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First physics from the ALICE electromagnetic calorimeters

Gustavo Conesa Balbastrefor the ALICE collaboration

0 and spectraNeutral-charged correlations

2/25

First physics from electromagnetic calorimeters

Calorimeters offer the unique capability to identify photons, electrons and hadrons (neutral mesons) in a wide momentum range 0<pT<100 GeV/c

Elementary QCD calculation in pp perturbative: NLO, NNLO for various processes including exclusive processes

with photon in final state Non perturbative: structure function, fragmentation function, initial and final

state effects Reference data for AA

Medium generated effects in AA Medium color density: quenching of high pt hadrons, photons unaffected (?),

modification of FF, Additional photon sources: thermal, jet conversion, bremsstrahlung

The observables 0, , direct photon spectra Correlation with hadron correlation -jet

Q vs g quenching

3/25

RHIC experience: Direct photons 0 and in AA collisions

[PHENIX, QM2009]

Neutral meson spectra at RHIC was the first evidence of a parton energy loss in a quark matter. RAA scales with Npart. What expects us at LHC?

4/25

RHIC experience: -hadron and hadron-hadron correlations

-h correlations [PHENIX, QM2008]

h-h correlations

[STAR]

Suppression of away-side peak in central Au-Au collisions proves a parton energy loss in a quark matter.

5/25

ALICE: The dedicated HI Experiment

6/25

ALICE setup for 2010

4/10 EMCAL=40, ||<0.7

0

1

2345

6

7

9

8

1112 13 14

15

17

0

12

3

4

1610

3/5 PHOS=60, ||<0.12

Full TPC+ITS=360, |TPC|<0.9, |ITS|<1.2

7/25

PHOton Spectrometer: PHOS

High granularity and resolution spectrometer:

10,752 (17,920) lead-tungstate crystals (PbWO4), 3(5) modules (5664 crystals per module)

crystal size: 22 22 180 mm3

depth in radiation length: 20 Distance to IP: 4.4 m

Acceptance:

pseudo-rapidity [-0.12,0.12] azimuthal angle 60º(100o)

For E > 10 GeV, E/E < 1.5% and x = [0.5,2.5] mm

Focus on low and moderate pT

High resolution 0 and Thermal photons

CPV (not installed yet)

CrystalsEMC

8/25

Module:

2x2 towers

• Coverage =1.4, =40o (107o)• Distance to IP: 4.3 m• Granularity = = 0.014• Resolution E/E=11%/√E,

x=[3,50] mm

• Focus on moderate to high pT

0 and prompt direct photonjet

Pb/Sc Shashlik– 4k (11K) channels– 4 Super Modules for 2009-2010

runs– Complete (10 SM) for 2011? runs

EMCAL

9/25

DCAL

•Same towers than the EMCAL, shorter Super Modules in .•Including PHOS, acceptance is =1.4, =60º•To be installed for 2012 runs•Focus on /0/jet-jet correlations

10/25

Scope of first physics

Inclusive spectrum of 0 production in pp collisions at 900 GeV and 7 TeV in mid-rapidity and pT range from 0.3-0.5 to 20-30 GeV/c

Measure inclusive spectrum of , and other neutral mesons production in pp collisions at 7 TeV in pT range from 3-5 to 15-20 GeV/c

Physics: Constrain pQCD and non perturbative aspects of QCD Provide reference spectrum for Pb-Pb collisions at 2.76 and 5.5

TeV

11/25

Neutral meson measurement in ALICE

ALICE provides 3 independent ways to identify 0 and mesons, through invariant mass analysis of photon pairs and external conversion electrons:

H-> (both on PHOS or EMCAL) H->

e+e- (CTS, PHOS or EMCAL) H->

e+e- e+e- (CTS)

Performance plots, p+p at 7 TeV, coming next

12/25

PHOS h-> +

175 million minimum bias events.

Cluster selection (better tuning under study). Ecl>0.3 GeV Ncell3

0 plots lines: Red line: fit to combinatorial.

Blue points: histogram minus combinatorial fit.

Blue line: - fit of blue points.

0

13/25

PHOS h-> +

Estimation of decalibration and comparison with MC Current PHOS decalibration is 7%

0 reconstruction efficiency Efficiency limited to < 30-40 GeV

when the 2 photons merge into a single cluster in the calorimeter.

14/25

PHOS h-> + raw yield

175 million Minimum Bias events.

We identify 0 up to 20 GeV, we expect to arrive to 30 GeV.

15/25

EMCAL h-> +

188 million minimum bias events.

Cluster selection (better tuning under study) Ecl>0.3 GeV Ncell2

0

16/25

EMCAL h-> +

0 width vs pT in real data and MC Still important decalibration in EMCAL,

we are working to get the MC values.

Reconstruction efficiency descends fast after 6-7 GeV because of the large cell size / clusterizer, being our measurement limit actually about 10 GeV We are working in a new clusterization

procedure that will allow us to arrive to 20 GeV.

MCData

Data

17/25

EMCAL h-> +

188 million minimum bias events

pT reach 10 GeV due to size of cells and clusterizer used.

We plan to improve clusterizer and arrive to 20 GeV.

18/25

h-> + -> e+e-e+e-, data candidate

19/25

CTS h-> + -> e+e-e+e-

For pT > 1 GeV Photon conversion

probability of about 8%

Photon reconstruction efficiency is of 70% with close to 100% purity

20/25

CTS h-> + -> e+e-e+e-, raw yields

For ~108 minimum bias p+p events at 7 TeV, the accessible pT range is:

0 : 0.3-0.4 to 10 GeV/c : 0.6 to 6 GeV/c

21/25

PHOS-CTS h-> + -> e+e-

0 can be identified with pT>0.5 GeV/c is visible with pT>2 GeV/c

140 million p+p events at 7 TeV

0

pp @ √s= 7 TeV

pp @ √s= 7 TeV

Eve

nts

pe

r 5

Me

V/c

2

Eve

nts

pe

r 1

0 M

eV

/c2

22/25

PHOS-CTS h-> + -> e+e-

pp @ √s= 7 TeV

pp @ √s= 7 TeV

23/25

EMCAL-CTS h-> + -> e+e-

140 million minimum bias events.

Non linearity correction not applied yet

masks the

pp @ √s= 7 TeVE

ven

ts p

er

5 M

eV

/c2

24/25

EM Cluster - Hadron correlation analysis

• Correlation of Charged Tracks / PHOS clusters / EMCAL clusters with charged hadrons measured in TPC+ITS.

•Left Plot: Near (mainly 0 for EM calorimeters) and away side correlation shows a jet-like structure•Right plot: Applying isolation cuts to clusters or 0, the away side correlation remains: single pi0 - jets and/or direct-photon - jet ?

• Consolidate the isolation cut, extract kT, FF.

performance01/09/2010

performance01/09/2010 pp @ √s= 7 TeVpp @ √s= 7 TeV

See Yaxian’s presentation

25/25

Summary

ALICE has identifed 0 and neutral mesons with its calorimeters and central tracking system.

The agreement between the analysis seems to converge, but work is needed, specially on calibration and non linearity effects in the calorimeters.

For the end of the p+p collisions at 7 TeV data taking period at LHC we expect to measure 0 in the range 0.3 < pT <30 GeV and in the range 0.6 < pT < 10 GeV.

We are getting ready for and looking forward to Pb+Pb collisions in a couple of months …