Speaker
Dr
Matthew Barrett
(University of Hawai'i at Manoa)
Description
Using samples of 102 million $\Upsilon(1S)$ and 158 million $\Upsilon(2S)$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider, we study hadronic exclusive decays of these two bottomonium resonances to the three-body final states $\phi KK$, $\omega \pi\pi$ and $K^{\ast 0}(892) K^- \pi^+ + {\rm c.c.}$, as well as two-body processes including the Vector--Tensor ($\phi f_2'(1525)$, $\omega f_2(1270)$, $\rho a_2(1320)$, $K^{\ast 0}(892) \bar{K}_2^{\ast 0}(1430)+{\rm c.c.}$) and Axial-vector--Pseudoscalar ($K_1(1270)^+ K^-+{\rm c.c.}$, $K_1(1400)^+ K^- +{\rm c.c.}$, $b_1(1235)^+ \pi^-+{\rm c.c.}$) modes. Branching fractions are determined for processes with a statistical significance greater than $3\sigma$; otherwise, the upper limits on the branching fractions are set at 90% confidence level. The ratios of the branching fractions of $\Upsilon(2S)$ and $\Upsilon(1S)$ decay into the same final state are used to test the perturbative QCD prediction.
The hadronic decays of the narrow $\Upsilon (nS)$ resonances ($n={}$1, 2, or 3) produce large numbers of $u\bar{u}\$, $d\bar{d}$, and $s\bar{s}$ pairs concentrated in a limited phase-space volume, which makes them ideal for searching for multiquark states with non-zero strangeness. Here we report on high sensitivity searches for inclusive production of the predicted $S=-2$ pentaquark baryon $\Xi^{--}$ and six-quark $H$ dibaryon using the 102 million event $\Upsilon (1S)$ and 158 million event $\Upsilon (2S)$ data samples collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The $\Xi^{--}$ search concentrates on the $\Xi\rightarrow \Xi^-\pi^-$ decay mode and has a branching fraction sensitivity at the $10^{-5}$ level; the $H$-dibaryon search includes the $H\rightarrow\Xi^- p$, $\Lambda\Lambda$ and $\Lambda p\pi^-$ decay channels with branching fraction sensitivities approaching $10^{-6}$. Decay branching fractions and momentum distributions for topologically similar inclusive processes $\Upsilon(nS)\rightarrow\Xi^0(1530)X$ and $\Xi_c^0 X$ are measured for the first time.
Using samples of 102 million $\Upsilon(1S)$ and 158 million $\Upsilon(2S)$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider, we search for the first time for double charmonium decays from $\chi_{bJ}$, $\Upsilon(1S)$ and $\Upsilon(2S)$ states. No significant signal is observed in these modes and the upper limits on the decay rates are obtained at the 90% confidence level. These limits are consistent with calculations using the NRQCD factorization approach.
Using samples of 158 million $\Upsilon(2S)$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider, we study the hadronic exclusive decays of $\Upsilon(1,2S)$ to baryon-antibaryon ($p\bar{p}, \Lambda\bar{\Lambda}, \Sigma\bar{\Sigma},\Xi\bar{\Xi}$) and 0, 1, or 2 mesons ($\pi^0$, $\eta$, and $\pi^{\pm}$). Branching fractions are determined for processes with statistical significance greater than $3\sigma$; otherwise, the upper limits on the branching fractions are set at 90% confidence level. The ratios of the branching fractions of $\Upsilon(2S)$ and $\Upsilon(1S)$ decay into the same final state are used to test the perturbative QCD prediction.
The double cascade radiative transitions $\Upsilon(2S) \to \gamma\chi_{bJ}\to \gamma\gamma \Upsilon(1S)$ have been studied using a sample of 158 million $\Upsilon(2S)$ decays recorded with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. These provide the most precise measurement to date of the branching ratios ${\cal B}(\chi_{b0,1,2}(1P) \to \gamma\Upsilon(1S))$ and limits on the total widths of the $\chi_{b}$ states. Results are compared with potential models and recent NRQCD predictions.
Primary authors
Dr
Matthew Barrett
(University of Hawai'i at Manoa)
Matthew Barrett
(Brunel University)
