Post on 19-Feb-2019
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Heavy Ions physicsuncovering the quark-gluon coloured world (QGCW)
R. Nania- INFN Bologna
Bologna oct 2016
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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
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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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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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
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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𝑦 𝑝 ≫ 𝑚 ≈ 𝜂 = − ln tan𝜃
2
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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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.