Results on charged charmoniumlike states observed in B-meson decays at Belle are reviewed. The review also includes the results on these states from other experiments (BABAR and LHCb).
We perform a full amplitude analysis of the process e+e−→J/ψDD¯, where D refers to either D0 or D+. A new charmoniumlike state X*(3860) that decays to DD¯ is observed with a significance of 6.5σ. Its ...mass is (3862−32+26 −13+40) MeV/c2, and its width is (201−67+154 −82+88) MeV. The JPC=0++ hypothesis is favored over the 2++ hypothesis at the level of 2.5σ. The analysis is based on the 980 fb−1 data sample collected by the Belle detector at the asymmetric-energy e+e− collider KEKB.
A search for the decays B+→hcK+ and B0 → hcKS0 is performed. Evidence for the decay B+ → hcK+ is found; its significance is 4.8σ. No evidence is found for B0 → hcKS0. The branching fraction for ...B+→hcK+ is measured to be (3.7−0.9+1.0 −0.8+0.8)×10−5; the upper limit for the B0 → hcKS0 branching fraction is 1.4×10−5 at 90% C.L. In addition, a study of the pp¯π+π− invariant mass distribution in the channel B+→(pp¯π+π−)K+ results in the first observation of the decay ηc(2S) → pp¯π+π− with 12.1σ significance. The analysis is based on the 711 fb−1 data sample collected by the Belle detector at the asymmetric-energy e+e− collider KEKB at the ϒ(4S) resonance.
SuperKEKB, the next generation B factory, has been constructed in Japan as an upgrade of KEKB. This brand new e+ e- collider is expected to deliver a very large data set for the Belle II experiment, ...which will be 50 times larger than the previous Belle sample. Both the triggered physics event rate and the background event rate will be increased by at least 10 times than the previous ones, and will create a challenging data taking environment for the Belle II detector. The software system of the Belle II experiment is designed to execute this ambitious plan. A full detector simulation library, which is a part of the Belle II software system, is created based on Geant4 and has been tested thoroughly. Recently the library has been upgraded with Geant4 version 10.1. The library is behaving as expected and it is utilized actively in producing Monte Carlo data sets for various studies. In this paper, we will explain the structure of the simulation library and the various interfaces to other packages including geometry and beam background simulation.
The experimental results on the ratios of branching fractions R(D)=B(Bover ¯→Dτ^{-}νover ¯_{τ})/B(Bover ¯→Dℓ^{-}νover ¯_{ℓ}) and R(D^{*})=B(Bover ¯→D^{*}τ^{-}νover ¯_{τ})/B(Bover ¯→D^{*}ℓ^{-}νover ...¯_{ℓ}), where ℓ denotes an electron or a muon, show a long-standing discrepancy with the standard model predictions, and might hint at a violation of lepton flavor universality. We report a new simultaneous measurement of R(D) and R(D^{*}), based on a data sample containing 772×10^{6} BBover ¯ events recorded at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. In this analysis the tag-side B meson is reconstructed in a semileptonic decay mode and the signal-side τ is reconstructed in a purely leptonic decay. The measured values are R(D)=0.307±0.037±0.016 and R(D^{*})=0.283±0.018±0.014, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the standard model predictions within 0.2, 1.1, and 0.8 standard deviations for R(D), R(D^{*}), and their combination, respectively. This work constitutes the most precise measurements of R(D) and R(D^{*}) performed to date as well as the first result for R(D) based on a semileptonic tagging method.
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.
With the full data sample of 772×106 BB¯ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay B¯→D*τ−ν¯τ is studied with the hadronic τ decays τ−→π−ντ and τ−→ρ−ντ. ...The τ polarization Pτ(D*) in two-body hadronic τ decays is measured, as well as the ratio of the branching fractions R(D*)=B(B¯→D*τ−ν¯τ)/B(B¯→D*ℓ−ν¯ℓ), where ℓ− denotes an electron or a muon. Our results, Pτ(D*)=−0.38±0.51(stat)−0.16+0.21(syst) and R(D*)=0.270±0.035(stat)−0.025+0.028(syst), are consistent with the theoretical predictions of the standard model. The polarization values of Pτ(D*)>+0.5 are excluded at the 90% confidence level.
We present a measurement of angular observables and a test of lepton flavor universality in the B→K^{*}ℓ^{+}ℓ^{-} decay, where ℓ is either e or μ. The analysis is performed on a data sample ...corresponding to an integrated luminosity of 711 fb^{-1} containing 772×10^{6} BBover ¯ pairs, collected at the ϒ(4S) resonance with the Belle detector at the asymmetric-energy e^{+}e^{-} collider KEKB. The result is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ.
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.
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