arXiv subjects

P. Križan

Publications and source records attributed to P. Križan.

At least 91 records · Page 5Linked to original sources

arXiv2021

Measurement of Differential Branching Fractions of Inclusive ${B \to X_u \, \ell^+\, ν_{\ell}}$ Decays

The first measurements of differential branching fractions of inclusive semileptonic ${B \to X_u \, \ell^+\, ν_{\ell}}$ decays are performed using the full Belle data set of 711 fb$^{-1}$ of integrated luminosity at the $Υ(4S)$ resonance and for $\ell = e, μ$. Differential branching fractions are reported as a function of the lepton momentum, the four-momentum-transfer squared, light-cone momenta, the hadronic mass, and the hadronic mass squared. They are obtained by subtracting the backgrounds from semileptonic ${B \to X_c \, \ell^+\, ν_{\ell}}$ decays and other processes, and corrected for resolution and acceptance effects. The measured distributions are compared to predictions from inclusive and hybrid ${B \to X_u \, \ell^+\, ν_{\ell}}$ calculations.

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arXiv2021

Search for $B^0$ meson decays into $Λ$ and missing energy with a hadronic tagging method at Belle

We present a search for the decays of $B^0$ mesons into a final state containing a $Λ$ 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 $Υ(4S)$ 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 $Λ$. 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.

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arXiv2021

Measurement of the branching fraction of $Λ_c^+ \to p ω$ decay at Belle

Using 980.6 $\rm fb^{-1}$ of data collected with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we present a measurement of the branching fraction of the singly Cabibbo-suppressed decay $Λ_c^+ \to p ω$. A clear $Λ_c^+$ signal is observed for $Λ_c^+ \to p ω$ with a statistical significance of 9.1 standard deviations, and we measure the ratio of branching fractions ${\cal B}(Λ_c^+ \to p ω)/{\cal B}(Λ_c^+ \to p K^- π^+) = (1.32 \pm 0.12 (\rm stat) \pm 0.10 (\rm syst))\times 10^{-2}$, from which we infer the branching fraction ${\cal B}(Λ_c^+ \to p ω) = (8.27 \pm 0.75 (\rm stat) \pm 0.62 (\rm syst) \pm 0.42 (\rm ref))\times 10^{-4}$. The first quoted uncertainty is statistical, the second systematic, and the third from the reference mode $Λ_c^+ \to p K^- π^+$.

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arXiv2021

Measurements of the branching fractions of the semileptonic decays $Ξ_{c}^{0} \to Ξ^{-} \ell^{+} ν_{\ell}$ and the asymmetry parameter of $Ξ_{c}^{0} \to Ξ^{-} π^{+}$

Using data samples of 89.5 and 711 fb$^{-1}$ recorded at energies of $\sqrt{s}=10.52$ and $10.58$ GeV, respectively, with the Belle detector at the KEKB $e^+e^-$ collider, we report measurements of branching fractions of semileptonic decays $Ξ_{c}^{0} \to Ξ^{-} \ell^{+} ν_{\ell}$ ($\ell=e$ or $μ$) and the $CP$-asymmetry parameter of $Ξ_{c}^{0} \to Ξ^{-} π^{+}$ decay. The branching fractions are measured to be ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} e^{+} ν_{e})=(1.31 \pm 0.04 \pm 0.07 \pm 0.38)\%$ and ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} μ^{+} ν_μ)=(1.27 \pm 0.06 \pm 0.10 \pm 0.37)\%$, and the decay parameter $α_{Ξπ}$ is measured to be $0.63 \pm 0.03 \pm 0.01$ with much improved precision compared to the current world average. The corresponding ratio ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} e^{+} ν_{e})/{\cal B}(Ξ_{c}^{0} \to Ξ^{-} μ^{+} ν_μ)$ is $1.03 \pm 0.05\pm 0.07$, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter ${\cal A}_{CP} = (α_{Ξ^{-}π^{+}} + α_{\barΞ^{+}π^{-}})/(α_{Ξ^{-}π^{+}} - α_{\barΞ^{+}π^{-}}) = 0.024 \pm 0.052 \pm 0.014$ is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the $Ξ_{c}^{0} \to Ξ^{-} π^+$ branching fraction.

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arXiv2021

Study of $e^+e^-\to Υ(\rm1S,2S)η$ and $e^+e^-\to Υ(\rm 1S)η^{\prime}$ at $\sqrt{s}=10.866$ GeV with the Belle detector

We report the first observation of the processes $e^+e^-\toΥ(\rm 1S,2S)η$ at $\sqrt{s}=10.866$~GeV with a $10.2σ$ and $16.5σ$ significance respectively. The measured Born cross sections are $σ(e^+e^- \to Υ(2S)η)=2.07 \pm 0.21 \pm 0.19$~pb, and $σ(e^+e^- \to Υ(\rm 1S)η)=0.42 \pm 0.08 \pm 0.04$~pb. We also set the upper limit on the cross section of the process $e^+e^- \to Υ(\rm 1S)η^{\prime}$ to be $σ(e^+e^- \to Υ(\rm 1S)η^{\prime})<0.035$~pb at $90\%$ CL. The results are obtained with the data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider in the energy range from $10.63$~GeV to $11.02$~GeV.

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arXiv2021

Search for the Decay $B_s^0 \rightarrow η^\prime η$

We report the results of the first search for the decay $B_s^0 \rightarrow η^\prime η$ using $121.4~\textrm{fb}^{-1}$ of data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe no significant signal and set a 90\% confidence-level upper limit of %$7.1 \times 10^{-5}$ $6.5 \times 10^{-5}$ on the branching fraction of this decay.

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arXiv2021

Measurement of the energy dependence of the $e^+e^-\to B\bar{B}$, $B\bar{B}^$ and $B^\bar{B}^*$ exclusive cross sections

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.

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arXiv2021

Search for $B_{s}^{0} \rightarrow η^{\prime} X_{s\bar{s}}$ at Belle using a semi-inclusive method

We report the first search for the penguin-dominated process $B_{s}^{0} \rightarrow η^{\prime} X_{s\bar{s}}$ using a semi-inclusive method. A 121.4 $\mathrm{fb}^{-1}$ integrated luminosity $Υ(5S)$ data set collected by the Belle experiment, at the KEKB asymmetric-energy $e^+e^-$ collider, is used. We observe no statistically significant signal and including all uncertainties, we set a 90\% confidence level upper limit on the partial branching fraction at 1.4 $\times$ 10$^{-3}$ for $M(X_{s\bar{s}})$ $\leq$ 2.4 GeV/$c^{2}$.

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arXiv2021

Search for the $η_{c2}(1D)$ in $e^+e^-\toγη_{c2}(1D)$ at $\sqrt{s}$ near 10.6 GeV at Belle

For the first time we search for the $η_{c2}(1D)$ in $e^+e^-\toγη_{c2}(1D)$ at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV with data samples of 89.5 fb$^{-1}$, 711 fb$^{-1}$, and 121.4 fb$^{-1}$, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant $η_{c2}(1D)$ signal is observed in the mass range between 3.8 and 3.88 GeV/$c^2$. The upper limit at 90\% confidence level on the product of the Born cross section for $e^+e^- \to γη_{c2}(1D)$ and branching fraction for $η_{c2}(1D)\to γh_c(1P)$ is determined to be $σ(e^+e^- \to γη_{c2}(1D)){\cal B}(η_{c2}(1D)\to γh_c(1P))$ $<$ 4.9 fb at $\sqrt{s}$ near 10.6 GeV.

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arXiv2021

Evidence for the decay $Ω_{c}^{0} \to π^+Ω(2012)^- \to π^+ (\bar{K}Ξ)^{-}$

Using a data sample of 980~fb$^{-1}$ collected with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we present evidence for the $Ω(2012)^-$ in the resonant substructure of $Ω_{c}^{0} \to π^+ (\bar{K}Ξ)^{-}$ ($(\bar{K}Ξ)^{-}$ = $K^-Ξ^0$ + $\bar{K}^0 Ξ^-$) decays. The significance of the $Ω(2012)^-$ signal is 4.2$σ$ after considering the systematic uncertainties. The ratio of the branching fraction of $Ω_{c}^{0} \to π^{+} Ω(2012)^- \to π^+ (\bar{K}Ξ)^{-}$ relative to that of $Ω_{c}^{0} \to π^{+} Ω^-$ is calculated to be 0.220 $\pm$ 0.059(stat.) $\pm$ 0.035(syst.). The individual ratios of the branching fractions of the two isospin modes are also determined, and found to be ${\cal B}(Ω_{c}^0 \to π^+ Ω(2012)^-) \times {\cal B}(Ω(2012)^- \to K^-Ξ^0)/{\cal B}(Ω_{c}^0 \to π^+ K^- Ξ^0)$ = (9.6 $\pm$ 3.2(stat.) $\pm$ 1.8(syst.))\% and ${\cal B}(Ω_{c}^0 \to π^+ Ω(2012)^-) \times {\cal B}(Ω(2012)^- \to \bar{K}^0 Ξ^-)/{\cal B}(Ω_{c}^0 \to π^+ \bar{K}^0 Ξ^-)$ = (5.5 $\pm$ 2.8(stat.) $\pm$ 0.7(syst.))\%.

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arXiv2021

Search for the dark photon in $B^0 \to A^{\prime} A^{\prime}$, $A^{\prime} \to e^+ e^-$, $μ^+ μ^-$, and $π^+ π^-$ decays at Belle

We present a search for the dark photon $A^{\prime}$ in the $B^0 \to A^{\prime} A^{\prime}$ decays, where $A^{\prime}$ subsequently decays to $e^+ e^-$, $μ^+ μ^-$, and $π^+ π^-$. The search is performed by analyzing $772 \times 10^6$ $B\overline{B}$ events collected by the Belle detector at the KEKB $e^+ e^-$ energy-asymmetric collider at the $Υ(4S)$ resonance. No signal is found in the dark photon mass range $0.01~\mathrm{GeV}/c^2 \le m_{A^{\prime}} \le 2.62~\mathrm{GeV}/c^2$, and we set upper limits of the branching fraction of $B^0 \to A^{\prime} A^{\prime}$ at the 90\% confidence level. The products of branching fractions, $\mathcal{B}(B^0 \to A^{\prime} A^{\prime}) \times \mathcal{B}(A^{\prime} \to e^+ e^-)^2$ and $\mathcal{B}(B^0 \to A^{\prime} A^{\prime}) \times \mathcal{B}(A^{\prime} \to μ^+ μ^-)^2$, have limits of the order of $10^{-8}$ depending on the $A^{\prime}$ mass. Furthermore, considering $A^{\prime}$ decay rate to each pair of charged particles, the upper limits of $\mathcal{B}(B^0 \to A^{\prime} A^{\prime})$ are of the order of $10^{-8}$-$10^{-5}$. From the upper limits of $\mathcal{B}(B^0 \to A^{\prime} A^{\prime})$, 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 $m_{h'} \simeq m_{B^0} \pm 40~\mathrm{MeV}/c^2$ and $10^{-1}$-$1$ at $m_{h'} \simeq m_{B^0} \pm 3~\mathrm{GeV}/c^2$.

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arXiv2021

Measurement of the Branching Fraction of the Decay $\boldsymbol{B^{+}\toπ^{+}π^{-}\ell^{+}ν_\ell}$ in Fully Reconstructed Events at Belle

We present an analysis of the exclusive $B^{+}\toπ^{+}π^{-}\ell^{+}ν_{\ell}$ decay, where $\ell$ represents an electron or a muon, with the assumption of charge-conjugation symmetry and lepton universality. The analysis uses the full $Υ(4S)$ data sample collected by the Belle detector, corresponding to 711 fb$^{-1}$ of integrated luminosity. We select the events by fully reconstructing one $B$ meson in hadronic decay modes, subsequently determining the properties of the other $B$ meson. We extract the signal yields using a binned maximum-likelihood fit to the missing-mass squared distribution in bins of the invariant mass of the two pions or the momentum transfer squared. We measure a total branching fraction of ${{\cal B}(B^{+}\to π^{+}π^{-}\ell^{+}ν_{\ell})= [22.7 ^{+1.9}_{-1.6} (\mathrm{stat}) \pm 3.5(\mathrm{syst}) ]\times 10^{-5}}$, where the uncertainties are statistical and systematic, respectively. This result is the first reported measurement of this decay.

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arXiv2021

Test of lepton flavor universality and search for lepton flavor violation in $B \to K \ell\ell$ decays

We present measurements of the branching fractions for the decays $B\to K μ^{+}μ^{-}$ and $B\to K e^{+}e^{-}$, and their ratio ($R_{K}$), using a data sample of 711 $fb^{-1}$ that contains $772 \times 10^{6}$ $B\bar{B}$ events. The data were collected at the $Υ(4S)$ 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 ($q^{2}$): $q^{2} \in (0.1, 4.0), (4.0, 8.12), (1.0, 6.0)$, $(10.2, 12.8)$ and ($>14.18) GeV^{2}/c^{4}$, along with the whole $q^2$ region. The $R_{K}$ value for $q^{2} \in (1.0, 6.0) GeV^{2}/c^{4}$ is $1.03^{+0.28}_{-0.24} \pm 0.01$. 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 $C\!P$-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 $q^{2}\in(1.0,6.0) GeV^{2}/c^{4}$ bin in the mode with muon final states. The measured differential branching fractions, ${d\cal B}/{dq^{2}}$, 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 $B \rightarrow Kμ^{\pm}e^{\mp}$ decays and set $90\%$ confidence-level upper limits on the branching fraction in the range of $10^{-8}$ for $B^{+} \rightarrow K^{+}μ^{\pm}e^{\mp}$, and $B^{0} \rightarrow K^{0}μ^{\pm}e^{\mp}$ modes.

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arXiv2021

Measurements of the branching fractions of $Λ_c^+ \to p η$ and $Λ_c^+ \to p π^0$ decays at Belle

We report measurements of the branching fractions of singly Cabibbo-suppressed decays $Λ_c^+ \to p η$ and $Λ_c^+ \to p π^0$ using the full Belle data sample corresponding to an integrated luminosity of 980.6 $\rm fb^{-1}$. The data were collected by the Belle detector at the KEKB $e^{+}$$e^{-}$ asymmetric-energy collider. A clear $Λ_c^+$ signal is seen in the invariant mass distribution of $p η$. The signal yield of the $Λ_c^+ \to p η$ process is $7734 \pm 263$; from this, we measure the ratio of branching fractions ${\cal B}(Λ_c^+ \to p η)/{\cal B}(Λ_c^+ \to p K^- π^+) = (2.258 \pm 0. 077(\rm stat. ) \pm 0.136(\rm syst. ))\times 10^{-2}$, from which we infer the branching fraction ${\cal B}(Λ_c^+ \to p η) = (1.42 \pm 0.05(\rm stat.) \pm 0.11(\rm syst.)) \times 10^{-3}$. In addition, no significant signal for $Λ_c^+ \to p π^0$ is found so an upper limit on the branching fraction of ${\cal B}(Λ_c^+ \to p π^0)<8.0 \times 10^{-5}$ at 90\% credibility level is set, more than three times better than the best current upper limit.

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arXiv2021

Measurement of branching fractions and $CP$ asymmetries for $D_s^{+} \rightarrow K^+ (η, π^0) $ and $D_s^{+} \rightarrow π^+ (η, π^0)$ decays at Belle

We report measurements of the branching fractions and $CP$ asymmetries for $D_s^{+} \rightarrow K^{+} η$, $D_s^{+} \rightarrow K^{+} π^0 $, and $D_s^{+} \rightarrow π^{+} η$ decays, and the branching fraction for $D_s^{+} \rightarrow π^{+} π^0$. Our results are based on a data sample corresponding to an integrated luminosity of 921 fb$^{-1}$ collected by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. Our measurements of $CP$ asymmetries in these decays are the most precise to-date; no evidence for $CP$ violation is found.

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arXiv2021

Evidence for $X(3872)\rightarrow J/ψπ^+π^-$ produced in single-tag two-photon interactions

We report the first evidence for $X(3872)$ production in two-photon interactions by tagging either the electron or the position in the final state, exploring the highly virtual photon region. The search is performed in $e^+e^- \rightarrow e^+e^-J/ψπ^+π^-$, using 825 fb$^{-1}$ of data collected by the Belle detector operated at the KEKB $e^+e^-$ collider. We observe three $X(3872)$ candidates with an expected background of $0.11\pm 0.10$ events, with a significance of 3.2$σ$. We obtain an estimated value for $\tildeΓ_{γγ}{\cal B}(X(3872)\rightarrow J/ψπ^+π^-$) assuming the $Q^2$ dependence predicted by a $c\bar{c}$ meson model, where $-Q^2$ is the invariant mass-squared of the virtual photon. No $X(3915)\rightarrow J/ψπ^+π^-$ candidates are found.

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arXiv2021

Measurement of Branching Fraction and Search for $CP$ Violation in $B\to ϕϕK$

We report the measurement of branching fractions and $CP$-violation asymmetries in $B\to ϕϕK$ decays based on a $711\,{\rm fb}^{-1}$ data sample containing $772\times 10^6$ $B\bar{B}$ events. The data were recorded at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. For $B^+ \to ϕϕK^+$, the branching fraction and $CP$-violation asymmetry measured below the $η_{c}$ threshold ($m_{ϕϕ}<2.85\,{\rm GeV}/c^2$) are $[3.43^{\,+\,0.48}_{\,-\,0.46}({\rm stat})\pm 0.22({\rm syst})] \times10^{-6}$ and $-0.02\pm0.11({\rm stat})\pm0.01({\rm syst})$, respectively. Similarly, the branching fraction obtained for $B^0 \toϕϕK^0$ below the $η_{c}$ threshold is $[3.02^{\,+\,0.75}_{\,-\,0.66} ({\rm stat})\pm \,0.20({\rm syst})]\times10^{-6}$. We also measure the $CP$-violation asymmetry for $B^+ \toϕϕK^+$ within the $η_{c}$ region ($m_{ϕϕ}\in [2.94,3.02]\,{\rm GeV}/c^2$) to be $+0.12\pm0.12({\rm stat})\pm0.01({\rm syst})$.

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arXiv2021

Search for lepton-number- and baryon-number-violating tau decays at Belle

We search for lepton-number- and baryon-number-violating decays $τ^{-}\to\overline{p}e^{+}e^{-}$, $pe^{-}e^{-}$, $\overline{p}e^{+}μ^{-}$, $\overline{p}e^{-}μ^{+}$, $\overline{p}μ^{+}μ^{-}$, and $pμ^{-}μ^{-}$ using 921 fb$^{-1}$ of data, equivalent to $(841\pm12)\times 10^6$ $τ^{+}τ^{-}$ events, recorded with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. In the absence of a signal, $90\%$ confidence-level upper limits are set on the branching fractions of these decays in the range $(1.8$-$4.0)\times 10^{-8}$. We set the world's first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels.

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