1. Studies of Zγ electroweak production in association with a high-mass di-jet system in pp collisions at √s = 8 TeV with the ATLAS detector
LeptonPhoton Conference, 7-12 August 2017,GuangZhou China
Motivation
Test of the Electroweak (EWK) Sector
search for anomalous quartic couplings (aQGC)
First probe of neutral aQGC at ATLAS in 2->2 process in two decay channels:
Charged lepton channel: cleaner final state, various fiducial cross sections measured (different fractions of EWK and QCD production) and aQGC limits
Neutrino channel: complex backgrounds but large branching ratio allows extraction of aQGC limits, cross-section measured only in high 𝛾 ET region.
Zγjj production topologies
Zγjj cross section measurement
Z(ll)γjj channel fid. cross section measured by a simultaneous likelihood fit to distributions of Zy-centrality in CR and SR, constraining Zγ-QCD bgd
cross section measured in llγjj channel EWK-only in SR and EWK+QCD in both CR and SR
Z(νν)γjj fid. cross section measured in an aQGC sensitive high Et(γ) region via log-likelihood fit
Control regions (CR)
Search regions (SR)
Measured Z(l+l-)γjj phase space
Measured Zγjj fiducial cross section
Measured Z(νν)γjj phase space
[1]
aQGCs Methodology
An effective field theory (EFT) [2] with higher-dimensional operators is adopted to parameterize the anomalous couplings
The charged anomalous couplings of WWZγ can be induced by fM,x (x=0-7) , fT,x(x=0-7)
Neutral aQGCs of ZZZγ and ZZγγ also possible via fM,x
Photon ET spectrum is sensitive to aQGCs.
EFT Lagrangian[2]
aQGCs results
Z(l+l-)γjj aQGCs region
[1]
Z(νν)γjj aQGCs region
Reference:
[1] The ATLAS Collaboration. , JHEP07(2017)107
[2] C. Degrande et al, Annals Phys. 335 (2013) 21
Zhijun Liang (Institute of High Energy Physics, CAS)
On behalf of the ATLAS Collaboration