Heavy flavour and Quarkonium measurements with ALICE at LHC
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Transcript of Heavy flavour and Quarkonium measurements with ALICE at LHC
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Heavy flavour and Quarkonium measurements with ALICE at LHC
Javier Castillo for the
ALICE Collaboration
Rencontres QGP-France – Étretat – 22/09/2010
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Outline• Physics motivations• ALICE experiment• ALICE capabilities
– Open heavy flavour– Quarkonia• First results from 7 TeV p-p collisions• Conclusions
• Disclaimer:– Details in
• C. Geuna, 20/9/2010• L. Bianchi, 22/9/2010• X. Zhang, 22/9/2010• S-U. Ahn, 22/9/2010• B. Boyer, 22/9/2010
Rencontres QGP-France – Étretat – 22/09/2010
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Heavy flavours
• In Pb-Pb collisions: probe the properties of the medium– created in the hard initial collisions
• experience the whole collision history– possible comparison heavy quarks/light partons
• energy loss:
• In p-p collisions: – baseline for Pb-Pb– measure charm and beauty cross section– compare to pQCD predictions
Rencontres QGP-France – Étretat – 22/09/2010
medium density and size
dead cone effect (mass)
Casimir factor (colour charge)
tHpp
tHAA
collt
HAA dpdN
dpdNN
pR//1)( B
AADAAAA RRR
bcsdug EEEE ,,
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Heavy quarks with PHENIX @ RHIC
Rencontres QGP-France – Étretat – 22/09/2010
As a test of pQCD …
… or of heavy quark energy loss.
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Quarkonia, heavy ions and the QGP?
• A long lasting story…– 1986, Matsui and Satz: J/ψ
suppression as a QGP signature– NA38, NA50, NA60 at SPS– PHENIX, STAR at RHIC• … and many open
questions– similar suppression at RHIC
and at SPS– larger suppression at larger
rapidities– cold nuclear matter effect
(still) weakly constrained– statistical hadronization,
recombination?
… and then??
Rencontres QGP-France – Étretat – 22/09/2010
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J/ψ polarization
Rencontres QGP-France – Étretat – 22/09/2010
Helicity frame
λ>0 transverseλ<0 longitudinal
L. Levy @ ICHEP 2010
• no model explains cross section and polarization simultaneously
• many models on the market‣ Color Singlet Model: LO, NLO, NNLO‣ Color Octet Mechanism: NRQCD...
many more
Should help constrain production models
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CNM Effects
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NDSG σ = 0,1,2,3,4,…15
EPS08
σ = 0 mb
σ = 4 mb
R. Vogt private communication
arXiv:0912.4498
Ask Elena about this one!
High statistics data provides a strong test of CNM models
Bottom line:CNM could explain
the mid-forward rapidity difference
L. Levy @ ICHEP 2010
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ϒ @ RHIC
Rencontres QGP-France – Étretat – 22/09/2010
RdA = 0.78 ± 0.28(stat.) ± 0.20(sys.)
L. LevyD. Kikola @ ICHEP2010
Au+Au |y|< 0.35RAA < 0.64 at 90% CL for Upsilon at RHIC (PHENIX).
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More J/ψ mess
Rencontres QGP-France – Étretat – 22/09/2010
L. LevyD. Kikola @ ICHEP2010
Disagreement at high pT
No suppression at high pT
RAA(pT > 5 GeV/c) = 1.4 ± 0.4 ±
0.2
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The LHC and its features• Large energy step (RHIC
x30)– A QGP that will be
• hotter,• bigger,• longer lived,• earlier thermalized.
– Large hard probe production cross-sections
SPSPbPbCent
RHICAuAuCent
LHCpp
LHCpPb
LHCPbPb
Centcc 0.2 10 0.2 1 115bb - 0.05 0.007 0.03 5
SPS17 GeV
RHIC200 GeV
LHC5.5 TeV
initial T ~ 200 MeV ~ 300 MeV > 600 MeV
volume 103 fm3 104 fm3 105 fm3
lifetime < 2 fm/c 2-4 fm/c > 10 fm/c
Rencontres QGP-France – Étretat – 22/09/2010 At top energies
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ALICE• Central barrel (|η|<0.9) • Muon spectrometer (-4.0<η<-2.5)
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– Open heavy flavour• hadronic channel• semi-leptonic decays (e)
– Quarkonia• e+e-
– Tracking: ITS+TPC+TRD– PID: TPC+TRD+TOF– Secondary vertexing:
ITS
– Open heavy flavour• semi-leptonic
decays (µ) – Quarkonia
• µ+µ-
– Absorber– Tracking chambers– MUON Trigger
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Heavy flavour measurement potential
Rencontres QGP-France – Étretat – 22/09/2010
Comparison with pQCD Energy loss studies
Good discriminating
power!
MC
MC
MC
MC
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Muons from charm at forward rapidity
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• Unfold single muon pt and dimuon invariant mass spectra• No dca cuts use large statistics to constrain the fits
1 month at reduced luminosity (1030 cm-2s-1, 7 x 1010 pp events)
pp, single muon pt
pp, di-muon invariant mass
pp
2.5<h<4, pt > 3 GeV/c x ~ 10-5
MC
MC
MC
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Quarkonia in dielectron channel
J/ψ
Υ
J/ψ Υ
Mass resolution ~30 MeV/c2 ~90 MeV/c2
Signal/Noise 1.2 1.0
Counts (nominal PbPb year) 10% 120k 900
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Quarkonia in dimuon channel
mμμ (GeV/c2) mμμ (GeV/c2)
J/ψ Υ
Mass resolution ~70 MeV/c2 ~100 MeV/c2
Signal/Noise 0.3 2.5
Counts (nominal PbPb year) MB 680k 6000
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Quarkonia: what will be done
• The bread and butter of J/ψ– Production yields, cross-sections
• High statistics• From pT = 0 GeV/c
– Detailed “suppression” studies • With respect to
– Beauty– pp (RAA)
• As a function of– Centrality – Transverse momentum (0-20 GeV/c)– Rapidity (two domains)
– Precise pp measurement• 3.106 J/ψ in nominal pp run• Sensitivity to low x‐Bjorken
–probing gluon distribution atxBj= 2x10‐4 – 4x10‐6 ;
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Secondary J/ψ• χc: contribution ~30%– χcJ/ψ+γ
• J/ψ in dielectron channel• γ in γ-conversion
– feasible in pp collisions• ~7k χc but requires a trigger strategy which is under
study
• ψ’: contribution ~10%– challenging
• B mesons: contribution ~20%– BJ/ψ+X
• Non photonic electrons• à la CDF: simultaneous fit
– Invariant mass distribution– Pseudo proper decay time
– In muon arm • method using 3 muon events is under study
− tot J/ψ− J/ψ from B− bkg− sum
χc1
χc2
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MCMC
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• Polarization– Angular distribution of μ+ in the quarkonium
rest frame.
•
•
– Υ polarization• 1 nominal year for integrated studies• Several years for differentials
Quarkonia: what could be achieved• Upsilon measurements– Separation of family states is possible (100
MeV resolution)
– Good sensitivity to “suppression” scenarii• Suppression 1: TC = 270 MeV; TD/TC = 4.0 (1.4) for ϒ(ϒ’);• Suppression 2: TC = 190 MeV; TD/TC = 2.9 (1.1) for ϒ(ϒ’);
− No suppression− Suppression 1− Suppression 2
€
dσdcosθH
∝1+α cos2θH
€
α σT − 2σ Lσ T + 2σ L
⇒ 1 transverse 0 no polarization−1 longitudinal
⎧ ⎨ ⎪
⎩ ⎪
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MC
MC
See L. Bianchi @ 18h10See S.-U. Ahn @ 16h45
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First results from 7 TeV p-p collisions
• CINT1B: interaction trigger– at least one charged particle in 8 η units• CMUS1B: single-muon trigger:– forward muon in coincidence with
interaction trigger
Rencontres QGP-France – Étretat – 22/09/2010
Further background-event rejection is performed offline by selecting events which:1. have the correct event type (physics);2. trigger on bunch crossings;3. fulfill at least -one- of the three following
conditions:a) 2 fired chips in the SPD*b) 1 fired chip in the SPD* and a beam-beam
flag in either V0A or V0C**c) beam-beam flags on both sides V0A and
V0C**;4. are not flagged as beam-gas by either V0A
or V0C**.
* calculated offline from reconstructed clusters ** calculated offline from the V0 signals
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Particle Identification
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Complementary momentum coverage
ITSTPC
TOF
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Open heavy flavour: D0 mesons
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Observed differentially in pT
• up to pT=12 GeV/c• down to 1 GeV/c
Expected to cover 0.5 < pT <15 GeV/c with 109 events
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Open heavy flavour: other D mesons
Expected to cover 0.5 < pT <15 GeV/c with 109 events
Rencontres QGP-France – Étretat – 22/09/2010
Observed differentially in pT
• up to pT=12 GeV/c
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Open heavy flavour in the electron channel• Compute the inclusive cross section using electrons• For high pT, the contribution from charm and beauty
becomes dominant• Essential ingredient for the analysis: electron Identification
– For the moment: TPC + TOF– Hard work to add the TRD is going on!– EMCAL will also contribute
Rencontres QGP-France – Étretat – 22/09/2010
TPC signal after a 3σ electron selection from TOF signal
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Open heavy flavour from single muons• Trigger matching– Iron wall stop hadrons produced in the
absorbers• Distance of Closest Approach– Could be used to separate c and b signal
from π and K background (using simulations)
• π and K contribution– subtracted using Pythia simulations
normalized at low pT
• c and b contribution– dominates for pT>2 GeV/c
Rencontres QGP-France – Étretat – 22/09/2010
See X. Zhang @ 17h45
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Quarkonium measurements
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J/ψ in the di-electron channel• 110M p-p events at 7 TeV
– 1/3 of available statistics• Track reconstruction
– TPC + ITS• Electron identification (and pion
rejection) – TPC – TRD could be included later• Fit with a Cristal Ball function• |η|<0.9
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J/ψ in the di-muon channel
• The alignment of the tracking chambers is a critical step for the J/ψ measurements– First alignment: straight tracks
from B=0 T data
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σJ/ψ (MeV)Without
alignment 230
First alignment 90Target 70
Saw C. Geuna @ 20/9/10 ?
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Transverse momentum dependence
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The width of the J/ψ peak is well reproduced by our Monte Carlo including residual misalignment and other realistic conditions! See B. Boyer @ 16h20
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Transverse momentum distribution
Rencontres QGP-France – Étretat – 22/09/2010
To extract <pT2> we use the fit function first
proposed by Yoh et al., PRL 41 (1978) 684 and also used by previous experiments
• Quoted uncertainties include systematics from the fit function
• Full systematic uncertainties are being evaluated
See B. Boyer @ 16h20
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Conclusion• The LHC provides a new and promising environment for
the study of open heavy flavour and quarkonium production• ALICE is well suited for the study of heavy flavours
– Two rapidity domains
• Exciting results from first pp data at 7 TeV– J/psi transverse momentum distribution
• Coming soon– J/ψ differential cross-section– Corrected open heavy flavour measurements
• Looking forward for Pb-Pb data et the end of the year
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Back-Up
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The LHC and its other “features”• Only 1 month per year for the heavy ion program
– Including pA or lighter ions• Lead beam luminosity is limited by the magnets “quench
limit” due to EM processes induced by PbPb collisions;• Large contribution from B-hadron decays to charmonia
yields – ~20% for J/ψ• Cold nuclear matter effects are not well under control
– Could try different normalizations– Will be measured with pA runs
• Heavy Ion running plan (1 month per year)– First 5 years: 1 PbPb low luminosity, 2 PbPb runs at nominal
luminosity, 1 pPb and 1 lighter ion runs– Next 5 years (based on results): lower energies, pp at 5.5 TeV, other
AA or pA, more stat …
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D+ Invariant Mass Spectra in pT bins
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D* Invariant Mass Spectra in pT bins
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Monte Carlo comparison
• “CDF pp 7TeV” parameterization – pT extrapolated from CDF results– y obtained from CEM calculations– No polarization ( = 0)
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The acceptance and efficiency corrected distributions are compared to generated MC distribution
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ALICE performances in μ+μ-
State S[103] S/B S/(S+B)1/2
J/Y 200 0.49 250Y’ 5.5 0.03 13
(1S) 2.0 3.6 39
(2S) 0.52 1.4 18
(3S) 0.28 0.95 12
State S[103] S/B S/(S+B)1/2
J/Y 130 0.20 150Y’ 3.7 0.01 6.7
(1S) 1.3 1.7 29
(2S) 0.35 0.68 13
(3S) 0.20 0.48 8.1
State S[103] S/B S/(S+B)1/2
J/Y 22 3.14 130Y’ 0.6 0.18 9.7
(1S) 0.21 9.5 15
(2S) 0.06 3.6 6.5
(3S) 0.03 1.9 4.2
0<b<3 fm
6<b<9 fm b>12 fm
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