Measurement of vector boson scattering and constraints on anomalous quartic couplings from events with four leptons and two jets in proton–proton collisions at s=13 TeV

Abstract

A measurement of vector boson scattering and constraints on anomalous quartic gauge couplings from events with two Z bosons and two jets are presented. The analysis is based on a data sample of proton-proton collisions at √ s = 13 TeV collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb −1 . The search is performed in the fully leptonic final state ZZ → , where , = e or µ. The electroweak production of two Z bosons in association with two jets is measured with an observed (expected) significance of 2.7 (1.6) standard deviations. A fiducial cross section for the electroweak production is measured to be σ EW (pp → ZZjj → jj) = 0.40 +0.21 −0.16 (stat) +0.13 −0.09 (syst) fb, which is consistent with the standard model prediction. Limits on anomalous quartic gauge couplings are determined in terms of the effective field theory operators T0, T1, T2, T8, and T9. This is the first measurement of vector boson scattering in the ZZ channel at the LHC.The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are silicon pixel and strip tracking detectors, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections. Forward calorimeters extend the pseudorapidity η coverage provided by the barrel and endcap detectors up to |η| < 5. Muons are measured in gas-ionization detectors embedded in the steel flux-return yoke outside the solenoid.The silicon tracker measures charged particles within the pseudorapidity range |η| < 2.5. It consists of 1440 silicon pixel and 15 148 silicon strip detector modules. For nonisolated particles with 1 < p T < 10 GeV and |η| < 1.4, the track resolutions are typically 1.5% in p T and 25-90 (45-150) µm in the transverse (longitudinal) impact parameter [19].Electrons are measured in the pseudorapidity range |η| < 2.5 using both the tracking system and the ECAL. The momentum resolution for electrons with p T ≈ 45 GeV from Z → e + e − decays ranges from 1.7% for nonshowering electrons in the barrel region (|η| < 1.479) to 4.5% for showering electrons in the endcaps [20].

Consistency of the standard model effective field theory

“…Yet those same dimension-six operators also induce anomalous triple gauge-boson couplings, on which the LHC has significantly extended the constraints from LEP [120], leaving room for aQGCs from dimension-eight operators. Deviations from the SM in these channels have been searched for at both ATLAS [27][28][29] and CMS [30][31][32];…”

“…Such deviations from the SM, induced by new high-scale physics, can be encoded as operators of higher mass dimension in an effective field theory (EFT) of the SM [22][23][24][25][26]. Using current measurements from the LHC [27][28][29][30][31][32], bounds have begun to be placed on the Wilson coefficients of some of the operators in the SMEFT; for a single example see Ref. [33].…”

Polarized vector boson scattering in the fully leptonic WZ and ZZ channels at the LHC

“…The cross section for ZZ production in VBS has been measured by the CMS Collaboration in the fully leptonic channel [1]. In the fiducial region, at 13 TeV, it is less than 1 f b.…”

“…In Run 2 CMS and ATLAS have finally produced convincing evidence that VBS actually takes place in the complex environment of the LHC [1][2][3][4][5]. Unfortunately, the statistics is still too small for any attempt to analyze vector boson polarizations.…”

Polarization fraction measurement in ZZ scattering using deep learning

“…ZZ scattering has recently been observed by ATLAS with a significance larger than 5 standard deviations, using 139 f b −1 of LHC Run II data collected at √ s = 13 TeV [7]. A prior measurement made by CMS with 35.9f b −1 collected at √ s = 13 TeV reported an observed significance of 2.7 standard deviations [8]. Measuring the longitudinally polarized component of VBS (the LL component) is a critical next step for the field, as it is closely related to the important theoretical property of unitarity restoration, through Higgs and possible new physic [9,10].…”