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Towards CP violation results from D Ø

Towards CP violation results from D Ø. This talk: Progress on CP violation measurements Expectations. Paul Balm, NIKHEF (for the D Ø collaboration) EPS meeting July 2003, Aachen. Why do B-physics at the Tevatron?. Producing large numbers of bb pairs: s (pp  bb) = 1.5 10 5 nb @ 2TeV

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Towards CP violation results from D Ø

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  1. Towards CP violation results from DØ • This talk: • Progress on CP violation measurements • Expectations Paul Balm, NIKHEF (for the DØ collaboration) EPS meeting July 2003, Aachen Paul Balm - EPS 2003 - July 17, 2003

  2. Why do B-physics at the Tevatron? • Producing large numbers of bb pairs: • s(pp  bb) = 1.5 105 nb @ 2TeV • s(e+e- Z0 bb) = 7 nb • s(e+e-(4S) bb) = 1 nb • Expect 1010 bb pairs/year at 4 1031 cm-2s-1 • fragmenting into all B-species: Bd, Bu, Bs, Lb, … • But: much higher backgrounds, need more sophisticated triggering/event selection Paul Balm - EPS 2003 - July 17, 2003

  3. Rich B-physics menu • cross-sections: improve precision and extend pT–range over Run I • B hadron spectroscopy: study and discovery of new particles: Bc, Xb, Wb, … • Many CP violation measurements possible • CKM angles from decays like • Bd J/y KS • Bs  J/y f • Mixing measurements: Bs, Bd Paul Balm - EPS 2003 - July 17, 2003

  4. Performance of DØ • Silicon Microstrip Tracker (SMT): 91% operational • Central Fiber Tracker (CFT): 99% operational • Calorimeter: 99.9% operational • Muon system 99.5% operational • over entire rapidity range • Over past year, running efficiency greatly improved • taking data at 50 Hz • June ’03 average 88% Paul Balm - EPS 2003 - July 17, 2003

  5. Tracker performance • Distance of closest approach (DCA): resolution closing in on MC • At pT=1 GeV, s(DCA)=53 mm • Better for higher pT Paul Balm - EPS 2003 - July 17, 2003

  6. Tracker feats • photon conversions: p • X- decay: 10 cm L0 p- X- p- XLp Paul Balm - EPS 2003 - July 17, 2003

  7. Today’s B sample • 114 pb-1 taken with dimuon trigger • requires muon scintillator coincidence at L1 • At the Tevatron, a J/y trigger yields a lot of B’s: 15-20% • Current baseline Tevatron plan: 2 fb-1 at the end of 2005 • All J/y modes suffer from (implicit) |p| cut in L1 muon trigger • Awaiting trigger completion • (see later slides) m(m+m-) 114 pb-1 Paul Balm - EPS 2003 - July 17, 2003

  8. Baseline lifetime measurement:B J/y K 47 pb-1 114 pb-1 123535 B J/y K • Combining J/y and one track • we have only limited K/p separation using dE/dx from the SMT • Lifetime fit to ct distribution, use • Gaussian for combinatorics • exp. convoluted with Gaussian for B bkg • exp. convoluted with Gaussian for B+ signal • Result: <t> = 1.761  0.24 (stat) ps • Compare PDG: <t> = 1.671  0.018 ps Paul Balm - EPS 2003 - July 17, 2003

  9. Decays for CKM angles:Bs  J/y f b c J/y c Bs s f s s Bs  J/y f N(Bs) = 133 17 • CP violation in this channel allows measurement of CKM angle bs • Effect expected to be small (few %), but directly proportional to h (Wolfenstein param.) • Lifetime fits are in progress • see LeptonPhoton03 ! Paul Balm - EPS 2003 - July 17, 2003

  10. sin(2b) = Accurate measurement requires: initial-flavour tagging trigger completion Decays for CKM angles: Bd J/y KS Bd J/y KS N(Bd)=15420 • Bd mass formed from mass-constrained KS and J/y A(Bd) - A(Bd) A(Bd) + A(Bd) KSp+p- Paul Balm - EPS 2003 - July 17, 2003

  11. Initial Flavour Tagging • Jet charge tag: sum of charge of tracks in opposite-side jet • Soft muon tag: use opposite-side muon charge • Using exclusively reconstructed B+ J/y K+ sample Same-side tag being worked on signal + bkg for B signal (errors are statistical) Efficiency: e = (Nright + Nwrong) / Nall Dilution: D = (Nright - Nwrong) / (Nright + Nwrong) Paul Balm - EPS 2003 - July 17, 2003

  12. Bs mixing: Dms significance Dms [ps-1] • Dms reach in hadronic channel: BsDs(*)p • used soft muon tag • proper time res. used: 75 fs, reco. effiency 15% • in 2 fb-1, expect 1300-1900 events (single-m trigger) With 2 fb-1, can make 3s measurement to Dms of ~23 ps-1 - also looking into semileptonic channel Reach determined by vertexing resolution and trigger efficiencies 2 fb-1 Excluded PDG 95% Paul Balm - EPS 2003 - July 17, 2003

  13. Trigger completion • CTT: L1 Central Track Trigger • Track finding at L1, allows match with muon system • Effectively allows lowering pT threshold on muon triggers • Coming online now! (installed, running tests) • STT: L2 Silicon Track Trigger • Displaced track trigger allowing b-tagging at L2 • Expected after the summer • Expect large increase in J/y yield Paul Balm - EPS 2003 - July 17, 2003

  14. Conclusions • B’s in 114 pb-1 sample have been studied • Results promising: compatible with expectations • With more data and completed trigger, DØ will make accurate CP violation measurements Stay tuned! Paul Balm - EPS 2003 - July 17, 2003

  15. Back-up slides Paul Balm - EPS 2003 - July 17, 2003

  16. RunI dataset Paul Balm - EPS 2003 - July 17, 2003

  17. Algorithm: Remove daughter tracks from the reconstructed B Remove tracks w. 2D impact parameter greater than 0.2 cm Remove tracks with | z(DCA) – z(PV) | > 2.0 cm Use remaining tracks in j window opp. B to calculate the jet charge Q (weighing tracks with pT) Events with |Q|>0.2 are “tagged” Efficiency = (Nright + Nwrong)/ Nall Dilution = (Nright - Nwrong)/ Nall Flavour tagging: Jet charge (using 47 pb-1 ) • Errors only statistical • Errors in fractions of signal, bgd events in mass window (from fit) are ignored Paul Balm - EPS 2003 - July 17, 2003

  18. Flavour tagging: Soft muon tag (using 47 pb-1 ) • Algorithm: • must have ΔR > 2.0 separation from reconstructed B • must have pT > 1.9 GeV • charge of highest-pT muon in event gives (opposite-side) B-tag • Errors only statistical • Errors in fractions of signal, bgd events in mass window (from fit) are ignored Paul Balm - EPS 2003 - July 17, 2003

  19. Mass spectrum used for lifetime fit: mass 5.254 GeV  8 MeV 179 signal events Mass spectrum with add’l lifetime cut: 96 signal events B+  J/y K+ mass plots 47 pb-1 47 pb-1 Paul Balm - EPS 2003 - July 17, 2003

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