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. Fig1a.pdf [13 KiB] HiDef png [113 KiB] Thumbnail [42 KiB] *.C file Fig1b.pdf [13 KiB] HiDef png [113 KiB] Thumbnail [43 KiB] *.C file 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. Fig2.pdf [18 KiB] HiDef png [169 KiB] Thumbnail [56 KiB] *.C file 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. Fig3a.pdf [26 KiB] HiDef png [231 KiB] Thumbnail [62 KiB] *.C file Fig3b.pdf [25 KiB] HiDef png [178 KiB] Thumbnail [51 KiB] *.C file 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. Fig4a.pdf [13 KiB] HiDef png [62 KiB] Thumbnail [15 KiB] *.C file Fig4b.pdf [13 KiB] HiDef png [61 KiB] Thumbnail [14 KiB] *.C file 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 $\Delta_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} f_0 }$. Fig5.pdf [14 KiB] HiDef png [103 KiB] Thumbnail [37 KiB] *.C file Animated gif made out of all figures. PAPER-2012-017.gif Thumbnail

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. Table_1.pdf [32 KiB] HiDef png [102 KiB] Thumbnail [14 KiB] tex code

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.