1. Gábor I. Veres Massachusetts Institute of Technology for the Collaboration International Workshop on Hot and Dense Matter in Relativistic Heavy Ion Collisions March 24-27, 2004, Budapest Hadron p T Spectra by PHOBOS from 0.03 to 6 GeV/c

2. Gábor I. Veres Collaboration (March 2004) Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Michael Ricci, Christof Roland, Gunther Roland, Joe Sagerer, Helen Seals, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Siarhei Vaurynovich, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch ARGONNE NATIONAL LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

3. Gábor I. Veres Outline  Hadron p T -spectra: why and how to study them?  The extremes: low and high p T  Small (d+Au) to large (Au+Au) colliding systems  Flavour dependence – charged and identified hadron spectra. Particle ratios.  Importance in the details: centrality and rapidity dependence

4. Gábor I. Veres Low p T  Probing long distances  Radial flow  “soft” physics (N part ?) Longitudinal and Transverse Dynamics High p T  Suppression, E loss, quenching…  Initial/final state effects (different systems)  “hard” physics (N coll ?) dN ch /d 

5. Gábor I. Veres The PHOBOS Detector (2001) 137000 Silicon Pad Channels 1m 12m Be Beampipe Spectrometer Octagon Vertex Ring Counters Paddle Trigger Counter Čerenkov Counter DX magnetDX Magnet ZDC NIM A 499, 603-623 (2003) Au+Au

6. Gábor I. Veres Octagon & Vertex Spectrometer arm Ring Silicon Detectors

7. Gábor I. Veres dN/dp T PID Mass +Charge 0.03 0.2 1.0 p T, GeV/c up to 6 GeV/c Stopping in Si dE/dx in Si ToF+Si Si Mass near mid-rapidity Z ToF Spectra and PID in Charge

8. Gábor I. Veres Yields of (  + +   ), (K + + K  ), (p + p) p T = 30 – 200 MeV/c (depending on particle mass) I. Hadrons in the low p T range Negligible B field + multiple scattering: charge sign cannot be measured  Probing long distances (truly non-perturbative QCD regime)  Radial flow  DCC (enhanced pion yields??)  Dynamical fluctuations at phase transition??

9. Gábor I. Veres PHOBOS Capability of Low p T Measurements z -x 10 cm y 70 cm B=2T Drawback: Advantages:  Sensitive detector layers close to the IP  Little material between the IP and Si layers  High segmentation of the Si detectors  small acceptance of the spectrometer

10. Gábor I. Veres Mass measurements (‘energy-range’ method)  Cuts on dE/dx per plane mass hypothesis X[cm ] A B C D E F Z[cm] Beam pipe 0 10 20 0 10 20 Z [cm] Search for particles stopping in the 5 th spectrometer plane A B C D E dE/dx  E k = 8 MeV P E k =21 MeV K E k =19 MeV  Cuts on E loss (E k =kinetic energy) momentum hypothesis E i kin =dE i +dE i+1 +dE i+2 … M i p = dE/dx i * E i kin  m (  1/  2 ) (  m  2 )  Corrections acceptance, efficiency absorption, background silicon plane Finding very low p T particles MC

11. Gábor I. Veres Test of the method: Reconstruction of low momentum MC particles Au+Au  s NN =200 GeV 15% central MC Measuring particle mass p+p K++K–K++K– ++ ++ DATA

12. Gábor I. Veres Au+Au  s NN =200 GeV 15% central -0.1< y <0.4 Invariant yields (Au+Au) ++++ K + +K – p+p nucl-ex/0401006, submitted to PRL  Momentum and energy: From carefully calibrated MC  Yields: binned in p T and corrected

13. Gábor I. Veres Comparison to the Spectra Measured at Intermediate p T Range PHENIX - open symbols PHOBOS –closed symbols Log scale! Fit PHENIX spectra (nucl-ex/0307022) for m T <1 GeV/c 2 : +1 for baryons -1 for mesons Fits: solid curves Extrapolations: dashed curves T fit :   +  - 0.229  0.005 K  + K - 0.293  0.010 p + p 0.392  0.015 Extrapolation of the fits to low p T agrees with our low-p T yields. T fit increases with mass  consistent with the collective transverse expansion 1/[exp(m T /T fit )±1]

14. Gábor I. Veres Model Comparisons Event generators are not able to consistently describe low p T yields. HIJING overpredicts all yields

15. Gábor I. Veres I. Low p T : Summary  No enhancement of low p T yields is observed (compared to extrapolations of intermediate p T spectra).  Spectra flatten at low p T transverse expansion  Constraints for models and integrated yields.  Centrality dependence of the low p T yields  Negatively charged particle yields  Attempt to measure BE correlations at very low m T Future (high statistics Au+Au run):

16. Gábor I. Veres II. High-p T spectra. Tracking x 10 cm 1 2 ByBy z Beam 1) find straight tracks in the field- free region 2) curved tracks found in B field by clustering in (1/p,  ) space 3) Pieces matched 4) Momentum fit using the full track, and detailed field map 5) Quality cuts, DCA cuts Very clean track sample with high efficiency

17. Gábor I. Veres High-p T spectra: acceptance AcceptanceMomentum resolution 2001 Au+Au run (200 GeV): Data Sample:  7.8 M minimum bias Au+Au events (2004: over 200 M)  32 M reconstructed particles

18. Gábor I. Veres Data+MC N part Triggering on Collisions & Centrality HIJING + GEANT Model of paddle trigger Data Centrality Determination %  (dN ch signal) %  (N part, N coll, b) 3% uncertainty in  TOT (trigger efficiency)  less than 10% uncertainty in N part for N part >100 Paddle Signal (a.u.)

19. Gábor I. Veres “Participant” Scaling N coll = # of NN collisions: ~A 4/3 L~A 1/3 N part /2 ~ A “Collision” Scaling Why Centrality Matters? N coll N part b [fm]

20. Gábor I. Veres PHOBOS-Spectra @ 200GeV Au+Au  Spectra corrected for Acceptance/efficiency Ghost tracks Momentum resolution Variable bin width Secondaries, feed-down  At 200 GeV, min. bias p+p reference data exists (UA1) (GeV/c) -2 0.2<y   <1.4 x 10 -1 x 10 -2 x 10 -3 x 10 -4 x 10 -5 0.2<y  <1.4 (h + +h - )/2 Phys.Lett. B 578 (2004) 297

21. Gábor I. Veres Scaled Au+Au Spectra / p+p-Fit 344 ± 11 276 ± 9 200 ± 8 138 ± 6 93 ± 5 65 ± 4 0-6% 6-15% 15-25% 25-35% 35-45% 45-50% Centrality Centrality range: from 10 to 3 fm from 3 to 6 Phys.Lett. B 578 (2004) 297

22. Gábor I. Veres Evolution with Centrality (Au+Au)  gradual change of shape  peak develops at 1.5 GeV/c Phys.Lett. B 578 (2004) 297 Spectra normalized to a fit to the p T spectrum at N part = 65 (most peripheral bin) Low and high p T : approximate scaling with N part

23. Gábor I. Veres Is Suppression an Initial or Final State Effect? Strong suppression of hadron yields at high p T !  high density strongly interacting matter (final state)? OR  multi-partonic effects in the nuclear wave-function (initial state)? Turn off final state to discriminate between the two scenarios  d+Au collisions

24. Gábor I. Veres Predictions for d+Au Vitev, Phys.Lett.B 562 (2003) 36 Vitev and M.Gyulassy, Phys.Rev.Lett. 89 (2002) Kharzeev, Levin, McLerran, Phys.Lett.B 561 (2003) 93 “~30%suppression of high p T particles” (central vs peripheral) 16% increase central vs peripheral Parton Saturation (initial state) pQCD (final state)

25. Gábor I. Veres PHOBOS Results from d+Au Centrality 70-100% 3.3  0.7 2.2  0.6 40-70% 6.7  0.9 5.4  0.8 20-40% 10.9  0.9 9.7  0.8 0-20% 15.5  1.0 14.6  0.9

26. Gábor I. Veres Cronin Effect in d+Au vs. Centrality 6% most central Au+Au Phys.Rev.Lett. 91, 072302 (2003) peripheral central

27. Gábor I. Veres PRL 91, 072302 (2003)

28. Gábor I. Veres No high-p T suppression at y~0 in d+Au Initial state effects may show up at HIGHER rapidities?! (small-x region of the Au nucleus is probed)

29. Gábor I. Veres Cronin Effect as a Function of  (d+Au) - all centrality bins together -

30. Gábor I. Veres Cronin Effect as a Function of  (d+Au) - all centrality bins together -

31. Gábor I. Veres Evolution of R dAu with 

32. Gábor I. Veres II. Inclusive p T spectra: Summary  Charged hadron spectra measured in d+Au and Au+Au collisions vs. p T and centrality  High-p T suppression in Au+Au observed (compared to N coll scaling)  Control experiment: d+Au spectra Suppression is not an initial state effect (strongly interacting quark-gluon liquid?) Latest findings show suppression at high rapidities in d+Au!

33. Gábor I. Veres  Antiparticle/particle ratios as a function of N part and p T  Identified particle spectra III. Identified Hadrons  Flavour dependence of the effects shown  Baryon transport in small and large systems  Properties of the system at chemical freezeout  Scaling features of different species (m T ) Important to compare more elementary (d+Au) and heavy ion (Au+Au) collisions Motivation:

34. Gábor I. Veres p T (GeV/c) 0.05 0.5 5.0 Stopping particles dE/dxTOF Particle ID from low to high p T PHOBOS PID Capabilities 1 23 4 50 p (GeV/c) 30 40 50 60 70 1/v (ps/cm) 0 5 10 15 20 25 E TOT (MeV) 0 1 M P (10 -3 GeV 2 /cm)

35. Gábor I. Veres z -x 10 cm y 70 cm Reversible 2T magnetic field Two symmetric spectrometer arms  Independent measurements  Acceptance & efficiency corrections cancel B=2T Antiparticle to particle ratios in Au+Au Careful corrections for feed-down, absorption in the material, secondaries

36. Gábor I. Veres / = 1.025 ± 0.006(stat.) ± 0.018(syst.) / = 0.95 ± 0.03(stat.) ± 0.03(syst.) / = 0.73 ± 0.02(stat.) ± 0.03(syst.) Au+Au  s NN = 200 GeV, 12% most central High precision measurements Corrections to the measured ratios : +3.7% absorption +0.7% secondary negligible -1.2% feed-down p/p K - /K +  - /  + Result: ratios at  s NN = 200 GeV Au+Au Phys.Rev.C 67, 021901R, 2003

37. Gábor I. Veres d+Au: =N coll /N part d Particle Ratios Using dE/dx PID Submitted to Phys.Rev.C, nucl-ex/0309013 PHOBOS 200 GeV Mean number of collisions per projectile nucleon

38. Gábor I. Veres...p/p Compared to Models (p+p, d+Au) 200 GeV PHOBOS Preliminary Mean number of collisions per projectile nucleon

39. Gábor I. Veres Particle Ratios Using dE/dx PID PHOBOS 200 GeV Subm. to Phys.Rev.C nucl-ex/0309013 Au+Au: =N coll /(N part /2) d+Au: =N coll /N part d Mean number of collisions per projectile nucleon

40. Gábor I. Veres Identified spectra in d+Au Only ToF wall can identify above 1 GeV momentum in PHOBOS Many experimental challenges to solve 1.) high p T -reach desired 2.) high collision rate (10-100 kHz) and low multiplicity in d+Au, p+p x150 – x500 improving TOF RESOLUTION:  new start time detector  increased distance from interaction point improving STATISTICS:  new high-p T trigger system (x15 – x50)  DAQ upgrade (x10)

41. Gábor I. Veres SPECTRIG T0 mini-pCal pCal  Moved TOF walls far (5 m) from IP  New, on-line high p T Spectrometer Trigger  New start-time (T0) Čerenkov detectors  On-line vertexing and ToF start time  Forward proton calorimeters on Au and d sides  DAQ upgrade (x10 higher rate!) Response to Importance of High P T Studies Upgrades in PHOBOS for the d+Au run (2003) Au+Au d+Au, p+p TOF

42. Gábor I. Veres Trigger detectors (d+Au) Segmented scintillator detectors at 45 and 90 degrees from beam line Combined with the ToF walls:  selects events with particle hitting ToF and SpecTrig walls  enhances high-p T (straight) tracks: “online” tracking  decision-making in 50 ns SpecTrig ToF rejected accepted

43. Gábor I. Veres High statistics d+Au track sample 1 23 4 50 p (GeV/c) 30 40 50 60 70 1/v (ps/cm) p K  positives, 1.6<p<1.8 GeV/c p K 

44. Gábor I. Veres Particle/Antiparticle Ratios using the TOF d+Au T per projectile nucleon

45. Gábor I. Veres Identified p T -spectra in d+Au Not feed-down corrected Scale uncertainty: 15%

46. Gábor I. Veres Particle Composition in d+Au Not feed-down corrected

47. Gábor I. Veres Comparison: Low Energy d+Au Cronin, PRD 11, 3105 (1975) -0.1< <0.2 y y 0.2< <1.2 -0.5< <-0.2 y  lab =3.26 Not feed-down corrected

48. Gábor I. Veres Identified m T -spectra in d+Au Scale uncertainty: 15% m T =m +p T 222 Not feed-down corrected

49. Gábor I. Veres Identified m T -spectra at 200 GeV Subm. to Phys.Rev.Lett. nucl-ex/0401006 d+Au Scale uncertainty: 15% Not feed-down corrected Au+Au Spectra normalized at 2 GeV/c 200 GeV 

50. Gábor I. Veres 22 PHOBOS Preliminary (no feed-down corrections) Identified m T -spectra at 200 GeV d+Au Scale uncertainty: 15% Not feed-down corrected Au+Au Spectra normalized at 2 GeV/c 200 GeV  Subm. to Phys.Rev.Lett. nucl-ex/0401006

51. Gábor I. Veres III. Identified Hadrons: Summary PHOBOS has PID coverage from 0.03 to 3.5 GeV/c in p T  First PID ratios and spectra shown from the PHOBOS TOF  Surprisingly small centrality dependence of p/p ratios  Approximate m T scaling in d+Au as opposed to Au+Au  Particle composition in d+Au: similar p T -dependence to lower energy data (but different overall proton fraction)

52. Gábor I. Veres Outlook Future of the PHOBOS hadron spectra program:  Further R AA measurements Energy scan (63 GeV, …?) Species scan (Cu+Cu ? Si+Si ?)  Identified spectra in p+p and Au+Au at 200GeV  Charged spectra at very low p T with charge separation …and many other observables besides spectra!

53. Gábor I. Veres