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Identical Particle Correlations in STAR

Identical Particle Correlations in STAR. Zbigniew Chaj ę cki The Ohio State University for the STAR Collaboration. Outline and motivation. R(√S NN , m T , b, N part , A, B , PID ). R(√S NN ) – simple signal ?. data@QM2004. No glaring signal in simple measures. R out /R side.

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Identical Particle Correlations in STAR

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  1. Identical Particle Correlations in STAR Zbigniew ChajęckiThe Ohio State University for the STAR Collaboration Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  2. Outline and motivation R(√SNN, mT, b, Npart, A, B, PID) R(√SNN) – simple signal ? data@QM2004 No glaring signal in simple measures Rout/Rside “e” Rischke, Gyulassy, NP A 608 (1996) 479 Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  3. Outline and motivation NEW NEW NEW NEW R(√SNN, mT, b, Npart, A, B, PID) • Beyond „simple” geometry – physics of spacetime dynamics (mT) • Vary spatial scales (b, Npart, A, B) • Scaling variable? (Which „geometrical quantity” drives the radii?) • Onset of bulk behaviour? • New (changing) physics? (√SNN, b, Npart, A, B) • ____________________________________________________ • Consistency check (PID) • Shape analysis of correlation function Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  4. „Universal” scaling ? RHIC/AGS/SPS Systematics Pion HBT radii from different systems and at different energies scale with (dNch/dη)1/3 <kT>≈ 400 MeV (RHIC)<kT>≈ 390 MeV (SPS) STAR DATA (pp,dAu,CuCu,AuAu@62GeV - prelim.) Radii scale with multiplicity Forget A,B,√s, Npart...dN/d determines HBT radii,at all mT(!!!!) is it „trivial” ? Lisa, Pratt, Soltz, Wiedemann, nucl-ex/0505014 Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  5. System expansion: Initial vs Final Size Collisions at 200GeV only Smooth expansion of the system from p+p to Au+Au… but not trivial AuAu: system expands pp (dAu): no or less expansion Proton initial size = 0.89 fm from e-scattering Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  6. Transverse mass dependence in Au+Au STAR, Au+Au@200GeV, PRC71 (2005) 044906 .2 0.2 0.3 0.4 0.5 0.2 0.3 0.4 0.5 0.6 In Au+Au pT (mT) dependence attributed to collective expansion of the source 0. 0. 0. Calc. with Blast-Wave -Retiere, Lisa,PRC 70 (2004) 044907 Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  7. Consistency check on flow – kaons QM poster: M. JedynakKaon correlations Au+Au 62GeV – STAR preliminary bx=0.907 bx=0.974 p K p Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  8. More confirmation QM poster:H. Gosproton correlations STAR preliminary Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  9. Transverse mass dependence: p+p, d(p)+Au 4. Hydrodynamical expansion in pp? flow not expected in such a small system as p+p see e.g. Shuryak:hep-ph/0405066 • Csorgoet al.: mT dependence of HBT radii in pp is not generated by the transverse flow, but by the transverse temperature inhomegeneities of hadron-hadron collisions due to the freezing scale –hep-ph/0406042 1/(2pmT)d2n/(dmTdy) mT-m (GeV) • d+Au : Rlong doesn’t change with centrality RSIDE ROUT RLONG Note y-scale change! 1. String fragmentation STAR preliminary • p+p: HBT radii decrease with increase of mT • mT dependencein elementary collisions has been observed e.g. in OPAL, DELPHI, E735 2. Resonance contribution 3. Heisenberg uncertainty 4.Hydrodynamical expansion in pp? • d+Au : Rside sensitive to the size of a smaller nucleus (d+Au vs p+Au) DELPHI - e+e- annihilation G. Alexander, hep-ph/0302130 Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  10. Surprising („puzzling”) scaling Ratio of (AuAu, CuCu, dAu) HBT radii by pp • All pT(mT) dependences of HBT radii observed bySTAR scale with pp although it’s expected that different origins drivethese dependences HBT radii scale with pp Scary coincidence or something deeper? pp, dAu, CuCu - STAR preliminary Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  11. Let's look in more detail at where these radii come from Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  12. Decomposition of CF onto Spherical Harmonics d+Au: peripheral collisions RL < RT ~acceptance free RL > RT b RO < RS Simple, Gaussian source calculations |Q| |Q| z RO > RS |Q| Au+Au: central collisions d+Au: peripheral collisions Au+Au: central collisions C(Qout) C(Qside) C(Qlong) Z.Ch., Gutierrez, Lisa, Lopez-Noriega, nucl-ex/0505009 Pratt, Danielewicz [nucl-th/0501003] STAR preliminary Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  13. Scaling (fit w/o baseline param.) Ratio of (AuAu, CuCu, dAu) HBT radii by pp STAR preliminary NEW fit w/ baseline parameterization Fit w/o baseline parameterization Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  14. Summary NEW Physics summary • STAR data – Au+Au@62GeV, Cu+Cu@200GeV, (d(p)+Au, p+p)identical kaon and proton correlations • Smooth transition from SPS/AGS to RHIC in HBT excitation function • „universal scaling” of HBT radii with dNch/dh1/3from RHIC to AGS/SPS • mT dependence of HBT radii for Au+Au, Cu+Cu, d+Au and p+p seems to be the same although it’s expected to have different origins • System expands x2 in Au+Au collisions and no or little expansion is p+p • Decomposition of CF in terms of spherical harmonics • Spherical harmonics allow efficent diagnostic of the correlation function • Use symmetry of the Q-space • Pratt and Danielewicz [nucl-th/0501003]: connection of one-to-one CF and spatial anisotropies Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  15. STAR HBT Posters D. Das – Preliminary results on direct photon-photon HBT measurements in √SNN=62.4 GeV and 200 GeV Au+Au collisions at RHIC H. Gos – Baryon-baryon correlations in Au+Au collisions at √SNN=62 GeV and 200 GeV measured in STAR experiment at RHIC M. Jedynak – Charged kaon correlations at STAR T. Taluc – Centrality dependence of pion-proton correlations at STAR Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  16. . SUPPORT SLIDES Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  17. Decomposition of CF onto spherical harmonics QLONG Q  QOUT  QSIDE Z.Ch., Gutierrez, Lisa, Lopez-Noriega, nucl-ex/0505009 • Cartesian-space (out-side-long) naturally encodes physics, but is poor/inefficient representation • Recognize symmetries of Q-space -- decompose by spherical harmonics! • Direct connection to source shapes [Danielewicz,Pratt: nucl-th/0501003] – decomposition of CF on cartesian harmonics • ~immune to acceptance • full information content at a glance[thanks to symmetries]  : [0,2p]  : [0,p] Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  18. Some properties of Alm coefficients • Alm = 0 for l or m odd – identical particle correlations (for non-id particles, odd l encodes shift information) • A00(Q) ≈ one-dimensional “CF(Qinv)” (bump ~ 1/R) • Alm(Q) = l,0 where correlations vanish • Al≠0,m(Q) ≠ 0  anisotropy in Q space • Im[Alm] = 0 Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  19. Baseline in p+p, d+Au and Au+Au • Some coefficients don’t vanish for large Q • Bias from zero is larger for more peripheral collisions • This problem is getting more significant for small systems (pp & dAu) • It can be due to • an experimental artifact • long range correlations (e.g. Jets) • problem with momentum conservation ? • or ? Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  20. Long-range correlations : JETS ? • Jets as a origin of the baseline problem ?? • The idea was to try to eliminate pions coming from jet fragmentation from data sample. It can be done by applying an event cut which accepts only events that have no high-pt tracks (jets). HBT analyses where done for three classes of events • all- all events accepted – as a reference • soft – only events without high-pT tracks ( highest-pT < 1.2 GeV/c was chosen) • hard- only events with least one track with pT > 2 GeV/c Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

  21. Momentum conservation study with Nexus • Correlation function for pions from events generated with EPOS • No correlation effect included (as BE, FSI) • Background created by mixing particles comming from different events (same procedure like for experiemental CF) No evidence of a problem with baseline of CF ! Nexus, p+p @ 200 GeV D Quark Matter 2005 - Zbigniew Chajęcki for the STAR Collaboration

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