OPEN CHARM CROSS-SECTION MEASUREMENTS OF

D0 & D*Alexandr Kozlinskiy (Nikhef), Markward Britsch (MPI Heidelberg),

Marco Gersabeck (CERN) et al.LHCb Week St Petersburg, 30 June 2010

OUTLINE

• Introduction

• D0 cross-section measurements using D0→Kπ

• D* cross-section measurement using D*→D0(Kπ)π

• Conclusion

AIM

• Use early charm data to measure D production in as function of rapidity (y) and transverse momentum (pT)

• Use acceptance down to pT = 0

• Chosen binning (driven by statistics):6 bins in y from 2 to 58 bins in pT from 0 GeV/c to 8 GeV/c

INGREDIENTS• Data taken with TCK 0x00051710 after run 71474

• Raw yields in bins of y and pT

• Corrections for efficiencies (MC generator cuts, selection cuts, corrections for differences between data and MC)

• Correction for contribution from secondary decays from long-lived particles

• Branching ratio measurement → external input

• Luminosity measurement → separate study

D0 SELECTIONS

• Markward Britsch:

• offline selection only

• signed flight distance > 1 mm

• DOCA < 1 mm

• ν2,pt > 15.3

• nPV = 1

• MG:

• standard cut-based strip+offl.

• pT (daughter), p (mother)

• track, FD, IP(d+m), vertex χ2

• cosθ>0.99993

• PIDK(K)>0; PIDK(π)<0optimised for S/√S+B on 10M min bias data optimised for S/B on MC

RAW YIELDS

• MB: large yield, large background

• MG: lower yield, high purity

), PIDK(K)>PIDK(2 in MeV/cKm1820 1840 1860 1880 1900

2en

trie

s pe

r 2 M

eV/c

0

50

100

150

200

250

300

350

400

450

= 7 TeV DatasPreliminaryLHCb

54± = 2992 signalN

mass [MeV]1700 1800 1900 2000

entr

ies

/ 4 M

eV

0

200

400

600

800

1000

1200

1400

1600

1800

-1bµLHCb preliminary, 1791 2010 data

EFFICIENCIES• Generator cut efficiencies calculated in bins of y and pT

using generator level simulation

• Selection efficiencies calculated in bins of y and pT using full MC

• PID cut efficiency from data binned in daughter η and pT using Andrew Powell’s tables applied to daughter distribution from MC

• Tracking efficiencies: use information from tracking group

• Corrections needed for variables whose distributions vary between data and MC

O(1%)

CORRECTIONS• MG: Cut on D0 IP χ2 to

suppress secondaries

• D0 IP χ2 distribution different in data and MC

• Correction by estimating cut efficiency through fit to distribution

• Estimate correction from ratio:95.2% ± 3.4%

)0(D2IP0 2 4 6 8 10

entr

ies

per 0

.2

0

5000

10000

15000

20000

25000

30000

35000

40000

45000DataMC

CORRECTIONS - II• MB: Require number of reconstructed

PVs = 1

• Study yield as function of number of reconstructed PVs in MC and extract cut efficiency

• Systematic uncertainty due to differences in PV reconstruction in data and MC

• Correction: 14% ± 3%

• MG: No efficiency difference as function of number of generated PVs

PROMPT-SECONDARY

• Separate prompt D candidates from those from decays of long-lived particles

• Use bifurcated Gaussians to fit prompt/secondary components in log(IP) distribution

• Fix secondary distribution to MC values

• Secondary fraction ~1% - 2%

))0ln(IP(D-6 -4 -2 0

entr

ies

per 0

.2

1

10

210

310 MG

MB

TOWARDS CROSS-SECTIONS• Apply efficiencies and corrections to raw yields

• Correct for branching ratios (from PDG)

• Correct for luminosity:Current placeholder: online luminosity value

724076±3.69523e+06

241713±1.69562e+06

69238.3±456370

34743.3±163147

31491.3±154090

31644.5±366251

11631.7±159783

5495.47±71040.2

2501.9±21808.9

2063.98±9251.75

1678.59±5493.89

14237±121029

11800.3±164279

5346.68±82626.9

2592.76±31211.1

1672.31±12790

1040.35±3585.09

9760.04±77865.1

8993.2±106404

4000.98±48285

2205.11±15757.5

1175.77±5763.59

6659.81±35575.7

8323.55±37850.3

4805.01±15517.1

) in MeV/c0(DT

p0 2000 4000 6000 8000

y

2

2.5

3

3.5

4

4.5

5 MGMB

D* SELECTION & YIELD

• standard cut-based strip+offl.

• daughter IP & vertex χ2

• lifetime & lifetime χ2

• cosθ

• PIDK(K)>0; PIDK(π)<0

• several methods to cross-check yield extraction

optimised for S/√S+B on 133M min bias data

sideband subrtacted D0 mass distribution

0

D* EFFICIENCIES• Efficiencies calculated from

MC

• PID cut efficiencies extracted from data using Andrew Powell’s tables

• Generator efficiencies calculated at generator level

• Secondary contribution extracted from log(IP) distribution: <5%

• 4% systematic from variation of lifetime χ2 cut

D* YIELDSraw yields

efficiency corrected yields

CONCLUSION

• First cross-section results corrected

• Systematic studies well underway

• Largest systematics: IP/lifetime χ2 cuts (AK & MG): ~4%nPV requirement (MB): ~3%

• Note: first draft nearly complete, difficult to collaborate without internet

BACKUP

16

NUMBER OF REC. PVS

PVn0 2 4 6 8 100

2000

4000

6000

8000

10000

12000

14000

16000 DataMC

17

KPI-PIK RATIO

0.696857±1.70281

0.195402±0.969011

0.176054±1.04321

0.159135±0.864882

0.210123±0.790366

0.844412±2.46673

0.211115±1.32355

0.134676±0.8779

0.204998±0.993636

0.253439±0.795672

0.286184±1.33178

0.30912±1.45167

) in MeV/c0(DT

p0 2000 4000 6000 8000

y

2

2.5

3

3.5

4

4.5

5

18