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STAR results on pp vs heavy ions

Workshop on Particle Correlations and Femtoscopy KROMĚŘÍŽ, CZECH REPUBLIC, August 15-17, 2005. STAR results on pp vs heavy ions. Zbigniew Chaj ę cki The Ohio State University for the STAR Collaboration. Pion Interferometry in STAR. p p dAu AuAu.

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STAR results on pp vs heavy ions

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  1. Workshop on Particle Correlations and FemtoscopyKROMĚŘÍŽ, CZECH REPUBLIC, August 15-17, 2005 STAR results on pp vs heavy ions Zbigniew ChajęckiThe Ohio State University for the STAR Collaboration

  2. Pion Interferometry in STAR pp dAu AuAu Width of the correlation function ~ 1/RRAuAu >> RdAu > Rpp the same experiment, collision energy, detector acceptance ! WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  3. Outline and motivation • Vary spatial scale of the collisions - p+p, d(p)+Au, Cu+Cu*, Au+Au • mT dependence of pion HBT radii in p+p, d(p)+Au, Au+Au • Scaling variable? (Which „geometrical quantity” drives the radii?) • p+p → Au+Au : New (changing) physics? • Shape analysis of correlation function • problem with baseline of CF in low multiplicity collisions * see: S. Panitkin, Latest femtoscopic results from Cu+Cu collisions at RHIC (STAR) WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  4. Transverse mass dependence: p+p, d(p)+Au mT dependencein elementary collisions (e.g. OPAL, DELPHI, E735) usually attributed to • String fragmentation • Resonance contribution • Heisenberg uncertainty DELPHI - e+e- annihilation DELPHI - e+e- annihilation DELPHI - e+e- annihilation G. Alexander, hep-ph/0302130 • p+p: HBT radii decrease with increase of mT STAR preliminary WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  5. Transverse mass dependence: p+p, d(p)+Au • p+p: HBT radii decrease with increase of mT Note y-scale change! STAR preliminary • d+Au collisions • centrality dependence observed • Rside sensitive to the size of a smaller nucleus (d+Au vs p+Au) DELPHI - e+e- annihilation WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  6. Au+Au like superposition of p+p? • AuAu = N*(strings in pp) ? • AuAu = N*(„blast-waves”) ? NO! – that would generate local space-momentum correlations but in AuAu we see global correlations – although both scenarios would lead to the identical p-space observables WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  7. p+p like a little Au+Au ? 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 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  8. Surprising 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 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

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

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

  11. NA22 parametrization of CF ? WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  12. NA22: 1D projections of 3D CF NA22, Z. Phys. C71 (1996) 405 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  13. NA22 parametrization of CF STAR preliminary d+Au peripheral collisions NA22 fit d+Au peripheral collisions WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

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

  15. „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(!!!!) Lisa, Pratt, Soltz, Wiedemann, nucl-ex/0505014 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

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

  17. Summary Physics summary • 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 • „universal scaling” of HBT radii with dNch/dh1/3 • 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 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  18. . SUPPORT SLIDES WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  19. 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] WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  20. 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 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  21. 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 ? WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  22. 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 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  23. 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 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  24. Transverse mass dependence inAu+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. Calc. with Blast-Wave -Retiere, Lisa,PRC 70 (2004) 044907 WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  25. Consistency check on flow – kaons Au+Au 62GeV – STAR preliminary bx=0.907 bx=0.974 p K p WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

  26. More confirmation STAR preliminary WPCF 2005 - Zbigniew Chajęcki for the STAR Collaboration

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