Recent Results from RHIC

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Recent Results from RHIC

• David Hofman
• University of Illinois at Chicago

EPS 2003July 17-24, 2003 Aachen
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Relativistic Heavy Ions

• AGS fixed target, 4.8 GeV/u pair
• SPS fixed target, 17 GeV/u pair
• RHIC collider, 200 GeV/u pair
• LHC collider, 5.4 TeV/u pair

RHIC

• Two concentric superconducting magnet rings, 3.8
  km circum.
• Funded by U.S. Dept. of Energy (616 million)
• Construction began Jan. 1991, first collisions
  June 2000
• Au Au vsNN (19.6, 56) 130, 200 GeV
• p p vsNN 200 GeV
• d Au vsNN 200 GeV (Just finished spring
  2003!)

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Relativistic Heavy Ions
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Four Complementary Experiments
303 collaborators
307 collaborators
Large solid angle tracking Complete
events
Leptons, (hs, gs) High rate, Sophisticated
triggering
68 collaborators
52 collaborators
4p accept. Good vtx. resolution (All Si det.)
Tracking PID at high y
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Participant Scaling
p p Collisions
Npart/2 of participating pairs of nucleons
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Binary Collision Scaling
Ncoll of NN collisions 1
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Participant Scaling
AuAu Collisions
Head-On Collision
Npart/2 of participating pairs of nucleons
A
Binary Collision Scaling
Head-On Collision
LA1/3
A
Ncoll of NN collisions A4/3
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Number of Binary Collisions vs. Centrality and
Energy
Glauber Monte Carlo for Au Au Collisions
sinel42 mb (RHIC)
nmax 6 (RHIC)
AuAu
nmax 5 (SPS)
n Ncoll/(Npart/2)
sinel33 mb (SPS)
nmax 3 (AGS)
sinel21 mb (AGS)
nmax 1 (pp)
Peripheralcollisions
Centralcollisions
ltNpartgt (vsNN200) 100
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Charged Particle Density near Midrapidity
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Charged Particle Density near Midrapidity
AuAu Min-bias
Most Naïve Model Possible AA Incoherent
Superposition of binary pp collisions
(n3.6)
(n3.1)
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Charged Particle Density near Midrapidity
Central Collisions (for Heavy Ion data)
RHIC - combined
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Charged Particle Density near Midrapidity
Central Collisions (for Heavy Ion data)
dN/dyT (for ee- data)
RHIC - combined
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RHIC Results for Au Au Charged Particles
mid-rapidity

• Multiplicities at the very low end of model
  expectation.
• (vs 200 GeV)
• Energy-density estimates
• eBJ 4.6 GeV/fm3 (vs 130 GeV)(PHENIX PRL 87
  (2001) 052301)
• eBJ 5.5 GeV/fm3 (vs 200 GeV)(PHENIX
  preliminary)
• Expectation for a new form of matter at
  energy-densities
• e gt 1 GeV/fm3

Mid-Rapidity Density
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Charged Particle Production at Midrapidity
Energy and Centrality Dependence
Data is normalized by pp value for each energy.
Binary collision scaling
200 GeV
AuAu
130 GeV
19.6 GeV preliminary
Participant scaling
peripheral
central
? Very flat particle production with
centrality! ? Importance of comparing results to
proton baseline.
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Suppression in AuAu Hadron Spectra
Picture FromT. Peltzmann, QM02
Binary collision scaling
Central collisions at midrapidity
BRAHMSSTARPHOBOS
h
h p0
PHENIX 0-10
Participant scaling
? High pT yields in AuAu are strongly suppressed
for central collisions relative to pp data
and collision scaling expectation. ? Trend is
seen in all four RHIC experiments.
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Suppression in AuAu Hadron Spectra
STAR nucl-ex/0305015
0 2 4 6 8
10 12
pT (GeV/c)
pQCD Wang, nucl-th/0305010 (see also Vitev and
Gyulassy, PRL 89, 252301)
Saturation KLM, Phys Lett B561, 93
Initial state effect
Final state effect
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Jets at RHIC
From P. Jacobs, RHIC special colloquium
Find this
in this
pp ?jetjet (STAR_at_RHIC)
AuAu ???? (STAR_at_RHIC)
Select highest pT (gt4 GeV/c) trigger jet
nucleon
nucleon
? create Df distribution for 2 lt pT lt
pT(trigger)
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Azimuthal Jet Distributions in AuAu
STAR PRL 90, 082302
Figs FromP. Jacobs
AuAu peripheral
AuAu central
pedestal and flow subtracted
pedestal and flow subtracted
Near-side peripheral and central AuAu similar
to pp
Far-side strong suppression of back-to-back
correlations in central AuAu
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Suppression Initial or Final State Effect?
Pics FromP. Jacobs
Initial state?
Final state?
partonic energy loss
gluon saturation
High pT suppression in Au Au explained by both
models.
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Suppression Initial or Final State Effect?
Pics FromP. Jacobs
Initial state?
Final state?
partonic energy loss
gluon saturation
High pT suppression in Au Au explained by both
models.
How to discriminate? Turn off final state.?
dAu collisions
?
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Charged Hadron Results _at_ RHIC
dAu vs. AuAu at vsNN 200 GeV
STAR dAu nucl-ex/0306024
PHENIX dAu nucl-ex/0306021
dAu
AuAucentral
0 1 2 3 4 5 6 7 8
9 10
pT (GeV/c)
BRAHMS dAu nucl-ex/0307003
dAu
AuAucentral
(BRAHMS same in AuAu for h2)
pT (GeV/c)
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p0 Yields Relative to Binary Scaled pp
Color Fig FromT. Hemmick
dAu
Binary Collision Scaling
AuAu
AuAu strong suppression
dAu no suppression
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Azimuthal Jet Distributions in dAu
Fig FromP. Jacobs
pedestal and flow subtracted
D f (radians)
Near-side similar result for pp, dAu and AuAu.
Far-side strong suppression of back-to-back
correlations only in central AuAu NOT in dAu,
pp nor peripheral AuAu.
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June 18th 2003 RHIC special symposium

• Evidence for jet quenching in central AuAu at
  RHIC
• Evidence of jet non-quenching in dAu (and
  peripheral AuAu)

Data suggest we have observed a final state
effect produced in a hot dense medium.

• A few (of many) other hot topics at RHIC
• Statistical model and particle ratios
• Everything fits with T 176 MeV.
• HBT Radii
• No change in Rside and Rout!
• Elliptic Flow
• Saturates hydrodynamics limit at low pT!
• Interesting mass, pT and h dependence!
• First glimpses of J/Y at RHIC

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Particle Ratios Fit Beautifully in Statistical
Model
Fig FromB. Norman
? Statistical/Thermal model represents data well.
? No change in freezeout temperature from 130 to
200 GeV, but decreasing baryon chemical potential.
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Two pion correlations at RHIC
vsNN 130 GeV

• Source dimensions by measuring HBT radii.
• Essentially no change (in Rside and Rout) from
  AGS (vsNN4.7) to RHIC (vsNN200)!
• Short lived source.
• Not described in current dynamical models.

PHENIX PRL 88 (2002) 192302 STAR PRL 87
(2001) 082301
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Elliptic Flow a Collective Effect
Initial spatial anisotropy
z
z
Reaction plane (YR)
y
f
x
y
y
x
x (defines YR)
Final momentum anisotropy
dN/d(f -YR ) N0 (1 2v1cos (f-YR)
2v2cos (2(f-YR)) ... )
py
px
Anisotropy parameter v2
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RHIC Results Reach Hydro at low pT
(PHENIX nucl-ex/0305013)
STAR nucl-ex/0306007

• STAR PHENIX have similar results for the mass
  and pT dependence of elliptic flow (v2).
• Reach hydro limit only at low pT. Different
  particles deviate from this limit at different
  values of pT.
• Mass and pT dependence removed if scale by number
  of constituent quarks (n).
• Quark coalescence?

? More detailed studies needed.
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Charged Particle v2 vs. h and Energy
PHOBOS PRL 89, 222301 (2002)
Hydrodynamic limit illustration
Anisotropy parameter v2
vsNN 130 GeV (PRL 89)
vsNN 200 GeV (preliminary)
h (pseudorapidity)
? Lack of boost invariance. Poses a challenge for
theory.
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J/y from PHENIX

• The suppression of J/y yields in heavy-ion
  collisions at SPS is believed to be an important
  signal for a de-confined state of matter.
• Important to measure at RHIC.
• PHENIX has successfully measured J/y at RHIC for
  pp collisions.
• Full story in the next talk!

pp collisions at vs 200 GeV
(In case you forgot Mass J/y 3.1 GeV)
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Conclusion Recent Results from RHIC

• Clear signatures of high pT suppression (jet
  quenching) in central Au Au collisions at
  RHIC that are not present in d Au.
• Indication of final state interactions in bulk
  dense matter.
• Much more data exists than I had time to
  show.(Stay in session today and tomorrow for
  more results.)
• Many exciting puzzles remain

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More RHIC Experimental Talks to Follow

• J/y production (PHENIX)
• Nichelle Bruner
• Charged particle production (PHOBOS)
• Gerrit van Nieuwenhuizen
• Freeze-out temperatures and transverse flow
  (BRAHMS)
• Oana Ristea
• Identified Low pT spectra (PHOBOS)
• Adam Trzupek
• Identified High pT production (BRAHMS)
• Zhongbao Yin
• Charged particle pT spectra (PHOBOS)
• Rachid Nouicer
• Strangeness production at RHIC (BRAHMS)
• Jens I. Jordre

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Backup Slides
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Reminder Centrality in AuAu
Data
Paddle Multiplicity in 3 lt h lt 4.5
HIJING GEANT Glauber calculation Model of
paddle trigger
Paddle signal
DataMC
Npart
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Charged Particle Production at Midrapidity
Energy and Centrality Dependence
PRC 65, 061901(R) (2002) 19.6 GeV in Preparation
AuAu
200 GeV
Midrapidity hlt1
dNch/dh
130 GeV
19.6 GeV preliminary
pp
two component fit with x 0.1
? See same fraction of about 10 collision
scaling fits all energies.
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Charged Particle Production at Midrapidity
Energy and Centrality Dependence
? Data described by model with
Data is normalized by corresponding pp value for
each energy.
200 GeV
130 GeV
AuAu
19.6 GeV preliminary
Kharzeev, Levin, McLerran (KLM)(e.g. PLB 561
(2003) 93)
? Initial state (KLM) saturation model also
describes full dN/dh shapes including new effect
seen by PHOBOS in the fragmentation region.
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PT Distribution of Charged Particles
Soft part of spectrum
Phobos Preliminary
Systematic Errors not shown
? What about high pT? Have a quick look at the
Hard part of the spectrum.
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Energy evolution of ?B
Using measured ltKgt/ltKgt,ltpgt/ltpgt and statistical
model of F. Becattini et al.,(PRC64,024901,2001)
with Tch ? 160 170 MeV
Estimated baryochemical potential at ?sNN 200
GeV ?B 26 ? 2 MeV

• LHC 1 MeV?

Fit P.Braun-Munzinger NP. A697,902,2002
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Theory Calculations
Energy loss applied M. Gyulassy, I. Vitev, X.N
Wang and B.W. Zhang nucl-th/0302007
dE/dxo is the only free parameter. It is
determined by fitting to STAR central RAA(pt)
Cronin Effect X.N. Wang, Phys. Rev C61, 064910
(2000). Attributed to initial state multiple
scattering. Implemented by Q2(pt) dependent
Gaussian kt broadening