A
bstract
We present measurements of the branching fractions for the decays
B
→
Kμ
+
μ
−
and
B
→
Ke
+
e
−
, and their ratio (
R
K
), using a data sample of 711 fb
−
1
that contains 772 × 10
6
B
B
¯
...events. The data were collected at the ϒ(4
S
) resonance with the Belle detector at the KEKB asymmetric-energy
e
+
e
−
collider. The ratio
R
K
is measured in five bins of dilepton invariant-mass-squared (
q
2
):
q
2
∈ (0
.
1
,
4
.
0)
,
(4
.
00
,
8
.
12)
,
(1
.
0
,
6
.
0), (10
.
2
,
12
.
8) and (
>
14
.
18) GeV
2
/c
4
, along with the whole
q
2
region. The
R
K
value for
q
2
∈ (1
.
0
,
6
.
0) GeV
2
/c
4
is
1.03
−
0.24
+
0.28
± 0
.
01. The first and second uncertainties listed are statistical and systematic, respectively. All results for
R
K
are consistent with Standard Model predictions. We also measure
CP
-averaged isospin asymmetries in the same
q
2
bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the
q
2
∈ (1
.
0
,
6
.
0) GeV
2
/c
4
bin in the mode with muon final states. The measured differential branching fractions,
d
ℬ
/dq
2
, are consistent with theoretical predictions for charged
B
decays, while the corresponding values are below the expectations for neutral
B
decays. We have also searched for lepton-flavor-violating
B
→
Kμ
±
e
∓
decays and set 90% confidence-level upper limits on the branching fraction in the range of 10
−
8
for
B
+
→
K
+
μ
±
e
∓
, and
B
0
→
K
0
μ
±
e
∓
modes.
A
bstract
Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays
τ
±
→
ℓ
±
γ
(
ℓ
=
e, μ
) are ...predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via
τ
±
→
ℓ
±
γ
using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb
−
1
, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions,
B
(
τ
±
→
μ
±
γ
) ≤ 4
.
2 × 10
−
8
and
B
(
τ
±
→
e
±
γ
) ≤ 5
.
6 × 10
−
8
, are set at 90% confidence level.
Study of γγ→γψ(2S) at Belle Wang, X. L.; Aihara, H.; Asner, D. M. ...
Physical review. D,
06/2022, Letnik:
105, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Using 980 fb-1 of data at and around the Υ(nS)(n = 1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy e+e- collider, the two-photon process γγ → γψ(2S) is ...studied from the threshold to 4.2 GeV for the first time. Two structures are seen in the invariant mass distribution of γψ(2S): one at MR1 = 3922.4 ± 6.5 ± 2.0 MeV/c2 with a width of ΓR1 = 22 ± 17 ± 4 MeV, and another at MR2 = 4014.3 ± 4.0 ± 1.5 MeV/c2 with a width of ΓR2 = 4 ± 11 ± 6 MeV; the signals are parametrized with the incoherent sum of two Breit- Wigner functions. The first structure is consistent with the X(3915) or the χc2(3930), and the local statistical significance is determined to be 3.1σ with the systematic uncertainties included. The second matches none of the known charmonium or charmonium like states, and its global significance is determined to be 2.8σ including the look-elsewhere effect. The production rates are Γγγ B(R1 → γψ(2S)) = 9.8 ± 3.6 ± 1.2 eV assuming (JPC, |λ|) = (0++, 0) or 2.0 ± 0.7 ± 0.2 eV with (2++, 2) for the first structure and Γγγ B(R2 → γψ(2S)) = 6.2 ± 2.2 ± 0.8 eV with (0++, 0) or 1.2 ± 0.4 ± 0.2 eV with (2++, 2) for the second one. Furthermore, the first errors are statistical and the second systematic, and λ is the helicity.
Abstract We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle ϕ 3 (also known as γ) using a model-independent Dalitz plot analysis of B + → D ( K S 0 $$ {K}_S^0 $$ h + h ...− )h +, where D is either a D 0 or D ¯ $$ \overline{D} $$ 0 meson and h is either a π or K. This is the first measurement that simultaneously uses Belle and Belle II data, combining samples corresponding to integrated luminosities of 711 fb −1 and 128 fb −1, respectively. All data were accumulated from energy-asymmetric e + e − collisions at a centre-of-mass energy corresponding to the mass of the Υ(4S) resonance. We measure ϕ 3 = (78.4 ± 11.4 ± 0.5 ± 1.0)°, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the D-decay strong-phase parameters.
This work reports the first observation of azimuthal asymmetries around the thrust axis in e+e− annihilation of pairs of back-to-back charged pions in one hemisphere, and π0 and η mesons in the ...opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The π0 and η asymmetries rise with the relative momentum z of the detected hadrons as well as with the transverse momentum with respect to the thrust axis. These asymmetries are sensitive to the Collins fragmentation function H1⊥ and provide complementary information to previous measurements with charged pions and kaons in the final state. In particular, the η final states will provide additional information on the flavor structure of H1⊥. This is the first measurement of the explicit transverse-momentum dependence of the Collins fragmentation function from Belle data. It uses a dataset of 980.4 fb−1 collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV.
We search for lepton-number- and baryon-number-violating decays τ− → ¯pe+e−, pe−e−, ¯pe+μ−, ¯pe−μ+, ¯pμ+μ−, and pμ−μ− using 921 fb−1 of data, equivalent to (841 ± 12) × 106 τ+τ− events, recorded with ...the Belle detector at the KEKB asymmetric-energy e+e− collider. In the absence of a signal, 90% confidence-level upper limits are set on the branching fractions of these decays in the range (1.8 − 4.0) × 10−8. We set the world's first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels.
A
bstract
We present a search for the charged lepton-flavor-violating decays ϒ(1
S
)
→
ℓ
±
ℓ
′
∓
and radiative charged lepton-flavour-violating decays ϒ(1
S
)
→ γ
ℓ
±
ℓ
′
∓
ℓ
,
ℓ
′ =
e, μ, τ
using ...the 158 million ϒ(2
S
) sample collected by the Belle detector at the KEKB collider. This search uses ϒ(1
S
) mesons produced in ϒ(2
S
)
→ π
+
π
−
ϒ(1
S
) transitions. We do not find any significant signal, so we provide upper limits on the branching fractions at the 90% confidence level.
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.
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 the measurement of the two-photon decay width of
χ
c
2
(1
P
) in two-photon processes at the Belle experiment. We analyze the process
γγ
→
χ
c
2
(1
P
) →
J/ψγ
,
J/ψ
→
ℓ
+
ℓ
−
(
ℓ
...=
e
or
μ
) using a data sample of 971 fb
−
1
collected with the Belle detector at the KEKB
e
+
e
−
collider. In this analysis, the product of the two-photon decay width of
χ
c
2
(1
P
) and the branching fraction is determined to be
Γ
γγ
χ
c
2
1
P
B
χ
c
2
1
P
→
J
/
ψγ
B
J
/
ψ
→
ℓ
+
ℓ
−
=
14.8
±
0.3
stat
.
±
0.7
syst
.
eV, which corresponds to Γ
γγ
(
χ
c
2
(1
P
)) = 653
±
13(stat.)
±
31(syst.)
±
17(B.R.) eV, where the third uncertainty is from
B
(
χ
c
2
(1
P
)
→ J/ψγ
) and
B
(
J/ψ → ℓ
+
ℓ
−
).
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