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Crossing a New Threshold First Results from the Relativistic Heavy Ion Collider

Crossing a New Threshold First Results from the Relativistic Heavy Ion Collider. Science is a wonderful thing if one does not have to earn one's living at it – Einstein (1879—1955). Motivation. Why Relativistic Heavy Ion Collisions? To study a hadronic matter at high energy density

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Crossing a New Threshold First Results from the Relativistic Heavy Ion Collider

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  1. Crossing a New Threshold First Results from the Relativistic Heavy Ion Collider Science is a wonderful thing if one does not have to earn one's living at it – Einstein (1879—1955)

  2. Motivation Why Relativistic Heavy Ion Collisions? To study a hadronic matter at high energy density Early universe Center of stars To study the deconfined state of QCD Where is the phase transition? What order is it? To study the Vacuum – Chiral symmetry restoration Origin of (hadronic) mass

  3. The Phase Space Diagram TWO different phase transitions at work! – Particles roam freely over a large volume – Masses change Calculations show that these occur at approximately the same point Two sets of conditions: High Temperature High Baryon Density Lattice QCD calc. Predict: Deconfinement transition Chiral transition Tc ~ 150-170 MeV ec ~ 0.5-0.7 GeV/fm

  4. Don’t Panic!!! - New Scientist most dangerous event in human history: - ABC News –Sept ‘99 "Big Bang machine could destroy Earth" -The Sunday Times – July ‘99 No… the experiment will not tear our region of space to subatomic shreds. - Washington Post – Sept ‘99 the risk of such a catastrophe is essentially zero. – B.N.L. – Oct ‘99 Apocalypse2 – ABC News – Sept ‘99 Will Brookhaven Destroy the Universe? – NY Times – Aug ‘99

  5. Welcome to BNL- RHIC!

  6. The Collisions The End Product

  7. The STAR Detector (Year-by-Year) Magnet Time Projection Chamber Coils Silicon Vertex Tracker * TPC Endcap & MWPC ZCal ZCal FTPCs (1 +1) Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter Central Trigger Barrel + TOF patch RICH * yr.1 SVT ladder • Year 2000, year 2001,year-by-year until 2003, installation in 2003

  8. How a TPC works 420 CM • Tracking volume is an empty volume of gas surrounded by a field cage • Drift gas: Ar-CH4 (90%-10%) • Pad electronics: 140000 amplifier channels with 512 time samples • Provides 70 mega pixel, 3D image

  9. Needle in the Hay-Stack! How do you do tracking in this regime? Solution: Build a detector so you can zoom in close and “see” individual tracks high resolution Clearly identify individual tracks Good tracking efficiency Pt (GeV/c)

  10. Triggering/Centrality • “Minimum Bias” ZDC East and West thresholds set to lower edge of single neutron peak. REQUIRE: Coincidence ZDC East and West • “Central” CTB threshold set to upper 15% REQUIRE: Min. Bias + CTB over threshold ~30K Events |Zvtx| < 200 cm Spectators – Definitely going down the beam line Participants – Definitely created moving away from beamline Several meters Spectators Zero-Degree Calorimeter Participants Impact Parameter Spectators

  11. Au-Au Event at 130 A-GeV Peripheral Event From real-time Level 3 display.

  12. Au- Au Event 130 A-GeV Mid-Central Event From real-time Level 3 display.

  13. Au -Au Event 130 A-GeV Central Event From real-time Level 3 display.

  14. STAR Pertinent Facts Field: 0.25 T (Half Nominal value)  worse resolution at higher p  lower pt acceptance TPC: Inner Radius – 50cm (pt>75 MeV/c) Length – ± 200cm ( -1.5< h < 1.5) Events: ~300,000 “Central” Events –top 8% multiplicity ~160,000 “Min-bias” Events

  15. Particle ID Techniques - dE/dx Resolution: dE/dx No calibration 9 % With calibration 7.5% Design 6.7% Even identified anti-3He ! dE/dx PID range: ~ 0.7 GeV/c for K/ ~ 1.0 GeV/c for K/p

  16. Particle ID Techniques - Topology X+ Decayvertices Ks p + + p - L  p + p - L  p + p + X-  L + p - X+L + p + W  L + K- L Vo “kinks”: K  + 

  17. STAR STRANGENESS! (Preliminary) K+ L̅ f K0s L X- X̅+ K*

  18. Physics Measurements • dN/dh for h- (|h|<= ~1.5) particle density, entropy • Flow early dynamics, pressure • p/p, L/L stopping • Particle spectra temperature, radial flow • Particle ratioschemistry • Particle correlations geometry, collective flow • High Pt jet quenching _ _ • Neutral particle decays L,K0s, X strangeness production

  19. The Serious Predictions >factor 2 variation in yields Radii increase from SPS R0/Rs >= 1.6 (long lifetime) Little Stopping – Net proton yield = 4 – 20 Transverse flow – Same a SPS - much higher Heavier particles not see flow

  20. Negative Hadrons:  Distribution and Multiplicity dN(h-)/dh = 264  1  18 (extrap. to all pt) At low end of predictions – Kills many models h- Increased particle production per participant pair: 43% compared to Pb+Pb @ 17.2 GeV 30% compared to pp @ 200 GeV More than just pp happening h- Full efficiency corrections

  21. Transverse Energy Phenix Electromagnetic Calorimeter measures transverse energy in collisions Central Events: Lattice predicts transition at PHENIX Preliminary ~ 5.0 GeV/fm3 ecritical ~ 0.5-0.7 GeV/fm3 Have the Energy Density!!

  22. Is there Thermalization? Look at “Elliptic” Flow Origin: spatial anisotropy of the system when created and rescattering of evolving system Almond shape overlap region in coordinate space

  23. Hydro Calculation of Elliptic Flow Hydro Calculations STAR PRL 86 (2001) 402 || < 1.3 0.1 < pt < 2.0 First time in Heavy-Ion Collisions a system created which approaches hydrodynamic model predictions • Flow: • A pressure build up -> Explosion with azimuthal asymmetry • zero for central events • Hydrodynamics: • Assumes continuum matter with local equilibrium • Locally equilibrated or “thermalized”. Equal energy density lines • Elliptic flow observable sensitive to early evolution of system • Large v2 is an indication of early thermalization P. Kolb, J. Sollfrank, and U. Heinz

  24. OK • Have a high enough energy density to cause transition • Have a source that is consistent with being thermalized and has a large elliptic flow • But what did we create?

  25. Baryon Stopping/Transport Anti-baryons - all from pair production Baryons - pair production + transported B/B ratio =1 - Transparent collision B/B ratio ~ 0 - Full stopping, little pair production Measure p/p, L/L , K-/K+ (uud/uud) (uds/uds) (us/us) _ _ _ _ - - - - - - - -

  26. _ p/p Ratio Ratio is flat as function of pt and y Slight fall with centrality Phys. Rev. Lett March 2001 Ratio = 0.65 ±0.03(stat) ±0.03(sys)

  27. Strange Baryon Ratios Reconstruct: Reconstruct: _ ~0.84 L/ev, ~ 0.61 L/ev ~0.006 X-/ev, ~0.005 X+/ev STAR Preliminary Ratio = 0.73 ± 0.03 (stat) Ratio = 0.82 ± 0.08 (stat)

  28. Anti-baryon/Baryon Ratios versus s _ _ ¯ _ _ _ _ _ Baryon-pair production increases dramatically with s – still not baryon free Pair production is larger than baryon transport STAR preliminary 2/3 of protons from pair production , yet pt dist. the same – Another indication of thermalization

  29. Simple Model Measure D=1.08± 0.08 Assume fireball passes through a deconfined state can estimate particle ratios by simple quark-counting models No free quarks so all quarks have to end up confined within a hadron Predict D=1.12 Predict D=1.12 System consistent with having a de-confined phase

  30. Kinetic Freeze-out and Radial Flow 1/mt d2N/dydmt Look at mt = (pt2 + m2 )distribution A thermal distribution gives a linear distribution dN/dmt  e-(mt/T) mt Slope = 1/T If there is transverse flow Slope = 1/Tmeas ~ 1/(Tfo+ 0.5mo<vt>2) Want to look at how energy distributed in system. Look in transverse direction so not confused by longitudinal expansion

  31. Increase with collision centrality  consistent with radial flow. mt slopes vs. Centrality mid-rapidity Tp = 565 MeV TK = 300 MeV Tp = 190 MeV

  32. Radial Flow: mt - slopes versus mass Naïve: T = Tfreeze-out + m  r 2 where  r  = averaged flow velocity • Increased radial flow at RHIC ßr (RHIC)  ßr (SPS/AGS) = 0.6c = 0.4 - 0.5cTfo (RHIC)  Tfo (SPS/AGS) = 0.1-0.12 GeV = 0.12-0.14 GeV

  33. Particle Ratios and Chemical Content mj= Quark Chemical Potential T = Temperature Ej – Energy of quark gj– Saturation factor Use ratios of particles to determine m, Tchand saturation factor

  34. Chemical Fit Results Not a 4-yields fit! s  1 2  1.4 Thermal fit to preliminary data: Tch (RHIC) = 0.19 GeV  Tch (SPS) = 0.17 GeV q (RHIC) = 0.015 GeV << q (SPS) = 0.12-0.14 GeV

  35. Chemical Freeze-out early universe LEP/ SppS 250 RHIC quark-gluon plasma 200 SPS AGS Lattice QCD deconfinement chiral restauration Chemical Temperature Tch [MeV] 150 thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 200 400 600 800 1000 1200 0 Baryonic Potential B [MeV] P. Braun-Munzinger, nucl-ex/0007021

  36. OK (2) • Shown that the collision region: • Some evidence that source is thermalized • Particles kinetically freeze-out with common T • Large transverse flow - • common to all species • Particles chemically freeze out earlier (higher T) • Near y axis on phase diagram • Relative particle production consitant with having • had free quarks

  37. Measuring the Source “Size” (HBT) 1D: overall rough “size” y1 x1 K y2 ~1 m x2 Rout Rside ~5 fm 3D decomposition of relative momentum provides handle on shape and time as well as size

  38. HBT and the Phase Transition with transition without transition “e” ec Generic prediction of 3D hydrodynamic models ~ emission timescale Rischke & Gyulassy NPA 608, 479 (1996) PrimaryHBT “signature” of QGP Phase transition  longer lifetime; Rout/Rside ~ 1 + (bt)/Rside

  39. Correlation function for identical bosons: 1d projections of 3d Bertsch-Pratt 12% most central out of 170k events Coulomb corrected |y| < 1, 0.125 < pt < 0.225 Two-particle interferometry (HBT) qout STAR preliminary qlong STAR preliminary

  40. Radii dependence on centrality and kt y (fm) x (fm) central collisions low kT p- p+ STAR preliminary • Radii increase with multiplicity - Just geometry (?) • Radii decrease with kt – Evidence of flow (?) “multiplicity”

  41. Pion HBT Excitation Function Compilation of world 3D -HBT parameters as a function of s STAR Preliminary • Central AuAu (PbPb) • Decreasing  parameter • Decreased correlation strength • More baryon resonances ? • Saturation in radii • Geometric or dynamic (thermal/flow) saturation • No jump in effective lifetime • No significant rise in size of the  emitting source • Lower energy running needed!

  42. The ROut/RSide Ratio Emission duration for transparent sources: STAR Preliminary Tomášik, Heinz nucl-th/9805016 =0.0 =0.5 opaqueness Small radii + short emission time + opaqueness short freeze-out

  43. K0s-K0s Correlations • No coulomb repulsion • No 2 track resolution • Few distortions from resonances • K0s is not a strangeness eigenstate - unique interference term that provides additional space-time information l = 0.7 ±0.5 R = 6.5 ± 2.3 K0s Correlation will become statistically meaningful once we have ~10M events

  44. “hard” probes: cc, bb and jets during formation phase parton scattering processes with large Q2 create high mass or high momentum objects penetrate hot and dense matter sensitive to state of hot and dense matter Hard Probes in Heavy-Ion Collisions vacuum QGP • a) formation phase • parton scattering • b) hot and dense phase • Quark Gluon Plasma • Hadron Gas • c) freeze-out • emission of hadrons color screening: J/y suppression dE/dx  jet quenching

  45. Negative Hadrons: pt - distributions Power Law A (1 + pt /p0) - n p0 = 2.74 ± 0.11 GeV/c n = 13.65 ± 0.42 STAR <pt> = 0.514 ± 0.012 GeV/c NA49 <pt> = 0.414 ± 0.004 GeV/c UA1 <pt> = 0.392 ± 0.003 GeV/c STAR preliminary Mean pt higher than SPS and pp

  46. “Hard” Scaling Nuclear Overlap Integral TAA = 26 mb-1 for 5% most central NAA / Npp= Nbin coll = 1050 “Soft” Scaling NAA / Npp= ( 344 / 2 ) Au+Au/pp: Compare pt - distributions STAR preliminary Jet Quenching: First hint for QGP formation at RHIC ?

  47. Mapping out “Soft Physics” Regime Net-baryon  0 at mid-rapidity! ( y = y0-ybeam ~ 5 ) Chemical parameters Chemical freeze-out appears to occur at same ~T as SPS Strangeness saturation similar to SPS Kinetic parameters Higher radial flow than at SPS Thermal freeze out same as at SPS Unexpected: small HBT radii Strong elliptic flow Pion phase-space density at freeze-out seems to be universal Promising results from “Hard Physics” pt spectra from central collisions show clear deviation from p-p extrapolation high-pt data are consistent with “jet quenching” predictions ! Conclusions More than we ever hoped for after the first run !!!

  48. The STAR Collaboration The Group Profs: PostDocs: Students: T.Humanic Me S.Bekele M.Lisa B.Neilson M.Lopez- Noriega E.Sugarbaker R.Wells R.Wilson Brazil: Universidade de Sao Paolo China:IHEP - Beijing, IPP - Wuhan England:University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt Poland:Warsaw University, Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR–Dubna, IHEP-Protvino U.S. Labs:Argonne, Berkeley, Brookhaven National Labs U.S. Universities:Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue,Rice, Texas A&M, UT Austin, Washington, Wayne State, Yale Institutions: 36 Collaborators: 415

  49. The  Phase Space Density STAR Preliminary Radius Fits STAR NA49 áfBE;flowñ T0=94.3 MeV T0=89.7 MeV áfBE;no flowñ T0=99.5 MeV T0=94.3 MeV T0=89.7 MeV pion occupation of cell in coordinatemomentum space: • “Universal” phase space density observed at SPS appears to hold at RHIC as well • Consistent with thermal distribution (T94MeV) and strong collective flow ( 0.58) • Fundamental phase space saturation may relate increases in geometry, temperature, multiplicity

  50. Calibration – Cosmic Rays Determine momentum resolution dp/p < 2% for most tracks

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