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ANISOTROPIC FLOW MEASUREMENTS IN ALICE

ANISOTROPIC FLOW MEASUREMENTS IN ALICE. Sudhir Raniwala for the ALICE collaboration. Department of Physics University of Rajasthan Jaipur. PROLOGUE. ALICE Letter of Intent in 1993: motivated by results from relativistic heavy ion collisions from AGS and

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ANISOTROPIC FLOW MEASUREMENTS IN ALICE

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  1. ANISOTROPIC FLOWMEASUREMENTS IN ALICE Sudhir Raniwala for the ALICE collaboration Department of Physics University of Rajasthan Jaipur

  2. PROLOGUE • ALICE Letter of Intent in 1993: motivated by • results from relativistic heavy ion collisions from AGS and • results from ultra-relativistic heavy ion collisions at SPS • ALICE Technical Proposal: 1995 • summary of proposed signals listed in chapter 1 • open charm production to study parton kinematics • prompt photons for thermal radiation • high pT hadrons for energy loss in plasma • J/ψ production to probe deconfinement • Strangeness production and chiral symmetry restoration • multiplicity fluctuations and critical phenomena • particle ratios for probing evolution • line shape parameters for probing evolution • interferometry to determine freeze-out radius • Flow was not a consideration for the experiment, or its design…… Sudhir Raniwala

  3. INTRODUCTION • Jean-Yves Ollitrault’s suggestion (1992): • Finite impact parameter collisions => anisotropic spatial density; unequal pressure gradients (assuming thermalisation) produces an anisotropic momentum distribution of particles. The strength of the anisotropy, and its systematic dependence on various parameters, provides information on the equation of state. • Flow at the SPS energies was first reported by WA93 experiment (PL B403 (1997) 390). Measurement included contribution from non-flow  • Discovery of flow at higher energies…… the essence: • realisation of existence of a reaction plane in AA collisions at high energies • One of the first results published at RHIC were on observation of flow. Sudhir Raniwala

  4. RESULTS FROM SPS AND RHIC WA98 Collaboration, EPJ C41 (2005) 287 • SPS • Consistent results(WA98, NA49, CERES), v2 = v2 (pT, y, part-id, b) STAR Collaboration PR C72 (2005) 014904 • RHIC • ~Consistent results • pT dependence shows 3 regions • Low pT => hydrodynamics • Intermediate pT => quark coalescence • High pT => hard scattering, parton energy loss Sudhir Raniwala

  5. IDEAL MEASUREMENTS • v2 = v2 (pT, y, particle-id) for each event => complete event shape. • Measure v2 = v2 (s, pT, y, particle-id, b), an average event shape (just need azimuthal angle) • Different techniques with relative merits • Reaction Plane Method • Cumulants • Lee Yang Zeroes • General rule: more is the multiplicity and flow, better is the determination • What values do we expect at LHC? Sudhir Raniwala

  6. SCALING OF MULTIPLICITY Chargedmultiplicityis parametrizedasafunctionofNpart where : λ= 0.288 GBW parameter δ = 0.79 ± 0.02 fit parameter N0 = 0.47 overall normalization The model perfectly fits RHIC data, and can be easily extrapolated to LHC energy Result for PbPb, expect dN/dη ~ 2000 for central PbPb at LHC. Armesto,Salgado,Wiedemann – PRL 94 (2005) 022002 Sudhir Raniwala

  7. EXPECTED v2 at LHC Heinz, Kolb, Sollfrank Hirano et al , nucl-th/0701075v2 Hirano, to check reference…. N.Borghini and U.A.Weidemann, J.Phy.G 35 (2008) 023001 Sudhir Raniwala

  8. FLOW MEASUREMENTS IN ALICE • TPC (-0.9 < η < 0.9) • ITS: SPD(-2 < η < 2 (layer 1)) • FMD(-3.4 < η < -1.7, 1.7 < η < 5.0) • PMD (2.3 < η < 3.5) • ZDC (beam rapidity) • And everything else, once the reaction plane is known  • Measure in the range -3.4 < η < 5.0 • Fairly good particle identification over large range. Details in poster by Naomi (P-127) • Feasibility of measurements: • Full simulation(ALIROOT) • Independent simulations (a) generator level (b) fast simulation folding detector response • Variety of combination of multiplicity and v1 (for ZDC) v2 (for others) Sudhir Raniwala

  9. Designed for dN/dη ~ 8000 Maximum occupancy throughout the volume varies between 15% - 40% Momentum resolution ~1-2% for particles with momentum 100 MeV/c to 1 GeV/c Particles up to 100 GeV/c will be tracked with a 10% resolution (combined tracking including ITS and TRD) -0.9 < η < 0.9 Sudhir Raniwala

  10. RECONSTRUCTION ABILITY &TWO PARTICLE NON-FLOW CORRELATIONS Poster by Naomi van der Kolk (P-127) Sudhir Raniwala

  11. Layer 1 ׀η׀ < 2.0 Layer 2 ׀η׀< 1.4 • SPD alone useful for low mult. events, and has higher acceptance (low pT threshold ~15 MeV) • Simulations suggest • flow for negative and positively charged particles separately • coarse pT binning may be possible T. Virgili Sudhir Raniwala

  12. FLOW USING THE FMD C.Nygaard (Master’s Thesis) Can reconstruct v2 to better than 10% accuracy. Sudhir Raniwala

  13. Directed Flow and Zero Degree Calorimeter • Reaction Plane best determined by measuring spectator neutrons • Good check on estimated second order event plane. • Estimate independent (or less dependent) of eccentricity arguments • Minimal non-flow effects because of large rapidity gap • Estimate independent of details of evolution of hot and dense matter • Estimate will yield sign of elliptic flow • Need to measure this away from mid-rapidity • Experience from RHIC suggests values of ~ 20% • Can ALICE do it? • Poster: Nora de Marco (P-190) Sudhir Raniwala

  14. First order Event Plane Estimate 1st-order Event Plane Resolution v/s Centrality 50000 Pb-Pb minimum bias events at 2.76 TeVA have been simulated by means of HIJING generator. A fast simulation takes into account nuclear fragmentation, Fermi momentum, beam parameters, detector smearing and directed flow of spectator neutrons. full event plane resolution (2 arms) sub-event plane resolution (1 arm) The reconstructed resolution is same (Poster P-190, Nora de Marco) Sudhir Raniwala

  15. FLOW USING THE PMD • Determine the event plane: accurate resolution • For 5% flow and multiplicity 2400 in PMD (1.8 <η < 2.6) • No Scattering Moderate Scattering • Expected Resolution 0.831 0.808 • Estimated Resolution 0.836 +/- 0.002 0.812 +/- 0.003 WA98 Collaboration, EPJ C41 (2005) 287 Measure pT integrated flow for photons (low pT threshold, deduce for neutral pions?) Sudhir Raniwala

  16. ANISOTROPIC EMISSION OF J/Ψ IN FORWARD RAPIDITY USING EVENT PLANE FROM PMD • Away from midrapidity • Glauber absorption isotropic and comover absorption anisotropic • =>v2 (J/ψ ) ~ - 0.025 (Heiselberg and Mattielo PRC60 (1999) 44902) • J/ψ from dimuon channel • measured in DiMuon Spectrometer( – 4.0 < η < -2.5) • Data taking rate of PMD and DiMuon Spectrometer is same • Hijing parametrisation, folding detector response • Luminosity 5. 1026 (Results for 106 seconds of running) • Different centralities Sudhir Raniwala

  17. INVARIANT MASS SPECTRA OF LIKE SIGN AND UNLIKE SIGN MUONS Sudhir Raniwala

  18. BACKGROUND SPECTRA IN 12 AZIMUTHAL BINS Sudhir Raniwala

  19. Flow in unlike sign pairs Signal in 12 bins Wider mass region => lower S/B => lower flow v2 = v2meas (1+S/B)/(S/B) Sudhir Raniwala

  20. RESULTS DETERMINE “REQUIRED SIGNIIFICANCE” Significance depends upon large number of factors Significance α√Nevts Significance ~ 0.7 / (v2* f) To measure 5% flow with 10% accuracy requires a significance of ~140 for a given S/B. To probe 2.5% flow with similar accuracy will require 4 times as many events. Sudhir Raniwala

  21. EPILOGUE • Though none of the ALICE sub-detectors were initially designed keeping flow in mind, ALICE is now ready to measure flow and every other signal with respect to the reaction plane. Sudhir Raniwala

  22. BACK UP SLIDES Sudhir Raniwala

  23. CONCLUSIONS Sudhir Raniwala

  24. E.Simili Sudhir Raniwala

  25. ZN ALICE Zero Degree Calorimeter The 2 neutron zero degree calorimetersZNs have full acceptance for spectator neutrons (ZN > 8.7). GEANT-based simulation The 2x2 ZN segmentation gives a rough localization of the spectator neutron’s spot on the front face of the calorimeter. This localisation provides the first order event plane (spectator neutrons) Sudhir Raniwala

  26. ESD RECONSTRUCTION ABILITY E.Simili Sudhir Raniwala

  27. FLUCTUATIONS A ALICE PPR Large multiplicity environment enables determination of fluctuations….. Sudhir Raniwala

  28. Sudhir Raniwala

  29. Sudhir Raniwala

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