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 $\sqrt{s}=13\mathrm{TeV}$. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum ($p_{\mathrm{T}}$) jets must have $p_{\mathrm{T}}^{\mathrm{jet}}>40\mathrm{GeV}$ and pseudorapidity $1.4<|{\eta }^{\mathrm{jet}}|<4.7$, with ${\eta }^{\mathrm{jet}1}{\eta }^{\mathrm{jet}2}<0$, where jet1 and jet2 are the leading and subleading jets in $p_{\mathrm{T}}$, respectively. The analysis is based on data collected by the CMS and TOTEM experiments during a low luminosity, high-${\beta }^{*}$ run at the CERN LHC in 2015, with an integrated luminosity of $0.66{\mathrm{pb}}^{-1}$. Events with a low number of charged particles with $p_{\mathrm{T}}>0.2\mathrm{GeV}$ in the interval $|\eta |<1$ between the jets are observed in excess of calculations that assume only color-exchange. The fraction of events produced via color-singlet exchange, $f_{\mathrm{CSE}}$, is measured as a function of $p_{\mathrm{T}}^{\mathrm{jet}2}$, the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction $f_{\mathrm{CSE}}$ 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 $0.40{\mathrm{pb}}^{-1}$ is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The $f_{\mathrm{CSE}}$ in this sample is $2.91\pm 0.70{(\mathrm{stat})}_{-1.01}^{+1.08}(\mathrm{syst})$ times larger than that for inclusive dijet production in dijets with similar kinematics.

• Received 13 February 2021
• Accepted 20 May 2021

DOI:https://doi.org/10.1103/PhysRevD.104.032009

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© 2021 CERN, for the CMS and TOTEM Collaboration