Rare Decays of B Hadrons at CDF

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Rare Decays of B Hadrons at CDF
Matthew Jones
October 3, 2005
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Oh my!
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Rare Decays of B Hadrons at CDF
In this talk, rare means branching fractions ?
10-6.

• Search Bs,Bd ?µµ-
• Charmless B decays
• Bd,Bs,?b ? hh
• B ? fK, Bs ? ff
• Not covered
• B masses
• Bs?Dsp, ?b??cp and kin
• D0 ? K-p,K-K,p-p

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The CDF Detector
Muon systems
CMP CMX CMU
Tracking systems SVX-II COT
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Search for Bs ?µµ-

• Heavily suppressed in Standard Model
• Approximately 2 orders of magnitude below current
  experimental sensitivity
• Significant enhancements from contributions of
  new physics processes

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• Bs ?µµ- enhancement by SUSY
• Correlation between Br(Bs ?µµ-) and (g-2)µ
  measurement
• BNL result could imply a10-100 enhancement
  compared with SM.
• Different behavior for Bs/Bd? µµ- possible

(tan ß)6 ? up to 3 orders of magnitude
enhancement
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Search for Bs ?µµ-

• Di-muon trigger, pT1.5 or 2 GeV/c
• Limit normalized to B?J/?K signal
• Significant backgrounds from
• Sequential semileptonic
• Double semileptonic decays
• Fake leptons
• Discriminate using multivariate likelihood
  (isolation, 3D vertex quantities)

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Search for Bs,Bd ?µµ-

• Good mass resolution allows separation of Bs?
  µµ- and Bd? µµ-

• No events observed in either mass window
• 90 C.L. limits
• Expected background

1.5?0.2 events
hep-ex/0508036 submitted to PRL
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Example of Constraints on Models
Minimal SO10 SUSY
R. Dermíek, et al., hep-ph/0507233
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Hadronic Decays

• B?pp/Kp/KK original motivation for Secondary
  Vertex Trigger in CDF-II
• Level 1 trigger require two tracks with
  requirements on pT and ?F
• Dominates level 1 trigger rate!
• Level 2 trigger vertex displaced with respect to
  beam axis ? heavy flavor trigger.
• Applications at CDF
• Two-body B-decays, B0?pp-, B0?Kp-, ...
• Non-leptonic B-decays (eg., Bs?D-s?)
• Semi-leptonic decays (eg. Lepton displaced
  track)
• Charm physics

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Charmless B?hh Decays

• CDF observes overlapping contributions from
  B0?pp-, B0?Kp-, Bs0?KK-

Update of result from Summer 2004 Same data
sample, uncertainties reduced.
900 candidates
Wider than expected for a single channel
Separate individual decays using kinematics and
particle identification.
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Charmless B?hh Decays

• Discriminating variables
• Invariant mass, m(pp-),
• Signed momentum imbalance, aQ1(1-p1/p2)
• Energy loss in tracking chamber, dE/dx
• Total momentum
• Corrections applied for relative efficiencies
• Measure relative branching fractions
  and ACP in B0?Kp-
• Time-dependent asymmetries possible
• already
  demonstrated
• In 1 fb-1 we expect of order 50 tagged events
• G(Bs?KK)/G(Bd?pp) needed for extraction of ?.

(hep-ph/0404009)
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Charmless B?hh Decays
f(Bd?Kp) 0.600?0.034 f(Bs?KK)
0.262?0.035 f(Bd?pp) 0.134?0.030 f(Bs?Kp)
0.003?0.028
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Search for ?b?pp-/pK-

• Charmless ?b decays yet to be observed
• Large ACP expected in baryons
• Branching fraction could be 1-2 x10-6

Count excess over background in distribution of
m(pp-)
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Search for ?b?pp-/pK-

• Normalize with respect to B0?Kp- signal
• No events observed, set upper limit
• Significant improvements possible with particle
  identification and larger data sample.

(90 C.L.)
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B?fK and Bs?ff

• More examples of charmless B decays selected
  using secondary vertex trigger
• Pure penguin transitions may
  differ from SM expectations
• ACP can be measured in B?fK
• In principle, CP composition in Bs?VV obtained
  from angular analysis
• B?fK already seen but this is the first
  observation of Bs?ff

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B?fK Analysis

• Candidates are 3-track vertices containing two
  trigger tracks
• Discriminating variables
• M(KK-K) signal and physics backgrounds
• M(KK-) f?KK- signal
• f decay helicity angle, Hf
• dE/dx kaon identification
• Likelihood fit to determine yield of B?fK and
  CP asymmetry.

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B?fK Analysis
Signal
B? fK
Physics backgrounds
B?KK-KX B?f0K B?K0? B?KK-K B?K??-
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B?fK CP Asymmetry
Br(B?fK) x 10-6
ACP(B?fK)
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Observation of Bs?ff
179 pb-1
8 events in search window 0.75?0.41 BG expected
hep-ex/0502044 and PRL 95, 031801 (2005)

• Angular analysis possible with 1 fb-1.

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2005
2002
2004
2003
Bs?µµ-
B?hh, B?fK, Bs?ff
1 fb-1 of data for analysis by 2006 spring
shutdown.
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What to do with 1 fb-1

• Expected limit on Br(Bs?µµ-) sensitivity in Run-II could reach 3x10-8
• Resolution on ACP(B0?Kp-) should approach ?0.025
  with 1 fb-1
• Ultimate precision of 1
• Bs?ff background free 120 events in 1 fb-1
  ? angular analysis.
• Good prospects for observing ?b?pp/pK

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Additional Material
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CDF Triggers for B Physics

• Beam crossings every 396 ns
• Level 1 trigger
• Axial tracks from segments found in COT
• Association with hits in muon chambers
• Level 2 trigger
• Silicon hits added to tracks found at level 1
• Finer granularity in muon systems
• Level 3 trigger
• Full event reconstruction

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CDF Detector Performance

• J/? trigger
• 8x106 J/? with hits in SVX-II in 1 fb-1
• B?J/?K

Includes c?60 µm
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J/? Trigger at CDF

• Level 1 Two muons with pT 1.5 GeV
• Level 2 Opposite charge
• Level 3 Full event reconstruction

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Charmless B?hh Decays

• Contributions to systematic uncertainty
• m(pp-) resolution from Monte Carlo
• Shapes of dE/dx p.d.f.s, dE/dx correlations
• Electron/proton backgrounds
• B meson masses
• Background shape, momentum spectrum
• ?(B), ??s through decay length requirements
• Isolation requirement used in reconstruction
• Track trigger K/p bias
• Proton/anti-proton asymmetry in background
• Correlations between discriminating variables
• Final state radiation (Cirigliano, et al.)

not fundamental limitations
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B?hh systematics

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dE/dx Calibration at CDF

• High statistics calibration samples
• D?D0?
• ? ? p?-
• K0S???-
• J/??µµ-
• 1.4s K/p separation for p2 GeV/c

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The Future