polarization in proton-proton collisions with the ALICE detector at the LHC

199 Pages·2017·14.38 MB·English

by  Arianna Batista Camejo

Study of J/ψ polarization in proton-proton collisions
with the ALICE detector at the LHC
Arianna Batista Camejo
To cite this version:
Arianna Batista Camejo. Study of J/ψ polarization in proton-proton collisions with the ALICE
detector at the LHC. Accelerator Physics[physics.acc-ph]. Université Clermont Auvergne [2017-2020],
2017. English. ￿NNT: 2017CLFAC004￿. ￿tel-01610078￿
HAL Id: tel-01610078
https://theses.hal.science/tel-01610078
Submitted on 4 Oct 2017
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N0 d’ordre : D. U. 2790 PCCF T 1701
´
UNIVERSITE CLERMONT AUVERGNE
U.F.R. Sciences et Technologies
´
ECOLE DOCTORALE DES SCIENCES FONDAMENTALES
N0 d’ordre : 904
`
THESE
pr´esent´ee pour obtenir le grade de
´
DOCTEUR D’UNIVERSITE
Sp´ecialit´e : Physique des particules
par : Arianna Batista Camejo
Master on Nuclear Physics
Study of J/ψ polarization in proton-proton collisions
with the ALICE detector at the LHC
Th`ese soutenue le 20 janvier 2017, devant le jury d’examen :
Pr´esident M. P. Dupieux LPC (Clermont-Ferrand)
Rapporteurs Mme R. Arnaldi INFN (Turin, Italie)
M. I. Laktineh IPNL (Lyon)
Examinateurs M. J. E. Castillo Castellanos CEA/Irfu (Saclay)
Mme K. Shtejer Diaz CEADEN (La Havane, Cuba)
Directeurs de th`ese Mme V. Ramillien LPC (Clermont-Ferrand)
M. P. Rosnet LPC (Clermont-Ferrand)

Contents
Abstract 1
1 Introduction to quarkonia 3
1.1 Standard Model and the strong interaction . . . . . . . . . . . . . . . . . . 3
1.1.1 Standard Model of Particle Physics . . . . . . . . . . . . . . . . . . 3
1.1.2 Characteristics of the strong interaction . . . . . . . . . . . . . . . 5
1.2 Heavy quarkonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.1 Discovery of quarkonium states . . . . . . . . . . . . . . . . . . . . 7
1.2.2 Charmonium spectrum . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2.3 J/ψ yields and decays . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 Theoretical description of quarkonium production . . . . . . . . . . . . . . 10
1.3.1 Nonrelativistic QCD factorization . . . . . . . . . . . . . . . . . . . 12
1.3.2 The Color-Singlet model . . . . . . . . . . . . . . . . . . . . . . . . 12
1.3.3 CDF results: ψ(2S) anomaly and polarization puzzle . . . . . . . . 13
1.4 Quarkonia in heavy ions collisions . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.1 Quarkonium polarization in a quark-gluon plasma . . . . . . . . . . 17
2 Polarization concepts 19
2.1 Decay distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1.1 One-dimensional method . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1.2 Asymmetry of angular distribution method . . . . . . . . . . . . . . 23
2.2 Reference systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.1 Classical reference axis . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.2 Frame invariant formalism . . . . . . . . . . . . . . . . . . . . . . . 26
2.3 Experimental review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.1 Quarkonium polarization measurements at collider experiments . . 27
2.3.2 Results from fixed-target experiments . . . . . . . . . . . . . . . . . 34
2.3.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3 Experimental facility 37
3.1 The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2 The ALICE detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.1 The ALICE coordinate system . . . . . . . . . . . . . . . . . . . . . 40
3.2.2 The ALICE trigger system . . . . . . . . . . . . . . . . . . . . . . . 40
3.3 Central Barrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
i
3.3.1 Inner Tracking System . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.3.2 Time Projection Chamber . . . . . . . . . . . . . . . . . . . . . . . 44
3.3.3 Transition Radiation Detector . . . . . . . . . . . . . . . . . . . . . 45
3.3.4 Time Of Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3.5 High Momentum Particle Identification . . . . . . . . . . . . . . . . 48
3.3.6 Photon Spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3.7 Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . . . . . 50
3.4 Global Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.1 Zero Degree Calorimeters . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.2 V0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4.3 T0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.4.4 Forward Multiplicity Detector . . . . . . . . . . . . . . . . . . . . . 53
3.4.5 Photon Multiplicity Detector . . . . . . . . . . . . . . . . . . . . . 53
3.5 Forward muon spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.5.1 Absorbers and shielding . . . . . . . . . . . . . . . . . . . . . . . . 55
3.5.2 Tracking system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5.3 Trigger system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.6 ALICE Upgrade project . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4 Performance of a new Front-End Electronics (FEERIC) for the Muon
Trigger RPCs 67
4.1 RPCs original working conditions . . . . . . . . . . . . . . . . . . . . . . . 67
4.2 Perspectives for the LHC Run 3 . . . . . . . . . . . . . . . . . . . . . . . . 68
4.3 RPC performance monitoring . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3.1 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3.2 Cluster size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.3.3 Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.3.4 Charge per hit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.3.5 Summary of RPC performance during Run 1 . . . . . . . . . . . . . 72
4.4 FEERIC performance study in cavern . . . . . . . . . . . . . . . . . . . . . 74
4.4.1 Setting the RPC working conditions . . . . . . . . . . . . . . . . . 74
4.4.2 Charge per hit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.4.3 Recent performance results . . . . . . . . . . . . . . . . . . . . . . . 81
5 Polarization Analysis 83
5.1 Data selection and analysis cuts . . . . . . . . . . . . . . . . . . . . . . . . 84
5.1.1 Event selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.1.2 Single muon track cuts . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.2 Data sample and simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.2.1 Raw data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.2.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.2.3 Acceptance efficiency maps . . . . . . . . . . . . . . . . . . . . . 90
×
5.3 Study of polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.3.1 Signal extraction and raw angular distributions . . . . . . . . . . . 91
5.3.2 Corrected angular distributions . . . . . . . . . . . . . . . . . . . . 98
ii
5.3.3 Polarization parameters as a function of p . . . . . . . . . . . . . . 100
T
5.4 Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5.4.1 Systematics associated to the input MC . . . . . . . . . . . . . . . 102
5.4.2 Trigger response function . . . . . . . . . . . . . . . . . . . . . . . . 107
5.4.3 J/ψ from b-hadron decays . . . . . . . . . . . . . . . . . . . . . . . 111
5.4.4 Combination of systematics . . . . . . . . . . . . . . . . . . . . . . 113
6 Results and discussion 115
6.1 J/ψ polarization in pp collisions at √s = 8 TeV . . . . . . . . . . . . . . . 115
6.1.1 Inclusive J/ψ results . . . . . . . . . . . . . . . . . . . . . . . . . . 115
6.1.2 Prompt J/ψ results . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
6.2 Comparison with previous experimental results . . . . . . . . . . . . . . . . 123
6.3 Comparison with theoretical predictions . . . . . . . . . . . . . . . . . . . 124
Conclusions 129
A Angular distributions 131
B Checks on the signal extraction and A ε correction 139
×
C Systematic uncertainties 140
C.1 Systematic uncertainties associated to the signal extraction . . . . . . . . . 140
C.2 Systematic uncertainties associated to the MC input . . . . . . . . . . . . 143
C.3 Summary of all systematic uncertainties . . . . . . . . . . . . . . . . . . . 145
Acknowledgements 148
iii
iv
Abstract
The main purpose of the ALICE experiment is the study and characterization of the
Quark Gluon Plasma (QGP), a state of nuclear matter in which quarks and gluons are
¯
deconfined. Quarkonia (bound states of a heavy quark Q and its anti-quark Q) consti-
tute one of the most interesting probes of the QGP. Besides this motivation, the study of
quarkonium production is very interesting since it can contribute to our understanding of
Quantum Chromodynamics, the theory of strong interactions.
The formation of quarkonium states in hadronic collisions is not yet completely under-
stood. The two main theoretical approaches to describe the production of quarkonium
states, theColorSingletModelandtheNon-RelativisticQCDframework(NRQCD),have
historically presented problems to simultaneously describe the production cross section
and polarization of such states. On the experimental side, quarkonium polarization mea-
surements have not always been complete and consistent between them. So, neither from
the theoretical nor from the experimental point of view the situation was clear.
Improved methods for the measurement of quarkonium polarization have been recently
proposed, highlighting the necessity to perform the measurements of all polarization pa-
rameterswithrespecttodifferentreferenceaxes. Inthiscontext, newmeasurementscould
help to improve and set new constraints to the calculations. ALICE has measured the
J/ψ polarization in pp collisions at √s= 7 TeV. The higher statistics of the 8 TeV data
with respect to the 7 TeV data allows to extend the p range of the measurements. This
T
thesis presents a complete measurement of J/ψ polarization, i.e. the three polarization
parameters, in two polarization frames: the Collins-Soper and Helicity frames.
The results show no significant J/ψ polarization in the kinematic domain studied: 2.5 <
˜
y < 4.0 and 2 < p < 15 GeV/c. The measurement of a frame invariant parameter λ,
T
was also performed to ensure that no bias was present in the analysis procedure. The
comparison with different theoretical predictions shows that there is not yet a satisfactory
description of quarkonium production. None of the present theoretical approaches is able
to describe both, the cross section and polarization measurements.
1
2
Chapter 1
Introduction to quarkonia
In this chapter a general introduction to heavy quarkonium systems is given, with em-
phasis on charmonia (and specifically J/ψ). The main characteristics of such systems,
the theoretical considerations in the description of their production, and the motivations
for their study in hadron and heavy ions collisions will be covered.
1.1 Standard Model and the strong interaction
1.1.1 Standard Model of Particle Physics
The Standard Model (SM) is the theory that describes the properties of elementary par-
ticles and their electromagnetic, weak and strong interactions. It was established in the
1960s and it has been confirmed by a large number of experimental results (historical and
recent results are highlighted in [1]).
In the SM, particles are of two kind: fermions, which are the matter particles and bosons,
responsible of interactions. According to their mass hierarchy, the matter particles are
grouped in three generations, their properties are summarized in Table 1.1 for quarks
(left) and leptons (right).
Table 1.1: Quarks and leptons of the Standard Model. From [2].
Flavour Mass Charge (e) Flavour Mass (MeV/c2) Charge (e)
u 2.2+0.6 MeV/c2 2/3 e 0.51 0.31 -1
0.4
±
−
d 4.7+0.5 MeV/c2 -1/3 ν < 2 10 3 0
0.4 e −
×
−
c 1.27 0.03 GeV/c2 2/3 µ 105.7 2.4 -1
± ±
s 96+8 MeV/c2 -1/3 ν < 2 10 3 0
4 µ −
×
−
t 173.5 0.6 GeV/c2 2/3 τ 1776.86 0.12 -1
± ±
b 4.18+0.04 GeV/c2 -1/3 ν < 2 10 3 0
0.03 τ −
×
−
The force carriers (vector bosons) are: the photon which mediates the electromagnetic
interactions, the W and Z0 bosons responsible for the weak interaction and gluons which
±
3