Status of the analysis

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Status of the analysis
used for measuring CP-violating angle
Overview

• The cuts used to select
• Comparison with background from
• Efficiencies for selecting
• Reconstructing decay times

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Topology
9 mm
4 mm
Primary vertex
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Main selection criteria

• Find DS - find 3 tracks with -
  corresponding RICH probabilities - originating
  from common vertex - invariant mass corresponds
  to DS
• Find BS - take DS and find kaon with -
  corresponding RICH probability - originating
  from common vertex - invariant mass corresponds
  to BS
• BS flight direction must point back to a
  primary vertex

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Event samples

• 10k signal events
• 25k background

(without resonances)

• Other background sources
• still to be analyzed
• Generic B-events
• Minimum bias events

Analysis Brunel v1r4
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• Preselection with loose cuts
• Preselect well reconstructed tracks -min. p
  2.0 GeV/c -max. sp 4.5 -min. tracker hits
  25 -min. RICH probab. 0.18
• Preselect DS and BS vertices -max. ?mDs 25
  MeV/c2 -max. ?2 DS vertex 20.0 -max. ?mBs
  1.75 GeV/c2 -max. ?2 BS vertex 20.0

write to ntuple
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Overview final cuts 1. RICH cuts important for
background of ,
since B.R. is 15 times higher 2. Mass
constrained vertex cuts uses the Bs and Ds
masses to fit the vertex. 3. BS flight
direction cuts - Impact parameter - Angle of
flight direction
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Selection cut values
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Efficiencies as a function of K probability cut
for
and
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BS mass with and without RICH particle
identification
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Efficiencies unconstrained vs mass constrained fit
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Flight direction cut The has to point back
to the PV

• Different cuts possible
• Impact Parameter (IP)
• Angle ?
• (Impose this as a constraint in the fit)

momentum direction
?
IP
decay vertex
Primary vertex
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Efficiencies impact parameter vs angle ? cut
(Only constrained BS vertex cut applied)
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BS-decay time
Time resolution
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Acceptance curve for BS-decay times
Parametrization
Only trigger and BS flight-direction cut
applied
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BS decay times before and after trigger and cuts
selection. (decay time after includes acceptance
curve A(t))
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Summary efficiencies

• Acceptance is calculated w.r.t. MC events
  produced within polar angle of 0.4 rad
• Efficiencies still to be tuned to background

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• Summary
• Mass constrained vertex fit is slightly better
  than unconstrained.
• background can almost be cut away completely.
• Implement BS flight direction constraint in
  vertex fit.
• More background sources need to be analyzed.
• Tune selection cuts for maximal physics
  performance