alice physics week, muenster, 13.02.07 andrea dainese 1 status of b analysis via single electrons...

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


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


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?


Background 1: charm decays

pp

Heavy-quark decays:

• b→B→e

• b→B→D→e

• c→D→e

beauty

charm (background)


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


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


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outdated: latest info from TRD group on rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff.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outdated: latest info from TRD group on p rejection probability 99.3% – 0.3% p (GeV/c), for 90% electron eff.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


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


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


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”


Statistics Summary

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

“old TRD PID”“new TRD PID” “old TRD PID”


Errors Summary109 pp events 107 central (0-5%) Pb-Pb events

“old TRD PID”“old TRD PID”


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”


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”


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”


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


First year: Statistical error

TPC+TRD TPC

C.Bombonati


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)


EXTRA SLIDES


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


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


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.


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


- 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]


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)


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


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

alice physics week, muenster, 13.02.07 andrea dainese 1 status of b analysis via single electrons...

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