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Measurement of the $B_{s}^{0} \rightarrow J/\psi \eta$ lifetime

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Abstract

Using a data set corresponding to an integrated luminosity of $3 fb^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the $B^0_s \rightarrow J/\psi \eta$ decay mode, $\tau_{\textrm{eff}}$, is measured to be $\tau_{\textrm{eff}} = 1.479 \pm 0.034 \textrm{(stat)} \pm 0.011 \textrm{(syst)}$ ps. Assuming $CP$ conservation, $\tau_{\textrm{eff}}$ corresponds to the lifetime of the light $B_s^0$ mass eigenstate. This is the first measurement of the effective lifetime in this decay mode.

Figures and captions

Total acceptance function, $A_{\textrm{tot}}$ for 2011 data (black dashed line) and 2012 data (solid red).

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Mass and decay time distributions for the 2011 dataset (top row) and 2012 dataset (bottom row). The fit model described in the text is superimposed (red line). The partially reconstructed component is shown in solid yellow (dark grey), the combinatorial background in solid green (light grey) and the $ B ^0 $ component as open blue. The pull, i.e. the difference between the observed and fitted value divided by the uncertainty, is shown below each of the plots.

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Summary of measurements of $\tau_{\rm L}$. The yellow band corresponds to the 2015 HFAG central value and uncertainty.

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Animated gif made out of all figures.

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Tables and captions

Acceptance parameters due to the selection requirements ($A_{\textrm{sel}}$). The correlation coefficients are $\rho_{c_0 c_1} = 0.51 $, $\rho_{c_0 c_2} = 0.62 $ and $\rho_{c_1 c_2} = 0.95$.

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Values of the $\beta$ and $\gamma$ factor fitting the quadratic form. The first uncertainty is statistical and the second from the propagation of the uncertainty on the efficiency versus the distance of closest approach obtained with the $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+$ calibration sample. The correlation coefficienct between $\beta$ and $\gamma$ is 0.8.

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Parameters of the fit to $B^0_{(s)} \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta$ candidates for the 2011 and 2012 datasets. Uncertainties are statistical only.

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Systematic uncertainties on the lifetime measurement. Uncertainties less than $0.1 \mathrm{ \,fs} $ are indicated by a dash.

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Supplementary Material [file]

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Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.