PHENIX Direct Photons in 200 Ge V p p

PHENIX Direct Photons in 200 Ge. V p+p and Au+Au Collisions: Probing Hard Scattering Production Justin Frantz Columbia University for the PHENIX Collaboration Quark Matter 2004

Direct Photon Measurements in Particle Physics Gluon Compton Scattering Annihilation & Bremsstrahlung • Interesting probe: half a di-“jet”—same collision process but g has no fragmentation • No measurements of direct photons at sqrt(s) = 200 Ge. V • Probes x = 0. 02 -0. 14 @ p. T = 2 -14 Ge. V/c • Compton scattering dominates--probes the gluon distribution – eventually do AN, ALL measurement with direct photons • Reduces uncertainty on p. QCD photons in Au. Au – Background to thermal photons in Au. Au at mid p. T? – Excellent control for strong modification effects–better than d-Au

Direct Photons in Au. Au • Many sources, different p. T regions – Thermal Sources (p. T < 3 -4 Ge. V) -Partonic (QGP!) , Hadronic Gas (new resonance diagrams theoretical uncertainties) -Largest Backgrounds, PHENIX systematics still under investigation in this momentum region -In central Au. Au, p 0/meson background suppressed -”Cleanest” region (p. QCD dominates) -PHENIX has good sensitivity here— e. g. excellent triggering capabilities. log(Ed 3 /dp 3) – Hard Scattering (p. T > 3 -4 Ge. V) p. T

PHENIX Direct g’s: Step 1) Measure Inclusive Photon Spectrum Inclusive Single g Run 2 Au. Au 200 Ge. V PHENIX Preliminary • Emcal Cluster Spectrum • w/ Corrections for (e. g. ) – Hadronic Shower Contamination (pp ~25 -18%, Au. Au 15 -5%) (see G. David, T. Sakaguchi posters) – Conversions (4%) – In central Au. Au, overlap efficiencies through embedding – Off-vertex background (3%)

PHENIX Direct g’s: Step 0) Measure Background • We are looking for the signal over a large background • Requires precise knowledge of the p 0’s PHENIX Run 2 200 Ge. V p-p Calculated g from p 0 Phys. Rev. Lett. 91, 241803 (2003) p+p->p 0 + X Vogelsang calculation reference: JHEP 9903 (1999) 025/ Private Comm.

Other Background (h, h’, w, …) • • h – 18% of bkgrd: for calc. , fixed by p 0 through m. T-scaling (h/p -> 0. 55) New Preliminary pp h measurement (see H. Hiejima poster) consistent with Calculated g from all (% level) m. T scaled calculation Other “cocktail” (h’, w) contributionsdecays also m. TEvidence from p 0 h/p ~same as pp (see S. Mioduszewski poster) scaled that Au. Au Calculated g from p 0 h Calculated h Invariant Yields g from all decays PHENIX Preliminary Run 2 p-p 200 Ge. V m. T-scaling spectra used in background simulation

Finally, Divide By Pizero g/p 0 Measurement Calculated g from all decays gall decay background / p 0 • We do this because doing the same with the actual point by point p 0 and inclusive g measurements will cancel many systematics • Variations: Tagging Methods (reject g pairs in p 0 mass window), Isolation Methods Remove inherent background so smaller (g/p)expected backgrd • Then we can compare measured g/p with background g/p …

Run 2 p-p Results Ratio g/p 0 measured g/p 0 expected bkg PHENIX Preliminary • Excess Above Background Double Ratio: [g/p]measured / [g/p]background gmeasured/gbackground • The excess above 1 is the direct photon signal • Direct g signal found in 200 Ge. V pp

PHENIX Run 2 p-p Direct Photon Measurement PHENIX Preliminary Vogelsang NLO • Vogelsang calculation: different scale factors (0. 5, 1. 0, 2. 0), using CTEQ 6 gluon pdf: JHEP 9903 (1999) 025/ private communication • See K. Reygers poster for analysis details (Tagging statistical method)

From p-p to Au. Au: Binary Collision (Ncoll) Scaling • Look at, e. g. , p 0 in Peripheral Au. Au: A Peripheral Central 1. 0 } B RAA , Glauber Nucl. Overlap • In central events, scaling broken suppression! Jet suppression? But the dense strong charge final state shouldn’t inhibit direct g • d-Au control experiment shows scaling is not affected by initial state effects but does so only at small values of Ncoll

Neutrinos, Direct Photons, they are very small. They have no charge and have no mass And do not interact at all. fire? QGP The earth is just a silly ball To them, through which they simply pass, Like dustmaids down a drafty hall. . . -John Updike -Michael J. Tannenbaum

From p-p to Au. Au: Binary Collision (Ncoll) Scaling • Look at, e. g. , p 0 in Peripheral Au. Au: A Peripheral Central 1. 0 } B RAA , Glauber Nucl. Overlap • In central events, scaling broken suppression! Jet suppression? But the dense strong charge final state shouldn’t inhibit direct photons • d-Au control experiment shows scaling is not affected by initial state effects but does so only at small values of Ncoll

From p-p to Au. Au: Binary Collision (Ncoll) Scaling • Look at, e. g. , p 0 in Peripheral Au. Au: A Peripheral Central 1. 0 } B RAA , Glauber Nucl. Overlap • In central events, scaling broken suppression! Jet suppression? But the dense strong charge final state shouldn’t inhibit direct photons • d-Au control experiment shows scaling is not affected d by initial state effects but does so only at small values of Ncoll A

High p. T Direct Photons: A Better Control • • “Side by Side” at same Ncoll Rates calculable in p. QCD, measurable in p-p Less sensitive to non-perturbative QCD Once signal is identified, measure jet-g correlation Eg accurately studies Ejet modification • Promising future: (no separate run) q g

PHENIX QM’ 02 Preliminary Result (g/p) / (g/p) Au. Au 200 Ge. V Central Peripheral Improvements: • • • New level 2 triggered data set 4 more Ge. V of p 0’s at high p. T! Efficiency with full embedding Pb. Sc single g systematics under control Multiple independent analyses Au. Au Central 0 -10 % PHENIX Run 2 p 0 Phys. Rev. Lett. 91, 072301 (2003) New Data PHENIX Preliminary 14

New Results Central 0 -10% PHENIX Preliminary Pb. Gl Au. Au 200 Ge. V [g/p 0]measured / [g/p 0]background = Central 0 -10% gmeasured/gbackground

New Results Central 0 -10% PHENIX Preliminary Pb. Gl / Pb. Sc Combined (large new p. T region) Au. Au 200 Ge. V [g/p 0]measured / [g/p 0]background = Central 0 -10% gmeasured/gbackground

New Results Central 0 -10% PHENIX Preliminary Pb. Gl / Pb. Sc Combined 1 + (g p. QCD direct x Ncoll) / (g phenix pp backgrd [if there were no p suppression] x Ncoll) Au. Au 200 Ge. V Central 0 -10% Theory curves include PHENIX gexpected background calculation based on p 0: (g direct + gexp. bkgd. ) / gexp. bkgd. = 1 + (gdirect/gexp. bkgd. )

New Results Central 0 -10% PHENIX Preliminary Pb. Gl / Pb. Sc Combined 1 + (g p. QCD direct x Ncoll) / g phenix backgrd Vogelsang NLO [w/ the real, suppressed background] 1 + (g p. QCD direct x Ncoll) / (g phenix pp backgrd x Ncoll) Au. Au 200 Ge. V Central 0 -10% Theory curves include PHENIX gexpected background calculation based on p 0: (g direct + gexp. bkgd. ) / gexp. bkgd. = 1 + (gdirect/gexp. bkgd. )

New Results Central 0 -10% PHENIX Preliminary Pb. Gl / Pb. Sc Combined 1 + (g p. QCD direct x Ncoll) / g phenix backgrd Vogelsang NLO 1 + (g p. QCD direct x Ncoll) / g phenix backgrd Vogelsang, mscale = 0. 5, 2. 0 1 + (g p. QCD direct x Ncoll) / (g phenix pp backgrd x Ncoll) Au. Au 200 Ge. V Central 0 -10% Theory curves include PHENIX gexpected background calculation based on p 0: (g direct + gexp. bkgd. ) / gexp. bkgd. = 1 + (gdirect/gexp. bkgd. )

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 80 -92% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 70 -80% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 60 -70% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 50 -60% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 40 -50% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 30 -40% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 20 -30% Central Au. Au 200 Ge. V 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc 10 -20% Central 200 Ge. V Au. Au 1 + (g p. QCD x Ncoll) / g Vogelsang phenix backgrd [g/p 0]measured / [g/p 0]background = gmeasured/gbackground

Excess Over Background Ratios, All Centralities PHENIX Preliminary Pb. Gl / Pb. Sc Combined 0 -10% Central 200 Ge. V Au. Au 1 + (g p. QCD x Ncoll) / g phenix backgrd [g/p 0]measured / [g/p 0]background = Vogelsang NLO gmeasured/gbackground

Systematic Errors On g/p Double Ratio (1 s in %) Central Periph. 3 Ge. V 7 11 3 Ge. V 7 Totals: 21 15 17 18 15 3 Ge. V 7 Ge. V 11 Ge. V 3 Ge. V 7 Ge. V Central Periph.

Conclusions • First PHENIX full measurement of direct g made in pp. • p-p result consistent with p. QCD direct g calc. • In Au. Au, a large photon excess above expected background is observed in central events – a very significant direct photon signal! • In central 20%, direct g dominate decay g above ~7 Ge. V/c • This signal gets stronger with increasing centrality. • This behavior is consistent with the measured suppression of the p 0 along with an unsuppressed, binary scaled p. QCD pp prediction. • Binary scaling holds, even at Au. Au values of Ncoll ! • With apparent continued p 0 suppression, direct g’s will be an excellent control complement to study very high p. T suppression in current Run 4!

Brazil China University of São Paulo, São Paulo Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, Beijing France LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN 2 P 3, Orsay LLR, Ecòle Polytechnique, CNRS-IN 2 P 3, Palaiseau SUBATECH, Ecòle des Mines at Nantes, Nantes Germany University of Münster, Münster Hungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, Bombay Israel Weizmann Institute, Rehovot Japan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY USA Rikkyo University, Tokyo, Japan Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, Seoul Russia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg State Technical University, St. Petersburg Sweden Lund University, Lund 12 Countries; 58 Institutions; 480 Participants* *as of January 2004 Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida State University, Tallahassee, FL Florida Technical University, Melbourne, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, Urbana-Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ. , Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ. , Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

Backup: Rcp for Eta, Pi 0