Jet-hadron correlations relative to the event plane Pb--Pb collisions at the LHC in ALICE

224 Pages·2017·19.03 MB·English

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Doctoral Dissertations Graduate School
5-2017
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Joel Anthony Mazer
University of Tennessee, Knoxville, [email protected]
Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss
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Mazer, Joel Anthony, "Jet-hadron correlations relative to the event plane Pb--Pb collisions at the LHC in
ALICE. " PhD diss., University of Tennessee, 2017.
https://trace.tennessee.edu/utk_graddiss/4482
This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee
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[email protected].
To the Graduate Council:
I am submitting herewith a dissertation written by Joel Anthony Mazer entitled "Jet-hadron
correlations relative to the event plane Pb--Pb collisions at the LHC in ALICE." I have examined
the final electronic copy of this dissertation for form and content and recommend that it be
accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a
major in Physics.
Christine Nattrass, Major Professor
We have read this dissertation and recommend its acceptance:
Soren Sorensen, Edmund Perfect, Kenneth Read
Accepted for the Council:
Dixie L. Thompson
Vice Provost and Dean of the Graduate School
(Original signatures are on file with official student records.)
Jet-hadron correlations relative to
the event plane in Pb–Pb collisions
at the LHC in ALICE
A Dissertation Presented for the
Doctor of Philosophy
Degree
The University of Tennessee, Knoxville
Joel Anthony Mazer
May 2017
(cid:13)c by Joel Anthony Mazer, 2017
All Rights Reserved.
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Acknowledgements
I would first like to express my gratitude to my supervisor, Christine Nattrass, who
kept a sense of humor even when I lost mine. Her selfless time and care to offer help,
review my work, and answer my endless questions were of most help to me producing
this thesis work and building me as a graduate student. She also makes a heck of a
mead.
Iwouldliketothanktherestofmydoctoralcommittee: SorenSorensen,KenRead
andEdPerfect. EdforservingasmymemberfromoutsideofthePhysicsDepartment.
Soren and his enthusiam, discussions, and hospitality were very appreciated. Ken for
his lengthy conversations, error analysis advice, and his ability to bring a unique witt
to ourgroup. Irakli, Adam, Charles, and Kylefor useful discussions. Tosome genuine
friends, who had helpful conversations along the way: Adam Holt, Craig, and Brett.
And also Chris, for lending an ear, his time, and providing help when he could. I also
thank the rest of the RHIP group at both UTK and ORNL.
I am further grateful to the analysis groups of ALICE: PWGJE, EMCal Jet, Jet-
hadron correlations, EMCal and Correlations groups. I thank the jetters who came
to the meetings and listened to all my analysis updates. To Joern, Oliver, Jana,
and Marco, who served as jet conveners and provided helpful discussions and offered
insightful suggestions to the analysis. To Alice and Jochen for serving as my ARC.
To Rosi, Salvatore, Redmer, and Marta for your aid in coding, framework logistics,
GIT commits, and the occassional lego train. To the Yale group for our continued
jet-hadron team work. To Megan Connors for insight, discussion and providing me
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with my first jet-related code. Which I would transform and build off of into my
main AliROOT task. To Terry, for introducing me to the EMCal lab, the “tunnel”
and for mentoring with everything EMCal. To Martin, who continued with EMCal
support. To David, for Physics and life discussions, ping pong, your skis and boots,
mentorship, and a great supervisor while at CERN.
I would lastly like to extend my thanks and appreciation to my family, my
grandmother and mother in particular. They both kept on me to stay focused and
knew I would never give up. My mom listened to tons of rants and complaints about
how much I always had to do. I can never fully thank my girlfriend, JoAnna, who
supported me unconditionally during the last 2+ years of the analysis, which were
the hardest on many levels. She put up with my crankiness, sleeplessness, tons of
complaints, watched me go crazy, and still loved me.
THANK YOU!
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Abstract
In relativistic heavy ion collisions at the Large Hadron Collider (LHC), a hot,
dense and strongly interacting medium known as the Quark Gluon Plasma (QGP)
is produced. Quarks and gluons from incoming nuclei collide to produce partons
at high momenta early in the collisions. By fragmenting into collimated sprays of
hadrons, these partons form ’jets’. Within the framework of perturbative Quantum
Chromodynamics (pQCD), jet production is well understood in pp collisions. We can
use jets measured in pp interactions as a baseline reference for comparing to heavy ion
collisionsystemstodetectandstudyjetquenching. Thejetquenchingmechanismcan
be studied through the angular correlations of trigger jets with charged hadrons and
is examined in transverse momentum bins of the trigger jets, transverse momentum
bins of the associated hadrons, and studied as a function of collision centrality. A
highly robust and precise background subtraction method is used in this analysis to
remove the complex, flow dominated, heavy ion background. The analysis of angular
correlations for different orientations of the trigger jet relative to the event plane
allows for the study of the path length dependence of medium modifications to jets.
The event plane dependence of azimuthal angular correlations of charged hadrons
with respect to the axis of an R=0.2 reconstructed ’trigger’ full (charged + neutral)
√
jet in Pb–Pb collisions at s = 2.76 TeV in ALICE will be discussed. Results will
NN
be compared for three angular bins of the trigger jet relative to the event plane in
mid-peripheral events. The status of jet yields and widths relative to the event plane
will be discussed. There is no significant event plane dependence within the current
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uncertainties. Path length dependence of energy loss is seen to be a secondary effect
to statistical fluctuations and in-medium energy loss mechanisms.
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Table of Contents
1 Introduction 1
1.1 Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Quantum chromodynamics (QCD) . . . . . . . . . . . . . . . . . . . 4
1.3 Phases of nuclear matter . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Heavy-ion collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Studying the QGP and its signatures 11
2.1 The beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 QGP studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3 Soft Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.1 Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.2 Baryon enhancement . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.3 Transverse energy measurement (E ) . . . . . . . . . . . . . . 17
T
2.3.4 Photons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Hard Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.1 Jet quenching . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.2 Nuclear modification factor R . . . . . . . . . . . . . . . . . 24
AA
2.4.3 Quarkonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Jets 28
3.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
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3.2 Jet Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 Factorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4 Jet-finding algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.5 Why measure jets in heavy-ion collisions? . . . . . . . . . . . . . . . . 33
3.6 Ways of studying jets and using them to study the QGP . . . . . . . 35
3.7 Current status in jet research . . . . . . . . . . . . . . . . . . . . . . 36
3.7.1 Partonic Energy Loss at RHIC . . . . . . . . . . . . . . . . . 36
3.7.2 Jet Suppression at the LHC . . . . . . . . . . . . . . . . . . . 36
3.7.3 Dijet Asymmetries at the LHC . . . . . . . . . . . . . . . . . 38
3.7.4 Modification to the Fragmentation Functions in different cen-
tralities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.7.5 Jet-Hadron Correlations . . . . . . . . . . . . . . . . . . . . . 40
4 Experimental Setup 45
4.1 Large Hadron Collider (LHC) . . . . . . . . . . . . . . . . . . . . . . 45
4.2 A Large Ion Collider Experiment (ALICE) . . . . . . . . . . . . . . . 47
4.2.1 Inner Tracking System (ITS) . . . . . . . . . . . . . . . . . . . 49
4.2.2 Time Projection Chamber (TPC) . . . . . . . . . . . . . . . . 49
4.2.3 VZERO detector system . . . . . . . . . . . . . . . . . . . . . 49
4.2.4 Electromagnetic Calorimeter (EMCal) . . . . . . . . . . . . . 51
5 Analysis 54
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.2 Event selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.3 Track reconstruction and selection . . . . . . . . . . . . . . . . . . . . 58
5.3.1 Tracking Efficiency . . . . . . . . . . . . . . . . . . . . . . . . 58
5.4 EMCal cluster selection . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.4.1 EMCal timing . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.4.2 Cluster-Track matching . . . . . . . . . . . . . . . . . . . . . . 66
5.5 Jet reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
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