what’s missing in our current picture from high p t measurements at rhic?
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What’s Missing in our Current Picture from High p T Measurements at RHIC?. Saskia Mioduszewski Texas A&M University. 23 March, 2007. Single-Particle Spectra – What have we learned?. - PowerPoint PPT PresentationTRANSCRIPT
What’s Missing in our Current Picture from High pT
Measurements at RHIC?
Saskia Mioduszewski
Texas A&M University
23 March, 2007
Single-Particle Spectra – What have we learned?
Hadrons are suppressed, photons are not – photons serve as the “control” experiment
High-pT suppression comparison to theory: GLV dNg/dy ~ 1000 I. Vitev and M. Gyulassy, PRL 89 (2002) 252301
Initial energy density: 0 ~ 15 GeV/fm3
PHENIX, Phys. Rev. Lett. 96, 202301 (2006)
What can we learn about Energy Loss?
Fractional effective energy loss: Sloss (MJT)
“Effective” because of surface bias when analyzing single particle spectra
PHENIX 0 SpectrumRenk and Eskola, hep-ph/0610059
8 < pT < 15 GeV/c
PHENIX, nucl-ex/0611007
New Understanding of Energy Loss through Heavy Flavor?
GLV calculation requires collisional energy loss to describe electrons from heavy-flavor decays
perhaps collisional energy loss not negligible as previously assumed
STAR: nucl-ex/0607012, PHENIX (QM2006): nucl-ex/0611018
S. Wicks, QM 2006
Heavy flavor suppression– Challenge to Theory
Electrons from heavy-flavor decays are more suppressed than expected, in particular with non-zero contribution from bottom
p+p collisionsX. Lin, QM 2006
pedestal and flow subtracted
4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig
Di-Jets through Hadron-Hadron Correlations
“Disappearance of away-side jet” in central Au+Au collisions
0-5%
Escaping Jet“Near Side”
Lost Jet“Far Side”
STAR, PRL 90 (2003) 082302
IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)
Evolution of Jet Structure
At higher trigger pT (6 < pT,trig < 10 GeV/c), away-side yield varies with pT,assoc
For lower pT,assoc (1.3 < pT,assoc <1.8 GeV/c), away-side correlation has non-gaussian shape becomes doubly-peaked for lower pT,trig
pedestal and flow subtracted
4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig
M. Horner, QM 2006
STAR preliminary
0-12% 200 GeV Au+Au
Hard-soft correlations
Hard-soft: away-side spectra approaching the bulk.
Inclusive in top 5%?
Three-particle correlation – N.N. Ajitanand, J. Ulery
Mediumaway
near
deflected jets
away
near
Medium
mach cone
STAR, PRL 95,152301 (2005)
4 < pT,trig< 6 GeV/c
Near-side Correlation
Additional long-range correlation in
Au+Au 20-30%
the “ridge”
Coupling of high pT partons to longitudinal expansion - Armesto et al, PRL 93 (2004)QCD magnetic fields- Majumder et al, hep-ph/0611035In recombination framework: Coupling of shower partons to thermal partons undergoing longitudinal expansion- Chiu & Hwa Phys. Rev. C72:034903,2005Radial flow + trigger bias –S.A. Voloshin, Nucl. Phys. A749, 287 (2005)
J. Putschke, QM 2006Au+Au 0-10%
STAR preliminary
(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
J. Putschke, QM 2006
STAR preliminary
“Jet” spectrum vs. “Ridge” spectrum
“jet” slope“ridge” slopeinclusive slope
efft Tptt epdpdN //
J. Putschke, QM 2006
STAR preliminary STAR preliminary
Ridge Yieldpt,assoc. > 2 GeV
STAR preliminary
Ridge yield persists up to highest trigger pT and approximately constant yield
J. Putschke, QM 2006
“Reappearance of away-side jet”
With increasing trigger pT, away-side jet correlation reappears
4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig
STAR, Phys. Rev. Lett. 97 (2006) 162301
Surface Bias of Di-Jets?
Renk and Eskola, hep-ph/0610059
8 < pT,trig< 15 , 4< pT,assoc< 6 GeV/c
8 < pT,trig< 15 GeV/c
STAR, Phys. Rev. Lett. 97 (2006) 162301
Comparison of IAA to RAA
IAA = Yield(0-5% Au+Au) Yield(d+Au)
In the di-jets where trigger pT is 8-15 GeV/c, the suppression is same as for single particles as a function of pT
= Near-side IAA
= Away-side IAA
8 < pT(trig) < 15 GeV/c
D. Magestro, QM 2005
Near-side Yields vs. zT
After subracting the Ridge M. Horner, QM 2006
Away-side Yields vs. zT
M. Horner, QM 2006
Away-side suppression as a function of pT,trig
M. Horner, QM 2006
Away-side IAA
Away-side suppression reaches a value of 0.2 for trigger pT > 4 GeV/c, similar to single-particle suppression
IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)
What other handles do we have?
Centrality, trigger and associated pT,…..
….Reaction plane
In-plane
Out-planeSTAR
4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig
STAR, Phys. Rev. Lett. 93 (2004) 252301
Another handle: -jet
q
Photon-jet measurement is, in principle, sensitive to full medium
Bias to where away-side jet is close to surface?
Together with di-jet measurement for comparison
Another differential observable
Increasing ratio of direct photons to decay photons with centrality due to hadron suppression at high pT
PHENIX, Phys. Rev. Lett. 94, 232301 (2005)
Wang et al., Phys.Rev.Lett. 77 (1996) 231-234
1
/Ntr
igdN
/d
(rad)
Another handle: -jet
Current Results from Run-4 Au+Au collisions:
J. Jin, QM 2006T. Dietel, QM 2005
q
Summary
• Limited information extracted from single-particle pT spectra – Effective fractional energy loss reaches 20% for most
central collisions– Initial energy density ~ 15 GeV/fm3 from radiative
energy loss models
• Di-Jets (those that are observed) may have less surface bias
• Photon-Jet Measurement will complement the di-jet for more complete probe
• Heavy-flavor suppression not consistently described by theoretical models with light meson suppression – need elastic energy loss
Conclusions What is missing from our picture?
• Need a consistent theoretical approach to describe different observables
• Need more quantitative model predictions for “ridge” explanation
• Need more quantitative descriptions of jet modifications from experimenters– Particle species in ridge vs. in jet (J. Bielcikova’s talk)– Path-length dependence of jet-correlated yields (using
reaction plane dependence)
• Need a great deal of statistics for -jet measurement (J. Dunlop’s talk)
STAR preliminaryJet+Ridge ()
Jet ()
Jet)
yiel
d
,)
Npart
3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV
Sloss
• S(pT )/pT = S0,• is a constant for all pT > 3 GeV/c, which also results in a• constant ratio of the spectra, RAA(pT ). For the constant• fractional shift, the Jacobean is simply dS(pT )/dpT = S0
• RAA(pT ) = (1 + S0)−n+2
• RAA(pT )1/(n−2) =1/(1 + S0)• The effective fractional energy loss, Sloss, is related to• the fractional shift in the measured spectrum, S0. The• hadrons that would have been produced in the reference• p + p spectrum at transverse momentum pT + S(pT ) =• (1 + S0)pT , were detected with transverse momentum,• pT , implying a fractional energy loss:• Sloss = 1 − 1/(1 + S0) = 1 − RAA(pT )1/(n−2)