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Hadron p T Spectra by PHOBOS from 0.03 to 6 GeV/c

This study focuses on the analysis of hadron pT spectra in different collision systems and their dependence on flavor. The importance of centrality and rapidity dependence is also highlighted. The PHOBOS detector and its capability for low pT measurements are discussed, along with comparisons to other experimental data and event generators.

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Hadron p T Spectra by PHOBOS from 0.03 to 6 GeV/c

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  1. Hadron pT Spectra by PHOBOS from 0.03 to 6 GeV/c 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

  2. 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 LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER Gábor I. Veres

  3. Outline • Hadron pT-spectra: why and how to study them? • The extremes: low and high pT • 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 Gábor I. Veres

  4. Longitudinal and Transverse Dynamics dNch/dh • High pT • Suppression, E loss, quenching… • Initial/final state effects (different systems) • “hard” physics (Ncoll?) Low pT • Probing long distances • Radial flow • “soft” physics (Npart?) Gábor I. Veres

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

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

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

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

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

  10. F E D C B A X[cm] Beam pipe Z[cm] Finding very low pT particles Search for particles stopping in the 5th spectrometer plane Mass measurements (‘energy-range’ method) 20 • Cuts on dE/dxper plane mass hypothesis 10 0 • Cuts on Eloss(Ek=kinetic energy) momentum hypothesis 0 10 20 Z [cm] • Corrections acceptance, efficiency absorption, background MC P Ek=21 MeV K Ek=19 MeV dE/dx  Ek= 8 MeV • Eikin=dEi+dEi+1+dEi+2… • Mip= dE/dxi * Eikinm • (1/2) ( m2) A B C D E Gábor I. Veres silicon plane

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

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

  13. Tfit: + - 0.2290.005 K + K- 0.2930.010 p + p 0.3920.015 Comparison to the Spectra Measured at Intermediate pT Range Fit PHENIX spectra (nucl-ex/0307022) for mT<1GeV/c2: PHENIX - open symbols PHOBOS –closed symbols +1 for baryons -1 for mesons 1/[exp(mT/Tfit)±1] Fits: solid curves Extrapolations: dashed curves Log scale! Extrapolation of the fits to low pT agrees with our low-pT yields. Tfit increases with mass  consistent with the collective transverse expansion Gábor I. Veres

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

  15. I. Low pT: Summary • No enhancement of low pT yields is observed (compared to • extrapolations ofintermediate pT spectra). • Spectra flatten at low pT transverseexpansion • Constraints for models and integrated yields. Future (high statistics Au+Au run): • Centrality dependence of the low pT yields • Negatively charged particle yields • Attempt to measure BE correlations at very low mT Gábor I. Veres

  16. II. High-pT spectra. Tracking z By 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 2 1 x 10 cm Very clean track sample with high efficiency Gábor I. Veres

  17. High-pT spectra: acceptance Acceptance Momentum 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 Gábor I. Veres

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

  19. Why Centrality Matters? L~A1/3 “Participant” Scaling Ncoll Npart/2 ~ A Npart b [fm] Ncoll= # of NN collisions: ~A4/3 “Collision” Scaling Gábor I. Veres

  20. 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) x 10-1 x 10-2 x 10-3 x 10-4 x 10-5 (h++h-)/2 0.2<yp<1.4 0.2<y<1.4 PHOBOS-Spectra @ 200GeV Au+Au Phys.Lett. B 578 (2004) 297 (GeV/c)-2 Gábor I. Veres

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

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

  23. Is Suppression an Initial or Final State Effect? Strong suppression of hadron yields at high pT! • 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 Gábor I. Veres

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

  25. PHOBOS Results from d+Au Centrality <Npart> <Ncoll> 70-100% 3.30.7 2.20.6 40-70% 6.70.9 5.40.8 20-40% 10.90.99.70.8 0-20% 15.51.014.60.9 Gábor I. Veres

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

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

  28. No high-pT 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) Gábor I. Veres

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

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

  31. Evolution of RdAu withh Gábor I. Veres

  32. II. Inclusive pT spectra: Summary • Charged hadron spectra measured in d+Au and Au+Au collisions vs. pT and centrality • High-pT suppression in Au+Au observed (compared to Ncoll 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! Gábor I. Veres

  33. III. Identified Hadrons Motivation: • 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 (mT) Important to compare more elementary (d+Au) and heavy ion (Au+Au) collisions • Antiparticle/particle ratios as a function of Npart and pT • Identified particle spectra Gábor I. Veres

  34. 70 1 60 MP (10-3GeV2/cm) 50 40 0 0 5 10 15 20 25 30 ETOT (MeV) 0 5 4 2 3 1 p (GeV/c) Particle ID from low to high pT PHOBOS PID Capabilities 1/v (ps/cm) Stopping particles dE/dx TOF 5.0 0.5 0.05 pT (GeV/c) Gábor I. Veres

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

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

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

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

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

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

  41. Upgrades in PHOBOS for the d+Au run (2003) TOF TOF mini-pCal d+Au, p+p T0 Response to Importance of High PT Studies SPECTRIG T0 pCal • Moved TOF walls far (5 m) from IP • New, on-line high pT 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!) Au+Au Gábor I. Veres

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

  43. 70 60 50 1/v (ps/cm) 40 30 0 5 4 2 3 1 p (GeV/c) High statistics d+Au track sample p p K positives, 1.6<p<1.8 GeV/c p p K Gábor I. Veres

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

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

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

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

  48. 2 2 2 mT=m +pT Identified mT-spectra in d+Au Scale uncertainty: 15% Not feed-down corrected Gábor I. Veres

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

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

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