Study of dijet events with a large rapidity gap between the two leading jets in pp collisions at $\sqrt{s}$ = 7 TeV

TL;DR

This study investigates dijet events with large rapidity gaps in proton-proton collisions at 7 TeV, measuring the gap fraction and comparing results to theoretical models and previous experiments.

Contribution

It provides the first measurement of rapidity gap events at the LHC energy and compares the data to QCD predictions including gap survival probabilities.

Findings

Rapidity gap events constitute 0.5-1% of dijet events.

Measured gap fraction varies with jet $p_T$ and separation.

Data show excess over no-color-singlet-exchange models.

Abstract

Events with no charged particles produced between the two leading jets are studied in proton-proton collisions at $\sqrt{s}$ = 7 TeV. The jets were required to have transverse momentum $p_\mathrm{T}^{\text{jet}}$ > 40 GeV and pseudorapidity 1.5 $<|\eta^{\text{jet}}| <$ 4.7, and to have values of $\eta^{\text{jet}}$ with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8 pb$^{-1}$. Events with no charged particles with $p_\mathrm{T}$ > 0.2 GeV in the interval -1 < $\eta$ < 1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5-1% of the selected dijet sample, is measured as a function of the $p_\mathrm{T}$ of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky-Fadin-Kuraev-Lipatov evolution equations, including different modelings of the non-perturbative gap survival probability.