near-side correlations of high-p t hadrons from star jörn putschke for the star collaboration

Near-side

correlations of high-pt

hadrons from STAR

Jörn Putschke for the STAR collaboration

Lawrence Berkeley National Laboratory

2Jörn Putschke, Hard Probes 2006, Monterey

“Ridge” observation

Additional near-side long range corrl. in (“ridge

like” corrl.) observed.

Dan Magestro, Hard Probes 2004, STAR, nucl-ex/0509030 and P. Jacobs,

nucl-ex/0503022

d+Au, 40-100% Au+Au, 0-5%

3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)


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

Au+Au 0-10%preliminary

3<pt,trigger<4 GeV

pt,assoc.>2 GeV


Components of correlations

Au+Au 20-30%

a

b

c c

b

a) Near-side jet-like corrl.+ ridge-like corrl. + v2 modulated bkg.

b) Ridge-like corrl. + v2 modulated bkg.

c) Away-side corrl.+ v2 modulated bkg.

Au+Au 0-10%preliminary

Strategy: Subtract from projection to isolate the ridge-like correlation


(J+R)

||<1.7

J = near-side jet-like corrl.

R = “ridge”-like corrl.

v2 modulated bkg. subtracted

(J+R)

||<1.7

flow (v2)corrected

Extracting near-side “jet-like” yields

1

Au+Au 20-30%

2

2

(J+R)- (R)

con

st b

kg.

sub

tra

cte

d

(J

)

||

<0.

7

(J)

no bkg. subtraction

const bkg. subtracted

(J)

||<0.7


pt,assoc. > 2 GeV

preliminary

Jet+

Rid

ge y

ield

(

)

Jet yield ()

Jet and Jet+Ridge yields & widths

• Jet+Ridge yield increasing with centrality

•Jet+Ridge shape asymmetric in and

preliminary

pt,assoc. > 2 GeV

Jet+

Rid

ge w

idth

(

)

central

Correlate Jet ((J)) and Jet+Ridge ((J+R)) widths & yields via centrality

Jet width ()

preliminarycentral

periph.

periph.Yield Width


Jet yields & widths: vs.

Correlate Jet ((J)) and Jet ((J)) widths and yields via centrality

pt,assoc. > 2 GeV pt,assoc. > 2 GeV

•Jet yield ~ symmetric in • Jet shape ~ symmetric in for pt,trig > 4 GeV

(asymmetric in for pt,trig < 4 GeV)

preliminary preliminary

centralperiph.

Jet yield ()

Jet y

ield

(

)

Jet width ()Je

t wid

th (

)

Yield

Width


Extracting the ridge yield

Definition of “ridge yield”:

i) ridge yield := Jet+Ridge( Jet()

ii) relative ridge yield := ridge yield / Jet()

preliminaryJet+Ridge ()

Jet ()

Jet)

yiel

d

,)

Npart

3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV


Ridge shape measurement in central Au+Au

• ridge yield as function of saturates at high non-uniform ridge shape in • ridge more collimated in for higher trigger pt

Au+Au 0-10%

preliminary

pt,assoc. > 2 GeV r

idge

yie

ld


Ridge yield in Au+Au

pt,assoc. > 2 GeV

preliminary

Ridge yield slightly decreasing (~ constant) as function of trigger pt


“Jet yield” vs. pt,assoc. in central Au+Au

“Jet spectrum” much harder than inclusive h and increasing with pt,trigger

preliminaryJe

t yi

eld

inclusive


Ridge yield vs. pt,assoc. in central Au+Au

preliminary

“Ridge spectrum” slightly harder than inclusive h and ~ independent of pt,trigger

inclusive


“Jet”/ridge yield vs. pt,assoc. in central Au+Au

preliminaryAu+Au 0-10%preliminary

Rid

ge

/ Jet

yie

ld

preliminary

RidgeJet

preliminary“jet” sloperidge slopeinclusive slope€

dN /dpt ∝ pte−p t /T


Pion vs. Proton ridge yield

preliminary

pt,assoc. > 2 GeV

Au+Au 0-10%

Proton content of ridge larger than of jet part(more from strange assoc. particles in Janas talk)

Assoc. ProtonsAssoc. PionsAssoc. h


Ridge yield in Au+Au and Cu+Cu

Relative ridge yield comparable at same Npart in Au+Au and Cu+Cu

pt,assoc. > 2 GeV

preliminary

preliminary

relative ridge yield relative ridge yield

rela

tive

ridge

yie

ld

rela

tive

ridge

yie

ld


Scenarios

i) 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

contradicts surface bias emission picture !

ii) 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 + jet-queching (Voloshin nucl-th/0312065)

Armesto et al, nucl-ex/0405301


Discussion

pt,assoc.

ridge

/jet y

ield

h+,-

ridgejet

increasing

pt,trig

• ridge spectrum harder than inclusive 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


Outlook

• 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

Part/Col Au+Au 30-40% Part/Col Cu+Cu 0-10%

Part ~ energy density

Coll ~ parton origin

x [fm] x [fm]

y [f

m]

y [f

m]

very preliminary !

12

1

3


Backup slides


Analysis methods cont.

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:

a) Used v2 values = v2{CuCu-pp}

b) Systematic errors mainly due to uncertainties in v2;

use v2 RP and no flow as upper and lower limit

QM051. Use event-mixing to account for pair

acceptance & use eff. correction for ass. particles

2. Background:

a) Subtract constant backgroundfor (J) method

b) Subtract v2 modulated background for (J+R) method

3. Assume Gaussian correlation shape:yield() = gaus integral / bin counting () = gaus width


Au+Au near-side (J)(J+R) yields & widths II

pt,assoc. > 3 GeV

yiel

d

(J+

R))

yield(J))

preliminary

Correlate (J) and (J+R) widths & yields via centrality

•(J) yield ~ J+R)yield

• J) and J+R)widths ~ constant

pt,assoc. > 3 GeV

preliminary

(J)

(J+

R)


Relative ridge yield in Au+Au

pt,assoc. > 2 GeV

preliminary

Relative ridge yield strong increasing with centrality for lower trigger pt

rela

tive

ridge

yie

ld


Summary

• Ridge shape non-uniform in in central Au+Au collisions

• Ridge yield slightly decreasing (~ constant) as function of pt,trigger

• 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

near-side correlations of high-p t hadrons from star jörn putschke for the star collaboration

Documents

central au au ridge

relative ridge yield

thjrn putschke

montereyridge yield

hard probes

gevjet yield

montereyjet yield

jet shape