Post on 19-Dec-2015
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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