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STAR highlights and physics update of the FTPCs Joern Putschke

STAR highlights and physics update of the FTPCs Joern Putschke. Outline. The FTPCs at STAR Jet quenching (initial/final state ?) Flow measurements Directed Flow v 1 Elliptic Flow v 2 Charged particle spectra Au+Au analysis d+Au analysis. RHIC. The STAR detector. The Forward TPCs.

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STAR highlights and physics update of the FTPCs Joern Putschke

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  1. STAR highlights and physics update of the FTPCs Joern Putschke

  2. Outline • The FTPCs at STAR • Jet quenching (initial/final state ?) • Flow measurements • Directed Flow v1 • Elliptic Flow v2 • Charged particle spectra • Au+Au analysis • d+Au analysis

  3. RHIC

  4. The STAR detector

  5. The Forward TPCs • 2 FTPCs • 2.5 < || < 4.0 • 6 azimuthal sectors (~60 deg.) with 10 rows in z- direction • Electron drift radial and perpendicular to the magnetic field • Spatial res.  0.1 mm • Two track res.  1.5 mm

  6. Heavy Ion Collision (animation)

  7. Heavy Ion Collisions Time • 1) Initial condition: 2) System evolves: 3) Bulk freeze-out: • Baryon transfer - parton/hadron expansion - hadronic dof • - ET production - final state interactions - inel. interactions cease: • Partonic dof particle ratios, Tch, mB • - elas. interactions cease • particle spectra, Tth, <bT>

  8. Collision Geometry z Au + Au sNN = 200 GeV x impact parameter Non-central Collisions Uncorrected • No direct measure of impact parameter • Use track multiplicity to define collision centrality

  9. Azimuthal distributions in Au+Au Au+Au peripheral Au+Au central pedestal and flow subtracted ? Phys Rev Lett 90, 082302 Near-side: peripheral and central Au+Au similar to p+p Strong suppression of back-to-back correlations in central Au+Au

  10. Is suppression an initial or final state effect? Initial state? Final state? gluon saturation partonic energy loss How to discriminate? Turn off final state d+Au collisions

  11. Azimuthal distributions pedestal and flow subtracted Near-side: p+p, d+Au, Au+Au similar Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au Suppression of the back-to-back correlation in central Au+Au is a final-state effect

  12. Motivation of flow measurements • Equation of State of nuclear matter under extremeconditions unknown • Investigation of „early times“ in the evolutionof the hot, dense central collision region possible • FTPCs allow substantial extension of TPCmeasurements (sign of elliptic flow / directed flow)

  13. Definition of anisotropic flow py directed flow elliptic flow px z y anisotropy in mometum space x initial spatial anisotropy Anisotropic flow  any correlationwith respect to the reaction plane

  14. Directed flow v1 at RHIC FTPC TPC FTPC • First measurement of directed flow at RHIC • Correlationof directed and elliptic flow axes shows that v2 is in the reaction plane • Consistent with a “limiting fragmentation” hypothesis.

  15. v2 measurements in the FTPCs v2 can be determined with FTPC alone ! STAR preliminary STAR preliminary h Good agreement between FTPC & TPC! pT (GeV/c)

  16. v2 comparison with Hydro Adler et al., Phys.Rev.Lett.90:032301,2003 • v2 at low pt reach Hydro limit => collective motion • v2 at high pt in qualtiative agreement with “jet-quenching” scenario

  17. FTPC track finding efficiencies AuAu minbias (FTPC west) track eff. pt [GeV] 0.1< pt<1 GeV track eff.   20k AuAu minbias embedded - (5% of total FTPC mult.) with flat pt dist. FTPC track finding eff. flat over selected pt and  range for all centrality classes (expect ~90% for dAu).

  18. FTPC momentum resolution pt [GeV] momentum res. [%] pt shift[%]   • FTPC momentum resolution around 15%, degrades to 40% at =3.5 and pt=1 GeV/c • FTPC  resolution better than 0.02 units • Systematic underestimation of pt up to 5% at =3.5 for 0.1<pt<1 GeV/c

  19. Pseudorapidity distribution in Au+Au dN/d dN/d STAR preliminary STAR preliminary   200k minbias AuAu events dots = PHOBOS [Phys. Rev. Lett. 91,052303 (2003)] Good agreement between PHOBOS and FTPC dN/d dist. applying constant eff. corrections depending on centrality.

  20. <pt> as a function of centrality STAR preliminary (power-law fit) 0.1 < pt < 1 GeV <pt> increases with centrality and seems to saturate at high centrality. Consistent picture with <pt> vs. centrality at mid-rapidity and Hydro.

  21. d+Au pt spectra STAR preliminary (uncorrected) 3 <  < 3.2 0.1 < pt < 1 GeV 1/pt dN2/(dpt d) <pt> [GeV/c] FTPC west FTPC east 3 <  < 3.2 STAR preliminary (uncorrected) 40-100% 20-40% 0-20% pt [GeV/c] <pt> for Au-side seems to increase faster with centrality than the deuteron-side. 200k minbias dAu events corrected for vertex-finding efficiency Centrality selection with TPC multiplicity FTPC west = d-side FTPC east = Au-side (power-law fit)

  22. d+Au particle density asymmetry Au-side dN/d STAR preliminary D. Kharzeev (CGC) [arXiv:hep-ph/0212316] X. Wang (HIJING) [arXiv:nucl-th/0303004] d-side  • charged particle asymmetry clearly visible in the FTPCs • Saturation model (CGC) inconsistent with data • qualitative agreement with microscopic HIJING model

  23. d+Au RCP in the FTPCs RCP STAR preliminary Au-side d-side pt [GeV/c] Strong centrality dependence at d-side for RCP visible. Could be explained by the “stopping” of the deuteron.

  24. Summary • Strong suppression of the back-to-back correlations (and the inclusive yields) in central Au+Au collisions are due to final-state interactions with the dense medium generated in such collisions • Directed flow (v1) measurement confirms in-plane elliptic flow (v2) • v2 reaches Hydro limit at low pt and indicates a pressure driven collective expansion at the early stage of a heavy ion collision • v2 at high pt in qualitative agreement with jet-quenching scenario • Centrality dependence of <pt> at mid- and forward rapidity follows the same behaviour and consistent with Hydro expectations • Charged particle density asymmetry measurements in d+Au disfavor parton saturation model => consistent picture with back-to-back correlation observations in d+Au

  25. The STAR FTPC group • Volker Eckardt • Maria Mora Corral • Joern Putschke • Norbert Schmitz • Janet Seyboth • Peter Seyboth • Frank Simon Weissmies (4023m), Switzerland [2003]

  26. backup slides

  27. Inclusive yield relative to binary-scaled p+p • d+Au : enhancement • Au+Au: strong suppression • pT=4 GeV/c: • cent/minbias= 1.110.03 • central collisions enhanced wrt minbias Suppression of the inclusive yield in central Au+Au is a final-state effect

  28. Event plane angle correlations FTPC & FTPC+TPC second harmonic (FTPC) preliminary ! first harmonic (FTPC+TPC) first harmonic (FTPC) second harmonic (FTPC+TPC)

  29. Particle ratios • STAR excels in particle yields study! (and good agreement between different experiments ). • Evidence for thermal equilibrium at high temperature and density. • RHIC increasing s: same temperature, decreasing baryon density.

  30. FTPC pion acceptance

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