Study of hard color singlet exchange in dijet events with proton-proton collisions at $\sqrt{s}$ = 13 TeV

This paper presents a study of proton-proton collision events where the two leading jets are separated by a large pseudorapidity interval devoid of particle activity, known as jet-gap-jet events. Both jets have transverse momentum $p_{T, jet}$ > 40 GeV and pseudorapidity 1.4 < $|\eta_{jet}|$ < 4.7, with $\eta_{jet 1} \times \eta_{jet 2} < 0$. The analysis is based on data collected by the CMS experiment in proton-proton collisions during a low luminosity, high-$\beta^{*}$ run in 2015 at $\sqrt{s}$ = 13 TeV, with an integrated luminosity of 0.66 pb$^{-1}$. The number of charged particles detected with transverse momentum $p_{T}$ > 200 MeV in the fixed pseudorapidity interval -1 < $\eta$ < 1 between the jets is used to discriminate jet-gap-jet events from color exchange dijet events. The fraction of jet-gap-jet events to all dijet events with similar kinematics, $f_{CSE}$, is presented as a function of the pseudorapidity difference between the leading two jets, the transverse momentum of the subleading jet, and the azimuthal angle separation between the leading two jets. The results are compared to previous measurements and to perturbative quantum chromodynamics predictions. In addition, the paper presents the first study of jet-gap-jet events with a leading proton, interpreted as a proton-gap-jet-gap-jet topology, using a subsample of events collected by the CMS and TOTEM experiments with an integrated luminosity of 0.40 pb$^{-1}$. The leading protons are detected with the Roman pot detectors of the TOTEM experiment. The ratio $f_{CSE}$ in this sample is found to be $2.91 \pm 0.70 (\rm stat) ^{+1.02}_{-0.94} (\rm syst)$ times larger than that for inclusive dijet production for dijets with similar kinematics.