the 7th international conference on hyperons, charm and beauty hadrons - beach 2006
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The 7th International Conference on Hyperons, Charm And Beauty Hadrons - BEACH 2006 Lancaster, July 2-8 / 2006 Open Heavy Flavour Detection in ALICE Marcello Lunardon for the ALICE collaboration. Open Heavy Flavour Detection in ALICE. Contents Why heavy ion collisions at the LHC - PowerPoint PPT PresentationTRANSCRIPT
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The 7th International Conference on Hyperons, The 7th International Conference on Hyperons, Charm And Beauty Hadrons - BEACH 2006Charm And Beauty Hadrons - BEACH 2006
Lancaster, July 2-8 / 2006
Open Heavy Flavour Detection in ALICE
Marcello Lunardon for the ALICE collaboration
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Contents Why heavy ion collisions at the LHC
Heavy flavour at the LHC with ALICE
The ALICE detector
Exclusive charm reconstruction in the hadronic decays
Inclusive beauty detection in the semi-leptonic channels
Conclusions
Open Heavy Flavour Detection in ALICE
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Why heavy ions at the LHCAt the LHC we expect “deep deconfinement”
At the LHC: higher energy density, higher temperature and longer fireball lifetime• closer to “ideal” QGP• easier comparison with theory
LHC
In a Pb-Pb collision at √sNN = 5.5 TeV we expect to reach a huge energy density > 100 GeV/fm3 in a large volume entering deeply into the deconfined phase (QGP)
QGP signatures already observed at SPS (CERN) • multistrange baryon enhancement• J/ suppressionand RHIC (BNL)• jet quenching
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gluon radiation
Heavy ion collisions: some result from RHICCompare pT distributions of leading particles in pp and
nucleus-nucleus collisions (+ p-nucleus as a control)
tpp
tAA
colltAA dpdN
dpdNN
pR//1)(
What about heavy quarks?
light-flavored hadrons @ RHIC
RAA measured at RHIC with light-flavoured hadrons: clear suppression at high pT interpreted as due to parton energy loss in medium
The nuclear modification factor
Jet correlations in Au-Au Central collisions (high ) compared to pp min. bias (low ) : clear suppression of the away-side jet interpreted as due to energy loss in the medium
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Heavy flavour at the LHC in AA
• Novelty of the LHC: large cross section
FONLO calculations with MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.
Heavy flavours are useful probes:
SPS → RHIC → LHCHard processes contribute significantly to the total AA cross-section (σhard/σtot=98%): – Bulk properties dominated by hard processes– Very hard probes are abundantly produced
bbRHIC
bbLHC
ccRHIC
ccLHC
100
10
• NLO predictions (ALICE baseline for charm & beauty)
system, s pp, 14 TeV Pb-Pb (0-5%), 5.5 TeV
11.2 / 0.5 4.3 / 0.20.16 / 0.007 115 / 4.6
[mb] QQNN
QQtotN
theoretical uncertainties of a factor 23
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Heavy flavour at the LHC in AA
Heavy flavours are useful probes:
• Large virtuality Q happen at initial time (small “formation time” t ~ 1/Q << tQGP ~ 510 fm/c ) sample the whole collision history
Pb Pb bb
b
b
• Heavy quark pT distribution sensitive to many competing nuclear effects
• low-pT (<6 GeV/c at LHC) region sensitive to non-perturbative effects (flow, quark coalescence, gluon shadowing, CGC state…)
• high-pT region sensitive to jet quenching (mass and/or colour-charge dependence?)
WhichEnergy Loss?
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Measuring Open Heavy Flavour at the LHC: Measuring Open Heavy Flavour at the LHC: the ALICE Detectorthe ALICE Detector
-4 < -4 < < < 2.52.5
TOFPID
TRDElectron ID
ITSVertexing,Low pt tracking
TPCTracking, dEdx
MUON ARM tracking
||| < 0.9| < 0.9
The dedicated HI experiment at the LHC with a large number of detectors with high tracking efficiency and particle identification across a wide range of momenta from below 100 MeV to above
100 GeV
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Open heavy flavour at the LHC with ALICEALICE is a powerful tool to measure heavy flavour observables
• Multi-purpose detector specifically designed for HI collisions• can resolve tracks in a very high density environment (up to dNch/dy ~ 8000 )• can provide several different HF measurements within the same experiment
• Precise tracking and vertexing• can resolve D’s and B’s decay vertices• can measure pT distributions down to a few 100 MeV/c
• Particle identification• good PID for e,,K,p
60 < < 62
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D mesons: c ~ 100 300 m and significant BR for kaon-pion(s) decay modes
• exclusive reconstruction of D0 K-+
• exclusive 3-body reconstruction of D+ and Ds+
B mesons: c ~ 500 m and large semi-leptonic BR (~20%)
Studies of the expected ALICE performances in open heavy flavour detection
Full performance studyUnder evaluation
• inclusive single electron measurement of B e e X at || < 0.9
• inclusive muon/dimuon measurement of B X at -4 < < -2.5 (not presented here)
Open heavy flavour at the LHC with ALICE
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Measurement of displaced tracks (track impact parameter resolution)
the track position resolution is mainly provided by the 2 layers of silicon pixelsITS
PIXEL CELL
z: 425 m
r: 50 m
Two layers:r = 4 – 7 cm
9.8 Mch
SPD
Open heavy flavour at the LHC with ALICE
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Charm reconstruction in the D0 K-+ “golden” decay channel
- large combinatorial background in AA (for this study dNch/dy ~ 6000 was used): S/B ~ 10-6 in MD0 3 before selection
need to reduce bkg by 6-7 orders of magnitude!
- main selection on displaced vertices asking for opposite-sign track pairs with large impact parameter
- the reconstructed D0 momentum should point to the primary vertex (point ~ 0)
- (K,) invariant mass analysis to extract the D0 yield
Direct measurement of the pT distribution of the D0 mesons
Detection strategy
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Charm reconstruction in the D0 K-+ “golden” decay channel
D0 candidate selection in Pb-Pb
d0Kxd0
< -40000 m && cosθpoint 0.98 increase S/B by a factor 103!
Invariant mass analysis to count D0’s
%10/ BS
35/ BSSN.Carrer, A.Dainese and R.Turrisi, J. Phys. G29 (2003) 575. - A.D. PhD thesis (2003), nucl-ex/0311004.
Statistical significance:Pb-Pb
pT integrated
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Charm reconstruction in the D0 K-+ “golden” decay channel
Charm reconstruction final performance results
pT-differential cross section can be reconstructed down to pT~0! Estimated significance for 1 year at nominal
luminosity and dNch/dy = 6000 in Pb-Pb
With dNch/dy ~ 3000
S/B x4 Signif. x2
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Beauty detection via displaced electrons
PrimaryVertex B
e
Xd0
rec. track
Distributions normalized to the same integral in order to compare their shapes
d0 distributions for “electrons” from different sources:
Inclusive measurement of electrons coming from semi-electronic decay of beauty hadrons
• need good electron identification: combined PID in TPC (dE/dx) + TRD
• key selection point: again good measurement of the track impact parameter
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1) Electron PID: reject most of the hadrons
PrimaryVertex B
e
Xd0
rec. track
3) Subtract (small) residual background2) Impact parameter cut: reduce charm and bkg electrons
|d0| distributions for “electrons” from different sources:
Beauty detection via displaced electronsSelection of the beauty electron candidates in 3 steps
beauty dominates
left charm
left bkg
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107 central (0-5%) Pb-Pb events
expected statistics and systematic uncertainties
pT-differential electron cross section reconstructed from ~ 1 to 20 GeV/c
Beauty detection via displaced electrons
Results for beauty in Pb-Pb(same analysis done for pp @ 14 TeV)
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tDpp
tDAA
collt
DAA dpdN
dpdNN
pR//1)(
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
Sensitivity to Energy Loss ObservablesHigt pT suppression and energy loss for Charm
2 ˆ LqCE Rs
medium transport coefficient: depends on the medium properties
no energy loss
Theory predictions* :• large suppression with ~ 25100 GeV2/fm• charm less suppressed than light hadrons
(colour-charge effect) but more than beauty (mass effect)
Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Salgado, Wiedemann, PRD 68(2003) 014008 * Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027
BDMPS model
q̂
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)()()(/ tDAAt
BAAtDB pRpRpR
Mass dependence of E loss with Beauty-to-Charm ratio
Adapted from Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027
Compare c and b: same colour charge
Mass effect Enhancement of factor ~2independent of (for )/fmGeV 20ˆ 2qq̂
Sensitivity to Energy Loss Observables
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Conclusions
• Heavy flavours are fundamental probes for testing QCD in AA collisions at the LHC (non perturbative effects, energy loss in medium,...)
• ALICE is well equipped for measuring open heavy flavour production cross sections and pT differential distributions both in pp and AA (vertexing and particle identification down to low pT)
• ALICE has a large heavy flavour program for both open heavy flavours and quarkonia: a lot of work for the next years!