inclusive production of neutral mesons in alice
DESCRIPTION
Inclusive production of neutral mesons in ALICE. Adam Matyja for the ALICE Collaboration Subatech, Nantes. Outline Motivation Experimental apparatus Results Summary. Cracow Epiphany Conference On the first year of the LHC 10 - 12 January 2011 Kraków, Poland. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
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
210-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
310-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
410-12 January 2011, Cracow Epiphany Conference Adam Matyja
/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
510-12 January 2011, Cracow Epiphany Conference Adam Matyja
ALICE detectorEMCAL
PHOSCTS = ITS + TPC
Experimental apparatus
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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
Experimental apparatus
710-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
Experimental apparatus
CPV - charged particle veto
810-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
Experimental apparatus
910-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
1010-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
1110-12 January 2011, Cracow Epiphany Conference Adam Matyja
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)
1210-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
1310-12 January 2011, Cracow Epiphany Conference Adam Matyja
0 → invariant mass in pp
PHOSPHOS
EMCAL
EMCAL
EMCAL
Results
1410-12 January 2011, Cracow Epiphany Conference Adam Matyja
0 → →e+e- e+e- invariant mass in ppResults
CTS
Data
Combinatorial background
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and invariant mass in pp
EMCAL
EMCAL
EMCAL
PHOSPHOS
Results
→0
→ →
→ →
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→ →e+e- e+e- invariant mass in ppResults
CTSCTS
CTSCTS
Data
Combinatorial background
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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
1810-12 January 2011, Cracow Epiphany Conference Adam Matyja
peak and width
EMCAL
EMCAL
PHOS
PHOS
Measured mass consistent with PDG value → good energy linearity
Results
CTS
CTS
1910-12 January 2011, Cracow Epiphany Conference Adam Matyja
Raw 0 and spectra in PHOS
Range 0.5 < pT < 5 GeV/c
for pp @ s = 900 GeV
Range 0.5 < pT < 20 GeV/c
for pp @ s = 7 TeV
Range 5 < pT < 10 GeV/c
for pp @ s = 7 TeV
0 spectra spectrum
Results
2010-12 January 2011, Cracow Epiphany Conference Adam Matyja
Raw 0 and spectra in EMCAL
Range 0.5 < pT < 20 GeV/c
for pp @ s = 7 TeV
Range 2.5 < pT < 20 GeV/c
for pp @ s = 7 TeV
0 spectrum spectrum
Results
2110-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
2210-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
2310-12 January 2011, Cracow Epiphany Conference Adam Matyja
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)
2410-12 January 2011, Cracow Epiphany Conference Adam Matyja
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)
2510-12 January 2011, Cracow Epiphany Conference Adam Matyja
/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
2610-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
2710-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
2810-12 January 2011, Cracow Epiphany Conference Adam Matyja
DCal
Same towers as for EMCal, but shorter Super Modules in
Acceptance (including PHOS): = 1.4 = 60o
To be installed in 2012
Experimental apparatus
DCal-1DCal-2
DCal-3
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BACKUP
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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
3110-12 January 2011, Cracow Epiphany Conference Adam Matyja
Reconstruction efficiency
MC with single 0 or and flat pT distribution
hgen
hrecrec N
N
.
.
EMCAL 0
PHOS PHOS 0
y = 1, = 2
Results
3210-12 January 2011, Cracow Epiphany Conference Adam Matyja
Reconstruction efficiency
MC with single 0 and flat pT distribution
hgen
hrecrec N
N
.
.|y| < 0.9, = 2
Results
CTS 0
3310-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
3410-12 January 2011, Cracow Epiphany Conference Adam Matyja
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
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Combined analysis (CTS+PHOS/EMCal)
h → (→e+ e-) +
PHOS + CTS
PHOS + CTSEMCAL + CTS