ElectroMagnetic probes

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ElectroMagnetic probes with MPD Calorimeter
Dubna JINR VBLHEP, DLNP September 2009
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• 1. Physical motivations
• Electromagnetic probes
• Particle rate
• 2. Requirements to the Ecal
• 3. Performance
• 4. Prototype status
• 5. Electron identification
• 6.Conclusions

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Electromagnetic Probes virtual (appearing as
ee- or µµ- pairs) real photons are tools
to diagnose the hot and dense matter produced in
relativistic heavy-ion collisions.
They are not distorted by final state
interactions and once produced can escape
unaffected the interaction region, carrying to
the detectors information about the conditions
and properties of the medium at the time of their
creation.
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• thermal radiation emitted by the strongly
  interacting Quark-Gluon Plasma
• in the early phase of the collision. The
  elementary processes involved are
• annihilation
• QCD Compton
• identification of this signal ?
• 1. proof of deconfined phase
• 2. direct measurement the temperature, readily
  given by the inverse slope.
• Theory has singled out the thermal radiation from
  the
• Quark-Gluon Plasma phase
• .

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b) Thermal radiation emitted by the high-density
hadron gas in the later phase of the collision.
The main elementary process here is the pion
annihilation , mediated through vector meson
dominance. This component, controlled by the
pole at the rho mass of the pion electromagnetic
form factor, contributes primarily to the
low-mass region, around and below the ? mass.
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• There are two main difficulties in the
  experimental measurements
• Huge combinatorial background of uncorrelated
  lepton pairs.
• This background therefore depends quadratically
  on the particle multiplicity and
• strongly increases as the coverage moves to
  low-pT leptons.
• In the measurement of ee- pairs, p Dalitz
  decays and conversions.
• Physics background.
• Photons and dileptons can be emitted by a
  variety of sources and
• therefore before claiming observation of any new
  effect, it is mandatory
• to have a thorough understanding of the expected
  contribution
• from all known sources.
• Gammas created due to electromagnetic decays of
  hadrons after
• the freeze-out carry no information about excited
  system and
• should be subtracted.

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PHENIX
The fraction of the direct photon component as a
function of Pt in (a) pp and (b) AuAu (min.
bias) at vS 200 GeV. The error bars and the
error band represent the statistical and
systematic uncertainties, respectively. The
curves are from a NLO pQCD calculation.
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Low mass enhancement seen in AuAu invariant mass
spectrum measured by CERES (left) and
PHENIX (right)
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Anomaly observed in energy dependence for the
K/p ratio Systematical uncertainty can be
reduced by involving K/p or K/? ratio in the
analisys
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Phase transition should be indicated by increase
in photon activity p rate vs beam energy? ?
rate vs beam energy? Prompt ? rate vs beam
energy?
AuAu collisions at vSNN9GeV UrQMD
Photons associated to the p
100/Pt 50/Pt 20/Pt 10/Pt 5/Pt
N? /Np
Np/Np
N? pr /Np
Pt(GeV)
Pt(GeV)
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Requirements to the Ecal
Energy spectra and multiplicity distribution are
determine lateral and longitudinal size of
calorimeter cell
AuAu collisions at vSNN9GeV UrQMD
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Calorimeter energy resolution strongly determine
psignal to combinatorial background ratio and
resolution in the ?? invariant mass spectra
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Main option Shashlyk type of calorimeter
KOPIO
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Granularity -3x3 cm
AuAu collisions at vSNN9GeV
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p
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Energy resolution (2.90.1)/vE(GeV). Time
resolution (8010)psec / vE(GeV).
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Detector response vs beam energy
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MIP
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• Conclusions
• Wide range of physics tasks can be studied
• including ECal into the MPD detector
• Proposed "SHASHLYK" type of calorimeter is
  adequate to the physics tasks
• Prototype of calorimeter module has been built
  and tested with CERN and DESY beams.
• Expected parameters have been reached.

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