Nachweis von B0sOszillationen mit dem ATLAS Detektor am LHC

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Nachweis von B0s-Oszillationen mit dem ATLAS
Detektor am LHC

• ÖPG-JahrestagungWien, 28. 9. 2005

B. Epp1, V.M. Ghete2, E. Kneringer1, D. Kuhn1, A.
Nairz3 1Institut für Experimentalphysik,
Universität Innsbruck 2jetzt Institut für
Hochenergiephysik, ÖAW, Wien 3jetzt CERN, Genf
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Übersicht über den Vortrag

• Einführung
• ATLAS Detektor
• Theorie, Motivation
• Hauptteil
• Analyse
• Genauigkeit experimenteller Messgrössen
• Masse, Zerfallseigenzeit
• Monte-Carlo Programm
• Amplituden-Scan/Fit
• Sensitivität der Analyse
• Ausblick
• aktuelle Experimente
• CDF, D0

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ATLAS installation schedule
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ATLAS cavern (Sept. 26, 2005)
Barrel Toroid
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Accuracy on Vtd is limited to 15 due to
theoretical uncertainties.
Can determine Vts/Vtd with 5 theoretical
uncertainty.
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Due to the size of the CKM matrix elements Dms
gtgt Dmd
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CKM Matrix
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Data Challenge 1
software chain
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Bs0 ? Ds ?

• Fully reconstruct Bs decay

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How to know if an oscillation occurred?
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• Tag Bs or Bs at production and decay
• production
• sign of lepton of decay of (non oscillating)
  B-hadron in opposite hemisphere (level 1 trigger
  ?) B ? ? ? Bs0
• decay
• sign of D-meson Bs0 ? Ds

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Ideal oscillation
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Oscillation in an experiment
?ms 14 ps1
resolution of t is very important
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Oscillation?
?ms 24 ps1
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d c????t , ?? p/m
proper time resolution
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Oscillation signal significance
?
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Extracting information on ?ms from data

• How to extract the oscillation frequency ?ms from
  the measurements
• Max. Likelihood method (for parameter estimation)
• was found to have several disadvantages
• needs lots of MC
• sensitivity of analysis not easy to define or
  estimate
• combination of several analyses is difficult
• ?ln L w.r.t. minimum or infinity? (different
  results)
• Amplitude method
• invented by H.G. Moser from ALEPH
• 1 1?cos (?mst) ? 1 A?cos (?mst)

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A limit may be placed in regions of ?ms where
amplitudes of unityare excluded (at 95 C.L.).
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?md measurement CDF_at_Tevatron
At each value of ?ms in the interesting rangean
amplitude is measured, where an amplitude of
unity indicates a successful observation of
oscillation with that frequency.
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CDF ?ms Semileptonic Channel
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CDF ?ms Hadronic Channel
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?ms CDF World Combined
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Conclusions

• Clean measurement of ?ms serves as input to fit
  Bs0 ? J/? ?
• determination of ??s (among other parameters)
• Already with 10 fb1 Atlas is capable to achieve
  the sensitivity that is obtained by the SM-fit to
  all available data today
• The analysis is also sensitive in the SUSY regime