A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb −1 of √ s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark,t, which decays promptly into two quarks through Rparity-violating couplings. Top squarks with masses in the range 100 GeV < mt < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < mt < 470 GeV and 480 GeV < mt < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.
IntroductionMassive coloured particles decaying into quarks and gluons are predicted in several extensions of the Standard Model (SM). At hadron colliders, the search for new phenomena in fully hadronic final states, without missing transverse momentum, is experimentally challenging due to the very large SM multijet production cross-section. This paper describes a search for pair-produced particles each decaying into two jets using 36.7 fb −1 of √ s = 13 TeV proton-proton ( pp) collision data recorded in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider (LHC).Supersymmetry (SUSY) [1][2][3][4][5][6][7] is a generalisation of the Poincaré symmetry group that relates fermionic and bosonic degrees of freedom. In the generic superpotential, Yukawa couplings can lead to baryon-and lepton-number violation:where i, j, and k are quark and lepton generation indices. The L i and Q i represent the lepton and quark SU(2) L doublet superfields and H u the Higgs superfield that couples to e-mail: atlas.publications@cern.ch up-type quarks. TheĒ i ,D i , andŪ i are the lepton, downtype quark and up-type quark SU(2) L singlet superfields, respectively. For each term the couplings are λ, λ , λ , as well as κ which is a dimensional mass parameter. The λ and λ couplings are antisymmetric in the exchange of i → j and j → k, respectively. While these terms in many scenarios are removed by imposing an additional Z 2 symmetry (R-parity) [8], the possibility that at least some of these Rparity-violating (RPV) couplings are not zero is not ruled out experimentally [9,10]. This family of models leads to unique collider signatures which can escape conventional searches for R-parity-conserving SUSY.Naturalness arguments [11,12] suggest that higgsinos and top squarks 1 (stops) should be light, with masses below a TeV [13,14]. Third-generation squarks in R-parityconserving scenarios, and top squarks in particular, have been the subject of a thorough programme of searches at the LHC [15][16][17][18][19][20][21][22].If the top squark decays through RPV couplings, however, the existing bounds on its mass can be significantly relaxed [23][24][25][26]. Indirect experimental constrain...
