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The Quest for Quark-Gluon Plasma Global Observables at RHIC with an outlook to LHC

STAR. The Quest for Quark-Gluon Plasma Global Observables at RHIC with an outlook to LHC. Julia Velkovska. Outline for all 3 lectures. The QGP phase transition and the properties of the produced medium The questions we want to ask The experimental observables at hand

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The Quest for Quark-Gluon Plasma Global Observables at RHIC with an outlook to LHC

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  1. STAR The Quest for Quark-Gluon PlasmaGlobal Observables at RHIC with an outlook to LHC Julia Velkovska

  2. Outline for all 3 lectures • The QGP phase transition and the properties of the produced medium • The questions we want to ask • The experimental observables at hand • A survey of (selected) results from global observables and what we learned so far • Experimental methods– for each measured quantity ! • Outlook to LHC and RHIC II Julia Velkovska

  3. Interesting questions • Is the energy density at RHIC high enough for nuclear matter to undergo a phase transition? • Measure transverse energy and multiplicity of particle production • Is the matter thermalized ? Can we determine the timescale of equilibration? What is the pressure and can we determine EoS ? • Elliptic flow • What is the temperature ? • Particle abundances, particle spectra • How does the matter respond to a fast parton moving through it • Jets and jet quenching, jet correlations Julia Velkovska

  4. 2 counter-circulating rings 2.4 miles circumference 1740 super conducting magnets Collides any nucleus on any other Top energies: 200 GeV Au-Au 500 GeV polarized p-p Four experiments: BRAHMS, PHOBOS PHENIX, STAR The Relativistic Heavy Ion Collider RHIC 2000 Run Au+Au snn = 56, 130 GeV RHIC 2001-2 Au+Au & p+p Run snn = 200 , 19 GeV RHIC 2003 d+Au & p+p Run snn = 200 GeV RHIC 2004 Au+Au & p+pRun snn = 200 GeV, 62 GeV RHIC 2005 Cu+Cu Run snn = 200 GeV, 62, 22 GeV RHIC 2006 p+p Run snn = 200 GeV Julia Velkovska

  5. The Big Experiments in Real Life Undergoing upgrades. Will take data into the RHIC II stage STAR specialty: large acceptance measurement of hadrons PHENIX specialty: rare probes, leptons, and photons Julia Velkovska

  6. Phobos and Brahms • Brahms: good PID, small acceptance, movable spectrometer • Phobos: Si based spectrometer, PId by TOF and dE/dx in Si, large rapidity coverage Julia Velkovska

  7. Lattice QCD – QGP phase transition eSB = nfp2 /30 T4 TC ~ 155-175 MeV eC ~ 0.3-1.0 GeV/fm3 nf in hadron gas: 3 (p+, p- , p0 ) Julia Velkovska

  8. L-QCD – the only theory that can compute the EoS from first principles But, l-QCD lacks dinamical effects of the finite nuclear collision system. Many of the global observables are strongly influenced by the dynamics of the collisions. Microscopic (for the initial state) and macroscopic (hydrodynamics) transport models describe the collective dynamics: EoS is used as an input, local thermal equilibrium is assumed at all stages, system evolution is computed => results compared to data L-QCD : EoS EoS for pure glue: strong deviations from ideal gas up to 2 Tc Julia Velkovska

  9. p L p p K p p jet J/Y Freeze-out Hadronization QGP Thermaliztion Hard Scattering Au Au Space-time Evolution of Collisions time g g e  Expansion  space Julia Velkovska

  10. Energy  to beam direction per unit velocity || to beam pR2 ct0 energy density = E/volume Colliding system expands: E Question: What is the relevant time during the collision at which we need to calculate the energy density ? Julia Velkovska

  11. Estimating energy density • Time less than the time needed for the nuclei to pass through doesn’t make sense , because e becomes unphysically large trivially ( just by overlap mass) • For RHIC full energy g = 106 => tpass through ~ 0.13 fm/c • We need to consider “formed” or secondary particles – following Bjorken ( PRD 27 (1983) 140 ) - tform ~ 1 fm/c • So, let’s measure the transverse energy and get the energy density • We need to know how to define centrality, too ( to get the volume) • Experimental methods # 1 : centrality, multiplicity, ET Julia Velkovska

  12. Centrality Selection ZDC vs BBC Define centrality classes: ZDC vs BBC Extract N participants: Glauber model ET EZDC b QBBC Nch Nch ET Julia Velkovska

  13. Charged Multiplicity Measurements Count tracks on a statistical basis (no explicit track reconstruction) • Combine all hits in PC3 with all hits in PC1. • Project resulting lines onto a plane through the beam line. • Count tracks within a given radius. • Determine combinatorial background by event mixing technique B=0 • MC corrections for acceptance, detector effects, decays, background Julia Velkovska

  14. Systematic error estimate • No measurement is complete without a systematic error estimate! • Example from multiplicity measurement: • Acceptance: vary fiducial detector volume – see how the result changes • You may have particle inflow in the acceptance from decay products of particles that were not in the acceptance. These particles will be produced at different rapidity. How well do you know the rapidity distribution near the edge of the acceptance ? Not important at high energy, but maybe significant at low energy. • Particle composition: vary the ratio of different hadrons in MC and see what happens to the result • Particle <pT> : probability of detecting decay particles depends on their momentum. You may find that you need to do a momentum dependent correction • Systematic error due to centrality determination: how well do you know the trigger efficiency ? Is the total measured cross-section 92% of the total inelastic cross section , or is it 92.4 % ? • In the end of the day – add all systematic errors in quadrature Julia Velkovska

  15. How do we measure ET ? We measure the particles coming out, so add up their energy Julia Velkovska

  16. Transverse Energy Measurements • EMCal absolute energy calibration • MIP peak • E/p matching peak for e • 0 mass peak • Convention: • Ei= Eitot-mN for baryons • Ei= Eitot+mN for antibaryons • Ei= Eitot for others EMCal is “almost” hadronic calorimeter (depth 18 radiation lengths, or 0.85 interaction lengths) EEMC= 1.0 Etotfor , 0 EEMC= 0.7 Etotfor  • EEMC ET transformation: • ET= 1.23EEMC • Do a MC simulation with realistic particle composition 0 Julia Velkovska

  17. Results for ET and Nch : centrality dependence ET and Nch exhibit consistent behavior at sNN=130 GeV and 200 GeV ET @130 GeV ET @200 GeV • Stat. errors • Negligible • Syst. errors • Band: possible common tilt • Bars: total syst. error Nch @130 GeV Nch @200 GeV Julia Velkovska

  18. ET / Nch • Remarkably, dET/dh / dNch/dh does not change much with sqrt (s) • The extra energy goes into particle production • From dET/dh / dNch/dh = 0.85 GeV after converting to dN/dh , we get <mT> ~ 0.57 GeV • If we assume that We get tform ~ 0.35 fm/c . This is smaller than the “nominal” , but larger than 2R/g Julia Velkovska

  19. Now … estimate e • With the “ nominal “ tform = 1 fm/c , e = Peak energy density Thermalized energy density • e 5.5 GeV/fm3 (200 GeV Au+Au) well above predicted transition! Julia Velkovska

  20. Energy dependence of energy density • Both dNch /dh and dET/dh show logarithmic growth with sqrt (sNN) • At LHC expect ~ factor 20 increase in e. dNch/dh ~1200 • At RHIC central U+U collisions (nose-on-nose) are proposed (Kuhlman, Heinz ) to increase the initial energy density • Possible with the new EBIS ion source Julia Velkovska

  21. Nch comparison to models • HIJING – pQCD based model with soft and hard component of particle production X.N.Wang and M.Gyulassy, PRL 86, 3498 (2001) • KLN – gluon saturation in the initial state D.Kharzeev and M. Nardi, Phys.Lett. B503, 121 (2001) D.Kharzeev and E.Levin, Phys.Lett. B523, 79 (2001) • EKRT – saturation in the final state K.J.Eskola et al, Nucl Phys. B570, 379 and Phys.Lett. B 497, 39 (2001) Julia Velkovska

  22. And a full pallet of Nch to theory comparison from PHOBOS Julia Velkovska

  23. Nch rapidity dependence • Integrate the distribution to get total multiplicity – study the production as a function of energy • Explore scaling behavior • Is there longitudinal boost invariance ? Plateau around h = 0 increasing with energy. BUT, pseudo-rapidity maybe misleading… Julia Velkovska

  24. Look at dN/dy – no boost invariance • No plateau is present in the dN/dy distributions of pions Julia Velkovska

  25. Total multiplicity: energy and centrality dependence • Total multiplicity ( fixed energy/system) scales with Npart . With the change in centrality – change the system size and Ncoll , Npart • Au+Au : increase in particle production with the available energy • d+Au : not all “participants” are equal Julia Velkovska

  26. Longitudinal scaling • Particles near beam and target rapidity governed by limiting fragmentation • Projectile hadron viewed in the rest frame of the target is highly Lorenz contracted. It passes through the target leaving it in an excited state which is independent of energy or even the identity of the projectile. It then fragments to produce hadrons Julia Velkovska

  27. Lecture 2 • Is the system thermalized ? • Can we determine the temperature ? • We will study spectra and flow of identified particles to get estimates of the temperature at kinetic and chemical freeze-out • But, since we’ll need identified particles, I’ll start with methods for particle identification Julia Velkovska

  28. Methods for PID: TOF • Time of flight measurement: measure momentum and velocity => determine mass Time of Flight - /K separation ~ 3 GeV/c • K/p separation ~ 5 GeV/c st ~115 ps PHENIX EmCal (PbSc) Electromagnetic Calorimeter - /K separation ~ 1 GeV/c - K/p separation ~ 2 GeV/c st ~400 ps Julia Velkovska

  29. PHENIX high-pT detector • Combine multiple detectors to get track-by-track PID to pT ~ 9 GeV/c • Aerogel detector available since Run 4 . MRPC-TOF installed for Run 7 Julia Velkovska

  30. PID using Cerenkov detectors FS PID using RICH Multiple settings Julia Velkovska

  31. p P, GeV/c K p PID using characteristic energy loss: STAR TPC Good separation at low pt At high pt – extract yields on a statistical basis Julia Velkovska

  32. 70 60 50 + - K+K 40 30 0 5 4 2 3 1 p (GeV/c) Particle ID from low to high pT PHOBOS PID Capabilities p+p 1/v (ps/cm) ++- Eloss(MeV) p (GeV/c) Stopping particles dE/dx TOF 3.0 0.3 0.03 pT (GeV/c) Julia Velkovska

  33. Neutral particles can be reconstructed through their decay products 0 F-> K+ K- • p+p-podecay channel in pp: • : m = 782.7  0.1 MeV, BR = 89.1  0.7%  : m = 547.8  0.1 MeV, BR = 22.6  0.4% • po gdecay channel in pp: • - meson: m = 782.65  0.1289 MeV, % Julia Velkovska

  34. Resonance Signals in p+p and Au+Au collisions from STAR p+p  p+p Au+Au K(892) (1385) Au+Au K(892)  K+  D(1232)  p+   (1020)  K + K (1520)  p + K S(1385)  L + p D++ p+p (1020) p+p p+p (1520) Au+Au Au+Au Julia Velkovska

  35. Measure particle spectra • Corrections • Acceptance, efficiency ( maybe multiplicity dependent) • PID purity • Feed-down from decays • ……. Julia Velkovska

  36. What can we learn from spectra ? • Fit with hydrodynamics models to learn about the dynamical evolution of the system • Integrate them – get total particle production for each species, then learn about the “chemistry” in the system • Fit particle ratios with statistical thermal model of particle production => get Tch and mb • Look at scaling behavior to infer production mechanisms Julia Velkovska

  37. Spectral shapes in pp collisions Mt-scaling for soft particles Power-law tail from hard scattering Increasing with energy Julia Velkovska

  38. Scaling of spectra in dA and AA collisions • mT scaling in pp and dA, but NOT in AA. Signature of radial flow. Julia Velkovska

  39. Fitting p,K,p with hydrodynamics model c2/NDF = 59.4/46 c2/NDF = 72.6/46 80-92% 40-50% c2/NDF = 89.1/46 0-5% Julia Velkovska

  40. − π,K,p: Tfo decreases with centrality • - Multistrange (higher Tfo) with low hadronic cross section but strong radialflow Model the system as an ensemble of transversely boosted Boltzmann distributions: Transverse rapidity: Julia Velkovska

  41. Flow velocity vs energy < bT > slowly increasing from AGS to SPS to RHIC Julia Velkovska

  42. Statistical model fits: Tch and mb • Look like the system has established thermal equilibrium at some point in its evolution ( we don’t know when from this type of analysis, but we have other handles) • The chemical abundances correspond to Tch ~ 157+/- 3 MeV , mB ~ 30 MeV • Short lived resonances fall off the fits Julia Velkovska

  43. p L* K p p L* K Time in Heavy Ion Reactions Christina Markert Hot Quarks, Sardinia, May 2006 p+p • p+p interactions: • No extended initial medium • Chemical freeze-out (no thermalization) • Kinetic freeze-out close to the chemical freeze-out Particle yields Particle spectra Au+Au • Au+Au interactions: • Extended hot and dense phase • Thermalization at chem. freeze-out • Kinetic freeze-out separated from • chemical freeze-out Hot and dense medium time Julia Velkovska

  44. Interactions of Resonance in Hadronic Nuclear Medium Life-time [fm/c] : K(892) ~ 4.0 S(1385) ~ 5.7 L(1520) ~ 13  (1020) ~ 44 Dt Preliminary UrQMD Dt =10±3 fm/c [1] P. Braun-Munzinger et.al.,PLB 518(2001) 41, priv. communication [2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker J. Phys.G30 (2004) 111. K* and L* show rescattering S* shows regeneration Regeneration/Rescattering cross section: s(K+p) <s (K+p) < s (L+p) ? L* K* S* Slide from Christina Markert Julia Velkovska

  45. Tchemical Tchemical Lifetime of Nuclear Medium • From hydro: fitting spectra 9-10 fm/c till hadronization and another 7-8 fm/c to completely decouple at a temperature of Tkinetic ~ 100 MeV. • From HBT: t ~10fm/c • Resonances Dt > 4 fm/c • Who is right ? Dt > 4 fm/c resonances Au+Au t ~ 10 fm/c (HBT) Partonic phase  < 6 fm/c C. Markert, G. Torrieri, J. Rafelski, hep-ph/0206260 + STAR  delta lifetime > 4fm/c Julia Velkovska

  46. The baryon chemical potential Julia Velkovska

  47. Where are we on the phase diagram ? PBM et al, nucl-th/0304013 Julia Velkovska

  48. Is there a phase transition at RHIC and LHC ? From lattice – it is a cross-over Then QGP or not is not a “yes” or “no” answer Smooth change in thermodynamic observables Can we find the critical point ? Then we’ll have dramatic fluctuations in <pT> and baryon number Data on fluctuations at SPS and RHIC – very similar results and no dramatic signals. Are we on the same side of the critical point ? While Tc is rather well established, there is a big uncertainty in mb mbendpoint/ Tc ~ 1 (Gavai, Gupta), ~ 2 (Fodor,Katz), ~ 3 (Ejiri et al) mbfreezout450 MeV (AGS) -- 30 MeV (RHIC) m bfreezout ~ Tc corresponds to sqrt(s) = 25 GeV What is the order of the phase transition ? 1st order Julia Velkovska

  49. Large range of mB still unexplored : no data in the range mB = 70 -240 MeV You can run RHIC at low energies ( with some work on the machine which seems feasible). The cover mB = 30-500 MeV (√sNN from 5 GeV to 200 GeV) The baryon chemical potential coverage at FAIR will be approximately 400-800 MeV. Can we find the critical point ? Julia Velkovska

  50. Lecture 3 • We found that particle abundances look like they come from a thermalized source with Tch ~ Tc • Today we’ll try to address the timescale of thermalization • Need a clock that ticks fast => elliptic flow • We’ll compare the data to hydrodynamics – can we learn something about the equation of state ? • I’ll also cover methods for measuring elliptic flow Julia Velkovska

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