Probing Dense Partonic Matter at RHIC

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Probing Dense Partonic Matter at RHIC
News from PHENIX
Barbara Jacak for the PHENIX
Collaboration Feb. 8, 2004
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Outline

• Characterizing plasmas with PHENIX
• Initial state
• pQCD via direct photons
• Shadowing via RdA in dAu
• Initial state multiple scattering in dAu
• Thermalization
• Elliptic flow dependence on particle type, vs
• F production
• Charm flow
• Probes of the partonic state
• Heavy quark energy loss
• Away-side jet modification
• What baryons tell about coupling to the medium

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Properties of plasmas

• Plasma physicists always want to know (and so do
  we)
• pressure, viscosity, equation of state,
• thermalization time extent
• determine from collective behavior at RHIC
• Other useful plasma properties
• radiation rate, collision frequency,
  conductivity, opacity, Debye screening length
• what is interaction s of q,g in the medum?
• need short wavelength strongly interacting
  probe
• transmission probability
• jet quenching via RAA
• high momentum q,g are our external probes!

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PHENIX
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Direct photons (pp)
see talk of S. Bathe
LO
NLO Bremsstrahlung
pQCD works!
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Direct photons in AuAu

• pQCD works too (with nuclear Sa/A(xa,r) , TA(r)
  observed p0 s)
• ? can reliably calculate rate distribution of
  short wavelength probes of hot, dense partonic
  matter!

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kT smearing?

• g data allow kT smearing
• But, certainty awaits higher statistics
  (currently being analyzed)

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Charm production also calculable
nucl-ex/0409028
total yield scales with Ncoll. I will return
to charm again there is a long-standing
problem with sc
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Charm via single e in pp
PHENIX preliminary
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Single e in vsNN 62.4 GeV AuAu
Compatible with ltNcollgt scaling
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Nuclear initial state effects

• shadowing, saturation, multiple initial state
  scattering
• PHENIX has a wide range of dAu data
• tools
• shadowing via heavy quark or high pT hadron
  production
• PHENIX can probe saturation (super-shadowing)
• via rapidity dependence of hadron production
• Initial state multiple scattering via dependence
  of hadrons upon number of collisions per
  participant

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Nuclear medium modifies initial state

• Probe cold nuclear matter by varying number of
  collisions.
• Shadowing initial semi-hard scatterings
• (Accardi, Gyulassy) reproduce the data

PRELIMINARY
Very little room for additional dynamical
shadowing at mid-y
Phys. Lett. B586, 244 (2004)
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Cronin effect for protons greater than for p

• would not expect this from initial state
• partonic multiple scattering!

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Need something else too

• Recombination?!

PROTON PRODUCTION IN DAU COLLISIONS
AND THE CRONIN
EFFECT HWA YANGPhys.Rev.C70037901,2004
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Muon arms probe forward rapidity
see talk of Anuj Purwar
MUON ARMS CAN DETECT stopped muons from hadron
decays hadrons which punch thru absorber and
interact in m arm
study central vs. peripheral in dAu
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dAu central/peripheral
PTH Punch Through HadronsHDM Hadronic Decay
Muon
1.5 gt pT (GeV/c) gt 4.0
PHENIX nucl-ex/0411054
x0.2-0.3
d
Au
Au
x0.2x10-3
Suppression at forward ? and enhancement in the
back ?.
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Compare with BRAHMS
nucl-ex/0411054
Overall consistent.
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Color glass condensate?
Kharzeev, hep-ph/0405045
Hadron Punch Through
Centrality, pT dependence correct
Slightly better agreement with BRAHMS
data normal shadowing cannot explain (R. Vogt
hep-ph/0405060) could be sign of CGC
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But, recombination lurks

• shower medium recombination ? reductes soft
  parton density on deuteron side
• Can explain fward-bward asymmetry AND RCP
  (protons) gt RCP (mesons) at midrapidity.

Hwa, Yang and Fries nucl-th/0410111
BRAHMS data
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f does it fit with the non-strange mesons?
see talks of D. Pal and D. Mukhopadhyay
f ? KK- Au Au _at_ vSNN 200 GeV
nucl-ex/0410102

• AuAu width centroid as in PDG

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f spectra radial flow
nucl-ex/0410102

• dAu f yields slopes KK and ee consistent
• AuAu f slopes nearly independent of Npart
• but this is at high pT
• consistent with blast wave fit to p, K, p
• Tfo 109 2.6 MeV, bT,max 0.77 0.004

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v2 and scaling with nquark
62.4 GeV AuAu preliminary 200 GeV AuAu,
charged p,K,p PRL91, 182301 (2003)
p0 work in progress
stat. error only sys. error lt20 (62GeV)
15 (200GeV)
v2 /nquark
62.4 GeV AuAu scaling, v2/quark similar to 200
GeV
pT /nquark GeV/c
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Collision energy dependence
nucl-ex/0411040

• smooth rise of v2 from AGS to SPS to RHIC
  energies.
• v2 saturates evidence for soft EOS? how soft?

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Are the v2 trends hydrodynamic?

• use Buda-Lund model (nucl-th/0402036)
• particle emission from ellipsoidal expanding
  source
• v2 in terms of Bessel functions from Boltzmann
  distrib.
• converting to transverse rapidity
• so v2 should have the form

we then define a fine structure variable
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The data transform
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Caveat v2 spectra vs. hydrodynamic models
nucl-ex/0410003
Hydro models Teaney (w/ w/o RQMD) Hirano (3d)
Kolb Huovinen (w/ w/o QGP)
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How about heavy quarks? do they flow?
nucl-ex/0502009

• PHENIX measures v2 of non-photonic e
• electron ID in AuAu via RICH EMCAL
• measure and subtract photonic sources using
  converter

YES v2 ? 0 at 90 confidence level data
consistent with heavy q thermalization also
predicted by Teaney but large errors run4
will tell
Greco,Ko,Rapp. PLB595, 202 (2004)
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Short wavelength probes of partonic matter
coupling to the medium probes medium properties

• HOW is jet fragmentation modified by the medium?
• do heavy quarks lose energy as the light quarks
  do?
• Kharzeev Dokshitzer PLB519, 199 (2001) eloss
  smaller
• dead cone due to large mass decreases gluon
  radiation
• by 20 at moderate pT
• Djordjevic, Gyulassy, Wicks hep-ph/0410372
  smaller
• dead cone, charm pT spectrum B contribution
  cause RAA 0.6-0.8 for 2.5lt pT lt4 GeV/c
• Cronin effect collective flow also important
• Armesto, Dainese, Salgado, Wiedeman
  hep-ph/0501225 smaller
• dead cone, g vs. q eloss differences ? smaller
  RAA for c
• Teaney eloss significant if charm thermalizes!

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Non-photonic single electron spectra
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Use pp single e as reference ? RAA
RAA
clear evidence for energy loss of charm
quarks in central Au Au! (NB likely to also be
some e from B decays)
pT (GeV/c)
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Consistent with light quarks?
non-pert. effects on normal g radiation
data say same transport coefficient, smaller
hadron suppression
q consistent w/ light quark eloss
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jet probes of the medium
see talk of N. Ajitanand

• Hard scattered partons traverse the interesting
  stuff
• Energy loss by induced gluon radiation
• where does the energy go?
• Modification of fragmentation outside the
  medium??
• ? recombination with medium partons
• ? radiated gluons nearby!

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correlation functions of two high pT hadrons
Elliptic flow component measured vs. BBC reaction
plane
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decompose to get jet pair distribution
Away-side jets broadened non-Gaussian! 2s dip at
p peak at 1.25 rad around hard parton thru
medium integrating entire away side recovers jet
partners
Casalderry, Shuryak, Teaney say 1.1 rad cone
hep-ph/0411315
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identify triggers, count partners
nucl-ex/0408007
Jet partner likely for trigger baryons as well as
mesons! Same side slight decrease with
centrality for baryons Dilution from boosted
thermal p, pbar? Away side partner rate as in
pp confirms jet source of baryons! disappearance
of away-side jet into narrow angle for both
baryons and mesons
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Whats going on?
Radiated gluons are collinear (inside jet
cone) Increases partner yield
Thermal quark recombination
Dilutes jet partner yield
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Jet partner distribution on trigger side
nucl-ex/0408007
Corrected to jet yield according to
fragmentation symmetric in f,h Partner spectrum
flatter, as expected for jet source Partners
soften in most central collisions
Jet partners Inclusive
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Compare to hard-soft recombination
p trigger p associated Hwa Yang
nucl-th/0407081
Soft-hard recomb. also explains baryon Cronin
effect! No jet-correlated medium flow
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Conclusions

• Direct g hard processes in AuAu calculable in
  pQCD
• we observe nuclear shadowing at RHIC
• no room for saturation at mid-y forward could
  be
• baryon mysteries already present in dAu
• Hadron v2 trends support rapid thermalization
  hypothesis
• theorists have homework to see how soft is EOS
• heavy quarks do flow (and thermalize)
• Heavy quarks lose energy in the medium!
• jet fragmentation is modified lost energy
  excites the medium
• baryon formation in/near medium in AA and dA
• Opacity/collision frequency, screening length
  await run4 analysis completion ( theory work!)
• radiation rate (low mass leptons, soft g) ?
  PHENIX upgrades

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• backup slides

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Compare to AuAu
PRELIMINARY

• p RAA as expected in AuAu dAu slightly
  enhanced
• p RAA scales with Ncoll in AuAu, but s higher
  than pp

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Turn to nuclear collisions single particles
PRELIMINARY
h/p0 ratio shows baryons enhanced for pT lt 5
GeV/c
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yields
nucl-ex/0410102

• rapid rise in f/participant in peripheral
  collisions
• then constant per participant - as for kaons

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Interacting Hadrons
Stopped muons (peak)
Interacting Hadrons (tail)
MuID
Gap (Layer) 0 1 2 3 4
1 GeV ?
3 GeV ?
3 GeV ?
Hadrons interactelectromagneticallyAND strongly.
steel
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Muons from Light Meson Decays

• Muon event collision vertex distribution

• D c? 0.03 cm Decays before absorber
• ? c? 780 cm Most are absorbed, but
  some decay first
  
• K c? 371 cm Most are absorbed, but
  some decay first
• ?ct gtgt 80cm ? Decay Probability nearly constant
  between nosecones

? gt 0
Detector
Muon pT 0.85 parent pT
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FONLL Predictions

• Mateo Cacciari provided a prediction using the
  Fixed Order Next Leading Logarithm pQCD approach
• His calculation agrees perfectly with our poor
  mans HVQLIBPYTHIA predictions
• Data exceed the central theory curve by a factor
  of 2-3
• Possible explanations
• NNLO contribution
• Fragmentation mechanisms need to be studied in
  more details

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centrality dependence?

• need to complete analysis of run4 data
• first glimpse

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Pions in 3 detectors in PHENIX

• Charged pions from TOF
• Neutral pions from EMCAL
• Charged pions from RICHEMCAL

Cronin effect gone at pT 8 GeV/c
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Subtract the underlying event
includes ALL triggers (even those with no
associated particles in the event)
combinatorial background large in AuAu!
CARTOON
dN
1
flowjet
Ntrig d??
flow
jet
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2 particle correlations
Select particles with pT 2.5-4.0GeV/c Identify
them as mesons or baryons via Time-of-flight Find
second particle with pT 1.7-2.5GeV/c Plot
distribution of the pair opening
angles integrate over 55
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Thermalization? particle ratios and spectra
Statistical fitTch 160MeV, gs1.0 Strangeness
saturation at RHIC?
p/K/p measurement in a Broad pt range
Chemical freezeout
Thermal freezeout
stronger radial flow at RHIC?
RHIC

• consistent with strongly expanding thermalized
  source
• observed strangeness production ? complete
  chemical equilibrium

Expansion velocity
Tkin 100 MeV ltbTgt 0.5
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HBT vs. hydro models
NB Rside ? source transverse radius!
Nobody gets HBT right! Origin of the HBT
puzzle Generic explanation Nobody does
freezeout of final state right Another
explanation Maybe were fooled by the extraction
of the radius parameters somehow
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Empirical energy loss from data
For power-law spectrum with A/pTn (we find n 8.1
in pp) Final spectrum initial - ltfractional
shiftgt ltshiftgt due to eloss of parent
parton Parent pT would be pT (1S)
pT(pp) Fractional energy loss Sloss 1 -
1/(1S) 10 GeV DE/Dx 0.5 GeV/fm
Fractional energy loss
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State-of-Art Zooming into low pT

• Most realistic calculation
• Including all the contributions
• We may be able to see QGP contribution in
  1-3GeV/c in Run4!

Thanks to Ralf Rapp for providing theoretical
points!
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Results (RAA)

• Photon RAA is consistent with unity over all the
  centrality compared to ?0 results.
• Clear evidence of that the yield follows
  thickness-scaled hard scattering
• p-p reference from NLO pQCD Calculation
• ?0 RAA decreases to 0.2 at Npart320
• Dotted line shows uncertainty of thickness
  function
• Error bars show total error (systematics
  statistical) except thickness function error

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Centrality (in)dependence in dAu collisions
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Does Cronin enhancement saturate?

• A different approach
• Intrinsic momentum broadening in the excited
  projectile proton
• hpA average number of collisions

X.N.Wang, Phys.Rev.C 61 (2000) no upper
limit. Zhang, Fai, Papp, Barnafoldi Levai,
Phys.Rev.C 65 (2002) n4 due to proton

d

dissociation.
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Jets in PHENIX

• Trigger
• hadron with pT gt 2.5 GeV/c
• Biased, low energy, high z jets!
• Plot Df of associated partners
• Count associated lower pT particles for each
  trigger
• conditional yield
• Make correlation functions
• ? disentangle flow and jet contributions

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Initial state pp collisions
p0 well described by pQCD and usual fragmentation
functions
p0
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pQCD in AuAu? direct photons
Probe calculation works!
AuAu 200 GeV/A 10 most central collisions
Preliminary
pT (GeV/c)
????measured / ????background
?measured/?background
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Brazil University of São Paulo, São
Paulo China Academia Sinica, Taipei,
Taiwan China Institute of Atomic Energy,
Beijing Peking University, Beijing France LPC,
University de Clermont-Ferrand,
Clermont-Ferrand Dapnia, CEA Saclay,
Gif-sur-Yvette IPN-Orsay, Universite Paris Sud,
CNRS-IN2P3, Orsay LLR, Ecòle Polytechnique,
CNRS-IN2P3, Palaiseau SUBATECH, Ecòle des Mines
at Nantes, Nantes Germany University of Münster,
Münster Hungary Central Research Institute for
Physics (KFKI), Budapest Debrecen University,
Debrecen Eötvös Loránd University (ELTE),
Budapest India Banaras Hindu University,
Banaras Bhabha Atomic Research Centre,
Bombay Israel Weizmann Institute,
Rehovot Japan Center for Nuclear Study,
University of Tokyo, Tokyo Hiroshima University,
Higashi-Hiroshima KEK, Institute for High Energy
Physics, Tsukuba Kyoto University,
Kyoto Nagasaki Institute of Applied Science,
Nagasaki RIKEN, Institute for Physical and
Chemical Research, Wako RIKEN-BNL Research
Center, Upton, NY Rikkyo University,
Tokyo Tokyo Institute of Technology,
Tokyo University of Tsukuba, Tsukuba Waseda
University, Tokyo S.
Korea Cyclotron Application Laboratory, KAERI,
Seoul Kangnung National University,
Kangnung Korea University, Seoul Myong Ji
University, Yongin City System Electronics
Laboratory, Seoul Nat. University, Seoul Yonsei
University, Seoul Russia Institute of High Energy
Physics, Protovino Joint Institute for Nuclear
Research, Dubna Kurchatov Institute,
Moscow PNPI, St. Petersburg Nuclear Physics
Institute, St. Petersburg St. Petersburg State
Technical University, St. Petersburg Sweden Lund
University, Lund
12 Countries 58 Institutions 480
Participants
USA Abilene Christian University, Abilene,
TX Brookhaven National Laboratory, Upton,
NY University of California - Riverside,
Riverside, CA University of Colorado, Boulder,
CO Columbia University, Nevis Laboratories,
Irvington, NY Florida State University,
Tallahassee, FL Florida Technical University,
Melbourne, FL Georgia State University, Atlanta,
GA University of Illinois Urbana Champaign,
Urbana-Champaign, IL Iowa State University and
Ames Laboratory, Ames, IA Los Alamos National
Laboratory, Los Alamos, NM Lawrence Livermore
National Laboratory, Livermore, Ca University of
New Mexico, Albuquerque, NM New Mexico State
University, Las Cruces, NM Dept. of Chemistry,
Stony Brook Univ., Stony Brook, NY Dept. Phys.
and Astronomy, Stony Brook Univ., Stony Brook, NY
Oak Ridge National Laboratory, Oak Ridge,
TN University of Tennessee, Knoxville,
TN Vanderbilt University, Nashville, TN
as of January 2004