Transcript DPP Annual Report

Hot and dense matter:
from RHIC to LHC
“Trends in heavy ion physics research”
Dubna May 22-24, 2008
Itzhak Tserruya
Itzhak Tserruya
JINR, May 22, 2008
1
Hot and dense matter:
from RHIC to RHIC and LHC
“Trends in heavy ion physics research”
Dubna May 22-24, 2008
Itzhak Tserruya
Itzhak Tserruya
JINR, May 22, 2008
2
Outline
Introduction
Highlights from RHIC
 Flow
 Charmonium
 Low-mass dileptons
 Thermal radiation
 High pT suppression
Summary
Itzhak Tserruya
JINR, May 22, 2008
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Introduction
Itzhak Tserruya
JINR, May 22, 2008
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Eight years of RHIC operation
RHIC’s main goals
– Nuclear collisions
To provide definitive experimental evidence for/against Quark Gluon Plasma (QGP)
and study its properties under the much better conditions offered by RHIC
Large √s  Access to reliable pQCD probes
– Polarized p+p collisions
Accelerator complex
– Impressive machine performance:
Routine operation at 2-4 x design luminosity (Au+Au)
– Extraordinary variety of operational modes
Collided four different species: Au+Au, d+Au, Cu+Cu, p+p
4 Energies: 20 GeV (Au+Au, Cu+Cu), 62 GeV (Au+Au,Cu+Cu, p+p) ,
130 GeV (Au+Au), 200 GeV (Au+Au, Cu+Cu, d+Au, p+p)
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PHENIX Run History
Year
Species
√s [GeV ]
∫Ldt
Ntot (sampled)
Data Size
Run1
2000
Au - Au
130
1 µb-1
10 M
3 TB
Run2
2001/02
Au - Au
200
24 µb-1
170 M
10 TB
Au - Au
19
p-p
200
0.15 pb-1
3.7 B
20 TB
d - Au
200
2.74 nb-1
5.5 B
46 TB
p-p
200
0.35 pb-1
6.6 B
35 TB
Au - Au
200
241 µb-1
1.5 B
270 TB
Au - Au
62.4
9 µb-1
58 M
10 TB
Cu - Cu
200
3 nb-1
8.6 B
173 TB
Cu - Cu
62.4
0.19 nb-1
0.4 B
48 TB
Cu - Cu
22.4
2.7 µb-1
9M
1 TB
p-p
200
3.8 pb-1
85 B
262 TB
p-p
200
10.7 pb-1
233 B
310 TB
p-p
62.4
0.1 pb-1
10 B
25 TB
Au - Au
200
725 µb-1
4.6 B
570 TB
d - Au
200
p-p
200/500
Run3
Run4
Run5
Run-6
2002/03
2003/04
2005
2006
Run-7
2007
Run-8
2007/08
Itzhak Tserruya
JINR, May 22, 2008
<1M
6
Eight years of RHIC operation
RHIC’s main goals
– Nuclear collisions
To provide definitive experimental evidence for/against Quark Gluon Plasma (QGP)
and study its properties under the much better conditions offered by RHIC
Large √s  Access to reliable pQCD probes
– Polarized p+p collisions
Accelerator complex
– Impressive machine performance:
Routine operation at 2-4 x design luminosity (Au+Au)
– Extraordinary variety of operational modes
Collided four different species: Au+Au, d+Au, Cu+Cu, p+p
4 Energies: 20 GeV (Au+Au, Cu+Cu), 62 GeV (Au+Au,Cu+Cu, p+p) ,
130 GeV (Au+Au), 200 GeV (Au+Au, Cu+Cu, d+Au, p+p)
Two small detectors, two large detectors
– Complementary capabilities. Worked !
Itzhak Tserruya
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RHIC and Its Experiments
STAR
Itzhak Tserruya
JINR, May 22, 2008
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Eight years of RHIC operation
RHIC’s main goals
– Nuclear collisions
To provide definitive experimental evidence for/against Quark Gluon Plasma (QGP)
and study its properties under the much better conditions offered by RHIC
Large √s  Access to reliable pQCD probes
– Polarized p+p collisions
Accelerator complex
– Impressive machine performance:
Routine operation at 2-4 x design luminosity (Au+Au)
– Extraordinary variety of operational modes
Collided four different species: Au+Au, d+Au, Cu+Cu, p+p
4 Energies: 20 GeV (Au+Au, Cu+Cu), 62 GeV (Au+Au,Cu+Cu, p+p) ,
130 GeV (Au+Au), 200 GeV (Au+Au, Cu+Cu, d+Au, p+p)
Two small detectors, two large detectors
– Complementary capabilities. Worked !
Science
– Unexpected results, major discoveries
– More than 170 papers in refereed literature, among them ~100 PRL
Future: RHIC and LHC
– Key science questions identified
– Accelerator and experiment upgrade program underway to perform that science
– LHC to open a new energy frontier (increase by a factor of ~30!)
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Geometry of Heavy Ion Collisions
Non-central Collisions
Reaction plane

N_participants: number of incoming nucleons in the overlap region
N_participants:

N_binary: number of inelastic nucleon-nucleon collisions
N_collisions:

Centrality of the collision expressed as percentile of the total cross section.
Centrality
Itzhak Tserruya
JINR, May 22, 2008
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Flow
(second major discovery at RHIC)
Itzhak Tserruya
JINR, May 22, 2008
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Flow: Evidence of Pressure and
Collective Effects
Origin:
In non-central collisions, the
pressure converts the initial spatial
asymmetry (almond shape of overlap
region) into azimuthal anisotropy of
particle emission
Reaction
plane
Collective effect
Absent in pp collisions
The flow is quantified by v2 (elliptic flow
parameter) determined from the
azimuthal distribution of particles with
respect to the reaction plane ψR
d2N
 1  2 v 2 (p T ) cos 2(  R )
d

dp
T
Itzhak Tserruya
JINR, May 22, 2008
2v2
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Every particle flows
Itzhak Tserruya

Mass hierarchy

Large v2 of heavier particles: ,
X, W, d.

Even open charm flows
(measured through single
electrons)

Strong interactions at early
stage  early thermalization.
JINR, May 22, 2008
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The “Flow” Is ~ Perfect
The mass hierarchy disappears if one uses the
transverse kinetic energy:
KET  m2  pT  m  mT  m
2
baryons
mesons
as
expected
from
“perfect
fluid”
hydrodynamics.
Itzhak Tserruya
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JINR, May 22, 2008
The “Flow” knows quarks
Scaling the flow parameters by the valence quark content nq
resolves the meson-baryon separation
baryons
mesons
All this makes the case for sQGP with early
thermalization of partonic matter made of
constituent quarks and
behaving like a perfect fluid
Itzhak Tserruya
JINR, May 22, 2008
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How Perfect is “Perfect” ?
First hydrodynamic calculations for RHIC matter have all
assumed zero viscosity h = 0  “perfect fluid”
But there is a (conjectured) quantum limit:
h
s


4k B
“A Viscosity Bound Conjecture”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231
Where do “ordinary”
fluids sit wrt this limit?
RHIC “fluid” might
be at ~1 on this
scale (!)
Itzhak Tserruya
T=1012 K
Open charm flows!
Elliptic flow of heavy flavor via non-photonic electrons
PRELIMINARY
minimum-bias
Run-4
Run-7
Rapp & van Hees,
PRC 71, 034907 (2005)
Do bottom quarks flow too, or just charm? ANS: VTX in Run-11
Does thermalized charm contribute to J/ via recombination ?
i.e. does J/ flow too? ANS: Run-9 + Run-7!
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Itzhak
Tserruya
JINR, May 22, 2008
J/ψ
(the deconfinement probe?)
Itzhak Tserruya
JINR, May 22, 2008
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Physics motivation
ccbar predominantly produced by gluon fusion in the initial
parton collisions  probe the created medium :
– ccbar (quarkonia) suppressed by color screening  deconfinement
– open charm (or beauty) energy loss  energy density
T=0
NA50 : Pb + Pb
√sNN ~ 17 GeV
c
c
T≠0
color screening
Color Screening
nuclear absorption
Screening length
hadron size
σabs = 4.18 ± 0.35 mb
Anomalous J/ suppression seen at CERN SPS by NA50
At RHIC energy (10x√sNN ) expect much higher suppression
Itzhak Tserruya
JINR, May 22, 2008
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First surprise: RHIC vs SPS comparison
 SPS @ 0<y<1 :
– √s ~ 17 GeV
– CNM = normal nuclear
absorption σabs = 4.18 ± 0.35mb
 RHIC @ |y|<0.35 :
• √s = 200 GeV
• CNM = shadowing + nuclear
absorption σabs from 0 to 3 mb
(Vogt, nucl-th/0507027)
Very similar suppression at RHIC and SPS
contraryJINR,
to May
expectations.Itzhak Tserruya
22, 2008
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Second surprise: Rapidity dependence
Stronger suppression at forward rapidity
compared to mid-rapidity
Itzhak Tserruya
JINR, May 22, 2008
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J/ Au+Au: suppression vs CNM Effects
Cold nuclear matter (CNM) effects derived from d+Au data (run 3):
CNM = Shadowing(EKS) + Breakup = 2.8
+1.7
mb
-1.4
J/ RAuAu 200 GeV (Run4)
1.2 < |y| < 2.2
|y| < 0.35
More forward suppression beyond CNM than at mid-rapidity
Large errors - need higher statistics d+Au data (Run 8)
arXiv:0711.3917
J/ at RHIC: present status
 Suppression compensated by Recombination ?
1) Models with only cold nuclear matter effects don’t quite have
enough suppression
2) Models with color screening (or comovers) have too much suppression
3) Models with color screening (or comovers) AND recombination are
in reasonable agreement with the data
OR
Satz, J.Phys.G32:R25,2006
 Sequential dissociation?

Dissociation temperature Td :
J/
χc
’(2S)
ΔE [GeV]
0,64
~ 0,22
0,05
Td/Tc
2,10
1,16
1,12
F. Karsch et al. (Nucl. Phys. A698(2002) 199c; hep-lat/0106019)
’
χc
J/
J/: outlook
J/ from regeneration should
inherit the large charm-quark
elliptic flow
First J/ flow measurement by
PHENIX:
– v2 = –10 ± 10 ± 2 ± 3 %
FVTX:
•
•
4x less ,K decays
M: 170100 MeV
Vertex detectors (VTX,FVTX) &
forward calorimeter (NCC) will give:
• ’ with reduced combinatoric
background + sharper mass
resolution
LHC ?
• precise open-charm measurements
to constrain regeneration picture
Low-mass dileptons
(the chiral symmetry restoration probe)
Itzhak Tserruya
JINR, May 22, 2008
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Origin of mass
Constituent quark masses generated
by spontaneous chiral symmetry
breaking
1000000
100000
Origin of mass:
95% of the (visible) mass is due to
the spontaneous breaking of the
chiral symmetry.
QCD Mass
Higgs Mass
10000
X
1000
100
10
1
u
d
s
c
b
Current quark masses generated
by spontaneous symmetry
breaking (Higgs field)
t
Many models link the hadron
masses to the quark
condensate.
At high T or density qq  0
Pioneering CERES results at CERN SPS
Strong enhancement of low-mass e+e- pairs in A-A collisions
(wrt to expected yield from known sources)
Final CERES result
(from 2000 Pb run):
Enhancement factor (0.2 <m < 1.1 GeV/c2 ):
2.58 ± 0.32 (stat) ± 0.41 (syst)± 0.77 (decays)
No enhancement in pp
nor in pA
Itzhak Tserruya
JINR, May 22, 2008
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CERES and NA60
• Interpretation: thermal radiation from HG:
+-  *  e+e-
CERES Pb+Au
• Subtract the hadronic cocktail w/o the 
NA60 In+In
* Both NA60 and CERES attribute excess
to in-medium broadening of  spectral
shape (Rapp and Wambach) as opposed to
dropping  meson mass (Brown et al)
Itzhak Tserruya
JINR, May 22, 2008
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Low-mass dielectrons at RHIC
arXiv:0706.3034
All pairs
Combinatorial BG
Signal
PHENIX
 Significant enhancement of low-mass pairs
 Different origin from SPS?
 Limited by poor S/B ratio ( 1/200 at m=0.4 GeV/c2)
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Itzhak
Tserruya
JINR, May 22, 2008
Hadron Blind Detector
novel concept for e ID → Dalitz rejection
 Windowless Cherenkov detector
 50 cm CF4 radiator
 CsI reflective photocathode
 Triple GEM with pad readout
2 side covers
6 active panels
with frame
window support
2 vertical panels
HV panels
frame
Thermal Radiation
(the thermometer)
Itzhak Tserruya
JINR, May 22, 2008
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Thermal Photons
 High energy density matter is
formed at RHIC
 If the matter is thermailzed, it
should emit “thermal radiation”
 The thermal photon spectrum
provides a direct measurement of
the temperature of the matter
 Thermal photons are predicted to
be the dominant source of direct
photon for 1<pT<3 GeV/c at RHIC
energies.
Higher pT: pQCD photon
Lower pT: from hadronic phase
S.Turbide et al PRC 69 014903
Itzhak Tserruya
 Measurement is difficult since the
expected signal is only 1/10 of
photons from hadron decays
JINR, May 22, 2008
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Alternative approach:
virtual photons ( low-mass e+e- pairs)
 Any source of real  emits virtual
* with very low mass
 If the Q2 (=m2) of virtual photon is
sufficiently small, the source strength
is the same
 *direct
 *incl .

 direct
 incl .
The idea of measuring direct photon via low
mass lepton pair is not new one:
J.H.Cobb, et al, PL 78B, 519 (1978)
 The ratio of real photons and
virtual photons can be calculated by
QED
 The real photon yield can be
measured from the virtual photon
yield, which is observed as low mass
e+e- pairs
 Excess of low-mass dileptons (wrt
hadronic sources) is assigned to
direct photons
Tinit via low mass, high pT dileptons
M < 0.3 GeV/c2
pp
exp + TAA scaled pp
pT = 1-5 GeV/c
Au+Au min bias
Fit with exponential + TAA scaled p+p fit:
T = 221 ± 23 ± 18 MeV (central)
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Fit to pp
NLO pQCD (W. Vogelsang)
JINR, May 22, 2008
arXiv: 0804.4168
High pT
suppression
(first major discovery at RHIC)
Itzhak Tserruya
JINR, May 22, 2008
35
Nuclear modification factor
 Zero hypothesis: scale pp to AA with the number of nn collisions Ncoll:
? = N d2N /dp dh =  T (b)
d2NAA/dpTdh(b)
coll
pp
T
pp AA
 Quantify “effect” with nuclear modification factor:
d 2 N AA / dpT dh
d 2 NAA /dp T dh
R AA (pt ) 

2
Ncoll d N pp / dpT dh TAA d 2 pp /dp T dh
RAA
Ncoll /σinel pp
RAA = 1
•
If no “effect”:
RAA < 1 at low pT (soft physics regime)
RAA < 1
RAA = 1 at high-pT (hard scattering dominates)
•
If “jet quenching”:
RAA < 1 at high-pT
Itzhak Tserruya
JINR, May 22, 2008
36
0 pT spectra at √sNN = 200 GeV
p-p
AuAu Run4
0-10% central
70-80% peripheral
Ncoll =975 ± 94.0
Ncoll =12.3 ± 4.0
η=0
Excellent agreement between measured
π0’s inAu-Au
p-p collisions yield significantly
Central
0
and measured π ’s in Au-Au
peripheral collisions
Itzhak Tserruya
37
JINR, May 22, 2008
scaled by the number of collisions over ~ suppressed
5 decades relative to scaled pp yield
Control: Photons shine, Pions don’t
Direct photons are not affected by hot/dense medium
Rather: shine through consistent with pQCD
38
Quantitative Analysis of Energy Loss
Itzhak Tserruya
JINR, May 22, 2008
39
Jet correlations in Au+Au
Away side jet
strongly modified in
Au+Au compared to
p+p collisions
Low/intermediate pT:
-broad away-side
-maxima at Δφ= π +/- 1 rad
High pT
-away-side shape like p+p
-but suppressed yield
Current conjecture:
•Head region -> jet modification (dominant at high pT)
•Shoulder region -> medium response (dominant at intermediate pT)
•
Fluid Effects on Jets ?
Mach cone?
☑ Jets travel faster than the
speed of sound in the medium.
☑ While depositing energy
via gluon radiation.
QCD “sonic boom” (?)
To be expected
in a dense fluid
which is
strongly-coupled
Itzhak Tserruya
JINR, May 22, 2008
41
Summary and Outlook
 RHIC
has so far been very successful . Much is left to do to further
characterize the properties of the “perfect fluid”
62.4 GeV Au+Au
 LHC is behind the corner.
It will offer an unparalleled increase in √s. Will this still create a
strongly coupled perfect fluid? Or will we approach the ideal QGP
of free gas of quarks and gluons as originally sought?
 Active pursuit via

Dedicated experiment (ALICE)
 Targeted studies (CMS, ATLAS)






Onset of heavy flavor energy loss?
Emergence of opacity
Onset of RHIC’s perfect fluid
Energy Scans: where is the critical point?
Low-mass dileptons
Photon + Jets
 Ambitious upgrade program underway
 RHIC  RHIC II x40 luminosity increase
 Detectors and DAQ upgrades