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Rapporteur II: Global & Flow Observables

Rapporteur II: Global & Flow Observables. Peter Steinberg Brookhaven National Laboratory. Global Flow. Peter Steinberg BNL. Global Variables Event shape dN/d h Centrality dependence dN/d h dE T /d h  p T  Initial Energy density. “Flow” Event shape dN/d f

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Rapporteur II: Global & Flow Observables

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  1. Rapporteur II:Global & Flow Observables Peter Steinberg Brookhaven National Laboratory

  2. Global Flow Peter Steinberg BNL

  3. Global Variables Event shape dN/dh Centrality dependence dN/dh dET/dh pT Initial Energy density “Flow” Event shape dN/df Centrality dependence dN/df Species v1,v2, Initial Pressure Outline • In principle, we are looking at two important pieces of the equation of state…

  4. Centrality: Participants vs. Spectators The collision geometry (i.e. the impact parameter) determines the number of nucleons that participate in the collision “Spectators” Only ZDCs measure Npart Zero-degreeCalorimeter “Participants” “Spectators” • Many things scale with Npart: • Transverse Energy • Particle Multiplicity • Particle Spectra Produced Particles

  5. Fluctuations modify the response less central events fluctuate to central bins The final “measurement” of Npart is the best attempt to factor out the facts of life! In principle, we could work with % of cross section Final measurement of Npart is best attempt to correct for facts of life Measuring Centrality Npart Multiplicity in 3<|h|<4.5 • Clearly, fluctuations affect your centrality estimator

  6. Why we should use Npart • Very difficult to compare experimental results without serious estimate of Npart • Must incorporate fluctuations in the measurement of the centrality estimators • OK, Glauber implementation is a real uncertainty • Even if you don’t “like” participants, the exercise is critical for inter-experiment comparisons

  7. ZDC BBC Percentile ZDC as centrality device • Only shared detector • Rates: luminosity via well-known reference process • Timing: substantial background rejection • Pulse height: measures centrality • Directly confirms monotonic relationship between participants with multiplicity

  8. Reference: szdc =10.7+/-0.5 b Measurement: (geo / tot)exp = (Nbbc/ Ntot)exp/ bbc= (0.668  0.022) Theory: geo / tot = (0.673  <0.034) Mutual Coulomb Dissociation (measured) (from Glauber)

  9. Multiplicity: what is learned • Can the models get the “big picture” right? • However, let’s not ignore the details… • Magnitude • Integral over energy density, stopping, shadowing, quenching, flow • Centrality dependence • Study effect of system size (onset of interesting effects above critical volume) • Interplay between Npart and Ncoll • Shape • Stopping, Final state interactions

  10. Energy dependence PHENIX STAR prelim. 10% PHOBOS BRAHMS prelim.

  11. dN/dh: Predictions with quenching no quenching

  12. dN/dh: Post-dictions LEXUS • AMPT, LEXUS, DSM, HIJING, EKRT • Please be careful about scaling y to h • Not boost invariant! • Not .9, .95 etc. • Jacobian depends on velocity: dy = b dh • Depends on species and mean pT! • Still not sure who gets the champagne…wait for 200 GeV AMPT

  13. dN/dh vs Centrality at h=0 dN/dh / .5Npart Npart

  14. Measurement sensitive to trigger bias “Minimum-bias” still has bias Affects most peripheral events Uncertainty on Npart % Error on Npart This measurement Npart • Estimating 96% when really 90% overestimates Npart • Creates “pivot point” at central events • Hard to rule out EKRT…

  15. PH: OBOS vs. ENIX dN/dh / .5Npart Npart

  16. Octagon Rings dNch/dh vs. Centrality dNch/dh 45-55% 35-45% 25-35% dNch/dh 15-25% 6-15% 0-6% h h h

  17. Shapes of dNch/dh for different Npart %s Mean Npart 0-3 Data HIJING 354 15-20 216 35-40 102 dNch/dh dNch/dh Data HIJING (dNch/dh)/(½Npart) (dNch/dh)/(½Npart) h h Systematic error ±(10%-20%)

  18. PHOBOS Prelim. Centrality dependence of dNch/dh|h Solid lines: HIJING Symbols: Errors are systematic |h| <1 2-2.4 (dNch/dh)/(½Npart) 3-3.4 4-4.4 5-5.4 Npart

  19. PHOBOS Prelim. Total Multiplicity (|h|<5.4) Nch HIJING Npart

  20. Multiplicity Results • EKRT, HIJING disfavored by both PHENIX & PHOBOS • Initial state saturation looks like modified Glauber • No way to resolve using Nch alone • What about ET? • Hydro does p dV work during longitudinal expansion, decreases dET/dh • Eskola: “ET will be more efficient model killer”… • So far, few papers predicting ET, but surely on the way • PHOBOS got 9 in two months after the first paper…

  21. Centrality dependence of ET PHENIX submitted PHENIX Preliminary • ET and charged particles appear to vary in lockstep • Fits are a modified WNM, possibly allow extraction of fraction of hard production (NB. ambiguities persist…)

  22. Independent of centrality Appears to be same as WA98 (@SPS) Energy dependence Possible 20% discrepancy betw. NA49/WA98 Where is the increased <pT> seen by STAR/PHENIX? ET per charged particle PHENIX Preliminary PHENIX Preliminary

  23. Sorry, I won’t tell you… Implication of PHENIX Constant ET/charged particle Energy density (via Bj formula) simply scales with multiplicity! (Even PHOBOS can do it!) ~50% higher than SPS… Ambiguities persist Formation time might be substantially less “So what’s the Energy Density?”

  24. Radial flow Not seen in angular distributions Use HBT, spectra (T = To + m<b2> - Nu Xu) Directed flow Forward rapidities Not measured yet Sensitivity estimated at PHOBOS/STAR Interesting predictions for phase transition… Elliptic flow Early time push, hydrodynamic evolution Strongest at midrapidity “Flow”

  25. Method used by PHENIX Similar information content as Fourier method OK for partial acceptance Sensitive to other correlations Jets (at 180o) , HBT (at 0o) But is that bad? CERES data v2 from azimuthal correlations 0-5% Df 5-15% 15-30%

  26. v2 versus centrality • Boxes show “initial spatial anisotropy”e scaled by 0.19-0.25 PRL 86, (2001) 402 || < 1.3 0.1 < pt < 2.0

  27. Centrality Dependence midrapidity : |h| < 1.0 V2 Hydrodynamic model Preliminary SPS AGS Normalized Paddle Signal

  28. CERES slides • Excitation function • CERES 40 GeV fits in with existing energy systematics • Back-to-Back correlations • Extraction of v2 is substantially higher than normal event plane analysis

  29. pT dependence for p,p • Hydro calculations: P. Huovinen, P. Kolb and U. Heinz

  30. v2 at high pT PHENIX Preliminary • Hydro fails at large transverse momentum • Possible interpretations suggested by jet quenching (wait for A. Drees talk) • However, perhaps composition is a critical part of this effect…

  31. Comparison of all v2 results v2 PHENIX (pT>500 MeV) nch/nmax

  32. v2 vs. (pseudo)rapidity v2 v2 • NA49 (y), PHOBOS(h) (mainly pions) • Different shape at midrapidity • PHOBOS shape similar to dN/dh! • Low-density limit?? v2 ~ e dN/dy • However, v2 appears to fall faster than multiplicity PHOBOS Preliminary y h PHOBOS Preliminary dN/dh h

  33. Conclusions

  34. ÖsNN dependence • Assumptions: in Lab in C.M. • Energy density (Bjorken): • From SPS to RHIC • ~50% increase in dNch/dy • ~50% increase in dEt/dy • at least 50% increase in e

  35. Mean pt versus number of participants • Pions steep rise and plateau • Protons gradual rise and higher <pt>

  36. Sub Event Correlation • Non-Flow Effects • Momentum conservation • HBT, Coulomb (final state) • Resonance decays • Jets

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