Science Bulletin 68 (2023) 583 We report a study of $\Lambda_c^+\to\Lambda h^+$ and
$\Lambda_c^+\to\Sigma^{0} h^+$ ($h\!=\!K,\,\pi$) decays based on a data sample
of 980~${\rm fb}^{-1}$ collected ...with the Belle detector at the KEKB
energy-asymmetric $e^+e^-$ collider. The first results of direct $C\!P$
asymmetry in two-body singly Cabibbo-suppressed (SCS) decays of charmed baryons
are measured, $A_{C\!P}^{\rm{dir}}(\Lambda_c^+\to\Lambda
K^+)\!=\!+0.021\pm0.026\pm0.001$ and
$A_{C\!P}^{\rm{dir}}(\Lambda_c^+\to\Sigma^0K^+)\!=\!+0.025\pm0.054\pm0.004$. We
also make the most precise measurement of the decay asymmetry parameters
($\alpha$) for the four modes of interest and search for $C\!P$ violation via
the $\alpha$-induced $C\!P$ asymmetry ($A_{C\!P}^{\alpha}$). We measure
$A_{C\!P}^{\alpha}(\Lambda_c^+\to\Lambda K^+)\!=\!{-0.023\pm0.086\pm0.071}$ and
$A_{C\!P}^{\alpha}(\Lambda_c^+\to\Sigma^0K^+)\!=\!{+0.08\pm 0.35\pm 0.14}$,
which are the first $A_{C\!P}^{\alpha}$ results for SCS decays of charmed
baryons. We search for $\Lambda$-hyperon $C\!P$ violation in
$\Lambda_c^+\to(\Lambda,\,\Sigma^0)\pi^+$ and find
$A_{C\!P}^{\alpha}(\Lambda\to p\pi^{-})\!=\!{+0.013\pm0.007\pm0.011}$. This is
the first time that hyperon $C\!P$ violation has been measured via
Cabibbo-favored charm decays. No evidence of baryon $C\!P$ violation is found.
We also obtain the most precise branching fractions for two SCS $\Lambda_c^+$
decays, $\mathcal{B}(\Lambda_c^+\to\Lambda
K^+)\!=\!(6.57\pm0.17\pm0.11\pm0.35)\times10^{-4}$ and
$\mathcal{B}(\Lambda_c^+\to\Sigma^0K^+)\!=\!(3.58\pm0.19\pm0.06\pm0.19)\times10^{-4}$.
The first uncertainties are statistical and the second systematic, while the
third uncertainties come from the uncertainties on the world average branching
fractions of $\Lambda_c^+\to(\Lambda,\,\Sigma^0)\pi^+$.
Phys. Rev. D 107, 032003 (2023) We report a study of $\Lambda_c^+ \to \Sigma^+ \pi^0$, $\Lambda_c^+ \to
\Sigma^+ \eta$, and $\Lambda_c^+ \to \Sigma^+ \eta'$ using the data sample
corresponding to an ...integrated luminosity of 980 $\rm fb^{-1}$ collected with
the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The
branching fractions relative to $\Lambda_c^+ \to \Sigma^+ \pi^0$ are measured
as: $\mathcal{B}_{\Lambda_c^+ \to \Sigma^+ \eta}/\mathcal{B}_{\Lambda_c^+ \to
\Sigma^+ \pi^0}=0.25 \pm 0.03 \pm 0.01$ and $\mathcal{B}_{\Lambda_c^+ \to
\Sigma^+ \eta'}/\mathcal{B}_{\Lambda_c^+ \to \Sigma^+ \pi^0}=0.33 \pm 0.06 \pm
0.02$. Using $\mathcal{B}_{\Lambda_c^+ \to \Sigma^+ \pi^0}=(1.25 \pm 0.10)\%$,
we obtain $\mathcal{B}_{\Lambda_c^+ \to \Sigma^+ \eta}=(3.14 \pm 0.35 \pm 0.11
\pm 0.25)\times10^{-3}$ and $\mathcal{B}_{\Lambda_c^+ \to \Sigma^+ \eta'}=(4.16
\pm 0.75 \pm 0.21 \pm 0.33)\times10^{-3}$. Here the uncertainties are
statistical, systematic, and from $\mathcal{B}_{\Lambda_c^+ \to \Sigma^+
\pi^0}$, respectively. The ratio of the branching fraction of $\Lambda_c^+ \to
\Sigma^+ \eta'$ with respect to that of $\Lambda_c^+ \to \Sigma^+ \eta$ is
measured to be $\mathcal{B}_{\Lambda_c^+ \to \Sigma^+
\eta'}/\mathcal{B}_{\Lambda_c^+ \to \Sigma^+ \eta}=1.34 \pm 0.28 \pm 0.06$. We
update the asymmetry parameter of $\Lambda_c^+ \to \Sigma^+ \pi^0$,
$\alpha_{\Sigma^+ \pi^0} = -0.48 \pm 0.02 \pm 0.02$, with a considerably
improved precision. The asymmetry parameters of $\Lambda_c^+ \to \Sigma^+ \eta$
and $\Lambda_c^+ \to \Sigma^+ \eta'$ are measured to be $\alpha_{\Sigma^+ \eta}
= -0.99 \pm 0.03 \pm 0.05$ and $\alpha_{\Sigma^+ \eta'} = -0.46 \pm 0.06 \pm
0.03$ for the first time.
We present the analysis of two-particle angular correlations using coordinate
systems defined with the conventional beam axis and the event thrust axis, and
propose the latter to be a useful ...representation for the correlation structure
interpretation in the $e^+ e^-$ collision system. The $e^+ e^-$ collisions to
hadronic final states at center-of-mass energies of $\sqrt{s} = 10.52$ GeV and
$10.58$ GeV are recorded by the Belle detector at KEKB. In this paper, results
on the first dataset are supplementary to the previous Belle publication
arXiv:2201.01694 while the latter one is the first two-particle correlation
measurement at a collision energy on the $\Upsilon(4S)$ resonance and sensitive
to its decay products. Measurements are reported as a function of the
charged-particle multiplicity. Finally, a qualitative understanding of the
correlation structure is discussed using a combination of Monte Carlo
simulations and experimental data.
Based on a data sample of 983 fb$^{-1}$ collected with the Belle detector at
the KEKB asymmetric-energy $e^+e^-$ collider, we present the study of the
heavy-flavor-conserving decay $\Xi_{c}^{0}\to ...\Lambda_{c}^{+}\pi^{-}$ with
$\Lambda_{c}^{+}$ reconstructed via its $pK^{-} \pi^{+}$ decay mode. The
branching fraction ratio $\mathcal{B}(\Xi_{c}^{0}\to
\Lambda_{c}^{+}\pi^{-})/\mathcal{B}(\Xi_{c}^{0}\to \Xi^{-}\pi^{+})$ is measured
to be $0.38 \pm 0.04 \pm 0.04$. Combing with the world average value of
$\mathcal{B}(\Xi_{c}^{0}\to \Xi^{-}\pi^{+})$, the branching fraction
$\mathcal{B}(\Xi_{c}^{0}\to \Lambda_{c}^{+}\pi^{-})$ is deduced to be $(0.54
\pm 0.05 \pm 0.05 \pm 0.12)\%$. Here, the uncertainties above are statistical,
systematic, and from $\mathcal{B}(\Xi_c^{0} \to \Xi^{-}\pi^{+})$, respectively.
Upgrading the SuperKEKB electron-positron collider with polarized electron beams opens a new program of precision physics at a center-of-mass energy of 10.58 GeV. This white paper describes the ...physics potential of this `Chiral Belle' program. It includes projections for precision measurements of \(\sin^2\theta_W\) that can be obtained from independent left-right asymmetry measurements of \(e^+e^-\) transitions to pairs of electrons, muons, taus, charm and b-quarks. The \(\sin^2\theta_W\) precision obtainable at SuperKEKB will match that of the LEP/SLC world average, but at the centre-of-mass energy of 10.58 GeV. Measurements of the couplings for muons, charm, and \(b\)-quarks will be substantially improved and the existing \(3\sigma\) discrepancy between the SLC \(A_{LR}\) and LEP \(A_{FB}^b\) measurements will be addressed. Precision measurements of neutral current universality will be more than an order of magnitude more precise than currently available. As the energy scale is well away from the \(Z^0\)-pole, the precision measurements will have sensitivity to the presence of a parity-violating dark sector gauge boson, \(Z_{\rm dark}\). The program also enables the measurement of the anomalous magnetic moment \(g-2\) form factor of the \(\tau\) to be made at an unprecedented level of precision. A precision of \(10^{-5}\) level is accessible with 40~ab\(^{-1}\) and with more data it would start to approach the \(10^{-6}\) level. This technique would provide the most precise information from the third generation about potential new physics explanations of the muon \(g-2\) \(4\sigma\) anomaly. Additional \(\tau\) and QCD physics programs enabled or enhanced with having polarized electron beams are also discussed in this White Paper. This paper includes a summary of the path forward in R&D and next steps required to implement this upgrade and access its exciting discovery potential.
Phys. Rev. D 105, 012007 (2022) We report results from a search for the decay $B_s^0\rightarrow\eta\eta$
using 121.4 fb$^{-1}$ of data collected at the $\Upsilon(5S)$ 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
$14.3\times 10^{-5}$ at $90\%$ confidence level. This result represents a
significant improvement over the previous most stringent limit.
Phys. Rev. D 105 (2022) L051101 We present a search for the decays of $B^0$ mesons into a final state
containing a $\Lambda$ baryon and missing energy. These results are obtained
from a ...$711\text{fb}^{-1}$ data sample that contains $772 \times 10^6$ $B{\kern
0.18em}\overline{\kern -0.18em B}$ pairs and was collected near the
$\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy
$e^+e^-$ collider. We use events in which one $B$ meson is fully reconstructed
in a hadronic decay mode and require the remainder of the event to consist of
only a single $\Lambda$. No evidence for these decays is found and we set
$90\%$ confidence level upper limits on the branching fractions in the range
$2.1$-$3.8\times 10^{-5}$. This measurement provides the world's most
restrictive limits, with implications for baryogenesis and dark matter
production.
Belle II Executive Summary Asner, D M; Atmacan, H; Banerjee, Sw ...
arXiv (Cornell University),
03/2022
Paper, Journal Article
Odprti dostop
Belle II is a Super \(B\) Factory experiment, expected to record 50 ab\(^{-1}\) of \(e^+e^-\) collisions at the SuperKEKB accelerator over the next decade. The large samples of \(B\) mesons, charm ...hadrons, and tau leptons produced in the clean experimental environment of \(e^+e^-\) collisions will provide the basis of a broad and unique flavor-physics program. Belle II will pursue physics beyond the Standard Model in many ways, for example: improving the precision of weak interaction parameters, particularly Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and phases, and thus more rigorously test the CKM paradigm, measuring lepton-flavor-violating parameters, and performing unique searches for missing-mass dark matter events. Many key measurements will be made with world-leading precision.
JHEP09(2021)075 We measure the branching fractions and $CP$ asymmetries for the singly
Cabibbo-suppressed decays $D^{0}\to\pi^{+}\pi^{-}\eta$, $D^{0}\to
K^{+}K^{-}\eta$, and $D^{0}\to\phi\eta$, using ...980 fb$^{-1}$ of data from the
Belle experiment at the KEKB $e^+e^-$ collider. We obtain \begin{eqnarray}
\mathcal{B}(D^{0}\to\pi^{+}\pi^{-}\eta) & = & 1.22\pm 0.02\,({\rm stat})\pm
0.02\,({\rm syst})\pm 0.03\,(\mathcal{B}_{\rm ref})\times 10^{-3}\,, \nonumber
\\ \mathcal{B}(D^{0}\to K^{+}K^{-}\eta) & = & 1.80\,^{+0.07}_{-0.06}\,({\rm
stat})\pm 0.04\,({\rm syst})\pm 0.05\,(\mathcal{B}_{\rm ref})\times 10^{-4}\,,
\nonumber \\ \mathcal{B}(D^{0}\to\phi\eta) & = & 1.84\pm 0.09\,({\rm stat})\pm
0.06\,({\rm syst})\pm 0.05\,(\mathcal{B}_{\rm ref})\times 10^{-4}\,, \nonumber
\end{eqnarray} where the third uncertainty ($\mathcal{B}_{\rm ref}$) is from
the uncertainty in the branching fraction of the reference mode $D^{0}\to
K^{-}\pi^{+}\eta$. The color-suppressed decay $D^{0}\to\phi\eta$ is observed
for the first time, with very high significance. The results for the $CP$
asymmetries are \begin{eqnarray} A_{CP}(D^{0}\to\pi^{+}\pi^{-}\eta) & = &
0.9\pm 1.2\,({\rm stat})\pm 0.5\,({\rm syst})\%\,, \nonumber \\
A_{CP}(D^{0}\to K^{+}K^{-}\eta) & = & -1.4\pm 3.3\,({\rm stat})\pm 1.1\,({\rm
syst})\%\,, \nonumber \\ A_{CP}(D^{0}\to\phi\eta)&= & -1.9\pm 4.4\,({\rm
stat})\pm 0.6\,({\rm syst})\%\,. \nonumber \end{eqnarray} The results for
$D^{0}\to\pi^{+}\pi^{-}\eta$ are a significant improvement over previous
results. The branching fraction and $A_{CP}$ results for $D^{0}\to
K^{+}K^{-}\eta$, and the $A_{CP}$ result for $D^{0}\to\phi\eta$, are the first
such measurements. No evidence for $CP$ violation is found in any of these
decays.
JHEP 06 (2021), 137 We report the first measurement of the exclusive cross sections $e^+e^-\to
B\bar{B}$, $e^+e^-\to B\bar{B}^*$, and $e^+e^-\to B^*\bar{B}^*$ in the energy
range from 10.63 GeV to ...11.02 GeV. The $B$ mesons are fully reconstructed in a
large number of hadronic final states and the three channels are identified
using a beam-constrained-mass variable. The shapes of the exclusive cross
sections show oscillatory behavior with several maxima and minima. The results
are obtained using data collected by the Belle experiment at the KEKB
asymmetric-energy $e^+e^-$ collider.
