We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ based on the analysis of semileptonic $B$ decays from a sample of $88\times {10}^6$ ${\rm Y}(4S)$ decays collected with the BABAR detector at the SLAC PEP-II $e^{+}{e}^{-}$ storage ring. Charmless semileptonic $B$ decays are selected using measurements of the electron energy and the invariant mass squared of the electron-neutrino pair. We obtain $|V_{ub}|=(3.95\pm {0.26}_{-0.42}^{+0.58}\pm 0.25)\times {10}^{-3}$, where the errors represent experimental uncertainties, heavy quark parameter uncertainties, and theoretical uncertainties, respectively.

We report two novel determinations of $|V_{ub}|$ with reduced model dependence, based on measurements of the mass distribution of the hadronic system in semileptonic $B$ decays. Events are selected by fully reconstructing the decay of one $B$ meson and identifying a charged lepton from the decay of the other $B$ meson from ${\rm Y}(4S)\to B\overline{B}$ events. In one approach, we combine the inclusive $\overline{B}\to X_u\ell \overline{\nu }$ rate, integrated up to a maximum hadronic mass $m_X<1.67\mathrm{GeV}/c^2$, with a measurement of the inclusive $B\to X_s\gamma$ photon energy spectrum. We obtain $|V_{ub}|=(4.43\pm {0.38}_{\mathrm{stat}}\pm {0.25}_{\mathrm{syst}}\pm {0.29}_{\mathrm{theo}})\times {10}^{-3}$. In another approach we measure the total $\overline{B}\to X_u\ell \overline{\nu }$ rate over the full phase space and find $|V_{ub}|=(3.84\pm {0.70}_{\mathrm{stat}}\pm {0.30}_{\mathrm{syst}}\pm {0.10}_{\mathrm{theo}})\times {10}^{-3}$.

To predict future performance, coaches rely on their previous experiences with a relatively small number of adolescent competitive swimmers to estimate the rate of improvement. The purpose of this study is to quantify the annual change in competition performance as backstroke swimmers mature. Data from 2006 to 2017 provided 9,956 swimming years of accumulated data which was used to estimate the rate of improvement of male and female backstroke swimmers as they aged from 8 to 18 years. Swimming performance improved rapidly between 8 and 13 years, and improvements diminished as swimmers approached their performance potential around 18 years old. These results provide accurate age-based progression data for adolescent backstroke swimmers, providing baseline performance prediction for coaches to predict future performance as swimmers mature, and providing a measure against which potential improvements from novel coaching and training methods can be objectively evaluated.