Measuring Bremsstrahlung Photons in s = 200GeV p-p Collisions Columbia University, for the PHENIX Collaboration Ali Hanks, ahanks@nevis.columbia.edu Zakharov hep-ph/0405101 no quenching with quenching Just bremsstrahlung photons Motivation Photons radiated will not interact with the medium - make a good probe In heavy ion collisions as jets propogate through the medium they lose energy through gluon radiation Radiated gluons are lost through interaction with the medium Provide direct measure of radiation spectrum Expect strong final state interaction effects on bremsstrahlung photon cross-section Gluon radiation spectrum cannot be measured directly RAA predictions show significant enhancement for pT<10GeV/c p-p reference In pp collisions the "bremsstrahlung" photons are produced as the jets fragment At next-to-leading-order pQCD describes the proton-proton photon cross-section well Includes fragmentation component ≥ 20% The distinction between direct and fragmentation photons blurs Isolation cuts can be used to distinguish direct photons experimentally however it is difficult to incorporate these cuts into the theory calculations A direct measurement of the fragmentation component will provide a good test of the theory INCNLO(v1.4): J. Ph. Guillet, M. Werlen et al trigger hadrons are detected using DC-PC1 tracks and PC3 projections photons are detected using the the EMC Method two particle acceptance - all  in accpetance three particle acceptance -  pair in acceptence Tagging efficiency calculated from fastmc  and pT dependent input distribution taken from data to simulate 0's correlated with high pT hadrons Fragmentation photons are picked out by selecting photons associated with a high pT hadron Hadron trigger from 2-20 GeV/c, assoc from 1.8 - 15 GeV/c Inclusive yield contains both fragmentation photons and the hadronic decay background p0 trigger   for all accepted  vs  when sister  falls in acceptence as well 0 tagging method to calculate decay background photons that fall in the 0 mass peak window are tagged This gives us the corrected 0 decay yield: Assuming a similar shape for other hadronic decays, the 0 decay yield can be used to calculate total decay yield: The yield for tagged photons now needs to be corrected for efficiency h-frag per trigger yield calculated using fully corrected decay per trigger yield The tagged  yield, including corrections, can be subtracted from the inclusive yield, leaving only the fragmentation photons remaining 19thInternational Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: 14-20 November, 2006; Shanghai, China