UNIVERSIDADE ESTADUAL DE CAMPINAS Instituto de F sica Gleb Wataghin Jo ao Paulo Picchetti

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UNIVERSIDADE ESTADUAL DE CAMPINAS

Instituto de F´ısica “Gleb Wataghin”

Jo˜ao Paulo Picchetti

Estudando o impacto do tamanho do nucleon em

colis˜

oes de ´

ıons pesados relativ

ısticos

Studying the impact of the nucleon size in relativistic

heavy-ion collisions

Campinas

2022

arXiv:2210.03186v1 [nucl-th] 6 Oct 2022

Jo˜ao Paulo Picchetti

Studying the impact of the nucleon size in relativistic

heavy-ion collisions

Estudando o impacto do tamanho do nucleon em

colis˜

oes de ´

ıons pesados relativ

ısticos

Disserta¸c˜ao apresentada ao Instituto de F´ısica

“Gleb Wataghin” da Universidade Estadual de Campinas

como parte dos requisitos exigidos para obten¸c˜ao do

t´ıtulo de Mestre em f´ısica, na ´area de f´ısica.

Dissertation presented to the “Gleb Wataghin”

Institute of Physics of the University of Campinas

in partial fulﬁllment of the requeriments for the

degree of Master in Physics, in the area of Physics.

Supervisor: Jun Takahashi

ESTE TRABALHO CORRESPONDE `

A VERS ˜

AO FINAL

DA DISSERTAC¸ ˜

AO DEFENDIDA PELO ALUNO

JO˜

AO PAULO PICCHETTI, E ORIENTADO

PELO PROF. DR. JUN TAKAHASHI.

Campinas

2022

Abstract

Under the extreme conditions of temperature generated in relativistic heavy-ion collisions, a fasci-

nating ﬂuid-like state of matter where quarks and gluons are no longer conﬁned is formed, the Quark

Gluon Plasma (QGP). The most modern computational approaches are multi-stage (hybrid) simula-

tions, in which diﬀerent models are used in a chain structure, each one dedicated to the description

of a speciﬁc stage of the collision.

The hydrodynamic stage of the simulation requires an energy density proﬁle of the system as an

initial condition. In the process of converting the two colliding nuclei in such an energy distribution,

some speciﬁcation about the nucleon size inevitably has to be made. Nucleons are usually modeled

as bidimensional Gaussians, and the Gaussian width (the nucleon-width) is a free parameter of the

simulation. A best-ﬁt value of the nucleon-width can be inferred by Bayesian Analyses, where the

model is confronted with experimental data.

Some of the most recent analyses have obtained surprisingly large values for the nucleon width

parameter, exceeding in over 50 % the current value for the proton charged radius. This motivates

the development of a better understanding of the role played by this parameter inside the simulation.

In this work, we perform simulations of relativistic heavy-ion collisions using a state-of-the-art

hybrid simulation chain, using three diﬀerent values of the nucleon width inside the initial condition

generator TRENTo, and systematically investigate its eﬀects on the initial condition characteristics

and observables. The nucleon-width strongly aﬀects the eccentricity harmonics and the gradients in

the initial condition. The mean pTof particles in the simulation using w= 0.5 fm is much larger than

experimental data. We associate this to the combination of stronger gradients in the initial condition

and the coupling of a conformal pre-equilibrium dynamics to the hydrodynamic simulation.

Keywords: Heavy-ion phenomenology, Heavy-ion collisions, High-energy nuclear physics.

Contents

1 Introduction 6

1.1 TheStandardModel..................................... 6

1.2 Quantum Chromodynamics (QCD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.3 TheQCDPhaseDiagram .................................. 10

2 Relativistic heavy-ion collisions 13

2.1 Historicaloverview...................................... 13

2.2 Space-time evolution of relativistic heavy-ion collisions . . . . . . . . . . . . . . . . . . 14

2.3 Basic kinematic variables, coordinate system and centrality . . . . . . . . . . . . . . . 16

2.4 Experimental observables and evidences of QGP formation . . . . . . . . . . . . . . . 18

2.4.1 Multiplicity...................................... 18

2.4.2 Transverse momentum distributions . . . . . . . . . . . . . . . . . . . . . . . . 20

2.4.3 Anisotropicﬂow ................................... 21

2.5 TheInitialCondition..................................... 23

2.5.1 TheGlauberModel ................................. 23

2.5.2 Eccentricity harmonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3 Simulating heavy-ion collisions 28

3.1 The initial condition: TRENTo ............................... 28

3.2 Pre-equilibrium dynamics: KøMPøST . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.3 Hydrodynamic evolution: MUSIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.4 Particlization:iSS ...................................... 35

3.5 Hadronicphase:UrQMD .................................. 37

4 Motivation 39

4.1 Thenucleonsize ....................................... 39

4.2 Constraining the hybrid simulations: Bayesian Analysis . . . . . . . . . . . . . . . . . 41

4.3 The nucleon-width parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5 Results 48

5.1 Characterizing the initial condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.1.1 Participants and binary collisions . . . . . . . . . . . . . . . . . . . . . . . . . . 51

5.1.2 Eccentricity harmonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

5.2 Finalstateobservables.................................... 55

5.2.1 Charged particle multiplicity density at mid-rapidity . . . . . . . . . . . . . . . 55

5.2.2 Mean transverse momentum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

5.2.3 Anisotropicﬂow ................................... 58

5.2.4 BlastWaveanalysis ................................. 61

6 Conclusions 63

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摘要：

UNIVERSIDADEESTADUALDECAMPINASInstitutodeFsica\GlebWataghin"Jo~aoPauloPicchettiEstudandooimpactodotamanhodonucleonemcolis~oesdeonspesadosrelativsticosStudyingtheimpactofthenucleonsizeinrelativisticheavy-ioncollisionsCampinas2022Jo~aoPauloPicchettiStudyingtheimpactofthenucleonsizeinrelativistic...

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UNIVERSIDADE ESTADUAL DE CAMPINAS Instituto de F sica Gleb Wataghin Jo ao Paulo Picchetti

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