T'M' Cormier

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Jet Physics in ALICE and a Proposed
Electromagnetic Calorimeter
T.M. Cormier Wayne State University
for the ALICE USA Collaboration
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Creighton University Kent State
University Lawrence Berkeley National
Laboratory Michigan State University Oak Ridge
National Laboratory Purdue University The Ohio
State University University of California,
Berkeley University of California,
Davis University of California, Los
Angeles University of Houston University of
Tennessee University of Texas at
Austin University of Washington Wayne State
University
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Why Jets in Heavy Ion Collisions? or Isnt
there a better way to make a living?
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• Why Jets in Heavy Ion Collisions?
• Jets in Heavy Ion Collisions Provide
• A unique look at the QCD Radiation length of
  Dense,
• Strongly Interacting (Colored) matter (QGP).
• A tomographic tool to quantitatively study
  the QGP medium when benched marked with pp
  running or peripheral heavy ion collisions.

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The basic physics ..
Parton energy loss via induced gluon
radiation in the dense medium
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Collision Centrality Scaling of Inclusive hadron
Spectra at RHIC
Central
Peripheral
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Baryons versus Mesons
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Recent data from STAR at RHIC Away-side Jet
Absorbed in Central Collisions!
Central Collisions
Peripheral Collisions
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How will this physics look in ALICE?
Inclusive po prediction
Vitev and Gyulassy
Data
SPS WA98 RHIC PHENIX
Range of initial state gluon Density dN/dy 2000
- 3500
Perhaps as little as a few of hadrons from hard
collisions will survive in this PT range
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ALICE TPC is the perfect tool for this Physics
STAR TPC data AuAu
Simulation of f-correlation due to mini jets in
central PbPb
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Low PT jets and mini-jets
1/R dN/dR correlation of high PT hadrons
Fragmentation Function of Correlated Particles
Background of uncorrelated Particles
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TPC and inner tracker allow flavor tagging in low
PT jets
Hadronic Charm reconstruction
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• What about jets at high PT in ALICE?
• Rates / Signal to Background?
• What can be measured?
• Trigger?
• TPC at high PT?
• Reconstruction in the presence of
• complex underlying event?

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Opportunity at the LHC to go beyond inclusive
measurements 100 and 200 GeV Jets
imbedded in Central PbPb Event
Underlying Event dominates jet energy resolution
at lower PT
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Jet energy resolution is not a significant issue
because there is no significant jet energy loss
to be measured..
100 GeV PYTHIA Compared to Wiedeman et al for 20
GeV parton energy loss
Jet energy loss is apparent only for limited
cone radii.
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Primary jet quenching effect is thus
redistribution of energy along and perpendicular
to the jet axis. The goal of the ALICE jet
physics program is to measure this energy
redistribution, its dependence on centrality and
flavor.
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Pb/Sci EMCal Dh x Df 1.4
x 2p/3 (Trigger, h, po, direct and thermal g)
RICH
TPC TRD TOF PHOS
ITS
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Trigger with EMCal electromagnetic energy
40 - 50 hadronic
energy
Trigger bias independent of PT Of charged hadrons
within 10
Trigger turn-on versus Ejet
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DPT/PT ()
ITSTPCTRD long tracking lever arm in ALICE 9
at 100 GeV/c
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100 GeV/c jets in pp
Jet reconstruction Poor mans energy flow
analysis Ejet ASPTch BSEMCal
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Resolution for 100 GeV jets in pp and PbPb versus
cell ET cut
pp 16
PbPb Central 25
PbPb events include full mini jet background from
HIJING
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The bottom line . The distribution of energy
parallel to (PL ), and perpendicular to ( jT),
the jet axis..
Reconstructed PL distributions for 50 and 100 GeV
jets in central PbPb collisions.
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Reconstructed jT distributions for 50 and 100 GeV
jets in central PbPb collisions. These
distributions are particularly interesting to
search for transverse heating in the
fragmentation process should it proceed within
the dense medium
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Flavor dependence of jet quenching two examples
of many
Leading particle spectrum for K and L lead jets
with PT gt 75 GeV/c, baryon versus meson quenching
Baryon/anti-Baryon led jets With PT gt 75 GeV/c -
distinction of quark / gluon quenching
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The Detector Pb/Scintillator with mega-tile
technology 20k towers in Df x Dh 2p/3 x
1.4 Towers exactly projective with tiles 5cm x
5cm Resolution (simulated) (sE/E )2 (12.2/?E)2
(0.4)2 Photo Detectors 5mm x 5mm
APDs Modular design permitting late
installation
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Technical issues Optical studies with 5cm x 5cm
tiles and WLS readout via 0.5mm fiber
Achieve 1.5 RMS spatial uniformity
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• Summary
• ALICE-USA collaboration is in the process of
  proposing
• a modest investment in instrumentation for an
  EMCal to better
• enable high PT jet physics in ALICE.
• The combined power of the EMCal and the ALICE
  TPC and
• other detectors permit a complete measurement of
  the redistribution
• of jet energy parallel to and perpendicular to
  the jet axis. Medium
• modification of the parton fragmentation process
  including its
• dependence on energy and flavor (s,c,b) will be
  measured. These
• measurements constitute an important extension of
  on going RHIC
• measurements to a to a much hotter, denser and
  longer lived plasma.

200k per ALICE-USA institution per year for
three years
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Summary

• All of the above can be studied separately for
  baryon
• and meson led jets. Early RHIC data suggests
  there are
• significant differences in the quenching in these
  two cases.
• The calorimeter permits the study of exclusive
  hard scattering
• processes such as g jet and Zo jet.

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