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Recent Results from STAR
14th Topical Conference on Hadron Collider Physics Recent Results from STAR Markus D. Oldenburg Munich, Germany For the STAR Collaboration
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14th Topical Conference on Hadron Collider Physics
Outline RHIC STAR Analyses Anisotropic Flow Jets at RHIC Ultra-Peripheral Collisions Summary Outlook Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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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 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) STAR Long Island Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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The STAR experiment at RHIC
STAR uses the world’s largest Time Projection Chamber
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One of the first Au on Au Events at CM Energy of 200 GeVA
STAR
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14th Topical Conference on Hadron Collider Physics
Anisotropic Flow x y z 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 px py y x 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 14th Topical Conference on Hadron Collider Physics
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Anisotropic transverse flow is large at RHIC
v2 vs. Centrality (130 GeV) PRL 86, (2001) 402 more central 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 Hydro predictions Anisotropic transverse flow is large at RHIC Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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v2 vs. pt and Particle Mass (130 GeV)
PRL 86, 402 (2001) & nucl-ex/ 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/ Hydro does a surprisingly good job Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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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/ Data is in qualitative agreement with ‘jet-quenching’ scenario Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Centrality dependence of v2(pt)
130 GeV peripheral central 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) Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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v2 seems to remain saturated
v2 up to 12 GeV/c v2 seems to remain saturated Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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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 leading particle leading particle schematic view of jet production QGP Vacuum Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Jets in Hadronic Collisions
Au+Au ??? p+p jet+jet Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Identifying jets on a statistical basis in Au-Au
STAR Preliminary 200 GeV/c, 0-5% most central 4 < pt(trig) < 6 GeV/c, 2 < pt(assoc.) < pt(trig) 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 All Small Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Peripheral Au+Au data vs. pp+flow
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 14th Topical Conference on Hadron Collider Physics
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Central Au+Au data vs. pp+flow
Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Suppression of back-to-back correlations in central Au+Au collisions
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: p+Au or d+Au Theory: Add realistic nuclear kT to the models ? Suppression of back-to-back correlations in central Au+Au collisions Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Ultra-Peripheral Collisions
b > 2RA; no hadronic interactions <b> ~ fermi at RHIC Ions are sources of fields Fields couple coherently to ions pt < h/RA, ~30 MeV/c for heavy ions p|| < 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 Au Coupling ~ nuclear form factor g, P, or meson - Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Exclusive r0 Preliminary 200GeV r0 pt M(p+p-)
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 p+p+ and p-p- give background shape scaled up by 2.1 200GeV Signal region: pt<0.15 GeV Preliminary r0 pt pt<0.15 GeV M(p+p-) Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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Minimum Bias Data Preliminary Preliminary 200 GeV 200 GeV
800,000 triggers neutron signals in ZDCs Nuclear excitation ‘tag’s small b interactions excitation and r0 are independent Analysis same as in peripheral Signal region: pt<0.15 GeV Preliminary r0 pt 200 GeV Normalized to 7.2 b hadronic cross section Systematic uncertainties: luminosity, overlapping events, vertex & tracking simulations, single neutron selection, etc. ds/dMpp (mb/GeV) Preliminary M(p+p-) Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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14th Topical Conference on Hadron Collider Physics
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 Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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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 14th Topical Conference on Hadron Collider Physics
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14th Topical Conference on Hadron Collider Physics
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 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 - 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 Markus D. Oldenburg 14th Topical Conference on Hadron Collider Physics
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