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