Intermediate and highpT physics from STAR

1
Intermediate and high-pT physics from STAR
Jana Bielcikova

Nuclear Physics
Institute ASCR
and Center
for physics of ultra-relativistic heavy-ion
collisions
Prague, Czech Republic


for the STAR Collaboration
2
What did we find at RHIC so far?

• central AuAu collisions produce
• dense and rapidly thermalizing matter
• it behaves almost like
• a perfect liquid
• (elliptic flow well described
• by ideal hydrodynamics)
• the relevant degrees of freedom seem to be
  partonic (constituent quark scaling)
• it is opaque to jets
• It is not the asymptotically free plasma of
  quarks and gluons.
• strongly coupled plasma (sQGP) ?

STAR Collaboration, NPA 757,102 (2005)
See e.g. STAR White Paper Nucl.Phys. A757, 102
(2005)
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• Outline
• STAR experiment at RHIC
• Particle production at intermediate and high-pT
• - nuclear modification factors,
  baryon/meson ratios
• recombination vs pQCD, energy
  loss
• - two- and three-particle correlations
• Mach cone, ridge
• Summary

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Solenoidal Tracker At RHIC

• Detectors
• Time Projection Chamber
• (TPC) particle tracking, PID
• Electromagnetic Calorimeter
• (EMCal) trigger, g, p0,e PID
• Time of Flight (TOF) PID
• Silicon Vertex Tracker (SVT)
• Forward Time Projection
• Chamber (FTPC)2.7lthlt3.9
• PID particle identification
• h pseudorapidity

Magnetic field solenoidal, B0.5 T Acceptance
full azimuth, hlt1
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AuAu collision as seen by STAR

TPC EMC
1500 charged hadrons and leptons in
central AuAu collisions
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Particle identification
Identification of strange particles from
V0-decay vertices ? ? p p- BR64
K0S ? p p- BR69
TPC

• cuts on dE/dx of daughters
• topological cuts

L
K0S
TOF
mass (GeV/c2)
mass (GeV/c2)
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Probing QCD matter with high-pT particles and jets
pp
AuAu
What happens to high-pT particles/jets which
pass through the medium? Are they - similar to
pp ? - modified by the medium?
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High-pT particle production
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Radiative energy loss in QCD

• found to be dominant for light quarks
• independent of parton energy but
• depends on the path length L in the medium
• two example approaches
• medium properties can be characterized by a
  single constant

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How well does pQCD describe pp?
STAR Phys Lett B, 637 (2006) 161

• Do we understand our pp baseline?

p p ? ?0 X
NLO pQCD calculations by W. Vogelsang
Depends on particle species and choice of
fragmentation function.
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Strange particle production in pp
STAR, PRC 75 (2007)

• STAR measurement of strange particles in pp
  constrained AKK FF
• AKK fragmentation functions agree well with both
  mesons and baryons at mid-rapidity.
• KKP (Kniehl-Kramer-Potter) NPB 582 (200)
• AKK (Albino-Kniehl-Kramer) NPB 734, 50
  (2006)
• 
  
  DSV (DeFlorian-Stratmann-Vogelsang) PRD57,
  58111 (1998)

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Nuclear modificiation factor in AuAu

• Direct photons
• - not suppressed
• do not interact strongly
• - binary scaling works
• Light hadrons
• - strongly suppressed
• (factor 5x) in central
• AuAu collisions

T. Isobe (PHENIX), QM06
Large energy loss of light partons in the formed
nuclear matter at RHIC
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What do we learn from RAA ?
Use RAA to extract medium density e transport
coefficient

• large values of q 5-15 GeV2/fm compatible
  with the data
• suppression only supplies a lower bound on
  medium density ?

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Limited sensitivity of RAA
thin plasma (GLV)
thick plasma (BDMPS)
Wicks,Horowitz,Djordjevic,Gyulassy NPA 784, 426
(2007)
Renk, Eskola, PRC 75, 054910 (2007)
Energy loss distributions very different
for BDMPS and GLV formalisms BUT!
RAA is similar
Reason leading hadrons come preferentially
from the surface ? RAA has
limited sensitivity to the region of the
highest energy density More
differential probes needed JETS
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Do baryons and mesons behave similarly?
STAR, PRL 97, 152301 (2006)

• Intermediate-pT (pT 2-5 GeV/c) baryon/meson
  splitting
  RCP(meson)ltRCP(baryon)
• High-pT (pT gt 5 GeV/c)
• RCP(?)RCP(p)
• RCP(K)RCP(?)
• Does it mean similar energy loss of quarks and
  gluons ?

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Gluon vs quark energy loss
Gluon jet contribution factor increases from ?,
K, p towards?? e.g. pT 8 GeV/c 50 for
p 90 for p
If and At high pT for same beam energy,
system and centrality
RCP(?) gt RCP(p) RCP(K) gt
RCP(?)



AKK particle anti-particle
AKK (Albino-Kniehl-Kramer) NPB 734, 50 (2006)
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Baryon/meson ratios at RHIC
STAR, PRL 97 (152301) 2006
AuAu p/? 1 ?/K0S 1.8 pp p/?
0.3 ?/K0S 0.6 ee- p/? 0.1-0.2

• large enhancement of B/M ratio in AuAu relative
  to pp collisions
• - reaches maximum at pT3 GeV/c
• jet fragmentation is not a dominant source of
  particle production

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Parton recombination at intermediate pT

• in vacuo fragmentation of a high momentum quark
  to produce hadrons competes with in medium
  recombination of lower momentum quarks to produce
  hadrons
• 6 GeV/c particle via
• fragmentation from high pT
• meson
• - 2 quarks at pT3 GeV/c
• baryon
• - 3 quarks at pT2 GeV/c

baryon
meson
Recombination produces more baryons than mesons
at intermediate pT
R.J. Fries et al., PRL 90 (202303) 2003 V. Greco
et al., PRL 90 (202302) 2003
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Towards more differential probes
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Jet-like correlations

• Full jet reconstruction in AA
• collisions at RHIC difficult
• due to underlying background
• use azimuthal correlations
• of high-pT particles

Correlated yield is related to ratio of
di-hadron to single hadron fragmentation
functions
near-side
away-side
RAA
zTpTassoc/pTtrig
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Jet-like correlations at RHIC
STAR, Phys. Rev. Lett. 97 (2006) 162301
STAR, Phys Rev Lett 91, 072304

• central AuAu collisions
  _at_ 200 GeV
• disappearance of away-side correlations observed
  at intermediate pT
• dAu and pp similar -gt jet suppression is a
  final state effect
• Is there a punch through? YES

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Fragmentation near vs away side
STAR, Phys. Rev. Lett. 97 (2006) 162301
8 lt pT(trig) lt 15 GeV/c
Away-side yield strongly suppressed to level of
RAA No dependence on zT in measured range
Near side no suppression

• Away side
• - strongly suppressed
• to level of RAA
• - no dependence on zT

Widths unchanged with centrality seeing those
partons that fragment in vacuum?
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Away-side di-hadron suppression at high pT
Zhang,Owens,Wang,Wang, PRL 98 212301 (2007) NLO
pQCD KKP FF expanding medium

• di-hadrons have a smaller surface bias
• ? a better differential probe
• ?2-minimum narrower for di-hadrons
• ?stronger constraint on density
• extracted medium properties
• e0 1.68 GeV/fm
• q 2.80.3 GeV2/fm

c2 (IAA)
c2(RAA)
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System size dependence of the away-side
suppression

• IAA ratio calculated relative to d-Au
• model comparisons
• modified fragmentation
• - Npart scaling, but misses shape
• Parton Quenching Model (PQM)
• - wrong relationship between
• CuCu and AuAu
• (wrong q evolution or geometry?)

Data O. Catu (STAR), DNP 2007
suppression scales with Npart
H.Zhang, J.F. Owens, E. Wang, X.N. Wang,
based on PRL 98 (2007), private communication
4lt pT trig lt 6 GeV
STAR preliminary
C. Loizides, Eur. Phys. J. C 49, 339-345 (2007)

agreement with models better at
higher pTtrig
6lt pT trig lt 10 GeV
STAR preliminary
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Away-side di-hadron fragmentation functions
O. Catu (STAR), DNP 2007
zTpTassoc /pTtrig
Theory curves nucl-th/0701045 - H.Zhang, J.F.
Owens, E. Wang, X.N. Wang
Model X.N.Wang private communication see also
H.Zhang, J.F. Owens, E. Wang, X.N. Wang, PRL 98
(2007)

• fragmentation functions more suppressed for
  higher Npart
• theory curves using parameters from the fit to
  previous
• AuAu data at higher-pT match the CuCu data

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Where did the energy go?
STAR, Phys Rev Lett 91, 072304
STAR, PRL 95 (2005) 152301
lowering associated pT - resurrects
correlated yield at away side - near and
away-side yields are enhanced with respect to
dAu - shape of the away-side peak is not
Gaussian
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Azimuhal correlations pT dependence
M. Horner (STAR), J.Phys.G34, S995,2007

• increased statistics (year4)
• ? full exploration of trigger and
  associated pT range
• Medium response
• at lower pT,assoc
• away side enhanced
• and shape modified
• broad peak with
• angular substructure

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Away-side peak Mach cone?
2.5 lt pTtriglt 4 GeV/c and 1lt pTassoc lt 2.5 GeV/c
Stoecker, Casalderry-Solana et al, Muller et
al. Ruppert et al.,
M. Horner (STAR), J.Phys.G34, S995,2007
vs0.33 c
3-particle correlation studies needed!
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Conical flow vs deflected jets
J. Ulery (STAR), arXiv0704.0224
3 lt pT,trig lt 4 GeV/c 1 lt pT,assoc lt 2 GeV/c

• STAR uses two methods
• 1. Cumulant
• unambiguous evidence for 3-particle correlations,
  although not definitive about conical emission.
• 2. Jet-flow background (shown)
• Model dependent analysis.
• Evidence for conical emission.

Note Large and complicated backgrounds.
C. Pruneau (STAR), J.Phys.G34,S667,2007 J. Ulery
(STAR), arXiv0704.0224 nucl-ex
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A closer look at the near-side peak
Additional near-side correlation in
pseudo-rapidity (??) observed

The near-side jet interacts with the
medium!
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Centrality dependence of near-side yield (I)
J. Putschke (STAR), J.Phys.G34S679 (2007)

• jet yield independent of Npart and consistent
  with dAu
• ridge yield increases linearly with Npart

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Centrality dependence of near-side yield (II)
-gt ridge yield increases with
centrality ridge for K0S
trigger lt ridge for ? trigger

• steep increase of near-side yield with
  centrality in AuAu
• ratio of yields in central AuAu/dAu 4-5

-gt jet yield
is independent of centrality and agrees with dAu

J.B. (STAR), QM2006 J.Phys.G34S929 (2007)
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Jet and ridge pT dependence
pT assoc gt 2 GeV/c
Ridge solid symbols Jet open symbols
J. Putschke (STAR), J.Phys.G34S679 (2007)
J. Putschke (STAR), J.Phys.G34S679 (2007)
Jet T(jet) gt T(bulk) T(jet)
increases with pTtrig Ridge
T(ridge) T(bulk) T(ridge) independent
of pTtrig ridge persists up to pTtrig 10
GeV/c
h-h correlations pTassociatedgt2GeV/c
jet slope ridge slope inclusive slope
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Particle composition in jet and ridge
J.B. (STAR), arXiv0707.3100 nucl-ex
A hint? Ridge B/M ratio closer to bulk
Jet B/M ratio pp
More data
needed !
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Is there ridge at forward rapidity?
L. Molnar (STAR), J.Phys.G34, S593 (2007)
pTassoc 0.2-2.0 GeV/c no near-side peak within
systematic errors pTassoc gt 1 GeV/c
data suggest a non-zero correlation at near side
(?)
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What is the origin of the ridge? (I)

• 1) Medium heating and parton recombination
• Chiu Hwa Phys. Rev.
  C72034903,2005
• hard parton enhances thermal parton distribution
• (?T15 MeV)
• ? recombination of thermal partons forms
• a pedestal (ridge)
• enhanced baryon/meson ratio
• 2) Parton radiation and its coupling
• to the longitudinal flow
• gluon bremsstrahlung of hard-scattered parton
• radiated gluon contributes to broadening

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What is the origin of the ridge? (II)

• 3) Longitudinal broadening of quenched
• jets in turbulent color fields
• A. Majumder, B. Mueller, S.A.Bass,
  hep-ph/0611135
• plasma instabilities in expanding medium
• ? non-thermal color fields
• ? broadening of jet cone
• ? wide ridge in rapidity at low
  pTassoc

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What is the origin of the ridge? (III)

• 4) Correlations between jet and radial flow
• S. Voloshin, nucl-th/0312065, Nucl.Phys.
  A749, 287 (2005)
• E. Shuryak, arXiv 0706.3531 nucl-th
• radial expansion jet quenching ? correlation
• ridge is independent of jet
• particle spectra in ridge
• points of origin are biased towards surface
  
• ? a bit stiffer slope than that of bulk
• 5) Momentum kick
• C.-Y. Wong , arXiv 0707.2385,
  arXiv0712.3282
• medium partons acquire kick from propagating
  jet
• T470 MeV, q1 (mom. kick) and sy (rapidity
  distribution)
• narrow peak in Df depends mainly on momentum
  kick
• ridge in Dh depends on initial parton y
  distribution

More quantitative theoretical predictions are
needed!
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Summary

• 
  Modification of jets
• inclusive measurements large suppression of
  yields,
• but RAA has only limited sensitivity to
  the medium density ?
• di-hadron measurements
• away-side associated jet-yield
  suppressed to the level of RAA
• but shape of fragmentation function unmodified
  (pT, assoc gt 3 GeV/c)
• 
  Medium response
• away-side broadening, angular substructure
• possible evidence of conical
  emission
• near-side ridge bulk-like properties
• coupling of jet to the medium
• Stay tuned for the upcoming Quark Matter
  Conference in India which is just around the
  corner
  THANK YOU!

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BACKUP
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Extracting near-side jet and ridge yields
J jet, R ridge
pTtrig3-4 GeV/c, pTassocgt2 GeV/c

J. Putschke (STAR),QM2006
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Testing recombination with W and f
The production of f and O is almost exclusively
from thermal s-quarks even out to pT 6-8
GeV/c (shower jet contributions are strongly
suppressed)
S shower (jet) T thermal
Prediction 1. O/f ratio should rise linearly
with pT 2. There should be no O or f di-hadron
correlations at near side!
R. Hwa, C.B. Yang , nucl-th/0602024
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Test 2 correlations with multi-strange particles
B. Abelev (PhD 2007, Yale), J.B.
(STAR) QM2006
There is a near-side peak for L, X and
W-triggered correlations and its magnitude is
independent of strangeness content ! This is in
disagreement with the recombination picture.
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Baryon/meson enhancement model comparisons
SOFTQUENCH Gyullassy, Levai, Vitev,
PRL 85 (2000),
Nucl.Phys. A 715, 779 (2003)
TEXAS Greco, Ko, Levai, PRL 90 (2003), DUKE
Fries, Mueller, Nonaka, Bass, PRC 68
(2003) OREGON Hwa, Yang, PRC 67, 034902 (2003)
Both, softquench and recombination type
of models, predict a peak in ?/K ratio,
however they cant reproduce the peak
location in pT, its magnitude and shape in
detail.
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Elliptic flow constituent quark scaling
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Di-hadron correlations near-side peak
3 GeV/c lt pT trigger lt 4 GeV/c, pT,assoc. gt 2
GeV/c
Near-side jet peak Near-side ridge Modified
away-side ( v2)
The near-side jet interacts with the
medium!
What is the ridge? 1) Medium heating and parton
recombination Chiu Hwa PRC 72, (034903)
2005 2) Radial flow high-pT trigger particle
Voloshin, nucl-th/0312065 NPA 749, 287 (2005)
3) Parton radiation and its coupling to the
longitudinal flow Armesto et al, PRL 93
(2004)
J. Putschke (STAR), HP2006, QM2006
4) Momentum broadening in an anisotropic QGP
Romatschke, PRC 75, 014901 (2007) 5)
Longitudinal broadening of quenched jets in
turbulent color fields Majumder, Mueller,
Bass, hep-ph/0611135
47
System size dependence of ridge yield
relative ridge yield ridge yield / jet(??)
J. Putschke (STAR), QM2006
pTassoc. gt 2 GeV/c
STAR preliminary
AuAu _at_ 200 GeV CuCu _at_ 200 GeV
AuAu _at_ 200 GeV (30-40 ) CuCu _at_ 200 GeV (0-10
)
relative ridge yield
relative ridge yield
3 GeV/c ltpTtriggerlt4 GeV/c
STAR preliminary
Relative ridge yield comparable in AuAu and
CuCu at same Npart
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Correlations at near-side
v2 away-side peak
Near-side yield ?? (JR) ?? (J) ?? (R)
Jet yield ?? (J) ?? (?? lt 0.7) -
?? (?? gt 0.7) ?? (J)
Ridge yield ?? (R) ?? (JR) - ??(J)

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Energy dependence anti-particle/particle ratios
STAR, nucl-ex/0703040
STAR, PRL 97, 152301 (2006)
STAR, nucl-ex/0703040
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Relativistic Heavy Ion Collider
1 km
PHOBOS
BRAHMS
RHIC
PHENIX
STAR
v 0.99995?c
BOOSTER
AGS
TANDEMS

• 3.8 km circumference
• 2 concentric rings of 1740 superconducting
  magnets
• counter-rotating beams of ions from p to Au
• vsNN 20, 62, 130, 200 GeV

Long Island, NY
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Energy content in the ridge
STAR, Phys. Rev. Lett. 95 (2005) 15230, J.
Putschke (STAR),J.Phys.G34S679 (2007)
4 lt pt,trigger lt 6 GeV/c 6 lt pt,trigger lt 10
GeV/c
0.15 lt pt,assoc lt 4 GeV/c

• near-side modification in published results also
  due to ridge
• energy content deposited in the ridge is few GeV