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Rare Decays of B Hadrons at CDF

Matthew Jones

October 3, 2005

2Oh my!

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Rare Decays of B Hadrons at CDF

• Search Bs,Bd μ+μ-

• Charmless B decays– Bd,Bs,Λb hh’

– B+ φK+, Bs φφ

• Not covered– B masses

– BsDsπ, ΛbΛcπ and kin

– D0 K-π+,K-K+,π-π+

In this talk, “rare” means branching fractions ≲ 10-6.

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The CDF Detector

Muon systems:

Tracking systems: SVX-II COT

CMP CMX CMU

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• Heavily suppressed in Standard Model:

• Approximately 2 orders of magnitude below current experimental sensitivity

• Significant enhancements from contributions of new physics processes

Search for Bs μ+μ-

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• Bs μ+μ- enhancement by SUSY:

• Correlation between Br(Bs μ+μ-) and (g-2)μ measurement

– BNL result could imply a10-100 enhancement compared with SM.

• Different behavior for Bs/Bd μ+μ- possible

~ (tan β)6 up to 3 orders of magnitude enhancement

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Search for Bs μ+μ-

• Di-muon trigger, pT>1.5 or 2 GeV/c• Limit normalized to B+J/ψK+ 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 μ+μ-

• Good mass resolution allows separation of Bs μ+μ- and Bd μ+μ-:

• No events observed in either mass window

• 90% C.L. limits:

• Expected background:

hep-ex/0508036 submitted to PRL

1.50.2 events

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Example of Constraints on Models

R. Dermíšek, et al., hep-ph/0507233

Minimal SO10 SUSY

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Hadronic Decays• Bππ/Kπ/KK: original motivation for Secondary

Vertex Trigger in CDF-II– Level 1 trigger: require two tracks with requirements

on pT and ΔΦ

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, B0π+π-, B0K+π-, ...

– Non-leptonic B-decays (eg., BsD-s+)

– Semi-leptonic decays (eg. Lepton + displaced track)– Charm physics

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Charmless Bhh’ Decays• CDF observes overlapping contributions

from B0π+π-, B0K+π-, Bs0K+K-:

Update of result from Summer 2004:

Same data sample, uncertainties reduced.

Separate individual decays using kinematics and particle identification.

~ 900 candidates

Wider than expected for a single channel

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Charmless Bhh’ Decays• Discriminating variables:

– Invariant mass, m(π+π-),– “Signed momentum imbalance”, α=Q1(1-p1/p2)– Energy loss in tracking chamber, dE/dx– Total momentum

• Corrections applied for relative efficiencies• Measure relative branching fractions and

ACP in B0K+π-

• Time-dependent asymmetries possible: already demonstrated• In 1 fb-1 we expect of order 50 tagged events• Γ(BsKK)/Γ(Bdππ) needed for extraction of

(hep-ph/0404009)

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Charmless Bhh’ Decays

f(BdKπ) = 0.6000.034

f(BsKK) = 0.2620.035

f(Bdππ) = 0.1340.030

f(BsKπ) = 0.0030.028

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Search for Λbpπ-/pK-

• Charmless Λb 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(π+π-):

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Search for Λbpπ-/pK-

• Normalize with respect to B0K+π- 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+φK+ and Bsφφ

• 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+φK+

• In principle, CP composition in BsVV obtained from angular analysis

• B+φK+ already seen but this is the first observation of Bsφφ

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B+φK+ Analysis

• Candidates are 3-track vertices containing two trigger tracks

• Discriminating variables:– M(K+K-K+): signal and physics backgrounds– M(K+K-): φK+K- signal

– φ decay helicity angle, Hφ

– dE/dx: kaon identification

• Likelihood fit to determine yield of B+φK+ and CP asymmetry.

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B+φK+ Analysis

Physics backgrounds:

B+K+K-K+X

B+f0K+

B+K*0+

B+K+K-K+

B+K++-

Signal:

B+ φK+

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B+φK+ CP AsymmetryB

r(B

+

φK

+)

x 10

-6A

CP(B

+

φK

+)

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Observation of Bsφφ

• Angular analysis possible with 1 fb-1.

179 pb-1

hep-ex/0502044 and PRL 95, 031801 (2005)

8 events in search window

0.750.41 BG expected

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2005200420032002Bsμ+μ-

Bhh’, B+φK+, Bsφφ

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(Bsμ+μ-): <10-7 Ultimate sensitivity in Run-II could reach 3x10-8

• Resolution on ACP(B0K+π-) should approach 0.025 with 1 fb-1

Ultimate precision of ~1%

• Bsφφ background free – 120 events in 1 fb-1 angular analysis.

• Good prospects for observing Λbpπ/pK

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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/ψ trigger:

– 8x106 J/ψ with hits in SVX-II in 1 fb-1

• B+J/ψK+:

Includes c>60 μm

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J/ψ 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 Bhh’ Decays• Contributions to systematic uncertainty:

– m(π+π-) 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/π bias– Proton/anti-proton asymmetry in background– Correlations between discriminating variables– Final state radiation (Cirigliano, et al.)

not fundamental limitations

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Bhh’ systematics

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dE/dx Calibration at CDF

• High statistics calibration samples:– D*+D0+

– p-

– K0S+-

– J/ψμ+μ-

• 1.4σ K/π separation for p>2 GeV/c

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The Future