10 - H1 - Desy

xiv
Contents
the two photon decay channel for relatively small Higgs particle masses (M H < 140 GeV).
In this thesis the prompt photon measurement in photoproduction is presented. The
study is based on data collected by the H1 detector in the years 2004-2007 with an
integrated luminosity of 340 pb −1 . The study significantly extends the phase space of the
previous prompt photon measurement in photoproduction towards photons produced in
the forward region of the detector and lower event inelasticities. The extension enhances
the contribution of resolved events and consistently improves the sensitivity to the parton
density function of the photon.
The main experimental difficulty are secondary photons produced in the decays of unstable
neutral hadrons, such as π 0 → γγ. The prompt photon signal is extracted with a
multivariate analysis based on the shape of the energy deposits in the calorimeter. The
high statistics of HERA II data used for this analysis, increased by a factor of three compared
to the previous measurement, allows to use a sophisticated unfolding method to
separate photons from background and determine the cross sections. The production of
prompt photons is studied in the inclusive phase space and in the phase space of photons
accompanied by the hadronic jet.
The results of this work have been approved by the H1 collaboration, have been shown
on several conferences and are in the process of being published.
The outline of this work is as follows:
• Chapter 1, Theoretical framework, lays the basis needed for the understanding of this
study. General concepts of particle physics are introduced with a special emphasis
on the prompt photon production. A review on recent prompt photon measurement
is also given.
• Chapter 2, Theoretical predictions, describes the QCD calculations and the Monte
Carlo predictions used in this analysis.
• Chapter 3, The H1 experiment at HERA, provides an overview of the HERA collider
and the H1 detector, with the most important detector compontents for this analysis
briefly highlighted.
• Chapter 4, Event reconstruction and preselection, gives the basic informations of the
data used in this analysis and its reconstruction. The trigger used and the selection
of electron-proton interactions is also discussed.
• Chapter 5, Prompt photon selection, presents the prompt photon in photoproduction
event signature with detailed description of cuts applied to obtain the final selection.
• Chapter 6, Photon signal extraction, gives an overview of the method employed to
discriminate between prompt photon signal and neutral hadron background. It is
based on the cluster shapes combined with a multivariate analysis.
• Chapter 7, Calibration and tuning, shortly summarises efforts made to improve the
Monte Carlo description of the data, particularly to correct the simulation of the
cluster shapes which is essential for the final results.