.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Dutschke, Markus [Verfasser], and Liviu [Akademischer Betreuer] Chioncel. "Systematic Analysis of the Lock-Crisp-West Theorem in Electron-Positron Annihilation / Markus Dutschke ; Betreuer: Liviu Chioncel." Augsburg : Universität Augsburg, 2019. http://d-nb.info/1180286197/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Dutschke, Markus Thomas [Verfasser], and Liviu [Akademischer Betreuer] Chioncel. "Systematic Analysis of the Lock-Crisp-West Theorem in Electron-Positron Annihilation / Markus Dutschke ; Betreuer: Liviu Chioncel." Augsburg : Universität Augsburg, 2019. http://d-nb.info/1180286197/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Deng, Xin, and 鄧欣. "Positron studies of silicon and germanium nanocrystals embedded in silicon dioxide." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B41508749.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Deng, Xin. "Positron studies of silicon and germanium nanocrystals embedded in silicon dioxide." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B41508749.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Lam, Tat-wang, and 林達宏. "Construction of a positron-lifetime spectrometer and its application to studying electron irradiation induced defects in 6H siliconcarbide." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31549913.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

[Verfasser], Maneenate Wechakama, and Matthias [Akademischer Betreuer] Steinmetz. "Multi-messenger constraints and pressure from dark matter annihilation into electron-positron pairs / Maneenate Wechakama. Betreuer: Matthias Steinmetz." Potsdam : Universitätsbibliothek der Universität Potsdam, 2013. http://d-nb.info/1041521669/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Hasan, Anwarul. "Search for neutralions in electron-positron annihilation at LEP energies : data collected by the L3 detector at CERN /." Zürich, 1995. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10993.

Full text

Abstract:

Diss. Naturwiss. ETH Zürich, Nr. 10993, 1995. Ref.: Hans Hofer ; Korref.: Maurice Bourquin ; Korref.: Juergen Ulbricht.
Am Kopf der Titelseite: Bericht des Instituts für Hochenergiephysik der ETH Zürich.

APA, Harvard, Vancouver, ISO, and other styles

34

Hui, I. Pui. "Construction of the preparation, growth and characterization chamber of molecular beam epitaxy system and some studies of the iron-gallium nitride system with a view to spintronics applications." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39558435.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Naik, Pranab Sabitru. "Design and implementation of a fully automated real-time s-parameter imaging system." Thesis, Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B30708758.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Smith, Bryan R. (Bryan Richard) 1971. "High energy pair production of muons in electron-positron annihilation at center of mass energies ranging from 130 to 183Gev." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50011.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Hui, I. Pui, and 許貽培. "Construction of the preparation, growth and characterization chamber of molecular beam epitaxy system and some studies of the iron-galliumnitride system with a view to spintronics applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39558435.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

González, Martirena Saúl. "A calorimetric measurement of the strong coupling constant in electron-positron annihilation at a center-of-mass energy of 91.6 GeV." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28139.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Hill, P. V. "A model insensitive determination of the strong coupling constant and a measurement of the energy spread of quark jets in electron positron annihilation." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379148.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Zimnik, Samantha Maria [Verfasser], Christoph P. [Akademischer Betreuer] [Gutachter] Hugenschmidt, and Johannes [Gutachter] Barth. "Surface segregation studied by time-resolved positron annihilation induced Auger electron spectroscopy / Samantha Maria Zimnik ; Gutachter: Johannes Barth, Christoph P. Hugenschmidt ; Betreuer: Christoph P. Hugenschmidt." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1135385696/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Mariano, Leandro. "Estudo da distribuição de momento de elétrons ligados por correlação ângulo-energia da radiação de aniquilação elétron-pósitron." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26012011-154606/.

Full text

Abstract:

Neste trabalho foi medido o alargamento Doppler de uma aniquilação elétron pósitron com o uso de um filtro angular. O Filtro angular reduz, substancialmente, a detecção de fótons provenientes de aniquilações de elétrons com baixo momento, enfatizando, desta forma, a contribuição de aniquilações com elétrons fortemente ligados. Foram medidos os espectros de coincidência para os ângulos de corte de 0,28°, 0,42° e 1.2°. Os resultados obtidos mostram que, conforme se aumenta o ângulo de corte, há uma redução das aniquilações com elétrons de valência em proporção muito maior do que para elétrons fortemente ligados. Foi determinada a transmissibilidade do filtro em função do ângulo entre as direções de emissão dos gamas, levando em conta todos os elementos do arranjo experimental para cada ângulo crítico, assim como a distribuição espacial da atividade da fonte radioativa. Um modelo simples foi utilizado para estimar teoricamente a dependência da dispersão da energia em função do ângulo de corte. Este modelo permitiu calcular o alargamento Doppler da radiação de aniquilação elétron pósitron. Os resultados obtidos mostram um bom acordo com os dados experimentais. Geralmente, estudos de aniquilação de pósitrons com elétrons fortemente ligados dependem de uma modelagem detalhada do espectro de coincidência, ou da medida dos fótons provenientes da aniquilação em coincidência com elétrons Auger. O filtro angular, desenvolvido neste trabalho se coloca como uma boa alternativa a estes métodos.
This work reports the measurement of the Doppler broadening of the electron-positron annihilation radiation using an angular filter. The angular filter substantially reduces the number of detected gamma-rays from positron annihilation with low momentum electrons, therefore emphasizing the contribution of bound electron. Four coincidence measurements of the emitted gamma-rays were done with arrangements corresponding to critical angles of 0.28°, 0.42°, 1.2°. The obtained results show that the relative intensity of annihilation with valence electrons decreases as the critical angle increases. The filter transmissibility as a function of the angle between the two gamma-rays emission directions was determined taking into account all the elements of the experimental arrangement for every critical angle as well as the spatial distribution of the source activity. A simple model was used to theoretically estimate the dependence of the energy dispersion on the critical angle. The model allows us to calculate the Doppler broadening of the electron-positron annihilation radiation, and the obtained results show good agreement with the experimental data. Usually, the study of positrons annihilation with inner electrons requires good detectors\' energy resolution and depends on either sophisticated modeling and statistical analysis of the coincidence spectra or the measurement of the annihilation gamma-rays in coincidence with Auger electrons. The use of the angular filter developed in this work is a good alternative to those procedures.

APA, Harvard, Vancouver, ISO, and other styles

42

Huguenin, Denis. "Effets induits par irradiation électronique dans les alliages austénitiques Fe-Ni-Cr." Grenoble 1, 1989. http://www.theses.fr/1989GRE10034.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Kayal, Philip Issa. "Search for vector leptoquarks in electron-positron annihilations at 183 GeV." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0027/NQ39550.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Clarke, P. E. L. "A study of tau leptons in electron-positron annihilations at high energies." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370242.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Edwards, Adam Jacob. "A study of double-charm and charm-strange baryons in electron-positron annihilations /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Hara, Takayuki. "A calculation of fermi energy in selected materials using doppler broadened positron annihilation spectroscopy." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/20238.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Koch, Leonard [Verfasser]. "Search for Resonant X(3872) Formation in Electron Positron Annihilations and the Development of a Prototype Data Acquisition for the Crystal Zero Degree Detector at BESIII / Leonard Koch." Gießen : Universitätsbibliothek, 2019. http://d-nb.info/1188563718/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Stone, Howard D. "Experimental Tests of QCD and Fragmentation Models in Electron-Positron Annihilation." Thesis, 1988. https://thesis.library.caltech.edu/7502/1/Stone%201988.pdf.

Full text

Abstract:

This thesis presents a detailed study of the hadronic data obtained with the MARK J detector from e⁺e⁻ annihilation. The predictions of several new combinations of Monte Carlo parton generators and fragmentation schemes have been tuned and compared directly to the data.

A study, performed in the limit of perfect detector resolution and efficiency, has shown that the string effect, which some groups claimed to have observed, cannot be attributed to soft gluon coherence effects occurring at the soft perturbative stage of the event evolution.

It is found that all the fragmentation schemes employing the string formalism are unable to correctly describe the form of the Thrust and Energy-Energy Correlation distributions obtained with the high energy data above 40 GeV center-of-mass energy. The problems encountered have their origins in the modelling of the fragmentation process rather than in the perturbative QCD aspects of the models. All the models investigated, however, are capable of describing a broad range of distributions at the lower center-of-mass energies.

No evidence for the presence of the string effect has been found in the MARK J data.

The new fragmentation models have been used to extract values for the strong coupling constant from the data. The systematic uncertainties assigned to previous α₈ measurements have been re-assessed in the light of this study, and it has been found that previous error assignments require no adjustment.

A recent 2nd order calculation for the three-jet partial cross section has been investigated and converted into a form where it can be directly compared to previous calculations. The calculations are found to be in excellent agreement, and it is concluded that the systematic errors that should be assigned to α₈ measurements due to theoretical uncertainties are negligible.

Motivated by the observation of an excess number of low thrust inclusive muon events at the highest PETRA energies, the MARK J hadronic data above 46.3 GeV has been compared to a lower energy data sample. The presence of new phenomena in the highest energy hadronic data has been ruled out at the level of available statistics.

A brief study of the characteristics to be expected at LEP energies for events originating in the production of top quarks has been made, and a method for isolating a top-enriched sample has been investigated.

APA, Harvard, Vancouver, ISO, and other styles

49

Pu, Anle. "Positron annihilation investigation of vacancies in as-grown and electron irradiated dia onds." 2000. http://hdl.handle.net/1993/2337.

Full text

Abstract:

Vacancy-type defects in the four main types of diamond (Ia, Ib, IIa and IIb) were investigated using positron lifetime, Doppler broadening and optical absorption spectroscopies. In unirradiated samples vacancy clusters were found in all types, synthetic as well as natural. These clusters are situated in highly defected regions, rather than homogeneously distributed, and their concentration varies significantly from sample to sample. For synthetic Ib diamonds vacancy clusters were investigated as a function of nitrogen content. We have developed a simplified model for the trapping of positrons by ' negatively' charged vacancies. By solving the differential equations pertaining to the population of positron states, expressions for the experimentally observable positron parameters (lifetimes, their intensities and the Doppler broadening parameter S) were obtained. (Abstract shortened by UMI.)

APA, Harvard, Vancouver, ISO, and other styles

50

Morris, Duncan Andrew. "The Relativistic String in the Caltech-II Model of Hadronization and Electron-Positron Annihilation." Thesis, 1987. https://thesis.library.caltech.edu/11407/1/Morris_DA_1987.pdf.

Full text

Abstract:

This study uses the full equations of motion of the massless relativistic string as a phenomenological model of color flux tubes in the process of hadronization in electron-positron annihilation. Perturbatively generated sets of partons are mapped onto color singlet strings, which fragment according to a generalization of the covariant decay law for point relativistic particles. String evolution is terminated when string masses are a few GeV above particle production threshold. Low-mass strings are decayed into primary hadrons using a parameterization of low-mass data. The complete model, which factorizes event evolution into three stages including perturbative QCD, string fragmentation and parameterized low-mass decays, is implemented as a Monte Carlo program known as the Caltech-II model of hadronization. An exact formalism is presented for the fragmentation function of heavy quarks within the string model.

The main results are, in their order of appearance: (1) The kinematics of the evolution and decay of arbitrarily complex massless relativistic strings is most conveniently expressed in terms of momentum currents. (2) The Caltech-II model, which uses the momentum current formalism to describe relativistic strings, provides a good description of electron-positron annihilation data over a wide range of center-of-mass energies. (3) Introducing transverse momentum at the sites of string breaks is conceptually necessary and may be required to further improve agreement between the Caltech-II model and data. (4) Fragmentation functions are predictions, not assumptions, of the string model in Caltech-II. The fragmentation function of heavy quarks in the Caltech-II string model is shown to exhibit the behavior expected from model-independent arguments. The discovery of the top quark or additional generations of heavy quarks will be a testing ground for future studies of hadronization.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Electron-positron annihilation'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles