Energy Flow and Rapidity Gaps Between Jets in Photoproduction at HERA
H1 Collaboration, C. Adloff
TL;DR
The paper investigates energy flow and rapidity gaps between jets in photoproduction at HERA to test QCD dynamics in dijet events with large pseudorapidity separation. It measures inclusive dijet cross sections as functions of $x_{pjet}$, $x_{gjet}$, $\,Delta \,eta$, and $E_T^{gap}$, with rapidity-gap events defined by $E_T^{gap} < E_T^{cut}$ and $E_T^{cut}$ varied from $0.5$ to $2.0$ GeV. An excess of rapidity-gap events at low $E_T^{cut}$ is observed beyond standard photoproduction expectations, consistent with exchange of a strongly interacting color-singlet object between the jets. This supports the presence of color-singlet exchange processes in high-energy photoproduction and informs understanding of diffraction-like phenomena in QCD.
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.