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Measurement of the $\bar{B}^0_s$ effective lifetime in the $J/\psi f_0(980)$ final state

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Abstract

The effective lifetime of the Bs meson in the decay mode Bs->J/\psi f0(980) is measured using 1.0/fb of data collected in pp collisions at sqrt(s) = 7 TeV with the LHCb detector. The result is 1.700 +/- 0.040 +/- 0.026 ps where the first uncertainty is statistical and the second systematic. As the final state is CP-odd, and CP violation in this mode is measured to be small, the lifetime measurement can be translated into a measurement of the decay width of the heavy Bs mass eigenstate, \Gamma_H = (0.588 +/- 0.014 +/- 0.009)/ps.

Figures and captions

Invariant mass distributions of selected (a) $\pi ^+\pi ^-$ and (b) $ K ^- \pi ^+ $ combinations (solid histograms) for events within $\pm20$ MeV of the respective $\overline{ B }{} ^0_ s $ and $\overline{ B }{} ^0$ mass peaks. Backgrounds (dashed histograms) are determined by fitting the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- $ ($ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^- \pi ^+ $) mass in bins of $\pi ^+\pi ^- $ ($ K ^- \pi ^+ $) mass. Regions between the arrows are used in the subsequent analysis.

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Ratio of decay time acceptances between $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0(980)$ and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} $ decays obtained from simulation. The solid (blue) line shows the result of a linear fit.

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Invariant mass distributions of selected (a) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- $ and (b) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^- \pi ^+ $ candidates. The solid (blue) curves show the total fits, the long dashed (purple) curves show the respective $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0(980)$ and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} $ signals, and the dotted (gray) curve shows the combinatorial background. In (a) the short dashed (blue-green) curve shows the $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- $ background and the dash dotted (green) curve shows the $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} $ { $ K ^-$ $\pi ^+$ } reflection. In (b) the short dashed (red) curve near 5370 MeV shows the $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^- \pi ^+ $ background.

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Decay time distributions for (a) $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0(980)$ and (b) $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} $ . In (b) the error bars are smaller than the points.

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Decay time ratio between $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0(980)$ and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} $ , and the fit for $\Delta_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0 }$.

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Tables and captions

Summary of systematic uncertainties on the $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0(980)$ effective lifetime.

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Created on 27 April 2024.