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

TL;DR

This study uses the $ ext{γ}+$jet invariant mass distribution at the LHC to set the most stringent direct limits on quark chromoelectric and chromomagnetic dipole moments, improving constraints significantly.

Contribution

It demonstrates the sensitivity of the $ ext{γ}+$jet process to quark dipole moments and derives new bounds using CMS data, considering various uncertainties.

Findings

Excludes dipole moments above $10^{-5}$ at 95% CL.

Provides the most stringent direct upper limits on $ ext{κ}$ and $ ilde{ ext{κ}}$.

Shows the impact of dipole moments on the $ ext{γ}+$jet invariant mass distribution.

Abstract

In this paper we show that the $\gamma+$jet invariant mass distribution in proton-proton collisions at the LHC is significantly sensitive to the quarks chromoelectric ($\kappa$) and chromomagnetic ($\tilde{\kappa}$) dipole moments. It is shown that the presence of $\kappa$ or $\tilde{\kappa}$ leads to an increment of the cross section of $\gamma+$jet process in particular in the tail of $\gamma+$jet invariant mass distribution. Using the measured $\gamma+$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 $\gamma+$jet invariant mass. We exclude $\kappa$ or $\tilde{\kappa}$ above $10^{-5}$ at 95$\%$ confidence level. This is the most stringent direct upper limit on $\kappa$ or $\tilde{\kappa}$.