Download - Cynthia HadjidakisTerzo Convegno sulla Fisica di ALICE Detection of photons and electrons in EMCAL Photons, Electrons and 0 at large p T Identification

Cynthia Hadjidakis Terzo Convegno sulla Fisica di ALICE

Detection of photons and electrons in EMCAL

Photons, Electrons and 0 at large pT

Identification of photons and 0 with EMCAL Detection of electrons in EMCAL

Cynthia Hadjidakis

Terzo Convegno sulla Fisica di ALICE Wednesday, November 14, 2007


Photons, 0 and electrons at large pT

Direct photonsprompt photons

hard processes: compton (g q q) and annihilation (q q test QCDproduction unperturbed by the medium-jet events

Neutral mesonsvia decay photons detection

medium effect observation of hadron suppression in Heavy Ion collisions

Electronsfrom semi-leptonic decays of b and c quarks

medium effect different suppression for light and heavy quarks in Heavy Ion collisions

_


Calorimetry in ALICE

PHOS: = 0.24, =100ºDistance to I.P 4.40 mhigh granularity: 17.920 crystalsE > 10 GeV E/E < 1.5%

11 Super Modules2 SM per 20o sector

EMCAL = 1.4, = 110o

Distance to I.P 4.28 mgranularity: 12.672 towers ×~ 0.014×0.014E>10 GeV E/E < 4%

Y

X


EMCal and high pT physics

EMCAL capabilities:

inclusive jets : ET ~ 200 GeV

dijets: ET ~ 170 GeV

inclusive : pT ~ 90 GeV/c

inclusive : pT ~ 70 GeV/c + jet pT ~ 40 GeV/c

e (semi-leptonic decay of heavy quarks ): pT ~ 25 GeV/c

10k/year

Annual yields in ALICE with EMCAL


Identification of photons and 0 in EMCAL

pT< ~ 10 GeV/c 10 ~ < pT< ~ 40 GeV/c

merged cluster→ shower shape analysis

resolved clusters → invariant mass

analysis

small aperture angle isolation cut

→ talk by Gustavo

R

TPC

candidate

IP

three regions of analysis


0 reconstruction via invariant mass

→ effect of the HI environment: efficiency decreases (<10%)→ measured 0 yield as input of simulation to obtain the decay distribution

→ measurement of direct

effi

cien

cy only EMCAL● single particles○ + HI

even

ts

1 2 invariant mass (GeV)

simulation for pp and PbPb conditionshigh occupancy in PbPb: increase cluster energy threshold

100 MeV (pp) → 500 MeV (PbPb)

mGeV

simulation: single particles+HI only EMCAL

only EMCAL- single particles + HI


Shower shape analysis

0, longest axis of cluster ellipsoid

Bayesian method developed for the PID based on a parametrization of 0

, e-

°

charged hadrons

0 27 GeV

fit: Landau+Gaussian

02

dn

/d 0

2

Guénole Bourdaud


rejection () about 5 Ndirect /N from NLO calculations:

→ isolation cut needed to improve rejection

Shower shape analysis

→ HI environment: lower efficiency (10 to 20%)

→ Identification of and 0 from ~10 GeV to ~40 GeV with this method

(preliminary results: studies with realistic background needed)

pp PbPb

0.002-0.02 0.01-0.1

PID for0PID for

effi

cien

cy/p

urity

effi

cien

cy/p

urity

simulation: single particles full ALICE flat and 0 distributions


Detection of electrons in EMCaLtrack matching: each charged track is associated with a EMCAL cluster (if any)

→ add ALICE PID information from EMCAL to high pT charged tracks (TRD rejection for high pT)

simulation: single particles full ALICE

Alberto Pulvirenti

Mark Heinz, Jennifer Klay, Alex Donoghue

pTPC / EEMCAL


Electron identification

→ rejection of 100-500


Photon Conversion

Center of Collision

Time Projection Chamber

EMCAL

Inner Tracking System

TRD and TOF

50% of photons convert into e+e-

→ 45% of photons convert into TRD and TOF→ removed by p/E cut

Other sources of background: photon conversion and Dalitz decay

X (cm)

Y (

cm)


Conclusion

EMCAL improves ALICE capabilities to measure high pT photons, electrons and 0

Direct photons and 0 measurements Identification with invariant mass technique up to pT ~ 10 GeV/cIdentification with shower shape analysis up to pT ~ 40 GeV/cIsolation cut to improve rejection and for higher pT region

Detection of electrons

Electron identification and good rejection with track matching

Download - Cynthia HadjidakisTerzo Convegno sulla Fisica di ALICE Detection of photons and electrons in EMCAL Photons, Electrons and 0 at large p T Identification

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