Abstract
Collision of particles at high energies at accelerators is the main source of data used to obtain deeper understanding of the fundamental interactions and the structure of the matter. Processes of isolated photon production have provided many tests of theoretical descriptions of the universe on scales smaller than the proton. This work is dedicated to the analysis of the large amount of collision data that has been accumulated at ZEUS in 2004-2007 period and new methods of processing isolated photons that have been proposed. The authors develop software algorithms that allow obtaining the signal of isolated photons from the data collected on the ZEUS detector at electron-proton collider HERA, calculating the differential cross sections, and comparing the measured data with PYTHIA Monte Carlo predictions. Taking into account the features of the ZEUS detector, the photon signal is separated from the background events and the number of isolated photons is calculated. Computational mathematical and numerical methods have been used to simulate the interaction of particles in the detector. Monte Carlo predictions for differential cross sections as functions of the pseudorapidity and transverse energy of the photon ηg, ETg and the jet ηjet, ETjet, and the fraction of the photon momentum хgmeas carried by the interacting parton have been calculated and compared with the experimental data. The results of the study are compared with the previous studies and show for the first time that all isolated photon HERA measurements are consistent with each other. New results show improved uncertainties. The formation of isolated inclusive photons and photons with the accompanying jet was measured in photoproduction with ZEUS detector at HERA collider using the integrated luminosity of 374 ± 7 pb-1. For the first time, more complex Monte-Carlo simulation models of isolated photons for ZEUS detector were generated and applied, and the description of the photon signal was improved. It has been found that PYTHIA describes the shape of the cross section as a function of ηg well enough, but does not fully reproduce the shape of ETg, ETjet, and the middle region of хgmeas, while ηjet is described not very well. The reason for this discrepancy can be the lack of corrections of higher orders in the predictions for cross sections of direct photons. Scaling of the cross sections obtained with PYTHIA improves the description of ETg and ηg. The unsatisfactory description of ηjet indicates that further studies are required.
Highlights
Collision of particles at high energies at accelerators is the main source of data used to obtain deeper understanding of the fundamental interactions and the structure of the matter
The following cuts were used to obtain a clean sample of photoproduction events: - If an event has a candidate for deep inelastic scattering (DIS) electron in SINISTRA [32, 33] with a probability of more than 90% and yel < 0.7, such event is removed from the final stack of candidate events for photon. - 0.2 < yJB < 0.7 A method that has been well established in other ZEUS publications [34,35,36] has been used here as well
The lower limit is set due to poor energy resolution at low energies: 6 < ET γ < 15 GeV. - By requiring that at least 90% of the energy of a candidate for the photon is stored in electromagnetic calorimeter layer, we reduce the hadron background: FEMC = EEMC / Etot > 0.9, where EEMC – the energy in the electromagnetic calorimeter layer, Etot – the total measured energy
Summary
Collision of particles at high energies at accelerators is the main source of data used to obtain deeper understanding of the fundamental interactions and the structure of the matter. FORMULATION OF THE PROBLEM The purpose of this work is to develop algorithms for obtaining with a high precision the signal of isolated photons from the sample of data collected by the ZEUS detector at the electron-proton collider HERA during 2004-2007 period [13, 14], calculate the differential cross sections using this signal and compare them with predictions of Monte Carlo simulations (MC). The radiated photons, both in the direct and resolved mode, are selected from the two-jet MC sample obtained with the subprocesses shown in Table 2 with hard photon emission in the final state These are the processes of photon-lepton - Compton scattering, prompt photons, point photons in the photoproduction and QCD jet. Table. 2 lists the processes depicted in Fig. 1 (c, d)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
