Inclusive production of neutral mesons in ALICE

110-12 January 2011, Cracow Epiphany Conference Adam Matyja

Inclusive production of neutral mesons in ALICE

Outline Motivation Experimental

apparatus Results Summary

Adam Matyja

for the ALICE Collaboration

Subatech, Nantes

Cracow Epiphany Conference

On the first year of the LHC

10 - 12 January 2011

Kraków, Poland


Motivation Electromagnetic calorimeters offer a possibility to identify photons and

neutral mesons in a wide pT range Charged hadrons identification limited to low pT

Inclusive meson production spectrum is a good probe for pQCD and necessary for direct photons search

Neutral hadrons, detected via their photonic decays, carry information about medium Studies of transport properties of quark-gluon matter Initial gluon density

constraint of parameters of theoretical models in both perturbative (NLO, NNLO) and non-perturbative regime (structure function, fragmentation function)

Measurements in pp collisions give reference data to compare with AA 's from neutral meson decays are background for other processes

- jet studies


Experience from RHIC

0, and direct photons in AA collisions from PHENIX

The first evidence of a parton energy loss in a quark-gluon matter

RAA scales with Npart

What is expected at LHC energies?

arXiv:0806.0261v1 (2008)

PHENIX, QM2008

Motivation


/0 ratio in pp and AA collisions Ratio is universal for a wide

energy range Needed for nuclear transport

models

PHENIX, PRC 75, 024909 (2007)

f(mT)=(mT+a)-n, a=1.2, n=10-14

ALICE capabilities:

• Large pT region

• Both pp and Pb-Pb measurement

Motivation


ALICE detectorEMCAL

PHOSCTS = ITS + TPC

Experimental apparatus


EMCal

12 Modules per Strip

Module

24 Strip Modules per Super Module

Shashlik technology Tower - 77 layers:

Pb - 1.4 mm Scintillator - 1.7 mm Size - 6 6 25 cm3

Module (2 2 towers) Geometry

4/10 Super Modules are installed Next 6 are being installed in Dec.

2010 - Jan. 2011 24 48 towers in each Super

Module Coverage: || < 0.7, 80o < < 120o

Distance to IP: 4.5 m Material budget from IP: 0.8 X0

Energy range: 0 < E < 250 GeV Energy resolution:

%8.4)(

%3.11)(

%7.1 GeVEGeVEE

E

10 Super Modules in

EMCal



PHOS Technology Crystal of lead tungstate (PbWO4)

Size: 2.2 2.2 18 cm3

Geometry 3/5 Super Modules are installed

1 more expected in 2012 64 56 crystals in each Super

Module Coverage:

|| < 0.13 260o < < 320o

Distance to IP: 4.6 m Material budget from IP: 0.2 X0

Energy range: 0 < E < 100 GeV Energy resolution:

%12.1)(

%3.3)(

%3.1 GeVEGeVEE

E

CPV (not installed yet)

Crystals


CPV - charged particle veto


CTS = ITS + TPC

5 m

2.5 m

2.5 m

CTS energy resolution: E/E 2%

TPC: Diameter Length : 5 m 5 m Acceptance: = 2, ||<0.9 Readout chambers: 72 Pad readout (3 types): 557 568 Drift field: 400 V/cm Maximum drift time: 94 s Central electrode HV: 100 kV Gas:

Active volume: 90 m3

Ne-CO2-N2: 85.7% - 9.5% - 4.8%

ITS: Layout

2 layers of pixel detectors 2 layers of drift detectors 2 layers of strip detectors

Acceptance: = 2, ||<0.9



Method Three ways of neutral meson (, 0) measurement via invariant

mass analysis in ALICE→ photon pairs or external conversion electrons h → + (PHOS, EMCAL) h → (→e+ e-) + (→e+ e-) (CTS)

Distribution of conversionsReconstructed 0 candidate through conversions

Results


Data sample

ALICE minimum bias trigger ALICE has collected:

about 9 M pp minimum bias events @ s = 900 GeV (0.15 nb-1) about 800 M pp minimum bias events @ s = 7 TeV (11 nb-1)

Reconstruction of data just after being transferred to GRID after the end of each run

Presented analysis based on subset of data sample about 8 M pp minimum bias events @ s = 900 GeV (0.12 nb-1) about 360 M pp minimum bias events @ s = 7 TeV (4.3 nb-1) - PHOS about 100 M pp minimum bias events @ s = 7 TeV (1.2 nb-1) - CTS

Results


Analysis selection Event selection:

Correct event type and interaction trigger pp interaction At least 1 hit in SPD or beam-beam interaction by V0 detectors MB event Beam-gas events suppressed offline Primary vertex: |Z| < 10 cm

Photon candidate selection: PHOS

Ncells 3

Ecl > 0.3 GeV |A| < 1 (0) or |A| < 0.7 ()

EMCal Ncells 2

Ecl > 0.5 GeV (0) or Ecl > 0.3 GeV () |A| < 1 (0) or |A| < 0.6 ()

Results

A = (E1 - E2)/(E1 + E2)


Calibration PHOS

Pre-calibration: adjusting the high voltage bias to provide the same gain Accuracy: 20-50 %

Equalization of the mean deposited energy per channel by events from pp collisions

Accuracy: 6.5 % Equalization of 0 peak channel-by-channel

Not enough statistics yet Goal accuracy: 1 %

EMCAL Pre-calibration: adjusting the high voltage bias to provide the same gain

Accuracy: 20 % Calibration with cosmic rays before installation Calibration with pp data using MIP signals Equalization of 0 peak channel-by-channel

Current accuracy: 7 % Goal accuracy: 1 %

Results


0 → invariant mass in pp

PHOSPHOS

EMCAL

EMCAL

EMCAL

Results


0 → →e+e- e+e- invariant mass in ppResults

CTS

Data

Combinatorial background


and invariant mass in pp

EMCAL

EMCAL

EMCAL

PHOSPHOS

Results

→0

→ →

→ →


→ →e+e- e+e- invariant mass in ppResults

CTSCTS

CTSCTS

Data

Combinatorial background


0 peak and width

PHOS

PHOS

EMCAL

EMCAL

• MC/MC with realistic calibration and non-linearity (calibration ongoing)

Measured 0 mass consistent with PDG value → good energy linearityabove pT6 GeV/c cluster unfolding

Notice different ranges!

Results

CTS

CTS

• DATA


peak and width

EMCAL

EMCAL

PHOS

PHOS

Measured mass consistent with PDG value → good energy linearity

Results

CTS

CTS


Raw 0 and spectra in PHOS

Range 0.5 < pT < 5 GeV/c

for pp @ s = 900 GeV


for pp @ s = 7 TeV

Range 5 < pT < 10 GeV/c

for pp @ s = 7 TeV

0 spectra spectrum

Results


Raw 0 and spectra in EMCAL


for pp @ s = 7 TeV


for pp @ s = 7 TeV

0 spectrum spectrum

Results


Raw 0 and spectra in CTS

0 range 0.4 < pT < 7 GeV/c

for pp @ s = 7 TeV

range 0.6 < pT < 6 GeV/c

for pp @ s = 7 TeV

Results


Systematic uncertainties

Raw spectra in PHOS Absolute energy scale and

decalibration: 6.5 % decalibration leads to

systematic error 5 % Energy non-linearity:

17 % @ pT = 1 GeV/c

< 2 % @ pT > 1.5 GeV/c

Geometrical acceptance: 2 % Raw spectrum extraction from

invariant mass peaks: 2 % Conversion probability: 3.3 % Particle identification: 3 %

Total: 10 % @ pT > 1.5 GeV/c

Results

Raw spectra in CTS Material budget: - 6.2 %

Minimum pT of the electron/positron: < 2 %

dE/dx of the electron/positron: < 1 % 2 for the photon reconstruction: < 2 % Track reconstruction in the TPC: < 2 % Energy assymetry of meson decay

products: 1 - 2 % Backgrond calculations: 2 - 7 % Signal integration: < 0.5 %

Total: 5 - 13 % in wide range

+ 3.3


0 production spectrum, pp @ 900 GeV

L = 0.12 nb-1Tsallis fit with:T = 0.15N = 8.5

Data points normalized for the cross section = 50 10 mb

NLO: CTEQ5M, KKP

Results

P. Aurenche et al., Eur. Phys. J C13, 347 (2000)


0 production spectrum, pp @ 7 TeV

LPHOS = 4.3 nb-1Tsallis fit for PHOS with:T = 0.14N = 6.8

Data points normalized for the cross section = 67 10 mb

NLO: CTEQ5M, KKP

Results

LCTS = 1.2 nb-1

P. Aurenche et al., Eur. Phys. J C13, 347 (2000)


/0 ratio in pp @ 7 TeV (CTS)Results

World data taken from

Phys RevC 75(2007) 0224909

Good agreement with PYTHIA predictions and world data measured in hadron-hadron collisions


0 in Pb-Pb PHOS data @ 2.76 A TeV 1.7 M minimum bias events Cluster energy E>0.3 GeV |A| < 0.7 No track extrapolated to

clusters in PHOS within 10cm

Requirement on dispersion axis

Combinatorial background described by event mixing

0 peak well visible above background

Analysis ongoing

Results


Summary and Outlook Neutral mesons 0 and are observed in ALICE calorimeters and CTS Good agreement between independent analyses Production spectra are measured in pp collisions

0 spectrum @ 900 GeV up to pT = 5 GeV/c

@ 7 TeV up to pT = 25 GeV/c

meson spectrum observed in pp collisons 3 < pT < 20 GeV/c in EMCAL

5 < pT < 10 GeV/c in PHOS

0.6 < pT < 6 GeV/c in CTS

0 / ratio in good agreement with previous mesurements 0 meson visible in Pb-Pb @ s = 2.76 A TeV Ongoing analyses with Pb-Pb @ s = 2.76 A TeV in a wide range 1 < pT <

10 GeV/c RAA measurement

RCP measurement

New components of the ALICE detector will be inserted soon


DCal

Same towers as for EMCal, but shorter Super Modules in

Acceptance (including PHOS): = 1.4 = 60o

To be installed in 2012


DCal-1DCal-2

DCal-3


BACKUP


Calculation of event rate

N0 - number of detected 0 in selected pT-bin (raw spectrum)

L - luminosity T - run time Br - branching ratio Ceff - geometrical acceptance

Crec - reconstruction efficiency

Cconv - correction due to conversion loss

Ctrig - trigger bias correction

Results


Reconstruction efficiency

MC with single 0 or and flat pT distribution

hgen

hrecrec N

N

.

.

EMCAL 0

PHOS PHOS 0

y = 1, = 2

Results


Reconstruction efficiency

MC with single 0 and flat pT distribution

hgen

hrecrec N

N

.

.|y| < 0.9, = 2

Results

CTS 0


Theory predictions Cross section in pp

pp → 0 X

NLO pQCD + CTEQ5M + KPPBands indicate possible uncertainties in QCD scaleP.Aurenche, et al,., Eur. Phys. J. C13,347 (2000)

LO pQCD: Pythia 6

pp → X

Motivation


Expected event rates in pp ALICE PHOS

pp → 0 X, 0 → pp → X, →

Expected pT range of neutral meson spectrum

pT < 25 GeV/c for 0 pT < 20 GeV/c for

Motivation

Pythia 6

NLO pQCD + CTEQ5M + KPP


Combined analysis (CTS+PHOS/EMCal)

h → (→e+ e-) +

PHOS + CTS

PHOS + CTSEMCAL + CTS

Documents

Inclusive production of neutral mesons in ALICE