High pT Hadron Correlation

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High pT Hadron Correlation

and No Correlation
Rudolph C. Hwa University of Oregon
Hard Probes 2006 Asilomar, CA, June 10, 2006
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A. Conventional scenario
Hard scattering ? high pT jet ? hadron
correlation
(usual conductor has resistance)
(superconductor has no resistance)
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same side
STAR
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Associated particle pT distribution
p1 -- trigger
p2 -- associated
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Associated particle distribution in the
recombination model -- for ?? only Hwa
Tan, PRC 72, 057902 (2005)
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Medium modified dihadron fragmentation function
-- more relevant at higher pT.
Majumder, Wang, Wang nucl-th/0412061
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Away side
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? production in AuAu central collision at 200 GeV
recombination
fragmentation
Hwa CB Yang, PRC70, 024905 (2004)
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pT(assoc)
4
0
4
8
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pT(trig)
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Trigger-normalized fragmentation function
Trigger-normalized momentum fraction
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STAR, nucl-ex/0604018
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12
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pT(assoc)
4
0
4
8
12
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pT(trig)
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Correlation on the near side
?? and ?? distributions
STAR, PRL 95, 152301 (2005)
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Chiu Hwa, PRC 72, 034903 (2005)
At low trigger momentum, hard partons can
originate farther in.
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Away-side distribution
Casalderrey-Solana, Shuryak, Teaney Mach
cone Dremin Cherenkov gluons Ruppert, Muller
color wake Koch, Majumder, Wang
Cherenkov radiation Vitev jet
quenchingfragm . . Chiu, Hwa parton multiple
scattering
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Parton multiple-scattering model
Sample trajectories for 2.5ltp(trig)lt4,
1ltp(assoc)lt2.5
absorbed (thermalized) tracks
exit tracks
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Away-side ?? distribution
Event averaged, background subtracted.
Cannot distinguish between 1-jet and 2-jet
contributions (e.g., Mach cone)
Chius talk in parallel session on Monday
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Autocorrelation

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Correlation function
Treat 1,2 on equal footing --- no trigger
No ambiguous subtraction procedure only do as
defined.
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STAR data on Autocorrelation for central AuAu at
130 GeV for ??1.3, 0.15ltpTlt2 GeV/c
NO trigger, no subtraction
nucl-ex/0605021
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? and ? production at intermediate pT
strange-quark shower is very suppressed.
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Hwa CB Yang, nucl-th/0602024
If they are produced by hard scattering followed
by fragmentation, one expects jets of particles.
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We claim that no shower partons are involved in
???? production, so no jets are involved.
Select events with ? or ? in the 3ltpTlt6 region,
and treat them as trigger particles.
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charged hadrons
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Forward production of hadrons
Without knowing pT, it is not possible to
determine xF
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Theoretically, can hadrons be produced at xF gt 1?
(TFR)
It seems to violate momentum conservation, pL gt
vs/2.
In the recombination model the produced p and ?
can have smooth distributions across the xF 1
boundary.
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proton

• momentum degradation factor

pion
Hwa Yang, PRC 73,044913 (2006)
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BRAHMS, nucl-ex/0602018
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Hwa Yang, nucl-th/0605037
Thermal distribution fits well
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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.
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The particle detected has some associated
partners.
There should be no observable jet structure
distinguishable from the background.
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Proton-to-pion ratio at LHC
? -- probability of overlap of 2 jet cones
Hwa Yang nucl-th/0603053
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We predict for 10ltpTlt20 Gev/c at LHC

• Large p/? ratio

• NO associated particles above the background

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Summary