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Itzhak Tserruya 29.5.011 Initial Conditions at RHIC: an Experimental Perspective RHIC-INT Workshop LBNL, May31 – June 2, 2001 Itzhak Tserruya Weizmann Institute
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Itzhak Tserruya 29.5.012 Global Observables at RHIC: an Experimental Perspective RHIC-INT Workshop LBNL, May31 – June 2, 2001 Itzhak Tserruya Weizmann Institute
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Itzhak Tserruya 29.5.013 Outline Introduction * Global Observables : Why and What * From Global Observables to Initial Conditions RHIC results * Consistency between different experiments * Consistency between different quantities * Centrality dependence * Model comparison * Comparison to lower energies and to pp Summary
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Itzhak Tserruya 29.5.014 Global Observables WHAT ? * dN ch /d , dE T /d , * Reflect the conditions of the system well after freeze-out, after resonance decays WHY ? * “Easy” measurements * Constrain models * Initial Conditions
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Itzhak Tserruya 29.5.015 dN/d Predictions
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Itzhak Tserruya 29.5.016 Initial Conditions centrality defined as percentile of tot N part, N coll, b WHAT ? * energy density * formation time * initial temperature Not measured Inferred thru models
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Itzhak Tserruya 29.5.017 PHOBOS : | |<1, 1%? 2 layers of Si detectors close to vertex (B=0) dN ch /d = 555 ±12 ±35 (6% most central) PRL dN ch /d = 579 ±12 ±22 (6% most central) PHENIX : | |<0.35, = 90 o 2 layers of PC at 2.5 and 5 m from vertex (B=0) dN ch /d = 622 ±1± 41 (5% most central) STAR : | |<1.8, = 2 Tracking in TPC, p t >100 MeV (B#0) dN ch /d = 567±1±38 (5% most central) 3 completely different methods remarkable agreement dN ch /d = 584 ±18 RHIC : dN ch /d
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Itzhak Tserruya 29.5.018 RHIC : PHENIX: (preliminary) average p t per event, p T > 200 MeV = 523 ± 29 MeV Good guess: 450 MeV - Centrality: - 0-5% t PHENIX preliminary p T (GeV/c) (overestimate? NA49 measures h - 385 MeV power law fit gives 429 MeV) STAR: power-law fit to h - = 508 ±12 MeV HIJING: p T >0 MeV = 450 MeV p T >200 MeV = 522 MeV
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Itzhak Tserruya 29.5.019 PHENIX : | |<0.35, = 45 o dE T /d = 503 ±1±23 (5% most central) RHIC : dE T /d
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Itzhak Tserruya 29.5.0110 PHENIX: Consistency Check Are PHENIX 0-5% results consistent? dE T /d = 503 GeV, dN ch /d = 622, = 450 MeV Simple approximation: ? 503 ±23 = 429 ±37 19% difference Applying the same approximation to HIJING yields a difference of 12%
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Itzhak Tserruya 29.5.0111 Minimum-bias distribution at s NN = 130 GeV at s NN = 130 GeV PHENIX Au-Au s NN = 130 GeV PHENIX Au-Au s NN = 130 GeV
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Itzhak Tserruya 29.5.0112 Centrality dependence (I): PHENIX dN ch / d and dE T / d show consistent behaviour Clear increase of dN ch / d and dE T / d per participant pair vs N part Data compatible with pp measurement PHENIX
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Itzhak Tserruya 29.5.0113 Centrality Dependence (II): PHOBOS
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Itzhak Tserruya 29.5.0114 Centrality Dependence (III): PHENIX - PHOBOS PHENIX - PHOBOS
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Itzhak Tserruya 29.5.0115 PHENIX preliminary Centrality Dependence (IV): Comparison to CERN results Comparison to CERN results WA97 Transverse energy Multiplicity -value WA98 PHENIX
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Itzhak Tserruya 29.5.0116 Particle production mechanism (I) PHENIX Consistent results: Hard processes contribution increases with centrality: from ~30% mid-central to ~50% most central dN ch /d per participant increases vs N par In contrast with EKRT saturation model Similar to HIJING (although data ~15% higher)
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Itzhak Tserruya 29.5.0117 Particle production mechanism (II) Kharzeev, Nardi, Phys. Lett. B 507 (2001) A. Capella, D. Sousa, nucl-th/0101023 BUT: Capella, D. Sousa, nucl-th/0101023 No hard component. Soft processes scale with N coll Kharzeev, Nardi, Saturation model agrees with data
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Itzhak Tserruya 29.5.0118 SPS Results: Summary dN ch /dydE T /dy h - 0-5%0-2% 0-5%
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Itzhak Tserruya 29.5.0119 Intermezzo : a few O(10%) factors (I): E T Definition Definition A: E-m = KE for nucleons + Total energy E for all other particles Definition B: E-m = KE for nucleons + E+m for antinucleons + Total energy E for all other particles i.e. total energy generated in the transverse plane (count mass of produced baryons but does not count mass of participating nucleons) WA98 uses definition B PHENIX A NA49 ?
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Itzhak Tserruya 29.5.0120 Intermezzo : a few O(10%) factors (II): Central Collisions WA98 : 0 –1% 100 0 – 5% 92 0 – 10% 85 top 5% corresponds to b 0 – 3 fm Adopt 0-1% or 0-2% Nuclear Radius NA49: Pb radius R = r -o A 1/3 r -o = 1.12 fm PHENIX: Au radius r -o = 1.18 fm 10% difference in energy density
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Itzhak Tserruya 29.5.0121 Intermezzo : a few O(10%) factors (III): dN/d and dN/dy dN/d dN/dy |y|<0.5 : |y|<1 : RHIC: mid-rapidity is at y( ) = 0 SPS: mid-rapidity is at y( ) = y beam /2 dN/dy dN/d
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Itzhak Tserruya 29.5.0122 Energy density a la Bjorken: Energy Density From SPS to RHIC: at least 70% increase in
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Itzhak Tserruya 29.5.0123 From SPS to RHIC ~70% increase in dN ch /dy ~70% increase in dE T /d ln( s NN ) dependence from AGS to RHIC s NN Dependence
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24 dN/d : Predictions with quenching No jet quenching STAR PHENIX from s NN ) dN ch /d increase from s NN ) = 130 to 200 GeV: ln( s NN ) dependence: ln( s NN ) dependence: 9% HIJING with quenching: 30%
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25 Transverse energy per charged particle dE T /dN ch independent of s NN dE T /dN ch independent of N part Consistent with very moderate increase of from AGS to RHIC: NA49 h - = 385 MeV RHIC 450 MeV UA1: =392 MeV dE T / dN ch = 0.9
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Itzhak Tserruya 29.5.0126 Summary E T per N ch independent of centrality and of energy Systematic study of dE T /d and dN ch /d vs. Npart: * Stronger increase than at the CERN SPS *Evidence for role of hard processes ? dN ch /dy, dE T /dy and Bjorken energy density in central Au+Au collisions at RHIC ~70% higher than in Pb+Pb collisions at CERN SPS Very moderate increase O(20%) of between SPS and RHIC
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Itzhak Tserruya 29.5.0127 Are NA49 0-5% results consistent? dE T /dy = 405 GeV, dN ch /dy = 410, = 385 MeV Simple approximation: NA49 Consistency Check ? 405 = 237 70% difference !! (but dE T /dy is for 0-2% and dN ch /dy is for 0-5%)
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