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Title: Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector

Abstract

In this thesis we present the measurement of the inclusive isolated prompt photon cross section with a total integrated luminosity of 2.5 fb -1 of data collected with the CDF Run II detector at the Fermilab Tevatron Collider. The prompt photon cross section is a classic measurement to test perturbative QCD (pQCD) with potential to provide information on the parton distribution function (PDF), and sensitive to the presence of new physics at large photon transverse momentum. Prompt photons also constitute an irreducible background for important searches such as H → γγ, or SUSY and extra-dimensions with energetic photons in the final state. The Tevatron at Fermilab (Batavia, U.S.A.) is currently the hadron collider that operates at the highest energies in the world. It collides protons and antiprotons with a center-of-mass energy of 1.96 TeV. The CDF and the D0 experiments are located in two of its four interaction regions. In Run I at the Tevatron, the direct photon production cross section was measured by both CDF and DO, and first results in Run II have been presented by the DO Collaboration based on 380 pb -1. Both Run I and Run II results show agreement with the theoretical predictions exceptmore » for the low p T γ region, where the observed and predicted shapes are different. Prompt photon production has been also extensively measured at fixed-target experiments in lower p T γ ranges, showing excess of data compared to the theory, particularly at high x T. From an experimental point of view, the study of the direct photon production has several advantages compared to QCD studies using jets. Electromagnetic calorimeters have better energy resolution than hadronic calorimeters, and the systematic uncertainty on the photon absolute energy scale is smaller. Furthermore, the determination of the photon kinematics does not require the use of jet algorithms. However, the measurements using photons require a good understanding of the background, mainly dominated by light mesons (π 0 and η) which decay into two very collinear photons. Since these photons are produced within a jet, they tend to be non-isolated in most of the cases, and can be suppressed by requiring the photon candidates to be isolated in the calorimeter. In the case the hard scattered parton hadronizes leaving most of its energy to the meson, the photon produced in the decay will not be surrounded by large energy depositions. To further reduce this remaining isolated background, we present a new technique based on the isolation distribution in the calorimeter. The measured cross section is compared to next-to-leading order (NLO) pQCD calculations, which have been corrected for non-perturbative contributions. This thesis is organized as follows: we start with a brief review of QCD theory and the formalism to calculate cross sections in Chapter 2, where we also introduce the physics of prompt photon production and summarize the current status of the prompt photon phenomenology. Chapter 3 contains a description of the Tevatron and the CDF detector. The experimental measurement is described in Chapter 4, where we provide details on the different datasets used in the measurement, the trigger, and the event selection requirements. Most of this Chapter is devoted to the explanation of the background subtraction method and the determination of the photon signal fraction. The systematic uncertainties on the measurement are evaluated in Chapter 5, while Chapter 6 discusses the final results and the comparison to the theoretical predictions. Finally, the conclusions are presented in Chapter 7.« less

Authors:
 [1]
  1. Autonomous Univ. of Barcelona (Spain)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
957565
Report Number(s):
FERMILAB-THESIS-2009-18
TRN: US1000646
DOE Contract Number:  
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ALGORITHMS; ANTIPROTONS; CALORIMETERS; CROSS SECTIONS; DECAY; DISTRIBUTION; DISTRIBUTION FUNCTIONS; ENERGY RESOLUTION; FERMILAB; FERMILAB COLLIDER DETECTOR; FERMILAB TEVATRON; HADRONS; LUMINOSITY; MESONS; PHOTONS; PHYSICS; PROTONS; QUANTUM CHROMODYNAMICS; TRANSVERSE MOMENTUM; Experiment-HEP

Citation Formats

Deluca Silberberg, Carolina. Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector. United States: N. p., 2009. Web. doi:10.2172/957565.
Deluca Silberberg, Carolina. Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector. United States. https://doi.org/10.2172/957565
Deluca Silberberg, Carolina. Wed . "Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector". United States. https://doi.org/10.2172/957565. https://www.osti.gov/servlets/purl/957565.
@article{osti_957565,
title = {Measurement of the inclusive isolated prompt photon production cross section at the Tevatron using the CDF detector},
author = {Deluca Silberberg, Carolina},
abstractNote = {In this thesis we present the measurement of the inclusive isolated prompt photon cross section with a total integrated luminosity of 2.5 fb-1 of data collected with the CDF Run II detector at the Fermilab Tevatron Collider. The prompt photon cross section is a classic measurement to test perturbative QCD (pQCD) with potential to provide information on the parton distribution function (PDF), and sensitive to the presence of new physics at large photon transverse momentum. Prompt photons also constitute an irreducible background for important searches such as H → γγ, or SUSY and extra-dimensions with energetic photons in the final state. The Tevatron at Fermilab (Batavia, U.S.A.) is currently the hadron collider that operates at the highest energies in the world. It collides protons and antiprotons with a center-of-mass energy of 1.96 TeV. The CDF and the D0 experiments are located in two of its four interaction regions. In Run I at the Tevatron, the direct photon production cross section was measured by both CDF and DO, and first results in Run II have been presented by the DO Collaboration based on 380 pb-1. Both Run I and Run II results show agreement with the theoretical predictions except for the low pTγ region, where the observed and predicted shapes are different. Prompt photon production has been also extensively measured at fixed-target experiments in lower pTγ ranges, showing excess of data compared to the theory, particularly at high xT. From an experimental point of view, the study of the direct photon production has several advantages compared to QCD studies using jets. Electromagnetic calorimeters have better energy resolution than hadronic calorimeters, and the systematic uncertainty on the photon absolute energy scale is smaller. Furthermore, the determination of the photon kinematics does not require the use of jet algorithms. However, the measurements using photons require a good understanding of the background, mainly dominated by light mesons (π0 and η) which decay into two very collinear photons. Since these photons are produced within a jet, they tend to be non-isolated in most of the cases, and can be suppressed by requiring the photon candidates to be isolated in the calorimeter. In the case the hard scattered parton hadronizes leaving most of its energy to the meson, the photon produced in the decay will not be surrounded by large energy depositions. To further reduce this remaining isolated background, we present a new technique based on the isolation distribution in the calorimeter. The measured cross section is compared to next-to-leading order (NLO) pQCD calculations, which have been corrected for non-perturbative contributions. This thesis is organized as follows: we start with a brief review of QCD theory and the formalism to calculate cross sections in Chapter 2, where we also introduce the physics of prompt photon production and summarize the current status of the prompt photon phenomenology. Chapter 3 contains a description of the Tevatron and the CDF detector. The experimental measurement is described in Chapter 4, where we provide details on the different datasets used in the measurement, the trigger, and the event selection requirements. Most of this Chapter is devoted to the explanation of the background subtraction method and the determination of the photon signal fraction. The systematic uncertainties on the measurement are evaluated in Chapter 5, while Chapter 6 discusses the final results and the comparison to the theoretical predictions. Finally, the conclusions are presented in Chapter 7.},
doi = {10.2172/957565},
url = {https://www.osti.gov/biblio/957565}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2009},
month = {4}
}

Thesis/Dissertation:
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