cynthia hadjidakisterzo convegno sulla fisica di alice detection of photons and electrons in emcal...

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

cynthia hadjidakisterzo convegno sulla fisica di alice detection of photons and electrons in emcal...

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