Measurements of the $B^+$, $B^0$, $B_s^0$ meson and $\Lambda_b^0$ baryon lifetimes

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Abstract

Measurements of $b$-hadron lifetimes are reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0fb$^{-1}$, collected by the LHCb detector at a centre-of-mass energy of $7$Tev. Using the exclusive decays $B^+\to J/\psi K^+$, $B^0\to J/\psi K^*(892)^0$, $B^0\to J/\psi K^0_{\rm S}$, $\Lambda_b^0\to J/\psi \Lambda$ and $B^0_s\to J/\psi \phi$ the average decay times in these modes are measured to be $\tau_{B^+\to J/\psi K^+}$ = $1.637 \pm$ 0.004 $\pm$ 0.003 ps, $\tau_{B^0\to J/\psi K^*(892)^0}$ = $1.524 \pm$ 0.006 $\pm$ 0.004 ps, $\tau_{B^0\to J/\psi K^0_{\rm S}}$ = $1.499 \pm$ 0.013 $\pm$ 0.005 ps, $\tau_{\Lambda_b^0\to J/\psi \Lambda}$ = $1.415 \pm$ 0.027 $\pm$ 0.006 ps and $\tau_{B^0_s\to J/\psi \phi}$ = $1.480 \pm$ 0.011 $\pm$ 0.005 ps, where the first uncertainty is statistical and the second is systematic. These represent the most precise lifetime measurements in these decay modes. In addition, ratios of these lifetimes, and the ratio of the decay-width difference, $\Delta\Gamma_d$, to the average width, $\Gamma_d$, in the $B^0$ system, $\Delta \Gamma_d/\Gamma_d = -0.044 \pm 0.025 \pm 0.011$, are reported. All quantities are found to be consistent with Standard Model expectations.

Figures and captions

 Distributions of the (left) mass and (right) decay time of $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+$ , $B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0}$ and $B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^0_{\rm\scriptscriptstyle S}$ candidates and their associated residual uncertainties (pulls). The data are shown by the black points; the total fit function by the black solid line; the signal contribution by the red dashed line and the background contribution by the blue dotted line. BuJpsi[..].pdf [185 KiB] HiDef png [270 KiB] Thumbnail [212 KiB] *.C file BdJpsi[..].pdf [180 KiB] HiDef png [262 KiB] Thumbnail [211 KiB] *.C file Bd2Jps[..].pdf [176 KiB] HiDef png [265 KiB] Thumbnail [213 KiB] *.C file Distributions of the (left) mass and (right) decay time of $B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi$ and $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda$ candidates and their associated residual uncertainties (pulls). The data are shown by the black points; the total fit function by the black solid line; the signal contribution by the red dashed line and the background contribution by the blue dotted line. BsJpsi[..].pdf [180 KiB] HiDef png [270 KiB] Thumbnail [215 KiB] *.C file Lambda[..].pdf [184 KiB] HiDef png [270 KiB] Thumbnail [224 KiB] *.C file VELO-track reconstruction efficiency for kaon tracks reconstructed using the (a) online and (b) offline algorithms as a function of the kaon $\rho$ , as defined in Eq. (3). The red solid lines show the result of an unbinned maximum likelihood fit using the parameterisation in Eq. (4) to the background subtracted data (black points). data_o[..].pdf [15 KiB] HiDef png [96 KiB] Thumbnail [86 KiB] *.C file data_o[..].pdf [15 KiB] HiDef png [95 KiB] Thumbnail [85 KiB] *.C file Combined trigger and selection efficiency, $\varepsilon_{\rm selection}(t)$, for $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+$ candidates. BuJpsi[..].pdf [14 KiB] HiDef png [74 KiB] Thumbnail [74 KiB] *.C file Animated gif made out of all figures. PAPER-2013-065.gif Thumbnail

Tables and captions

 Theoretical predictions and current world-average values [13] for $b$-hadron lifetimes and lifetime ratios. Table_1.pdf [59 KiB] HiDef png [69 KiB] Thumbnail [34 KiB] tex code Estimated event yields for the five $b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} X$ channels selected using the criteria described in Sec. 3.1 to 3.5. Table_2.pdf [58 KiB] HiDef png [137 KiB] Thumbnail [57 KiB] tex code VELO reconstruction efficiency in data for kaon tracks reconstructed with the online and offline algorithms. In both cases, the correlation coefficient between $a$ and $c$ is 0.2. Table_3.pdf [42 KiB] HiDef png [45 KiB] Thumbnail [21 KiB] tex code Statistical and systematic uncertainties (in femtoseconds) for the values of the $b$-hadron lifetimes. The total systematic uncertainty is obtained by combining the individual contributions in quadrature. Table_4.pdf [70 KiB] HiDef png [91 KiB] Thumbnail [42 KiB] tex code Statistical and systematic uncertainties (in units of $10^{-3}$) for the lifetime ratios and $\Delta\Gamma_d/\Gamma_d$. For brevity, $\tau_{ B ^0 }$ $(\tau_{\overline{B}^0})$ corresponds to the measurement of $\tau_{ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} }$ $(\tau_{\overline{B}^0\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{K}^{*0}})$. The total systematic uncertainty is obtained by combining the individual contributions in quadrature. Table_5.pdf [61 KiB] HiDef png [79 KiB] Thumbnail [36 KiB] tex code Fit results for the $B ^+$ , $B ^0$ , $B ^0_ s$ mesons and $\Lambda ^0_ b$ baryon lifetimes. The first uncertainty is statistical and the second is systematic. Table_6.pdf [72 KiB] HiDef png [44 KiB] Thumbnail [22 KiB] tex code Lifetime ratios for the $B ^+$ , $B ^0$ , $B ^0_ s$ mesons and $\Lambda ^0_ b$ baryon. The first uncertainty is statistical and the second is systematic. Table_7.pdf [71 KiB] HiDef png [57 KiB] Thumbnail [28 KiB] tex code

Created on 18 January 2020.