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Bottom and Charm Quark Production in Two-Photon Collisions at LEP

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  e + e -  cc,bb X )  charm tagged by D* ± (L3)  beauty, charm tagged by leptons (DELPHI, L3)

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Bottom and Charm Quark Production in Two-Photon Collisions at LEP

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  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 e+e-cc,bb X )  charm tagged by D*± (L3)  beauty, charm tagged by leptons (DELPHI, L3) Summary - - EPS2003 Aachen 17-23 july 2003

  2. J/ production at LEP2 (DELPHI) e+e-e+e-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 TagJ/with muon pairs N=36±7 evts Background: J/coming from bb estimated 2.1± 0.6 evts - N(e+e_ ZJ/X) < 0.2evts N(c2 J/) < 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. - Measurement of (e+e- e+e-ccX) and (e+e-e+e- bbX) - • 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. - Measurement of (e+e- e+e-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 || < 1.4 and 1. GeV < pT < 12. GeV D*± Visible region Comparison with PYTHIA LO Frixione NLO MC (e+e- e+e-D*±X)vis = 71.2 ± 5.3 (stat)±9.8 (syst) pb Extraction of the charm cross section - +0.54 (e+e- e+e-ccX) = ( 1.12 ±0.09 (stat)±0.16 (syst) -0.25 ) nb

  5. P T - Measurement of (e+e- e+e-ccX) and (e+e-e+e- bbX) - 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. estimated background from MC fixed by LEP average charm cross section  - Measurement of (e+e-e+e- 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  Nbbfit parameter variable  Nuds contribution estimated from the data Result Charm Beauty

  7. - - Measurement of (e+e- e+e-ccX) and (e+e-e+e- 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 - (e+e- e+e-bbX)muons = 13.0±2.3 (stat)±2.3 (syst) pb (e+e- e+e-bbX)electrons = 12.6 ±2.4 (stat)±2.3 (syst) pb - and e tag results are consistent Charm Beauty - (e+e- e+e-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 - (e+e- e+e-ccX)combined = 998 ±117 (stat) pb (in agreement with L3 previous measurement )

  8. - - Measurement of (e+e- e+e-ccX) and (e+e-e+e- bbX) K-lepton charge correlations for beauty or charm enrichment NEW 2003 Identify a K in lepton jet with RICH and TPC cc :K+l- charge correlation fix Nbb:value given by the previous measurement fit Ncc - - bb : K+l+ charge correlation fixNcc :value given by LEP average fit Nbb - in agreement with previous DELPHI measurement

  9. - Measurement of (e+e- e+e-ccX) and (e+e-e+e- bbX) - 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

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