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Near-side  correlations of high-p t hadrons from STAR

Near-side  correlations of high-p t hadrons from STAR Jörn Putschke for the STAR collaboration Lawrence Berkeley National Laboratory. Weisshorn (4505m), Switzerland. “Ridge” observation. d+Au, 40-100%.

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Near-side  correlations of high-p t hadrons from STAR

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  1. Near-side  correlations of high-pt hadrons from STAR Jörn Putschke for the STAR collaboration Lawrence Berkeley National Laboratory Weisshorn (4505m), Switzerland

  2. “Ridge” observation d+Au, 40-100% Additional near-side long range corrl. in  (“ridge like” corrl.) observed. Dan Magestro, Hard Probes 2004, STAR, nucl-ex/0509030, Phys. Rev. C73 (2006) 064907 and P. Jacobs, nucl-ex/0503022 Phys. Rev. C73 (2006) 064907 Au+Au, 0-5% pt < 2 GeV 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

  3. Outline 2-particle  correlations: • How to extract the “ridge” yield ? (additional near-side long range corrl. in ) • Quantify ridge properties in Au+Au (Cu+Cu)200 GeV collisions • Summary & discussion 3<pt,trigger<4 GeV pt,assoc.>2 GeV Au+Au 0-10% STAR preliminary

  4. Scenarios Armesto et al, PRL 93 (2004), nucl-ex/0405301 i) Parton radiates energy before fragmenting and couples to the longitudinal flow • Gluon bremsstrahlung of hard-scattered parton • Parton shifted to lower pt • Radiated gluon contributes to broadening •  near-side jet also looses energy (finite pathlength)! ii) Medium heating + Parton recombination(Chiu & Hwa Phys. Rev. C72:034903,2005) • Recombination of thermal partons only indirectly affected by hard scattering  not part of the jet • iii) Radial flow + trigger bias(Voloshin nucl-th/0312065, S. A. Voloshin, Nucl. Phys. A749, 287 (2005))

  5. Components of  correlations Au+Au 20-30% a b b c c Near-side jet-like corrl.+ ridge-like corrl. + v2 modulated bkg. Ridge-like corrl. + v2 modulated bkg. Away-side corrl.+ v2 modulated bkg. Au+Au 0-10% STAR preliminary Strategy: Subtract  from  projection to isolate the ridge-like correlation

  6. Extracting near-side “jet-like” yields J = near-side jet-like corrl. R = “ridge”-like corrl. 2 (J) ||<0.7 (J) ||<0.7 1 2 const bkg. subtracted const bkg. subtracted  (J+R) - (R) (J) flow (v2) corrected (J+R) ||<1.7 (J+R) ||<1.7 no bkg. subtraction v2 modulated bkg. subtracted Au+Au 20-30%

  7. Extracting the ridge yield     3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV Jet+Ridge () Jet () Jet) STAR preliminary yield,) Jet yield independent of Npart and consistent with d+Au reference measurements ! Npart • Definition of “ridge yield”: i) ridge yield := Jet+Ridge(  Jet() ii) relative ridge yield := ridge yield / Jet()

  8. Ridge shape measurement in central Au+Au I 3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV STAR preliminary yield) STAR preliminary yield) 3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV STAR preliminary   

  9. Ridge shape measurement in central Au+Au II Au+Au 0-10% pt,assoc. > 2 GeV ridge yield STAR preliminary  Ridge yield as function of  saturates at high  • non-uniform ridge shape in 

  10. Ridge yield in Au+Au pt,assoc. > 2 GeV STAR preliminary Ridge yield persists to highest trigger pt correlated to jet production

  11. “Jet yield” vs. pt,assoc. in central Au+Au STAR preliminary Jet yield Jet yield (pt,assoc > pt,assoc,cut) inclusive pt,assoc,cut “Jet spectrum” much harder than inclusive h and increasing with pt,trigger

  12. Ridge yield vs. pt,assoc. in central Au+Au STAR preliminary Ridge yield (pt,assoc > pt,assoc,cut) inclusive pt,assoc,cut “Ridge spectrum” slightly harder than inclusive h and ~ independent of pt,trigger

  13. “Jet”/ridge yield vs. pt,assoc. in central Au+Au “jet” slope ridge slope inclusive slope STAR preliminary Ridge Jet STAR preliminary preliminary Au+Au 0-10% preliminary Ridge / Jet yield Ridge/Jet yield (pt,assoc > pt,assoc,cut) pt,assoc,cut

  14. “Jet”/Ridge energy • Applying this “2-component picture” to lower pt,assoc measurements (see M. Horner’s talk: zt,jet(Au+Au) • ~ zt,jet(d+Au)  subtracting p+p jet energy from Au+Au) • upper estimate of the energy deposit in the ridge ~ few GeV Consistent with energy loss picture ? } “Ridge energy” } “Ridge energy” STAR, Phys. Rev. Lett. 95 (2005) 15230 0.15 < pt,assoc < 4 GeV 4 < pt,trigger < 6 GeV 6 < pt,trigger < 10 GeV

  15. Ridge yield in Au+Au and Cu+Cu relative ridge yield := ridge yield / Jet() pt,assoc. > 2 GeV relative ridge yield relative ridge yield Au+Au 200 GeV Cu+Cu 200 GeV STAR preliminary Au+Au 200 GeV (30-40 %) Cu+Cu 200 GeV (0-10 %) relative ridge yield relative ridge yield 3<pt,trigger<4 GeV STAR preliminary Relative ridge yield comparable at same Npart in Au+Au and Cu+Cu

  16. Ridge characteristics Weisshorn (4505m), Switzerland • ridge persists up to highest trigger pt correlated to jet production (~ independent on trigger pt) • ridge spectrum ~ “bulk-like” • ridge energy roughly a few GeV • ridge comparable in Au+Au and Cu+Cu at same Npart • non-uniformity of ridge shape in observed; needs further investigation STAR Au+Au 0-10%, RHIC, US (~0m) preliminary (only small effect expected)

  17. Discussion ridge/jet yield increasing pt,trig h+,- ridge jet pt,assoc. • ridge spectrum slightly harder (?) than inclusive h+,- (tens of MeV) consistent with medium heatingparton recombination (T~15 MeV) ? • agreement with radial flow + jet quenching ? • ridge spectrum qualitatively in agreement with parton energy loss and coupling to longitudinal flow • quantitative calculation for comparison needed

  18. Outlook y [fm] y [fm] 13 STAR very preliminary ! Part/Col Au+Au 30-40% Part/Col Cu+Cu 0-10% Part ~ energy density Coll ~ parton origin 12 x [fm] x [fm] • Study geometry effects in more detail:  Look at near-side modifications in Au+Au with respect to the reaction plane • PID ridge yield study with , protons and strange particles (see J. Bielcikova’s talk) • Systematic studies of the ridge shape at higher trigger pt and  • 3-particle  near-side correlations

  19. Backup slides

  20. Analysis methods cont. QM05 preliminary v2 subtraction and systematic error estimation Au+Au: Used v2 values = mean between v2 RP and v2{4} measurements Systematic errors mainly due to uncertainties in v2;use v2 RP and v2{4} as upper and lower limit v2 subtraction and systematic error estimation Cu+Cu: Used v2 values = v2{CuCu-pp} Systematic errors mainly due to uncertainties in v2;use v2 RP and no flow as upper and lower limit • Use event-mixing to account for pair acceptance & use eff. correction for ass. particles • Background: • Subtract constant backgroundfor (J) method • Subtract v2 modulated background for (J+R) method • Assume Gaussian correlation shape:yield() = gaus integral / bin counting () = gaus width

  21. Jet and Jet+Ridge yields & widths central periph. Correlate Jet ((J)) and Jet+Ridge ((J+R)) widths & yields via centrality pt,assoc. > 2 GeV pt,assoc. > 2 GeV Yield Width STAR preliminary preliminary Jet+Ridge yield () Jet+Ridge width () central periph. STAR preliminary Jet yield () Jet width () • Jet+Ridge yield increasing with centrality • Jet+Ridge shape asymmetric in and

  22. Jet yields & widths:  vs.  periph. central Correlate Jet ((J)) and Jet ((J)) widths and yields via centrality pt,assoc. > 2 GeV pt,assoc. > 2 GeV Yield Jet yield () Jet width () Width STAR preliminary STAR preliminary Jet yield () Jet width () • Jet yield ~ symmetric in  • Jet shape ~ symmetric in  for pt,trig > 4 GeV(asymmetric in  for pt,trig < 4 GeV)

  23. “Jet”/Ridge energy/multiplicity STAR, Phys. Rev. Lett. 95 (2005) 15230 “Ridge Nch” “Ridge energy” “Ridge energy” 0.15 < pt,assoc < 4 GeV

  24. Pion vs. Proton relative ridge yield pt,assoc. > 2 GeV STAR preliminary Au+Au 0-10% Assoc. Protons Assoc. Pions Assoc. h Proton content of ridge larger than of jet part (more from strange assoc. particles in J. Bielcikova’s talk)

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