Pakhlov Pavel (ITEP, Mosc ow) Why B physics is still Why B physics is still interesting interesting Belle detector Belle detector Measurement of sin2 Measurement of sin2 Rare B decays Rare B decays Future plans Future plans University of Lausanne 11/12/2001
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Pakhlov Pavel (ITEP, Moscow) Why B physics is still interesting Belle detector Measurement of sin2 Rare B decays Future plans University of Lausanne.
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Pakhlov Pavel (ITEP, Moscow)
Why B physics is still Why B physics is still
interestinginteresting
Belle detectorBelle detector
Measurement of sin2Measurement of sin2
Rare B decays Rare B decays
Future plansFuture plans
University of Lausanne11/12/2001
Pakhlov Pavel (ITEP, Moscow) 2
B-physicsB-physics • Test of the Standard Model (SM) mechanisms
• hadronic models, CKM, etc…
• Measurement of the fundamental parameters of SM• exact values can be a hint for new phenomenology
• Search for physics beyond SM• large b-quark mass
• SM decays suppression (Vcb<<1)
• large contribution from loop and box diagrams
Pakhlov Pavel (ITEP, Moscow) 3
Why CP is importantWhy CP is important
• Test CKM mechanism as a single source of CP violation:• During 35 years CP violation measured only in K system. CKM
theory single (free) parameter; Experiment single measurement .
• Measurement of CKM matrix elements:• sin2: constrain on CKM matrix elements without QCD
uncertainties.• sin2 from BDK, xd/xs, B : free of model uncertainties, but
requires much more statistics.
• New physics:• Need overfull constrain on CKM parameters (better if without
QCD uncertainties) to test the SM• … or to observe very large discrepancy
Pakhlov Pavel (ITEP, Moscow) 4
CPV in B mesons at eCPV in B mesons at e++ee-- colliders colliders
• B0 B0 are produced and remain in coherent p-state until one of them decays.
• If the first B decays to flavor specific mode, the state of the other B is orthogonal at this time.
• Then the second B propagates (oscillating).• If it decays to a CP-final state: two contributions from
B and B interfere.• If the first B decays to the CP final state and the
second to a specific flavor state – the interference results into opposite sign of CP asymmetry. The time integrated asymmetry vanishes!
• Each class of tagging / each specific tagging particle have different tagging purity. If sum all events with different purity loose accuracy.
• Divide all events into several categories depending on tagging purities, then average over independent measurements: • Calculate probability for each track to belong to one of the
flavor tagging class.• Combine information about all tracks into likelihood for event
to be B0 or B0. • Divide the whole likelihood range into 6 bins of different
purities.• Extract dilution factor for each bin from the data. Use specific
flavor channels: B0 D(*)-+ ,B0 D(*)-+
Pakhlov Pavel (ITEP, Moscow) 18
Determination of wrong tag fractionDetermination of wrong tag fraction
• A(t)measured~(1-2)sin(md t); =Nwrong/N.
• For sin(2) we need to know !
• Get from B0B0 mixing amplitude ~(1-2)cos(md t);
• Fit to the data with free (r). Efficiency >99%
effective=27.01.2%
Pakhlov Pavel (ITEP, Moscow) 19
• CP-side vertexing: • use prompt tracks from J/,
(2S), c
• Reject poorly fit vertices z 75m
• Tagging B vertexing:• Use well fit tracks• Iterative procedure: fit discard worst track z 140m
• Efficiency: 87%, t 1.5ps
• not-Gaussian tails 3%,
Vertex reconstructionVertex reconstruction
1137 events areused for CP fit
Pakhlov Pavel (ITEP, Moscow) 20
Check vertex resolution function Check vertex resolution function
BBDD((**)-)-++BB00 =1.55=1.550.02 0.02
pspsBB+ + =1.64=1.640.03 0.03
psps
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CP-fitCP-fit
• Each event has individual sensitivity to sin2 (depending on signal purity, tagging dilution, z and vertex fit accuracy, etc…)
• For each event calculate its likelihood as a function of sin2:
signal fraction wrong tag fraction PDG free
parameter
• Calculate sin2 which maximize the total likelihood Li
Resolution function
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sin2sin2 results results
sin2=0.990.140.06
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Cross-checksCross-checks
Mode dependencies:Check asymmetries in Non-CP sample.“sin2”=0.050.
04
Pakhlov Pavel (ITEP, Moscow) 24
Compare with other experimentsCompare with other experiments
Pakhlov Pavel (ITEP, Moscow) 25
Rare B-decaysRare B-decays
• New level of sensitivity to the rare B-decays:• Cabibbo-suppressed decays: B D(*)K+,D*+D(*)-