Measurement of the $D_s^{+}$ Lifetime

A high statistics measurement of the $D_s^{+}$ lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis of the two decay modes, $D_s^{+}\to \varphi (1020){\pi }^{+}$ and $D_s^{+}\to {\overline{K}}^{*}(892{)}^0{K}^{+}$, used for the measurement. The measured lifetime is $507.4\pm 5.5(\mathrm{stat})\pm 5.1(\mathrm{syst})\mathrm{fs}$ using $8961\pm 105$ $D_s^{+}\to \varphi (1020){\pi }^{+}$ and $4680\pm 90$ $D_s^{+}\to {\overline{K}}^{*}(892{)}^0{K}^{+}$ decays. This is a significant improvement over the present world average.

Figure 1

The $K^{+}{K}^{-}{\pi }^{+}$ invariant mass distributions for the (a) $\varphi (1020){\pi }^{+}$ and (b) ${\overline{K}}^{*}(892{)}^0{K}^{+}$ decay modes. The data is given by the points while the solid line gives the fit with the hatched region showing the fitted background level. The vertical dotted lines gives the $D_s^{+}$ signal and sideband regions.

Figure 2

The $f(t^{\prime })$ correction functions for the two decay modes and two run periods (a) $\varphi (1020)\pi$ run period $B$, (b) $\varphi (1020)\pi$ run period $A$, (c) ${\overline{K}}^{*}(892{)}^{0}K$ run period $B$, and (d) ${\overline{K}}^{*}(892{)}^{0}K$ run period $A$. Deviation from a flat line indicates the correction from a pure exponential.

Figure 3

The lifetime distribution for all decays in the data SR (points), and the fit (histogram). The shaded distribution shows the lifetime distribution of the background component in the SR. The data and fit are shown for run periods $A$ and $B$ combined in the same plot for the two decay modes (a) $\varphi (1020)\pi$ and (b) ${\overline{K}}^{*}(892{)}^{0}K$.