Download - High p T Hadron Correlation
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High pT Hadron Correlation
Rudolph C. HwaUniversity of Oregon
Hard Probes 2006
Asilomar, CA, June 10, 2006
and No Correlation
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A. Conventional scenario
Hard scattering high pT jet
hadron correlation
(usual conductor has resistance)
(superconductor has no resistance)
High pT hadrons high pT jet
correlation
B. Unconventional scenario
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B. No Jet Correlation
1. and production up to pT ~ 6 GeV/c
2. Forward production at any pT
3. Large pT at LHC
A. Jet Correlation
pT1-pT2 1-2 1-2
near sideaway sideauto-correl
1
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Associated particle pT distribution
dNπp2dp2
trig =dp1p1
dNππp1dp1p2dp24
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∫dp1p1
dNπp1dp14
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∫p1 -- trigger
p2 -- associated
F4 =(TT+ST+SS)13(TT+ST+SS)24
k
q3
q
1
q4
q2
dNππp1dp1p2dp2
=1
(p1p2)2
dqiqii
∏⎡
⎣ ⎢ ⎤
⎦ ⎥ ∫ F4(q1,q2,q3,q4)R(q1,q3,p1)R(q2,q4,p2)
In the recombination model
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Associated particle distribution in the recombination model
-- for only
Hwa & Tan, PRC 72, 057902 (2005)
STAR
4 < pTtrig < 6
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QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
in white paper
Remember p/ ratioAll in recombination/ coalescence model
Medium modified dihadron fragmentation function -- more relevant at higher pT.
Majumder, Wang, Wang nucl-th/0412061
S S -- fragmentation
T S
Jet tomography CGC forward production
All use fragmentation for hadronization -- but not reliable at intermediate pT
If proton production cannot be described by fragmentation at intermediate pT, how much trust can be placed on pion production by fragmentation?
Dp / D
TTT TT
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production in AuAu central collision at 200 GeV
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Hwa & CB Yang, PRC70, 024905 (2004)
fragmentation
recombination
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Trigger-normalized fragmentation functionD(zT )
Trigger-normalized momentum fraction
zT =pT (assoc)pT (trig)
D(zT ) is measurable without direct knowledge of the parton energy.
X.-N. Wang, Phys. Lett. B 595, 165 (2004)
J. Adams et al., nucl-ex/0604018
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STAR claims universal behavior in D(zT)
fragmentation
violation of universal behavior due to medium effect ---- thermal-shower recombinationSuggestion: look for p/ ratio in this
region. Large if dominated by recombination.
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Chiu & Hwa, PRC 72, 034903 (2005)
hard partonshower
parton, leads to the trigger particle
energy loss converts to soft particles
At higher trigger momentum, the hard parton originate closer to the surface, so less energy is lost. Hence no pedestal.
hard parton
trigger hadron
At low trigger momentum, hard partons can originate farther in.
Δ
Those soft particles form the pedestal.
pedestal ΔT=15 MeV
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Casalderrey-Solana, Shuryak, Teaney Mach cone
Dremin Cherenkov gluons
Ruppert, Muller color wake
Koch, Majumder, Wang Cherenkov radiation
Vitev jet quenching+fragm
.
.
Chiu, Hwa parton multiple scattering
Away-side distribution
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Parton multiple-scattering model
Sample trajectories for 2.5<p(trig)<4, 1<p(assoc)<2.5
exit tracksabsorbed (thermalized) tracks
high pT parton
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Away-side Δ distribution
-
PHENIX 2.5<p(trig)<4 parton
p=4.5
energy loss thermalized
Event averaged, background subtracted.
Cannot distinguish between 1-jet and 2-jet contributions (e.g., Mach cone)
A new measure proposed that suppresses statistical background event-by-event
Chiu & Hwa, nucl-th/0605054
Chiu’s talk in parallel session on Monday
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Autocorrelation
Trainor (STAR) Jamaica workshop (2004)
QuickTime™ and a
TIFF (LZW) decompressorare needed to see this picture.
Consider an example in time series analysis
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Correlation function C2 (1,2) =ρ2 (1,2)−ρ1(1)ρ1(2)
Treat 1,2 on equal footing --- no trigger
The only non-trivial contribution to near , would come from jets
θ− : 0 φ− : 0
A(θ−,φ−)
Define
θ−=θ2 −θ1φ−=φ2 −φ1
C2(1,2)
Fix and , and integrate over all other variables in
θ− φ−
A(θ−,φ−) =1
Rθ+
dθ+Rθ+
∫ C2 (θ+,θ−,φ−)Autocorrelation
No ambiguous subtraction procedure; only do as defined.
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hard parton momentum k
Radiated gluon momentum q
two shower partons with angular difference
(a much larger set)
jet axis
q2
q1
x
yz
2
1
k
thermal partons
p2
p1
x
yz
θ1θ2
pion momenta (observable)
-
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STAR data on Autocorrelation for central Au+Au at 130 GeV for ||<1.3, 0.15<pT<2 GeV/c
nucl-ex/0605021
NO trigger, no subtraction
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Chiu & Hwa, PRC 73, 014903 (2006)
TS recombination in a jet with pT>3 GeV/c
dominated by soft partons
Δρρref
=C2 (
rp1,
rp2 )
ρ ref (rp1,
rp2 )
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A. Jet Correlation
pT1-pT2 1-2 1-2
near sideaway sideauto-correl
1
2
3
4
5
B. No Jet Correlation
1. and production up to pT ~ 6 GeV/c
2. Forward production at any pT
3. Large pT at LHC
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and production at intermediate pT
For
strange-quark shower is very suppressed.
pT distribution of by recombination
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are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
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s
hard parton scattering
fragmentation
If they are produced by hard scattering followed by fragmentation, one expects jets of particles.
There are other particles associated withφ and
Hwa & CB Yang, nucl-th/0602024
recombination s s φ0
sss −recombination
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QuickTime™ and aTIFF (LZW) decompressor
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QuickTime™ and aTIFF (LZW) decompressor
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Select events with or in the 3<pT<6 region, and treat them as trigger particles.
Predict: no associated particles giving rise to peaks in Δ,
near-side or away-side.
We claim that no shower partons are involved in production, so no jets are involved.
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Δ
(1/N
trig)
dN
/d(Δ)
background
SignalAu+Au top 5%
trigger (pT>3 GeV/c) in Au+Au
?
charged hadrons
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A. Jet Correlation
pT1-pT2 1-2 1-2
near sideaway sideauto-correl
1
2
3
4
5
B. No Jet Correlation
1. and production up to pT ~ 6 GeV/c
2. Forward production at any pT
3. Large pT at LHC
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Forward production of hadrons
PHOBOS, nucl-ex/0509034
Without knowing pT, it is not possible to determine xF
Back et al, PRL 91, 052303 (2003)
' = η − ybeam
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Theoretically, can hadrons be produced at xF > 1?It seems to violate momentum conservation, pL > √s/2.
In pB collision the partons that recombine must satisfy
xii∑ <1
p
B
But in AB collision the partons can come from different nucleons
BA
xii∑ >1
(TFR)
In the recombination model the produced p and can have smooth distributions across the xF = 1 boundary.
37proton-to-pion ratio is very large.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
proton
pionHwa & Yang, PRC 73,044913 (2006)
: momentum degradation factor
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no shower partons involved no jets involved
no jet structure no associated particles
Hwa & Yang, nucl-th/0605037
Thermal distribution fits well
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A. Jet Correlation
pT1-pT2 1-2 1-2
near sideaway sideauto-correl
1
2
3
4
5
B. No Jet Correlation
1. and production up to pT ~ 6 GeV/c
2. Forward production at any pT
3. Large pT at LHC
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and p production at high pT at LHC
New feature at LHC: density of hard partons is high.
High pT jets may be so dense that neighboring jet cones may overlap.
If so, then the shower partons in two nearby jets may recombine.
2 hard partons
1 shower parton from each
p
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The particle detected has some associated partners.
There should be no observable jet structure distinguishable from the
background.
10 < pT < 20 GeV/c
That is very different from a super-high pT jet.
But they are part of the background of an ocean of hadrons from other jets.
A jet at 30-40 GeV/c would have lots of observable associated
particles.
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Proton-to-pion ratio at LHC -- probability of overlap of 2 jet cones
single jet
Rp / : 50
Hwa & Yang nucl-th/0603053
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We predict for 10<pT<20 Gev/c at LHC
• Large p/ ratio
• NO associated particles above the
background
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Summary
B. No Jet Correlation
1. and production up to pT ~ 6 GeV/c
2. Forward production at any pT
3. Large pT at LHC
A. Jet Correlation
pT1-pT2 1-2 1-2
near sideaway sideauto-correl
Jet fragmentation at high andpTtrig pT
assoc
Recombination at pTtrig , pT
assoc < 6GeV / c
No trigger bias, need more data at high pT
There’s jet quenching, but not necessarily fragmentation
?
?
?When recombination dominates over fragmentation, B/M ratio can be very large, and there would be no jets, no jet structure and no correlation above background.