Recent Results from STAR Markus D. Oldenburg 14 th Topical Conference on Hadron Collider Physics Munich, Germany For the STAR Collaboration

Recent Results from STARMarkus D. Oldenburg

14th Topical Conference on Hadron Collider Physics

Munich, Germany

For the STAR Collaboration

Markus D. Oldenburg


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Outline

• RHIC

• STAR

• Analyses– Anisotropic Flow

– Jets at RHIC

– Ultra-Peripheral Collisions

• Summary

• Outlook

Markus D. Oldenburg


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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)• 7.5108 Au/bunch @ storage energy• Storage energy: 100 GeV/A• Peak luminosity: 51026 cm-2 s-1

Running conditions: pp 2001• 55 bunches per ring• 0.81011 p/bunch• Energy/beam: 100 GeV• Peak luminosity: 1.51030 cm-2 s-1

• Beam polarization ~ 25% ( AGS)Long IslandLong Island

STAR

The STAR experiment at RHIC

STAR uses the world’s largest Time Projection Chamber

One of the first Au on Au Events at CM Energy of 200 GeVA

STARSTAR

Markus D. Oldenburg


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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

x

yz

px

py

y

x

nvn cosx

y

p

patan

• 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”

Markus D. Oldenburg


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PRL 86, (2001) 402

more central

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 timesAnisotropic transverse flow is large at RHIC

Hydro predictions

Markus D. Oldenburg


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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

PRL 86, 402 (2001) & nucl-ex/0107003

Hydro does a surprisingly good job

D. Teaney et al., QM2001 Proc.P. Huovinen et al., nucl-th/0104020

Markus D. Oldenburg


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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 > 2 GeV/c

Adler et al., nucl-ex/0206006

Data is in qualitative agreement

with ‘jet-quenching’ scenario

Markus D. Oldenburg


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Centrality dependence of v2(pt)

• 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)

130 GeV

peripheral

central

Markus D. Oldenburg


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v2 up to 12 GeV/c

v2 seems to remain saturated

Markus D. Oldenburg


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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

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

QGP

Vacuum

Markus D. Oldenburg


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Jets in Hadronic Collisions

p+p jet+jet (STAR@RHIC)

Au+Au ??? (STAR@RHIC)

Markus D. Oldenburg


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Identifying jets on a statistical basis in Au-Au

• Given a trigger particle with pt > pt (trigger), associate particles with pt > pt (associated)

• Au+Au– flow

• p+p and Au+Au collisions:– dijets– momentum

conservation– jets – resonances

STAR Preliminary Au+Au @ 200 GeV/c, 0-5% most central

4 < pt(trig) < 6 GeV/c, 2 < pt(assoc.) < pt(trig)

Small

All

),()(11

)(2 NdefficiencyN

Ctrigger

Markus D. Oldenburg


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Peripheral Au+Au data vs. pp+flow

C2(Au Au) C2(p p) A *(1 2v22 cos(2))

Ansatz: A high pt triggered Au+Au event is a superposition of a high pt triggered p+p event plus anisotropic transverse flow

v2 from reaction plane analysis

“A” is fit in non-jet region (0.75 < || < 2.24)

Markus D. Oldenburg


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Central Au+Au data vs. pp+flow

C2(Au Au) C2(p p) A *(1 2v22 cos(2))

Markus D. Oldenburg


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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?

Suppression of back-to-back correlations in central Au+Au collisions

• Other explanations for the disappearance of back-to-back correlations in central Au-Au?

– Investigate nuclear kT effects

• Experiment: p+Au or d+Au

• Theory: Add realistic nuclear kT to the models

Markus D. Oldenburg


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Ultra-Peripheral Collisions

• b > 2RA;

– no hadronic interactions– <b> ~ 20-60 fermi at RHIC

• Ions are sources of fields– Fields couple coherently to ions

• pt < h/RA, ~30 MeV/c for heavy ions

• p|| < h/RA ~ 3 GeV/c at RHIC

• Photonuclear (Photon-Pomeron) Interactions

A ’, , , J/,… A – Vector Meson Dominance

• A ’ qqA ’ (elastic scattering) ’ VA

– ~ 350 mb at 130 GeV/nucleon• 5% of AuAu(had.)

• Electromagnetic particle production

’leptons, mesons– Strong Field (nonperturbative?) QED

Au

Au

Coupling ~ nuclear form factor

, P, or meson

-

Markus D. Oldenburg


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Exclusive 0

pt<0.15 GeV

0 pt

Signal region:

pt<0.15 GeV

200GeV

Preliminary

• Trigger on low multiplicity events• veto on cosmic rays

• 2 track vertex w/ charge 0– reject (coplanar) cosmic rays

• peak for pt < 150 MeV/c

• and give background shape– scaled up by 2.1

-)

Markus D. Oldenburg


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Minimum Bias Data

• 800,000 triggers neutron signals in ZDCs

• Nuclear excitation ‘tag’s small b interactions– excitation and 0 are independent

• Analysis same as in peripheral Preliminary

200 GeV

Signal region:

pt<0.15 GeV

d/

dM

m

b/G

eV 200 GeV

Preliminary

0 pt

-)

130 GeV STAR Theory0 with XnXn 36.6 2.4 8.9 mb 27 mb0 with 1n1n 2.50.40.6 mb 2.6 mbExclusive 0 410190100 mb 350 mb

• Normalized to 7.2 b hadronic cross section

• Systematic uncertainties: luminosity, overlapping events, vertex & tracking simulations, single neutron selection, etc.

Markus D. Oldenburg


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Summary of Analyses

shown:• Anisotropic Flow

• Jets at RHIC

• Ultra-Peripheral Collisions

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

• Spin physics program

Results:• Large anisotropic flow, consistent

with hydrodynamical picture

• Saturation of v2 at high pt

Jet quenching?

• Suppression of back-to-back ‘jets’ Surface emission?

• 0 cross sections measured in ultra-peripheral Au-Au collisions, good agreement to theory

Markus D. Oldenburg


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RHIC Performance Goals for 2003

• 29 weeks of d-Au (including cooldown)

• 8 weeks of pp• (We won’t have Si-Si nor Au-Au next year.)

More interesting physics to come ...

Markus D. Oldenburg


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STAR InstitutionsU.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 A&M, 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 - BhubaneswarIIT - Mumbai, VECC - Calcutta Jammu University, Panjab UniversityUniversity of Rajasthan

The Netherlands:NIKHEF

Poland: Warsaw University of TechnologyRussia:

MEPHI - Moscow, IHEP - ProtvinoLPP & LHE JINR - Dubna

Documents

Recent Results from STAR Markus D. Oldenburg 14 th Topical Conference on Hadron Collider Physics Munich, Germany For the STAR Collaboration