Recent Results from STAR

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Recent Results from STAR
14th Topical Conference on Hadron Collider Physics

• Markus D. Oldenburg

Munich, Germany
For the STAR Collaboration
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Outline

• RHIC
• STAR
• Analyses
• Anisotropic Flow
• Jets at RHIC
• Ultra-Peripheral Collisions
• Summary
• Outlook

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The Relativistic Heavy Ion Collider

• Two independent accelerator rings
• 3.83 km in circumference
• Accelerates everything from p to Au
• Running conditions Au-Au 2001
• 55-56 bunches per ring (tested up
  to 110)
• 7.5?108 Au/bunch _at_ storage energy
• Storage energy 100 GeV/A
• Peak luminosity 5?1026 cm-2 s-1
• Running conditions p?p? 2001
• 55 bunches per ring
• 0.8?1011 p?/bunch
• Energy/beam 100 GeV
• Peak luminosity 1.5?1030 cm-2 s-1
• Beam polarization 25 (? AGS)

Long Island
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The STAR experiment at RHIC
STAR uses the worlds largest Time Projection
Chamber
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One of the first Au on Au Events at CM Energy of
200 GeV?A
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Anisotropic Flow

• Look at peripheral collisions
• Overlap region is not symmetric in coordinate
  space
• Almond shaped overlap region
• Easier for particles to emerge in the direction
  of x-z plane
• Larger area shines to the side

• Spatial anisotropy ? Momemtum anisotropy
• Interactions among constituents generate a
  pressure which transforms the initial spatial
  anisotropy into the observed momentum anisotropy

• Perform a Fourier decomposition of the momentum
  space particle distributions in the x-y plane
• vn is the n-th harmonic Fourier coefficient of
  the distribution of particles with repsect to the
  reaction plane
• v1 directed flow
• v2 elliptic flow

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v2 vs. Centrality (130 GeV)

• v2 is large
• 6 in peripheral collisions
• Smaller for central collisions
• Hydro calculations are in reasonable agreement
  with the data
• In contrast to lower collision energies where
  hydro over-predicts anisotropic flow
• Anisotropic flow is developed by
  rescattering
• Data suggests early time history
• Quenched at later times

Anisotropic transverse flow is large at RHIC
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v2 vs. pt and Particle Mass (130 GeV)

• The mass dependence is reproduced by hydrodynamic
  models
• Hydro assumes local thermal equilibrium
• At early times
• Followed by hydrodynamic expansion

D. Teaney et al., QM2001 Proc.P. Huovinen et
al., nucl-th/0104020
Hydro does a surprisingly good job
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v2 for High pt Particles (130 GeV)

• pQCD inelastic energy loss parameterized hydro
  component (M. Gyulassy, I. Vitev and
  X.N. Wang, PRL 86 (2001) 2537)
• value of v2 at high pt sensitive to the initial
  gluon density
• saturation and decrease of v2 as a function of pt
  at higher pt
• data starts to deviate from hydrodynamics at pt gt
  2 GeV/c

Adler et al., nucl-ex/0206006
Data is in qualitative agreement with
jet-quenching scenario
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Centrality dependence of v2(pt)
130 GeV

• v2 is saturated at high pt and it does not come
  back down as rapidly as expected
• What does v2 do at very high pt ?

200 GeV (preliminary)
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v2 up to 12 GeV/c
v2 seems to remain saturated
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Hard Probes in Heavy-Ion Collisions

• New opportunity using Heavy Ions at RHIC ? Hard
  Parton Scattering
• ?sNN 200 GeV at RHIC
• 17 GeV at CERN SPS
• Jets and mini-jets
• 30-50 of particle production
• High pt leading particles
• Azimuthal correlations
• Extend into perturbative regime
• Calculations reliable (?)
• Scattered partons propagate through matter
• radiate energy (dE/dx x) in colored medium
• Interaction of parton with partonic matter
• Suppression of high pt particles jet quenching
• Suppression of angular correlations

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Jets in Hadronic Collisions
AuAu ???? (STAR_at_RHIC)
pp ?jetjet (STAR_at_RHIC)
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Identifying jets on a statistical basis in Au-Au
STAR Preliminary AuAu _at_ 200 GeV/c, 0-5 most
central 4 lt pt(trig) lt 6 GeV/c, 2 lt pt(assoc.) lt
pt(trig)

• Given a trigger particle with pt gt pt (trigger),
  associate particles with pt gt pt (associated)
• AuAu
• flow
• pp and AuAu collisions
• dijets
• momentum conservation
• jets
• resonances

All ??
Small ??
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Peripheral AuAu data vs. ppflow

• Ansatz
• A high pt triggered AuAu event is a
  superposition of a high pt triggered
• pp event plus anisotropic transverse flow
• v2 from reaction plane analysis
• A is fit in non-jet region (0.75 lt ?? lt
  2.24)

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Central AuAu data vs. ppflow
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Jets at RHIC

• The backward going jet is missing in central
  Au-Au collisions when compared to p-p data flow
• Other features of the data
• High pt charged hadrons dominated by jet
  fragments
• Relative charge
• Azimuthal correlation width
• Evolution of jet cone azimuthal correlation
  strength with centrality

Surface emission?

• Other explanations for the disappearance of
  back-to-back correlations in central Au-Au?
• Investigate nuclear kT effects
• Experiment pAu or dAu
• Theory Add realistic nuclear kT to
  the models

?
Suppression of back-to-back correlations in
central AuAu collisions
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Ultra-Peripheral Collisions

• b gt 2RA
• no hadronic interactions
• ltbgt 20-60 fermi at RHIC
• Ions are sources of fields
• Fields couple coherently to ions
• pt lt h/RA, 30 MeV/c for heavy ions
• p lt gh/RA 3 GeV/c at RHIC
• Photonuclear (Photon-Pomeron) Interactions
• gA r0, w, f, J/y, A
• Vector Meson Dominance
• gA qqA (elastic scattering) VA
• s(r) 350 mb at 130 GeV/nucleon
• 5 of sAuAu(had.)
• Electromagnetic particle production
• gg leptons, mesons
• Strong Field (nonperturbative?) QED

-
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Exclusive r0
200GeV

• Trigger on low multiplicity events
• veto on cosmic rays
• 2 track vertex w/ charge 0
• reject (coplanar) cosmic rays
• peak for pt lt 150 MeV/c
• pp and p-p- give background shape
• scaled up by 2.1

Signal region ptlt0.15 GeV

• Preliminary

r0 pt
ptlt0.15 GeV
M(pp-)
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Minimum Bias Data
200 GeV

• 800,000 triggers neutron signals in ZDCs
• Nuclear excitation tags small b interactions
• excitation and r0 are independent
• Analysis same as in peripheral

Signal region ptlt0.15 GeV
Preliminary
r0 pt
200 GeV
Preliminary

• Normalized to 7.2 b hadronic cross section
• Systematic uncertainties luminosity, overlapping
  events, vertex tracking simulations, single
  neutron selection, etc.

ds/dMpp (mb/GeV)
M(pp-)
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Summary of Analyses

• Results
• Large anisotropic flow, consistent with
  hydrodynamical picture
• Saturation of v2 at high pt
• Jet quenching?
• Suppression of back-to-back jets
• Surface emission?
• r0 cross sections measured in ultra-peripheral
  Au-Au collisions, good agreement to theory

• shown
• Anisotropic Flow
• Jets at RHIC
• Ultra-Peripheral Collisions

• not shown
• Particle yields / ratios / spectra
• Interferometry (HBT)
• Fluctuations
• Gluon density saturation
• Spin physics program

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RHIC Performance Goals for 2003

• 29 weeks of d-Au (including cooldown)
• 8 weeks of p?p?
• (We wont have Si-Si nor Au-Au next year.)

More interesting physics to come ...
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STAR Institutions

• U.S. Labs
• Argonne, Brookhaven, and Lawrence Berkeley
  National Labs
• U.S. Universities
• UC Berkeley, UC Davis, UCLA, Carnegie Mellon,
  Creighton, Indiana, Kent State,
  Michigan State, CCNY, Ohio State, Penn State,
  Purdue, Rice,
• UT Austin, Texas AM, Valparaiso, Washington,
  Wayne State, Yale
• Brazil
• Universidade de Sao Paolo
• China
• IPP - Wuhan, IMP - Lanzhou USTC, SINR,
  Tsinghua University, IHEP - Beijing

England University of Birmingham France
IReS - Strasbourg SUBATECH -
Nantes Germany Max Planck Institute - Munich
University of Frankfurt India Institute of
Physics - Bhubaneswar IIT - Mumbai, VECC -
Calcutta Jammu University, Panjab
University University of Rajasthan The
Netherlands NIKHEF Poland Warsaw
University of Technology Russia MEPHI -
Moscow, IHEP - Protvino LPP LHE JINR - Dubna