Search for the decay B s 0 → η η Nath, K. J.; Adachi, I.; Aihara, H. ...
Physical review. D,
01/2022, Volume:
105, Issue:
1
Journal Article
Peer reviewed
We report results from a search for the decay $B^0_s$ → $ηη$ using 121.4 fb-1 of data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We do ...not observe any signal and set an upper limit on the branching fraction of 14.3 x 10-5 at 90% confidence level. This result represents a significant improvement over the previous most stringent limit.
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.
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$$\bar{B}$ from its hadronic decay modes and look for the decay B0→K*0τ+τ- in the rest of the event. No evidence for a signal is found. We report an upper limit on the branching fraction $\mathscr{B}$(B0→K*0τ+τ-) < $3.1 × 10^{-3}$ at 90% confidence level. This is the first direct limit on $\mathscr{B}$(B0→K*0τ+τ-).
We study B+ → π+π0π0 using 711 fb-1 of data collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. Here we measure an inclusive branching fraction of ...(19.0 ±1.5 ±1.4)×10-6 and an inclusive CP asymmetry of (9.2 ±6.8 ±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B+ → ρ(770)+π0 branching fraction of (11.2 ± 1.1 ± 0.9 $^{+0.8}_{-1.6}$)× 10-6, where the third uncertainty is due to possible interference with B+ → ρ(1450)+π0. We present the first observation of a structure around 1 GeV/c2 in the π0π0 mass spectrum, with a significance of 6.4σ, and measure a branching fraction to be (6.9 ±0.9 ±0.6) × 10-6. We also report a measurement of local CP asymmetry in this structure.
We report branching fraction measurements of four decay modes of the $Λ$$^{c}_{+}$ baryon, each of which includes an η meson and a Λ baryon in the final state, and all of which are measured relative ...to the $Λ$$^{c}_{+}$ → pK–π+ decay mode. The results are based on a 980 fb–1 data sample collected by the Belle detector at the KEKB asymmetric-energy e+e– collider. Two decays, $Λ$$^{c}_{+}$ → ηΣ0π+ and Λ(1670)π+, are observed for the first time, while the measurements of the other decay modes, $Λ$$^{c}_{+}$ → ηΛπ+ and ηΣ(1385)+, are more precise than those made previously. We obtain B($Λ$$^{c}_{+}$ → ηΛπ+)/B($Λ$$^{c}_{+}$ → pK–π+) = 0.293 ± 0.003 ± 0.014, B($Λ$$^{c}_{+}$ → ηΣ0π+)/B($Λ$$^{c}_{+}$ → pK–π+) = 0.120 ± 0.006 ± 0.006, B($Λ$$^{c}_{+}$ → Λ(1670)π+) × B(Λ(1670) → ηΛ)/B($Λ$$^{c}_{+}$ → pK–π+) = (5.54 ± 0.29 ± 0.73) × 10–2, and B($Λ$$^{c}_{+}$ → ηΣ(1385)+)/B($Λ$$^{c}_{+}$ → pK–π+) = 0.192 ± 0.006 ± 0.016. The mass and width of the Λ(1670) are also precisely determined to be 1674.3 ± 0.8 ± 4.9 MeV/c2 and 36.1 ± 2.4 ± 4.8 MeV, respectively, where the uncertainties are statistical and systematic, respectively.
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