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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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 3/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 4/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 5/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 6/16
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 =
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 7/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 8/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 9/16
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)
B→e+XBB→→e+Xe+X
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 10/16
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)
B→e+XBB→→e+Xe+X
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 11/16
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→e+XBB→→e+Xe+X
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 12/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 13/16
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)( ,
,, ×=
B→e+XBB→→e+Xe+X
NB: study of charm detection performance done!see ALICE “Physics Performance Report”, J. Phys. G30 1517-1763 & CERN/LHCC 2005-030
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 14/16
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±%
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 15/16
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]
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 16/16
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”…
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 17/16
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
B→e+XBB→→e+Xe+X
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 18/16
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
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 19/16
Charm/light ratioR(D)Bh mass+color charge effect
)()()(/ thAAt
DAAthD pRpRpR =
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 20/16
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)
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 21/16
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.
Extraction of a minimum-pT-differentialcross section for B mesons
Using UA1 MC method, also adopted by ALICE μ
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 22/16
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
Extraction of a minimum-pT-differentialcross section for B mesons
Using UA1 MC method, also adopted by ALICE μ
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 23/16
Be→FEvaluation of and determination of the optimal pTmin
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
∧
Extraction of a minimum-pT-differentialcross section for B mesons
Krakow, July 7, 2006 Rosario Turrisi "Perspectives for semileptonic beauty measurement with ALICE" 24/16
Can find an optimal pTmin
for pTe > 2 GeV/c
Be→FEvaluation of and determination of the optimal pTmin
ΔF ~ 1 %
Extraction of a minimum-pT-differentialcross section for B mesons