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B Physics at D0: An update

B Physics at D0: An update. Vivek Jain Cornell University Oct 1, 2004. Outline. Introduction D0 detector Recent Results New states Rare decays Lifetimes Mixing Conclusions. Why B physics?.

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B Physics at D0: An update

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  1. B Physics at D0: An update Vivek Jain Cornell University Oct 1, 2004

  2. Outline • Introduction • D0 detector • Recent Results • New states • Rare decays • Lifetimes • Mixing • Conclusions

  3. Why B physics? • Understanding structure of flavour dynamics is crucial 3 families,handedness, mixing angles, masses, … any unified theory will have to account for it – • Weak decays, especially Mixing, CP violating and rare decays provide an insight into short-distance physics • Short distance phenomena are sensitive to beyond-SM effects • Test bed for QCD, e.g., form factors, calculations of B hadron lifetimes, spectroscopy

  4. B physics at the Tevatron • At Ecm = 2 TeV • At Z pole • At Υ(4S) • All species produced, Environment not as clean as at electron machines Low trigger efficiencies

  5. B Physics Program at D0 • Unique opportunity to do B physics during the current run • Complementary to program at B-factories (KEK, SLAC, CLEO..) • mixing, • Rare decays: Large tanβ SUSY models enhance rate • Beauty Baryons, lifetime, … • expt: 0.80±0.06 (SL modes), theory ~ 0.95 • , , B lifetimes, B semi-leptonic, CP violation studies • Quarkonia - production, polarization … b production cross-section: In Run I, measd. Rates x(2-3) higher

  6. DZero Detector SMT H-disks SMT F-disks SMT barrels • Trackers • Silicon Tracker: |η|<3 • Fiber Tracker: |η|<2 • Magnetic field 2T • Muon system with coverage |η|<2 and good shielding

  7. CFT Readout by VLPC: High QE, very low dark noise Excellent PE resolution Each pixel has 1mm radius – well matched to fiber Operated at 8-9 (± 0.05)°K 8 Layers: Axial, Stereo (± 3°) Radius: 20-50 cm Good S/N. Signal ~ 5-9 pe Fast enough to be in L1 trigger

  8. VLPC performance Signal ON: LED was set to ~ 2 pe

  9. All tracks Analysis cuts – pT>0.7 GeV σ(DCA)≈53μm @ Pt=1GeV and better @ higher Pt data

  10. pT spectrum of soft pion candidate in D*D0 ~100 events/pb-1

  11. Excellent Lepton Acceptance Muon ID: • Overall efficiency (from data) • plateaus at about 85-90% • - at pT 4.5 GeV • pT 3.5 GeV • - at pT 2.5 GeV MC: Muon system in Level 1 of reconstructed muon

  12. Electron ID: • Calorimeter goes out to • Low pT electron ID is in progress • At present, we can detect electrons with pT>3 GeV and Average efficiency is about 75% • Working to extend to higher values of and lower pT threshold – use for tagging initial state flavour

  13. All trigger components have simulation software

  14. Triggers for B physics • Robust and quiet di-muon and single-muon triggers • Large coverage |h|<2, p>1.5-5 GeV – depends on Luminosity and trigger • Variety of triggers based on - Muon purity @ L1: 90% - all physics! • 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 (prescaled) • Current total trigger bandwidth 1600 Hz / 800 Hz / 60 Hz @ L1/L2/L3

  15. Recent Results • Many new analyses used ~ 250-350 pb-1 • Single muon triggers have variable prescales, non-trivial to determine luminosity for analyses using these triggers • Have more data on tape, but not yet analyzed • Details at: www-d0.fnal.gov/Run2Physics/ckm/

  16. Basic particles Plot is for illustrative purpose

  17. 2826±93 7217±127 624±41 ~ 350 pb-1 Large exclusive samples Impact parameter cuts

  18. Bs No IP cuts: Use for lifetime 337±25 Λb ~ 250 pb-1 Will reprocess w/ tracking optimized for long-lived part. (yield will ~50%)

  19. Observation of X(3872) 5.2 effect In 2003, Belle saw a 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 (accepted by PRL) 522 ± 100 events M = 0.7749  0.0031 (stat)  0.003 (syst) GeV/c2

  20. Charmonium J_PC (Estia Eichten)

  21. What kind of particle is the X ? - charmonium ? 1 ³D3, 2 ³P2 … - an exotic meson molecule ? - something else ? Compare X candidates to (2S), e.g. - split into two || regions - decay length, isolation, helicity

  22. No significant differences between (2S) and X have been observed yet. This comparison will be more useful once we have models of the production and decay of, e.g., meson molecules that predict the observables used in the comparison. |y|<1 Iso=1 Hel(μμ)<0.4 pT>15 Hel(ππ)<0.4 dl<0.01 cm Observation of the charged analog X+ J/ + 0 would rule out charmonium Observation of radiative decays X   c would favour charmonium Belle’s results rule out 1 ³D3, 2 ¹P1, ³D2, ¹D2, 0-+, 1++ Use Dzero’s calorimeter to identify low energy 0 and  : work in progress.

  23. Spectroscopy: L=1 B (and D) mesons • For Hadrons with one heavy quark, QCD has additional symmetries as (Heavy Quark Symmetry) • Spin of the heavy quark decouples and meson properties are given by the light degrees of freedom • Each energy level in the spectrum of such mesons has a pair of degenerate states:

  24. Lessons from charm (I) For non-strange L=1 Charm mesons jq = 1/2, 3/2 have been seen The wide states were observed via Dalitz plot analysis in Belle hep-ex/0307021

  25. D** at D0 Preliminary result on product branching ratio Br(B  {D10,D2*0}   X)  Br({D10,D2*0}  D*+ -) = 0.280  0.021 (stat)  0.088 (syst) % measured by normalizing to known Br (B  D*+   X)

  26. Lessons from charm (II) – Ds** Eichten For L=1 Ds mesons, preferred decay mode:DK jq = 3/2 -> DK, D*K jq = 1/2 below DK threshold, decay to Mass/widths unexpected! Maybe B** or Bs** have similar behaviour

  27. Previous results on B** Probably not the natural width of these states • Previous experiments did not resolve the four states: <PDG mass> = 5698±8 MeV • Theoretical estimates for M(B1)~ 5700 - 5755 and for M( ) ~ 5715 to 5767. Width ~ 20 MeV

  28. Signal reconstruction (I) • Search for narrow B** - Use B hadrons in the foll. modes and add coming from the Primary Vertex • Since ΔM between B**+ and B**0 is expected to be small compared to resolution, we combine all channels (e.g., ΔM for B+/B0 = 0.33±0.28 MeV) 7217±127 events 2826± 93 events 624± 41 events

  29. Signal Reconstruction (II) • Dominant decays modes of • ( forbidden by J,P conserv.) • (ratio of the two modes expected to be 1:1) • To improve resolution, we measure mass difference between and B, ΔM

  30. Signal reconstruction (III) • Now, ΔM(B* - B) = 45.78±0.35 MeV – small • Thus, if we ignore , ΔM shifts down ~ 46 MeV, • We get three peaks: • = M( ) – M(B*) – 46 MeV • = M( ) – M(B*) – 46 MeV • = M( ) – M(B) - in correct place

  31. First observation of the separated states From fit: N = All B** 536±114 events ~7σ signif. 273±59 events Interpreting the peaks as: (98) 131±30 events

  32. Consistency checks: B0** B±** required to have large Impact parameter signific. relative to Primary vertex – No Signal (as expected) 32±36 events

  33. Results of fit - Preliminary

  34. Standard Model predictions Exptl. Results 90% (95%) CL

  35. Beyond Standard Model • First proposed by Babu/Kolda as a probe of SUSY (hep-ph 9909476) • Branching fraction depends on tan(β) and charged Higgs mass • Branching fraction increases as in 2HDM (MSSM) Other models also have enhanced rates, e.g., Dedes, Nierste hep-ph 0108037 mSUGRA

  36. Experimental challenge: (L 200 pb-1)

  37. Optimization Procedure – “blind” analysis • ~ 80 pb-1of data was used to optimize cuts • After pre-selection, three additional variables were used to discriminate bkgd. from signal - • Isolation : Since most of b-quark’s mom. is carried by the B-hadron, track population around it is low • Decay Length significance: Lxy/δLxy– remove combinatoric background, e.g., fake muons • Pointing angle: Angle, α, between B_s decay vector and B_s momentum vector

  38. Result of optimization Isolation > 0.56 Pointing angle < 0.20 (rad) δLxy/ δL > 18.5 Background prediction from sidebands in (MB ± 2σ): 3.7 ± 1.1 events Punzi (physics/0308063)

  39. Opened the box (July 8’ 04) (L = 240 pb-1) Nothing remarkable about the four events – look like background!

  40. Calculate upper limit (I) • To calculate limit on branching fraction, normalize to PDG Feldman-Cousins MC: 0.229±0.016 MC 0.270±0.034 (PDG) Since our signal region overlaps Bd, can have contamination R: theoretical expectation for ratio of Br. frac. of Bd /Bs - set R=0 Iflimit will be better

  41. Upper Limit - Preliminary The 95% (90%) C.L. upper limit: Currently, the most stringent limit on this decay channel If we use Bayesian approach, we get 4.7 (3.8)

  42. Excluded by D0 Run II 240 pb-1 Implications of this result 4.6E-7 (95%CL) Dermisek et al Hep-ph 0304101 Dark Matter and Minimal SO10 with soft SUSY breaking Contours of constant Allowed by Dark Matter constraints

  43. 20.4 signal +6.2 - 5.5 +0.18 : 0.46 0.03 ps - 0.16 Observation of Bc • Last of ground state mesons to be definitively observed! • Theory: Lifetime 0.3-0.5 ps • Theory: Mass 6.4 GeV ±0.3 • Only previous evidence CDF RunI result Mass: 6.4±0.39±0.13 GeV

  44. Take advantage of easy-to-trigger-on final state – events come via the dimuon triggers m- m+ n Select 231 J/ymX candidates Background estimated with J/y+track data control sample, separated into prompt and non-prompt components m+ Bc+ PV

  45. Mass: 5.95 ±0.34 GeV +0.14 -0.13 Lifetime: 0.448 ±0.121 ps +0.123 -0.096 Do combined likelihood fit to invariant mass and pseudo-proper time distribution: #signal: 95±12±11

  46. Background-only fit: D2log(likelihood) is 60 for 5 degrees of freedom

  47. Other properties: Bc b c Forms weakly decaying charmed hadron c b Probability 4thm within f ±90 degrees of Bc candidate = 5±2% Probability 4thm within f ±90 degrees of background = 1%

  48. Lifetimes of B hadrons • Use modes with J/ψ final states, semi-leptonic decays • Predictions available from theory via OPE calculations • These calculations are rooted in QCD • Expansion is in inverse powers of heavy quark mass • Predictions are semi-quantitative for Charm • For B-hadrons, predictions are on much firmer footing

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