1 / 27

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

bedros
Télécharger la présentation

B physics and X(3872) production at DØ

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related