Nachweis von B0s-Oszillationen

mit dem ATLAS Detektor am LHC

B. Epp1, V.M. Ghete2, E. Kneringer1, D. Kuhn1, A. Nairz3

1Institut für Experimentalphysik, Universität Innsbruck2jetzt: Institut für Hochenergiephysik, ÖAW, Wien3jetzt: CERN, Genf

ÖPG-JahrestagungWien, 28. 9. 2005

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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: ms >> md

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Data Challenge 1

softw

are

chai

n

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Bs0 Ds +

Fully reconstruct Bs decay

–

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– – Bs

0

decay sign of D-meson: Bs

0 Ds–

_

How to know if an oscillation

occurred?

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Ideal oscillation

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Oscillation in an experiment

ms = 14 ps–1

resolution of t is very important

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Oscillation?

ms = 24 ps–1

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14

d = ct , = 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 + 1cos (mst) 1 + Acos (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@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 Bs

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