near-side di-hadron correlations at rhic

Jana Bielcikova (Yale) ISMD 2007, Berkeley 1

Near-side di-hadron correlations

at RHIC

Jana Bielcikova (Yale University)


Outline:• Introduction• Properties of ridge and jet-like correlations at

near side• Where does the ridge come from?• Summary

pTtrig=3-6 GeV/c, 2 GeV/c <pT

assoc< pTtrig

jet ridge

h-h correlation, central Au+Au @ 200 GeV

J. Pu

tschke

(ST

AR

), QM

20

06

STAR Preliminary

Jana Bielcikova (Yale) ISMD 2007, Berkeley3

Jet-like correlations at RHIC0.15 GeV/c <pT(assoc)< 4 GeV/c2 GeV/c <pT(assoc)<pT(trig)

4 <pT(trig)<6 GeV/c

ST

AR

, P

hys

Re

v L

ett

91

, 0

72

30

4 ST

AR

, PR

L 9

5 (2

00

5) 1

52

30

1

• disappearance of away-side correlations observed at intermediate pT

• lowering associated pT :

- resurrects correlated yield at away side - near and away-side yields are enhanced with respect to p+p/d+Au - shape of the away-side peak is not Gaussian Mach cone? Deflected jets?

Cherenkov radiation?


A closer look at near-side peak …S

TA

R, P

RC

73

(20

06

) 06

49

07

, J.P

hys.G

32

(20

06

) 37

pT < 2 GeV/c

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

3 < pT(trig) < 6 GeV/c2 < pT(assoc) < pT(trig)

D.

Ma

ge

stro

, H

ard

Pro

be

s 2

00

4P

. Ja

cob

s, E

PJ

C4

3 (

20

05

) 4

67

Additional near-side correlation in pseudo-rapidity () observed

The near-side jet interacts with the medium!


The ridge properties


(J+R)||<1.7

J = “jet”, R= “ridge”

(J+R)||<1.7

v2 subtracted

Extracting near-side “jet” and “ridge” yields

1

2

2

con

st b

kg.

sub

tra

cte

d(J

) |

|<

0.7

(J+R)- (R)(J)

no v2 subtraction needed

const bkg. subtracted

(J) ||<0.7

pTtrig=3-4 GeV/c, pT

assoc>2 GeV/c

J. P

utsc

hke

(ST

AR

),Q

M’2

006


Centrality dependence of near-side yield (I)

STAR preliminaryJet+Ridge ()

Jet ()

Jet)

yiel

d

,)

Npart

3 GeV/c < pTtrigger< 4 GeV/c and pT

assoc > 2 GeV/c

• jet yield independent of centrality (Npart) • ridge yield increases ~ linearly with Npart

ridge

ridge

jet

jet+ridge after v2 subtraction

J. Putschke (STAR),QM2006


• steep increase of near-side yield with centrality in Au+Au• ratio of yields in central Au+Au/d+Au ~ 4-5

-> “jet” yield is independent of centrality and agrees with d+Au

JetJet + Ridge

-> “ridge” yield increases with centrality ridge for K0

S trigger < ridge for Λtrigger

Ridge

Centrality dependence of near-side yield (II)

Jet

J.B. (STAR), QM’2006


pT spectra of associated particles at near side

M. Horner (STAR), QM2006

• increase of near-side yield at low pT

assoc (zT) observed by STAR and PHENIX

• subtraction of -independent ‘ridge-yield’ recovers centrality-independent jet yield

zT = pTassoc/pT

trig

STAR preliminary

STAR preliminary

C. Zhang, J. Jin (PHENIX), QM2006

STAR preliminary

8 <pTtrig< 15 GeV/c8 <pT

trig< 15 GeV/c

STAR preliminary

||<0.35

||<1.0


STAR preliminary

RidgeJet

Rid

ge

/Je

t y

ield

(p

Ta

ss

oc

> p

Ta

ss

oc

,cu

t )

pT spectra of associated particles

• jet spectrum harder than inclusive pT-spectrum T(jet) increases with pT

trigger

x• ridge spectrum similar to particles from bulk T(ridge) ~ independent of pT

trigger

pTassoc.cut (GeV/c)

STAR preliminary“jet” sloperidge slopeinclusive slope

pTtrig (GeV/c)

€

dN /dpt ∝ pte−p t /TJ. Putschke (STAR),QM’2006


pTtrigger dependence of ridge

pT assoc

> 2 GeV/c

STAR preliminary

Ridge yield: persists up to pTtrig

~ 10 GeV/c

Ridge is independent of jet energy

J. P

utsc

hke

(ST

AR

),Q

M’2

006


Particle composition in jet and ridge

A hint? Ridge: B/M ratio closer to bulk Jet: B/M ratio ~ p+p More data needed !

J.B. (STAR), WWND 2007


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

pTassoc

. > 2 GeV/c

STAR preliminary

STAR preliminary

rela

tive

ridge

yie

ld

rela

tive

ridge

yie

ld

relative ridge yield = ridge yield / jet()

Au+Au @ 200 GeV

Cu+Cu @ 200 GeV

3 GeV/c <pTtrigger<4 GeV/c

Au+Au @ 200 GeV (30-40 %)

Cu+Cu @ 200 GeV (0-10 %)

System size dependence of ridge yield

J. Putschke (STAR), QM2006


Energy content in the ridgeSTAR, Phys. Rev. Lett. 95 (2005) 15230, J. Putschke (STAR), QM2006

0.15 < pt,assoc < 4 GeV/c

4 < pt,trigger < 6 GeV/c

6 < pt,trigger < 10 GeV/c

“Ridge energy”

“Ridge energy”

}

}

• near-side modification in published results also due to ridge• energy content deposited in the ridge is few GeV


L. Molnar (STAR), QM’06, nucl-ex/0701061

Is there ridge at forward rapidity?

pTassoc = 0.2-2.0 GeV/c: no near-side peak within systematic errors

pTassoc > 1 GeV/c: : data suggest a non-zero correlation at near side (?)


Where does the ridge come from?


C. Chiu & R. Hwa, Phys. Rev. C72 (2005) 034903

• hard parton passing through the medium enhances thermal parton distribution (ΔT=15 MeV) recombination of thermal partons forms a pedestal (‘ridge’) • enhanced baryon/meson ratio

Parton recombination

ridge

jet


N. Armesto, C.A. Salgado, U.A. Wiedemann,

Phys. Rev. Lett. 93 (2004)

• parton energy loss is sensitive to energy density of medium + collective flow • medium induced gluon radiation• radiated gluon contributes to broadening in

Parton radiation and its coupling to longitudinal flow


A. Majumder, B. Mueller, S.A.Bass

hep-ph/0611135

plasma instabilities in longitudinally expanding medium non-thermal color fields broadening of jet cone in but not in wide ridge in rapidity at low pT

assoc

Longitudinal broadening of quenched jets in turbulent color fields


P. Romatschke, Phys.Rev. C75, 014901 (2007)

• momentum broadening in a homogeneous but locally anisotropic system

• calculation: eccentricity ~ √8/3 z/T ~ 3

• caveats: - calculation done only for charm quark and collisional energy loss - requires large anisotropy (ξ ~ 10) large shear viscosity (ξ~ 10/sT) but data suggest low shear viscosity (~0.1)

Momentum broadening in anisotropic QGP

z/T ≃ Δη/Δ > 1

data: D. Magestro (STAR), Hard Probes 2004


Correlations between jet and radial flow S. Voloshin, nucl-th/0312065, Nucl.Phys. A749, 287 (2005)

E. Shuryak, nucl-th/0706.3531

• transverse radial expansion in central collisions• correlation appears due to jet quenching

• averaging over jet origin and 1

width broader than that in data

• ridge is independent of jet• particle spectra in ridge: points of origin are biased towards surface ‘a bit’ stiffer slope than that of bulk• particle composition: N(baryons)>N(mesons)

)cos(r)(sinrR),r(L 11222

1 φ−φ−=φ

model

data

r

1

J.Putschke (STAR), QM2006

STAR preliminary


Momentum kick model C.-Y. Wong , hep-ph/0707.2385

• partons in medium acquire momentum ‘kick’ from propagating jet

• fix T = 470 MeV, vary q1 (mom. kick) or σy (rapidity distribution)

• narrow peak in depends mainly on momentum kick

• ridge structure in depends on initial parton rapidity distributionq1=0.6 GeV/cy= 5


Summary

Existence of ridge-like correlations at near side is well established and measured: - particles associated with the ridge are similar to bulk (pT spectra, particle composition)

- more data are becoming available for identified particles - studies with 3-particle correlations ongoing (2+1, 1+2) - studies at forward rapidity These are important measurements to pin down the physics origin of the ridge

BUT More quantitative theoretical predictions are needed as well!

near-side di-hadron correlations at rhic

Documents

gevc ridge

centrality ridge

ridge yield jetau au

berkeleyrelative ridge

d au ridge yield increases

putschke star

k0s trigger ridge

ridge energy content