University of Wisconsin Prompt Photons Eric Brownson University of Wisconsin HERA, ZEUS data(intended 96-00, current 96-97) 100GeV<Q2<10000GeV e+ energy 27.5GeV p energy 920Gev Introduction: SM QCD Various Methods to Determine αs DIS Structure Function PDF Feynman Diagrams (1,2,3 jets) The ratio of the three-jet to the dijet cross section R3/2 and αs Jet Algorithms Breit Frame Lab Frame MC Models NLO Experimental Context

Why Prompt Photons? First what is a Prompt photon? Short answer is that a prompt photon is a photon that is made promptly at the interaction point. There are two types of events that produce prompt photons as seen in (a) & (b). Give reasons here: There are also two types of irreducible background as seen in (c) & (d).

Why Prompt Photons? There are other reasons, e.g. Since prompt photons are produced at the interaction point and do not undergo any kind of decay they directly carry away information about the interaction. There are other reasons, e.g. When the photon is produced with a jet the momentum imbalance between the two is sensitive to the internal motion of the partons.

Event Selection Online: Prompt photon trigger bit (HPP16) TLT HPP16 Some vertex and tracking requirements. (E-Pz)<75 GeV ET,gamma>4.0 GeV and -3.0<etagamma<1.5 Sum of ET over the whole cal except for a 10 deg. Cone around the FCAL beam pipe>8.0 GeV SLT: HiEt1, HiEt2, HiEt3, SLT HPP04, or SLT HPP07. SLT Synopsis FLT:40, 41, 42, or 43 Also requirements on Z vertex, (E-Pz), at least one vertex track, Hadron and Parton Level Comparison? FLT 40 requires Cal_emc_E > … FLT 41 requires Cal_Et > … FLT 42 has requirements on Cal_E, Cal_emc_E, Bcal_emc_e, Rcal_emc_E, and a tracking requirement. FLT 43 has a Cal_Et and a tracking requirment.

Event Selection Off Line: To exclude DIS events there should be no sinistra electron found. .15 < Yjb < .7 Since there is no sinistra electron the sum of (E-Pz) used in calculating Yyb will be over the whole cal. A cut on -50<Z vertex<40cm. This will cut out beam-gas background. Requiring the number of tracks from the primary vertex > 3 will cut out wide angle bremsstrahlung events. There needs to be a photon candidate via the EM electron finder. This possible photon should have no track leading to it. It should have a high Et (Et>5GeV). It should be in the BCAL. And it needs to contain 90% of the Et in a cone of unit angular radius around it including charged particles that curved out of the isolation cone but were headed towards the possible photon. These conditions will cut out electron, and dijet events that contained a neutral meson. There should be one balancing jet via the KTCLUS algorithm. The total missing Pt in the Cal < 10 GeV. Since a photon with a balancing jet will mostly cancel out in the calculation of Pt the prompt photon events will have small net values of Pt. This will cut out PMT sparks, Cosmic rays, and DIS events with a final state neutrino. A cut on the ratio of non-vertex tracks to vertex tracks. This will cut out beam-gas background events.

Control Plots

Control Plots

Control Plots

Control Plots

Control Plots

For The Future Make more control plots in a more systematic way. Finish applying the cuts. Apply isolation cone around photon candidates. Calculate photon dependant quantities. e.g. Xg, f max Properly weight MC events.