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B physics and X(3872) production at DØ

B physics and X(3872) production at DØ. Introduction DØ-Detector Results on B physics Results on X(3872) Summary. All results are preliminary. Frank Lehner U Zurich DIS 2004, S trbske Pleso 15-18 April, 2004. Accelerator Status. excellent performance of Tevatron in 2004

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B physics and X(3872) production at DØ

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  1. B physics and X(3872) production at DØ • Introduction • DØ-Detector • Results on B physics • Results on X(3872) • Summary All results are preliminary Frank Lehner U Zurich DIS 2004, Strbske Pleso 15-18 April, 2004

  2. Accelerator Status • excellent performance of Tevatron in 2004 • DØ recorded 70 pb-1 in 2004 • important milestone: reprocessed full dataset in fall 2003 • greatly improved tracking performance • good fraction processed off-site • current datasets • ~300 pb-1 on tape • ~200-250 pb-1 analyzed • ~100 pb-1 Run I

  3. B production at Tevatron • Pro’s: • large cross section ~105 x larger than at present B-factories (4S) • all kinds of b hadrons produced: • Bd, Bs, Bc, b,.. • Con’s: • QCD background overwhelming • efficient trigger and reliable tracking necessary • soft pt spectrum, smaller boost than LEP • Key for B physics program at DØ: • Muon system • Muon trigger (single and dimuon triggers) • Silicon Vertex + Tracker

  4. DØ detector • upgraded Run II DØ detector: • beamline shielding • reduce background • new Forward Muon + Central Muon Scintillators • excellent coverage ||<2 • Preshowers • helping for e-ID • Fiber Tracker • Silicon Detector • 2T Solenoid

  5. DØ tracking region • Silicon detector • 6 barrels w/ 4 layers silicon- mostly double-sided silicon, axial and stereo • interspersed double-sided disks • large external area disks at end • tracking/vertexing up to ||<3 • Fiber Tracker • scintillating fibers Ø 0.82 mm • 8 layers - each axial/stereo • R/O through VLPC in LHe

  6. Tracking performance Data from semileptonic decays (B  m D X) || for kaons from D*D0 pT spectrum of soft pion from D*D0 • Tracks are reconstructed • over a wide  range • starting from pT = 180 MeV efficient muon and tracking system give us a large sample of semileptonic B decays

  7. Benchmark: exclusive B decays & yields • accumulated large exclusive samples of B+ and B0 • find in ~225 pb-1 • B0 J/y K* 1900 events • B+ J/y K+ 4300 events • B0 J/y Ks375 events • good S/B • Lifetime cuts applied

  8. 250 pb-1 Benchmark: exclusive B decays & yields • b-> J/  52 events • Bs -> J/  400 events • We have good potential in all B  J/y exclusive modes, work in progress on • Lifetime measurement of different B species • Studies of CP effects in Bs & Bd mesons

  9. Lifetime ratio (B+)/(B0) from semileptonic decays • measure from semileptonic B decays directly lifetime ratio instead of absolute lifetimes • select following samples: • Bm n D0 X • Bm n D* X • sample compositions: • “D0 sample”: + K+ - + anything • B+ 82%, B0 16%, Bs 2% • “D* sample”: + D0 - + anything • B+ 12%, B0 86%, Bs 2% • estimates based on measured BR and isospin relations • group events in 8 bins of visible proper decay length (VPDL) VPDL = LT / pT( D0)  MB LT = transverse decay length

  10. Lifetime ratio (B+)/(B0) from semileptonic decays Measure ratio r= N(+ D*-)/N(+ D0) in each bin i Combinatorial background with true D0 in D* sample is subtracted using wrong-sign distribution  no need for parameterisation of background VPDL distribution Additional inputs to the fit: - sample compositions (previous slide) - K-factors (from simulation) K = pT(D0) / pT(B) (separately for different decay modes) - relative reconstruction efficiencies for different B decay modes (from simulation) - slow pion reconstruction efficiency [flat for pT(D0) > 5 GeV (one of our cuts)] - decay length resolution (from simulation) - (B+) = 1.674  0.018 ps [PDG] one example VPDL bin

  11. Lifetime ratio (B+)/(B0) from semileptonic decays use binned c2 fit of event ratios to determine (B+)/(B0) • systematics currently dominated by • time dependence of slow pion reconstruction efficiency • relative reconstruction efficiencies CY • Br(B+ +  D*- + X) • K-factors • decay length resolution differences D0 D* Preliminary result: (B+)/(B0) = 1.093  0.021 (stat)  0.022 (syst)

  12. Lifetime ratio (B+)/(B0) from semileptonic decays This is one of the most precise measurements to date: New DØ result (average not updated, plot not official or approved by HFAG)

  13. B0/B0 mixing • in SM Bd mixing is explained by box diagrams • constrains Vtd CKM matrix element • mixing frequency mdhas been measured with high precision at B factories (0.502  0.007 ps-1) • use our large sample of semileptonic Bd decays to measure md • benchmark the initial state flavor tagging for later use in Bs and ms measurements

  14. B0/B0 mixing • initial flavor tagging • opposite side tight muon tag • muon pT > 2.5 GeV/c • cos Df(m, B) < 0.5 • asymmetry of ‘oscillated’ and ‘non-oscillated’ B mesons as function of VPDL • use binned 2 fit for asymmetry • this is already one of the best measurements in hadron colliders • work in progress to reduce systematics • use other tagging methods • add more D0 decay channels Preliminary results: md=0.5060.055(stat)0.049(syst) ps-1 Tagging efficiency: Tagging purity:

  15. Towards Bs mixing • semileptonic decays (Bs->m n Ds) • very good statistics • excellent yield: 9500 candidates in ~250 pb-1 • if ms  15 ps-1 a first indication of Bs mixing might be possible with 500 pb-1 • fully reconstructed hadronic decays: • poor statistics • excellent proper time resolution • need a few fb-1 of data to reach ms  18 ps-1

  16. Observation of B    D** X • D** are orbitally excited D meson states, see diagram • in heavy quark limit w/ L=1 expect two sets of doublet states • two broad (decay through S-wave) • two narrow (decay through D-wave) • narrow D** • D01(2420)-> D*+p- • D2*0(2460)-> D*+p- • D10, D2*0 have been observed and studied in several experiments, most recently by BaBar and Belle in B- D**0 - • we study D10, D2*0 produced in semileptonic B decays. Figure from Belle, hep-ex/0307021

  17. Observation of B    D** X • start from B  D*X sample, add another + • look at invariant mass of D*- + system • observed merged D10(2420) and D2*0(2460) • excess in right-sign combinations can be interpreted as interfering D10 and D2*0 • DØ’s preliminary result constrains the resonant contribution Work in progress: extract separate amplitude, relative phase Br(B  {D10,D2*0}   X)  Br({D10,D2*0}  D*+ -) = 0.280  0.021 (stat)  0.088 (syst) %

  18. Bs + - sensitivity study SM: • purely leptonic B decay is a flavor changing neutral current (FCNC) • forbidden at tree level • highly suppressed in SM • BR(Bs->mm)~ 3·10-9 • BR grows with tan6b in MSSM • very attractive probe for any new physics with extended Higgs sector (Two-Higgs Doublet models) Two-Higgs Doublet models:

  19. Bs + - sensitivity study • blind analysis: optimization cuts using Random Grid Search based on mass sideband • discriminating variables • isolation of mm pair • decay length • opening angle between mm pair and decay length direction • expected signal is normalized to B+-> J/ K+ • expect 7.3  1.8 background events in signal region The box has NOT been openedyet - Reoptimisation still in progress - further improvements expected Current expected limit (Feldman/Cousins): Br(Bs  + -) < 1.0  10-6 @ 95 % CL (stat + syst)

  20. X(3872)  J/ + - • last summer on LP ‘03, Belle announced new particle at ~3872 MeV/c2 • observed in B+ decays: • B+  K+ X(3872) • X(3872)  J/ + - • Belle’s discovery has been confirmed by CDF and DØ • DØ preliminary: • 300  61 events • 4.4 effect • M = 0.768  0.004 (stat)  0.004 (syst) GeV/c2

  21. X(3872)  J/ + - • nature of X(3872) is not known • mass surprisingly close to D*D threshold • could be charmonium, hybrid or meson molecule • compare sample of X particles to sample of (2S) using • ||<1 and 1<||<2 (plot) • decay length dl<0.2 mm and dl>0.2 mm • helicity of pp • isolation of X

  22. X(3872)  J/ + - • no significant differences between (2S) and X have been observed • surviving fraction of X behaves similar to (2S) • more useful once we have models of the production and decay of, e.g., meson molecules that predict the observables used in the comparison • Note that • observation of the charged analog X+ J/ + 0 would rule out cc hypothesis • observation of radiative decays X   c would favour cc hypothesis (Belle set limit). Use DØ’s calorimeter to identify low energy 0 and  : work in progress

  23. Summary • Preliminary results from DØ: • precise measurement of (B+)/(B0) • measurement of md, benchmark flavour tagging • Observation of B    D** X at DØ • DØ’s sensitivity to Bs    • Observation of the X(3872) at DØ and study of its production properties • The exciting times have started; stay tuned for more

  24. Spare slides

  25. DØ tracking performance (DCA)  53 m @ PT = 1 GeV and 15 m @ higher PT Can provide K/ separation for Ptot< 400 MeV p/ separation for Ptot<700 MeV NOT yet used for PID

  26. Triggers • Robust and quiet single- and di-muon triggers • Large coverage |h|<2 • Variety of triggers based on • L1 Muon & L1 CTT (Fiber Tracker) • L2 & L3 filters • Typical total rates at medium luminosity (40 1030 s-1cm-2) • Di-muons : 50 Hz / 15 Hz / 4 Hz @ L1/L2/L3 • Single muons : 120 Hz / 100 Hz / 50 Hz @ L1/L2/L3 • Rates before prescaling: typically single muon triggers are prescaled or/and used with raised pT threshold at L1 • Muon purity 90% - all physics! • Current total trigger bandwidth 1600 Hz / 800 Hz / 60 Hz @ L1/L2/L3 • B-physics semi-muonic yields are limited by L3 filters and L3 bandwidth

  27. Calibrations using J/y sample After magnetic field and material corrections Large J/y sample – currently 1.2 M events in 250 pb-1 Before corrections • J/y mass is shifted by 22 MeV • Observe dependence on Pt and on material crossed by tracks • Developed correction procedure based on field & material model • Finalizing calibration of momentum scale using J/y, Ks, D0 • NOT yet used Mass resolution 60 MeV/c2 in agreement with expectations

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