Detection of photons and electrons in EMCAL Photons

Detection of photons and electrons in EMCAL Photons, Electrons and 0 at large p. T Identification of photons and 0 with EMCAL Detection of electrons in EMCAL Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE Terzo. Cynthia Convegno Hadjidakis sulla Fisica di ALICE

Photons, 0 and electrons at large p. T Direct photons prompt photons _ hard processes: compton (g q g q) and annihilation (q q g g) test QCD production unperturbed by the medium g-jet events Neutral mesons via decay photons detection medium effect observation of hadron suppression in Heavy Ion collisions Electrons from semi-leptonic decays of b and c quarks medium effect different suppression for light and heavy quarks in Heavy Ion collisions Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Calorimetry in ALICE EMCAL D = 1. 4, DF = 110 o Distance to I. P 4. 28 m granularity: 12. 672 towers D ×D ~ 0. 014× 0. 014 E>10 Ge. V DE/E < 4% Y X 11 Super Modules 2 SM per 20 o sector Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE PHOS: D = 0. 24, DF =100º Distance to I. P 4. 40 m high granularity: 17. 920 crystals E > 10 Ge. V DE/E < 1. 5%

EMCal and high p. T physics Annual yields in ALICE with EMCAL capabilities: § inclusive jets : ET ~ 200 Ge. V § dijets: ET ~ 170 Ge. V § inclusive 0 : p. T ~ 90 Ge. V/c § inclusive g : p. T ~ 70 Ge. V/c § g + jet p. T ~ 40 Ge. V/c e (semi-leptonic decay of heavy quarks ): p. T ~ 25 Ge. V/c § Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE 10 k/year

Identification of photons and 0 in EMCAL three regions of analysis p. T< ~ 10 Ge. V/c resolved clusters → invariant mass analysis 10 ~ < p. T< ~ 40 Ge. V/c merged cluster → shower shape analysis small aperture angle isolation cut IP TPC R candidate Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE → talk by Gustavo

0 reconstruction via invariant mass simulation for pp and Pb. Pb conditions high occupancy in Pb. Pb: increase cluster energy threshold 100 Me. V (pp) → 500 Me. V (Pb. Pb) only EMCAL - single particles + HI efficiency events simulation: single particles+HI only EMCAL 0 only EMCAL ● single particles ○ + HI 0: E=9 Ge. V s/m = 11 % 1 2 invariant mass (Ge. V) → effect of the HI environment: efficiency decreases (<10%) → measured 0 yield as input of simulation to obtain the decay g distribution → measurement of direct g Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Shower shape analysis Bayesian method developed for the PID based on a parametrization of l 0 dn/d 02 Guénole Bourdaud 0 27 Ge. V , e- fit: Landau+Gaussian ° charged hadrons l 0, longest axis of cluster ellipsoid 02 Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Shower shape analysis efficiency/purity PID for g efficiency/purity simulation: single particles full ALICE flat g and 0 distributions PID for 0 0 rejection (eg/e 0) about 5 Ndirect g/N 0 from NLO calculations: pp Pb. Pb 0. 002 -0. 02 0. 01 -0. 1 → isolation cut needed to improve 0 rejection → HI environment: lower efficiency (10 to 20%) → Identification of g and 0 from ~10 Ge. V to ~40 Ge. V with this method (preliminary results: studies with realistic background needed) Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Detection of electrons in EMCa. L track matching: each charged track is associated with a EMCAL cluster (if any) → add ALICE PID information from EMCAL to high p. T charged tracks Alberto Pulvirenti (TRD rejection for high p. T) simulation: single particles full ALICE Mark Heinz, Jennifer Klay, Alex Donoghue p. TPC / EEMCAL Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Electron identification → rejection of 100 -500 Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Photon Conversion Other sources of background: photon conversion and Dalitz decay 50% of photons convert into e+e- Y (cm) EMCAL TRD and TOF Time Projection Chamber Inner Tracking System X (cm) → 45% of photons convert into TRD and TOF Terzo Convegno sulla di ALICE →Fisica removed by p/E cut Center of Collision Cynthia Hadjidakis

Conclusion EMCAL improves ALICE capabilities to measure high p. T photons, electrons and 0 Direct photons and 0 measurements Identification with invariant mass technique up to p. T ~ 10 Ge. V/c Identification with shower shape analysis up to p. T ~ 40 Ge. V/c Isolation cut to improve 0 rejection and for higher p. T region Detection of electrons Electron identification and good rejection with track matching Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE