OPEN CHARM CROSS-SECTION MEASUREMENTS...
Transcript of OPEN CHARM CROSS-SECTION MEASUREMENTS...
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
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= 7 TeV DatasPreliminaryLHCb
54± = 2992 signalN
mass [MeV]1700 1800 1900 2000
entr
ies
/ 4 M
eV
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-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
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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
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NUMBER OF REC. PVS
PVn0 2 4 6 8 100
2000
4000
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10000
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14000
16000 DataMC
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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
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