Diffractive processes in antiproton-proton collision at √s = 1.96 TeV in the D0 experiment

Abstract

A first study of single diffractive central high-pT dijet events in p$\bar{p}$ collisions at center-of-mass energy √s = 1.96 TeV is presented, using data recorded by the D0 detector at the Tevatron during RunIIa in 2002-2004. The total integrated luminosity corresponding to the data sample is 398 pb-1. A diffractive sample is selected using a rapidity gap approach. A precise definition of the rapidity gap constitutes the first part of the thesis. The rapidity gap is defined by means of two parts of the D0 detector--luminosity detectors and calorimeter. Luminosity detectors serve as a basic indicators of diffractive candidates and the calorimeter is used to confirm the low energy activity in the forward region (a rapidity gap). Presented studies of energy deposited in forward part of calorimeter by various types of events yield two rapidity gap definitions. Both of them use a fixed rapidity interval in calorimeter |η| ϵ [2.6,5.2] and introduce an upper limit on the energy deposited in this region. First definition, which corresponds to the lowest systematical errors, uses a limit of 10 GeV, an energy limit in the second definition is set to 3 GeV. This alternative definition corresponds to the lowest contamination of diffractive sample by non-diffractive events, on the other hand it is accompanied with rejection of high percentage of diffractive candidates. Using the gap definition dijet diffractive data are then selected and compared to inclusive dijet events in various distributions. The main focus is to measure the difference in azimuthal angles between two leading jets in events with at least two high pt central jets. This variable is sensitive to the dynamics of the process. Indeed, the results show the different behavior of ΔΦ distributions between the inclusive and diffractive samples. It is also shown that this difference is bigger for lower pT jets. Other distributions presented in the thesis show that most of the properties are the same for inclusive and diffractive events. The only observed difference is in the transversal properties of the jets, which could be explained as that diffractive jets are narrower than inclusive ones. Results are compared to Monte Carlo Pomwig (for diffractive sample) and Herwig (for inclusive sample); both show a good agreement with the data.

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