Bs ? Ds

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Bs ? DsK
????????

• Besma Mcharek
• Jeroen van Tilburg

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Introduction

• Understanding the decay of the B0s-meson and its
  antiparticle into DsK.
• This decay channel allows an observation of CP
  violation.
• Selection of the B0s?DsK events.
• Plans

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Decay of the Bso -meson to a Ds and a K particle

• Neutral B-mesons mix and oscillate and decay
  after a certain time
• After the B-meson is created it decays in a final
  state f or anti (f).
• This gives Bs ? f
• Bs ?anti(f)
• anti (Bs)? f
• anti (Bs) ? anti (f)

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Topology
p
K
K
Ds
Bs
p
p
K
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Bs ? Ds-K
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Bs ? DsK-
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Bs ? DsK-
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Bs ? Ds-K
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CP violation in the interference between decay
and mixing

• In our case there is an interference between
  mixing and decay amplitudes
• Only one diagram contributes to each of the decay
  amplitudes (no penguin pollution)
• The two parameters, ? and anti(?) defined as

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CP violation in the interference between decay
and mixing

• Because of the interference term a phase arises
  in the expression of the ?s ?DsK
• Which gives us

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Bs?DsK event selection preselection cuts

• Track selection momentum criterium particles
  originating from the Bs particle have relatively
  high momentum p and have a Sp above 2GeV )
• Ds vertex selection constrained mass fit,
  reconstructed Ds mass approximately 3s close to
  1969MeV and a good significance for the impact
  parameter for the track reconstructions of the
  products (all particles have SIP gt1)
• Bs vertex selection large bachelor-Ds opening
  angle and the reconstructed Bs should point back
  to the primary vertex, SIP gt4 for the bachelor
  and SIP lt4 for the Bs
• Cuts applied also as for the selection of
  background.

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Bs?DsK event selection preselection cuts

• All products p
• Ds products pt
• Ds products Spt
• SIP(Ds products)
• SIP(Ds)
• Ds mass window
• SIP(Bs product)
• SIP(Ds)
• Bs mass window
• Cos(?)
• Bachelor K ?LKp
• Bachelor K ?Lke

• 2 GeV
• 200 MeV
• 0
• 0
• 1
• 50MeV
• 1
• 20
• 500MeV
• 0.998
• -5
• -5

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Bs?DsK event selectionresults

• Bs?DsK signals and background (Bs?Dsp and
  bbinclusive)
• Number of events 5000.
• Bs?DsK selected 477
• Bs?Ds p selected 143
• bbinclusive selected 78 (oops we did it
  again!!)

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Bs?DsK event selection other interesting cuts

• Cosine(?)
• ?2 of the Bs vertex fit.
• ?2 of the Ds vertex fit (mass constrained fit).

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Further cuts
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Efficiencies e in Bs?DsK events selection
events 10000 events
Nprod Factors () contributing to e Factors () contributing to e Factors () contributing to e Factors () contributing to e Factors () contributing to e Nphys B/S
290 (2.00.8)M edet erec/det esel/rec etrg/sel edet (5.42.2)K ?? 0.1110.056
290 (2.00.8)M 5,1 5.4 88,1 82.0 22 20.6 ?? 29.5 ? 0.269 (5.42.2)K ?? 0.1110.056
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Plans