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Heavy Ions physicsuncovering the quark-gluon coloured world (QGCW)

R. Nania- INFN Bologna

Bologna oct 2016

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LHC

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How we understand matter

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u

u

d Proton = uud (+2/3, +2/3, -1/3)

Neutron =udd (+2/3, -1/3, -1/3)

u

d

d

Particle K =u anti-s (+2/3, +1/3)

s

u

Few examples of quark content

Gluons

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More examples of quark content…

THE STANDARD MODEL

But …..

Proton = uud Neutron = udd

mp =2.3+2.3+4.8 MeV/c2 938 MeV/c2

mn =2.3+4,8+4.8 MeV/c2 939 MeV/c2

99% of the mass of the

proton/neutron is related to

the confinement energy !!!

Electromagnetic force QED Strong force QCD

QCD Asymptotic FreedomGross, Politzer, Wilczek 1973

Running coupling constants

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QCD s

coupling constants

h c ≈ 200 Mev fm

in “Natural units” 1 fm ≈ 1/ (200 MeV)

0,2 0,02 0,002fm

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B𝑑𝐸

𝑑𝑅= -

2.04𝑁

𝑅2ℎ𝑐 + 4𝜋𝑅2𝐵 = 0

𝐸 = 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 + 𝑘𝑖𝑛𝑒𝑡𝑖𝑐 =

𝐵4

3𝜋𝑅3 +

2.04𝑁

𝑅(hc)

≈ℎ

𝜆𝑓𝑜𝑟 𝑚𝑞 ≈ 0

Confinement =

bag pressure compensating quark kinetic energy

The MIT Bag model ( ‘70)First theorethical approach to confinement

𝐵 =2.04𝑁

4𝜋

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𝑅4ℎ𝑐 = 1.2

ℎ𝑐

𝑓𝑚4=1.2

200 𝑀𝑒𝑉

𝑓𝑚3= 240 𝑀𝑒𝑉/𝑓𝑚3

N= 3 𝑟 = 0.8 𝑓𝑚ℎ𝑐

1𝑓𝑚= 200 𝑀𝑒𝑉

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Improving Tc evaluation(Stefan/Boltzmann limit)

Energy density

Per degree of freedom !

Pressure

𝜀 𝑇 =𝜋2

30𝑇4

𝑃 𝑇 =1

3𝜀 𝑇 =

𝜋2

90𝑇4

• System of n objects ( hadrons or q and g) thermalized• Massless and non interacting• Zero baryonic number

Hadron gas

Ndf = 3 (+0- )

Quark gluon gas ( for 2 flavours)

Gluons : 2sx8c = 162Quarks : (7/8) x( 2s x 2f x 3c + anti-q) = 21Ndf = 37 ( > factor 10 w.r.t. hadron gas)

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Pressure(MeV/fm3)

𝑃𝑄𝐺𝑃 𝑇 = 37𝜋2

90𝑇4 − 𝐵

𝑃ℎ𝑎𝑑 𝑇 = 3𝜋2

90𝑇4

QGP phase transition

at T 145 MeV

Deconfinement at high temperature

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Energy density in lattice QCD: an even more precise estimate of Tc

𝜺 𝑻 = 𝟒𝟔𝝅𝟐

𝟑𝟎𝑻𝟒

for 3 flavors

NB: includes effects of masses and interactions

Light quarks mq /T= 0.4

2+1 = 2 light quarks + 1 massive mq/T= 1

http://www.physics.adelaide.edu.au/theory/staff/leinweber/VisualQCD/QCDvacuum/

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Quark Gluon Plasma

Quarks and gluons are confined inside hadrons, but whathappens if they collapse in a wide space region ?

Possible answers1. Do not care , nothing changes2. Do care, new phenomena may appear

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Temperature decreases

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Energy-space

Hadrons typically 1 fm = 10-15 m

h c ≈ 200 MeV fmin “Natural units”

1 fm = 1/ (200 MeV)

Energy scale hadron ≈ 200 MeV

Energy-temperature

E= KB T 1/ KB = 1.16 104 K/eV

LHC E = 5 TeV = 5 1012 eV

Tcoll = 5 1012 eV 1.16 104 K/eV = 6.38 1016 K

GOAL : probe the system at very high density and temperature1- system consists of many particles2 – system in local equilibrium

Can we use p-p ?NO !

How to study QGP in Heavy Ions Collisions( low baryon densities and high temperatures)

The goal is to produce a matter with:

• Energy density >> 1 GeV/fm3

• Lasting for > 1 fm/c• In a volume much larger than a hadron

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Where to look for QGP : The Phase Diagram

• high temperature and low baryon density (RHIC + LHC) • Very high baryon density and low temperatures (neutron stars)• Intermediate baryon densities and temperatures (SpS, Fair) -> Critical point

18np nanti-p

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AGS fixed target

Protons → 33 GeV

Si, Au → 14,6 GeV/N

NB: Nuclei energy scaled by Z/A w.r.t. protons

RHIC Collider

Protons → 250 GeV

Au → 100 GeV/N

PHENIX STAR

Brookhaven National Labs - USA

202020

CERN Large Hadron Collider

SpS (fixed target)

Protons → 450 GeV

O, S, Pb → 200 GeV/N

LHC Collider

Protons → 7000 GeV

Pb → 2500 GeV/N

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CERN Large Hadron Collider

CMS

ALICE

LHCB

ATLAS

http://urqmd.org/~weber/CERNmovies/alice.mpg

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ALICE : A Large Ion Collider Experiment

• Optimized for Heavy Ions Physics high performances tracking and PID

• Complementary to the other LHC experiments

DCAL

ITS : SPD, SDD, SSD

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HI event

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TPC

ITS

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TOF

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https://www.youtube.com/watch?v=yWBWzIUCNpw

ITS

TPC

TOF

HMPID

ALICE main detector performances

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ATLAS

CMS

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𝑦 𝑝 ≫ 𝑚 ≈ 𝜂 = − ln tan𝜃

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𝑦 =1

2ln𝐸 + 𝑝𝑧𝐸 − 𝑝𝑧

Physics Letters B 726 (2013) 610–622

𝑑𝑁

𝑑𝑦

𝑦

Rapidity differences

are Boost invariant

<𝑑𝑁

𝑑𝜂>

𝜂

Pseudo-Rapidity

𝐹𝑟𝑜𝑚 𝐸 = 𝛾𝑚 𝑎𝑛𝑑 𝑝𝑧 = 𝛾𝛽𝑚→ 𝛽 = tanh 𝑦 → 𝑓𝑜𝑟 𝑠𝑚𝑎𝑙𝑙 𝑦 → 𝑦 ≈ 𝛽

𝛽Measuring the energy density of the system - I

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∆𝑧

𝜀 =∆𝑁<𝑚𝑇>

𝑆∆𝑧=∆𝑧

𝜏

𝑑𝑁

𝑑𝑦|𝑦=0

<𝑚𝑇>

𝑆∆𝑧=

1

𝜏𝑆

𝑑𝑁

𝑑𝑦< 𝑚𝑇 > =

1

𝜏𝑆

𝑑𝐸𝑇

𝑑𝑦

𝑆

𝑑𝑁

𝑑𝑦

mT2 = m2 +px2+py2

Same transverse energy distribution <mT>

Bjorken Phys. Rev. D 27, 40 (1983)

Total energy density as sum of all contributions

Region filled with particles with velocity

0 < 𝛽 < ∆𝑧/𝑐𝜏

Around y=0

∆𝑁 = 0

𝑑𝜏 𝑑𝑁

𝑑𝛽𝑑𝛽 =

𝑑

𝜏

𝑑𝑁

𝑑𝑦

Measuring the energy density of the system - II

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Nucleon 0,13 GeV/fm3

From Bjorken we get

RHIC

= 600 / (6.52 ) = 4.6 GeV/fm3

LHC

= 2100 / (6.52 ) = 15 GeV/fm3

= 3 times RHIC

[J. Phys. G 38:124041]

𝜀 =1

𝜏𝜋𝑅2𝑑𝐸𝑇

𝑑𝑦𝜏 ≈ 1 𝑓𝑚/𝑐

Measuring the energy density of the system - III

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Temperature LHC-HI 304±51 MeV≈1.4 x RHIC ≈ 105 x T at Center of the Sun

" cocktail" decay

Thermal photons

Measuring the temperature of the system

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Observe (co-moving) volume via QM interferometry (Bose-Einstein)Used also by astronomers to measure sizes of stars (Hanbury--‐BrownTwiss HBT)

Measuring the volume of the system

Define proximity of two same-signparticles

Measure

C(q) = Signal (q)/Background(q)

Fit with

• r effective radius source• Strenght of correlation• K Coulomb wave function• 𝒩 normalization factor

𝒒 = 𝒑𝟏-𝒑𝟐

𝐶 𝑞 = 𝒩[(1 − 𝜆) + 𝜆𝐾 𝑞𝑖𝑛𝑣 (1 + 𝐺 𝑞 )]

𝐺(q)=𝑒−(𝑞𝑟)2

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LHC 2 x RHIC up to 10 fmNotice the comparison with p-Pb

Measuring the volume of the system - II

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Heavy Ions physics

Progressively moving from a statistical/thermal to a QCD based approach.

Foundamental the comparison with pp collisions to understand what new is created in HI collisions.

However, latest measurements lead to new unexpected similarities among pp p-Pb and Pb-Pb collisions.

Universe evolution is based on QCD interactions in a coloured world and next steps is to try to uncover itsproperties.

Central (low %)Peripheral (high %)

Centrality : fraction of the total cross section

Variables definitions

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In this case with

the VZERO

trigger counter

Phys. Rev. C 88, 044909R. Glauber, Phys. Rev. 100 (1955)