Energy Flow and Rapidity Gaps Between Jets in Photoproduction at HERA

TL;DR

This study measures dijet production and rapidity gaps in photon-proton collisions at HERA, revealing an excess of gap events at low E_T^cut likely due to color singlet exchange.

Contribution

It provides the first detailed measurement of rapidity gap fractions in photoproduction, indicating evidence for color singlet exchange beyond standard models.

Findings

Observed excess of rapidity gap events at low E_T^cut.

Measured dijet cross sections as functions of multiple variables.

Evidence supporting color singlet exchange in photoproduction.

Abstract

Dijet events in photon-proton collisions in which there is a large pseudorapidity separation Delta eta > 2.5 between the two highest E_T jets are studied with the H1 detector at HERA. The inclusive dijet cross sections are measured as functions of the longitudinal momentum fractions of the proton and photon which participate in the production of the jets, x_pjet and x_gjet respectively, Delta eta, the pseudorapidity separation between the two highest E_T jets, and E_T^gap, the total summed transverse energy between the jets. Rapidity gap events are defined as events in which E_T^gap is less than E_T^cut, for E_T^cut varied between 0.5 and 2.0 GeV. The fraction of dijet events with a rapidity gap is measured differentially in Delta eta, x_pjet and x_gjet. An excess of events with rapidity gaps at low values of E_T^cut is observed above the expectation from standard photoproduction processes. This excess can be explained by the exchange of a strongly interacting colour singlet object between the jets.