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Ralf Averbeck
ExtreMe Matter Institute EMMI and Research Division
GSI Helmholtzzentrum für Schwerionenforschung
Darmstadt, Germany
Winter Term 2012
Ruprecht-Karls-University, Heidelberg
High Energy Frontier –
Recent Results from the
LHC: Heavy Ions I
R. Averbeck, 2 Heidelberg, 22.11.2012
Pb-Pb @ √sNN=2.76 TeV
R. Averbeck, 3 Heidelberg, 22.11.2012
lecture 1 (22.11.): introduction
basics of relativistic heavy-ion collisions
lecture 2 (29.11.): soft probes
hadron yields & spectra
hydrodynamics & collective motion
lecture 3 (13.12.): hard probes
jets
heavy-flavor hadrons
lecture 4 (20.12.): quarkonia & el.magn. probes
quest for J/y suppression/enhancement
direct & thermal photons
dileptons
Outline
R. Averbeck, 4 Heidelberg, 22.11.2012
Some books (not needed)
R. Averbeck, 5 Heidelberg, 22.11.2012
strong interaction binds quarks in hadrons
binds nucleons in nuclei
described by QCD interaction between particles
carrying color charge
mediated by gluon exchange
gluons are colored themselves! (→ complicated vacuum)
QCD: a very successful theory jets / particle production at high pT
heavy-flavor production
….
with two fundamental properties/puzzles
QCD (Quantum Chromo Dynamics)
R. Averbeck, 6 Heidelberg, 22.11.2012
strong color field
potential energy grows with distance !!! “white” proton
let’s look at an atom…
…isolating the constituents works
nucleus
electron
quark
quark-antiquark pair
from the vacuum
“white” proton (baryon) (confinement)
“white” 0 (meson) (confinement)
confinement: fundamental property of QCD:
- colored objects can’t be isolated
neutral atom
Confinement
Animation: C. Markert
isolated quarks have never been detected
R. Averbeck, 7 Heidelberg, 22.11.2012
Hadron masses
proton: two up quarks and a down quark sum of quark masses: ~12 MeV
proton mass: ~938 MeV
how does nature generate massive
hadrons from (almost) massless quarks? it happened a long time ago …
R. Averbeck, 8 Heidelberg, 22.11.2012
A short history of the universe
first step towards
the generation
of mass
T ~ 100 GeV elementary particles get mass via Higgs mechanism
R. Averbeck, 9 Heidelberg, 22.11.2012
current quark mass generated by spontaneous symmetry breaking
(Higgs mass)
contributes ~2% to the visible (our) mass
Quark masses
1
10
100
1000
10000
100000
1000000
u d s c b t
QCD Mass
Higgs Mass
constituent quark
mass (QCD mass) generated during
hadronization
related to chiral symmetry
breaking
quark & gluon condensates
R. Averbeck, 10 Heidelberg, 22.11.2012
A short history of the universe
second step towards
the generation
of mass
T ~ 100 MeV hadronization
R. Averbeck, 11 Heidelberg, 22.11.2012
Hadrons as complex objects hadron = complex excitation of valence
quarks in the presence of quark and gluon
condensates
Frank Wilczek: mass without mass
mass given by
energy stored in
motion of quarks
energy in color
gluon fields
R. Averbeck, 12 Heidelberg, 22.11.2012
mass of ordinary matter ~2% via Higgs
~98% via QCD
can we prove this experimentally?
Hadronization in vacuum
(successful?!) Higgs
search at the LHC
QCD:
study transition
between quark-gluon
and hadronic matter arXiv:1207.7235
R. Averbeck, 13 Heidelberg, 22.11.2012
Phase transitions hadronization took place a few
microseconds after the Big Bang
common phenomenon: phase transition examples
– water vapor water ide – electromagnetic interaction QED
– quarks/gluons protons/neutrons nuclei – strong interaction QCD
R. Averbeck, 14 Heidelberg, 22.11.2012
nuclear matter hadronic matter Quark-Gluon-Plasma
Strongly interacting matter
naive picture of different phases of strongly
interacting matter
increasing temperature thermal motion and production of mesons
increasing density
hadrons „overlap“
quarks and gluons
become the relevant
degrees of freedom
R. Averbeck, 15 Heidelberg, 22.11.2012
main goal of relativistic heavy-ion physics study the properties of nuclear matter,
hadronic matter, and partonic matter
Phase diagram
only (!) experimental approach in the lab:
nucleus-nucleus collisions
relations to
other fields nuclear physics
– collective effects
– in-medium effects
astrophysics – neutron stars
– Supernovae
cosmology – early universe
R. Averbeck, 16 Heidelberg, 22.11.2012
„Mini Bang“ in the laboratory
Quark-Gluon Plasma hadron gas at T ~ 1012 K ~100000 times hotter than the core of the sun
reflects the early universe at a few
microseconds after the Big Bang
R. Averbeck, 17 Heidelberg, 22.11.2012
Some relevant energy densities
inside an atomic nucleus nucleon density: 𝝆𝟎 = 𝟎. 𝟏𝟔 nucleons/𝒇𝒎𝟑
nucleon mass: 𝑴 ≈ 𝟎. 𝟗𝟑𝟏 𝑮𝒆𝑽
energy density: 𝜺𝟎 = 𝝆𝟎𝑴 ≈ 𝟎. 𝟏𝟓 𝑮𝒆𝑽/𝒇𝒎𝟑
inside a nucleon
radius: 𝒓 ≈ 𝟎. 𝟖 𝒇𝒎
mass: 𝑴 ≈ 𝟎. 𝟗𝟒 𝑮𝒆𝑽
energy density:
𝜺 =𝑴
𝟒𝟑 𝝅𝒓𝟑
≈ 𝟎. 𝟒𝟒 𝑮𝒆𝑽/𝒇𝒎𝟑
R. Averbeck, 18 Heidelberg, 22.11.2012
Phase transition in lattice QCD
“stolen” from K. Reygers
R. Averbeck, 19 Heidelberg, 22.11.2012
Pb-Pb collision in UrQMD
R. Averbeck, 20 Heidelberg, 22.11.2012
Schematic A-A collision time
hard parton scattering
Au Au
hadronization
freeze-out
formation of QGP and
thermalization
space
time Jet cc g g e m f p K L
QCD tests:
confinement
chiral symmetry
R. Averbeck, 21 Heidelberg, 22.11.2012
electromagnetic radiation: g, e+e-, m+m-
rare, probes for all time scales, because of lack of strong final state interaction –black body radiation
initial temperature
– in-medium properties of light vector mesons chiral symmetry restoration
hadrons: , K, p common, produced late
(at freeze out) – energy density
– thermalization
– collective motion
Probes for all time scales
production of ~18000 charged
particles per central collision
b ~ 0
Pb nucleus Pb nucleus
p
p
K
cc
J/y
q q
e- e+
g
hard probes: jets, heavy
quarks, direct g rare, produced very early
(prior to QGP formation) – interaction with produced hot and
dense medium
R. Averbeck, 22 Heidelberg, 22.11.2012
Heavy-ion physics programs
R. Averbeck, 23 Heidelberg, 22.11.2012
Bevalac-LBL
2.2 GeV
AGS-BNL
4.8 GeV
SPS-CERN
17.3 GeV
TEVATRON-FNAL
38.7 GeV
RHIC-BNL 200.0 GeV
LHC-CERN
2760.0 GeV
Net Baryon Density ~ Potential mB [MeV]
Te
mp
era
ture
Tc
h [
Me
V]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
LBL/SIS
SPS
RHIC/LHC
quark-gluon plasma
hadron
gas
atomic nuclei
Most of the important goals have
NOT changed over the last 20
years..
Properties of the produced
medium depend strongly on
energy.
High energies give access to
more experimental probes and
theoretical tools.
nuclear fragmentation
production of resonances
strangeness threshold
“resonance matter”
large baryon density
strangeness important
charm production relevant
small baryon density
hard parton scattering
beauty production
Why high energy?
R. Averbeck, 24 Heidelberg, 22.11.2012
BEVALAC = SuperHILAC + BEVATRON
BEVALAC @ Berkeley
R. Averbeck, 25 Heidelberg, 22.11.2012
AGS @ Brookhaven Alternating Gradient Synchrotron
R. Averbeck, 26 Heidelberg, 22.11.2012
Super Proton Synchrotron
SPS @ CERN
R. Averbeck, 27 Heidelberg, 22.11.2012
RHIC
NSRL LINAC Booster
AGS
Tandems
STAR 6:00 o’clock
PHENIX 8:00 o’clock
PHOBOS 10:00 o’clock Jet Target
12:00 o’clock
RF 4:00 o’clock
BRAHMS 2:00 o’clock
RHIC @ Brookhaven Relativistic Heavy-Ion Collider
p+p: √s ≤ 500 GeV (polarized p spin physics)
A+A: √sNN ≤ 200 GeV (per nucleon-nucleon pair)
STAR
experiments with
specific focus BRAHMS (- 2006)
PHOBOS (- 2005)
general purpose
experiments PHENIX
STAR
R. Averbeck, 28 Heidelberg, 22.11.2012
LHC
8.6 km
CMS
ATLAS
LHCb
ALICE
Large Hadron Collider @ CERN
dedicated heavy-
ion experiment:
ALICE
R. Averbeck, 29 Heidelberg, 22.11.2012
Facility for Antiproton and Ion Research
(Start SIS100: 2018)
FAIR @ GSI
at the moment (GSI):
- Z = 1 – 92 (p – U)
- beam energy: ≤2 AGeV
future:
- Z = -1 – 92 (p – U,
anti protons)
- beam energy:
≤35 AGeV
- beam intensities
10-1000 larger
than at SIS18
R. Averbeck, 30 Heidelberg, 22.11.2012
ALICE at the LHC
R. Averbeck, 31 Heidelberg, 22.11.2012
Inner Tracking System (ITS)
“stolen” from K. Reygers
R. Averbeck, 32 Heidelberg, 22.11.2012
Time Projection Chamber (TPC)
R. Averbeck, 33 Heidelberg, 22.11.2012
Time Projection Chamber
R. Averbeck, 34 Heidelberg, 22.11.2012
Transition Radiation
“stolen” from K. Reygers
R. Averbeck, 35 Heidelberg, 22.11.2012
Transition Radiation Detector (TRD)
R. Averbeck, 36 Heidelberg, 22.11.2012
ALICE TRD
R. Averbeck, 37 Heidelberg, 22.11.2012
Collision Geometry
R. Averbeck, 38 Heidelberg, 22.11.2012
Collision Geometry
R. Averbeck, 39 Heidelberg, 22.11.2012
Nucleus-Nucleus Collision Geometry
ultra relativistic energies DeBroglie wave length << radius of nucleons
nucleon wave character can be ignored for estimate of cross section
nucleus-nucleus collision as collision of two
„black disks“
2
31312
0unel
0
31
0fm2,1mit
BAr
rArR
geo
BA
A
+
+
R. Averbeck, 40 Heidelberg, 22.11.2012
Centrality in AA Collisions K. Reygers
centrality characterized (but NOT directly measured) via: b: impact parameter
Npart: number of nucleons, which took part in at least one inelastic nucleon-nucleon scattering
Ncoll: number of inelastic nucleon-nucleon collisions
b
R. Averbeck, 41 Heidelberg, 22.11.2012
Glauber Model Glauber model assumptions
nucleons travel on straight trajectories, even after (!) NN scattering processes
NN scattering cross section does NOT depend on the number of NN scatterings that took place before
crucial input: nuclear geometry Woods-Saxon parametrization
parameters from e scattering
ignore possible differences between proton and neutron distributions
aRr
Rwrr
/exp1
/1)(
22
0
-+
+
R. Averbeck, 42 Heidelberg, 22.11.2012
MonteCarlo Approach initialization: distribute
nucleons randomly
according to Woods-
Saxon distribution
select random impact
parameter b
two nucleons collide if
they come close enough
to each other
/NN
uneld
<Npart> and <Ncoll> from simulation of
many AA collisions
R. Averbeck, 43 Heidelberg, 22.11.2012
Glauber: Npart and Ncoll vs. b
approximately: Ncoll a Npart4/3
R. Averbeck, 44 Heidelberg, 22.11.2012
Impact parameter distribution Glauber MonteCarlo: b9,6
200@
+ GeVAuAu
unel
R. Averbeck, 45 Heidelberg, 22.11.2012
Centrality in ALICE
measurement ~ number of produced particles
particle yield in Glauber MC 𝑵𝒂𝒏𝒄𝒆𝒔𝒕𝒐𝒓 = 𝒇 ×𝑵𝒑𝒂𝒓𝒕 + (𝟏 − 𝒇) × 𝑵𝒄𝒐𝒍𝒍
each ancestor produces charged particles according to negative
binomial distribution (NBD)
same centrality selection in data and MC <Npart>, <Ncoll>
R. Averbeck, 46 Heidelberg, 22.11.2012
Pb-Pb @ √sNN=2.76 TeV
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