1. Introduction to ALICE Physics Eyyubova Gyulnara University of Oslo

2. ALICE — A Large Ion Collider Experiment — is being prepared to study the physics of nuclear matter under extreme conditions of temperature and density.
Schematic view of high energy PbPb collisions by URQMD model.

3. The Quark-Gluon Plasma
QCD theory predicts a new state of matter: Quark Gluon Plasma (QGP) 
the degrees of freedom are only quarks and gluons
Normal hadronic matter

4. QGP , the early state of matter of our universe
Big quark-gluon p + n low mass nuclei neutral atom star dispersion of TODAY
Bang plasma formation formation formation formation heavy elements
time s s min ,000 yr yr >109yr x109yr
Copyright 1998 Contemporary Physics Education Project (CPEP)

5. A process of collision
Many-body system, statistical approach, hydro approach
QG plasma formation
system expands and cools,
hadronization
One important feature of relativistic heavy ion collisions is that hadrons show a collective behavior.
The chemical freeze out fixes the particle yields at the hadronization stage
the kinetic freeze out affects particle momenta.

6. QGP observables (probes)

7. Particle production is dominated by soft particles
“Hard physics”
Particle production characterized
by large momentum transfer
Interactions occur at the partonic level
Small coupling constants
99.5% soft
“Soft physics”
pQCD is not valid
Phenomenological modeling
Particle production is dominated by soft particles

8. 4-10 1.5-4.0 <1 tQGP (fm/c) 2x104 7x103 103 Vf(fm3) 15-40 3.5 2.5
Effects of soft processes, dominating the low momentum region, are well interpreted by hydrodynamical models, in the intermediate momentum region (pT 2–5GeV/c) the role of soft and hard processes is still under investigation
4-10
<1
tQGP (fm/c)
2x104
7x103
103
Vf(fm3)
15-40
3.5
2.5
e (GeV/fm3)
3-8 x103
650
500
dNch/dy
5500
200 17
s1/2(GeV)
LHC
RHIC
SPS
Central collisions

9. Centrality “Centrality” characterizes a collision
and categorizes events.
peripheral event
central event
NPART number of participating nucleos
NCOLL number of binary (nucleon-nucleon) collisions

10. QGP observables (probes)
In ALICE, the QGP observables are traditionally subdivided into three classes:
soft probes (with the typical p <2 GeV/c)
heavy-flavour probes (using the particles having c- and b-quarks)
high-pt probes (in the p range above 5-6 GeV/c).

11. soft probes

12. Multiplicity Measurements!
Why ?
Multiplicity provides insights on:
Energy density of the system
(via Bjorken formula)
Mechanisms of particle production
(hard vs. soft)
Thermalization
In central AuAu collisions at RHIC (s=200 GeV) about 5000 particles are created
Bjorken
R ~ r0A1/3
ct0
Phenix: ET measurement at 130 GeV
e0 = 4.6 [GeV/fm3] PRL 87, (2001)
Above the critical value ec ~ 1 GeV/fm3

13. Multiplicity Measurements!
central
peripheral
energy s
The dN/dh per participant pair at mid-rapidity in central heavy ion collisions increases with ln s from AGS to RHIC energies

14. Saturation model (dN/dh  sl with l=0.288)
Soft physics at the LHC
Extrapolation of dNch/dhmax vs s
Fit to dN/dh  ln s
Saturation model (dN/dh  sl with l=0.288)
The first 10k events at the LHC could be decisive
Central collisions
Saturation model
Armesto Salgado Wiedemann, PRL 94 (2005)
Models prior to RHIC
Extrapolation of dN/dhln s
5500

15. Scaling properties of Multiplicity Measurements!
Total multiplicity:
Nch scales with Npart
Nch per participant pair different from p-p, but compatible with e+e-, collisions at the same energy
Simple scaling rules dominate! 15

16. Detailed Analysis of Particle Spectra
Retiere and Lisa – nucl-th/
Fit with hydro-dynamically motivated “blast waves” to gain insight into the dynamics of the collision.
Central
Mid-central
Peripheral
Can describe the data
with a common
transverse “flow” velocity.
This velocity is large <BT>~0.5c

17. Soft QGP probes Elliptic flow
No secondary interaction
Hydro behavior
2v2
Angle of reaction plane
Fourier coefficient

18. Fourier Analysis of Emission Patterns
PHOBOS: Phys. Rev. C72, (R) (2005)
Increasing Collision Centrality
Find significant values of
v2 for non-central collisions
Collective Behavior
Reaches Hydro Limit (first time seen in HI collisions)
Fast Equilibration Timescales

19. Momentum and Species Dependence of v2
Lower Momentum
Higher Momentum
STAR PRC 72 (05)
STAR PRC 72 (05)
200 GeV Au+Au
min-bias
the mass splitting can be described in full hydro models
(with, e.g., the additional collective transverse flow velocity from spectra fits)

20. Arrival at Hydrodynamic Limit
It’s been predicted (Phys Lett B474 (2000) 27.) in the low density limit, v2   and the density of scattering centres. Ie. v2/  (1/S) dNch/d
v2/ should saturate at large particle densities (hydro-limit). y x
Experimental data reach hydrodynamic limit curve for the first time at RHIC.

21. Is the QGP an ideal fluid ?C
Hydro limit
Will data trend continue or does it flatten?

22. heavy-flavour probes

23. The effective potential of interaction:
Quarkonium is bound state of a heavy quark and its antiquark
quark mass mQ >>ΛQCD and quark velocity v << 1
allows nonrelativistic treatment, production described in pQCD r
The effective potential of interaction:
The Coulomb part is potential
induced by one-gluon exchange
k- string tension coefficient (1 GeV/fm)

24. S(L=0) and P(L=1) states
Charmonium family
Bottomonium family

25. r>λD  No bound state
J/ψ suppression – classic QGP signature proposed by T. Masui, H. Satz, Phys. Lett. B178, 416 (1986).
The idea is :
The modification of charmonia in the QGP, in terms of suppressed (or enhanced) production
color screening
The potential in QGP:
λD(T) (Debye length) is the distance at which the effective charge is reduced 1/e
r>λD  No bound state
Tdiss(’)< Tdiss((3S) )< Tdiss(J/ )  Tdiss((2S) ) TC <Tdiss((1S)

26. Comparison of RHIC and SPS Results
J/Ψ Suppression─RAA PHENIX mid-rapidity the same as NA50
Recent lattice analyses indicate that that the ground state (J/ ,  ) survive at least up to T ≈2Tcrit, while the less bounded state  ‘ melt near Tcrit

27. Most actual models have
Suppression + various
regeneration mechanisms
Too much suppression at RHIC in Standard QGP Scenario
However, at higher energies (RHIC, LHC)
the situation becomes more complicated, because the charmonia can be regenerated in the hot
medium by recombination.

28. high-pt probes

29. Jets in heavy ion collisions
radiated
gluons
heavy nucleus
key QCD prediction: jets are quenched
X.-N. Wang and M. Gyulassy, Phys. Rev. Lett. 68 (1992) 1480
Fragmentation
di-quark
quark
Interaction at the quark (parton) level
Models of jet suppression
Various approaches; main points:
DEmed is independent of parton energy.
DEmed depends on length of medium, L.
DEmed gives access to gluon density dNg/dy or transport coefficient
Leads to a deficit of high pT hadrons compared to p+p collisions (no medium).

30. Comparing Au+Au Spectra to pp
Use The Nuclear Modification Factor
PHOBOS: Phys. Lett. B578, 297 (2004)
0.2<yp <1.4
RAA = 1 if Au+Au is simply an incoherent sum of pp collisions
Jet quenching was discovered for the first time at RHIC.

31. Suppression of High Momentum Particles
Peripheral
Mid-Central
Central
Binary collision expectation
 strong suppression of high pT yields in AuAu Central Collisions

32. Important Cross Check of Ncoll Expectation
Direct Photons
PHENIX: Phys.Rev.Lett. 96 (2006)
Binary collision expectation
Direct photons scale as Ncoll
(and they don’t interact with the medium)

33. high-pt probes heavy quarks energy loss in QGP
The heavy quarks at intermediate pt will lose less energy as compared with the light quarks at the same momenta due to the ‘dead-cone’ effect .
parton
hot and dense medium

34. Capability of ALICE detector
ALICE unique features:
Possibility to measure charged-particle density up to dNch/dy = 8000
Excellent tracking and impact parameter resolution.
(Typical p resolution obtained with the magnetic field of 0.5 T is 1% at pt 1 GeV/c and 4% at pt 100 GeV/c.)
Acceptance at low pT (~0.2 GeV)
Excellent PID capabilities
From p 0.1 GeV/c to a few GeV/c the charged particles are identified by combining the PID information provided by ITS, TPC, TRD, TOF and HMPID. Electrons above 1 GeV/c are identified by TRD, and muons are registered by the muon spectrometer.

35. Heavy-ion physics with ALICE
Pb-Pb (Summer 2010 – 4 weeks):
1/20 of nominal luminosity ∫Ldt = 5·1025 cm-2 s-1 x 106s
Alignment calibration available from pp
Global event properties (105 events):
Multiplicity, rapidity density
Elliptic flow
Source characteristic (106 events):
Particle spectra, resonances
Differential flow
interferometry
High pt and heavy flavours (107 events):
Jet quenching
Quarkonia production
An hour
A day
2 weeks