1 marcello lunardon - npdc18, praha, 2004 perspectives for the measurement of the beauty production...

Marcello Lunardon - NPDC18, Praha, 2004

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Perspectives for the measurement of the beauty

production cross section at LHC with ALICE

Marcello Lunardon for the ALICE collaboration

Phase Transitions in Strongly Interacting MatterPhase Transitions in Strongly Interacting Matter PRAHA 2004


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Contents

Why to measure beauty in AA at LHC

Performances study for the open beauty detection in Pb-Pb in the semi-electronic channel with ALICE

Conclusions and perspectives


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Measurement of b production in Pb-Pb, p-Pb and p-p

Why beauty?

• normalization for studies

• B J/ important background

- probe of the medium ( e. g.: energy loss of beauty in the medium to be compared with charm energy loss study of dead-cone effect );

- discovery potential (new physics window) ! • interesting in its own right:


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Hard processes in AA at the LHC

Useful tools:- significant part of the cross section- large virtuality Q happen at initial time (small “formation time” t ~ 1/Q << tQGP ~ 5–10 fm/c ) - Initial yields and pt distributions in AA can be predicted using pp measurements + pQCD + collision geometry + “known” nuclear effects

deviations from such predictions can be attributed to the medium

path length L

c

gb energy loss?


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Study of the nuclear modification factor to get information on

the medium

Experimental study of energy loss

Compare pt distributions of leading particles in pp and nucleus-nucleuscollisions (+ p-nucleus as a control)

tpp

tAA

colltAA dpdN

dpdNN

pR//1)(

RAA measured at RHIC with pions: clear suppression at high pT interpreted as due to parton energy loss in medium

h

What about heavy quarks?


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– dead cone for heavy quarks: gluons radiation is suppressed at < mQ/EQ lower energy loss for heavier partons (Dokshitzer-Kharzeev, 2001)

Which energy loss for Heavy Quarks?

Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202].

RAA ratio at LHC expected to be less suppressed for heavy flavours because:

– D,B come from c,b quarks, while , K, p come mainly (~80% in PYTHIA) from gluons, which are expected to lose 9/4 more energy w.r.t. quarks (due to

the difference in the Casimir coupling factor)

Expectation for charm: estimated RAA for D0 mesons at LHC (A. Dainese)

due to the mass dependence of dead cone effect lower energy loss for beauty compared to charm (Armesto-Dainese-Salgado-Wiedemann, 2004)

charm beauty

RAA for electrons from semi-electronic decay of D and B mesons (integrated pT)N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann, in preparation.


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The semi-electronic and semi-muonic decay channels have a good B.R.:

Open Beauty detection in AA at LHC:the semi-leptonic decay channel

B±/B0 l + + X 10.7 ± 0.3% (l = e or )

Good detection and identification capabilities for muons (MUON ARM) and electrons (TRD, TPC and Vertex detector) with ALICE down to low pT

(for semi-muonic beauty detection see talk of G. Martinez)


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X-section from NLO calculations : flavor N qq

in Pb-Pb @ 5.5 TeV (5% tot) charm 115beauty 4.6

in p-p 14 @ TeV charm 0.16beauty 0.007

high uncertainty:

1.8 - 7.3

Assumption on beauty production at LHC:

Open Beauty detection in Pb-Pb at LHC with ALICE:

perspectives for the semi-electronic decay channel

Semi-electronic channel ~ 10 % , ALICE acceptance for beauty ~ 24 % in Pb-Pb ~ 0.22 beauty electrons / event

Statistics for 107 central events (one year Pb-Pb run): ~ 2 M beauty electrons


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The ALICE Detector

ITSVertexing,Low pt tracking

TPCTracking, dEdx

TRDElectron ID

L3 MagnetB < 0.5 T: 0.2 T low pt acceptance, 0.5 T pt resolution at high pt

The dedicated HI experiment at LHCDesigned to measure most observables

ITS

PIXEL CELL

z: 425 m

r: 50 m

Two layers:r = 4 – 7 cm

9.8 Mch

SPD

< 60 mfor pt > 1 GeV/c

TOFPID


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1) electron identification in TRD+TPC

Semi-electronic Beauty:detection strategy

- track impact parameter in b.p. d0 long d0 for beauty electrons due to long B life c ~ 500 m

2) cuts on - transverse momentum pT B and B products have higher pT than primary particles


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d0 and pT distributions for electron from different sources

Distributions normalized to the same integral in order to compare their shapes

Semi-electronic Beauty:detection strategy


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Semi-electronic beauty detection:simulation details

Most relevant background sources included:1) hadrons misidentified as electrons2) conversions3) direct charm4) other decays (Dalitz, strange particles)

Separated generation of beauty, charm and background:beauty:

Pythia6 with MSEL=5, CTEQ4L, forced semi-electronic decaycharm:

similar to beautybackground:

HIJING central (b < 2 fm) events (dNCH/dy|y=0 = 6000)

Normalizations according to the NLO cross section calculations

Magnetic field: 0.4 T


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From test beam results:90% electron efficiency

1% misidentified pions (constant in 1-6 GeV/c pT range)

pion contamination ~ 1%

Semi-electronic beauty detectionbackground analysis: misidentified pions

Electron identification with Transition Radiation Detector (TRD)


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Combined TRD + TPC particle identification technique brings low momentum pion contamination to less than 10-4


Electron identification with dE/dx in TPC


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PID used in this simulation:

- can assume complete rejection of K,p and heavier particles from TRD and TOF

- 80% electron reduction factor for identification efficiencies of TRD (0.9) and TPC (0.9)

- pion contamination less than 0.01% at low momentum


relative magnitudes correct

Effect of the PID on the pion backgound

Number of pions much greater than number of electrons

good rejection using combined PID technique

pT > 1 GeV/c


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Semi-electronic charm measurement at RHIC from PHENIX: photon conversions are a large part of the background ( have to use a removable converter )

Semi-electronic beauty detectionbackground analysis: conversions

Similar situation expected atALICE for electrons entering theTPC, but:

a) request of 1st SPD layerb) select positive d0 electrons

a) first reduction asking for first SPD layer


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Semi-electronic beauty detectionbackground analysis: conversions

b) More reduction with d0 positive cut


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- 13% semi-electronic decay and much more charm than beauty expected significant background

- softer pT spectrum and d0 spectrum (c (D0) ~ 100 m, c(D+) ~ 300 m)

- separated generation with pythia6 and normalization according with NLO calculations

Semi-electronic beauty detectionbackground analysis: direct charm

Distributions normalized to the same integral in order to compare their shapes


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Simulation with HIJING

Strange particle decays:low pT but very long d0 upper d0 threshold at 600 m

Semi-electronic beauty detectionbackground analysis: other decays

generally: low pT, low d0


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Semi-electronic Beauty detectionsimulation results

Expected statistics (107 Pb-Pb events)

Signal-to-total ratio and expected statistics in 107 Pb-Pb events

pT>2 GeV/c , 180 d0 600m 90% purity 50,000 B's


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Analysis of the relative electron sample composition as a function of the electron pT

Semi-electronic Beauty detectionsimulation results

Expected statistics (107 Pb-Pb events)

Direct charm is the most important source of background ( cross check of the extracted c production with direct D0 K measurement )200 d0 600m


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Example: B e + D0 ( K+) + X

Semi-electronic Beauty detectionpT quark distribution

Analysis of the electron pT distribution useful for beauty production cross section measurement. But, what about the quark pT distribution?

Can get significantly better quark pT distribution if we are able to reconstruct a bigger fraction of the B meson mass.


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Semi-electronic Beauty detectionpT quark distribution

Under way: performance study to evaluate

- exclusive reconstruction of the D0 coming from semi-electronic B decay

- reconstruction of B secondary vertices using topological variables


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Summary• ALICE has a good potential to measure beauty production cross section ( vertexing and particle identification down to low pT)

this will allow us to extract information about the effect on heavy flavour production of the dense strongly interacting system created in ultra-relativistic heavy-ion collisions

• Coming up–semi-electronic b/c deconvolution–b’s pt distribution–exclusive b decays


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THE END


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BACKUP SLIDES


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< 60 mfor pt > 1 GeV/c

1 % at low pt

< 2% up to 10 GeV/c

TPC

TPC+ITS


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PID


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LHC: we expect “Deep de-confinement”

Lattice QCD, B=0

closer to “ideal” QGP easier comparison with theory


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N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann, in preparation.

Energy loss and semi-electronic channel

this region could be sensitive to different b/c dead-cone effect

charm beauty

minimum electron pT


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D/h ratio: RD/h = RAA

D / RAAh

Experimentally can use double ratio: RAAD/RAA

h –almost all systematic errors of both Pb-Pb and pp cancel out!

• RD/h is enhanced only by the dead-cone effect• Enhancement due to different quark/gluon loss not seen• It is compensated by the harder fragmentation of charm


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Possible direct measurement of conversions using invariant mass and topological variables


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Muon Arm simulations:

R. Guernane, Muon physics and offline meetingCERN, 22.4.2004


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B measurement a la CDF

Simulation by A. Dainese

1 marcello lunardon - npdc18, praha, 2004 perspectives for the measurement of the beauty production...

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