Abstract: Events where the two leading jets are separated by a pseudorapidity interval devoid of particle activity, known as jet-gap-jet events, are studied in proton-proton collisions at ffiffiffi s p ¼ 13 TeV. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum (pT) jets must have pjet T > 40 GeV and pseudorapidity 1.4 < j?jetj < 4.7, with ?jet1?jet2 < 0, where jet1 and jet2 are the leading and subleading jets in pT, respectively. The analysis is based on data collected by the CMS and TOTEM experiments during a low luminosity, high-? run at the CERN LHC in 2015, with an integrated luminosity of 0.66 pb?1. Events with a low number of charged particles with pT > 0.2 GeV in the interval j?j < 1 between the jets are observed in excess of calculations that assume only color-exchange. The fraction of events produced via color-singlet exchange, fCSE, is measured as a function of pjet2 T , the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction fCSE has values of 0.4?1.0%. The results are compared with previous measurements and with predictions from perturbative quantum chromodynamics. In addition, the first study of jet-gap-jet events detected in association with an intact proton using a subsample of events with an integrated luminosity of 0.40 pb?1 is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The fCSE in this sample is 2.91  0.70ðstatÞþ1.08 ?1.01 ðsystÞ times larger than that for inclusive dijet production in dijets with similar kinematics.

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