Highlights of the BNL press release

1
Highlights of the BNL press release
after the end of the dAu run at RHIC
Results of BRAHMS, PHENIX, PHOBOS and STAR
collaborations summarized by Tamás Csörgo

• Introduction to high energy heavy ion physics
• Conceptual similarities with modern cosmology
• Suppression in AuAu at high pt
• Absence of suppression in dAu
• Highlights from BRAHMS, PHENIX, PHOBOS, STAR
• Summary and interpretation

T. Cs. A. Ster, http//arXiv.org/abs/nucl-th/020
7016
lt- Allegory of Hung. Acad. Sci From darkness,
the light, painting by P. Endel
2
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/lit
  tle.bang/
• Big Bang machine gets down to work (MSNBC News,
  June 14, 2000) http//www.msnbc.com/news/314049.as
  p?cp11

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
3
Overview of the Big Bang
basic facts about our Universe
Age 13.7 x 109 (billionmilliard) 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
4
Overview of the Big Bang
Experimental signals of inflation Universe is
homogeneous The region of thermal
equilibrium is larger, than the particle
horizont
5
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

6
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 Mans
Supercomputer in Hungary. Crossover like phase
transition, e.g. in case of ionization of atoms
7
Accelerators and Experiments CERN (1)

• PbPb _at_ Elab 158 AGeV _at_ CERN SPS
• O Pb, SPb, hp, pp, pA collisions
• 7 big experiments took data NA44, NA45, NA49,
  NA50, NA52, NA57, WA98
• Collaboration of European countries with observer
  states from outside.

8
Accelerators and Experiments (2) Brookhaven,
RHIC, USA

• AuAu _at_ Ecms 100100 AGeV _at_ run2
• polarized p polarized p, pA 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
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4 RHIC experiments
10
Goals of the RHIC experiments
The broadest possible investigations studying
AB, pp and pA 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
11
The Medium and the Probe

• At RHIC energies different mechanisms are
  responsible for different regions of particle
  production.
• The rare process (Hard Scattering or Jets)
  probes whether the soft production products form
  a medium.
• Calibrated Probe
• The tail that wags the dog (M. Gyulassy)

pp-gtp0 X
hep-ex/0305013 S.S. Adler et al.
12
Jet quenching in Au Au observed. Why?
Initial conditions?
New matter?
Compressed gluons, color glass
How to distinquish? Swich off the medium ? dAu
collisions
13
Nuclear Modification Factor RAA

• We define the nuclear modification factor as
• RAA is what we get divided by what we expect.
• By definition, processes that scale with the
  number of underlying nucleon-nucleon collisions
  (aka Nbinary) will produce RAA1.

AuAu-gtp0X
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.
nucl-ex/0304022 S.S. Adler et al.
14
What happens at RHIC? New form of matter
Jets suppressed and decorrelated in AuAu at
RHIC, but not in dAu at RHIC! Press release,
BNL, June 18, 2003 Title page of PRL, Aug 15,
2003,
15
PHENIX results Particle Spectra Evolution
Central
Nuclear Physics
Particle Physics
K. Adcox et al, Phys Lett B561 (2003) 82-92
Peripheral
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dAu Control Experiment

• 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.

17
dAu Spectra

• Final spectra for charged hadrons and identified
  pions.
• Data span 7 orders of magnitude.

18
RAA vs. RdA for Identified p0
Initial State Effects Only
dAu
Initial Final State Effects
AuAu
d-Au results rule out CGC as the explanation for
Jet Suppression at Central Rapidity and high pT
19
Centrality Dependence
Au Au Experiment
d Au Control Experiment
Preliminary Data
Final Data

• Dramatically different and opposite centrality
  evolution of AuAu experiment from dAu control.
• Jet Suppression is clearly a final state effect.

20
The Away-Side Jet
dAu
AuAu
60-90
Min Bias
0-10
Near
Near
Far
Far
PHENIX Preliminary
PHENIX Preliminary

• Jets produced on the periphery of the collision
  zone coming out should survive.
• However, their partner jet will necessarily be
  pointed into the collision zone and be absorbed.

• Peripheral AuAu similar to dAu
• Central AuAu shows distinct reduction in far
  side correlation.
• Away-side Jet is missing in AuAu

21
PHOBOS results pT Spectra for AuAu _at_ 200 GeV
22
Centrality Dependence vs pT
PHOBOS, nucl-ex/0302015
Similar centrality dependence at pT 0.5 and 4
GeV/c !
23
Predictions for dAu
pQCD
Parton Saturation
Vitev, nucl-th/0302002, Phys.Lett.B in press
Vitev and M.Gyulassy, Phys.Rev.Lett. 89 (2002)
Kharzeev, Levin, McLerran, hep-ph/021332
30suppression of high pT particles (central
vs peripheral)
Central
Nuclear Modification Factor RdAu
Peripheral
16 increase central vs peripheral
24
PHOBOS Detector 2003
mini-pCal
SPECTRIG

• 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
25
dAu pT Spectra
PHOBOS dAu nucl-ex/0306025
26
RdAu vs pT
PHOBOS dAu nucl-ex/0306025
central AuAu
All syst. uncertainties 90 C.L.
27
Centrality dependence of RdAu
PHOBOS dAu nucl-ex/0306025
Data disfavor initial state interpretation of
AuAu high-pT suppression
N.B. Smaller sppinel would increase RdAu
central vs RdAu peripheral
All syst. uncertainties 90 C.L.
28
Connection to QCD
Initial State
Intermediate State Interactions
Interaction of fast partons with dense medium has
been observed Quantitative diagnostic tool now
established
Multiplicity systematics connected to initial
state Consistent with parton saturation picture
29
The STAR detector
E-M Calorimeter
Projection           Chamber
Time of    Flight
30
Partonic energy loss in dense matter
Bjorken, Baier, Dokshitzer, Mueller, Pegne,
Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang,
Wang, Salgado, Wiedemann,
Multiple soft interactions
Gluon bremsstrahlung
Opacity expansion
Strong dependence of energy loss on gluon density
?glue measure DE ? color charge density at
early hot, dense phase
31
Jets at RHIC
Find this.in this
pp ?jetjet (STAR_at_RHIC)
AuAu ???? (STAR_at_RHIC)
32
Partonic energy loss via leading hadrons
Energy loss ? softening of fragmentation ?
suppression of leading hadron yield

33
AuAu and pp inclusive charged hadrons
nucl-ex/0305015
PhysRevLett 89, 202301
pp reference spectrum measured at RHIC
34
Suppresion of inclusive hadron yield
AuAu relative to pp
RAA
AuAu central/peripheral
RCP
nucl-ex/0305015

• central AuAu collisions factor 4-5
  suppression
• pTgt5 GeV/c suppression independent of pT

35
Jets and two-particle azimuthal distributions
pp ? dijet

• trigger highest pT track, pTgt4 GeV/c
• Df distribution 2 GeV/cltpTltpTtrigger
• normalize to number of triggers

Phys Rev Lett 90, 082302
N.B. shifted horizontally by p/2 relative to
previous STAR plots!
36
Azimuthal distributions in AuAu
AuAu peripheral
AuAu central
pedestal and flow subtracted
Phys Rev Lett 90, 082302
Near-side peripheral and central AuAu similar
to pp
Strong suppression of back-to-back correlations
in central AuAu
37
Is suppression an initial or final state effect?
Initial state?
Final state?
partonic energy loss in dense medium generated in
collision
strong modification of Au wavefunction (gluon
saturation)
38
Inclusive suppression theory vs. data
pQCD-I Wang, nucl-th/0305010 pQCD-II Vitev and
Gyulassy, PRL 89, 252301 Saturation KLM, Phys
Lett B561, 93
Final state
Initial state
pTgt5 GeV/c well described by KLM saturation
model (up to 60 central) and pQCDjet quenching
39
dAu vs. pp Theoretical expectations
All effects strongest in central dAu collisions
40
Inclusive charged particle spectra
41
Inclusive yield relative to binary-scaled pp

• dAu enhancement
• AuAu strong suppression
• pT4 GeV/c
• cent/minbias 1.11?0.03
• central collisions enhanced wrt minbias

Suppression of the inclusive yield in central
AuAu is a final-state effect
42
Azimuthal distributions
Near-side pp, dAu, AuAu similar Back-to-back
AuAu strongly suppressed relative to pp and dAu
Suppression of the back-to-back correlation in
central AuAu is a final-state effect
43
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 AuAu 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!

44
Have we found the Quark Gluon Plasma at RHIC?

• We now know that AuAu 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
We have developed the tools necessary to complete
this program
45
What happens at lower energies, at CERN SPS?
Central PbPb (SPS)
Did the vikings have a Vinland map ??
Cronin effekt, increase instead of decrease,
multiple scattering szó Now new matter at CERN
SPS?
46
Overview and Outlook
A deeper meaning of the analogy CERN SPS lt-gt
Viking age, BNL RHIC lt-gt 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)