Using 980 fb−1 of data collected with the Belle detector operating at the KEKB asymmetric-energy e+e− collider, we report a study of the electromagnetic decays of excited charmed baryons Ξc(2790) and ...Ξc(2815). A clear signal (8.6 standard deviations) is observed for ... and we measure: ... We also present evidence (3.8 standard deviations) for the similar decay of the Ξc(2790)0 and measure: ... The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the Ξc(2815)+ and Ξc(2790)+ baryons and set upper limits at the 90% confidence level of: ..., and ... Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states. (ProQuest: ... denotes formula omitted.)
We report on a search for a heavy Majorana neutrino in the decays τ^{-}→π^{-}ν_{h}, ν_{h}→π^{±}ℓ^{∓}, ℓ=e, μ. The results are obtained using the full data sample of 988 fb^{-1} collected with the ...Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider, which contains 912×10^{6} ττ pairs. We observe no significant signal and set 95% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional standard model left-handed neutrinos in the mass range 0.2-1.6 GeV/c^{2}. This is the first study of a mixed couplings of heavy neutrinos to τ leptons and light-flavor leptons.
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.
A
bstract
We measure the cross section of
e
+
e
−
→
η
c
J/ψ
at the Υ(
nS
)(
n
= 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector ...with an integrated luminosity of 955 fb
−
1
. We also search for double charmonium production in
e
+
e
−
→
η
c
J/ψ
via initial state radiation near the
η
c
J/ψ
threshold. No evident signal of the double charmonium state is found, but evidence for the
e
+
e
−
→ η
c
J/ψ
process is found with a statistical significance greater than 3
.
3
σ
near the
η
c
J/ψ
threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.
We study B^{+}→π^{+}π^{0}π^{0} using 711 fb^{-1} of data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure an inclusive branching ...fraction of (19.0±1.5±1.4)×10^{-6} and an inclusive CP asymmetry of (9.2±6.8±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B^{+}→ρ(770)^{+}π^{0} branching fraction of (11.2±1.1±0.9_{-1.6}^{+0.8})×10^{-6}, where the third uncertainty is due to possible interference with B^{+}→ρ(1450)^{+}π^{0}. We present the first observation of a structure around 1 GeV/c^{2} in the π^{0}π^{0} mass spectrum, with a significance of 6.4σ, and measure a branching fraction to be (6.9±0.9±0.6)×10^{-6}. We also report a measurement of local CP asymmetry in this structure.
We report the first observation of the decay Λ_{c}^{+}→pK^{+}π^{-} using a 980 fb^{-1} data sample collected by the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. This is the ...first observation of a doubly Cabibbo-suppressed decay of a charmed baryon. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be B(Λ_{c}^{+}→pK^{+}π^{-})/B(Λ_{c}^{+}→pK^{-}π^{+})=(2.35±0.27±0.21)×10^{-3}, where the uncertainties are statistical and systematic, respectively.
Abstract This paper reports world averages of measurements of b-hadron, c-hadron, and $$\tau $$ τ -lepton properties obtained by the Heavy Flavour Averaging Group using results available through ...September 2018. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, $$C\!P$$ C P violation parameters, parameters of semileptonic decays, and Cabibbo–Kobayashi–Maskawa matrix elements.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report the first evidence for X(3872) production in two-photon interactions by tagging either the electron or the positron in the final state, exploring the highly virtual photon region. The ...search is performed in e^{+}e^{-}→e^{+}e^{-}J/ψπ^{+}π^{-}, using 825 fb^{-1} of data collected by the Belle detector operated at the KEKB e^{+}e^{-} collider. We observe three X(3872) candidates, where the expected background is 0.11±0.10 events, with a significance of 3.2σ. We obtain an estimated value for Γover ˜_{γγ}B(X(3872)→J/ψπ^{+}π^{-}) assuming the Q^{2} dependence predicted by a ccover ¯ meson model, where -Q^{2} is the invariant mass squared of the virtual photon. No X(3915)→J/ψπ^{+}π^{-} candidates are found.
A
bstract
We present a search for the dark photon
A
′ in the
B
0
→
A
′
A
′ decays, where
A
′ subsequently decays to
e
+
e
−
,
μ
+
μ
−
, and
π
+
π
−
. The search is performed by analyzing 772 × 10
6
B
...B
¯
events collected by the Belle detector at the KEKB
e
+
e
−
energy-asymmetric collider at the ϒ(4
S
) resonance. No signal is found in the dark photon mass range 0
.
01 GeV
/c
2
≤
m
A
′
≤ 2
.
62 GeV
/c
2
, and we set upper limits of the branching fraction of
B
0
→
A
′
A
′ at the 90% confidence level. The products of branching fractions,
ℬ
B
0
→
A
′
A
′
×
ℬ
A
′
→
e
+
e
−
2
and
ℬ
B
0
→
A
′
A
′
×
ℬ
A
′
→
μ
+
μ
−
2
, have limits of the order of 10
−
8
depending on the
A
′ mass. Furthermore, considering
A
′ decay rate to each pair of charged particles, the upper limits of
ℬ
B
0
→
A
′
A
′
are of the order of 10
−
8
–10
−
5
. From the upper limits of
ℬ
B
0
→
A
′
A
′
, we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10
−
2
–10
−
1
at
m
h
′
≃
m
B
0
± 40 MeV
/c
2
and 10
−
1
–1 at
m
h
′
≃
m
B
0
± 3 GeV
/c
2
.
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