Additional Hardware: Zero Degree Calorimeter

1
Additional Hardware Zero Degree Calorimeter

• Global Event characterization and trigger
• beam energy neutron spectators a feature of
  Heavy Ion Collisions
• Efficient MinBias trigger -also for peripheral
  events
• qneutron lt (150MeV/2.7 TeV) 10-4rad---gtsmall
  detector
• Segmented (Shower Max) calorimeter used to
  resolve reaction plane(PHENIX,STAR _at_ RHIC).
• Ultra Peripheral Physics
• High Luminosity gA collisions to SgAlt (1TeV)2 - a
  big increase over RHIC
• Neutron tag used for (lepton pairs, vector
  mesons) photoproduction at RHIC- needed for
  trigger.
• ATLAS UPC program likely to focus on di-jet and
  Heavy Quark production (ie small x nuclear parton
  distributions)

2
Event Characterization from spectators
PHENIX data
Impact Parameter and reaction plane

• Elliptic flow,
• Jet supression in vs.
• out of plane,
• etc.

• ZDC Shower posn SMD
• (as in PHENIX _at_ RHIC)
• beam ltx,ygt,ie during van derMeer scan
• Event-by-event reaction plane

y
x
Beam ltygt (/-0.6mm)
centrality
3
ATLAS ZDC design/performance
ZDC(1 module,retracted)
Design work started for ATLAS ZDC -integrated
with accelerator instrumentation in TAN
absorber -technology rad hard to 4Grad(ok for
1st
2yrs) -cooperation w. US LARP effort.

• Energy Resolution goal
• sEltEn20
• Simulation of proposed LHC ZDC_at_2.7GeV/u
• Negligible impact from LHC
  Instrumentation in TAN

4
Weizsacker-Williams spectrum and tagging
Calculated equivalent photon spectra from Au-Au
collisions _at_RHIC

• UPC physics
• gtrapidity gaps
• gtInterest in relatively low pt jets
• Neutron tag solved trigger problem _at_RHIC
• tag results harder photon spectrum

• Upper curveraw spectrum(as implemented
• in current ATLAS POMWIG event generator)
• Lower curvesmodified spectrum with ZDC
• tag