J. Burward-Hoy Department of Physics and Astronomy University at Stony Brook, New York

1. Mass-identified Particles Produced in s = 130 GeV Au-Au Collisions using the PHENIX Detector at RHIC J. Burward-Hoy Department of Physics and Astronomy University at Stony Brook, New York

2. Motivation Introduction to Relativistic Heavy Ion Collisions Introduction to RHIC The PHENIX Detector Identifying , K, p in PHENIX Data reduction and Corrections Single Particle Pt spectra Results Measured physics quantities Discussion Transition region between soft and hard physics Hydrodynamics model comparison (U. Heinz and P. Kolb) Conclusion Outline of Topics STAR event

3. Quark Gluon Plasma nuclei RHIC hadronization atoms ~few s now Physics Objective: nuclear matter under extreme conditionsNuclear Matter  Quark-Gluon Plasma Phase Create a hot region of high initial energy density 0 ~ few GeV/fm3 fm = 10-15 cm Quarks and gluons become unbound to form a Quark Gluon Plasma (QGP) Quarks and gluons coalesce into hadrons (hadronization) system expands and cools Detectors measure the produced hadrons and leptons probe transition region study properties of QGP

4. Collision Dynamics • low pt: soft processes • multiple rescattering • hydrodynamic behavior 0 R2 0 , K, p, anti-p carry most of energy collectively flow at t decouple at Tfo • high pt: hard processes • hard scattering, jets • pQCD

5. Longitudinal Rapidity y(E,pz) = 1/2 ln (E + pz/E - pz) Pseudorapidity () = -ln (tan (/2 ) Midrapidity y(E,0) = 0, (/2) = 0 Initial Total Energy E/A = mo Center of mass energy s = (p1 + p2) • (p1 + p2) s = 2mo ~ 130 GeV Relevant Kinematic Quantities  r = x2 + y2  beam axis +z y = 1 or  = 1 Transverse Transverse momentum pT = p sin  Transverse energy mT = pT2 +m02 Transverse Kinetic Energy mt - m0 p= (mTcoshy,pt cos ,pt sin ,mTsinhy) Energy and Momentum: p = (E,p)

6. Hydrodynamic Expansion Space-time Diagram of Expansion Contours of constant • proper time  = t2 -z2 • temperature T • number density n • entropy density s • energy density  Quarks/partons form at •  ~ 1 fm/c Hadronic matter (“liquid”) • collectively expands at t (surface velocity) Hadrons freeze-out at • temperature Tfo • radius ~ 6-7 fm/c (HBT)

7. Rapidity Distributions at RHIC: PHOBOS results • PHOBOS, nucl-ex/010600 • flat over at least 2 units of rapidity • symmetry along z  longitudinal boost invariance • hydrodynamic equations separable in longitudinal and transverse dimensions • transverse components independent of rapidity Reference: private communication with U. Heinz  ~ 4

8. The Relativistic Heavy Ion Collider • Two counter-rotating Au beams • 60 Au ion bunches • s apart • Year-1 •  ~ 70 for each beam • s = 130 GeV ~ 7 times higher CERN ~ 30 times higher AGS • Design value (Year-2) •  ~ 107 • s = 200 GeV

9. The PHENIX Detector -0.35 <  < 0.35,  = /2 TOF and DC:  ~ /4 Event and Trigger Selection BBC and ZDC both fire |zvtx| < 30 cm 4.5M min. bias events

10. 25-30% 20-25% /meastot(%) Events 0-5 7,895 5-15 15,188 15-30 22,684 30-60 45,643 60-92 47,860 min. bias 139,270 15-20% 10-15% 5-10% 0-5% Participant nucleons (Np) Collision axis Produced , K, p to central arm detectors Spectator nucleons To collision axis detectors Event centrality: how “head-on” is the collision? A. Denisov PHENIX uses a Glauber calculation to map centrality to number of participants

11. n1 b n2 Collision when b < inelnn / inelnn = 40 mb Number of Participants Model-dependent calculation called Glauber Thickness of nuclear matter direct path of each oncoming nucleon Inelastic nucleon-nucleon cross section determine if collision occurs ni A Woods-Saxon density profile distribution Reference: PHENIX Internal Analysis note

12. Detecting , K, p in PHENIX r z  ~ q/p y r 0 x DC main bend plane DC resolution p/p ~ 1%  3.5% p TOF resolution 115 ps pt = p sin(0) PC1 and Event vertex polar angle

13. The Track Model For each track, the track model. . . • Uses a field-integral look-up table • swim particles through measured magnetic field map with p, z0, 0 • numerically integrate the field integral values at each r • field-integral independent of momentum p > 2 GeV/c • resulting grid is 4D: z0, 0, r, p • Determines p, 0 ,0 • Determines the full trajectory in PHENIX • Calculates flight distance (length of trajectory) • Finds intersection points between trajectory and detectors • Projected points are then match to measured points

14. Require tracks to be 3D Project tracks to the TOF detector Define a search window and find a TOF hit In slices of momentum, determine (p,,z) Require tracks to be within 2 of a TOF hit Track Selection 3D tracks DC Tracks at TOF (p,z) (cm) (p,) (rad) p (GeV/c)

15. The mass-squared width: how particle identification is done. momentum p pathlength L m = p/ where  = L/ct time-of-flight t |mmeas2 - mcent2| < 2m22 Momentum resolution Time-of-Flight resolution H. Hamagaki

16. Sigma Mean p K  pt (GeV/c) Particle Identification m2 (GeV/c2)2 • Slice mass distribution in momentum • In each momentum slice, fit gaussian functions • Extract the mean for each momentum slice • Determine width of mass,  • Require particles to be within 2 of centroid p (GeV/c)

17. After Data Reduction (“raw” data) Centrality Selected Minimum Bias

18. Corrections to the Raw Spectra Used MC single particles and track embedding to correct for Tracking inefficiencies and momentum resolution Geometrical acceptance Decays in flight (’s and K’s) Correction is p and PID dependent Particle Acceptance 0.2 GeV/c -0.35 <  < 0.35

19. pt Spectra • measure (anti)p out to 3.5 GeV/c • Yield p   • pt ~ 1.5 - 2 GeV/c • Crossing region  as Np 

20. Transverse Kinetic Energy Spectra In the range mt - m0 < 1 GeV, fit to get effective temperature Teff

21. Effective Temperature If static thermal source, then spectra are parallel Minimum bias To measure the expansion parameters, use hydrodynamics parameterization. . .

22. (No QGP phase transition) t() 20 fm/c 2 fm/c  5 fm/c From Hydrodynamics:Radial Flow Velocity Profiles Velocity profile at  ~ 20 fm/c “freeze-out” hypersurface At each “snapshot” in time during the expansion, there is a distribution of velocities that vary with the radial position r Plot courtesy of P. Kolb

23. parameters normalization A freeze-out temperature Tfo surface velocity t 1/mt dN/dmt A Tfo t() mt f()   1 Hydrodynamics Parameterization 1/mt dN/dmt = A  f()  d mT K1( mT /Tfo cosh  ) I0( pT /Tfo sinh  ) t integration variable   radius r = r/R definite integral from 0 to 1 particle density distribution f() ~ const linear velocity profile t() = t surf. velocity t ave. velocity <t > = 2/3 t boost () = atanh( t() ) minimize contributions from hard processes fit mt-m0<1 GeV Ref: Sollfrank, Schnedermann, Heinz, et al

24. Hydrodynamic Parameterization 5% Most Central 2 Contours • Simultaneous fit to all • (mt -m0 )< 1 GeV • For  • Exclude resonances by fitting pt > 0.5 GeV/c • Including resonance region in pions: • Tfo ~ 104 MeV • Excluding resonance region: • Tfo ~ 121 MeV

25. Hydrodynamic Parameterization

26. Radial Flow and Number of Participants

27. Measuring the Yield and <pt> For all centralities: • Fit functions and integrate from 0 to  • Extrapolate function over unmeasured range • Add to data value in measured range • Extrapolated amount: •  30% • K 40% • (anti)p 25%  K p 5% most central

28. dN/dy and Participant Number Systematic uncertainty  ~ 13% K ~ 15% (anti)p ~ 14% • dN/dy scaled by Np pair • K and (anti)p scaled by 2 • nearly independent of Np • K and (anti)p dependence on • Ncoll NN binary collisions • Dashed lines • Systematic in Np (Glauber calculation)

29. <pt> and Participant Number Systematic uncertainty (anti)p ~ 8% K ~ 10%  ~ 7% • <pt> increases and saturates for all particles • most dramatic for p • compare with pp • interpolated to 130 GeV • open symbols at Np ~ 2 • similar to pp for most peripheral except (anti)protons • Need to measure pp and pA at RHIC

30. Particle Ratios and Np Independent of Np: • Negative to positive for , K, p Dependent on Np: K/ and p/+

31. Particle Ratios and pt 0.830.03 0.670.02 0.940.01

32. K+/+ and s NOTE: NA49 (CERN) measured yield integrated over y (different from NA44 at midrapidity)

33. Comparing apples to apples. ..y and  

34. Total Charged Multiplicity <0> ~ 5 GeV/fm3 This is 70% higher than at CERN-SPS energies

35. HIJING Spectra

36. HIJING  K p HIJING pt (GeV/c) HIJINGHeavy Ion Jet Interaction Generator No radial flow in HIJING 1/pt dN/dpt p crosses K

37. Relevant CERN SPS Observables Teff = Tfo + m<t>2 Teff depends on m0 radial flow Tfo A + A p + A < t> • Bjorken’s formula: • initial energy density • <0> ~ 1/R20 dEt/dy • <0> ~ 3 GeV/fm3 (NA49) System Size = A1 A2

38. CERN SPSRadial Flow Contribution to Hadron Spectra The spectra are well described by hydrodynamics. CERN Pb-Pb NA49: T ~ 120 MeV t ~ 0.55 20 MeV difference in Tfo due to resonances NA44: T ~ 140 MeV t ~ 0.55

39. Transition Between Soft and Hard Physicsat RHIC energies nucl-ex/0109003 QM Proceedings 2001

40. Hydrodynamics Model Comparison

41. Hydrodynamics Model Comparison

42. Conclusions • Significant p and pbar contribution to hadron spectra starting at ~ 1.5-2 GeV/c • crossing region increases with decreasing with Np • The data suggest sizeable radial flow at RHIC for the most central: Tfo ~ 12121 MeV t ~ 0.700.01 • Radial expansion decreases with decreasing number of participants • A hydrodynamics model (U. Heinz and P. Kolb) with Tfo fixed at 128 MeV describes the data • Consistent with measured radial flow from data • To measure jet quenching, hadron spectra should be measured • pt>2.5-3 GeV/c • At CERN-SPS energies soft physics dominate measured range. Should measure pt>5 GeV/c • Total dN/d is consistent with published results. Initial energy density is 70% greater than at CERN-SPS and is • consistent with PHENIX dEt/d of 5.0 GeV/fm3 • p/ and K/ increase with Np. • K+/+ for most central follows trend with s, most peripheral similar to pp

43. What the track model does in more detail. . . • assumes reconstructed track comes from z-vertex • uses reconstructed  to get p-guess and charge • uses z at DC (on reference radius) and z-vertex to calculate  (used as a guess to 0) • needs at least 2 X-wire hits in the drift chamber • uses 4D interpolation of field-integral grid to get the field-integral value (f) of each hit based on p-guess, z-vertex, 0-guess and r • fits a line to the hits in f and  to get p and 0 • repeat iteratively four times • at the reference radius of the drift chamber • uses 3D interpolation to get field-integral values in r-z plane based on p and 0 • calculates 0 at the vertex and  at DC

44. Two planes: r-phi and r-z y  i = 0 + qfi/p fi, i  0 DC  r  x  =  +  r = 220 cm o =  - g/p o z zed Z vertex

45. 2 (Tfo,t) Contours PHENIX Preliminary PHENIX Preliminary  positive negative PHENIX Preliminary PHENIX Preliminary K PHENIX Preliminary PHENIX Preliminary p

46. 5-15% Centrality

47. 15-30% Centrality

48. 30-60% Centrality

49. 60-92% Centrality

50. The H2H Model Comparison (Hydro 2 Hadrons)D. Teaney, E. Shuryak, et. al. flowing hadronic fluid AND particle cascade uses Hydrodynamics + Relativistic Quantum Molecular Dynamics (RQMD) cascade more constrained  predictive power no scaling of nucleons to match data 0 ~ 16.75 GeV/fm30 ~ 1.0 fm/c p/p ~ 0.5 <0> ~ 10.95 GeV/fm3 , K Tfo ~ 135 MeV <t > ~ 0.55 nucleons ~ 120 MeV <t > ~ 0.6 5% central NOTE: includes weak decays