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What Happened in China ?

What Happened in China ?. r/ . gg g. Gluon Saturation?. Gluons can begin to fuse with high enough gluon density. Saturation will limit parton production Final state charged particle yields per collision limited?. Eskola, Kajantie, and Tuominen: hep-ph/0009246

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What Happened in China ?

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  1. What Happened in China ?

  2. r/ ggg Gluon Saturation? • Gluons can begin to fuse with high enough gluon density. • Saturation will limit parton production • Final state charged particle yields per collision limited? Eskola, Kajantie, and Tuominen: hep-ph/0009246 Kharzeev, Nandi: nucl-th/0012025 Phys. Rev. Lett. 86, 3500 (2001) • Gluon Saturation does not appear to set in for peripheral collisions • Cannot yet rule out Eskola’s saturation for central collisions • Kharzeev’s initial-state saturation picture is consistent with data

  3. Energy density Bjorken formula for energy density in terms of measured transverse energy assuming a thermalized system at time t0. 6.88 fm (hard sphere radius) Time to thermalize the system (~ 1.0 - 0.2 fm/c?) PHENIX: Central Au-Au yields Phys. Rev. Lett. 87, 52301 (2001)

  4. eBj~ 23.0 GeV/fm3 eBj~ 4.6 GeV/fm3 Lattice ec J. Nagle Is the energy density high enough? The PHENIX EMCal measures transverse energy For the most central events: eBjorken~ 4.6-23 GeV/fm3 Lattice phase transition: ecritical~ 0.6-1.8 GeV/fm3 Roughly 1.5 to 2 times higher than previous experiments if assume same formation time thermalization time? Energy deposition is certainly adequate, but does it create a thermalized new phase of matter while e > ecrit?

  5. Central Scaled NN Peripheral Comparison with pp baseline Peripheral consistent with NN scaled by number of collisions Central below scaled NN spectrum p0 larger deficit than unidentified hadrons p0

  6. p0ratio’s with pp and peripheral Central/peripheral PT PT

  7. q q Complications • “Ordinary” Nuclear effects: • Cronin Effect and PT broadening • Nuclear shadowing of gluon structure functions • Issues: • Does the parton fragment inside the medium? • Particle composition is a strong function of pT • Other unknown effects?

  8. Year-1 High PT Conclusions Central collision data shows significant suppression relative to prediction without energy loss. Indicates a novel effect: deviation from point like scaling It is consistent with parton energy loss , but too early to make definitive conclusion. A systematic study including pA and higher PT reach is needed. Stay tuned …

  9. l = 0.49 .07 7.9  1.1 6.2  .5 5.9  0.4 “Other” Year-1 PHENIX results Electrons Fluctuations Gamma Distribution Calculation PHENIX Preliminary Centrality: 0-5% <Pt> (GeV/c) HBT Elliptic Flow PHENIX Preliminary PHENIX Preliminary

  10. BRAHMS acceptance 00 & 01 BFS FFS

  11. BRAHMS Subm. Phys. Lett. B 7/2001. 600 • N=dE /<dE> • P(0)/P(n1) • Background corr.due to secondaries (37-50%) • Consistency between 4 independent. detector systems • 65 AGeV+65 AGeV: •  N(ch)d= 4050±300 • Central 0-5% dN(ch)/d (=0) =550 • FWHM of distribution = 7.6  0.7 0-5% 5-10% 10-20% 20-30% 30-40% 40-50%

  12. SPS Charged Particle Mult. at 130 GeV BRAHMS. Subm. Phys Lett. B. 2001

  13. dNch/d for100 AGeV+ 100 AGeV BRAHMS 200AGEV • 100 AGeV + 100 AGeV AU+AU •  N(ch)d= 5100±300 • Central 0-6% dN(ch)/d (=0) =61050 • FWHM of distribution = 7.9  1.0

  14. Hard and Soft vs.High Density QCD @ 200 AGeV • Kharzeev and Levin (nucl-th/0108006) • Soft-Hard: dN/d=(1-X) npp <Npart>/2 + X npp <Ncoll> <Ncoll>=1049, <Npart>=339, npp=2.43 =>dN/d=668 (with X=0.9) • High Density QCD-saturation: dN/dy = f( Npart, Qs2, ,QCD,s,y) with =0.3 from HERA data => dN/d=620 (using dN/d=549 ats=130GeV) ( ) ( ) ( )

  15. 130 AGeV 4000 charged part. observed Nch  23.5 pr. part. pair cf. Nch  17 in p+p at s=130GeV 35-40% increase over p+p Total production of charged particles BRAHMS 200 AGeV Syst • 200 AGeV • 5100 charged part. observed • Nch  30 pr. part. pair • cf. Nch  20 in p+p at s=200GeV • 50% increase over p+p

  16. Bjorken limit reached for Au+Au s= 130AGeV? ISR R803 s=63 s=23 BRAHMS PRL sept. 2001

  17. p-bar/p ratio:Centrality dependence BRAHMS 2k

  18. How consistent are the models?

  19. RESULTS: 100+100 Nch (0-5%)  5100 dN/d (y=0)  625. FWHM  7.8 N(ch)  30 pr. participant-pair dN/d (y=0)  3.6 pr. part. Pair p-pbar/p 0.48±0.05 (y=2) p-/p+ 0.99±0.01(stat) (y=3) RESULTS: 65+65 Nch (0-5%)  4000 dN/d (y=0)  550. FWHM  7.6 N(ch)  23 pr. participant-pair dN/d (y=0)  3 pr. part. Pair AntiMeson/Meson close to unity p-bar/ p vs y shows increased but still incomplete transparency Midrapidity Plateau? y =0,0.7,2 : pbar/p  0.64, 0.66, 0.41 (±0.05 ± 0.06) Weak pt and centrality dependence Bjorken limit not reached Models inconsistent with data Summary

  20. Energy Dependence at h=0 Errors are dominated by systematics fpp(s) = AGS/SPS points extracted by measured dN/dy and <mT> New data at 200 GeV shows a continuous logarithmic rise at midrapidity

  21. Ratio of dN/dh at 200 & 130 GeV 90% Confidence Level

  22. Using Octagon and Ring subdetectors Measure out to |h|<5.4 Corrections Acceptance Occupancy Backgrounds (from MC) Systematic errors 10% near h=0 Higher near rings Pseudo-rapidity Distributions PRL 87 (2001) forthcoming Background Corr. h HIJING Simulation

  23. Total charged multiplicity is about 4200 ± 420 for central events At high h ~ 3-4 multiplicity starts to decrease as a function of Npart Similar feature seen in pA collisions Centrality Dependence vs. h PRL 87 (2001) forthcoming

  24. Comparison to pp and models PRL 87 (2001) forthcoming Systematic error not shown Central AMPT(rescattering) HIJING Peripheral Scaled UA5 data DeMarzo et al, 1984 h h (Y130/Y200) dN/dh = fpp(s) Ybeam

  25. Change in dN/dh with energy 200 GeV • UA5 looked for ‘limiting fragmentation’ by plotting dN/dh with hh - Ybeam • We can do the same thing with the PHOBOS data • agreement for AA in the fragmentation region 130 GeV UA5 200 GeV (NSD) UA5, Z.Phys.C33, 1 (1986)

  26. Saturation model fits to 130 Data Kharzeev & Levin, nucl-th/0108006, input from Golec-Biernat & Wüsthoff (1999) m2=2Qsmr, pT=Qs, l~.3 extracted from HERA F2 data

  27. Azimuthal Asymmetry at h=0 • X = Scos(nfi), Y = Ssin(nfi) • n = atan(Y/X) • v2 = <cos 2(f- 2)> • At midrapidity, using “SymOct” • Account for detector response using “weighting matrix”. • 130 GeV data from PHOBOS • Correct for occupancy, resolution of reaction plane estimate • Good agreement with hydro calcuations for central events (and STAR…) Padsin f Pads in z

  28. Compare Flow for mid-central events Multiplicity per participant pair for central events (only 10% variation down to Npart=100) Flow (for more peripheral events) seems to scale with particle density 200 GeV data should be interesting! Saturation or scaling? Asymmetry vs. Multiplicity PRELIMINARY

  29. Asymmetry vs. Rapidity P. Kolb, Utah proc. Systematic Error ~ .007 Preliminary Results – final results coming soon!

  30. Measured near midrapidity 0 < y <1 (species-dependent) Final results submitted to PRL (Apr. 2001) Consistent within systematic errors with results presented at QM2001 (Jan. 2001) Smaller systematic errors (10%  6%) Results on particle ratios

  31. Conclusions • Systematics of charged particle production have been explored by the PHOBOS experiment • Energy – multiplicity rises approximately logarithmically • Centrality – data shows simple interpolation between pp and central AA • Rapidity – scaling with Npart changes in fragmentation region • Azimuthal – elliptic flow appears to scale with multiplicity • Particle ratios are reaching zero net baryon number, small mB • Broad features of particle production are consistent with soft nature of strong interactions • pp and pA collisions are very instructive • Theoretical models are assimilating new data • None simultaneously describe full set of systematics!

  32. Logarithmic rise Energy dependence of v2

  33. Statistical models • Braun-Munzinger et al. (hep-ph/0106066) - Follows curve for <E>/<N> = 1 GeV at freezeout - Usesphenomenologicalparameterization: J. Cleymans & K. Redlich,PRL 81 (1998) 5284

  34. I. Increase instrange/non-strangeparticle ratios II. Maximum isreached III. Ratios decrease (Strange baryonsaffected more stronglythan strange mesons) Strangeness production Lines of constant lS where: <E>/<N> = 1 GeV Braun-Munzinger et al.hep-ph/0106066

  35. (PRELIMINARY)STAR 130 GeV14% central (/p Mid-rapidity ratios (PRELIMINARY)STAR 130 GeV14% central (L/p Implications for ratios (*0.2) Braun-Munzinger et al.hep-ph/0106066

  36. X+/h- X-/K- (7% central) (Preliminary) STAR 130 GeV14% central data Sensitivity to multi-strange baryons Braun-Munzinger et al.hep-ph/0105229 Thermal fit resultsin T = 174 MeV Ratios Model getsK/p correct,but misseson X ratios!!! T (MeV) Statistical errors only

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