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.
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. |
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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. |
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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). |
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Combined trigger and selection efficiency, $\varepsilon_{\rm selection}(t)$, for $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+$ candidates. |
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Animated gif made out of all figures. |
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Theoretical predictions and current world-average values [13] for $b$-hadron lifetimes and lifetime ratios. |
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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. |
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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. |
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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. |
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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 [65 KiB] Thumbnail [28 KiB] tex code |
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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. |
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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 [47 KiB] Thumbnail [22 KiB] tex code |
Created on 18 May 2024.