Nachweis von B 0 s -Oszillationen mit dem ATLAS Detektor am LHC B. Epp 1, V.M. Ghete 2, E. Kneringer 1, D. Kuhn 1, A. Nairz 3 1 Institut für Experimentalphysik, Universität Innsbruck 2 jetzt: Institut für Hochenergiephysik, ÖAW, Wien 3 jetzt: CERN, Genf ÖPG-Jahrestagung Wien,

2 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

3 ATLAS installation schedule

4 ATLAS cavern (Sept. 26, 2005) Barrel Toroid

5 Accuracy on |V td | is limited to ~15 % due to theoretical uncertainties. Can determine |V ts |/|V td | with ~5 % theoretical uncertainty.

6 Due to the size of the CKM matrix elements:  m s >>  m d

7 CKM Matrix

8 Data Challenge 1 software chain

9 B s 0  D s  + Fully reconstruct B s decay –  Tag B s or B s at production and decay  production  sign of lepton of decay of (non oscillating) B-hadron in opposite hemisphere (level 1 trigger  ): B –   –  B s 0  decay  sign of D-meson: B s 0  D s – _ How to know if an oscillation occurred?

10 Ideal oscillation

11 Oscillation in an experiment  m s = 14 ps –1 resolution of t is very important

12 Oscillation?  m s = 24 ps –1

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14 d = c  t,  = p/m proper time resolution

15 Oscillation signal significance ?

16 Extracting information on  m s from data How to extract the oscillation frequency  m s 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  cos (  m s t)  1 + A  cos (  m s t)

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20 A limit may be placed in regions of  m s where amplitudes of unity are excluded (at 95% C.L.).

21  m d – measurement: At each value of  m s in the interesting range an amplitude is measured, where an amplitude of unity indicates a successful observation of oscillation with that frequency.

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24 CDF:  m s – Semileptonic Channel

25 CDF:  m s – Hadronic Channel

26  m s : CDF + World Combined

27 Conclusions Clean measurement of  m s serves as input to fit B s 0  J/    determination of  s (among other parameters) Already with 10 fb –1 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