Direct photon production as a probe of quarks chromoelectric and chromomagnetic dipole moments at the LHC

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In this paper we show that the γ+jet invariant mass distribution in proton-proton collisions at the LHC is significantly sensitive to the quarks chromoelectric (κ) and chromomagnetic (κ) dipole moments. It is shown that the presence of κ or κ leads to an increment of the cross section of γ+jet process in particular in the tail of γ+jet invariant mass distribution. Using the measured γ+jet invariant mass distribution by the CMS experiment at the center-of-mass energy of 8 TeV, we derive bounds on the quarks chromoelectric and chromomagnetic dipole moments. In extraction of the limits, we consider both theoretical and systematic uncertainties. The uncertainties originating from variation of the renomalization/factorization scales and the choice of proton parton distribution functions are taken into account as a function of the γ+jet invariant mass. We exclude κ or κ above 10⁻⁵ at 95% confidence level. This is the most stringent direct upper limit on κ or κ.