This paper presents a search for the rare flavor-changing neutral current process B0→K*0τ+τ- using data taken with the Belle detector at the KEKB asymmetric energy $e^+$$e^-$ collider. The analysis ...is based on the entire $\Upsilon$$(4S)$ resonance data sample of $711$ $\mathrm{fb}^{-1}$, corresponding to $772 × 10^6$$B$$\bar{B}$ pairs. In our search we fully reconstruct the companion $B$ meson produced in the process $e^+$$e^-$ → $\Upsilon$$(4S)$ → $B$$\bar{B}$ from its hadronic decay modes and look for the decay B0→K*0τ+τ- in the rest of the event. No evidence for a signal is found. We report an upper limit on the branching fraction $\mathscr{B}$(B0→K*0τ+τ-) < $3.1 × 10^{-3}$ at 90% confidence level. This is the first direct limit on $\mathscr{B}$(B0→K*0τ+τ-).
We present a search for the lepton-flavour-violating decays $B^+ \to K^+ \tau^\pm \ell^\mp$, with $\ell = (e, \mu)$, using the full data sample of $772 \times 10^6$ $B\overline{B}$ pairs recorded by ...the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We use events in which one $B$ meson is fully reconstructed in a hadronic decay mode. We find no evidence for $B^\pm \to K^\pm \tau \ell$ decays and set upper limits on their branching fractions at the 90% confidence level in the $(1$-$3) \times 10^{-5}$ range. The obtained limits are the world's best results.
Using data samples of 89.5 fb−1, 711.0 fb−1, and 121.4 fb−1 collected with the Belle detector at the KEKB asymmetric-energy e+e− collider at center-of-mass energies 10.52, 10.58, and 10.867 GeV, ...respectively, we study the exclusive reactions e+e−→γχcJ (J=0, 1, 2) and e+e−→γηc. A significant γχc1 signal is observed for the first time at s=10.58 GeV with a significance of 5.1σ including systematic uncertainties. No significant excesses for γχc0, γχc2, and γηc final states are found, and we set 90% credibility level upper limits on the Born cross sections (σB) at 10.52 GeV, 10.58 GeV, and 10.867 GeV. Together with cross sections measured by BESIII at lower center-of-mass energies, the energy dependency of σB(e+e−→γχc1) is obtained.
A
bstract
We present a search for the lepton-flavor-violating decays
$$ {B}_s^0 $$
B
s
0
→
ℓ
∓
τ
±
, where
ℓ
=
e, μ
, using the full data sample of 121 fb
−
1
collected at the Υ(5
S
) resonance with ...the Belle detector at the KEKB asymmetric-energy
e
+
e
−
collider. We use
$$ {B}_s^0{\overline{B}}_s^0 $$
B
s
0
B
¯
s
0
events in which one
$$ {B}_s^0 $$
B
s
0
meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for
$$ {B}_s^0 $$
B
s
0
→ ℓ
∓
τ
±
decays and set upper limits on their branching fractions at 90% confidence level as
$$ \mathcal{B} $$
B
(
$$ {B}_s^0 $$
B
s
0
→ e
∓
τ
±
)
<
14
×
10
−
4
and
$$ \mathcal{B} $$
B
(
$$ {B}_s^0 $$
B
s
0
→ μ
∓
τ
±
)
<
7
.
3
×
10
−
4
. Our result represents the first upper limit on the
$$ {B}_s^0 $$
B
s
0
→ e
∓
τ
±
decay rate.
PDF
