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Studies of Zγ Production and Constraints on Anomalous Triple Gauge Couplings in pp Collisions at √s = 7 TeV


Veverka, Jan (2013) Studies of Zγ Production and Constraints on Anomalous Triple Gauge Couplings in pp Collisions at √s = 7 TeV. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/QTWD-J259.


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.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:high energy physics; experiment; CERN; LHC; CMS; large hadron collider; compact muon solenoid; proton-proton collisions; 7 TeV; Zgamma cross section; anomalous triple gauge couplings;
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Newman, Harvey B.
Thesis Committee:
  • Newman, Harvey B. (chair)
  • Wise, Mark B.
  • Weinstein, Alan Jay
  • Spiropulu, Maria
  • Patterson, Ryan B.
Defense Date:15 May 2013
Non-Caltech Author Email:jan.veverka (AT)
Record Number:CaltechTHESIS:05302013-043445308
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7770
Deposited By: Jan Veverka
Deposited On:03 Jun 2013 22:31
Last Modified:26 Oct 2021 18:33

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