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Heavy B Hadrons at Tevatron

Tevatron. Main Injector and Recycler. Heavy B Hadrons at Tevatron. Andrei Nomerotski (Fermilab). Introduction. Tevatron produces B hadrons inaccessible at B-factories Previous results mostly from LEP and Run I Tevatron Cross sections are large but so are the backgrounds

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Heavy B Hadrons at Tevatron

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  1. Tevatron Main Injector and Recycler Heavy B Hadrons at Tevatron Andrei Nomerotski (Fermilab)

  2. Introduction • Tevatron produces B hadrons inaccessible at B-factories • Previous results mostly from LEP and Run I Tevatron • Cross sections are large but so are the backgrounds • (bb)100b at 2 TeV ((bb) 1nb at B factories) • Mostly soft Pt processes : Triggers are very important • In Run II, Tevatron has two experiments doing B-physics : CDF and DZero • Take data the third year • Both had major upgrades for Run II • With magnetic field and Tracker DZero is much better suited for B-physics than before • With 0.5 fb-1 per experiment on tape Tevatron has world largest samples of heavy B hadrons

  3. SMT H-disks SMT F-disks SMT barrels DZero Detector • Excellent coverage of Tracking and Muon Systems • 2 T Solenoid, polarity inversed weekly • Quiet Muon Trigger with muon Pt measurement at Level1 by toroids • Fine segmentation Calorimeter and Preshower

  4. CDF Detector • Large Tracking volume in magnetic field – excellent mass resolution • Particle ID capabilities : TOF, dE/dx in drift chamber • Large bandwidth (50 kHz) Level1 Trigger and Displaced Track Silicon Trigger at Level2 • Access to purely hadronic B samples

  5. Datasets • Tevatron performance progressed very well in 2004 • 0.5 fb-1 per experiment by September 2004 • Typical analyses use ½ of total luminosity

  6. Will talk about • Bs and Lb Mass Measurements at CDF • Observation of narrow B** mesons at DZero • Observation of Bc at DZero • Branching Fractions of hadronic modes Bs and Lb (CDF) • Semileptonic samples of Bs and Lb (DZero) • Bs oscillations (DZero) • Bs and Lb lifetimes (DZero/CDF) • Summary

  7. Bs and Lb Masses (1) • Taking advantage of good mass resolution CDF greatly improved mass accuracy for Bs and Lb • Possible after careful calibration of the mass scale of the tracker • Material • Field • Track errors

  8. Bs and Lb Masses (2) • World’s best single measurements • In agreement with previous results

  9. B** Spectroscopy : Theory • B** are orbitally (L=1) exited states of B meson • In general there are two wide states and two narrow states • Narrow states decay through D-wave • Wide states decay through S-wave • Properties of B** are very similar to D** mesons • For charm mesons, M(D*)-M(D) ~ 140-145 MeV • For bottom, M(B*)-M(B) ~ 46 MeV Theory: Splitting within a doublet has 1/m_Q corrections • For non-strange charm, M(D**)-M(D) ~550-600 MeV Expect similar behavior for B mesons • M( D*2)-M(D1) ~ 32-37 MeV Expect this to be ~ 10-15 MeV for M(B*2)-M(B1)

  10. DZero : D** in Semileptonic B Decays Observed merged D10(2420) and D2*0(2460) wrong-sign combinations D*- + mass 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) %

  11. B** Spectroscopy : Experiment • B** have been observed before at LEP and CDF in Run I but the narrow states haven’t been resolved • DZero observed B** in Bp+ modes using exclusive B decay channels

  12. DZero : B** analysis (1) 2826±93 7217±127 L = 350 pb-1 624±41 Used exclusive B meson samples with J/psi in final state

  13. DZero : B** analysis (2) • Add charged pion coming from the Primary Vertex to exclusively reconstructed B • Since ΔM between B**+ and B**0 is expected to be small compared to resolution all channels are combined • Dominant decay modes • B*2 B p or B*p • B1 B*p • B*  B g • Since photon is not reconstructed two narrow B** states produce three peaks in ΔM • In addition there are wide states which cannot be distinguished from non-resonant background

  14. First Observation of Separated States From fit: N = All B** 536±114 events ~7σ signif. 273±59 events Interpreting the peaks as 131±30 events

  15. DZero : B** analysis (4) • FittingDM distribution • Three relativistic Breit-Wigner functions convoluted with Gaussian resolution • Theory motivated assumptions : G1 = G2and equal Br for two B*2decay modes • Results M(B1) = 5724 ± 4(stat) ± 7(syst) MeV M(B*2-B1) = 23.6 ± 7.7(stat) ± 3.9(syst) MeV G = 23 ± 12(stat) ± 9(syst) MeV f1= 0.51 ± 0.11(stat) ± 0.21(syst) f1 is relative yield of B1 meson • Systematic errors are dominated by fit assumptions and for G by uncertainty of mass resolution

  16. DZero : B** analysis (5) • Consistency checks: • Separate fits for neutral and charged B • No signal if charged pion is not coming from Primary Vertex Neutral B** Charged B**

  17. 20.4 signal +6.2 - 5.5 +0.18 t = 0.46 0.03 ps - 0.16 DZero: Bc Meson (1) • Last of ground state mesons to be definitively observed • Theory • Lifetime 0.3 - 0.5 ps • Mass 6.4 ± 0.3 GeV • Only previous evidence : CDF Run I result mass 6.4 ± 0.39 ± 0.13 GeV

  18. m- m+ n m+ Bc+ PV DZero: Bc Meson (2) • Use tri-muon final state • J/ymmand tight third m form a good vertex • Select 231 J/y m X candidates • Bc is not fully reconstructed  backgrounds are very important • Bkg with fake muon estimated with J/y+track data control sample separated into prompt and non-prompt components • bb/cc backgrounds are small due to vertex requirement • Include contributions to signal from • Feed-down from Bcy(2S) m p0 X • Bc J/ y m p0 X

  19. Dzero : Bc Meson (3) • Plot invariant mass of three muons • Not exclusive reconstruction • Use MC to get mass template shapes • Do combined likelihood fit to invariant mass and pseudo-proper time distribution • Number of Bc candidates: 95±12±11

  20. DZero: Bc Meson (4) Mass : 5.95 ± 0.34 GeV Lifetime : 0.45 ± 0.12 ps +0.14 +0.12 - 0.13 - 0.10 Mass log likelihood Results of the fit : Main systematics • Mass : signal sample composition, MC signal modeling, fraction of prompt bkg • Lifetime : Bias from vertexing algorithm, fraction of prompt bkg • Both could be improved Mass, GeV

  21. Bc b c b c Bc : Other Properties • Fragmentation process b Bc + c dominated production • Charm quark should form weakly decaying charmed hadron in vicinity of Bc • Measured probability to have muon within f ± 90o of Bc candidate • 5 ± 2 % for signal sample • 1%for background sample

  22. Branching Rates for Bs and Lb • Poorly known – see PDG summary below

  23. CDF : Br for hadronic modes • CDF collected excellent hadronic samples of Bs and Lb decays using Track Trigger • Measured Br of several decay modes • Earlier results • Br(BsDsp)/Br(B0Dp)=1.4±0.2(stat)±0.5(syst) • Br(LbLcp) = 6.0±1.0(stat)±0.8(syst)±2.1(Br) x10-3

  24. CDF : Br (Bs  ff) • Charmless BVV decay • Track Trigger : • Two oppositely charged tracks with Pt > 2 GeV at Level 1 • Impact Parameter > 0.12 mm at Level 2 • Normalized to BsJ/y f decay • Br(Bs ff) = (1.4+-0.6(stat)+-0.2(syst)+-0.5(Br)) 10-5

  25. CDF : CharmlessLbgppandLbgpK decays • Charmless Lbdecays may have large direct CPV • Proceeds via CKM suppressed and/or penguin (QCD,EW) • Expected Br ~ (1-2) 10-6 • Normalized to B  hh process • Search window in M(pp) optimizes separation from B  hh • 772 ±13 events expected • 767 observed • Br(Lb hh) < 22 x 10-6 M(pp)

  26. DZero : Bs semileptonic modes • Excellent yield for all semileptonic modes • Collected by Single Muon Triggers without online lifetime cuts • Used for Bs oscillations and lifetime measurements

  27. Tagging muon Y, cm BS μ+ μ+ D-S π- K- K+ φ X, cm Oscillated BS candidate • Opposite Side Muon tagging applied to semileptonic BS sample • Re performance of taggers see G.Borissov’s talk • Example of tagged BS candidate • Two same sign muons are detected • MKK=1.019 GeV, MKKπ=1.94 GeV • PT(μBs)=3.4 GeV; PT(μtag)=3.5 GeV

  28. DZero : Bs Mixing Projections • Plan to use both semileptonic and hadronic Bs samples • More statistics in semileptonics • Better proper decay time resolution in hadronics (no n) • Have access to hadronic Bs sampe triggering on opposite side muon • Muon is used as high purity tag • Work in progress - see signals Also hardware upgrades in 2005 • L3 bandwidth will be increased from 50 to 100 Hz in 2005 • Semileptonic sample limited by L3 and offline CPU – expect large gain in yield • Upgrade to 250 Hz under review • Partial silicon upgrade • New beampipe with smaller diameter • Add another innermost layer of silicon (Layer0) with analog cable readout Layer0 + L3 BW upgrades No upgrades

  29. DZero: Lb  Lc mnsample • Reconstructs Lb  Lc mnin twoLc decay modes • Lc  Ks p • Lc  L p • Samples will be used for lifetime ratio measurements 350 pb-1 350 pb-1 Lc mass agrees with PDG Second peak interpreted as Lc  S p ; S  L g

  30. B Hadron Lifetimes • Naive quark spectator model predicts equal lifetimes for all B hadrons (but Bc) • (NLO) QCD  Heavy Quark Expansion predicts deviations in rough agreement with data • Experimental and theoretical uncertainties are comparable • Lifetime differences probe the HQE to 3rd order in LQCD / mb • Goal: measure the ratios accurately Dzero: Recent result from semileptonic modes (B+)/(B0) = 1.093  0.021 (stat)  0.022 (syst)

  31. +0.008 t(Bs) = 1.369 ± 0.100 ps -0.010 Exclusive modes : Bs Lifetime • J/ modes are golden at the Tevatron since they allow for simple di-lepton trigger with low Pt threshold CDF : BsJ/ ( KK) based on 240 pb-1 • 12 parameter maximum likelihood fit

  32. 250 pb-1 DZero : Exclusive Bs Sample DZeroaccumulated the largest sample of exclusive Bs J/y f decays • J/y  mm • f  KK

  33. +0.052 +0.098 t(Bs) = 1.444 ±0.020 ps t(Bd0) = 1.473 ±0.023 ps -0.050 -0.090 +0.075 t(Bs)/t(B0) = 0.980 ±0.003 -0.070 DZero : Bs Lifetime • Use two similar topologies BsJ/ and BdJ/Ks*0to measure lifetime ratio • Simultaneous Likelihood fit to mass and lifetime distribution 250 pb-1 250 pb-1 BdJ/Ks*0 BsJ/

  34. +0.107 +0.217 t(Lb) = 1.221 ±0.043 ps t(Bd0) = 1.397 ±0.031 ps -0.098 -0.179 +0.169 t(Lb)/t(B0) = 0.874 ±0.028 -0.142 DZero : Lb Lifetime • Reconstruct Lb J/y L • Use process with similar topology Bd0 J/y Ks to measure the ratio • Result is statistically limited

  35. Summary • So far Tevatron experiments were doubling samples every year – that may continue • Exciting prospects for heavy B hadrons • Expect great improvement in accuracy of lifetime and Br measurements • Measurement of DGs, Dms within reach • There are still particles to discover in this sector: Xb, Sb, Wb , doubly heavy baryons • Be ready for new results

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