the 7th international conference on hyperons, charm and beauty hadrons - beach 2006

Marcello Lunardon - BEACH 2006, Lancaster, UK

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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

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• 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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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 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!

the 7th international conference on hyperons, charm and beauty hadrons - beach 2006

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