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P article correlations at STAR. Jan Pluta Heavy Ion Reactions Group (HIRG), Faculty of Physics, Warsaw University of Technology. Some results from the STAR HBT group, presented recently by: Z.Chajecki, A.Kisiel, M.Lisa, M.Lopez-Noriega, S.Panitkin, F.Retiere, P.Szarwas.

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## P article correlations at STAR

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**Particle correlationsat STAR**Jan Pluta Heavy Ion Reactions Group (HIRG), Faculty of Physics, Warsaw University of Technology Some results from the STAR HBT group, presented recently by: Z.Chajecki, A.Kisiel, M.Lisa, M.Lopez-Noriega,S.Panitkin, F.Retiere, P.Szarwas. 3-rd Budapest Winter School on Heavy Ion Physics, 10 XII 2003**Outline:**• The STAR experiment • RHIC HBT Puzzle • General analysis • asHBT • Two K0-short correlations • p-Au, d-Au data • Nonidentical particles - emission asymmetry • Plans for future**12:00 o’clock**BRAHMS PHOBOS 2:00 o’clock 10:00 o’clock RHIC PHENIX 8:00 o’clock 4:00 o’clock STAR 6:00 o’clock 9 GeV/u Q = +79 U-line BAF (NASA) m g-2 LINAC BOOSTER HEP/NP AGS 1 MeV/u Q = +32 TANDEMS Relativistic Heavy Ion Collider (RHIC) =3.8 km1740 superconducting magnets • Beam energy up to 100 GeV/A (250 GeV for p) • Two independent rings (asymmetric beam collisions are possible) • Beam species: from p to Au • Six interaction points • Four experiments:STAR, PHENIX, PHOBOS and BRAHMS**STAR Detector – side view**STAR Detector – side view and STAR Collaboration – face view**STAR Collaboration**• 500 Collaborators including • ~65 graduate students • ~60 postdocs • 12 countries • 49 institutions • Spokesperson: John Harris 1991 - 2002 Tim Hallman 2002 - now USA, Brazil, China, Croatia Czech Republich, England, France, Germany, India, Netherlands, Poland, Rusia**HBT+FSI**Particle correlations The idea: Quantum statistics and Final-State Interaction Space-time sizes and dynamics Correlation function Momenta and momentum difference**Central Event: AuAu 200GeV/A**STAR Event 2 4m Real-time track reconstruction Pictures from Level 3 Trigger, online display. Typically 1000 to 2000 tracks per event into the TPC**Minbias trigger**STAR PRELIMINARY N ch Event and Particle Selection Au+Au Collisions at Sqrt(SNN)=200GeV • Centrality selection based on number of charged hadrons. three different centralities • Midrapidity -0.5 < y < 0.5 • Particle identification via specific ionization (dE/dx) electron band removed by cuts • Optimum performance for p HBT: 0.150 < pT (GeV/c) < 0.550 for K0s: 0.100 < pT (GeV/c) < 3.500 STAR PRELIMINARY**Some base definitions - to be used for results presentation**Two-particle kinematics Main (approximative) relations: Qout <--> Pt Qside <--> Qlong <--> KT <--> Pt LCMS: (P1+P2)z=0**HBT Excitation Function**Comparison with lower energies for ~ 10% most central events at midrapidity kT ~ 0.17 GeV/c No significant increase in radii with energy RO/RS ~ 1 Gap in energy that needs to be closed**STAR 130 GeV**PHENIX 130 GeV p + p - RHIC HBT Puzzle Most “reasonable” models still do not reproduce RHIC sqrt(SNN) = 130GeV HBT radii Hydro + RQMD PHENIX PRL 88 192302 (2002) √SNN = 130GeV • “Blast wave” parameterization (Sollfrank model) can approximately describe data • …but emission duration must be small • = 0.6 (radial flow) • T = 110 MeV • R = 13.5 1fm (hard-sphere) • emission= 1.5 1fm/c (Gaussian) from spectra, v2**raw**Coulomb corrected q* (GeV/c) Sqrt(SNN) = 200 GeV 3Dimensional Pion HBT p –p– Pratt-Bertsch Parameterization LCMS frame: (p1+p2)z=0 Central Events pT = 0.15-0.25 GeV/c Coulomb correction → spherical Gaussian source of 5fm momentum resolution corrected(~1% effect at 200GeV, due to higher B-field) STAR PRELIMINARY Statistical errors only!!**200GeV**Central Midcentral Peripheral Centrality and mT dependence at 200 GeV STAR PRELIMINARY RL varies similar to RO, RS with centrality HBT radii decrease with mT (flow) Roughly parallel mT dependence for different centralities RO/RS ~ 1 (short emission time)**200GeV - 130 GeV**Central Midcentral Peripheral PHENIX Central Comparison: 200 to 130 GeV. Longitudinal radius (fit to STAR Y2 data only) STAR PRELIMINARY Longitudinal radius: at 200GeV identical to 130 GeV**200GeV - 130 GeV**Central Midcentral Peripheral PHENIX Central Evolution timescale from RL Simple Mahklin/Sinyukov fit (assuming boost-invariant longitudinal flow) Makhlin and Sinyukov, Z. Phys. C 39 (1988) 69 STAR PRELIMINARY Assuming TK=110 MeV(from spectra at 130 GeV) (fit to STAR Y2 data only)**200GeV - 130 GeV**Central Midcentral Peripheral PHENIX Central Comparison: 200 to 130 GeV. Transverse radii STAR PRELIMINARY * • Higher B-field higher pT • Transverse radii: • similar but not identical • low-pT RO, RS larger at 200 GeV • steeper falloff in mT • (PHENIX 130GeV) • Ro falls steeper with mT**P. Kolb and U. Heinz, hep-ph/0204061**Azimuthally sensitive HBT (asHBT) • sensitive to interplay b/t anisotropic geometry & dynamics/evolution • “broken symmetry” for b0 => more detailed, important physics information • another handle on dynamical timescales – likely impt in HBT puzzle**side**y K out Lines: projections of 3D Gaussian fit fp x b HBT respect Reaction Plane 1D projections, f=45° √SNN = 130GeV**Data corrected for both event plane resolution and merging**systematic HBT(φ) Results – 130 GeV T=100 MeV r0=0.6 ra=0.037, R=11.7 fm, t=2.2 fm/c Minbias events @130GeV Bolstered statistics by summing results of p- and p+ analyses Blast-wave calculation (lines) indicates out-of-plane extended source Star preliminary**RY**0 RX 0 • BW: hydro-inspired parameterization • of freezeout • longitudinal direction • infinite extent geometrically • boost-invariant longitudinal flow • Momentum space • temperature T • transverse rapidity boost ~ r A model of the freezeout - BlastWave • coordinate space • transverse extents RX, RY • freezeout in proper time • evolution duration 0 • emission duration **RY**RX • BW: hydro-inspired parameterization • of freezeout • Longitudinal direction • infinite extent geometrically • boost-invariant longitudinal flow • Momentum space • temperature T • transverse rapidity boost ~ r A model of the freezeout- BlastWave • Coordinate space • transverse extents RX, RY • freezeout in proper time • evolution duration 0 • emission duration 7 parameters describing freezeout**Central**Midcentral Peripheral T (MeV) 108 3 106 3 95 4 0 0.88 0.01 0.87 0.02 0.81 0.02 a 0.06 0.01 0.05 0.01 0.04 0.01 RX (fm) 12.9 0.3 10.2 0.5 8.0 0.4 RY (fm) 12.8 0.3 11.8 0.6 10.1 0.4 0 (fm/c) 8.9 0.3 7.4 1.2 6.5 0.8 (fm/c) 0.0 1.4 0.8 3.2 0.8 1.9 2 / ndf 80.5 / 101 153.7 / 92 74.3 / 68 central midcentral peripheral BlastWave fits to published RHIC data • reasonable centrality evolution • OOP extended source in non-central collisions**FO = INIT**Estimate of initial vs F.O. source shape • estimate INIT from Glauber • from asHBT: • FO < INIT→ dynamic expansion • FO > 1 → source always OOP-extended • constraint on evolution time**asHBT at 200 GeV in STAR – R() vs centrality**• 12 (!) -bins b/t 0-180 (kT-integrated) • 72 independent CF’s • clear oscillations observed in transverse radii of symmetry-allowed* type • Ro2, Rs2, Rl2 ~ cos(2) • Ros2 ~ sin(2) • centrality dependence reasonable • oscillation amps higher than 2nd-order ~ 0→ (*) Heinz, Hummel, MAL, Wiedemann, Phys. Rev. C66 044903 (2002)**Pion Correlations d-Au and p-Au**• Pion correlation in d – Au : data selection • p-Au selection • 1D correlation function • 3D correlation function • d-Au vs p-Au • KT dependence • Centrality dependence**ZDC-d**ZDC-Au p-Au selection: FTPC E -Au Au d All trigger events Using information from ZDC-d STAR can separate events with neutron spectator from deuteron**theoretical CF: Rinv=6 fm, l = 0.5**d*-Au : d-Au without p-Au 1D Correlation Function: Gaussian fit: STAR preliminary • CF is very wide (rel Au-Au) • Coulomb/merging less important • CF looks reasonable • 1D Gaussian fit is not good • needed more deeply study of fit method only statistical error included !**3D Correlation Function:**3D Gaussian fit: Gaussian parametrization is not perfect but HBT radii characterize the width of CF STAR preliminary Fit results: Rout, Rside sensitive to the number of participants cut on the others Q's components < 30 MeV/c [GeV/c]**KT dependence:**STAR preliminary • clear KT dependence • Rout and Rside - sensitive to the number of participants • Rlong – the same KT dependence for dAu and pAu p – Au d – Au**KT dependence: d-Au & Au-Au divided by p-p**STAR preliminary • the same trend of KT dependence for d-Au and Au-Au as for p-p • HBT radii are scaled by constant factors**MT dependence of Rlong:**STAR preliminary Sinyukov fit: Rlong= const (mT)-a mT = kT2 + massp2 a for different collisions STAR preliminary p-p d-Au Au-Au Au-Au peripheral midcentral**ZDC-d**ZDC-Au Centrality definition in d-Au: FTPC-Au: charged primary particle multiplicity in -3.8<<-2.8 most peripheral most central 1 2 3 FTPC E -Au Au d**centrality**Centrality dependence: • clear centrality dependence • similar to AuAu • connection to geometry STAR preliminary p – Au d – Au minbias [*] - Glauber calculations (Mike Miller)**mt scaling violation?**inv Next RHIC HBT puzzle ?**Non-identical particle correlations:**The asymmetry analysis Catching up • Interaction time larger • Stronger correlation Moving away • Interaction time smaller • Weaker correlation “Double” ratio • Sensitive to the space-time asymmetry in the emission Kinematics selection on any variable e.g. kOut, kSide, cos(v,k) R.Lednicky, V. L.Lyuboshitz, B.Erazmus, D.Nouais, Phys.Lett. B373 (1996) 30.**Double ratio definitions**2k* = p1 – p2 P = p1 + p2 simulation kside < 0 ksidesign selection arbitrary Correlation functions p1 kout > 0 p2 koutsign selection determined by the direction of the pair momentum P Double ratios kside > 0 kout > 0 p2 2k* [GeV/c] klong is the z component of the momentum of first particle in LCMS p1**We are directly sensitive to time shift, the space shift**arises from radial flow – possibility of a new radial flow measurement Out direction Flow velocity observed transverse velocity Side direction thermal velocity What to expect from double ratios • Initial separation in Pair Rest Frame (measured) can come from time shift and/or space shift in Source Frame (what we want to obtain)**Separation between source 1 and 2 in pair rest frame**What do we probe? Source of particle 1 Source of particle 2 sr* Boost to pair rest frame Dr Dt <Dr*> Dr* (fm) r (fm) Dr* = gpair (Dr– bpair Dt) Separation due to space and/or time shift • Mean shift (<Dr*>) seen in double ratio • Sigma (sr*) seen in height of CF**Correlation functions and ratios**Good agreement for like- sign and unlike-sign pairs points to similar emission process for K+ and K- CF Out Clear sign of emission asymmetry Side Two other ratios done as a double check – expected to be flat Long Preliminary**Results for Pion-Proton 130 AGeV**Λ peaks • Similar preliminary analysis done for pion-proton • We observe Lambda peaks at k*~minv of Λ • Good agreement for identical and non-identical charge combinations STAR preliminary**K+ p**K- anti-p Best Fit STAR preliminary Preliminary results for Kaon-Proton • Using data from Year2 (200 AGeV) – sufficient statistics • No corrections for momentum resolution done • No error estimation yet – fit indicates theoretical expectations**What do we measure and how to compare it to the models?**Is our fitting method working? And if yes, what does it tell us? Need to disentangle flow and time shift Modeling the emission asymmetry • Need models producing strong transverse radial flow: • Blast-wave as a baseline • RQMD • UrQMD • T. Humanic's rescattering model**t**Kt = pair Pt R Rside Rout Understanding modelsBlast wave = Flow baseline • Blast wave • Parameterizes source size (source radius) radial flow (average flow rapidity) and momentum distribution (temperature): • No time shift • Only spatial shift due to flow • Infinitely long cyllinder (neglects long contribution) Parameterization of the final state**Blast wave: how does the flow work**Average emission points Pion pt = 0.15 GeV/c t = 0.73 Kaon pt = 0.5 GeV/c t = 0.71 Proton pt = 1. GeV/c t = 0.73 Particle momentum Spatial shifts (Dr)**Fitting and quantitative comparisons**• Fits assume gaussian source in PRF • r*out distributions have non-gaussian tails • Use the same fitting procedure for models and data - correlation functions constructed with “Lednicky's weights” Example of r*out distribution from RQMD**More points in βt needed to map and discriminate the flow**profile – needs STAR upgrades in PID capability (TOF barrel) Comparing models to data • Rescattering models and blast-wave are consistent with data • Blast wave parameters constrained by STAR measurements • In models flow is required to reproduce the data**“traditional”**HBT axis STAR HBT Matrix (circa 2003) Analysis in progress published submitted Not shown: 3p Correlations (accepted PRL) asHBT Phase space density Correlations with Cascades dAu, pp Cascades

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