status of b analysis via single electrons
DESCRIPTION
Status of B analysis via single electrons. Andrea Dainese INFN – Legnaro based on work with: F.Antinori, C.Bombonati, M.Lunardon, R.Turrisi. Layout. Beauty measurement using displaced electrons Detection strategy Experimental issues: tracking and PID Results for pp and Pb-Pb - PowerPoint PPT PresentationTRANSCRIPT
ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese 1
Status of B analysisStatus of B analysisvia single electronsvia single electrons
Andrea DaineseAndrea Dainese
INFN – LegnaroINFN – Legnarobased on work with: based on work with:
F.Antinori, C.Bombonati, M.Lunardon, R.TurrisiF.Antinori, C.Bombonati, M.Lunardon, R.Turrisi
ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese 2
Layout
Beauty measurement using displaced electronsDetection strategy
Experimental issues: tracking and PID
Results for pp and Pb-Pb
Physics Performance: Sensitivity to pQCD predictions in pp
Beauty quenching
Conclusions / Outlook
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Measuring beauty via electronsExpected yields of charm (b.r.: 10%) and beauty (b.r.: 11% +10% as bc e) decay electrons:
b quark has c 500 m
decay electrons d0 ~ few-100 mPrimaryVertex B
e
Xd0
rec. track
system :
sNN :Pb-Pb (0-5% centr.)
5.5 TeV
pp
14 TeV
pp
900 GeV
115 / 4.6 0.16 / 0.007 0.025 / 0.00035
23 / 1 (+1) 0.03 / 0.0015 (+0.0015)0.005 / 0.00008
(+0.00008)
6 / 0.25 (+0.25)0.008 / 0.0004
(+0.0004)0.0013 / 0.00002
(+0.00002)
QQtotN
eN
eN 9.0||
transverse plane
What’s the background?
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Background 1: charm decays
pp
Heavy-quark decays:
• b→B→e
• b→B→D→e
• c→D→e
beauty
charm (background)
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Background 2: other sources1. Decays of light mesons and Dalitz decays (mostly 0)
2. Photon conversions (→e+e-) in the beam pipe and ITS innermost layer
3. Charged pions mis-identified as electrons
NO PID
pp
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Detection strategy
1) Electron PID: reject most of the hadrons
2) Impact parameter cut: reduce charm and bkg electrons
3) Subtract (small) residual background
PrimaryVertex B
e
Xd0
rec. track
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Electron identificationCombined info from TRD (trans. rad.) and TPC (dE/dx)
TRD rejects 99% of the and ALL heavier hadrons (pt > 1 GeV/c)
outdated: latest info from TRD group on rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff.
TPC further rejects residual pions (up to 99% at low p)
About 20% of electrons rejected
fra
ctio
n o
f mis
iden
tifie
d p
ion
s
outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff.
thanks to A.Andronic, S.Masciocchi
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In a given pt-bin, N “electrons” are counted, after PID and d0 cut:
N = Nb + Nc + Nbkg
1. Subtract the contribution from charm: Nb + Nbkg = N - Nc
estimated from D0 measurement (source of error)
2. Subtract the contribution from background: Nb = (N – Nc) - Nbkg
estimated from measured pions dN/dpt plus MC (source of error)
3. Correct for acceptance/efficiency: dNbcorr/dy = (Nb / )
efficiency calculated with MC (source of error)
4. Multiply by the inelastic pp cross section (or by Pb-Pb overlap functions): de from b/dy = pp
.dNbcorr/dy
pp cross section measured at LHC (source of error)
Cross section extraction procedure
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Error contributions
Statistical:
Systematic:
Error from subtractions:
Error from acc./effic. corrections: 10% (in principle pt-dependent)
Error from cross section normalization:
5% for pp, 9% for Pb-Pb (pt-independent)
b
bkgcb
b
b
N
NNN
N
N
b
bkg
bkg
bkg
b
c
c
c
b
b
N
N
N
N
N
N
N
N
N
N
~10%
dep. on d0 cut
dep. on d0 cut
pp
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Optimization of d0 cut in bins of ptpp, 109 events
Systematic error:
prefers tight cut (high signal purity)
dominates at low pt
Statistical error:
prefers loose cut (small d0 MIN)
dominates only at high pt
“old TRD PID”
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Statistics Summary
109 pp events 107 central (0-5%) Pb-Pb events
“old TRD PID”“new TRD PID” “old TRD PID”
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Errors Summary109 pp events 107 central (0-5%) Pb-Pb events
“old TRD PID”“old TRD PID”
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pp: Sensitivity vs. pQCD
109 pp events
From electrons in 2 < pt < 20 GeV/c, B mesons in 2 < ptmin < 30 GeV/c
“old TRD PID”
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tepp
teAA
collt
eAA dpdN
dpdN
NpR
/
/1)(
Beauty Energy Loss : RAA
dyppdN
dyppdN
NpR
ttBpp
ttBAA
collt
BAA /)(
/)(1)(
min
minmin
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events) Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027
“old TRD PID”
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Heavy-to-light ratios: RB/D
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
)()()( D from eB from e/ tAAtAAtDB pRpRpR
Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027
“old TRD PID”
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First-year scenario
Only few TRD supermodules for 2008 pp run
What can we do with TPC(&TOF) PID only?
Optimization of dE/dx cuts for electrons ID
Ne=N=N=NK=Np
p=4 GeV/c
40%
0.1%
TOF
C.Bombonati
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First year: Statistical error
TPC+TRD TPC
C.Bombonati
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OutlookOne year at nominal luminosity:
pp 1-18 GeV/c ➔ comparison with pQCD calc.Pb-Pb 1-18 GeV/c ➔ RAA & v2 of beauty
First year pp:up to 14 GeV/c (with larger errors) using ITS+TPC+TOF
Next steps:preparation of Analysis task for ESD/AODanalysis of PDC eventspreparation of procedure for background subtraction (charm, misid. pions) and for corrections (cuts, PID)
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EXTRA SLIDES
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LHC running conditions
Ldt = 5.1026 cm-2 s-1 x 106 s
5.1032 cm-2 PbPb run, 5.5 TeV
NPbPb collisions = 2 .109 collisions
Ldt dt = 3.1030 cm-2 s-1 x 107 s
5.1037 cm-2 for pp run, 14 TeV
Npp collisions = 2 .1012 collisions
Muon triggers: ~ 100% efficiency, ~ 1kHz Electron triggers: Bandwidth limitation NPbPb central = 2 .108 collisions
Muon triggers: ~ 100% efficiency, < 1kHz
Pb-PB nominal run pp nominal run
Electron triggers: ~ 50% efficiency of TRD L1 20 physics events per event
Hadron triggers: NPbPb central = 2 .107 collisions
Hadron triggers: Npp minb = 2 .109 collisions
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Model Comparisons(HERA-LHC Workshop)
Compare predictions by several different models
Good agreement between collinear-factorization-based calculations: FO NLO and FONLLkT factorization (CASCADE) higher at large pT
beautycharm
CERN/LHCC 2005-014hep-ph/0601164
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Energy extrapolation via pQCD?
Different systems (pp, p-Pb, Pb-Pb) will have different s values
Results in pp at 14 TeV will have to extrapolated to 5.5 TeV (Pb-Pb energy) to compute, e.g., nuclear modification factors RAA
pQCD: “there ratio of results at 14 TeV/5.5 TeV has ‘small’ uncertainty”
charm beauty
12% 8%
MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.
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Cuts Summary
pt bin [GeV/c]
|d0| cut [m]
1.0 – 1.5 400 200
1.5 – 2.0 400 200
2.0 – 2.5 300 200
2.5 – 3.0 200 200
3.0 – 4.0 150 200
4.0 – 5.0 150 200
5.0 – 7.0 100 200
7.0 – 9.0 100 200
9.0 – 12.0 100 200
12.0 – 16.0 50 200
16.0 – 20.0 50 200
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- Charmed hadrons (Hc=D0,D+,D+s,+
c) cross section assumed to be proportional to the D0 one. The Hc/D0
ratio is assumed to be 1.70 0.07 (*)
Errors propagated from Hc to e level:
- Monte Carlo corrections for the D0 measurement ~ 10%
- Statistical error on the D0 pT distribution
- NN normalization not considered at this level (same as beauty)
- The 69% uncertainty of D0 from b should become negligible after the beauty direct measurement
The charm contribution to the total electron spectrum is evaluated using the MC by introducing the charmed hadron pT distributions deduced from the D0K-+ measurement.
Estimation of uncertainties on the pT - differential cross section of beauty electrons
evaluation of charm background
(*) deduced by comparing the PYTHIA value with the ALEPH measured value [D.Abbaneo et al., Eur. Phys. J. C16 (2000) 597]
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Cross section of electrons from B
inner bars: stat. errorsouter bars: stat. pt-dep. syst. errorsnot shown: norm. error (5% pp, 9% Pb-Pb)
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
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Extraction of a minimum-pt-differential cross section for B mesons
Using UA1 MC method (*), also adopted by ALICE
(*) 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 for ptB > pt
min is
obtained from a scaling of the electron-level cross section measured within a given electron parameters space e
MC
eB
tBt
B
meas
ebeautyet
Bt
B ppdy
d
ppdy
d
)(
)()()(
min
,min
},,{ 0dpTe
Bemeas
ebeautye F)(,
The semi-electronic B.R. is included here
We use , where pT are the previously used bins,
= [-0.9, 0.9] and d0 = [d0 MIN, +] m
(thanks to R.Guernane for useful discussions)
Problem: depends on B cross section shape used in simulation
systematic error. How large?BeF
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Robusteness of the procedure
F ~ 1 %
Extraction of a minimum-pt-differential cross section for B mesons
For pte > 2 GeV/c, can
find an “optimal” ptmin,
for which the additionalsystematic error is negligible