20-apr-02w.a. zajc1 first results from rhic w.a. zajc columbia university
TRANSCRIPT
20-Apr-02 W.A. Zajc
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First Results First Results from RHICfrom RHIC
W.A. ZajcColumbia University
20-Apr-02 W.A. Zajc
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Is There An Ultimate Is There An Ultimate Temperature?Temperature?
From the National Research Council Committee on The Physics of the Universe report
No.
77Are there new
states of matter at ultrahigh
temperatures and densities?
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~1970: An Ultimate ~1970: An Ultimate Temperature?Temperature?
The very rapid increase of hadron levels with mass
Hadron 'level' diagram
0
500
1000
1500
0 10 20 30 40
Degeneracy
Mass (MeV)
Kfo
Density of States vs Energy
0
50
100
150
200
250
0 500 1000 1500 2000
Mass (MeV)
Number of available
states
~ equivalent to an exponential level density
HT /maem~dmdn
(m)ρ
dmem~
dm(m)eρ
)T1
T1
m(a
T /m
H
and would thus imply a “limiting temperature”TH ~ 170 MeV
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~2000: T~2000: TH H T TCCThat is: The ‘Hagedorn temperature’ TH is now
understood as a precursor of TC
TC = Phase transition temperature of QCD
0.66 TCT =0
0.90 TC
1.06 TC
F. Karsch, hep-ph/0103314
Current estimates from lattice calculations:
TC ~ 150-170 MeV
L ~ 0.70.3 GeV / fm3
(latent heat)
Study confining potentialin Lattice QCD at various temperatures
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The Landscape of The Landscape of QCDQCD
neutron stars
Baryon Potential B [MeV]
early universe
Che
mic
al T
empe
ratu
re T
ch [M
eV]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
SIS
SPS
RHIC quark-gluon plasma
hadron gas
thermal freeze-out
deconfinementchiral restauration
Lattice QCD
atomic nuclei
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RHIC SpecificationsRHIC Specifications 3.83 km
circumference Two independent
rings 120 bunches/ring 106 ns crossing time
Capable of colliding ~any nuclear species on ~any other species
Energy:
500 GeV for p-p 200 GeV for Au-Au
(per N-N collision) Luminosity
Au-Au: 2 x 1026 cm-2 s-1
p-p : 2 x 1032 cm-2 s-1 (polarized)
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How is RHIC How is RHIC Different?Different?
Different from p-p, l-p colliders
Atomic number A introduces new scale Q2 ~ A1/3 Q02
Different from previous (fixed target) heavy ion facilities ECM increased by order-of-magnitude
Accessible x (parton momentum fraction)decreases by ~ same factor
Access to perturbative phenomena Jets Non-linear dE/dx
Its detectors are comprehensive ~All final state species measured with a suite of
detectors that nonetheless have significant overlap for comparisons
s
p 2~x T
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RHIC RunningRHIC Running
FY2000(66 GeV/amu)
FY2001 – 02100 GeV/amu
PHENIX during last 10 days:24 (b)-1/week
Lave(week) = 0.4 1026 cm-2 s-1
Lave(week)/Lave(store) = 27 %
~All results presented here are from the RHIC
Run-1 data set
~All results presented here are those Run-1 data in the refereed
literature:
22 publications to date (19 PRL’s)
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1 RHIC Event1 RHIC EventData Taken June 25, 2000.
Pictures from STAR Level 3 online display.
Q. How to take the measure of such complexity??
(Is it possible?)
A. (Yes.) Begin with single-particle momentum spectrum of identified hadrons
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Results on Particle Results on Particle CompositionComposition
PHOBOS and BRAHMS:ratios of - / +
K- / K+
p / p
mid-rapidity
PHENIX, STAR: spectra of - , 0 , + ,
K- , Ks0 , K+ ,
p , p ,
,
, , …
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Central
Ratio (data)
Rat
io (
chem
ical
fit
)
BRAHMSPHENIXPHOBOSSTAR
K /K
/
/ /
p/p
K/h
K /h K
s/h
K / K / p/
p/K/h
/h
/h
/h
/h
/h
Model:N.Xu and M.Kaneta,
nucl-ex/0104021
Is there a Is there a ‘Temperature’?‘Temperature’?
Apparently: Assume distributions described by one temperature T
and
one ( baryon) chemical potential :
One ratio (e.g., p / p ) determines / T :
A second ratio (e.g., K / ) provides T Then predict all other hadronic yields and ratios:
pdedn E 3/)(~ Tμ
TμTμ
Tμ/2
/)(
/)(
ee
e
p
pE
E
130 GeV RHIC : STAR / PHENIX / PHOBOS / BRAHMS
17.4 GeV SPS : NA44, WA97
STAR preliminary Systematic errors ~10-20%
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Previous figure RHIC has net baryon density ~ 0: TCH = 179 ± 4 MeV, B = 51 ± 4 MeV (M. Kaneta and N. Xu, nucl-ex/0104021)
130 GeV RHIC : STAR / PHENIX / PHOBOS / BRAHMS
17.4 GeV SPS : NA44, WA97
STAR preliminary Systematic errors ~10-20%
Locating RHIC on Phase Locating RHIC on Phase DiagramDiagram
RHIC is as close as we’ll get to the early universe for some time
Previous Heavy Ion Experiments (CERN SPS)
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Where do the Baryons Where do the Baryons Go?Go?
There is a (not-quite-perfect) correspondence between longitudinal momentum (rapidity) and the angle of emission in the center-of-mass
Baryon number, found(?) at non-zero rapidities, must be measured away from 90 degrees
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BRAHMS ResultsBRAHMS Results Anti-proton/proton ratio as a function of rapidity:
(Three points are reflected about y=0)
Clear evidence for development of (nearly) baryon-free central region
0
0.2
0.4
0.6
0.8
1
-3 -2 -1 0 1 2 3
y
antiprotonto proton
ratio
BRAHMS
STAR
PHOBOS
PHENIX
Net baryon number ~2 units
from central rapidity
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Hydrodynamic Hydrodynamic BehaviorBehavior
Superimposed on the thermal (~Boltzmann) distributions: Collective velocity fields from
Momentum spectra ~
‘Test’ by investigating description for different mass particles:
Excellent description of particle production (P. Kolb and U. Heinz, hep-ph/0204061)
0j,0T μBμ
μνμ
)mp
v(fpd
)dn(Thermal~
pddn
HYDRO
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Late Breaking NewsLate Breaking News “Since the identified particle
spectra from PHENIX and STAR come continuously, we show the current comparison of experiment vs. model in this note.”
(W. Broniowski and W. Florkowski, 19-Apr-02 update to nucl-th/0112043)
4 parameters ( T , , velocity profile, freeze-out shape)
describe ~ all identified hadrons (spectrum and yields)
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Evidence that
initial spatial asymmetry is translated quickly to momentum space ( as per a
hydrodynamic description)
Hydrodynamics of Elliptic FlowHydrodynamics of Elliptic Flow Parameterize azimuthal asymmetry of charged
particles as
1 + 2 v2 cos (2 )
x
z
y
(scaled) spatial asymmetry
(PHOBOS : Normalized Paddle Signal)
Hydrodynamic limit
STAR: PRL86 (2001) 402
PHOBOS preliminary
Hydrodynamic limit
STAR: PRL86 (2001) 402
PHOBOS preliminary
Compilation and Figure from M. Kaneta
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Measuring Space-Time Measuring Space-Time DimensionsDimensions
Can we “image” the particle source? No – But Hanbury-Brown—Twiss (HBT) measurements
provide 3-D measure of spatial dimensions
p1
p2
Beamaxis
RSIDE
ROUT
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SizesSizes Measurements of RSIDE
‘Large’ source Transverse momentum
dependence strongly expanding source
In rough agreement with hydrodynamic description
But Complete disagreement
with predictions for ROUT / RSIDE
‘Freeze-out’ time development not understood?
Problems in formalism? An outstanding open
question
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Systematizing our Systematizing our KnowledgeKnowledge
To date, RHIC has run one heavy-ion species (Au atomic number A = 197 )
All four RHIC experiments have carefully developed techniques for determining the number of participating
nucleons NPART in each collision(and thus the impact parameter)
The number of binary nucleon-nucleon collisions NCOLL as a function of impact parameter
This effort has been essential in making the QCD connection Soft physics ~ NPART
Hard physics ~ NCOLL
Participants
Spectators
Spectators
Binary Collisions
Participants
b (fm)
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Making the QCD Making the QCD ConnectionConnection
A surprising connection has emerged between soft phenomena (charged multiplicity) and QCD
The measured multiplicities at RHIC are low compared to (pre-data) calculations
This is (now) understood* as a manifestation of saturation in the initial state gluon distributions Nch ~ Nuclear Gluon Density
~ A xg (x, Q2)not ~ A xg (x, Q2) xg (x, Q2)
‘Understood’ in the sense that this is an area of intense theoretical activity and discussion
Eskola, QM2001
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dN
/d
/ .5N
part
Npart
Large nucleus (A) at low momentum fraction x gluon distribution saturates ~ 1/s(QS
2) with QS2 ~ A1/3
A collision* puts these gluons ‘on-shell’ ~ A xg(x,Q2) / R2
Parton-hadron duality maps gluons directly to charged hadrons
Each collision varies the effective A , i.e, the number of participants NPART
Shattering the ‘Color Glass Condensate’)
Saturation in Saturation in MultiplicityMultiplicity
)ΛQ
ln(~)(Qα
1~
AN
2
2S
2SS
CH
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pp
Extensions of Saturation Extensions of Saturation ApproachApproach**
Use HERA data, counting rules x G(x,Q2) ~ x-(1-x)4
Describe rapidity dependence: y ~ ln(1/x)
QS2(s,y) = QS
2(s,y=0)ey
Predict energy dependence: x = QS / s
QS2(s,y) = QS
2(s0,y) (s/s0) /2
Predict10-14% increase between s = 130 and 200 GeV
Versus 146% reported by PHOBOS
* D. Kharzeev and E. Levin, nucl-th/0108006
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RHIC and HERA (?)RHIC and HERA (?) The gluon densities at low x
and their Q2 evolution are the same as those used in saturation models applied at HERA: A.M. Stasto, K. Golec-Biernat, J.
Kwiecinski, Phys. Rev. Lett. 86, 596 (2001)
J. Bartels, K. Golec-Biernat, H. Kowalski hep-ph/0203258
More detailed understanding of the precise connection implications for other RHIC
observables
an area of intense investigation
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Rare ProcessesRare Processes Particle production via rare processes should
scale with Ncoll , the number of underlying binary nucleon-nucleon collisions
Roughly: Small no shadowing per nucleon luminosity is relevant quantity
Take scaling with Ncoll as our null hypothesisfor hard processes
FunctionThickness
),()( dzzddTA dz
d
FunctionOverlap
)2
()2
()( sdb
sTb
sTbT BAAB
b
INTINT
)(2AB
AB
INT
small""for
1
then is section cross TOTAL the
section cross withinteract which
tsconstituen B has B"" Nucleus and
tsconstituen Ahas A"" Nucleus If
BA
ebd bTABINT
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Open Charm as a Rare Open Charm as a Rare ProcessProcess
Via analysis of single-electron spectrum: Measure electron pT
spectrum Quantify (or bound) all
other sources of e’s
Remaining excess: from semi-leptonic decays of D’s
0 ee
ee, ee
0ee, 3
0ee, ee
conversion
ee
ee
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NLO PQCD calculation
Pythia
PHENIX
Open Charm YieldsOpen Charm Yields Charm cross-sections in Au+Au at RHIC,
extracted assuming Ncoll scaling,in good agreement with world’s data, NLO pQCD PYTHIA
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Tremendous interest in hard scattering (and subsequent energy loss in QGP) at RHIC Production rate calculable
in pQCD But strong reduction
predicted due to dE/dx ~ path-length (due to non-Abelian nature of medium)
However: “Traditional” jet
methodology fails at RHIC Dominated by the soft
background Investigate by (systematics
of) high-pT single particles
‘‘Jets’ at RHICJets’ at RHIC
RJet
Axis
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Rare processes at RHICRare processes at RHICBoth PHENIX and STAR have measured
charged particle spectra out to “small” cross sections
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‘‘High’ pHigh’ pTT Data Data
PHENIX: Has published
both Charged
hadronsand Identified 0’sto pT ~ 5 GeV/c
(Run-1 Luminosity limit)
for peripheral and central events
Compared to expectations from binary scaling
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A*B scaling at A*B scaling at RHIC?RHIC?
NO! Compare per collision
yield RAA of 0’s for Pb+Pb CERN SPS (17 GeV)
exceed unity at pT ~ 2 GeV/c
> A*B scaling RAA > 1 ‘Cronin effect’
Au+Au RHIC (130 GeV) Never reach unity < A*B scaling
(as distinct from charm yields)
Clear deficit even at the highest pT
Deficit opposite sign of enhancements previously seen in nuclear collisions (Cronin effect)
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Probing the Probing the suppressionsuppression
Is it (predicted) enhanced energy loss in hot nuclear matter?: To be
determined!: Study particle
composition(next slide)
Extend to much higher pT
(Run-2 data) Study in proton-
nucleus collisions(to be scheduled)
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How Strong is the How Strong is the Suppression?Suppression?
Strong enough to nearly extinguish pions at high pT : At pT ~ 3 GeV/c
Protons ~ 2 x +
Anti-protons ~ -
Qualitatively different from all previous data
Again– requires investigation at higher pT (Run-2)
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Run-2 and BeyondRun-2 and Beyond Run-2 (Aug-01 to Jan-02)
Au-Au at full energy (200 GeV) RHIC reaches design luminosity Data sets increased by ~ order-of-magnitude over
Run-1 Detectors significantly upgraded from their initial
Run-1 configurations p-p comparison running (200 GeV)
RHIC commissions p-p collisions RHIC become first polarized hadron collider Experiments measure vital baseline data for
comparison Experiments start on spin physics
Run-3 (Nov-02 start) To be determined
(Program Advisory Committee 26-27 Aug-02 )
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RHIC DynamicsRHIC Dynamics
From (just) the first run: Thermodynamics
Established Hydrodynamics
Validated Chromodynamics
In progress
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Open QuestionsOpen Questions Is the quark-gluon plasma being formed in
RHIC collisions? To be determined: Does charmonium show the expected suppression
from (color) Debye screening?
Is there direct (photon) radiation from the plasma? Do the suppression effects extend to the highest pT’s?
What is the suppression pattern in cold nuclear matter? (proton-nucleus collisions)
What are the gluon and sea-quark contributions to the proton spin? (polarized proton running)
RHIC
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Closed QuestionsClosed Questions Has the accelerator worked?
Have the experiments worked?
Are the data analyzable?
Are they being analyzed?
Do the data validate the premise of RHIC? Collective, ~thermal behavior Contact with basic QCD phenomenology
Are there new phenomena?
Are there prospects for a long and fruitful experimental program?