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Search for new physics using the MT2 variable in all-hadronic final states produced in 13 TeV proton-proton collisions at the CMS detector


A search for phenomena beyond the Standard Model (BSM) is performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the Large Hadron Collider in 2016-2018 and corresponding to an integrated luminosity of 137 fb^-1. The search is based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of b-tagged jets, and the value of the kinematic variable MT2 for events with at least two jets. For events with exactly one jet, the transverse momentum of the jet is used instead. No significant excess event yield is observed above the predicted Standard Model background. This is used to constrain a range of BSM models that predict the following: the pair production of gluinos and squarks in the context of supersymmetry models conserving R parity; the resonant production of a colored scalar state decaying to a massive Dirac fermion and a quark; and the pair production of scalar and vector leptoquarks each decaying to a neutrino and a top, bottom, or light-flavor quark. In most of the cases, the results obtained are the most stringent constraints to date. The analysis is published in the European Physical Journal C vol. 80, #3.

Additionally, the first search at a hadron collider for elementary particles with charges much smaller than the electron charge is presented. These results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV provided by the LHC in 2018, corresponding to an integrated luminosity of 37.5 fb^-1. A prototype scintillator-based detector is deployed near the CMS interaction point to conduct a search sensitive to particles with charges <=0.3e. The existence of new particles with masses between 20 and 4700 MeV is excluded at 95% confidence level for charges varying between 0.006e and 0.3e, depending on their mass. New sensitivity is achieved for masses larger than 700 MeV.

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