Near-side  correlations of high-p t hadrons from STAR Jörn Putschke Lawrence Berkeley National Laboratory

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

Outline Trigger  Trigger  • Analysis methods ( and ) • Au+Au 200 GeV near-side / width and yield • “Ridge yield” in Au+Au and Cu+Cu at 200 GeV • Summary • Outlook: collision geometry

- 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 (“ridge like” corrl.)

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%

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 () = gaus width

Au+Au near-side (J)(J) yields & widths pt,assoc. > 2 GeV pt,assoc. > 2 GeV (J) yield(J)) 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

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

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

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)* * On the following slides for simplification: J+R)= and J)= 

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 

Ridge yield in Au+Au I 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

Ridge yield in Au+Au II pt,assoc. > 3 GeV relative ridge yield absolute ridge yield preliminary preliminary ridge yield relative ridge yield No significant ridge contribution visible for pt,assoc. > 3 GeV

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

Summary Armesto et al, nucl-ex/0405301 • 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 • 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 affectedby hard scattering  not part of the jet • Radial flow + jet-queching ? (Voloshin nucl-th/0312065) • 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

Outlook: collision geometry (Glauber) y [fm] y [fm] Part/Col Au+Au 30-40% Part/Col Cu+Cu 0-10% Part ~ energy density Coll ~ parton origin x [fm] x [fm] • Different geometry (and energy density) in periph. Au+Au and central Cu+Cu but same near-side modifications and nuclear modifications (RAA) • Study geometry effects in more detail: Look at near-side modifications in Au+Au with respect to the reaction plane

Backup slides

2D near-side fit  v2 Au+Au 10-20% 3 < pt,trigger < 4 GeV Data Fit /Ndf

2D fit /Ndf Cu+Cu (no ridge) Cu+Cu 0-10% 3 < pt,trigger < 4 GeV  v2

 : pT(trig) dependence of correlated yield Dan Magestro, Hard Probes 04 • Gaussian areas consistent within errors for all pT(trig) • Yield growth with pT(trig) → more assoc. particles for higher-pT parton • Correlation yield preserved despite broadening of correlation STAR preliminary

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

Near-side  correlations of high-p t hadrons from STAR Jörn Putschke Lawrence Berkeley National Laboratory