david winter
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Jets and High-p T (Di-hadron) Correlations in PHENIX Lake Louise Winter Institute 2005 Lake Louise, Alberta CA. David Winter. Outline. RHIC and PHENIX The nuclear medium and jet modifications Correlation Functions Hard scattering Near (Same)-side and Away-side (di-jet) correlations - PowerPoint PPT PresentationTRANSCRIPT
Jets and High-pT (Di-hadron) Correlations in PHENIX
Lake Louise Winter Institute 2005Lake Louise, Alberta CA
David Winter
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 2
Outline• RHIC and PHENIX• The nuclear medium and jet modifications
– Correlation Functions– Hard scattering– Near (Same)-side and Away-side (di-jet)
correlations
• Jet modifications in Heavy-Ion Collisions• Future measurement technique• Summary
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 3
RHIC and PHENIX• Brookhaven National Laboratory
– 70 mi from Manhattan
• Two rings / 3.83 km circumference• Capable of colliding ~ any nuclear species on
~ any other species• Energy:
500 GeV for p-p 200 GeV for Au-Au (per N-N collision)
• Luminosity– Au-Au: 2 x 1026 cm-2 s-1
– p-p : 2 x 1032 cm-2 s-1 (polarized)
Two central arms for measuring hadrons, photons and electrons
Two forward arms for measuring muons
Event characterization detectors in center
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 4
The Nuclear Medium• Nuclear modification factor
• Multiple scattering in the medium results in kT broadening
• Thought to be source of Cronin Enhancement
d+Au
Au+Au
• Nuclear modification factor
• Medium-induced energy loss?
x4-5 suppression
0
scaled,)(Yield
scaled),(Yield
pp
AARAA
scaled),Periph(Yield
scaled),Central(YieldcpR
Let’s go beyond single-particle observables -- What can study of jet observables tell us?
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 5
Correlation Functions• Azimuthal correlations are an alternative approach to jet studies where
full reconstruction is impractical
• is between leading and associated particles• Correlation functions typically defined as :
)(
)()(
mix
corr
N
NC
Same-event pairs
Mixed-event pairs
• Conditional Yields can be extracted from correlation when properly normalized and corrected for acceptance and efficiency:
R
NdN
N
Nd
dN
Nmixmix
corr
trigtrig )()(2
)(11 0
0
Correct for limited acceptance and single-particle efficiency
Observed yield per trigger
Real yield per trigger particle
3.0<pT<6.0
p+p h± Correlation Function
Fit with: 2 Gaussians + Constant Bg term
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 6
Partons have intrinsic transverse momentum kT:
Hard-scattering
, 1 , 2 ,1 ,2T jet T jet T Tp p k k
Leading hadron
Transverse plane:
jet
jT
jT = hadron’s momentum transverse to the jet axis
• Partons scatter with large Q2
• Outgoing partons fragment into cone of hadrons
• Parameters of interest
• Spread of particles around jet axis (jT)
• Acoplanarity of back-to-back jets (kT)
• Hadronic spectrum (Frag. Func. D(z))
7.022 R
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 7
Near-side Correlation
• Leading (highest pT) “Trigger” particle used as estimator for jet axis
• “Near-Side”: particles from same jet will be correlated in a peak around ~ 0
• Simple relations can be derived (assume pT,trig >> jTy):
Associated&Trigger between Angle
ajtj
Projection onto transverse planetj trigger-partonaj associated-parton
trigT
assocThhTassocTNout p
pxxjpp
y
,
,2222,
2, with,1sin
2
,
2,
2
2,
121h
assocTN
assocjh
Nout
RMSTx
p
xx
pjy
Assume angles are statistically independent
Near-side peak
Note there are corrections to these expressions, but they are smallSee J. Jia, nucl-ex/0409024 for further details
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 8
Away-side Correlation
• “Away-Side”: particles from (nearly) back-back jets form a peak at ~ • Average di-jet acoplanarity kT can be extracted from angles btn hadrons:
Projection onto transverse planetj trigger-partonaj associated-partonjj parton-parton
jjajtj
jetT
trigTtrig
NF
h
assocT
RMStrigT
p
pz
x
pzk
y
,
,
22
2
, sinsin2
cf. nucl-ex/0409024
Assume angles are statistically independent
Away-side peak
Again, there are small corrections…
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 9
Jet Modifications• One of the most exciting results at RHIC has been
the behavior of the away-side peak in azimuthal correlations
There is little if any difference between p+p, d+Au away-side peak (esp. at high pT), but the broadening of away-side peak in Au+Au is striking!
Courtesy W.Holzmann, 21st WWND PHENIX Preliminary
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 10
kT comparison
• Comparison of p+p/d+Au/Au+Au allows separation of medium effects• We see little, if any, difference between kT of p+p & d+Au
– Disappearance of away-side in Au+Au complicates this comparison...
2 2vac IS nucl
2AA
2FS nuclk kk k
2 2vac IS nucl
2AA
2FS nuclk kk k
p+p p+A A+A
1d RMS kTztrig product using 0 and ± as triggers
2ppRMS,
22
RMS,dAu
2TyTyTy kkk
PHENIX Preliminary
.)(27.0.)(68.025.02 sysstatkTy
0
PHENIX Preliminary
PHENIX Preliminary
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 11
Future Measurements• Correlation method requires rough
binning in pT
– Observables extracted as averages within these rough bins
– Corresponding bin widths also need to be “extracted”
• Alternatively, statistical weighting can be used to extract distributions directly
• Example:
– Away-side dN/dxE sensitive to the fragmentation function (e.g.. at high-pT, slopes of dN/dxE and D(z) are related)
• See upcoming d+Au Correlations paper, to be submitted to PRC
2,
,,
trigT
assocTtrigTE p
ppx
PHENIX Preliminary
PHENIX Preliminary
± ±
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 12
Summary• Traditional jet-finding methods are unpractical in RHIC
collisions. Azimuthal Correlations make jet studies possible this high multiplicity environment
• Study of the jet structure (jT, kT) allows us to distinguish between vacuum, initial-state, and final-state effects
• Evolution of jet structure from pp to AuAu collisions– No difference btn pp & dAu, but broadening of di-jet peak in AuAu
• Look for upcoming publications– (nucl-ex/0410003) “Formation of dense partonic matter in relativistic
heavy-ion nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration”
– (nucl-ex/0408007) “Jet Structure of Baryon Excess in Au+Au collisions at sNN = 200 GeV”
– (nucl-ex/0404024) J. Jia, HotQuarks04 proceedings– Jets and correlations: p+p, d+Au, and Au+Au
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 13
Backup SlidesBackup Slides
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 14
Relative Gluon/Quark Contrib.• In current measurement, 0s mainly produced by gg and qg
scattering
gggg gqgq qqqq
qg+gq
gg
Fra
ctio
n of
pro
duce
d 0 s
pT (GeV/c)
Kretzler,hep-ph/0410219
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 15
Is It Hard-scattering?• Single-particle spectrum and QCD predictions
Strong suppression
Au+Au 0 + X (central)Au+Au 0 + X (peripheral)
Peripheral spectra agree well with p+p (data & pQCD) scaled by Ncoll
PHENIX Collab.PRL91, 241803hep-ex/0304038
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 16
Correlations Exampled+Au s=200 GeV 5<pT,trig<10 GeV/c 2<pT,assoc<3 GeV/c
Same-event Mixed-event
Same / Mixed
Mimics acceptance
Fully-correctedAcceptance divides out
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 17
Comparison with Pythia
Red: dataBlue: pythia
5<pT,trig<6
p+p s=200 GeV (Run3)Pythia results agree within ~20%
Lake Louise Winter Institute20-26 Feb 2005
David Winter Jets and High-pt Azimuthal Correlations in PHENIX 18
How high is high (multiplicity)?• Central events: Npart ~ 300
• dNch/d ~ 450
• Most particles are ’s
dN/d ~ 670