Andr Mischke

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Hard and heavy probes Results from STAR and
perspectives for ALICE
André Mischke
NIKHEF Jamboree, 17-18 December 2007
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Au on Au collision at a cms energy 200 GeV per
nucleon-nucleon pair

• A central event
• Typically 1,000 to 2,000 tracks per event in the
  TPC

• Two-track separation 2.5 cm
• Momentum resolution lt 2
• Space point resolution 500 mm
• Rapidity coverage 1.8 lt h lt 1.8

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Exciting results from light quarks
factor 4-5

• Central AuAu collisions
• strong suppression of inclusive hadron
  production
• disappearance of the away-side jet
• dAu looks like pp
• Jet quenching in the dense medium
• Well described by energy loss models

Nuclear modification factor
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Limitations of RAA
K.J. Eskola et al., NP A747, 511
RAA at 10 GeV/c
central RAA data
(proportional to gluon density)

• Leading hadrons preferentially arise from the
  surface
• Limited sensitivity to the region of highest
  energy density
• Need - insensitive trigger particles Prompt
  photons
• - more penetrating probes Heavy quarks

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Towards prompt photon?jet azimuthal angular
correlations

• No interaction with the medium
• Sensitive to the whole volume
• No fragmentation bias E? ? Ejet
• Near-side correlation reduced due to prompt
  photons (?/?0 ? 1)
• Away-side correlation is a mixture of ?-jet or
  dijets
• ? Challenge Precise separation of neutral pions
  and prompt photons

AuAu _at_ 200 GeV
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Neutral pions
Oleksandr Grebenyuk (Ph.D.)

• Inclusive yield measured over several orders of
  magnitudes
• Extend kinematical range
• Remarkable agreement with NLO pQCD calculations
• Publication in preparation

dAu pp
RdAu
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Direct photons and ?0-h correlations
Martijn Russcher (Ph.D.) Federica Benedosso
(Ph.D.)
R 1 ?dir / ?decay

• Direct photon signal
• Double ratio R consistent with NLO pQCD
  calculations
• Publication in preparation
• ALICE has excellent capabilities for prompt
  photon-jet correlations
• Photon spectrometer (superb energy and spatial
  resolution)
• EMCal (from 2009)
• large volume TPC

dAu _at_ 200 GeV
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Detailed picture on energy loss in the medium
Marco van Leeuwen (Vidi)
AuAu 0-10 STAR preliminary
associated
dAu 40-100
Jet-like peak
3 lt pt,trigger lt 4 GeV pt,assoc. gt 2 GeV
Ridge associated yield at large ??
dN/d?? approximately independent of ??
Strong ?-? asymmetry indicates longitudinal flow
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Heavy quark energy loss
André Mischke (Veni)

• Heavy quarks are primarily produced in the
  initial state of the collision ? well calibrated
  probes
• Heavy quarks lose less energy due to suppression
  of small angle gluon radiation (so-called
  dead-cone effect)

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Electron tagged correlations

• Experimental approach
• electrons from semi-leptonic D/B decays are used
  to trigger on charm or bottom quark pairs
• associate D0 mesons are reconstructed via their
  hadronic decay channel (probe)
• Underlying production mechanism can be
  identified using second charm/bottom particle

trigger side
3.83 54 10
charm production
???0
????
probe side
flavor creation gluon splitting/fragmentation
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K-? invariant mass distribution
w/o electron trigger
pp 200 GeV STAR preliminary
dn/dm
combinatorial background is evaluated using
like-sign pairs
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Non-photonic electron?D0 azimuthal angular
correlations

• First heavy-flavor particle correlation
  measurement at RHIC
• Allows separation of charm and bottom production
  events
• ALICE Powerful tool for compre-hensive
  energy-loss measurements of heavy-quarks
• Starting Grant recommended for funding
  - budgetary restrictions
• ? Study the dynamical properties of the QGP
  initial gluon density, drag coefficient
• ? Opens up new horizons AdS/CFT
• energy loss of heavy quarks

essentially from B decays only
70 from charm 30 from bottom
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The ALICE experiment
A Large Ion Collider Experiment at CERN Large
Hadron Collider

• Especially designed for measure-ments in
  heavy-ion collisions
• Highest collision energy 1140 TeV
• Very high initial temperature
• relatively long-lived QGP
• high heavy-quark production rates

lead beam lead beam
Silicon strip detector
Utrecht University/ NIKHEF provided key hardware
component
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Heavy flavour measurements in ALICE
Cristian Ivan (Ph.D.) André Mischke
D0

• ALICE has excellent capabilities for charm and
  bottom measure-ments
• Inner Tracker for secondary vertex measurements
  (resolution better than 50?m)
• TPC and ToF for high precision tracking and
  particle ID (full azimuthal coverage around
  mid-rapidity)
• Efficiently trigger on heavy-quarks with high
  transverse momentum

1 year _at_ nominal luminosity 107 central PbPb
events
e-D0 azimuthal correlation _at_ 14 TeV (charm,
PYTHIA)
1B events with 60M electron triggers
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Conclusions

• The ALICE group
• provided a key detector component to ALICE
• is well prepared for the most striking
  measurements to study the dynamical properties of
  the QGP
• prompt photon jet azimuthal correlations
• heavy flavour azimuthal correlations
• ridge phenomenology
• has unique expertise on flow analysis ? next
  talk
• will test fundamental theoretical predictions
  and its limits at high energy densities

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Backup slides
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Electron tagged correlationsbottom production
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PYTHIA simulations 3ltpTtrglt7 GeV/c
André Mischke
like-sign e-K pairs
unlike-sign e-K pairs

• Different decay topology for charm and bottom
  production events
• Charge-sign requirement on electron-Kaon pairs
  gives additional constraint on production process
• ? Clear separation of charm and bottom
  contributions

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Theoretical model predictions
M. Cacciari et al., PRL 95, 122001 (2005)
D/B crossing point
Large uncertainty in the D/B crossing point