relativistic heavy ion physics: an experimental review
DESCRIPTION
Relativistic Heavy Ion Physics: An Experimental Review. Saskia Mioduszewski. 22 July 2003. Outline. Physics Goals: deconfinement and chiral symmetry restoration Overview of the Program Global Observables charged-particle multiplicity flow Other Experimental Highlights J/ y suppression - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/1.jpg)
Relativistic Heavy Ion Physics: An Experimental Review
Saskia Mioduszewski
22 July 2003
![Page 2: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/2.jpg)
2
Outline• Physics Goals: deconfinement and chiral symmetry
restoration
• Overview of the Program• Global Observables
– charged-particle multiplicity– flow
• Other Experimental Highlights– J/ suppression– low mass dilepton enhancement– high pT suppression
• Summary
![Page 3: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/3.jpg)
Lattice QCD at Finite Temperature• Coincident transitions: deconfinement and chiral symmetry restoration
F. Karsch, hep-ph/010314
Critical energy density:4)26( CC T
TC ~ 175 MeVC ~ 0.7 GeV/fm3
Ideal gas (Stefan-Boltzmann limit)
B=0)
Chiral symmetry spontaneously broken in nature. Quark condensate is non-zero:
At high temperature and/or baryon density
Constituent mass current mass Chiral Symmetry (approximately) restored.
MeVqq 3)250(
0qq
![Page 4: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/4.jpg)
4
Schematic Phase Diagram of Strongly Interacting MatterSchematic Phase Diagram of Strongly Interacting Matter
Baryonic Potential B [MeV]
T
em
pera
ture
T [
MeV
]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
SIS
SPS
RHIC
quark-gluon plasma
hadron gas neutron stars
early universe
thermal freeze-outdeconfinementchiral restoration
Lattice QCD
atomic nuclei
P. Braun-Munzinger, nucl-ex/0007021
Test QCD under extreme conditions and in large scale systems
Search for deconfined QGP phase
SISAGS SPS RHICLHC
From high baryon density regime to high temperature regime
![Page 5: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/5.jpg)
5
How to Observe QGP in Heavy Ion Collisions
Some tools to distinguish QGP from dense hadron gas:
– Direct observation of deconfinement: suppression of J/ – High energy density: interaction of jets with medium– High temperature: direct photons/dileptons– Chiral symmetry restoration: meson properties (m,) expected to be modified in medium– Equilibration at early stage large pressure collective expansion: flow
![Page 6: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/6.jpg)
6
History of High-Energy A+B Beams
• BNL-AGS: mid 80’s, early 90’s
O+A, Si+A 15 AGeV/c sNN ~ 6 GeV
Au+A 11 AGeV/c sNN ~ 5 GeV
• CERN-SPS: mid 80’s, 90’s
O+A, S+A 200 AGeV/c sNN ~ 20 GeV
Pb+A 160 AGeV/c sNN ~ 17 GeV
• BNL-RHIC: early 00’s
Au+Au sNN ~ 130 GeV
Au+Au, p+p, d+Au sNN ~ 200 GeV
![Page 7: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/7.jpg)
7
The RHIC Experiments
STAR
![Page 8: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/8.jpg)
8
Global Observables Reflect the conditions of the system after freeze-out,
after resonance decays
• Charged-Particle Multiplicity- helps constrain models- reflects produced entropy
• Flow- collective expansion, rescattering- pressure
![Page 9: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/9.jpg)
9
AA collisions are not all the same
Nuclei are extended objects– Impact parameter– Number of
participants– Centrality ( % from total inelastic
cross-section)
100% 0 %
Participants
Spectators
Spectators
![Page 10: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/10.jpg)
Charged-Particle Rapidity Distribution
BRAHMS (0-5%): Nch (||<4.7) = 3860 ± 300NA49 (0-5%): Nh
- (|y| < 3) = 695 ± 30
- Factor of 3 more particles produced at RHIC than at SPS - Wider distribution
Enhancement of particle production for central collisions at mid-rapidity.
Particle production scales with Npart at high rapidities ( >3).
h-
NA49
dn/dy
RHIC
SPS
BRAHMS
![Page 11: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/11.jpg)
11
From SPS to RHIC :
* dNch/dy increases by
~70% at sNN
= 130 GeV
* dNch/dy increases by
~90% at sNN
= 200 GeV
ln(sNN
) dependence from
AGS to RHIC
sNN
Dependence of dNch/dy
AGS
SPSRHIC
![Page 12: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/12.jpg)
12
Radial Flow
– Expansion of system due to pressure
– Heavier particles shifted to higher pT
– Observable: <T> from slopes of mT spectra as a function of mass
– Spectra can be described by hydrodynamic models for pT< 2-3 GeV/c and mid-peripheral to central events
![Page 13: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/13.jpg)
13
Single Particle Spectra (low pT)
• Decreasing slope for increasing particle mass and centrality
T. Ullrich QM2002
![Page 14: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/14.jpg)
14
Single Particle Spectra for most central events (0-5%)
• proton yield ~ pion yield @ 2 GeV• consistent with hydrodynamic model calculations (e.g. comparison to 130 GeV data - Teaney, Lauret, Shuryak nucl-th/0110037)
PHENIX Preliminary PHENIX Preliminary
Au+Au at sqrt(sNN) =200GeVAu+Au at sqrt(sNN) =200GeV
J. Burward-Hoy, QM2002
![Page 15: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/15.jpg)
Mean Transverse Momentum vs. Npart
<pT> increases with Npart and particle mass, indicative of radial expansion
Relative increase with Npart greater for (anti)p than for , K
J. Burward-Hoy, QM2002
closed symbols: 200 GeV
open symbols: 130 GeV
![Page 16: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/16.jpg)
Hydrodynamic Model Fit to the Spectra
PHENIX:Freeze-out Temperature
Tfo = 110 23 MeV
Transverse flow velocity
T = 0.7 0.2 < T> ~ 0.5
Most central collisionsfor 200 GeV data
Ref: E. Schnedermann, J. Sollfrank, and U. Heinz, Phys. Rev. C 48, 2462 (1993)
Au+Au at sqrt(sNN) =200GeV
STAR:
Tfo ~ 100 MeV
T ~ 0.6
J. Burward-Hoy, QM2002
![Page 17: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/17.jpg)
17
Mid-Rapidity mT spectra at SPS
M. van Leeuwen QM2002 (NA49)
NA57, H. Helstrup, this conference:
Tfo = 131 ± 10 MeV
<T> = 0.47 ± 0.02
![Page 18: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/18.jpg)
18
Elliptic Flow in Non-central Collisions
Early state manifestation of collective behavior: • Asymmetry generated early in collision, quenched by expansion observed asymmetry emphasizes early time
x
y
p
patan2cos2 vSecond Fourier coefficient v2:
Coordinate space: initial asymmetry
Momentum space: final asymmetry
multiple collisions (pressure)
py
px
![Page 19: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/19.jpg)
Strong elliptic flow signal strong (collective) pressure Large and fast rescattering (early thermalization) v2 dependent on mass (predicted by hydro P. Huovinen et al, PLB 503 (2001) 58).
Elliptic Flow
![Page 20: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/20.jpg)
20
Elliptic Flow
• SPS: v2 ~ 0.03
• RHIC: v2 ~ 0.055
Wetzler QM2002
E877: Phys.Lett.B474:27-32, 2000CERES: QM2001INPC 2001 nucl-ex/0109017 STAR: PRC66 (2002) 034904NA49 Preliminary
130 GeV data
![Page 21: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/21.jpg)
21
Flow: Comparison of SPS and RHIC
• Radial Flow: pressure can build up over entire dynamics– <T> ~ 0.4 - 0.5 at SPS– <T> ~ 0.5 - 0.6 at RHIC
• Elliptic Flow: pressure must build up before asymmetry of system has diminished– v2 ~ 0.03 at SPS– v2 ~ 0.06 at RHIC
• Moderate increase in <T> more pressure at RHIC• Significantly larger v2 is evidence for early build-up of
pressure• According to hydrodynamic models early
thermalization at RHIC (~0.6fm/c - Heinz, Kolb
Nucl.Phys.A702:269-280,2002 )
![Page 22: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/22.jpg)
22
Energy Density
Energy density a la Bjorken:
dy
dE
τπR
1ε T
2
fm/c 12.0τ
fm/c 1τ
A 1.18R
RHIC
SPS
1/3
38~6.0 GeV/fmfm/c
dET/dy ~ 720 GeV (S. Bazilevsky
QM2002, PHENIX PRELIMINARY)
35~1 GeV/fmfm/c
Estimate for RHIC:
![Page 23: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/23.jpg)
23
Other Highlights of Program
• Global observables properties of collision dynamics, EOS
• Other probes for signatures of QGP– J/ suppression deconfinement– low mass dileptons chiral symmetry restoration
– high pT suppression density of produced medium and energy loss
![Page 24: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/24.jpg)
24
J/ suppression: probe of deconfinement
• An “old” signature of QGP formation: (Matsui and Satz PL B178, (1986) 416).
• At high enough color density, the screening radius < binding radius J/ will dissolve
• Observation: Anomalous suppression in Pb-Pb collisions* beyond normal nuclear absorption abs
~ 4-6 mb
![Page 25: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/25.jpg)
25
J/ suppression: Evidence of deconfinement?L. Ramello, QM 2002NA50 Preliminary
Suppression increasing with centrality (discontinuities?)
Exceeds normal nuclear absorption (as measured in p+A)
Many models exist (hadronic and QGP) – data consistent with suggested QGP signature (Matsui, Satz, Kharzeev)
![Page 26: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/26.jpg)
26
• possible signature of the deconfinement phase transition– J/ yield can be
• suppressed more than at SPS - dissolve in QGP (longer lifetime, higher temperature than SPS)
• enhanced - cc coalescence as the medium cools (2 orders of magnitude more production of cc pairs at RHIC)
• important to measure J/ in p+p and d+Au to separate “normal” nuclear effects– shadowing– nuclear absorption in cold matter
• Jmeasurements in leptonic decay channels– J/ e+ e- and J/ in p+p at s = 200 GeV
– J/ e+ e- in Au+Au at sNN = 200 GeV
Charmonium (Jphysics at RHIC
(hep-ex/0307019)
(nucl-ex/0305030)
![Page 27: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/27.jpg)
27
J/ Production at RHIC
normal nuclear absorption:
Pb+Pb at CERN SPS (NA50)
PHENIX, sNN
= 200 GeV • J/-Suppression maybe most compelling QGP evidence at CERN SPS
• Expectation at RHIC energies unclear0 cc pairs
produced per central Au+Au collision
– Possibly enhanced J/- production due to charm-coalescence
-
PLB477(2000) 28 normalized to PHENIX p+p measurement
![Page 28: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/28.jpg)
28
coalescence model (Thews at al.)
y = 1.0
y = 4.0
statistical model (Andronic at al.)
absorption model (Grandchamp et al.)
Model comparisons
• models that predict enhancement relative to binary collision scaling are disfavored
• no discrimination between models that lead to suppression
![Page 29: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/29.jpg)
29
Low-Mass e+e- pairs
No enhancement in pp and pA collisions
Main CERES Result:Strong enhancement of low-mass pairs in A-A collisions
(wrt to expected yield from known sources)
Enhancement factor (.25 <m<.7GeV/c2): 2.6 ± 0.5 (stat) ± 0.6 (syst)
![Page 30: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/30.jpg)
30
Interpretations
scattering off baryons(Rapp, Wambach et al)
-meson broadening Dropping -meson mass(G.E. Brown et al)
annihilation: +- * e+e- (thermal radiation from HG)Cross section dominated by pole at the mass of the em form factor:
2222
42
m )m (m
m m)(F
Plus
or
Add
![Page 31: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/31.jpg)
Onset of Chiral Symmetry Restoration?Dropping -meson mass
(Rapp, Wambach et al)
In-medium -meson broadening(G.E. Brown et al)d.o.f.
hadrons quarks
What happens as chiral symmetry is restored? Dropping mass or broadening (melting)?
![Page 32: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/32.jpg)
32
Fate of Hard Scattered Partons in Au+Au Collisions
• Hard scatterings in nucleon-nucleon collisions produce jets of particles.
• In the presence of a color-deconfined medium, the partons strongly interact (~GeV/fm) losing much of their energy.
• “Jet Quenching”
hadrons
q
q
hadrons leadingparticle
leading particle
schematic view of jet production
![Page 33: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/33.jpg)
33
Nuclear Modification Factor RAA
• in absence of nuclear effects– RAA < 1 at low pT (soft physics regime)– RAA = 1 at high pT (hard scattering regime)
• “suppression” (enhancement, e.g. Cronin effect)– RAA < 1 (> 1) at high pT
Nuclear Modification Factor
RAA (pT ) d2N AA /dpT d
TAA d2 NN /dpT d
<Nbinary>/inelp+p
NN cross section
![Page 34: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/34.jpg)
34
By definition, processes that scale with Nbinary will produce RAA=1.
RAA is what we measure divided by what we expect.
RAA is < 1 at RHIC, but > 1 at SPS
SPS: “Cronin” effect dominatesRHIC: suppression dominates
RAA for 0
Nbinary-scaling
A.L.S.Angelis PLB 185, 213 (1987)WA98, EPJ C 23, 225 (2002)PHENIX, PRL 88 022301 (2002)PHENIX submitted to PRL, nucl-ex/0304022
![Page 35: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/35.jpg)
35
Jet Quenching ?• high pT suppression
reproduced by models with parton energy loss
• other explanations not ruled out, need to measure initial-state effects
without parton energy loss
with parton energy lossWang
Wang
Levai
Levai
Vitev
comparison with model calculations
with and without parton energy loss
Au+Au0+X at sNN = 200 GeV
Wang: X.N. Wang, Phys. Rev. C61, 064910 (2000).
Levai: P.Levai, Nuclear Physics A698 (2002) 631.
Vitev: I. Vitev and M. Gyulassy, hep-ph/0208108 + Gyulassy, Levai, Vitev, Nucl. Phys. B 594, p. 371 (2001).
![Page 36: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/36.jpg)
36
RAA for 0 and charged hadrons
pp
AuAubinaryAuAuAA Yield
NYieldR
/
PHENIX AuAu 200 GeV0 data: nucl-ex/0304022, submitted to PRL.charged hadron (preliminary) : NPA715, 769c (2003).
• RAA is well below 1 for both charged hadrons and neutral pions.
• The neutral pions fall below the charged hadrons since they do not contain contributions from protons and kaons (will be discussed later).
Strong Suppression!
- Consistent observation by all 4 experiments in charged hadron measurement
PHOBOS, R. Nouicer, this conferenceBRAHMS, Z. Yin, this conference
![Page 37: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/37.jpg)
Azimuthal distributions in Au+Au
Near-side: peripheral and central Au+Au similar to p+p
Strong suppression of back-to-back correlations in central Au+Au collisions
Au+Au peripheral Au+Au central
pedestal and flow subtracted
Phys Rev Lett 90, 082302
?
![Page 38: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/38.jpg)
38
d+Au
Au+Au
RAA vs. RdA for charged hadrons and 0
No Suppression in d+Au, instead small enhancement observed (Cronin effect)!!
d-Au results rule out initial-state effects as the explanation for Suppression at Central Rapidity and high pT
Initial State Effects Only
Initial + Final
State Effects
PHENIX (d+Au) hep-ex/0306021submitted to PRL
PHOBOS, R. Nouicer, this conference
BRAHMS, Z. Yin, this conference
![Page 39: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/39.jpg)
39
Azimuthal distributions
pedestal and flow subtracted
Near-side: p+p, d+Au, Au+Au similarBack-to-back: Au+Au strongly suppressed relative to p+p and d+Au
Suppression of the back-to-back correlation in central Au+Au is a final-state effect
![Page 40: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/40.jpg)
40
High pT Measurements at RHIC
d+Au collisions:• No suppression at high pT
• Away-side jet strength consistent with p+p collisions
Peripheral Au+Au collisions:• Hadron yields consistent with Nbinary-scaled yields in p+p
collisions
• Away-side jet strength consistent with p+p collisions
Central Au+Au collisions:• Hadrons are suppressed at high pT (up to 10 GeV/c)
• Away-side jet disappears
Particle Composition in Central Au+Au collisions: What is happening with the protons?
![Page 41: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/41.jpg)
41
Particle Species Dependence of High pT Suppression
No apparent proton suppression for 2-4 GeV/c – different production mechanism ?
PHENIX, nucl-ex/0305036
(Similar effect seen in STAR for vs. Kshort suppression)
peripheralbinaryperipheral
centralbinarycentral
NYield
NYield
//
![Page 42: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/42.jpg)
42
Particle Composition at High pT
• p/ < 0.25 expected from jet fragmentation• observed p/ ~ 0.4 in peripheral, ~ 1 in central
– protons from non-fragmentation sources ?
nucl-ex/0305036
![Page 43: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/43.jpg)
43
Summary
Physics highlights:
• Strong collective expansion at SPS and RHIC
• Evidence for early equilibration at RHIC• SPS: * Anomalous J/ suppression * Enhancement of low-mass dileptons• RHIC: * Suppression of high pT particles and disappearance of away-side jet
Very intriguing results. All consistent with QGP
formation
![Page 44: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/44.jpg)
44
Extra Slides
![Page 45: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/45.jpg)
45
Direct Photons (I)
• Evidence for direct photons in central Pb-Pb collisions?
10-20% excess but 1 effect only
• CERES preliminary result: enhancement = 12.4% ± 0.8% (stat) ± 13.5% (syst)
WA98 WA98
![Page 46: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/46.jpg)
46
Direct Photons (II)
• Comparison to scaled pA: similar spectrum but factor of ~2 enhanced yield in Pb-Pb, again ~1 effect.• pQCD underpredicts direct photon yield
WA98WA98
Hydro calculations :Prompt + QGP Mixed phase HG QGP dominates at high pT
Srivastava and Sinha nucl-th/0006018Srivastava and Sinha nucl-th/0006018
![Page 47: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/47.jpg)
47
Direct Photons Direct Photons:– Photons not originating
from hadron decays like 0
all
direct+
decay
• Direct photon signal seen in Pb+Pb at s
NN=17.3 GeV
• Stronger signal expected at RHIC, because 0 suppressed by factor 5– Suppression appears to
be a final state effect– Direct photons not
affected by final state interactions
pQCD calculation for direct and 0
in p+p at s=200 GeV(Werner Vogelsang):
![Page 48: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/48.jpg)
48
Direct Photon Search
• Au+Au at sNN
= 200 GeV
• No direct photon signal seen within errors
• With further analysis systematic errors will be reduced ...
preliminarypreliminary
preliminary
![Page 49: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/49.jpg)
49
Azimuthal asymmtery (v2) at high pT
STAR
Finite v2 up pT ~ 10 GeV
Hydrodynamics up to pT ~ 2-3 GeV
Jets correlated to reaction plane?
![Page 50: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/50.jpg)
50
Neutral Pion Production in central and peripheral Au+Au collisions
• reference p+p data with same detector
• binary scaling in peripheral Au+Au
• suppression factor
~ 5 in central Au+Au
Binary scaling
Participant scaling
×1/5
0 at sNN = 200 GeVnucl-ex/0304022, submitted to PRL
pp
AuAubinaryAuAuAA Yield
NYieldR
/
![Page 51: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/51.jpg)
51
Particle Spectra Evolution“Peripheral
”
Particle
Physics
“Central”
Nuclear
Physics
![Page 52: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/52.jpg)
52
Centrality Dependence
• Dramatically different and opposite centrality evolution of Au+Au experiment from d+Au control.
• High pT hadron suppression in AuAu is due to a final state effect.
“PHENIX Preliminary” results on centrality-dependence consistent with PHOBOS data
Au + Au Experiment d + Au Experiment
![Page 53: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/53.jpg)
53
What might all this mean?
?
Conjecture: core of reaction volume is opaque to jets
surface emission
Consequences: near-side fragmentation independent of system suppression of back-to-back jets suppression of inclusive rates strong elliptic flow at high pT
Compelling picture, but is it right?
![Page 54: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/54.jpg)
54
J/ suppression: Evidence of deconfinement?
PLB 477 (2000) 28
NA50 preliminaryNA50 preliminary
L. Ramello, QM 2002
melting of charmonium states: c (binding energy 250 MeV)
and J/ (650 MeV)
![Page 55: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/55.jpg)
55
Jet correlations: Au+Au vs. p+pSTAR PRL 90, 082302 (2003)
22 2 2( ) ( ) (1 cos(2 ))D Au Au D p p B v
Back-to-back jets are suppressed in central collisions!
near side
away side
peripheral central
Peripheral Au + Au
Central Au + Au
![Page 56: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/56.jpg)
56
Centrality Determination
For example, in PHENIX:
Use combination of • Zero Degree
Calorimeters• Beam-Beam
Counters(sensitive to 92% of geom)
to define centrality classes• Glauber modeling
to extract N-participants
0-5%
10-15%15-20%
5-10%
PHENIX
![Page 57: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/57.jpg)
57
Centrality Dependence: Comparison to Models
Saturation models reproduce the scaling with centrality and energy dependence!
dN
ch/d/
(0.5
Np
art)
Kharzeev & Levin, nucl-th/0108006Schaffner-Bielich et al, nucl-th/0108048
![Page 58: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/58.jpg)
58
- Centrality Dependence of Pion Suppression -
• smooth increase of suppression with centrality
• neither binary or participant scaling
0 at sNN = 200 GeVnucl-ex/0304022, submitted to PRL
![Page 59: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/59.jpg)
59
The SPS Experiments• 1986 - 1987 : Oxygen @ 60 & 200 GeV/nucleon• 1987 - 1992 : Sulphur @ 200 GeV/nucleon• 1994 - 2000 : Lead @ 40, 80 & 158 GeV/nucleon• 2002 - 2003 : Indium and Lead @ 158 GeV/nucleon
And proton beams for pp and pA reference
studies
NA35 NA36
NA49
NA34/2HELIOS2
NA34/3HELIOS3
NA44
NA45CERES
NA38
NA50
NA60
WA80
WA98
WA85
WA97
NA57
NA52
WA94SO
Pb
multistrangephotonshadrons
dimuons
dielectrons
1986
1994
2000
hadrons
strangeletshadrons
hadronsdimuons
1992
2003
Carlos Lourenco QM01Carlos Lourenco QM01
![Page 60: Relativistic Heavy Ion Physics: An Experimental Review](https://reader035.vdocument.in/reader035/viewer/2022062422/56813b5f550346895da457ba/html5/thumbnails/60.jpg)
60
Color Glass CondensateAlternate Explanation
• Nucleons contain many low x partons.
• At some scale, and particular to relativistically contracted nuclei, gluons will saturate phase space and essentially cancel.
• Jets are not quenched, but are apriority made in fewer numbers.
Color Glass Condensate hep-ph/0210033
Gribov, Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan, Balitsky, Kovchegov, Kovner, Iancu
High x
Low x