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Correlations of high-pt hadrons in Au+Au collisions: Near-side Δη

This study aims to characterize and analyze the near-side Δη correlations of high-pt hadrons in Au+Au collisions. The analysis methods include Δη and Δφ measurements, studying the ridge yield, and comparing results in different centrality and trigger pt ranges. The relative ridge yield is observed to decrease with trigger pt but increase with centrality. The findings also reveal similarities in the relative ridge yield between Au+Au and central Cu+Cu collisions.

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Correlations of high-pt hadrons in Au+Au collisions: Near-side Δη

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  1. Near-side  correlations of high-pt hadrons from STAR Jörn Putschke Lawrence Berkeley National Laboratory

  2. Outline Trigger  Trigger  • Analysis methods ( and ) • Au+Au 200 GeV - near-side / width and yield - “Ridge yield” centrality dep. in Au+Au at 200 GeV - “Ridge/Jet yield” vs. pt,assoc. in central Au+Au - Proton/Pion “ridge yield” in central Au+Au • “Ridge yield” in Au+Au and Cu+Cu at 200 GeV • Summary & discussion

  3. - correlations Au+Au 20-30% Au+Au, 0-5% a Near-side jet-like corrl.+ ridge-like corrl. + v2 modulated bkg. Ridge-like corrl. + v2 modulated bkg. Away-side corrl.+ v2 modulated bkg. b b c c Additional near-side long range corrl. in  (“ridge like” corrl.) observed. Dan Magestro, Hard Probes 2004 Topic of this talk: Characterize and study in more detail the properties of the additional longe range corrl. in  in Au+Au(“ridge like” corrl.)

  4. Analysis methods  J = near-side jet-like corrl. R = “ridge”-like corrl. 2 (J) Method ||<0.7 1 2 const bkg. subtracted  (J+R) - (R) (J) method (J+R) Method ||<1.7 (J+R) Method ||<1.7 no bkg. subtraction v2 modulated bkg. subtracted Au+Au 20-30%

  5. 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

  6. Au+Au near-side (J) (J+R) yields & widths pt,assoc. > 2 GeV pt,assoc. > 2 GeV central (J+R) yield(J+R)) central periph. periph. preliminary yield(J)) (J) Correlate (J) and (J+R) widths & yields via centrality preliminary • J+R)yield increasing with centrality • J) and J+R)widths increasing with centrality

  7. Au+Au near-side (J)(J) yields & widths pt,assoc. > 2 GeV pt,assoc. > 2 GeV (J) yield(J)) periph. central yield(J)) (J) Correlate (J) and (J) widths and yields via centrality preliminary preliminary • (J) yield ~ J)yield • J) width ~ J)width for pt,trig > 4 GeV

  8. method comparison 3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV (J+R) method (J) method (J) method preliminary yield,)     Npart • Definition of “ridge yield”: i) ridge yield := yield(J+R))-yield(J) ii) relative ridge yield := (yield(J+R))-yield(J) yield(J)

  9. Ridge yield as function of in Au+Au pt,assoc. > 2 GeV preliminary ridge yield signal region (gaus-fit done in || < 0.75) Ridge yield show linear dependence on projection window  ridge constant in 

  10. Ridge yield in Au+Au pt,assoc. > 2 GeV relative ridge yield absolute ridge yield preliminary preliminary ridge yield relative ridge yield • Relative ridge yield decreasing with trigger pt • Absolute ridge yield ~ constant as function of trigger pt

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

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

  13. “Jet”/ridge yield vs. pt,assoc. in central Au+Au “jet” ridge charged preliminary preliminary preliminary Au+Au 0-10% preliminary Ridge / Jet yield

  14. PID ridge yield in central Au+Au pt,assoc. > 2 GeV preliminary Au+Au 0-10% Relative ridge yield vs. pt,trig suppressedfor identified assoc. pions with respect to assoc. charged hadrons; identified assoc. protons enhanced (proton contentof ridge larger than of jet part)

  15. Ridge yield in Au+Au and Cu+Cu pt,assoc. > 2 GeV relative ridge yield relative ridge yield preliminary relative ridge yield relative ridge yield preliminary At the same Npart the relative ridge yield seems to be comparable in periph. Au+Au (30-40%) and in central Cu+Cu (0-10%) collisions

  16. Summary • Relative ridge yield increase with centrality and decrease with pt,trigger for pt,assoc. > 2 GeV (significantly suppressed for pt,assoc. > 3 GeV) • Absolute ridge yield ~ constant as function of pt,trigger for each centrality • Ridge spectrum independent of pt,trigger and slightly harder than inclusive charged hadron spectrum (~40-50 MeV in slope parameter) • Relative ridge yield for identified assoc. pions suppressed with respectto charged hadrons (identified assoc. protons enhanced) • At the same Npart the relative ridge yield seems to be comparable in periph. Au+Au (30-40%) and in central Cu+Cu (0-10%) collisions

  17. Discussion Armesto et al, nucl-ex/0405301 ridge/jet yield increasing pt,trig h+,- ridge jet pt,assoc. • Scenarios: • Parton radiates energy before fragmenting and couples to the longitidunal flow • Gluon bremmstrahlung of hard-scattered parton • Parton shifted to lower pt • Radiated gluon contributes to broadening • Parton recombination (Chiu & Hwa Phys. Rev. C72:034903,2005) • Recombination of thermal partons only indirectly affected by hard scattering  not part of the jet • Radial flow + jet-queching (Voloshin nucl-th/0312065) • ridge spectrum harder than h+,- (~ 40-50 MeV in slope parameter)  consistent with parton 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 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 pions, protons and strange particles (see Janas talk) • 3-particle  near-side correlations

  19. Backup slides

  20. Au+Au near-side (J) (J+R) yields & widths II pt,assoc. > 3 GeV pt,assoc. > 3 GeV (J+R) yield(J+R)) preliminary preliminary yield(J)) (J) Correlate (J) and (J+R) widths & yields via centrality • (J) yield ~ J+R)yield • J) and J+R)widths ~ constant

  21. Ridge yield in Au+Au II pt,assoc. > 3 GeV relative ridge yield absolute ridge yield preliminary preliminary ridge yield relative ridge yield update minbias (error) Ridge contribution significantly suppressed for pt,assoc. > 3 GeV

  22. Relative ridge yield in Au+Au pt,assoc. > 2 GeV preliminary relative ridge yield Relative ridge yield strong increasing with centrality for lower trigger pt

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