1 open-charm and j/ψ production at the alice experiment pietro cortese università del piemonte...
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Open-charm and J/ψ production at the ALICE experiment
Pietro CorteseUniversità del Piemonte Orientale and INFN
Alessandria, Italyon behalf of the ALICE Collaboration
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Outline
Open-charm in p-p collisions D meson reconstruction in ALICE central barrel D0 and D+ production measurement Single muons and single electrons
J/ψ in p-p First results: J/+- and J/e+e- in p-p collisions at 7 TeV
Perspectives for Pb-Pb
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The ALICE experiment• ALICE is the dedicated heavy-ion experiment at the LHC
p-p collisions: important aspect of the physics program
Pb-Pb collisions: main focus of the experiment
reference for heavy-ion collision studiesp-p physics
Central barrel (||<0.9)
Muon spectrometer (-4<<-2.5)
Tracking: ITS,TPC,TRDPID: ITS,TPC,TRD, TOF,EMCAL,PHOSTrigger: ITS, TOF, TRD…
Tracking: 10 CPC planesTrigger: 4 RPC planes
QGP studies
Event characterization:V0, T0, FMD, ZDC
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Charm in pp at LHC Important test of pQCD in a new energy domain (3.5 sTEVATRON)
c production on the upper edge of prediction, at Tevatron and RHIC Ultimately, ALICE aims at measuring charm production below pT~1 GeV/c
Probe gluon PDF down to xBjorken ~ 10-4
Does the factorization approach still hold? Gluon saturation? Reference for heavy quark quenching studies in Pb-Pb
CDF, PRL91 (2003) 241804FONLL: Cacciari, NasonGM-VFNS: Knihel et al.
PHENIX, STAR, 0.2 TeV, c,b e+XCDF, 1.96 TeV, D*
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D meson reconstruction in ALICE Main selection: displaced-vertex topology Example: D0K-p+
good pointing of reconstructed D momentum to the primary vertex pair of opposite-charge tracks with large impact parameters
K ID in TPC+TOF helps in rejecting background at low pt
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TPC
TOF
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Signals: D0K-p+
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108 events 1-12 GeV in 7 bins
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Signals: D+K-p+p+
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108 events; 2-12 GeV in 6 bins
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Corrections for D cross sections
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Corrections: 1) efficiency 1% 10% from low to high
pt
factor 2 larger for B feed-down D mesons
D0 D+
Corrections: 2) feed-down BD: ~20-25% for now, subtract using FONLL
BD predictions FONLL describes well B
production at Tev and LHC with full 2010 statistics will be
corrected based on data (D displacement to vertex, à la CDF)
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2 < pt < 10 GeV/c, with 1.4 nb-1 (~20% of 2010 statistics)
Total systematic error 20-40% pt-dep. + 10% on normalization pQCD predictions (FONLL and GM-VFNS) compatible with our data
D0 and D+ ds/dpt, |y|<0.5, pp 7 TeV
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Coming soon: D*+
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D*+D0p+
2-12 GeV/c
Soft pion reconstruction down to 100 MeV/c using ITS as standalone tracker
Evaluation of systematics ongoing
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D*+ dN/dpt and D ratios
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ee, H1, ZEUS: JHEP07 (2007) 074CDF: PRL 91 (2003) 241804
Only statistical errors Shape compares well with pQCD (FONLL)
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Other ongoing analyses:
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D0K-p+p-p+
Ds+K-K+p+
D0K-p+ below 1 GeV/c
Lc+pK-p+
(c t = 60 mm)
p/K/p ID crucial here!
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Heavy flavour in the muon spectrometer
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In p-p collisions charm and beauty decays are themain source of single muons with pT>2 GeV/c in -4<η<-2.5
Analysis chain:• Remove beam-gas (global event selection) • Remove punch-through hadrons and low-pT secondary µ
→ muon trigger• Remove background decay µ→ models and MC (present), exploit correlation with vertex displacement• Correct for acceptance/e ciencyffi• Estimate the cross-section
Monte-Carlo
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Single muons from HF decays
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• pQCD calculations are in agreement with data within the systematic errors
• the shape of the distribution is well reproduced• Analysis on the full statistics will improve the pT reach• data-driven methods will improve the background subtraction
(expecially important at low-pT)
Conservative systematics
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Coming soon: electrons from HF decays
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Electron ID with TOF time and TPC dE/dx cut (TRD and EMCAL will join soon)
Contamination from <1% to 15% at 4 GeV/c
Inclusive electron spectrum compared with cocktail of sources (conversion electrons from π0 decays are derived from data)
After TOF cut
HF signal above the electron cocktail
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Quarkonium measurement in ALICE
• Quarkonium in ALICE can be measured in two ways:• in the central barrel in the e+e- channel (|y|<0.9)• in the forward spectrometer in the +- channel (2.5<y<4)
• 3 sources of J/
1) Direct production2) Feed down from heavier cc states
3) J/ from b-hadron decay
Prompt J/
can be identified in the central barrel, good impact parameter resolution (r < 60 m for pT>1 GeV/c)
Preliminary ALICE results refer to inclusive J/ production
forward detection more difficult 3-muon events B cross section from single- Semileptonic decays of B pairs
radiative decay cJ/in the central barrel
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J/ +- : p+p @ √s=7 TeV sample• Data sample:
• Integrated luminosity = 13.6 nb-1, corresponding to data collected between May and July 2010 (~ 10-15% of the 2010 total statistics)
• Trigger: muon in the forward spectrometer, in coincidence with minimum bias interaction trigger
• Run Selection:• Runs selected according to quality checks on the stability of the
muon spectrometer tracking and trigger performances
• Event Selection:• at least one vertex reconstructed in the silicon pixel detector• at least one muon reconstructed in the tracking and trigger
chambers satisfying the trigger algorithm• cut on the track position at the end of the front absorber
(20<abs<90)
rapidity window: 2.5<y<4 transverse momentum window 0<pT<8 GeV/c (statistics)
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J/ +- : signal extraction• The number of J/ is extracted from a fit to the
invariant mass spectrum, using
Crystal Ball shape for the signal (J/ and ’)Sum of two exponentials for the background
The available J/ statistics, used for the cross section
determination is
NJ/ = 1909 ± 78
S/B (2.9<M<3.3) ~ 2.4With a suitable pT cut (smaller background),also the (2S) signal is visible, but with a much lower statistical significance
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J/ +- : acceptance efficiencyInputs:• realistic y and pT J/ distributions
• detector status and efficiency
pT CDF extrapolationy CEM calculation
• Study of differential distributions: 1D acceptance correction• Main source of uncertainty: unknown J/ψ polarization
Good coverage down to pT =0!
Polarization in Helicity reference frame
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J/ e+e- : p+p @ √s=7 TeV sampleand signal extraction
Track selection:
|e+,e-|<0.88 and |yJ/|<0.88 pT
e+,e- > 1 GeV/c
TPC-based PID
NJ/ = 123 15
• Analysis is based, for the moment, on a smaller data sample wrt to J/+-
L=4.0 nb-1 (~15% of 2010 stat.)
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Integrated cross section(s)• The ALICE results, integrated pT, are:J/ψ(-0.88<y<0.88)=12.952.15(stat)2.32(syst)+1.26
-2.55(syst. pol) μb
J/ψ(2.5<y<4)=7.250.29(stat)0.98(syst)+0.87-1.50(syst. pol) μb
Very good agreement with the corresponding LHCb result obtained at forward rapidity (ICHEP2010)
(polarization-related errors calculated in the helicity frame)
Main sources of systematic errors are:• Unknown polarization• Luminosity determination• In the dielectron channel:
• track quality cuts and PID• In the dimuon channel:
• signal extraction and trigger efficiency
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Differential cross section: dJ//dpT (2.5<y<4)
• Very good agreement with the LHCb result in the same rapidity range
(ICHEP 2010)
(stat errors only)
• Other sources of point to point systematic errors (signal extraction, acceptance input) vary between 3 and 10% (not yet fully evaluated)
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Differential cross section: dJ//dy (pT>0)
• ALICE can measure the distribution of the inclusive J/ production in a wide rapidity range
• coverage reaches zero pT at both central and forward rapidities
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Preliminary comparison(s)
• Model calculations:• R.Vogt, Phys. Rev. C 81 (2010) 044903• J.P. Lansberg, arXiv:1006.2750
• CMS: pT-integrated cross section 1.6<y<2.4 from (arXiv:1011.4193)• ATLAS: d/dy 1.5<y<2.25, ATLAS-CONF-2010-062• LHCb: d/dy 2.5<y<4 from LHCb-CONF-2010-010
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√s-dependence of inclusive J/
• NLO calculation for cc by Mangano et al., normalized to the CDF point• Same √s-dependence for the inclusive J/ cross section
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November 2010:moving from p-p to Pb-Pb
• Higher occupancy with respect to Pb-Pb• Re-tuning of reconstruction parameters
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First J/ signal from Pb-Pb collisions
• Expected final statistics for Pb run O(103)• Extract RAA in (some) centrality bins
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Prospects for Pb-Pb
~ 45 M Pb-Pb inelastic events on tape (~6 mb-1)
~ 4.5 M in 0-10% most central
Detectorperfoms
well!
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Summary on Open-Charm
Purdue University, Jan. 6, 2011 Pietro Cortese
D0 and D+ meson cross section at mid-y measured in 2-10 GeV/c pQCD predictions agree with data
Ongoing: increase statistics
o extend to lower and higher pt
B-feed-down from data will allow to reduce systematics
Coming soon: D*+
D*+ , other D0 channel, Ds, Lc
Single electrons
Will serve as a reference for Pb-Pb studies
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On Quarkonia
Next steps, in the dimuon channel, with higher statistics:
Extend the analysis to (2S) and to bottomonium states
Integrated and differential J/ polarization study
Pb-Pb run completed
J/ signal observed
ALICE has measured inclusive J/ production
Over a wide rapidity range (-0.88<y<0.88, 2.5<y<4)
With good coverage down to pT=0
Next step: nuclear modification factor vs centrality
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D backup slides
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“Minimum bias”, based on interaction trigger: SPD or V0-A or V0-C
o at least one charged particle in 8 h unitso ~95% of sinel
read out all ALICE single-muon trigger:
forward muon in coincidence with Min Bias read out MUON, SPD, V0, FMD, ZDC
Both activated in coincidence with the BPTX beam pickups
Since March 31st 2010, collected ~8.5×108 minimum bias triggers ~1.3×108 muon triggers
Results presented today based on ~108 minimum bias triggers
Trigger & Data sample, pp 7 TeV
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TPC (tracking, PID dE/dx)
TOF (PID)
ITS (tracking & vertexing)
K p
D0 Kp D+ Kpp D* D0p Ds KKp D0 Kppp Lc pKp
Charm reconstruction in the ALICE barrel, |h|<0.9
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D meson reconstruction in ALICE Main selection: displaced-vertex topology Tracking and vertexing precision is crucial here Inner Tracking System (ITS) was aligned using
cosmics and collisions current resolution for pixels: 14 mm (nominal: ≈11 mm) rf impact parameter resolution of 75 mm at 1 GeV/c particle-mass dependence well understood
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The inner pixel layer
7.8
cm
protonkaonpion
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From signals to cross sections
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Corrections: 1) efficiency 2) feed-down BD then, normalization to cross section, using sMB from VdM scan
Detector response well described in MC
D0:
D+:
massresolution
cutvariables
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FONLL vs. data, beauty production 2-7 TeV
CDF, B
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FONLL, MC@NLO:Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033
CMS, arXiv:1011.4193
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Only statistical errors Shape compares well with pQCD (FONLL)
D0 and D+ dN/dpt
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D mesons: from signals to cross sections
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Corrections: feed-down BD: ~15-20% main method (“Nb-subtraction”): FONLL input is only the DfromB cross section
where: second method (“prompt fraction fc”): FONLL input is the ratio of prompt to
total D meson cross sections use the total envelope of the
error bands (from FONLL) of two
methods as a systematic error
ddpt |y|0.5
1
2
1
y(pt )1
B.R.1
c fc (pt )
NrawD (pt ) |y|y(p t )
pt
(CINT1B /V 0AND)NCINT1B
V 0AND
fc (pt )NrawD (pt ) |y|y(p t )
NrawD (pt ) |y|y(p t )
NFONLLDfromB (pt ) |y|y(p t )
NFONLLDfromB (pt ) |y|y(p t )
FONLLDfromB (pt)DfromBypt2BRL int
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J/ψ backup slides
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J/ e+e- : acceptance efficiency
• Also in the electron channel, very good coverage down to pT = 0
Acc
epta
nce
e
ffic
ien
cy
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Systematic errorsSource of systematic error
Uncertainty on signal extraction
7.5 %
pT and y shapes in the MC 2%
Trigger efficiency 4%
Tracking efficiency 2%
Normalization 10 %
Total systematic error 13.5 %
Source of systematic error
Kinematics <1%
Track quality,#clusters TPC 10%
PID cuts 10%
Signal extraction range 4%
Normalization 10 %
Total systematic error 18 %
Muons
Electrons
polarization =-1 =1
Helicity -20% +10%
Collins-Soper -25% +12%
polarization =-1 =1
Helicity -21% +12%
Collins-Soper -31% +15%