FPCP2004, Daegu Andrei Nomerotski Fermilab 1

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Heavy B Hadrons at Tevatron
Andrei Nomerotski (Fermilab)

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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

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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

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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

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Datasets

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

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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)
• Lifetimes (DZero/CDF)
• Summary

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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

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Bs and Lb Masses (2)

• Worlds best single measurements
• In agreement with previous results

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B Spectroscopy Theory

• B are orbitally (L1) 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( D2)-M(D1) 32-37 MeV
• Expect this to be 10-15 MeV for M(B2)-M(B1)

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DZero D in Semileptonic B Decays

• Observed merged D10(2420) and D20(2460)

wrong-sign combinations
D- ? mass
Preliminary result on product branching ratio
Br(B ? D10,D20 ? ? X) ? Br(D10,D20 ? D
?-) 0.280 ? 0.021 (stat) ? 0.088 (syst)
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B Spectroscopy Experiment

• B have been observed before at LEP and CDF in
  Run I but the narrow states havent been resolved
• DZero observed B in Bp modes using exclusive B
  decay channels

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DZero B analysis (1)
282693
7217127
L 350 pb-1
62441
Used large exclusive B meson samples with J/psi
in final state
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DZero B analysis (2)

• Add charged pion coming from the Primary Vertex
  to exclusively reconstructed B
• Since ?M between B and B0 is expected to be
  small compared to resolution all channels are
  combined
• Dominant decay modes
• B2 ? B p or Bp
• B1 ? Bp
• B ? B g
• Since photon is not reconstructed two narrow B
  states produce three peaks in ?M
• In addition there are wide states which cannot be
  distinguished from non-resonant background

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First Observation of Separated States
From fit N All B 536114 events
7s signif.
27359 events
Interpreting the peaks as
13130 events
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DZero B analysis (4)

• Fitting DM distribution
• Three relativistic Breit-Wigner functions
  convoluted with Gaussian resolution
• Theory motivated assumptions G1 G2 and equal
  Br for two B2 decay modes
• Results
• M(B1) 5724 4(stat) 7(syst) MeV
• M(B2-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

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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
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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
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DZero Bc Meson (2)

• Use tri-muon final state
• J/y?mm and 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/ytrack 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

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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 951211

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DZero Bc Meson (4)
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 can be improved

Mass, GeV
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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

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Branching Rates for Bs and Lb

• Poorly known see PDG summary below

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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)1.40.2(stat)0.5(syst)
• Br(Lb?Lcp) 6.01.0(stat)0.8(syst)2.1(Br)
  x10-3

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CDF Br (Bs ? ff)

• Charmless B?VV decay
• Track Trigger
• Two oppositely charged tracks with Pt gt 2 GeV at
  Level 1
• Impact Parameter gt 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

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CDF Charmless Lbgpp and LbgpK decays

• Charmless Lb decays 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) lt 22 x 10-6

M(pp)
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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

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Oscillated BS candidate

• Opposite Side Muon tagging applied to
  semileptonic BS sample
• Re performance of taggers see G.Borissovs talk
• Example of tagged BS candidate
• Two same sign muons are detected
• MKK1.019 GeV, MKKp1.94 GeV
• PT(µBs)3.4 GeV PT(µtag)3.5 GeV

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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
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DZero Lb ? Lc mn sample

• Reconstructs Lb ? Lc mn in two Lc 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
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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)
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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

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DZero Exclusive Bs Sample

• DZero accumulated the world largest sample of
  exclusive Bs ? J/y f decays
• J/y ? mm
• f ? KK

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DZero Bs Lifetime

• Use two similar topologies Bs?J/? ? and Bd?J/?
  Ks0 to measure lifetime ratio
• Simultaneous Likelihood fit to mass and lifetime
  distribution

250 pb-1
250 pb-1
Bd?J/? Ks0
Bs?J/? ?
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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

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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