Search for low mass vector resonances decaying into quark-antiquark pairs in proton-proton collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

Abstract

A search for narrow vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in proton-proton collisions at √ s = 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb −1 . The hypothetical resonance is produced with sufficiently high transverse momentum that its decay products are merged into a single jet with two-prong substructure. A signal would be identified as a peak over a smoothly falling background in the distribution of the invariant mass of the jet, using novel jet substructure techniques. No evidence for such a resonance is observed within the mass range of 50-300 GeV. Upper limits at 95% confidence level are set on the production cross section, and presented in a mass-coupling parameter space. The limits further constrain simplified models of dark matter production involving a mediator interacting between quarks and dark matter particles through a vector or axial-vector current. In the framework of these models, the results are the most sensitive to date, extending for the first time the search region to masses below 100 GeV. [28][29][30][31][32][33][34][35] Collaborations have mostly focused on the production of heavy particles. For resonance masses below 1 TeV, the sensitivity is limited by high trigger thresholds and by the large expected backgrounds, notably from SM events consisting of jets produced through the strong interaction, referred to here as QCD multijet events.These difficulties can be avoided by an approach focused on the events where at least one high transverse momentum (p T ) jet from initial-state radiation (ISR) is produced in association with a light resonance decaying into a qq pair. The ISR requirement provides enough energy in the event to satisfy the trigger, either by the ISR jet or by the resonance itself. The minimum p T of the resonance considered in this search is sufficiently high that the hadronization products of the daughter quarks merge and are reconstructed as a -1 - JHEP01(2018)097single, large-radius jet. The only previous search in this topology to place constraints on resonance masses below 300 GeV was by the CMS Collaboration, applying this technique to data collected at the LHC in 2015 [36].In the current paper, the results of a search for leptophobic vector resonances (Z ) decaying to quark-antiquark pairs in pp collisions at √ s = 13 TeV are reported, using data collected by the CMS detector in 2016, corresponding to an integrated luminosity of 35.9 fb −1 . The search is performed by looking for a narrow resonance peak in the continuous jet mass distribution. The analysis exploits a new substructure variable that is decorrelated from the jet mass and p T and preserves the shape of the jet mass distribution used in the search. The jet is required to have the two-prong substructure expected from the signal. The dominant background from SM QCD multijet production is estimated from a signal-depleted control region created by inverting the substructure requir...

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