Search for Quark Compositeness at $\sqrt{s} = 14$ TeV at the Large Hadron Collider

Within the Standard Model(SM) of particle physics, quarks and leptons are understood to be the fundamental particles. Their existence and various properties have been verified experimentally. Further search for substructure of quarks or study of quark compositeness is one of the important physics motivations of the LHC. Many different models of excited quarks($\Lambda < \sqrt{\hat{s}}$) and quarks substructure study via contact interactions($\Lambda >> \sqrt{\hat{s}}$) has been put forward but till now none of the experiments have found any such evidence. Various past and present experiments have put different lower bound on compositeness scale($\Lambda$) and mass $M_{q^*}$ of the composite/excited quarks. We have studied one such model in detail where the magnetic transition of the excited quarks is considered with ordinary quarks. We have evaluated the search potential of these states in $\gamma+jet$ and $\gamma\gamma$ final states at the LHC center of mass energy of $\sqrt{s}=$14 TeV. The simulation was done at the generator level and we have used Compact Muon Solenoid(CMS) experimental setup for photon and jet candidate reconstruction. The track and calorimetric activities were used for isolation purpose to reduce SM backgrounds. The analysis shows that for a choice of $\Lambda=M_{q*}=$2 TeV, an excited state $ q^*$ in $\gamma+jet$ mode can be discovered with 200 $pb^{-1}$ of data, while a 5 TeV state can be confirmed with $\sim$140 $fb^{-1}$ of integrated luminosity. Restricting the event selection to central pseudorapidity region with $|\eta^{\gamma,jet}|\leq$1.5, a 3 TeV mass state can be discovered with less than 2 $fb^{-1}$ of data. In $\gamma\gamma$ search mode, considering the diphoton invariant mass in 450 GeV to 1.5 TeV range, we estimated the achievable 99$%$ CL exclusion contours in $\Lambda-M_{q^*}$ plane for 30, 50, 100 and 200 $fb^{-1}$ of data. For a $q^*$ mass state of 0.5 TeV, $\Lambda\leq$ 2.95(1.55) TeV can be excluded with 200(30) $fb^{-1}$ of data at 99$%$ CL. A detailed study of systematic uncertainty has been performed and its effect on results have been estimated.