perspectives for the measurement of beauty production via ......(p)qcd test bench aa, pa baseline in...

Perspectives for the measurement of beauty production via semileptonic decays in ALICE

Rosario TurrisiINFN Padova (Italy)for the ALICE collaboration

Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 2/16

Contents

Motivation: energy lossALICE detector highlightsPerformances: electron separation and vertexing B→e+X: attainable statistics and errorsB→e+X: sensitivity of energy loss measurementB→μ+X: strategy and performanceConclusions


Physics motivationb production cross sectiontransverse momentum spectrum

In pp:(p)QCD test benchAA, pA baseline

In AA:quarkonia dissociation

energy loss

(+pA) disentangle medium effects

not covered here

HERA-LHC workshopCERN-2005-14

Heavy quarks: • abundant yield• produced early• travel ~4 fm in the mediumprobe the collision dynamics! ALICE: very low pt explored,

complementary to other LHC exps.

0.00724.56NQQ per collision

0.510.21QQ(NN) [mb]

pp 14 TeV

PbPb (0-5% centr.)5.5 TeV


High pt suppression at RHICMethod: compare mesons’ ptdistribution in pp and AA:

tBD

pp

tBD

AA

collt

BDAA dpdN

dpdNN

pR//1)( ,

,, ×=

light-flavored hadrons

electrons from c/b decay

pT (GeV/c)Calculations: Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

Observed at RHIC for light flavors and charmReproduced by q = 4-14 GeV2/fm (see next slide)^

=1 if no medium effect


Possible explanation: gluonsstrahlunginteractions may occur by gluon in-medium radiation (quenching)the amount of quenching depends on:

color charge: CR=4/3, 3 if quark or gluon, resp. (Casimir factor)heavy/light probes (b,c vs. direct pions)

quark mass (beauty/charm comparison)dead cone effect

path length L

Q

222 ])/([1

QQ Em+∝

θ

Gluonstrahlung probability

2 ˆ LqCE Rsα∝Δ

Dokshitzer, Kharzeev, PLB519 (2001) 199Armesto, Salgado, Wiedemann, PRD69 (2004) 114003

medium dependence

mass dependence

Baier, Dokshitzer, Mueller, Peigné, Schiff, (BDMPS), NPB483 (1997) 291


Energy loss at LHCA promising strategy: study the pt-dependent ratio…

…RAA of D or B mesons produced in AA and pp: quark energy loss

…between RBAA and RD

AA (beauty/charm ratio): mass dependence

…between RB/DAA and Rh

AA (heavy/light probes): color charge dependence

NB: study of charm detection performance done!see ALICE “Physics Performance Report”, J. Phys. G30 1517-1763 & CERN/LHCC 2005-030

tBD

pp

tBD

AA

collt

BDAA dpdN

dpdNN

pR//1)( ,

,, ×=

)()()( )(/)( t

hAAt

BDAAthBD pRpRpR =

)()()(/)( tDAAt

BAAthBD pRpRpR =


The ALICE Detector

||ηη| < 0.9| < 0.9TPC + silicon tracker (ITS=SSD+SDD+SPD)TPC + silicon tracker (ITS=SSD+SDD+SPD)ee//ππ, K, p,, K, p,…… separation in TRDseparation in TRD

--4 < 4 < ηη < < --2.52.5muonsmuons


Detection strategy: B→e+X

Background sources:pions misidentified as electronscharm decay electronsDalitz decaysphoton conversionsstrangeness decays

signal: <1 electron/ev out of ~103

(all pt’s)!

B→e+XBB→→e+Xe+X

Detection strategyelectron ID in TPC + TRDpT cut-offimpact parameter cut-offspecific for pp: primary vertex optimization

cτ~500μm → compare with 100-300 μm from charm mb~5 GeV → hard pt spectrum

impact parameter in bending plane


Impact parameter resolution

pt > 1 GeV/c ⇒ σ < 60 μm (rφ)

~12 μm asymptotic

d0 resolution

d0 resolution Silicon Pixel Detector2 layers, R=4 and 7 cm, ~107 channels

pixel size

50×425 μm

BEAM (Z)



Electron separationfraction of misidentified pionsCombined strategy TRD+TPC

TRD rejects 99% of pions and 100% of heavier hadrons (90% electron efficiency)TPC (via dE/dx analysis) rejects again 99% of pions at 90% electrons efficiency (at low pt’s)



Electron spectra from bResults for electrons detection in:

pp, 14 TeV, 109 events (“one year run”)PbPb, “one month run” 107 events

ALICE standard ‘underlying’ event → dNCH/dy=6000systematic and statistical errors studied in detail

pp PbPb



B-meson level cross sectionUsing electrons in2 < pt < 20 GeV/c

obtain B meson2 < pt

min < 30 GeV/c

MC-based procedure à la UA1*

* C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405, Phys Lett B256 (1991) 121

inner bars: stat. errorsouter bars: stat. ⊕ pt-dep. syst. errorsnot shown: 9% normalization error

E Loss Calculation: Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

quenching curves for illustration


Beauty quenchingReconstruction of meson-level cross section (details on request…)RAA (RHIC-like analysis) sensitivity to quenching/massRBD (pure quark, no quark/gluon effect) prefers mass effect

)()(

__

__

)(t

DfromeAA

tBfrome

AA

pRpR

teBD pR =

tBD

pp

tBD

AA

collt

BDAA dpdN

dpdNN

pR//1)( ,

,, ×=


NB: study of charm detection performance done!see ALICE “Physics Performance Report”, J. Phys. G30 1517-1763 & CERN/LHCC 2005-030


Beauty in the muon channelMuon spectrometer:

pseudorapidity coverage: -4< η<-2.5absorber + tracking chambers layers + trigger chambers (22 layers)15 interaction lengths, but pt as low as 1-1.5 GeV/cpt resolution ~ 2%

B→μ+XBB→μ→μ+X+X

5 bb pairs / central Pb-Pb collision (5 %)

88%

7429εtrigger

231753εtrigger

342962 εtrack

514675Αtrack

3512Αgeom

μ±μ±μ+μ−μ±%


B-meson level cross sectionMethod:

combined fit of 3 muon data samples (singles, low mass OS, high mass OS) w/fixed shape and b amplitude as the only free parameterMC to derive with pt as low as 1 GeV/c !

(UA1 method, see C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405, Phys Lett B256 (1991) 121 )evaluate stat. and syst. errors

B→μ+XBB→μ→μ+X+X

min tB pvsσ

10%Total pT-indep

9%Normalisation

4%Decay of π,K

16%13%11%10%10%10%10%10%11%11%Total pT-dep.

10%Efficiency

12%8%4%3%2%2%3%3%4%4%Signal (fit)

15-2012-159-126-95-64-53-42.5-31-2.51.5-2pT[GeV/c]


ConclusionsHeavy flavors can play an outstanding role as QCD test bench in AA reactions at LHC:

at low pt explore small-x region

at high pt probe the QCD extended medium via energy loss

The studies outlined in this talk suggest that ALICE has a good potential in this field:semielectronic decays in central barrel (-0.9<η<0.9)semimuonic decays in muon arm (-4< η< -2.5)

Same observable (Eloss) from two different analyses in the same experiment!… and a lot has been left out:

charm hadronic and semileptonic decays

e-μ coincidences

indirect J/ ψb tagging via topological selections

(Lot of) work in progress in the ALICE Physics Working Group 3 “heavy flavors”…


Errors evaluation on e’s spectraEstimation of errors:

MC corrections (efficiency, acceptance, etc.) fixed at 10%, pt-independent.indetermination on charm subtraction evaluated using as reference our study on hadronic charm detection normalization error not shown



Energy loss at LHCA promising strategy: study the pt-dependent ratio…

Calculation of energy loss at LHC energies:Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.

…RAA of D or B mesons produced in AA and pp: quark energy loss

…between RBAA and RD

AA (beauty/charm ratio):pure quark analysis

study of charm energy loss done!see


Charm/light ratioR(D)Bh mass+color charge effect

)()()(/ thAAt

DAAthD pRpRpR =


Extraction of a minimum-pT-differentialcross section for B mesons

Using UA1 MC method (*), also adopted by ALICE μ

(*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121

The B meson cross section per unit of rapidity at midrapidity with pTB > pT

min

is obtained from a scaling of the electron-level cross section measured within a given electron phase space Φe

MC

eB

TBT

B

meas

ebeautyeT

BT

B ppdy

d

ppdy

d)(

)()()(

min

,min

Φ

>×Φ=>

σ

σ

σσ

},,{ 0dpTe ΔΔΔ≡Φ η

Bemeas

ebeautye→×Φ= F)(,σ

The semi-electronic B.R. is included here

The phase space used is where ΔpT are the previously used bins,Δη = [-0.9, 0.9] and Δd0 = [200,600] μm

(thanks to R.Guernane for useful discussions)


Be→FSystematic error for

- semi-electronic decay B.R.: ~ 3 %

- dependence on the shape of the B meson pT distribution used as input in the MC: can be minimized using a proper choice of pT

min

for a given phase space Φe → see following slides

- Monte Carlo correction for the efficiency of the selection cuts: this is, in principle, depending on the B meson pT distribution, and should be then evaluated at this stage of the analysis. For the present feasibility study we account for it with a 10% systematic.


Using UA1 MC method, also adopted by ALICE μ


Be→FEvaluation of and determination of the optimal pTmin

1) we used the B → e + X decays from PYTHIA.

is the ratio of the red area to the blue one.

Be→F

here ΔpTe = [3,4] GeV/c


Using UA1 MC method, also adopted by ALICE μ



2) in the HVQNMR program we changed the theory parameters: a) quark mass and scalesb) nuclear modification of the PDFsc) b → B fragmentation (Peterson)d) add the quenching

(q = 100 GeV2/fm (*))

(*) N. Amesto, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph/0501225

∧



Can find an optimal pTmin

for pTe > 2 GeV/c


ΔF ~ 1 %


perspectives for the measurement of beauty production via ......(p)qcd test bench aa, pa baseline in...

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