We present a measurement of R_{K^{*}}, the branching fraction ratio B(B→K^{*}μ^{+}μ^{-})/B(B→K^{*}e^{+}e^{-}), for both charged and neutral B mesons. The ratio for the charged case R_{K^{*+}} is the ...first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q^{2}. The analysis is based on a data sample of 711 fb^{-1}, containing 772×10^{6} BBover ¯ events, recorded at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The obtained results are consistent with standard model expectations.
We report the first observation of the double strange baryon Ξ(1620)0 in its decay to Ξ−π+ via Ξ+c → Ξ−π+π+ decays based on a 980 fb−1 data sample collected with the Belle detector at the KEKB ...asymmetric-energy e+e− collider. The mass and width are measured to be 1610.4 ± 6.0(stat)+6.1−4.2(syst) MeV /c2 and 59.9 ± 4.8(stat)+2.8−7.1(syst) MeV, respectively. We obtain 4.0σ evidence of the Ξ(1690)0 with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S = −2
The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$ using inclusive and exclusive decays is performed with the full Belle data set at ...the $\Upsilon(4S)$ resonance, corresponding to an integrated luminosity of 711 fb^{-1}$. We analyze collision events in which one $B$ meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic $X_u$ system of the semileptonic $b \to u \ell \bar \nu_\ell$ decay. We separate exclusive $B \to \pi \, \ell\, \bar \nu_{\ell}$ decays from other inclusive $B \to X_u \, \ell\, \bar \nu_{\ell}$ and backgrounds with a two-dimensional fit, that utilizes the number of charged pions in the $X_u$ system and the four-momentum transfer $q^2$ between the $B$ and $X_u$ system. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the $B \to \pi \, \ell\, \bar \nu_{\ell}$ form factor, we determine $\left|V_{ub}^{\mathrm{excl.}} \right| = (3.78 \pm 0.23 \pm 0.16 \pm 0.14)\times 10^{-3}$ and $\left|V_{ub}^{\mathrm{incl.}} \right| = (3.88 \pm 0.20 \pm 0.31 \pm 0.09)\times 10^{-3}$, respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of $\left|V_{ub}^{\mathrm{excl.}} \right| / \left|V_{ub}^{\mathrm{incl.}} \right| = 0.97 \pm 0.12$ is compatible with unity.
First measurement of the Λc+→ pη′ decay Li, S. X.; Shen, C. P.; Adachi, I. ...
The journal of high energy physics,
03/2022, Letnik:
2022, Številka:
3
Journal Article
Recenzirano
Odprti dostop
A
bstract
We present the first measurement of the branching fraction of the singly Cabibbo-suppressed (SCS) decay
Λ
c
+
→ pη
′ with
η
′
→ ηπ
+
π
−
, using a data sample corresponding to an integrated ...luminosity of 981 fb
−
1
, collected by the Belle detector at the KEKB
e
+
e
−
asymmetric-energy collider. A significant
Λ
c
+
→ pη
′ signal is observed for the first time with a signal significance of 5.4
σ
. The relative branching fraction with respect to the normalization mode
Λ
c
+
→ pK
−
π
+
is measured to be
B
Λ
c
+
→
pη
′
B
Λ
c
+
→
pK
−
π
+
=
7.54
±
1.32
±
0.73
×
10
−
3
,
where the uncertainties are statistical and systematic, respectively. Using the world-average value of
B
Λ
c
+
→
pK
−
π
+
= (6
.
28
±
0
.
32)
×
10
−
2
, we obtain
B
Λ
c
+
→
pη
′
=
4.73
±
0.82
±
0.46
±
0.24
×
10
−
4
,
where the uncertainties are statistical, systematic, and from
B
Λ
c
+
→
pK
−
π
+
, respectively.
We report the results of a search for the rare, purely leptonic decay B−→μ−ν¯μ performed with a 711 fb−1 data sample that contains 772×106 BB¯ pairs, collected near the ϒ(4S) resonance with the ...Belle detector at the KEKB asymmetric-energy e+e− collider. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic B-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of B(B−→μ−ν¯μ)=(6.46±2.22±1.60)×10−7 or a frequentist 90% confidence level interval on the B−→μ−ν¯μ branching fraction of 2.9,10.7×10−7.
A
bstract
We report a measurement of the electric dipole moment of the
τ
lepton (
dτ
) using an 833 fb
−
1
data sample collected near the Υ(4
S
) resonance, with the Belle detector at the KEKB ...asymmetric-energy
e
+
e
−
collider. Using an optimal observable method, we obtain the real and imaginary parts of
d
τ
as Re(
d
τ
) = (
−
0
.
62
±
0
.
63)
×
10
−
17
e
cm and Im(
d
τ
) = (
−
0
.
40
±
0
.
32)
×
10
−
17
e
cm, respectively. These results are consistent with null electric dipole moment at the present level of experimental sensitivity and improve the sensitivity by about a factor of three.
A
bstract
We report a new measurement of the
e
+
e
−
→
ϒ(
nS
)
π
+
π
−
(
n
= 1
,
2
,
3) cross sections at energies from 10
.
52 to 11
.
02 GeV using data collected with the Belle detector at the KEKB ...asymmetric-energy
e
+
e
−
collider. We observe a new structure in the energy dependence of the cross sections; if described by a Breit-Wigner function its mass and width are found to be
M
=
10752.7
±
5.9
−
1.1
+
0.7
MeV
/
c
2
and
Γ
=
35.5
−
11.3
−
3.3
+
17.6
+
3.9
MeV, where the first error is statistical and the second is systematic. The global significance of the new structure including systematic uncertainty is 5.2 standard deviations. We also find evidence for the
e
+
e
−
→
ϒ (1
S
)
π
+
π
−
process at the energy 10
.
52 GeV, which is below the
B
B
¯
threshold.
A
bstract
Charged-lepton-flavor-violation is predicted in several new physics scenarios. We update the analysis of
τ
lepton decays into a light charged lepton (
ℓ
=
e
±
or
μ
±
) and a vector meson (
...V
0
=
ρ
0
,
ϕ
,
ω
,
K
*0
, or
K
¯
*0
) using 980 fb
−
1
of data collected with the Belle detector at the KEKB collider. No significant excess of such signal events is observed, and thus 90% credibility level upper limits are set on the
τ
→
ℓV
0
branching fractions in the range of (1.7–4
.
3) × 10
−
8
. These limits are improved by 30% on average from the previous results.
A
bstract
We present a search for the lepton-flavor-violating decays
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
B
¯
s
0
events in which one
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
→ ℓ
∓
τ
±
decays and set upper limits on their branching fractions at 90% confidence level as
B
(
B
s
0
→ e
∓
τ
±
)
<
14
×
10
−
4
and
B
(
B
s
0
→ μ
∓
τ
±
)
<
7
.
3
×
10
−
4
. Our result represents the first upper limit on the
B
s
0
→ e
∓
τ
±
decay rate.
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