Highlights of the BNL press release
after the end of the d+Au run at RHIC
Results of BRAHMS, PHENIX,
PHOBOS and STAR collaborations
summarized by Tamás Csörgő
•Introduction to high energy heavy ion physics
•Conceptual similarities with modern cosmology
•Suppression in Au+Au at high pt
•“Absence of suppression” in d+Au
•Highlights from BRAHMS, PHENIX, PHOBOS, STAR
•Summary and interpretation
T. Cs. & A. Ster, http://arXiv.org/abs/nucl-th/0207016
<- Allegory of Hung. Acad. Sci: „From darkness, the light”, painting by P. Endel
Some recent “papers”:
 In a Lab on Long Island, a Visit to the Big Bang
New York Times, Jan. 14,2003 http://www.phy.bnl.gov/users/
-
 'Little' Big Bang stumps scientist (CNN, Nov. 20, 2002)
http://www.cnn.com/2002/TECH/space/11/13/little.bang/
 Big Bang machine gets down to work (MSNBC News, June 14, 2000)
http://www.msnbc.com/news/314049.asp?cp1=1
Major goals of high energy heavy ion physics:
i) Study of the collective properties of matter at the
highest experimentally available temperatures in the
largest available volumes
ii) Collision of heavy ions (almost fully ionized atoms, ~
atomic nuclei), with max. mass number and energy
iii) Experimentally prepare and identify the quark-gluon
plasma which is predicted by theory to exist
Overview of the Big Bang
basic facts about our Universe
Age: 13.7 x 109 (billion|milliard) years
Shape: flat
Age when light first appeared: 200
million years
Contents:
4% ordinary matter
23% „dark matter”, nature unknown
73% „dark energy”, nature unknown
Expansion rate (or Hubble Constant):
H0 = 71 km/sec/Megaparsec
New Scientist, 15.2 2003 p. 12-13
SI Units:
Age: 4.3 x 1017 sec
Expansion rate:
H0= (2.3 ± 0.2)x10-12 sec-1
Hubble law:
v = H0 r
velocity ~ distance
1 parsec = 3.26 lightyear ~ 3.1 x1016 m
Overview of the Big Bang
Experimental
signals of
inflation:
Universe is
homogeneous
The region of
thermal
equilibrium
is larger, than the
particle horizont
Big Bang and Little Bang (2)
heavy ion collisions
 Early Universe: hot and
expanding system
 High energy heavy ion
collisions: hot and expanding
systems
 Expansion velocity is
proportional to distance
(Hubble law)
 Protons and neutrons may melt
down, phase transition
 Quark Matter, Quark Gluon
Plasma
Phases of QCD Matter
 We have strong interaction analogues
of familiar phases
 Nuclei behave like a liquid
– Nucleons are like molecules
 Quark Gluon Plasma
– “Ionize” nucleons with heat
– “Compress” them with density
 New state of matter!
Fodor and Katz:
Tc ~ 170 MeV ~ 140x1012 K,
at finite baryon density.
Using Poor Man’s
Supercomputer in Hungary.
Crossover like phase
transition, e.g. in case of
ionization of atoms…
Accelerators and Experiments: CERN (1)




Pb+Pb @ Elab = 158 AGeV @ CERN SPS
O +Pb, S+Pb, h+p, p+p, p+A collisions
7 big experiments took data: NA44,
NA45, NA49, NA50, NA52, NA57, WA98
Collaboration of European countries
with observer states from outside.
Accelerators and Experiments (2):
Brookhaven, RHIC, USA





Au+Au @ Ecms = 100+100 AGeV @ run2
polarized p +polarized p, p+A collisions
4 experimental collaborations: BRAHMS,
PHENIX, PHOBOS, STAR
Hundreds of scientists/experiment, countries
from all over the world are participating
Visible from space!
Manhattan, New York
RHIC, Brookhaven
4 RHIC experiments
Goals of the RHIC experiments
The broadest possible investigations
studying A+B, p+p and p+A
collisions
- study of strongly interacting
matter
- leptonic and hadronic signals, both
„collective” and „individual”
- systematic studies with variation
of bombarding energy and system
size
- study of the structure of the spin
of the proton
The Medium and the Probe
 At RHIC energies different
mechanisms are
responsible for different
regions of particle
production.
Thermally The rare process (Hard shaped Soft
Production
Scattering or “Jets”)
probes whether the soft
production products form
a medium.
– Calibrated Probe
– “The tail that wags the
dog”
(M. Gyulassy)
p+p->p0 + X
“Well Calibrated”
Hard
Scattering
hep-ex/0305013 S.S. Adler et al.
Jet quenching in Au + Au observed. Why?
Initial
conditions?
New matter?
Compressed gluons,
color glass
How to distinquish? Swich off
the medium  d+Au collisions
absorption
Nuclear Modification Factor: RAA
 We define the nuclear
modification factor as:
Au+Au->p0+X
1 d 2 N A A
N evt dpT d
RAA ( pT ) 
 N binary  d 2 N  N
NN
 inel
dpT d
 RAA is what we get divided
by what we expect.
 By definition, processes
that scale with the number
RAA is well below 1 for both charged
of underlying nucleonnucleon collisions (aka
hadrons and neutral pions.
Nbinary) will produce RAA=1.
The neutral pions fall below the charged
hadrons since they do not contain
contributions from protons and kaons.
nucl-ex/0304022 S.S. Adler et al.
What happens at RHIC? New form of matter
Jets suppressed and decorrelated in Au+Au at RHIC,
but not in d+Au at RHIC!
Press release, BNL, June 18, 2003 Title page of PRL, Aug 15,
PHENIX results: Particle Spectra Evolution
“Central”
Nuclear
Physics
Particle
Physics
K. Adcox et al, Phys Lett B561 (2003) 82-92
“Peripheral”
d+Au Control Experiment
Nucleusnucleus
collision
Proton/deuteron
nucleus
collision
 Collisions of small with large nuclei were always foreseen as
necessary to quantify cold nuclear matter effects.
 Recent theoretical work on the “Color Glass Condensate”
model provides alternative explanation of data:
– Jets are not quenched, but are a priori made in fewer numbers.
– Color Glass Condensate hep-ph/0212316; Kharzeev, Levin, Nardi,
Gribov, Ryshkin, Mueller, Qiu, McLerran, Venugopalan, Balitsky, Kovchegov,
Kovner, Iancu
 Small + Large distinguishes all initial and final state effects.
d+Au Spectra
 Final spectra for charged hadrons and identified pions.
 Data span 7 orders of magnitude.
RAA vs. RdA for Identified p0
d+Au
Initial State
Effects Only
Au+Au
Initial + Final
State Effects
d-Au results rule out CGC as the explanation for Jet
Suppression at Central Rapidity and high pT
Centrality Dependence
Au + Au Experiment
d + Au Control Experiment
“PHENIX
Preliminary”
results,
consistent
with PHOBOS
data in
submitted
paper
Final Data
Preliminary Data
 Dramatically different and opposite centrality evolution of Au+Au
experiment from d+Au control.
 Jet Suppression is clearly a final state effect.
1.01
C
1.1
1.0
The “Away-Side”
Jet
1.00
0.9
1.3
2.0 < pT < 3.0 (GeV/c)
2.0 < pT < 3.0 (GeV/c)
1.03
1.2
1.02
C()
d+Au
1.1
1.01
60-90%
0-10%
Min Bias
1.0
1.00
0.9
0.99
0
Lost Jet
“Far Side”
Au+Au
30
Near
60
90
120
150
deg.
180
0
Far
30
60
Near
PHENIX Preliminary
90
120
150
deg.
180
Far
PHENIX Preliminary
 Jets produced on the periphery of the collision  Peripheral Au+Au similar to d+Au
zone coming out should survive.
 Central Au+Au shows distinct reduction in far
“PHENIX Preliminary”
side correlation.
 However, their partner jet will necessarily be
results, consistent with
pointed into the collision zone and be
 Away-side Jet is missing in Au+Au
absorbed.
STAR data in submitted
paper
C()
Escaping Jet
“Near Side”
0.99
PHOBOS results: pT Spectra for Au+Au @ 200 GeV
Relative to UA1 p+p
0.2<yp <1.4
Data: PHOBOS, nucl-ex/0302015
Submitted to Phys Lett B
Centrality Dependence vs pT
PHOBOS, nucl-ex/0302015
Initial State
Coherence?
Interaction in
Dense Medium?
Similar centrality dependence at
pT = 0.5 and 4 GeV/c !
Predictions for d+Au
pQCD
Parton Saturation
Vitev, nucl-th/0302002, Phys.Lett.B in press
Vitev and M.Gyulassy, Phys.Rev.Lett. 89
(2002)
“~30%suppression of high pT particles”
(central vs peripheral)
Nuclear Modification Factor
RdAu
Kharzeev, Levin, McLerran, hep-ph/021332
Central
Peripheral
16% increase central vs peripheral
PHOBOS Detector 2003
mini-pCal
T0
SPECTRIG
T0
i.
ii.
iii.
iv.
v.
Moved TOF walls back
•
5 m from interaction point
New on-line high pT Spectrometer Trigger
New “time-zero” (T0) Cerenkov detectors
•
On-line vertexing and ToF start time
Forward proton calorimeters on Gold and Deuteron sides
DAQ upgrade (x10)
pCal
d+Au pT Spectra
PHOBOS d+Au: nucl-ex/0306025
Compare to p+p reference…
41mb (same as for Glauber)
From Glauber
(HIJING 1.383)
From UA1, using
Pythia to go from
|| < 2.5 to 0.2 <  < 1.4
…for each centrality bin
RdAu vs pT
PHOBOS d+Au: nucl-ex/0306025
central Au+Au
All syst. uncertainties: 90% C.L.
Centrality dependence of RdAu
PHOBOS d+Au: nucl-ex/0306025
Data disfavor initial state
interpretation of Au+Au
high-pT suppression
N.B. Smaller ppinel would increase
RdAu central vs RdAu peripheral
All syst. uncertainties: 90% C.L.
Connection to QCD
Initial State
‘Intermediate State’
Interactions
Multiplicity systematics
connected to initial state
Interaction of fast partons
with dense medium has
been observed
Consistent with parton
saturation picture
Quantitative diagnostic
tool now established
The STAR detector
E-M
Calorimeter
Projection
Chamber
Time
of
Flight
Partonic energy loss in dense matter
Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy,
Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,…
Multiple soft interactions:
C R S 2
E 
qˆL
4
kT2
medium
qˆ 
  S  glue
Gluon bremsstrahlung
Opacity
expansion:

 2 E jet
E  pC ACa  d glue  , r  Log  2
 L
3
S



Strong dependence of energy loss on gluon density glue:
measure E  color charge density at early hot, dense phase
Jets at RHIC
Find this……….in this
p+p jet+jet
(STAR@RHIC)
jet
parton
nucleon
nucleon
Au+Au ???
(STAR@RHIC)
Partonic energy loss via leading hadrons
Energy loss  softening of
fragmentation  suppression of
leading hadron yield
d 2 N AA / dpT d
RAA ( pT ) 
TAAd 2 NN / dpT d
Binary collision scaling
-
p+p reference
Au+Au and p+p: inclusive charged hadrons
PhysRevLett 89, 202301
nucl-ex/0305015
p+p reference spectrum measured at RHIC
Suppresion of inclusive hadron yield
RAA
Au+Au relative to p+p
RCP
Au+Au central/peripheral
nucl-ex/0305015
• central Au+Au collisions: factor ~4-5 suppression
• pT>5 GeV/c: suppression ~ independent of pT
Jets and two-particle azimuthal distributions
p+p  dijet
• trigger: highest pT track, pT>4 GeV/c
•  distribution: 2 GeV/c<pT<pTtrigger
• normalize to number of triggers
Phys Rev Lett 90, 082302
N.B. shifted horizontally by p/2
relative to previous STAR plots!
trigger
Azimuthal distributions in Au+Au
Au+Au peripheral
Au+Au central
pedestal and flow subtracted
Phys Rev Lett 90, 082302
Near-side: peripheral and central Au+Au similar to p+p
Strong suppression of back-to-back
correlations in central Au+Au
?
Is suppression an initial or final state effect?
Initial state?
strong modification of Au
wavefunction (gluon saturation)
Final state?
partonic energy loss in
dense medium
generated in collision
Inclusive suppression:
theory vs. data
RCP
pQCD-I: Wang, nucl-th/0305010
pQCD-II: Vitev and Gyulassy, PRL 89, 252301
Saturation: KLM, Phys Lett B561, 93
nucl-ex/0305015
Final state
Initial state
pT>5 GeV/c: well described by KLM saturation
model (up to 60% central) and pQCD+jet quenching
d+Au vs. p+p: Theoretical expectations
RAB
Inclusive spectra
If Au+Au suppression is final state
1.1-1.5
1
If Au+Au suppression is initial state
(KLM saturation: 0.75)
~2-4 GeV/c
High pT hadron pairs
pT
broadening?
pQCD: no suppression, small
broadening due to Cronin effect
saturation models: suppression
due to mono-jet contribution?
0
0
p/2
p
 (radians)
All effects strongest in central d+Au collisions
suppression?
Inclusive charged particle spectra
Inclusive yield relative to binary-scaled p+p
RAB
dN AB / dpT d

TAB d pp / dpT d
• d+Au : enhancement
Au+Au: strong suppression
• pT=4 GeV/c:
cent/minbias = 1.110.03
 central collisions
enhanced wrt minbias
Suppression of the inclusive yield
in central Au+Au is a final-state effect
Azimuthal distributions
pedestal and flow subtracted
Near-side: p+p, d+Au, Au+Au similar
Back-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
Conclusion from STAR, BNL, June 18, 2003
The strong suppression of the inclusive yield and
back-to-back correlations at high pT previously
observed in central Au+Au collisions are due to
final-state interactions with the dense medium
generated in such collisions.
Comment (~Bo Andersson):
Can you discover something by observing the
absence of the suppression of an effect?
What would be a positive signal for QGP?
Young experimentalists
are welcome to find the answer!
Have we found the Quark Gluon Plasma at RHIC?
We now know that Au+Au collisions generate a medium that
 is dense (pQCD theory: many times cold nuclear matter
density)
 is dissipative
 exhibits strong collective behavior
This represents significant progress in our
understanding of strongly interacting matter
We have yet to show that:
 dissipation and collective behavior both occur at the partonic
stage
 the system is deconfined and thermalized
 a transition occurs: can we turn the effects off ?
Not yet, there is still work to do
What happens at lower energies, at CERN SPS?
p+A:
Central Pb+Pb (SPS
Did the vikings have
a „Vinland map” ??
“Cronin effekt”, increase instead of decrease, multiple
scattering szó
Now new matter at CERN SPS?
Overview and Outlook
A deeper meaning of the analogy
CERN SPS <-> Viking age,
BNL RHIC <-> Age of Columbus?
Personal view:
A new world discovered.
But is it India or America?
Is it QGP or some other new form of
matter?
Need to make the map.
(All information soft spectra, correlations, high pt are
needed)