We propose a new algorithm for the identification of the production flavor of neutral \(D\) mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a ...reconstructed neutral \(D\) meson (signal \(D\) meson) and the electric charges of particles reconstructed in the rest of the \(e^+e^-\to c \bar{c}\) event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal \(D\) meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral \(D\) meson. We use a data sample of \(e^+e^-\) collisions, corresponding to \(362\,\mathrm{fb}^{-1}\) of integrated luminosity, collected by Belle II at center-of-mass energies near the \(\Upsilon(4S)\) mass. The effective tagging efficiency in data is \((47.91 \pm 0.07 \mathrm{(stat)} \pm 0.51 \mathrm{(syst)})\%\), independent of the neutral-\(D\)-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many \(CP\)-violation and charm-mixing measurements that so far have exclusively relied on neutral \(D\) mesons originating from \(D^{*\pm}\) decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.
We report the first measurement of the inclusive $e^+e^- \to b\bar{b} \to
D_s^{\pm}X$ and $e^+e^- \to b\bar{b} \to D^0/\bar{D}^0X$ cross sections in the
energy range from $10.63$ to $11.02$. Based on ...these results, we determine
$\sigma(e^+ e^- \to B_s^0 \bar{B}_s^0 X)$ and $\sigma(e^+ e^- \to B\bar{B}X)$
in the same energy range. We measure the fraction of $B_s^0$ events at
$\Upsilon(10860)$ to be $f_{\rm s}=(22.0^{+2.0}_{-2.1})\%$. We determine also
the ratio of the $B_s^0$ inclusive branching fractions $\mathcal{B}(B_s^0 \to
D^0/\bar{D}^0X)/\mathcal{B}(B_s^0 \to D_s^{\pm} X)=0.416 \pm 0.018 \pm 0.092$.
The results are obtained using the data collected with the Belle detector at
the KEKB asymmetric-energy $e^+e^-$ collider.
PRL 131, 111803 (2023) We report a measurement of the $C\!P$-violating parameters $A$ and $S$ in
$B^{0}\to K_{S}^{0} \pi^{0}$ decays at Belle II using a sample of $387\times
10^{6}$ $B\bar{B}$ events ...recorded in $e^{+}e^{-}$ collisions at a
center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. These
parameters are determined by fitting the proper decay-time distribution of a
sample of 415 signal events. We obtain $A = 0.04^{+0.15}_{-0.14}\pm 0.05$ and
$S = 0.75^{+0.20}_{-0.23}\pm 0.04$, where the first uncertainties are
statistical and the second are systematic.
We report a search for lepton-flavor-violating decays $\tau^- \to \ell^-
\phi$ ($\ell^- =e^-,\mu^-$) at the Belle II experiment, using a sample of
electron-positron data produced at the SuperKEKB ...collider in 2019-2021 and
corresponding to an integrated luminosity of 190 fb$^{-1}$. We use a new
untagged selection for $e^+e^- \to \tau^+\tau^-$ events, where the signal
$\tau$ is searched for as a neutrinoless final state of a single charged lepton
and a $\phi$ meson and the other $\tau$ is not reconstructed in any specific
decay mode, in contrast to previous measurements by the BaBar and Belle
experiments. We find no evidence for $\tau^- \to \ell^- \phi$ decays and obtain
upper limits on the branching fractions at 90% confidence level of 23 $\times
10^{-8}$ and 9.7$\times 10^{-8}$ for $\tau^- \rightarrow e^-\phi$ and $\tau^-
\rightarrow \mu^-\phi$, respectively
We present improved measurements of CP-violation parameters in B(0) --> phiK(0), eta(')K(0), KS(0)KS(0)KS(0) decays based on a sample of 535 x 10(6) BB pairs collected at the Upsilon(4S) resonance ...with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We obtain sin2phi1(eff)=+0.64+/-0.10(stat)+/-0.04(syst) for B(0) --> eta(')K(0), +0.50+/-0.21(stat)+/-0.06(syst) for B(0) --> phiK(0), and +0.30+/-0.32(stat)+/-0.08(syst) for B(0) --> KS(0)KS(0)KS(0) decays. We have observed CP violation in the B(0) --> eta(')K(0) decay with a significance of 5.6 standard deviations. We also perform an improved measurement of CP asymmetries in B(0) --> J/psiK(0) decays and obtain sin2phi1=+0.642+/-0.031(stat)+/-0.017(syst).
We search for the $B^0\to p\bar{\Sigma}^0\pi^-$ decay with $\bar{\Sigma}^0
\to \bar{\Lambda}\gamma$, where the $\gamma$ is not measured, using a data
sample corresponding to an integrated luminosity ...of 711 $\rm{fb^{-1}}$ which
contains 772 $\times$ $10^{6}$ $B\bar{B}$ pairs, collected around the
$\Upsilon$(4S) resonance with the Belle detector at the KEKB asymmetric-energy
$e^{+}e^{-}$ collider. We measure for the first time the $B^0\to
p\bar{\Sigma}^0\pi^-$ branching fraction to be $\mathcal{B}(B^0 \to p
\bar\Sigma^0 \pi^-) = (1.17^{+0.43}_{-0.40}(\text{stat})\pm 0.07(\text{syst}))
\times 10^{-6}$ with a significance of $3.0\sigma$. We simultaneously measure
the branching fraction for the related channel $B^{0}\to p\bar{\Lambda}\pi^{-}$
with much improved precision.
Observation of the decay B(0)-->J/psieta Adachi, I; Arinstein, K; Barberio, E ...
Physical review letters,
2007-Mar-30, 20070330, Letnik:
98, Številka:
13
Journal Article
Recenzirano
We report the first observation of B(0)-->J/psieta decay. These results are obtained from a data sample that contains 449 x10(6) BBover pairs accumulated at the Upsilon(4S) resonance with the Belle ...detector at the KEKB asymmetric-energy e(+)e(-) collider. We observe a signal with a significance of 8.1 sigma and obtain a branching fraction of (9.5+/-1.7(stat)+/-0.8(syst)) x 10(-6).
We search for $C\!P$ violation using $T$-odd correlations in five
$D_{(s)}^{+}$ and $D_{(s)}^{-}$ four-body decays. Our analysis is based on 980
$\rm fb^{-1}$ of data collected by the Belle detector ...at the KEKB
energy-asymmetric $e^+e^-$ collider. Our results for the $T$-odd
$C\!P$-violating parameter $a^{T\text{-odd}}_{C\!P}$ are:
$a^{T\text{-odd}}_{C\!P}({D^{+}\to K^{-}K^{+}\pi^{+}\pi^{0}}) = (+2.6\pm 6.6\pm
1.3 )\times10^{-3}$, $a^{T\text{-odd}}_{C\!P}({D^{+}\to
K^{+}\pi^{-}\pi^{+}\pi^{0}}) = (-1.3\pm 4.2\pm 0.1 )\times10^{-2}$,
$a^{T\text{-odd}}_{C\!P}({D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}}) = (+0.2\pm
1.5\pm 0.8 )\times10^{-3}$, $a^{T\text{-odd}}_{C\!P}({D_s^{+}\to
K^{+}\pi^{-}\pi^{+}\pi^{0}}) = (-1.1\pm 2.2\pm 0.1 )\times10^{-2}$, and
$a^{T\text{-odd}}_{C\!P}({D_s^{+}\to K^{-}K^{+}\pi^{+}\pi^{0}}) = (+2.2\pm
3.3\pm 4.3 )\times10^{-3}$, where the uncertainties are statistical and
systematic, respectively. These results are the first such measurements and are
all consistent with zero. They include the first measurement for a $D^+_s$
singly Cabibbo-suppressed decay, and the first measurement for a $D$ meson
doubly Cabibbo-suppressed decay. We also measure $a^{T\text{-odd}}_{C\!P}$ in
different subregions of phase space, where the decays are dominated by
different intermediate resonance states such as $D^+\to\phi\rho^+$,
$\bar{K}^{*0}K^{*+}$, and $\bar{K}^{*0}\rho^+$; and $D_s^+\to K^{*+}\rho^{0}$,
$K^{*0}\rho^{+}$, $\phi\rho^+$, and $\bar{K}^{*0}K^{*+}$. No evidence for
$C\!P$ violation is found.
The inclusive production cross sections of the charmed mesons D0,D+,Ds+ and D*+ have been measured in interactions of 920 GeV protons on C, Ti, and W targets with the HERA-B detector at the HERA ...storage ring. Differential cross sections as a function of transverse momentum and Feynman’s x variable are given for the central rapidity region and for transverse momenta up to pT=3.5 GeV/c. The atomic mass number dependence and the leading to non-leading particle production asymmetries are presented as well.
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