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Near-side di-hadron correlations at RHIC. Jana Bielcikova (Yale University). p T trig =3-6 GeV/c, 2 GeV/c
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Jana Bielcikova (Yale) ISMD 2007, Berkeley 1
Near-side di-hadron correlations
at RHIC
Jana Bielcikova (Yale University)
Jana Bielcikova (Yale) ISMD 2007, Berkeley 2
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?
Jana Bielcikova (Yale) ISMD 2007, Berkeley4
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!
Jana Bielcikova (Yale) ISMD 2007, Berkeley5
The ridge properties
Jana Bielcikova (Yale) ISMD 2007, Berkeley 6
(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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 7
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 8
• 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
Jana Bielcikova (Yale) ISMD 2007, Berkeley9
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley10
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley11
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 12
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 13
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 14
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 15
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 (?)
Jana Bielcikova (Yale) ISMD 2007, Berkeley 16
Where does the ridge come from?
Jana Bielcikova (Yale) ISMD 2007, Berkeley 17
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 18
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 19
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 20
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 21
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 22
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
Jana Bielcikova (Yale) ISMD 2007, Berkeley 23
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!