Pr

1
Bottom and Charm Quark Production in Two-Photon
Collisions at LEP
Wilfrid da Silva
LPNHE, Paris
DELPHI Collaboration
J/? production in ?? collisions (DELPHI) Cross
section ???ee-??cc,bb X ) ? charm
tagged by D (L3) ? beauty, charm
tagged by leptons (DELPHI, L3) Summary
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EPS2003 Aachen
17-23 july 2003
2
J/? production at LEP2 (DELPHI) ee- ? ee-
J/? X

• Two independent leading processes

? VDM (pomeron exchange or diffractive
dissociation of the photon)
? Resolved processes color octet model most
probable hypothesis.
Data LEP2
161-207 GeV, L 617 pb-1
?

• MC PYTHIA 6.156

?Select ?? events
?Tag J/?? with muon pairs N36 7 evts
?Background J/??coming from bb estimated
2.1 0.6 evts
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N( ee_ ? Z? ? J/? X) lt 0.2 evts N( ?? ? ?c2 ?
J/? ?????? ) lt 0.3 evts
Results
Estimated fraction of resolved processes 74
22
Rate NJ/? / Nvis ?? ( 6.7 1.3 (stat)
0.2 (syst)) 10-3
?? J/????X?? 45 9 (stat) 17 (syst) pb
Klasen
3
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Measurement of ?(ee-? ee-ccX) and ?(ee-?ee-
bbX)
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• Open charm and beauty production measurement ?
  provide a good test of PQCD

• Two LO main contributions
• direct and single resolved terms

Large mb and mc ?? more reliable calculations.
NLO total cross sections computations available
Use the 10 years old Drees, Kraemer, Zunft, Zerwas
?
Direct term
at
180 GeV
?
At LEP2 energies direct and single resolved
contributions are of the same order
? VDM and double resolved contribution are
expected to be small

• Default MC used in all analyses PYTHIA / ?
  pdf SaS1D

Single resolved term
4
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Measurement of ?(ee-? ee-ccX) using D

• LEP II data 183 - 209 GeV???L
  683 pb-1
• ?????????

? ? selection and antitagged events
Charm tagged by D ??????
D?D0 ??S
?????? ?? ??????????????
Results
d?/dpT(D) with ? lt 1.4 and 1. GeV lt pT lt
12. GeV
D
Visible region
Comparison with PYTHIA LO
Frixione NLO MC
?(ee-? ee-DX)vis 71.2 5.3 (stat) 9.8
(syst) pb
Extraction of the charm cross section
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0.54
?(ee-? ee-ccX) ( 1.12 0.09 (stat) 0.16
(syst) -0.25 ) nb
5
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Measurement of ?(ee-? ee-ccX) and ?(ee-?ee-
bbX)
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Event selection strategy (for L3 and DELPHI)
Select anti-tagged????events
Identify a lepton as a signature for
semi-leptonic charm and beauty decays
Reconstruct jets and compute the
sensitive variable ( the lepton transverse
momentum with respect to the lepton jet axis)
Jet axis computed without the ?
6
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Measurement of ?(ee-?ee- bbX)
Fitting strategy
NEW 2003

• Data LEP2

189-209 GeV, L 413 pb-1
Use muons
Charm and beauty contributions well separated in
pT distribution
?
??? ? ????one variable fit
?
Nbb fit parameter variable
?
Nuds contribution estimated from the data
Result
Charm
Beauty
7
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Measurement of ?(ee-? ee-ccX) and ?(ee-?ee-
bbX)
? Upgrade of their previous measurement

• Data 189 209 GeV???L 627
  pb-1?????????

Muons

• Use muons and electrons

• ?? 3 variable fit Nbb, Ncc, Nuds

?Results
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??(ee-? ee-bbX)muons 13.0 2.3 (stat) 2.3
(syst) pb ???(ee-? ee-bbX)electrons 12.6
2.4 (stat) 2.3 (syst) pb
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? ??and e tag results are consistent
Charm
Beauty
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?(ee-? ee-bbX)combined 12.8 1.7 (stat)
2.3 (syst) pb
Electrons
?? result in agreement with L3 previous
measurement ?
?? as a subproduct of the control test of the
charm sample ?
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??(ee-? ee-ccX)combined 998 117 (stat) pb
(in agreement with L3 previous measurement ) ?
8
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Measurement of ?(ee-? ee-ccX) and ?(ee-?ee-
bbX)
K-lepton charge correlations for beauty or
charm enrichment
NEW 2003

Identify a K in lepton jet with RICH and TPC
cc Kl- charge correlation fix Nbb value
given by the previous measurement fit? Ncc
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bb Kl charge correlation fix? Ncc value
given by LEP average fit? Nbb
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??in agreement with previous DELPHI measurement
9
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Measurement of ?(ee-? ee-ccX) and ?(ee-?ee-
bbX)
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Summary
Single resolved processes are needed to describe
the data
Good agreement with QCD Drees, Kraemer, Zunft,
Zerwas
Consistent LEP results
New results from DELPHI with K-lepton charge
correlations for the first time in ???physics
DELPHI confirms the L3 and OPAL beauty excess