Search for new non-resonant phenomena in high-mass dilepton final states with the ATLAS detector

Abstract

A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV is presented. This is the first search for non-resonant signals in dilepton final states at the LHC to use a background estimate from the data. The data, corresponding to an integrated luminosity of 139 fb−1, were recorded by the ATLAS experiment in proton-proton collisions at a center-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV during Run 2 of the Large Hadron Collider. The benchmark signal signature is a two-quark and two-lepton contact interaction, which would enhance the dilepton event rate at the TeV mass scale. To model the contribution from background processes a functional form is fit to the dilepton invariant-mass spectra in data in a mass region below the region of interest. It is then extrapolated to a high-mass signal region to obtain the expected background there. No significant deviation from the expected background is observed in the data. Upper limits at 95% CL on the number of events and the visible cross-section times branching fraction for processes involving new physics are provided. Observed (expected) 95% CL lower limits on the contact interaction energy scale reach 35.8 (37.6) TeV.

Search for resonant and nonresonant new phenomena in high-mass dilepton final states at $$ \sqrt{s} $$ = 13 TeV

“…Additional constraints on these models have been reported by the CMS Collaboration from diphoton and dijet final states [29,30] and by the ATLAS Collaboration from dijet final states [31]. The ATLAS Collaboration has presented similar results for these models in the dilepton final state, the most recent using data at 8 TeV [32] for the ADD model and at 13 TeV [33] for the CI model. This paper significantly extends the previous CMS results by using the full data set recorded at √ s = 13 TeV during the years 2016-2018, corresponding to 137 (140) fb −1 in the dielectron (dimuon) channel [34][35][36].…”

“…The lower limit on Λ ranges from 23.9 to 36.4 TeV, depending on the model, an improvement over previous CMS results by . Using the same framework of contact interactions, ATLAS has set limits of up to 35.8 TeV [33]. Signal yields in the LR and RL models are reduced (enhanced) compared to LL and RR in the constructive (destructive) case.…”

Effective field theory versus UV-complete model: vector boson scattering as a case study

“…at high energy and, thus, reduces to a flavor universal, dimension-6 four-fermion interaction which affects left-chiral amplitudes only. Writing the coefficient of thē [43], aTGCs [45] and aQGCs [46,47]. The values for aQGCs from the CMS analyses are derived from leptonic decay channels in VBS processes only.…”

“…for a single fermion or scalar multiplet in the loop, respectively. In the EFT approximation, experimental bounds on four-fermion contact terms, such as recent ATLAS measurements [43], can thus be turned into the lower limits on M 2 R /T R which are shown in Fig. 1.…”

A new B-flavour anomaly in Bd,s → $$ {K}^{\ast 0}{\overline{K}}^{\ast 0} $$: anatomy and interpretation

“…On the one hand, the KK gluon may be part of the particle spectrum of a composite/extra-dimensional model and is then accompanied by a Z boson. This could explain b → s + − without violating LHC di-lepton bounds [48] due to the large sb coupling of the Z needed to explain L K * K * , leading to NP contributions with the correct sign in both types of anomalies. On the other hand, the model generating a large effect in C 8g could easily be extended by a vector-like lepton in order to account for b → s + − [47].…”