Academic literature on the topic 'Zγ production'

The recent D0 results on Wγ and Zγ production are presented. First, the cross-section and the difference in rapidities between photons and charged leptons for inclusive W(→lν)+γ production in eγ and μγ final states are discussed, then are the cross-section and differential cross-section as a function of photon transverse momentum for Zγ→l+l-(l = e, μ) process. Finally, I present the limits on anomalous WWγ, ZZγ and Zγγ couplings.

Indirect searches of beyond the Standard Model effects are discussed. The Z(νν−)γ process is considered in this respect. The limiting factors of the separation of this process from the background one are studied phenomenologically. New potential selection methods are proposed to increase the signal to background ratio.

The latest advances in Standard Model measurements performed by the ATLAS experiment at the LHC are discussed. Vector-boson scattering processes have been observed in several final states (ZZ, WZ, same-sign WW), and evidence has been reached in the Zγ final state. The experimental precision of QCD measurements has reached the same order as the theoretical uncertainties on the NNLO calculations. Evidence for the triboson WVV final state has been achieved. The latest results on V+jets, Zγ, W+W− and direct photons production are presented. New results on jet substructure and forward proton tagging program are also discussed.

The experimental results on physics of diboson production are reviewed. The measurements use pp collision at the LHC with center-of-mass energy [Formula: see text] and 8 TeV, and [Formula: see text] collision at the Tevatron with [Formula: see text]. These include measurements of Wγ, Zγ, WW, WZ and ZZ production. The results are compared with Standard Model predictions, and are interpreted in terms of constraints on charged and neutral anomalous triple gauge couplings.

This is a report at the conference Physics In Collision 2013. The experimental results on physics of diboson production are reviewed. The measurements use pp collision at the LHC with center-of-mass energy [Formula: see text] and 8 TeV, and [Formula: see text] collision at the Tevatron with [Formula: see text]. These include measurements of Wγ, Zγ, WW, WZ and ZZ production. The results are compared with Standard Model predictions, and are interpreted in terms of constraints on charged and neutral anomalous triple gauge couplings.

Le sujet physique de ma thèse est la mesure de la section efficace de di-boson Zgamma; production en association avec une paire de dijet à haute masse.Les données de collision protons-protons de l’expérience ATLAS au Grand collisionneur de hadrons du CERN à une énergie dans le centre de masse de13 TeV, recueillies en 2015 et 2016 et correspondant à une luminosité intégrée de 36.1 fb^{-1} sont analysées. La production électrofaible d’événements Zgammajj donne un accès direct à la nature du mécanisme de brisure spontanée de symétrie électrofaible, en sondant les couplages quantiques de boson WWZgamma,ZZZgamma, ZZgammagamma et Zgammagammagamma. Les trois derniers sont interdits à l’ordre le plus basdans le Modèle Standard. Tout écart par rapport aux prévisions du ModèleStandard pourrait être un indice d’une nouvelle physique.Jusqu’à présent, la production électrofaible de Zgammajj, qui consiste en desprocessus avec constante couplage électrofaible du quatrième ordre et qui inclut des processus de diffusion de vecteur-boson, n’a jamais été observée. Le même état final Zgammajj peut être produit par un processus fortement médié,avec un constante couplage électrofaible de second ordre et un couplage fortde second ordre, résultant en une section efficace de trois ordres de grandeur plus grande que la section électrofaible. La production de Zgammajj via un mécanisme électrofaible et fort interfère puisque les états initiaux et finaux sont les mêmes. La compréhension de cet effet est un aspect important de l’analyse.Dans ma thèse, j’ai étudié cet effet et son impact sur l’observation du pro-cessus et sur les mesures de le section efficace. Pour cette étude, après avoir effectué le calcul des trois contributions (électrofaible, forte et interférence) à la section efficace totale à l’aide de simulations de Monte Carlo, j’ai effectué une optimisation des coupes de sélection, afin de réduire l’impact de l’interférence, en définissant également une procédure pour la prise en compte de cette interférence dans l’analyse des données. Le point focal expérimental de mon travail est la mesure de la section efficace différentielle de l’état final Zgammajj en fonction de la masse invariante du système Zgamma, du momentum transversal du photon, de la multiplicité de jets et de la masse invariante du système Dijet. Les distributions sensibles à la nouvelle physique sont corrigées par les effets détecteur et comparées aux attentes des PM.Tous résultat de physique repose sur la reconstruction et la sélection d’états finaux composés de jets, d’électrons, de muons et de photons. Les électrons et leur identification jouent donc un rôle important dans l’analyse Zgammajj. Ce rapport de thèse documente également le travail que j’ai fait sur l’efficacité de l’identification des électrons, y compris d’une méthode supplémentaire axée sur les données. Les résultats que j’ai obtenus, sont utilisés dans toutes les analyses ATLAS dont la signature contient des électrons
The physics subject of my thesis work, is the measurement of the cross-section of the diboson Zgamma production in association with a high mass dijetsystem. Proton-proton collision data from the ATLAS experiment at theCERN Large Hadron Collider at a center-of-mass energy of 13 TeV,collected in 2015 and 2016 and corresponding to an integrated luminosity of36.1 fb^{-1} are analyzed. The electroweak production of Zgammajj events, provides a direct access to the nature of the electroweak symmetry breaking mechanism, by probing the quantum gauge boson couplings WWZgamma, ZZZgamma, ZZgammagamma and Zgammagammagamma. The last three are forbidden at the lowest order in the Standard Model. Any deviation from the Standard Model predictions could be a hint for new physics.Until now, the electroweak production of Zgammajj, which consist in pro-cesses with fourth-order electroweak coupling and include vector-boson scat-tering processes, has never been observed. The same Zgammajj final state canbe produced by a strongly-mediated process, with second order electroweakcoupling and second order strong coupling, resulting in a cross-section threeorder of magnitude larger than the electroweak cross-section. The Zgammajj pro-duction via electroweak and strong mechanism interfere since the initial andfinal states are the same. The understanding of this effect is an importantaspect of the analysis.In my thesis, I have studied this effect and its impact on the observationof the process and on the fiducial cross-section measurements. For this inves-tigation, after having performed the computation of the three contributions(electroweak, strong and interference) to the total cross-section using MonteCarlo simulations I have performed an optimization of the selection cuts, in order to reduce the impact of the interference, defining also a procedure onhow to account for the interference in the data analysis. The experimentalfocus of my work is the measurement of the differential cross section of theZgammajj final state as function of the invariant mass of the Zgamma system, the transverse momentum of the photon, the jet multiplicity and the invariantmass of the dijet system. Distributions sensitive to new physics are unfoldedand compared with MC expectations.All physics results rely on the reconstruction and selection of final statesconsisting of jets, electrons, muon and photons. Electrons and their identi-fication therefore play an important role in the Zgammajj analysis. This thesisreport documents also the work that I have done on the electron identification efficiency, including the implementation of an additional data drivenmethod. The results I have obtained, are used in all ATLAS analyses whosesignature contain electrons

博士
國立中央大學
物理研究所
99
The measurement of Zγ production can provide an opportunity for examining the gauge sector of the Standard Model, and evidences for the existence of new physics. This thesis presents the first cross-section measurement of Zγ → e+e-γ at √s = 7 TeV using 36 pb-1 of proton-proton collision data collected by CMS. The cross-section is measured for the photon transverse energy ETγ > 10 GeV, spatial separation from charged leptons ΔR(l, γ) > 0.7 and dilepton invariant mass Mll > 50 GeV. The σ(pp → Zγ + X) × B(Z → e+e-) is measured to be 9.5 ± 1.4 (stat.) ± 0.7 (syst.) ± 0.4 (lumi.) pb, in agreement with Standard Model prediction of 9.6 ± 0.4 pb.

In this thesis, we test the electroweak sector of the Standard Model of particle physics through the measurements of the cross section of the simultaneous production of the neutral weak boson Z and photon γ, and the limits on the anomalous Zγγ and ZZγ triple gauge couplings h3 and h4 with the Z decaying to leptons (electrons and muons). We analyze events collected in proton-proton collisions at center of mass energy of sqrt(s) = 7 TeV corresponding to an integrated luminosity of 5.0 inverse femtobarn. The analyzed events were recorded by the Compact Muon Solenoid detector at the Large Hadron Collider in 2011.

The production cross section has been measured for hard photons with transverse momentum greater than 15 GeV that are separated from the the final state leptons in the eta-phi plane by Delta R greater than 0.7, whose sum of the transverse energy of hadrons over the transverse energy of the photon in a cone around the photon with Delta R less than 0.3 is less than 0.5, and with the invariant mass of the dilepton system greater than 50 GeV. The measured cross section value is 5.33 +/- 0.08 (stat.) +/- 0.25 (syst.) +/- 0.12 (lumi.) picobarn. This is compatible with the Standard Model prediction that includes next-to-leading-order QCD contributions: 5.45 +/- 0.27 picobarn.

The measured 95 % confidence-level upper limits on the absolute values of the anomalous couplings h3 and h4 are 0.01 and 8.8E-5 for the Zγγ interactions, and, 8.6E-3 and 8.0E-5 for the ZZγ interactions. These values are also compatible with the Standard Model where they vanish in the tree-level approximation. They extend the sensitivity of the 2012 results from the ATLAS collaboration based on 1.02 inverse femtobarn of data by a factor of 2.4 to 3.1.

博士
國立中央大學
物理學系
107
Measurement of the Z plus γ production cross section is presented using proton-proton collisions at the LHC with the CMS detector. The data were collected in 2016 corresponding to an integrated luminosity of 35.9 fb＾−1 at the center-of-mass energy of 13 TeV. The events having a Z boson decaying to a pair of muons (μ+μ−) or electrons (e+e−) with Mll > 50 GeV and a high transverse momentum photon (pT ≥ 20 GeV) are selected. The fiducial cross sections are measured inclusively, exclusively and in terms of number of additional jets in the final state. Moreover, the differential cross sections in photon transverse momentum pT and three-body invariant mass Mllγ are also presented. The main background, Z+jets events in which a non-prompt photon is produced from the decay of π0 or from mis-identified particles, is estimated by template fitting with a signal template from simulation and background template obtained from the data sideband region. The measured inclusive fiducial cross section is: σmea = 1776 ± 11(stat) ± 15(syst) ± 44(lumi) fb and the exclusive result is σmea = 1328 ± 11(stat) ± 30(syst) ± 33(lumi) fb. The values are found to be in good agreement with prediction from MATRIX at next-to-next-to-leading order (NNLO) σNNLO = 1797 ± 41 fb and σNNLO = 1293 ± 48 fb for inclusive and exclusive, respectively.

博士
國立中央大學
物理學系
103
Measurements of Zγ production cross section in proton-proton collisions at √s =7 TeV are presented. The results are based on data recorded by the CMS detector at the LHC that correspond to an integrated luminosity of 5.0 fb−1. The cross sections are measured for photon transverse energy > 15 GeV, and for separations between photons and final-state electrons in the pseudorapidity-azimuthal plane of ΔR(e, γ) > 0.7 in eeγ final state. A dielectron invariant mass requirement of di-electron pair > 50 GeV is imposed. The σ(pp → Zγ) × B(Z → e+ e−) is measured to be 5.20 ± 0.13(stat) ± 0.32(syst) ± 0.11(lum) pb. The results are consistent with predictions from the standard model.