PrimEx II 0 analysis status

Runs analyzed Current analysis includes the part of total statistics beginning from the run 64707, when the new hardware has been installed, i.e.: Silicon runs: 64707 – 64988 Carbon runs: 65006 – 65059, 65096 – 65112 Empty target runs: 64989 – 65005, 65065 – 65095 runs 64704-64706 have missed reference TAGE TDC

Event selection Energy (E single>0.5GeV; E pair>3GeV) Timing (|Tdiff| < 10ns) Elasticity (by constrain procedure) Crystal only HyCal part Coincidence trigger (bit 10)

Energy distribution Two clusters energy Single cluster energy Analysis cut Analysis cut

HyCal clusters multiplicity in selected events PrimEx I PrimEx II <n>=2.40 <n>=2.28

Timing: time difference between Tagger and HyCal time PrimEx I PrimEx II  = 1.0ns  = 1.5ns

Two clusters elasticity distribution Si C  = 2.4%  = 2.4%  = 1.3%  = 1.3% Mass constraint applied

Two clusters elasticity distribution Empty target Mass constraint applied

Two gamma invariant mass C Si  = 3.1MeV  = 3.1MeV Empty Empty

Two gammas elasticity VS inv. mass Empty

Two gamma invariant mass with elasticity constraint Si Empty Empty

dN/d Silicon Theory c. s. at 5GeV PrimEx II Number of events corresponds ~71012 beam photons

dN/d Carbon PrimEx I PrimEx II Omega subtracted Omega unsubtracted Number of events corresponds ~11012 beam photons

Conclusion Further analysis will include HyCal veto and timing and more algorithm tunings Very preliminary number of Primakoff events for silicon ~20K, for carbon ~ 8K We have two more measurements of pi0 Primakoff cross section: on carbon and on silicon, each with higher than PrimEx I statistics Si has shown good coherent part (first Si measurement?)