Hard Colour Singlet Exchange Research Articles

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

We present a measurement of events with two jets separated by a pseudorapidity gap (jet-gap-jet). The signature is expected from hard color-singlet exchange. The jets are reconstructed with the CMS detector. The highest p_\text{T}pT jets have p_\text{T}^\text{jet1,2} > 40pTjet1,2>40 GeV, with 1.4 < |\eta^\text{jet1,2}| < 4.71.4<|ηjet1,2|<4.7 and \eta^\text{jet1} \eta^\text{jet2} < 0ηjet1ηjet2<0. We measure the fraction of color-singlet exchange dijet events, f_\text{CSE}fCSE, and compare it to previous measurements and to predictions. We also study jet-gap-jet events where the colliding protons remain intact and are detected with the Roman pots of TOTEM. A larger fraction f_\text{CSE}fCSE is found in the latter subsample.

Hard color-singlet exchange in dijet events in proton-proton collisions at s=13 TeV

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 $p_\mathrm{T}^\text{jet}$ $\gt$ 40 GeV and pseudorapidity 1.4 $\lt$ $|\eta^\text{jet}|$ $\lt$ 4.7, with $\eta^\text{jet1} \eta^\text{jet2}$ $\lt$ 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-$\beta^*$ 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 $p_\mathrm{T}$ $\gt$ 0.2 GeV in the interval $|\eta|$ $\lt$ 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) $^{+1.08}_{-1.01}$ (syst) times larger than that for inclusive dijet production in dijets with similar kinematics.

Recent forward physics and diffraction results from CMS

Recent CMS results on forward physics and diffraction are reviewed. The differential diffractive cross section is measured as a function of ξ = M 2 X / S in the region dominated by single dissociation (SD) and double dissociation (DD), where M X is the mass of one of the two final-state hadronic systems separated by the largest rapidity gap in the event. The total SD and DD cross sections are extracted. The observation of a hard color-singlet exchange process in events with a large rapidity gap between two leading jets (jet-gap-jet) is reported. The fraction of jet-gap-jet to all dijet events is measured as a function of the second leading jet transverse momentum and the size of the pseudorapidity gap. The measured fractions are compared with predictions as well as Tevatron data.

Hard colour singlet exchange and gaps between jets at the Tevatron

The new kind of events with a rapidity gap between two high-ET jets, observed in high energy pp̄ collisions at the Tevatron, is found to be well described by the exchange of a colour singlet gluon system in the BFKL framework. This requires going beyond the conventional asymptotic Mueller–Tang approximation, which results in qualitatively different features of the basic parton–parton scattering amplitude. Non-leading corrections to the BFKL equation are included by incorporation of the consistency constraint and the running QCD coupling. Hadronisation and other non-perturbative QCD effects are treated through a complete Monte Carlo simulation, providing a gap survival probability that varies event-by-event, facilitating comparison with experimental results.

Hard colour singlet exchange at the Tevatron

We have performed a detailed phenomenological investigation of the hard colour singlet exchange process which is observed at the Tevatron in events which have a large rapidity gap between outgoing jets. We include the effects of multiple interactions to obtain a prediction for the gap survival factor. Comparing the data on the fraction of gap events with the prediction from BFKL pomeron exchange we find agreement provided that a constant value of alpha_s is used in the BFKL calculation. Moreover, the value of alpha_s is in line with that extracted from measurements made at HERA.

Probing hard color-singlet exchange in [formula omitted] collisions at [formula omitted] = 630 GeV and 1800 GeV

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at s =630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.