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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

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status of b analysis via single electrons

Status of B analysisvia single electrons

Andrea Dainese

INFN – Legnaro

based on work with:

F.Antinori, C.Bombonati, M.Lunardon, R.Turrisi

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

layout
Layout
  • Beauty measurement using displaced electrons
    • Detection strategy
    • Experimental issues: tracking and PID
    • Results for pp and Pb-Pb
  • Physics Performance:
    • Sensitivity to pQCD predictions in pp
    • Beauty quenching
  • Conclusions / Outlook

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

measuring beauty via electrons

rec. track

e

Primary

Vertex

B

d0

X

Measuring beauty via electrons
  • Expected yields of charm (b.r.: 10%) and beauty (b.r.: 11% +10% as bc e) decay electrons:
  • b quark has ct  500 mm

decay electrons d0 ~ few-100 mm

What’s the background?

transverse plane

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

background 1 charm decays
Background 1: charm decays
  • Heavy-quark decays:
  • b→B→e
  • b→B→D→e
  • c→D→e

beauty

pp

charm(background)

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

background 2 other sources
Decays of light mesons and Dalitz decays (mostly p0)

Photon conversions (g→e+e-) in the beam pipe and ITS innermost layer

Charged pions mis-identified as electrons

Background 2: other sources

pp

NO PID

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

detection strategy

rec. track

e

Primary

Vertex

B

d0

X

Detection strategy
  • Electron PID: reject most of the hadrons
  • Impact parameter cut: reduce charm and bkg electrons
  • Subtract (small) residual background

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

electron identification

outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff.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

Electron identification
  • Combined info from TRD (trans. rad.) and TPC (dE/dx)
    • TRD rejects 99% of the p and ALL heavier hadrons (pt > 1 GeV/c)

outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff.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

fraction of misidentified pions

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

cross section extraction procedure
Cross section extraction procedure
  • In a given pt-bin, N “electrons” are counted, after PID and d0 cut:
  • N = Nb + Nc + Nbkg
  • Subtract the contribution from charm: Nb + Nbkg = N - Nc
    • estimated from D0 measurement (source of error)
  • Subtract the contribution from background: Nb = (N – Nc) - Nbkg
    • estimated from measured pions dN/dpt plus MC (source of error)
  • Correct for acceptance/efficiency: dNbcorr/dy = (Nb / e)
    • efficiency calculated with MC (source of error)
  • Multiply by the inelastic pp cross section (or by Pb-Pb overlap functions): dse from b/dy = spp.dNbcorr/dy
  • pp cross section measured at LHC (source of error)

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

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)

dep. on d0 cut

~10%

dep. on d0 cut

pp

Error contributions

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

optimization of d 0 cut in bins of p t
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

Optimization of d0 cut in bins of pt

pp, 109 events

“old TRD PID”

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

statistics summary

“new TRD PID”

Statistics Summary

109 pp events

107 central (0-5%) Pb-Pb events

“old TRD PID”

“old TRD PID”

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

errors summary

“old TRD PID”

Errors Summary

“old TRD PID”

109 pp events

107 central (0-5%) Pb-Pb events

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

pp sensitivity vs pqcd
pp: Sensitivity vs. pQCD

From electrons in 2 < pt < 20 GeV/c, B mesons in 2 < ptmin < 30 GeV/c

“old TRD PID”

109 pp events

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

beauty energy loss r aa
Beauty Energy Loss : RAA

“old TRD PID”

1 year at nominal luminosity

(107 central Pb-Pb events, 109 pp events)

Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

heavy to light ratios r b d
Heavy-to-light ratios: RB/D

“old TRD PID”

1 year at nominal luminosity

(107 central Pb-Pb events, 109 pp events)

Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

first year scenario
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

p=4 GeV/c

40%

TOF

0.1%

Ne=Np=Nm=NK=Np

C.Bombonati

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

first year statistical error
First year: Statistical error

TPC+TRD

TPC

C.Bombonati

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

outlook
Outlook
  • One 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/AOD
    • analysis of PDC events
    • preparation of procedure for background subtraction (charm, misid. pions) and for corrections (cuts, PID)

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

extra slides
EXTRA SLIDES

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

lhc running conditions
LHC running conditions

pp nominal run

Pb-PB nominal run

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

Ldt = 5.1026 cm-2 s-1 x 106 s

5.1032 cm-2 PbPb run, 5.5 TeV

NPbPb collisions = 2 .109 collisions





Muon triggers:

~ 100% efficiency, < 1kHz

Muon triggers:

~ 100% efficiency, ~ 1kHz

Electron triggers:

~ 50% efficiency of TRD L1

20 physics events per event

Electron triggers:

Bandwidth limitation

NPbPb central = 2 .108 collisions

Hadron triggers:

Npp minb = 2 .109 collisions

Hadron triggers:

NPbPb central = 2 .107 collisions





ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

model comparisons hera lhc workshop
Model Comparisons(HERA-LHC Workshop)

CERN/LHCC 2005-014

hep-ph/0601164

Compare predictions by several different models

charm

beauty

Good agreement between collinear-factorization-based

calculations: FO NLO and FONLL

kT factorization (CASCADE) higher at large pT

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

energy extrapolation via pqcd
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”

beauty

charm

12%

8%

MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

cuts summary
Cuts Summary

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

slide24

Estimation of uncertainties on the pT - differential cross section of beauty electrons

evaluation of charm background

The charm contribution to the total electron spectrum is evaluated using the MC by introducing the charmed hadron pT distributions deduced from the D0K-+ measurement.

- 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 pTdistribution

- NN normalization not considered at this level (same as beauty)

- The 69% uncertainty of D0 from b should become negligible after the beauty direct measurement

(*) deduced by comparing the PYTHIA value with the ALEPH measured value [D.Abbaneo et al., Eur. Phys. J. C16 (2000) 597]

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

cross section of electrons from b
Cross section of electrons from B

inner bars: stat. errors

outer bars: stat.  pt-dep. syst. errors

not shown: norm. error (5% pp, 9% Pb-Pb)

1 year at nominal luminosity

(107 central Pb-Pb events, 109 pp events)

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

slide26

Problem: depends on B cross section shape used in simulation

systematic error. How large?

Extraction of a minimum-pt-differential cross section for B mesons

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

(thanks to R.Guernane for useful discussions)

The B meson cross section per unit of rapidity at midrapidity for ptB > ptmin is obtained from a scaling of the electron-level cross section measured within a given electron parameters space e

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

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

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese

slide27

F ~ 1 %

Extraction of a minimum-pt-differential cross section for B mesons

Robusteness of the procedure

For pte > 2 GeV/c,can

find an “optimal” ptmin,

for which the additional

systematic error is negligible

ALICE Physics Week, Muenster, 13.02.07 Andrea Dainese