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Summary
UPC A+A collisions generate high-energy g beams for “non-QGP” studies: g+g, g+A physics at sgg,gA larger than LEP & HERA.
Main motivation: Precision QCD studies w/ low bckgd environment & simpler initial state than pp,A+A collisions.
Physics topics in UPC quarkonia photo-production:
- Nuclear GA(x,Q2) at small-x [Gluon saturation, CGC, ...], QQbar propagation in cold nuclear matter, QQbar spectroscopy: g+g 0+-2++ states, ...
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Lessons from RHIC:
- Efficient trigger w/ forward neutron tagging (A* dissoc.) + high-pT at y=0
- Physics signal accessible w/ relative “simple” cuts & analysis
- Good theoretical description of J/Ψ (pQCD) & high-mass e+e- (QED)
- Main source of syst. uncertainty: coherent g+g e+e- physics background
Prospects for LHC:
- Unexplored kinematic regime (max. energies ever, small-x, g+A ¡ , ...)
- Expected rates ~1000 higher than at RHIC.
- High sensitivity to nuclear GA(x,Q2) at small-x