Les Arcs, March 16-23 2002

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The XXXVIIth Rencontres de Moriond QCD AND HIGH
ENERGY HADRONIC INTERACTIONS
Les Arcs, March 16-23 2002
Results from CDF, SLD and the LEP experiments
New ALEPH results for these Winter
Conferences Combinations from BOSC working group
(many thanks to O. Schneider) Conclusions
CERN-EP/2002-016 Submitted to EPJ
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Phenomenology
Time-dependent asymmetry between mixed and
unmixed decays
Oscillating term damped by the exponential decay
and proper time resolution effects
st (m/p) sL ? (sp/p) t
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The basic strategy

• Choose a selection criterion
• determines directly the final state tag method
• and signal fraction

• Tag initial and final state
• total mistag h hi ( 1-hf ) hf ( 1-hi )

• Measure proper time
• resolution st (m/p) sL ? (sp/p) t

• Maximum likelihood fit to Dms
• (or to the oscillation amplitude with fixed
  frequency)

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Selection methods
Statistics

• Fully inclusive Delphi, SLD
• FS tag from dipole or NN
• Very high statistics ( N ? 105 _at_ LEP, N ? 104 _at_
  SLD )
• Natural signal purity ( fs 10)
• Semi-inclusive Aleph, Delphi, Opal, CDF, SLD
• Inclusive l, f-l, K
• Still high statistics ( N ? 104? 105 _at_ LEP, N ?
  103 _at_ SLD )
• Signal purity natural or slightly enhanced.
• Semi-exclusive Aleph, Delphi, Opal, SLD
• Ds-h, Ds-l
• Lower statistics ( N ? 102? 103 _at_ LEP, N ? 102 _at_
  SLD )
• Signal purity up to 60, controlled from data.
• Fully exclusive Aleph, Delphi
• Little statistics ( N ? 50 events )
• Purity ? 50, excellent proper time resolution!

Signal purity
Resolution
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The oscillation fit
For every event
sL, sp, fj, Pj estimated event-by-event Each
event is treated as a single experiment!
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The amplitude method
Set a limit by combining analyses unable to
resolve oscillations A 0 for Dms w A 1 for
Dms w
sA -1 (w) ? N½ fs (1-2h) F (sp,sL) F (sp,sL) ?
exp(-st w )
For w ? Dms, the shape A (w) depends on the
details of the analysis, and can be calculated
analytically in simple cases
Moser and Roussarie NIM A 384 (1997) 491
Abbaneo and Boix JHEP 08 (1999) 004
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The three ALEPH analyses
Released as preliminary in 2000 - now improved
and submitted for publication
Inclusive lepton final states
Fully reconstructed candidates
Ds - lepton final states
Old Ds hadron analysis dropped
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Fully reconstructed candidates
80 candidates (32 in the main peak) 11 with
purity gt 80 23 with purity gt 50
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Over 300 candidates
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Decay length for the inclusive l analysis
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Event-by-event treatment for the incl l analysis
Divide events in classes according to topological
properties vertex classes m(D), cosq(l,D),
ntr(D), c2(D), c2(B)
For each class
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Event-by-event treatment for the incl l analysis
Decay length uncertainty from the vertex fit
data
Decay length bias correction and pull
correction Momentum uncertainty and bias
correction
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Building a reliable analysis

• Control reliability of parameterizations MC

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The estimate of the systematic uncertainties
For each source considered, both a change of
the amplitude and of its statistical error are
observed
Calculate the total error taking into account
both effects by means of toy experiments
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The three analysis results
Inclusive lepton
Ds-lepton
Exclusive
?msgt7.2 ps-1 ?msgt7.4 ps-1 (was 6.6 ps-1)
Obs. limit ?msgt2.4 ps-1 Exp. limit ?msgt0.3 ps-1
?msgt11.4 ps-1 (was 9.5 ps-1) ?msgt14.0 ps-1 (was
9.8 ps-1)
1.645?A_at_15ps-1 2.5
1.645?A_at_15ps-1 1.2
1.645?A_at_15ps-1 2.1
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Fully inclusive final states
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SLD versus LEP
SLD privileged environment for Bs oscillation hunt
LEP SLD 4M qq events lt400K qq
events per experiment sL ? 250 mm (core) sL ?
60-70 mm (core) Initial State Tag Initial State
Tag heff ? 25 heff ? 10-15 (beam
polarization) Best analyses Best analyses
Ds lepton Inclusive lepton Inclusive lepton
Fully inclusive
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The world combination
Combined limit Dms gt 14.9 ps-1 _at_ 95
CL Expected limit Dms 19.3 ps-1
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Comparison by experiment
Weights in the combination
Sensitivities
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Conclusions
Bs oscillation searches have substantially
improved over the last two years in the absence
of new data! (e.g. the uncertainty at w ? 20 ps-1
was reduced by a factor ? 2) Some improvements
can still be expected, but not as significant
We know that Dms gt 14.9 ps-1 _at_ 95 CL and we
have a (mild) indication of a signal at w between
16 and 20 ps-1 The burden and the pleasure of
continuing the hunt goes now to CDF and D0