2 Talks For 1 Time Slot

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2 Talks For 1 Time Slot
EM Cluster Detection in AA

• Pablo P Yepes, Rice University

AA Ultra-Peripheral Collisions
Pablo P Yepes, Rice University
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EM Cluster Detection in AA

• MiniTalk I

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Why EM Clusters

• Compact MUON Solenoid HI studies have focused on
  Muons for Quarkonia.
• Electrons
• Physics Quarkonia (double stats and better
  handle on systematics), Z ? ee-, b ? e b ? m
• Current experiments
• PHENIX design for e detection (RICH)
• STAR studies indicate that J/Y should be possible
  with EMC, tracking and L3.

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Why EM Clusters

• Photons
• g-jet without jet reconstruction. Detect jet and
  look at hadronic activity in cone opposite to it.
  (à la X.N. Wang). Go down to low ET.
• p0
• Assume g/e look the same in calos. First step
  study g detection with calos only.

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Analysis

• Data samples
• 1000 photons ET1-100 GeV
• 40 Hijing PbPb central events
• Pass data samples through full simulation
• Reconstruct EM clusters in EMC
• Look for crystals ETgtETSeed (2 GeV).
• Sum energy around a R0.05 cone.

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ET per Crystal in Barrel ECAL in PbPb
Remember CMS EMC has around 80K crystals
Minbias
Central
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EM Cluster Angular Resolution
Generated - Reconstructed Angles
Eff. Cut
Eff. Cut
Eff. Cut
Eff. Cut
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Em Cluster Reco Efficiencywith Calorimetry only
Unmatched recoed EM Clusters in one Central
Event
For e tracking should add a significant rejection
factor!!!
Pt(GeV)
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EM Cluster Reconstruction Efficiency versus
rapidity
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EM Cluster Energy Resolution
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Conclusions

• It is possible to reconstruct EM clusters very
  well in the HI environment
• EM opens news possibilities ee, em
• Calos alone cannot do the job.
• High Level Trigger would be needed to get rid of
  large backgrounds.

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End of First MiniTalk
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Ultra-Peripheral Collisions in AA

• MiniTalk II

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Ultra-Peripheral Collisions (UPC)

• No direct nuclear interaction bgt2 R.
• Collision through EM or long range strong forces
  gg, gP.
• Only products of coherent interaction seeing at
  hltlthbeam
• When Coherence exists

gg, gP, PP, gA Collider
pL lt g h/RA 100 GeV/c pT lt h/RA 50 MeV/c
Falk Meissner
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gg Collider Luminosities(G. Baur et al.)
300
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UPC Physics

• Great Variety of topics
• White Paper Hot Topics in Ultra-Peripheral Ion
  Collisions, G. Baur et al (Erice Oct 2001).
• Gluon pdf in A
• Pomeron coupling to A
• Interferometry with short lived particles.
• UPC Workshop at CERN, March 8-9, Hencken PY
  HIF. TheoryExperiment http//quasar.unibas.ch/upc
  
• Working group

CaCa
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LHC gA (gP) Production

• Cross sections larger than gg
• Similar low total pT due to coherence condition
• Heavy Ion Colliders can be seen as vector meson
  factories.

Particle rates (Hz) for nominal
Luminosities (Klein and Nystrand, PRC 60, 014903)
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Ultra-Peripheral Collisions at STAR

• Proof of Principle
• UPC in HI is possible
• A Premiere

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Ultra-Peripheral Collisions (UPC)
time

• Nuclei miss each other (b gt 2RA)
• No hadronic interactions
• Ions are sources of fields
• Photons Z2 ? very high fluxes
• Pomerons A 2 (bulk)- A 4/3 (surface)
• Fields couple coherently to ions
• P? lt h/RA, 30 MeV/c for heavy ions
• P lt gh/RA 3 GeV/c at RHIC

(Au Au, 200GeV/nucleon, University of Frankfurt)
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Nuclear Excitation
In addition to UPC production, nuclei can
exchange one or more separate photons and become
mutually excited.
Process AuAu -gt AuAu
UPC

• It is thought to factorize as function of impact
  parameter
• Decay yields neutrons at zero degrees wrt beam
  direction (ZDC)

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A typical STAR eventsqrt(s)200 GeV/A
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r Analysis Selection

• Minbias
• 2 /- Primary Tracks
• rvertlt 15 cm, zvertlt200 cm
• Transverse Angle gt 2.7 rad
• Total pTlt0.2 GeV

• UPC Trigger
• As Minbias plus anti-cosmic cut Opening Angle lt
  3 rad.

• Backgrounds
• incoherent photonuclear interactions
• grazing nuclear collisions
• beam gas

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Minimum Bias PT
r0 PT
Preliminary
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r0 lineshape
STAR gAu --gt (r0 pp- )Au
ZEUS gp --gt (r0 pp- )p
Preliminary
Set 0 for STAR
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First Glance at 2001 Data

• Dedicated trigger for UPC running for several
  weeks

• Around 10 times more minbias events

Triggered
Minbias
Very Preliminary
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Can we trigger on those events?

• CMS triggers on energy in the calorimeters.
• Monte Carlo study requires 2 particles with
  energy gt 1 GeV in hlt3
• Trigger Eff
• f 20
• r 20

Efficiency
Invariant Mass (GeV)
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Conclusions

• Active community in UPC, with lots of physics
  topics.
• UPC seen at RHIC in the r, ee channel.
• Large rates at LHC
• CMS large coverage will be ideal to look at these
  events. Lower field would help.
• ZDC a must for UPC physics

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ET per Crystal in Endcap ECALin PbPb
Central
Minbias
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ET per Cell in HCAL in PbPb
Hijing, minbias 30k particles
Hijing, central 70k particles. Max 50 processed
events