STAR
Carl A. Gagliardi
Texas A&M University for the Collaboration
Carl Gagliardi – Recent Results from STAR – NN2006
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1 2 3 4
Two thin disks of Initial collision – quarks and gluons products of hard approach
Phase 2, then 3, then 1, then 4 heavy flavors, created
Hadron gas phase
Carl Gagliardi – Recent Results from STAR – NN2006
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RHIC
Carl Gagliardi – Recent Results from STAR – NN2006
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STAR
E-M
Calorimeter
Projection
Chamber
Time of
Flight
Carl Gagliardi – Recent Results from STAR – NN2006
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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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p
T

Pseudo-rapidity: p
||
   ln
 tan

Transverse momentum (p
T
) and pseudorapidity (

) provide a convenient description
Mid-rapidity: η = 0, perpendicular to the incident beams
η = 4: Scattering at θ = 2.1
o in the CM (or lab) frame
Terminology that has become common at RHIC:
“Low” p
T
:
“Intermediate” p
T
:
“High” p
T
: p
T
<~ 2 GeV/c
2 <~ p
T
<~ 6 GeV/c
6 GeV/c <~ p
T
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: π 0 STAR: Jets
At 200 GeV, pQCD does a very good job describing high-p
T 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,…
Gluon bremsstrahlung
Opacity expansion:
Multiple soft interactions:

E

C
R

S
4 q
ˆ
L
2 q
ˆ  k
T
2
 medium
 
S
 glue

E
 
C
A
C a

S
3
 d
 glue
 
, r
   
Log


2 E jet

2
L


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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Phys. Rev. Lett. 91, 072304 (2003).
STAR
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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AA
K.J. Eskola et al., NP A747, 511
?
Central R
AA
Data q
ˆ
(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
light
(M.Djordjevic
PRL 94 (2004))
STAR preliminary
• Charm mid-rapidity total cross section (dominated by low p
T with binary scaling
) consistent
• At high-p
T
, 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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Gluons and light quarks
Heavy quarks
See talk by
A. Suaide
STAR
STAR nucl-ex/
0607012
• High-p
T 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 really understand partonic energy loss?
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T
STAR nucl-ex/0604018
8 < p
T
(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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STAR nucl-ex/0604018
8 < p
T
(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
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Trigger direction
T. Renk, Hard Probes ‘06
Trigger direction
High-p
T di-jets provide better sensitivity to the interior of the reaction zone
Carl Gagliardi – Recent Results from STAR – NN2006
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Au+Au 0-10% preliminary
3<p t,trigger
<4
GeV p t,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!
Carl Gagliardi – Recent Results from STAR – NN2006
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How does the medium respond?
2.5 < p
T trig < 4.0 GeV/c
1.0 < p
T assoc < 2.5 GeV/c
Measure intermediate-p
T 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 < p
T trig < 4.0 GeV/c
1.0 < p
T assoc < 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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p y
  atan p y p x p x
  y 2 y 2 y
 x 2 x
 x 2 z v
2
 p x
2  p x
2  p y
2 p y
2
Initial coordinate-space anisotropy Final momentum-space anisotropy
 dN d


1

2 v
2 cos[ 2 (
  
R
)]

2 v
4 cos[ 4 (
  
R
)]

...
Elliptic term
Anisotropy self-quenches, so v
2 is sensitive to early times
Carl Gagliardi – Recent Results from STAR – NN2006
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See talk by M. Munhoz
• Expected mass splitting well reproduced up to p
T
• Elliptic flow saturates the hydrodynamic limit
~ 1.5 GeV/c
• Are we producing a “perfect liquid” at RHIC?
Carl Gagliardi – Recent Results from STAR – NN2006
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solid: STAR open: PHENIX
PRL91(03)
What if quarks coalesce to make hadrons?
dN d

 v p
T
  

1 2 v q
2
( p q
T

  n v q q
2

 p n
T q


  n q
 
Carl Gagliardi – Recent Results from STAR – NN2006 v
2 obeys constituent quark scaling
-- Hadronization through coalescence
-- Evidence for flowing quarks (?)
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Anomalous baryon/meson yields at intermediate p
T
STAR nucl-ex/0606003
Related material: talk by M. Lamont
• Large p and p to π ratio in central Au+Au at intermediate p
T
• Above p
T
~ 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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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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STAR nucl-ex/0602011
R dAu

1
2 * 197

 dAu pp
 dependence of R dAu
• Observe significant rapidity dependence.
• pQCD calculations significantly over predict R dAu
.
Carl Gagliardi – Recent Results from STAR – NN2006
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p+p: Di-jet d+Au: Mono-jet?
Dilute parton system
(deuteron)
P
T 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
Carl Gagliardi – Recent Results from STAR – NN2006
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STAR
Forward + mid-rapidity correlations in d+Au nucl-ex/0602011
• are suppressed at small <x
F
> and <p
T, π
> consistent with
CGC picture
25<E

<35GeV
<p
T, π
> ~
1.0 GeV/c
Fixed
, as
E & p
T grows
π 0 : |< η >| = 4.0
h
±
: | η | < 0.75; p
T
> 0.5 GeV/c
Carl Gagliardi – Recent Results from STAR – NN2006
<p
T, π
> ~
1.3 GeV/c
• are similar in d+Au and p+p at larger <x
F
> and <p
T, π
> as expected by
HIJING
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Many recent descriptions of lowx 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 Jalilian-
Marian, 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.
Carl Gagliardi – Recent Results from STAR – NN2006
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
Others?
●
...
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S *
Hadronic phase
Δ t
Chemical freeze-out
L

S *
S *

L

S *

L
L
S * measured
S * lost

Thermal freeze-out
L
S * measured time
• 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 p
T spectra
• Sensitive to the lifetime of the hadronic phase
Carl Gagliardi – Recent Results from STAR – NN2006
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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
Carl Gagliardi – Recent Results from STAR – NN2006
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• 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?
Carl Gagliardi – Recent Results from STAR – NN2006
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STAR
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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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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T
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-p
T
• Protons arise primarily from gluon fragmentation; pions receive a large quark contribution at high-p
T
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
• R cp for protons and pions converge at p
T
>~ 6 GeV/c
• Dominance of fragmentation over coalescence at high p
T
Carl Gagliardi – Recent Results from STAR – NN2006
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STAR
J Phys G 32, L37 (2006)
• Jet-like di-hadron correlations survive in Au+Au at low p
T
• 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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STAR nucl-ex/0602011 d+Au
  0
+X at 200 GeV p
T dependence of d+Au π 0 cross section at < described by a LO CGC calculation .
η > = 4.0 is best
(Dumitru, Hayashigaki, and Jalilian-Marian, NPA 765, 464)
Carl Gagliardi – Recent Results from STAR – NN2006
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