Review

An overview of the photon analysis strategy was given at a Spin PWG meeting last december.

Data Selection

The photon analysis utilizes data taken during the 2009 200 GeV running period.  In particular, the data set begins with the st_gamma production stream that took all events with L2BGamma nd L2EGamma triggers (technically these are stored in the File Catalog as two separate streams, st_gamma and st_gamma_adc).

After selecting the production2009_200GeV_Single were  runs, I required custom QA criteria using the same offline run QA that Brian had used to determine the first and second priority lists.  This QA was convolved with Grant's QA and lastly a few runs were removed due to poor bunch crossing reconstruction.

Simulation

The parameters of the filtered photon simulation produced at the MIT Tier2 facility are documented in the initial request.

Event Selection

Events are first required to have a StGammaCandidate, a 3x3 BEMC tower cluster with seed energy greater than 5.25 GeV and total transverse energy greater than 7 GeV.  In addition to the implied L2BGamma trigger from the stream selection, the event must also have a simulated trigger accept.  Lastly, only events with a reconstructed vertex with positive rank and | v_z | < 60 cm are accepted.

Data/Simulation Comparison

After reconstructing StGammaCandidates in both simulation and data, the simulation is weighted such that the vertex distribution matches that of data.  Various characteristics of the clusters (and the towers and tracks in the surrounding neighborhood) are compared, and those used in the final analyses are included in the attached document.  

Note that, while no variable is a great discriminator of photons and the QCD background, many are weak discriminants and the spectral comparisons are sensitive to the input prompt photon cross section in Pythia.  Because this is known to be incorrect (in general the Pythia cross section underestimates NLO and other measurements) the agreement in these variables is not expected to be perfect, especially in regions where photons peak.  The final check of consistency between and simulation must wait until the extraction fits discussed in my presentation.