Orateur
Dr
Remi Louvot
(EPFL, Lausanne)
Description
Using fully reconstructed $B_{s}$ mesons, we measure the
branching fractions for the decays of $B_s \to
D_s^{(*)+}D_s^{(*)-}$ exclusively. Assuming these decay modes
saturate decays to CP-even final states, the branching fraction
determines the relative width difference between the $CP$-odd and
$CP$-even $B_s$ states.
We study the decay $B^0_s\to J/\psi \phi$, $\phi \to K^+ K^-$. In
this sample $B^0_s$ mesons are produced in three $\Upsilon(5S)$ decays:
$\Upsilon(5S) \to B^*_s\overline{B}^*_s$, $B^*_s\overline{B}_s$ and
$B_s\overline{B}_s$, where the $B^*_s$ mesons decay to $B_s \gamma$.
We determine the absolute branching fraction of the decay
$B^0_s\rightarrow J/\psi \phi$, which is an important mode for measuring
the CP violating phase $\beta_s$ in the $B_s \overline{B}_s$ mixing.
The latter is of particular interest as it is sensitive to physics
beyond the Standard Model.
We also report the first observation of $B_s^0\to J/\psi f_0(980)$ and
first evidence for $B_s^0\to J/\psi f_0(1370)$, which are CP-eigenstate
decay modes. We measure the branching fractions
$\mathcal{B}(B_s^0\to J/\psi f_0(980);f_0(980)\to\pi^+\pi^-)=(1.16^{+0.
31}_{-0.19}(\mathrm{stat.})^{+0.15}_{-0.17}(\mathrm{syst.})^{+0.26}_{-0.
18}(N_{B_s^{(*)}\bar B_s^{(*)}})) \times 10^{-4}$ with a significance of
$8.4\sigma$,
and $\mathcal{B}(B_s^0\to J/\psi f_0(1370);f_0(1370)\to\pi^+\pi^-)=(0.34
^{+0.11}_{-0.14}(\mathrm{stat.})^{+0.03}_{-0.02}(\mathrm{syst.})^{+0.08}
_{-0.05}(N_{B_s^{(*)}\bar B_s^{(*)}})) \times 10^{-4}$ with a
significance of $4.2\sigma$.
The last error listed is due to uncertainty in the number of produced
$B_s^{(*)}\bar B_s^{(*)}$ pairs.
We have also performed the first search for charmed baryonic $B_s^0$
decay, $\bar{B}_s^0\rightarrow\Lambda_c^+\pi^-\bar{\Lambda}$.
The measurement precision of the $B_s^0$ branching fraction at Belle is
limited by the poor knowledge of the $B_s^0$ production fraction,
$f_s=\sigma(B_s^{(\ast)}\bar B_s^{(\ast)})/\sigma(b\bar b)$.
We present the status of the current measurements and discuss their main
limitations. Using dilepton events, a new independent measurement of
$f_s$ is presented, together with its impact on the precision of Belle's
$B_s^0$ measurements.
We present a measurement of the CP violation parameter sin2$\phi_1$ at
the $\Upsilon$(5S) resonance using a new tagging method called the
B-$\pi$ tagging. This method in general uses a $\Upsilon$(5S) decay to
a charged B meson, a neutral B meson, and a charged pion. The neutral
B meson decays to a CP eigenstate, and the charged B meson is
reconstructed
as missing mass of the neutral B meson and the charged pion. The initial
flavor of the neutral B meson is determined by the charge of the pion at
the moment of the $\Upsilon$(5S) decay. CP violating parameters can be
derived from asymmetry of the number of BB$\pi^+$ and BB$\pi^-$ events
without measuring decay time. Since the B-$\pi$ tagging method have
different systematic errors from the analyses on the $\Upsilon$(4S)
resonance and thus complementary. In this analysis, the neutral B meson
is reconstructed as J/$\psi$K$_{\rm S}$.
All these results are based on a data sample
collected with the Belle detector at the $\Upsilon(5S)$ resonance
with an integrated luminosity of 121.4 fb$^{-1}$ at the KEKB
asymmetric-energy $e^+ e^-$ collider.
Author
Dr
Remi Louvot
(EPFL, Lausanne)
