R. N. Cahn

We study initial-state radiation events, e+ e- --> gammaISR pi+ pi- J/psi, with data collected with the BABAR detector. We observe an accumulation of events near 4.26 GeV/c2 in the invariant-mass spectrum of pi+ pi- J/psi. Fits to the mass spectrum indicate that a broad resonance with a mass of about 4.26 GeV/c2 is required to describe the observed structure. The presence of additional narrow resonances cannot be excluded. The fitted width of the broad resonance is 50 to 90 MeV/c2, depending on the fit hypothesis.

We present a measurement of the cross section of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\psi}(2S)$ from threshold up to 8 GeV center-of-mass energy using events containing initial-state radiation, produced at the SLAC PEP-II ${e}^{+}{e}^{\ensuremath{-}}$ storage rings. The study is based on $298\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data recorded with the BABAR detector. A structure is observed in the cross section not far above threshold, near 4.32 GeV. We also investigate the compatibility of this structure with the $Y(4260)$ previously reported by this experiment.

We present evidence for ${D}^{0}\mathrm{\text{\ensuremath{-}}}{\overline{D}}^{0}$ mixing in ${D}^{0}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decays from $384\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of ${e}^{+}{e}^{\ensuremath{-}}$ colliding-beam data recorded near $\sqrt{s}=10.6\text{ }\text{ }\mathrm{GeV}$ with the BABAR detector at the PEP-II storage rings at the Stanford Linear Accelerator Center. We find the mixing parameters ${x}^{\ensuremath{'}2}=[\ensuremath{-}0.22\ifmmode\pm\else\textpm\fi{}0.30(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.21(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and ${y}^{\ensuremath{'}}=[9.7\ifmmode\pm\else\textpm\fi{}4.4(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}3.1(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and a correlation between them of $\ensuremath{-}0.95$. This result is inconsistent with the no-mixing hypothesis with a significance of 3.9 standard deviations. We measure ${R}_{D}$, the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates, to be $[0.303\ifmmode\pm\else\textpm\fi{}0.016(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.010(\mathrm{syst})]%$. We find no evidence for $CP$ violation.

The ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}p\overline{p}$ cross section is determined over a range of $p\overline{p}$ masses, from threshold to $4.5\text{ }\text{ }\mathrm{GeV}/{c}^{2}$, by studying the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}p\overline{p}\ensuremath{\gamma}$ process. The data set corresponds to an integrated luminosity of $232\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, collected with the BABAR detector at the PEP-II storage ring, at an ${e}^{+}{e}^{\ensuremath{-}}$ center-of-mass energy of 10.6 GeV. The mass dependence of the ratio of electric and magnetic form factors, $|{G}_{E}/{G}_{M}|$, is measured for $p\overline{p}$ masses below $3\text{ }\text{ }\mathrm{GeV}/{c}^{2}$; its value is found to be significantly larger than 1 for masses up to $2.2\text{ }\text{ }\mathrm{GeV}/{c}^{2}$. We also measure $J/\ensuremath{\psi}\ensuremath{\rightarrow}p\overline{p}$ and $\ensuremath{\psi}(2S)\ensuremath{\rightarrow}p\overline{p}$ branching fractions and set an upper limit on $Y(4260)\ensuremath{\rightarrow}p\overline{p}$ production and decay.