Transcript Recent Results from STAR

Recent Results from
STAR
Carl A. Gagliardi
Texas A&M University
for the STAR Collaboration
Carl Gagliardi – Recent Results from STAR – NN2006
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Time line of a relativistic heavy ion collision
1
2
3
4
Two thin disks of Initial collision –Dense partonic Hadron gas phase
quarks and
gluonsproducts
of hardto medium
Outline:
Introduction
RHIC and STAR
approach scattering,
including
QGP?1, then 4
Phase 2,
thenThe
3, then
heavy flavors, created
Carl Gagliardi – Recent Results from STAR – NN2006
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RHIC: the Relativistic Heavy Ion Collider
Carl Gagliardi – Recent Results from STAR – NN2006
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The STAR Detector
E-M
Calorimeter
Projection
Chamber
Time
of
Flight
Carl Gagliardi – Recent Results from STAR – NN2006
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Geometry of heavy ion collisions
Number of participants:
Number of incoming nucleons in the overlap region
Number of binary collisions:
Number of equivalent inelastic nucleon-nucleon collisions
Both depend on impact parameter or “centrality”
Carl Gagliardi – Recent Results from STAR – NN2006
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Kinematics for
colliders
Pseudo-rapidity:

p||
pT
   lntan 2
Transverse momentum (pT) and pseudorapidity ()
provide a convenient description
Mid-rapidity:
η = 4:
η = 0, perpendicular to the incident beams
Scattering at θ = 2.1o in the CM (or lab) frame
Terminology that has become common at RHIC:
“Low” pT:
pT <~ 2 GeV/c
“Intermediate” pT:
2 <~ pT <~ 6 GeV/c
“High” pT:
6 GeV/c <~ pT
Carl Gagliardi – Recent Results from STAR – NN2006
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Hard scattering at RHIC and NLO pQCD
PRL 91, 241803
hep-ex/0608030
PHENIX: π0
STAR: Jets
At 200 GeV, pQCD does a very good
job describing high-pT yields in p+p
Carl Gagliardi – Recent Results from STAR – NN2006
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Hard partonic collisions and energy loss
in dense matter
Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy,
Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,…
Multiple soft interactions:
CR S 2
E 
qˆL
4
kT2
medium
qˆ 
  S  glue
Gluon bremsstrahlung

Opacity
expansion:
 2 E jet 
E  C ACa  dglue  , r  Log 2 
 L
3
S
Strong dependence of energy loss on gluon density glue:
measure ΔE  color charge density at early hot, dense phase
Carl Gagliardi – Recent Results from STAR – NN2006
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From the first three years of RHIC
STAR
Phys. Rev. Lett. 91, 072304 (2003).
Pedestal&flow subtracted
• In central Au+Au collisions:
– Strong suppression of inclusive hadron production
– Disappearance of the away-side jet
• d+Au looks like p+p
• Jet quenching in the dense medium
Carl Gagliardi – Recent Results from STAR – NN2006
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Limitations of RAA
?
RAA at 10 GeV/c
K.J. Eskola et al., NP A747, 511
Central RAA Data
qˆ
(proportional to gluon density)
• Leading hadrons preferentially arise from the surface
• Limited sensitivity to the region of highest energy density
• Need more penetrating probes
Carl Gagliardi – Recent Results from STAR – NN2006
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See talk by A. Suaide
Heavy flavor yields
light
(M.Djordjevic PRL 94 (2004))
STAR preliminary
• Charm mid-rapidity total cross section (dominated by low pT) consistent
with binary scaling
• At high-pT, expect less suppression for c and b than for light hadrons
• Can study this using “non-photonic electrons” from heavy flavor decays
Carl Gagliardi – Recent Results from STAR – NN2006
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Suppression of non-photonic electrons
Gluons and
light quarks
Heavy quarks
See talk by
A. Suaide
STAR
STAR
nucl-ex/
0607012
• High-pT electron suppression is comparable to inclusive charged
hadron suppression
• Data agree with c  e predictions that assume a very high density
• But b  e should be there, too!
• Do
we Results
reallyfrom
understand
partonic energy loss?
Carl Gagliardi
– Recent
STAR – NN2006
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Di-jets at much higher pT
STAR
nucl-ex/0604018
8 < pT(trig) < 15 GeV/c
No background subtraction
Clear emergence of the away-side jet
-- Comparable yields on near side in all systems
-- Strong suppression of away-side in central Au+Au
Carl Gagliardi – Recent Results from STAR – NN2006
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Medium modification of di-jets
STAR
nucl-ex/0604018
8 < pT(trig) < 15 GeV/c
Scaling
factors
relative to
d+Au
0.57 ± 0.06
0.25 ± 0.06
Direct measurement of the medium modification (and lack thereof) of
the away-side jet
– Near side appears unmodified
– Away-side yield decreased, but spectrum shape unchanged
– – Can
partonic
energy
models describe these results simultaneously?
Carl Gagliardi
Recent
Results from
STARloss
– NN2006
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Di-jets and the medium
T. Renk, Hard Probes ‘06
Trigger
direction
Trigger
direction
High-pT di-jets provide better sensitivity to the interior
of the reaction zone
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How does the medium respond?
Au+Au 0-10%
preliminary
3<pt,trigger<4
GeV
pt,assoc.>2 GeV
Di-hadron correlations
in two dimensions:
Jet peak sits on top of
a long-ranged “ridge”
in Δη on the near side
• Jet peak:
– Yield independent of centrality
• Ridge:
– Yield grows dramatically with centrality
– Spectrum similar to that of the bulk, unlike the jet peak
• Qualitatively consistent with models including longitudinal or radial
flow, also with coalescence model; need detailed calculations!
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How does the medium respond?
2.5 < pTtrig < 4.0 GeV/c
1.0 < pTassoc < 2.5 GeV/c
Measure intermediate-pT di-hadron distributions
– Yield away from Δφ = π grows significantly
– Mach cone? Gluon Cherenkov radiation? Deflected jets?
Carl Gagliardi – Recent Results from STAR – NN2006
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Explore the dynamics with 3-particle correlations
p+p collisions
3.0 < pTtrig < 4.0 GeV/c
1.0 < pTassoc < 2.0 GeV/c
12% most central
Au+Au collisions
STAR preliminary
• Evidence for enhancements on the diagonals at ~ π ± 1.4 radians
• Very sensitive to the procedure used to subtract the 2-particle
correlations
Carl Gagliardi – Recent Results from STAR – NN2006
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Azimuthal anisotropy: “elliptic flow”
py
  atan
py
px
px
z
y

y2  x2
y
2
 x
x
2
Initial coordinate-space anisotropy

px  p y
2
px  p y
2
2
v2 
2
Final momentum-space anisotropy
dN
 1  2v2 cos[2(  R )]  2v4 cos[4(  R )]  ...
d
Elliptic term
Carl Gagliardi – Recent Results from STAR – NN2006
Anisotropy self-quenches, so
v2 is sensitive to early times
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Elliptic flow in the hydrodynamic regime
See talk by M. Munhoz
• Expected mass splitting well reproduced up to pT ~ 1.5 GeV/c
• Elliptic flow saturates the hydrodynamic limit
• Are we producing a “perfect liquid” at RHIC?
Carl Gagliardi – Recent Results from STAR – NN2006
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Constituent quark scaling
What if quarks coalesce
to make hadrons?
solid: STAR
open: PHENIX
PRL91(03)
dN
 1  2v2 ( pT ) cos(2 )  
d
 1  2v2q ( pTq ) cos(2 )  
nq
 pT 
 1  2n v 
cos(2 )  
 nq 


q
q 2
v2 obeys constituent quark scaling
-- Hadronization through coalescence
-- Evidence for flowing quarks (?)
Carl Gagliardi – Recent Results from STAR – NN2006
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Anomalous baryon/meson yields at intermediate pT
STAR
nucl-ex/0606003
Related material:
talk by M. Lamont
• Large p and p to π ratio in central Au+Au at intermediate pT
• Above pT ~ 6 GeV/c, ratio is the same in d+Au and central Au+Au
• Limit of the coalescence domain?
Carl Gagliardi – Recent Results from STAR – NN2006
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Glauber vs Color Glass Condensate
Hirano et al, PLB 636, 299
CGC
Glauber
CGC: Treats the nucleus
as a saturated gluon field
• Do we have Glauber matter distribution + perfect liquid, or
Color Glass Condensate distribution + viscous matter?
• Is the gluon field in the Au nucleus saturated?
• Forward d+Au collisions provide information about the gluon
density in Au at low gluon momentum fractions
Carl Gagliardi – Recent Results from STAR – NN2006
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 dependence of RdAu
STAR
nucl-ex/0602011
RdAu
1  dAu

2 *197  pp
• Observe significant rapidity dependence.
• pQCD calculations significantly over predict RdAu.
Carl Gagliardi – Recent Results from STAR – NN2006
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Any difference between p+p and d+Au?
p+p: Di-jet
d+Au: Mono-jet?
Dilute parton
system
(deuteron)
PT is balanced
by many gluons
Dense gluon
field (Au)
Kharzeev, Levin, McLerran gives
physics picture (NPA748, 627)
Color glass condensate predicts that the back-to-back
correlation from p+p should be suppressed
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Forward + mid-rapidity correlations in
STAR
d+Au
nucl-ex/0602011
• are suppressed at
small <xF> and <pT,π>
consistent with
CGC picture
25<E<35GeV
<pT,π> ~
1.0 GeV/c
Fixed ,as
E & pT grows
<pT,π> ~
1.3 GeV/c
π0: |<η>| = 4.0
h±: |η| < 0.75; pT > 0.5 GeV/c
Carl Gagliardi – Recent Results from STAR – NN2006
• are similar in d+Au
and p+p at larger <xF>
and <pT,π>
as expected by
HIJING
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Many recent descriptions of low-x suppression in d+Au
A short (and surely incomplete) list
Saturation (color glass condensate)
Jalilian-Marian, NPA 748 (2005) 664.
● Kharzeev, Kovchegov, and Tuchin, PLB
599 (2004) 23; PRD 68 (2003) 094013.
● Armesto, Salgado, and Wiedemann,
PRL 94 (2005) 022002.
● Dumitru, Hayashigaki, and JalilianMarian, NPA 765 (2006) 464
●
Multiple scattering
Qiu and Vitev, PRL 93 (2004) 262301;
hep-ph/0410218.
●
Factorization breaking
Kopeliovich et al., PRC 72 (2005)
054606.
● Nikolaev and Schaefer, PRD 71 (2005)
014023.
Shadowing
R. Vogt, PRC 70 (2004) 064902.
● Guzey, Strikman, and Vogelsang, PLB
603 (2004) 173.
●
Parton recombination
Hwa, Yang, and Fries, PRC 71 (2005)
024902.
●
Leading fragmentation
●
PHOBOS (several)
Black disk limit
Frankfurt and Strikman, nucl-th/
0603049
●
●
Carl Gagliardi – Recent Results from STAR – NN2006
Others?
●
...
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Resonance production at RHIC
Hadronic phase
Δt

S*

S*
L
S*
measured
S*
L
lost

S*

L
L
Chemical
freeze-out

S*
L S*
Thermal
freeze-out measured
• Resonances like K*, Λ*, Σ*
have very short lifetimes
• Many decays occur within the
reaction zone
• “Rescattering” and
“regeneration” can lead to:
– Mass shifts
– Width broadening
– Modifications of the pT
spectra
• Sensitive to the lifetime of the
hadronic phase
time
Carl Gagliardi – Recent Results from STAR – NN2006
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Resonance vs. non-resonance yields
STAR
nucl-ex/0604019
• K* and Λ* are suppressed in central Au+Au; Σ* isn’t suppressed
• Evidence that both rescattering and regeneration occur during
the hadronic phase
• Lifetime of the hadronic phase > 4 fm/c
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Conclusion
• STAR has a wealth of new data!
– We are learning new information the all phases of a relativistic
heavy ion collision
– Help us answer questions we’ve been asking
– Help us ask questions we weren’t smart enough to ask before
• The answers to those questions will tell us
– What is the strongly interacting matter that we are creating at
RHIC?
– What are its properties?
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STAR
The STAR Collaboration
U.S. Labs:
Argonne, Lawrence Berkeley, and
Brookhaven National Labs
U.S. Universities:
UC Berkeley, UC Davis, UCLA,
Caltech, Carnegie Mellon, Creighton,
Indiana, Kent State, MIT, MSU,
CCNY, Ohio State, Penn State,
Purdue, Rice, Texas A&M, UT
Austin, Washington, Wayne State,
Valparaiso, Yale
Brazil:
Universidade de Sao Paolo
China:
IHEP - Beijing, IPP - Wuhan, USTC,
Tsinghua, SINAP, IMP Lanzhou
Croatia:
Zagreb University
Czech Republic:
Nuclear Physics Institute
England:
University of Birmingham
Carl Gagliardi – Recent Results from STAR – NN2006
France:
Institut de Recherches Subatomiques
Strasbourg, SUBATECH - Nantes
Germany:
Max Planck Institute – Munich
University of Frankfurt
India:
Bhubaneswar, Jammu, IIT-Mumbai,
Panjab, Rajasthan, VECC
Netherlands:
NIKHEF/Utrecht
Poland:
Warsaw University of Technology
Russia:
MEPHI – Moscow, LPP/LHE JINR –
Dubna, IHEP – Protvino
South Korea:
Pusan National University
Switzerland:
University of Bern
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Carl Gagliardi – Recent Results from STAR – NN2006
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Non-photonic electrons in p+p
STAR
nucl-ex/0607012
See talk by
A. Suaide
• Fixed-order next-to-leading log calculations underpredict
non-photonic electron yield in p+p by a factor of ~5
• Significant theoretical uncertainty regarding relative
strength of c vs. b
Carl Gagliardi – Recent Results from STAR – NN2006
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High-pT identified particles in p+p and d+Au
STAR, PLB 637, 161 (2006)
•
•
•
pQCD calculations with recent (AKK) fragmentation functions give a
reasonable description of pion and proton yields in elementary collisions
Calculations with KKP significantly underestimate proton yields at high-pT
Protons arise primarily from gluon fragmentation; pions receive a large
quark contribution at high-pT
Carl Gagliardi – Recent Results from STAR – NN2006
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Identified particle nuclear modification factors
STAR
nucl-ex/0606003
Related material:
talk by M. Lamont
• Rcp for protons and pions converge at pT >~ 6 GeV/c
• Dominance of fragmentation over coalescence at high pT
Carl Gagliardi – Recent Results from STAR – NN2006
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Jet-like correlations in the soft sector
STAR
J Phys G 32, L37 (2006)
•
•
•
•
Jet-like di-hadron correlations survive in Au+Au at low pT
Correlation narrows in φ and broadens in η
Coupling to a longitudinally flowing medium?
Need detailed model calculations!
Carl Gagliardi – Recent Results from STAR – NN2006
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d+Au  0+X at 200 GeV
STAR
nucl-ex/0602011
pT dependence of d+Au π0 cross section at <η> = 4.0 is best
described by a LO CGC calculation.
(Dumitru, Hayashigaki, and Jalilian-Marian, NPA 765, 464)
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