Hard color-singlet exchange in dijet events in proton-proton collisions at $\sqrt{s}=$ 13 TeV

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 $\sqrt{s}=$ 13 TeV. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum ($p_{\mathrm{T}}$) jets must have $p_{\mathrm{T}}^{\text{jet}}$ $>$ 40 GeV and pseudorapidity 1.4 $<$ $|{\eta }^{\text{jet}}|$ $<$ 4.7, with ${\eta }^{\text{jet1}}{\eta }^{\text{jet2}}$ $<$ 0, where $\text{jet1}$ and $\text{jet2}$ 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-${\beta }^{\ast }$ 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 $p_{\mathrm{T}}$ $>$ 0.2 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, $f_{\text{CSE}}$, is measured as a function of $p_{\mathrm{T}}^{\text{jet2}}$, the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction $f_{\text{CSE}}$ 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 pb${}^{-1}$ is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The $f_{\text{CSE}}$ in this sample is 2.91 $\pm$ 0.70 (stat) ${}_{-1.01}^{+1.08}$ (syst) times larger than that for inclusive dijet production in dijets with similar kinematics.

Corrected the URL for the public results site. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/SMP-19-006 (CMS Public Pages)

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