Detection of photons and electrons in EMCAL
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE
Wednesday, November 14, 2007
Photons, Electrons and p0 at large pT
Identification of photons and p0 with EMCAL
Detection of electrons in EMCAL
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE
Photons, p0 and electrons at large pT
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 = 110o
Distance to I.P 4.28 m
granularity: 12.672 towers
D×Df ~ 0.014×0.014
E>10 GeV  DE/E < 4%
Y
X
11 Super Modules
2 SM per 20o 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 GeV  DE/E < 1.5%
EMCal and high pT physics
Annual yields in ALICE with EMCAL
EMCAL capabilities:

inclusive jets : ET ~ 200 GeV

dijets: ET ~ 170 GeV

inclusive p0 : pT ~ 90 GeV/c

inclusive g : pT ~ 70 GeV/c

g + jet pT ~ 40 GeV/c

e (semi-leptonic decay of heavy
quarks ): pT ~ 25 GeV/c
Cynthia Hadjidakis
10k/year
Terzo Convegno sulla Fisica di ALICE
Identification of photons and p0 in EMCAL
three regions of analysis
pT< ~ 10 GeV/c
resolved clusters
→ invariant mass
analysis
10 ~ < pT< ~ 40 GeV/c
merged cluster
→ shower shape analysis
small aperture angle
isolation cut
IP

TPC
f
R
candidate
→ talk by Gustavo
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE
0
p
reconstruction via invariant mass
simulation for pp and PbPb conditions
high occupancy in PbPb: increase cluster energy threshold
100 MeV (pp) → 500 MeV (PbPb)
only EMCAL
- single particles + HI
efficiency
events
simulation: single particles+HI
only EMCAL
p0
only EMCAL
● single particles
○ + HI
p0: E=9 GeV
s/mp= 11 %
g1 g2 invariant mass (GeV)
→ effect of the HI environment: efficiency decreases (<10%)
→ measured p0 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 l0
dn/dl02
Guénole Bourdaud
p0 27 GeV
g, e-
fit: Landau+Gaussian
p°
charged hadrons
l0, longest axis of cluster
ellipsoid
l02
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE
Shower shape analysis
PID for g
efficiency/purity
efficiency/purity
simulation: single particles
full ALICE
flat g and p0 distributions
PID for p0
p0 rejection (eg/ep0) about 5
Ndirect g/Np0 from NLO calculations:
pp
PbPb
0.002-0.02
0.01-0.1
→ isolation cut needed to improve p0 rejection
→ HI environment: lower efficiency (10 to 20%)
→ Identification of g and p0 from ~10 GeV to ~40 GeV with this method
(preliminary results: studies with realistic background needed)
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE
Detection of electrons in EMCaL
track matching: each charged track is associated with a EMCAL cluster (if any)
→ add ALICE PID information from EMCAL to high pT charged tracks
Alberto Pulvirenti
(TRD p rejection for high pT)
simulation: single particles
full ALICE
Mark Heinz, Jennifer Klay,
Alex Donoghue
pTPC / EEMCAL
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE
Electron identification
→ p 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)
Center of Collision
Cynthia Hadjidakis
→ 45% of photons convert into TRD and TOF
→ removed
by p/E cut
Terzo Convegno
sulla Fisica di ALICE
Conclusion
EMCAL improves ALICE capabilities to measure high pT photons, electrons and
p0
Direct photons and p0 measurements
Identification with invariant mass technique up to pT ~ 10 GeV/c
Identification with shower shape analysis up to pT ~ 40 GeV/c
Isolation cut to improve p0 rejection and for higher pT region
Detection of electrons
Electron identification and good p rejection with track matching
Cynthia Hadjidakis
Terzo Convegno sulla Fisica di ALICE