arXiv subjects

Z. Doležal

Publications and source records attributed to Z. Doležal.

At least 271 records · Page 15Linked to original sources

arXiv2017

Search for $\boldsymbol{B\to hν\barν}$ decays with semileptonic tagging at Belle

We present the results of a search for the rare decays $B\to hν\overlineν$, where $h$ stands for $K^+,\:K^0_{\mathrm{S}},\:K^{\ast +},\:K^{\ast 0},\:π^+,\:π^0,\:ρ^+$ and $ρ^{0}$. The results are obtained with $772\times10^{6}$ $B\overline{B}$ pairs collected with the Belle detector at the KEKB $e^+ e^-$ collider. We reconstruct one $B$ meson in a semileptonic decay and require a single $h$ meson but nothing else on the signal side. We observe no significant signal and set upper limits on the branching fractions. The limits set on the $B\to K^0_{\mathrm{S}}ν\overlineν$, $B^0\to K^{*0}ν\overlineν$, $B\to π^+ν\overlineν$, $B^0\toπ^0ν\overlineν$, $B^+\toρ^+ν\overlineν$, and $B^0\toρ^0ν\overlineν$ channels are the world's most stringent.

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arXiv2017

Measurement of the tau Michel parameters $\barη$ and $ξκ$ in the radiative leptonic decay $τ^- \rightarrow \ell^- ν_τ \barν_{\ell}γ$

We present a measurement of the Michel parameters of the $τ$ lepton, $\barη$ and $ξκ$, in the radiative leptonic decay $τ^- \rightarrow \ell^- ν_τ \barν_{\ell} γ$ using 711~f$\mathrm{b}^{-1}$ of collision data collected with the Belle detector at the KEKB $e^+e^-$ collider. The Michel parameters are measured in an unbinned maximum likelihood fit to the kinematic distribution of $e^+e^-\rightarrowτ^+τ^-\rightarrow (π^+π^0 \barν_τ)(\ell^-ν_τ\barν_{\ell}γ)$ $(\ell=e$ or $μ)$. The measured values of the Michel parameters are $\barη = -1.3 \pm 1.5 \pm 0.8$ and $ξκ= 0.5 \pm 0.4 \pm 0.2$, where the first error is statistical and the second is systematic. This is the first measurement of these parameters. These results are consistent with the Standard Model predictions within their uncertainties and constrain the coupling constants of the generalized weak interaction.

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arXiv2017

Search for $Λ_c^+\toϕp π^0$ and branching fraction measurement of $Λ_c^+\to K^-π^+ p π^0$

We have searched for the Cabibbo-suppressed decay $Λ_c^+\toϕpπ^0$ in $e^+e^-$ collisions using a data sample corresponding to an integrated luminosity of 915 $\rm fb^{-1}$. The data were collected by the Belle experiment at the KEKB $e^+e^-$ asymmetric-energy collider running at or near the $Υ(4S)$ and $Υ(5S)$ resonances. No significant signal is observed, and we set an upper limit on the branching fraction of $\mathcal{B}(Λ_c^+\to ϕpπ^0) <15.3\times10^{-5}$ at 90% confidence level. The contribution for nonresonant $Λ_c^+\to K^+K^- pπ^0$ decays is found to be consistent with zero and the corresponding upper limit on its branching fraction is set to be $\mathcal{B}(Λ_c^+\to K^+K^-pπ^0)_{\rm NR} <6.3\times10^{-5} $ at 90% confidence level. We also measure the branching fraction for the Cabibbo-favored decay $Λ_c^+\to K^-π^+pπ^0$; the result is $\mathcal{B}(Λ_c^+\to K^-π^+pπ^0)= (4.42\pm0.05\, (\rm stat.) \pm 0.12\, (\rm syst.) \pm 0.16\, (\mathcal{B}_{\rm Norm}))\%$, which is the most precise measurement to date. Finally, we have searched for an intermediate hidden-strangeness pentaquark decay $P^+_s\toϕp$. We see no evidence for this intermediate decay and set an upper limit on the product branching fraction of ${\cal B}(Λ_c^+\to P^+_s π^0)\times {\cal B}(P^+_s\toϕp) <8.3\times 10^{-5}$ at 90% confidence level.

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arXiv2017

Angular analysis of the $e^+ e^- \to D^{() \pm} D^{ \mp}$ process near the open charm threshold using initial-state radiation

We report a new measurement of the exclusive $e^+ e^- \to D^{(*) \pm} D^{*\mp}$ cross sections as a function of the center-of-mass energy from the $D^{(*) \pm} D^{* \mp}$ threshold through $\sqrt{s}=6.0$ GeV with initial-state radiation. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of $951$ fb$^{-1}$. The accuracy of the cross section measurement is increased by a factor of two over the first Belle study. We perform the first angular analysis of the $e^+ e^- \to D^{* \pm} D^{* \mp}$ process and decompose this exclusive cross section into three components corresponding to the $D^*$ helicities.

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arXiv2017

Study of $η$ and dipion transitions in $Υ(4S)$ decays to lower bottomonia

We study hadronic transitions between bottomonium states using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}e^{-}$ collider. We measure: ${\cal B}(Υ(4S)\toπ^+π^-Υ(1S))=(8.2\pm 0.5 {\rm(stat.)} \pm 0.4 {\rm(syst.)})\times10^{-5}$, ${\cal B}(Υ(4S)\toπ^+π^-Υ(2S))=(7.9\pm 1.0 {\rm(stat.)} \pm 0.4 {\rm(syst.)})\times10^{-5}$, and ${\cal B}(Υ(4S)\toηΥ(1S))=(1.70\pm 0.23 {\rm(stat.)} \pm 0.08 {\rm(syst.)})\times10^{-4}$. We measure the ratio of branching fractions ${\cal R} = {\cal B}(Υ(4S)\toηΥ(1S))/{\cal B}(Υ(4S)\toπ^+π^-Υ(1S)) = 2.07\pm 0.30 {\rm(stat.)} \pm 0.11 {\rm(syst.)}$. We search for the decay $Υ(1^3D_{1,2})\toηΥ(1S)$, but do not find significant evidence for such a transition. We also measure the initial state radiation production cross sections of the $Υ(2S,3S)$ resonances and we find values compatible with the expected ones. Finally, the analysis of the $Υ(4S)\toπ^+π^-Υ(1S)$ events shows indications for a resonant contribution due to the $f_0(980)$ meson.

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arXiv2017

Invariant-mass and fractional-energy dependence of inclusive production of di-hadrons in $e^+e^-$ annihilation at $\sqrt{s}=$ 10.58 GeV

The inclusive cross sections for di-hadrons of charged pions and kaons ($e^+e^- \rightarrow hhX$) in electron-positron annihilation are reported. They are obtained as a function of the total fractional energy and invariant mass for any di-hadron combination in the same hemisphere as defined by the thrust event-shape variable and its axis. Since same-hemisphere di-hadrons can be assumed to originate predominantly from the same initial parton, di-hadron fragmentation functions are probed. These di-hadron fragmentation functions are needed as an unpolarized baseline in order to quantitatively understand related spin-dependent measurements in other processes and to apply them to the extraction of quark transversity distribution functions in the nucleon. The di-hadron cross sections are obtained from a $655\,{\rm fb}^{-1}$ data sample collected at or near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.

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arXiv2017

Observation of an alternative $χ_{c0}(2P)$ candidate in $e^+ e^- \rightarrow J/ψD \bar{D}$

We perform a full amplitude analysis of the process $e^+ e^- \rightarrow J/ψD \bar{D}$, where $D$ refers to either $D^0$ or $D^+$. A new charmoniumlike state $X^*(3860)$ that decays to $D \bar{D}$ is observed with a significance of $6.5σ$. Its mass is ($3862^{+26}_{-32}{}^{+40}_{-13}$) MeV/$c^2$ and width is ($201^{+154}_{-67}{}^{+88}_{-82}$) MeV. The $J^{PC}=0^{++}$ hypothesis is favored over the $2^{++}$ hypothesis at the level of $2.5σ$. The analysis is based on the 980 $\mathrm{fb}^{-1}$ data sample collected by the Belle detector at the asymmetric-energy $e^+ e^-$ collider KEKB.

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arXiv2017

Measurement of the $τ$ lepton polarization and $R(D^)$ in the decay $\bar{B} \to D^ τ^- \barν_τ$

We report the first measurement of the $τ$ lepton polarization $P_τ(D^*)$ in the decay $\bar{B} \rightarrow D^* τ^- \barν_τ$ as well as a new measurement of the ratio of the branching fractions $R(D^{*}) = \mathcal{B}(\bar {B} \rightarrow D^* τ^- \barν_τ) / \mathcal{B}(\bar{B} \rightarrow D^* \ell^- \barν_\ell)$, where $\ell^-$ denotes an electron or a muon, and the $τ$ is reconstructed in the modes $τ^- \rightarrow π^- ν_τ$ and $τ^- \rightarrow ρ^- ν_τ$. We use the full data sample of $772 \times 10^6$ $B{\bar B}$ pairs recorded with the Belle detector at the KEKB electron-positron collider. Our results, $P_τ(D^*) = -0.38 \pm 0.51 {\rm (stat.)} ^{+0.21}_{-0.16} {\rm (syst.)}$ and $R(D^*) = 0.270 \pm 0.035{\rm (stat.)} ^{+0.028}_{-0.025}{\rm (syst.)}$, are consistent with the theoretical predictions of the Standard Model.

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arXiv2017

First measurement of $\boldsymbol{T}$-odd moments in $\boldsymbol{D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}}$ decays

We report the first measurement of the $T$-odd moments in the decay $D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}$ from a data sample corresponding to an integrated luminosity of $966\,{\rm fb}^{-1}$ collected by the Belle experiment at the KEKB asymmetric-energy $e^+ e^-$ collider. From these moments we determine the $CP$-violation-sensitive asymmetry $a_{CP}^{T\text{-odd}} = \left[-0.28 \pm 1.38 ~(\rm{stat.}) ^{+0.23}_{-0.76} ~(\rm{syst.})\right] \times 10^{-3}$, which is consistent with no $CP$ violation. In addition, we perform $a_{CP}^{T\text{-odd}}$ measurements in different regions of the $D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}$ phase space; these are also consistent with no $CP$ violation.

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arXiv2017

Precise determination of the CKM matrix element $\left| V_{cb}\right|$ with $\bar B^0 \to D^{*\,+} \, \ell^- \, \bar ν_\ell$ decays with hadronic tagging at Belle

The precise determination of the CKM matrix element $\left| V_{cb}\right|$ is important for carrying out tests of the flavour sector of the Standard Model. In this article we present a preliminary analysis of the $\bar B^0 \to D^{*\,+} \, \ell^- \, \bar ν_\ell$ decay mode and its charge conjugate, selected in events that contain a fully reconstructed $B$-meson, using 772 million $e^+ \, e^- \to Υ(4S) \to B \bar B$ events recorded by the Belle detector at KEKB. Unfolded differential decay rates of four kinematic variables fully describing the $\bar B^0 \to D^{*\,+} \, \ell^- \, \bar ν_\ell$ decay in the $B$-meson rest frame are presented. We measure the total branching fraction $\mathcal{B}( \bar B^0 \to D^{*\,+} \, \ell^- \, \bar ν_\ell ) = \left(4.95 \pm 0.11 \pm 0.22 \right) \times 10^{-2}$, where the errors are statistical and systematic respectively. The value of $\left|V_{cb} \right|$ is determined to be $\left( 37.4 \pm 1.3 \right) \times 10^{-3}$. Both results are in good agreement with current world averages.

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arXiv2017

Search for B decays to final states with the eta_c meson

We report a search for $B$ decays to selected final states with the $η_c$ meson: $B^{\pm}\to K^{\pm}η_cπ^+π^-$, $B^{\pm}\to K^{\pm}η_cω$, $B^{\pm}\to K^{\pm}η_cη$ and $B^{\pm}\to K^{\pm}η_cπ^0$. The analysis is based on $772\times 10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We set 90\% confidence level upper limits on the branching fractions of the studied $B$ decay modes, independent of intermediate resonances, in the range $(0.6-5.3)\times 10^{-4}$. We also search for molecular-state candidates in the $D^0\bar{D}^{*0}-\bar{D}^0D^{*0}$, $D^0\bar{D}^0+\bar{D}^0D^0$ and $D^{*0}\bar{D}^{*0}+\bar{D}^{*0}D^{*0}$ combinations, neutral partners of the $Z(3900)^{\pm}$ and $Z(4020)^{\pm}$, and a poorly understood state $X(3915)$ as possible intermediate states in the decay chain, and set 90\% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range $(0.6-6.9)\times 10^{-5}$.

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arXiv2017

Search for $D^{0}$ decays to invisible final states at Belle

We report the result from the first search for $D^0$ decays to invisible final states. The analysis is performed on a data sample of 924 $\rm{fb}^{-1}$ collected at and near the $Υ(4S)$ and $Υ(5S)$ resonances with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The absolute branching fraction is determined using an inclusive $D^0$ sample, obtained by fully reconstructing the rest of the particle system including the other charmed particle. No significant signal yield is observed and an upper limit of $9.4\times 10^{-5}$ is set on the branching fraction of $D^0$ to invisible final states at 90\% confidence level.

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arXiv2016

Search for a dark vector gauge boson decaying to $π^+ π^-$ using $η\rightarrow π^+π^- γ$ decays

We report a search for a dark vector gauge boson $U^\prime$ that couples to quarks in the decay chain $D^{*+} \to D^0 π^+, D^0 \to K^0_S η, η\to U^\prime γ$, $U^\prime \to π^+ π^-$. No signal is found and we set a mass-dependent limit on the baryonic fine structure constant of $10^{-3} - 10^{-2}$ in the $U^\prime$ mass range of 290 to 520 MeV/$c^2$. This analysis is based on a data sample of 976 fb$^{-1}$ collected by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider.

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arXiv2016

Observation of Transverse $Λ/\barΛ$ Hyperon Polarization in $e^+e^-$ Annihilation at Belle

We report the first observation of the polarization of $Λ/\barΛ$ hyperons transverse to its production plane in $e^+e^-$ annihilation. We observe a significant polarization that rises with the fractional energy carried by the hyperon as well as its transverse momentum. To define the production plane, we use the direction of the hyperon momentum together with either the thrust axis in the event or the momentum vector of a hadron in the opposite hemisphere. Furthermore, we investigate the contributions to the hyperon polarization from the feed-down from $Σ^0/\barΣ^0$ and $Λ_c^{\pm}$ decays. This measurement uses a dataset of 800.4fb$^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV.

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arXiv2016

Measurement of Michel Parameters ($\barη$, $ξκ$) in the radiative leptonic decay of tau at Belle

We present the first measurement of the Michel parameters $\barη$ and $ξκ$ in the radiative leptonic decay of the $τ$ lepton using 703 f$\mathrm{b}^{-1}$ of data collected with the Belle detector at the KEKB $e^+e^-$ collider. The Michel parameters are measured by an unbinned maximum likelihood fit to the kinematic information of $e^+e^-\rightarrowτ^+τ^-\rightarrow (π^+π^0 \barν)(l^-ν\barνγ)$ $(l=e$ or $μ)$. The preliminary values of the measured Michel parameters are $\barη = -2.0 \pm 1.5 \pm 0.8$ and $ξκ= 0.6 \pm 0.4 \pm 0.2$, where the first error is statistical and the second is systematic.

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arXiv2016

Measurement of $CP$ asymmetry in the $D^{0} \to K^0_S K^0_S$ decay at Belle

We report a measurement of the time-integrated $CP$ asymmetry in the neutral charm meson decay $D^0 \to K^0_S K^0_S$ using 921~fb$^{-1}$ data collected at the $Υ(4S)$ and $Υ(5S)$ resonances with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The observed asymmetry is $$ A_{CP}(D^0 \to K^0_S K^0_S) = (-0.02 \pm 1.53 \pm 0.17) \%, $$ where the first uncertainty is statistical and the second systematic. This latter uncertainty is dominated by the error of the normalisation channel. The result is consistent with Standard Model expectations and improves the uncertainty with respect to previous measurement of this quantity by more than a factor of three.

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arXiv2016

Measurements of the $Υ(10860)$ and $Υ(11020)$ resonances via $σ(e^+e^-\rightarrowΥ(n{\rm S})π^+π^-)$

We report new measurements of the total cross sections for $e^+e^-\to Υ(n{\rm S})π^+π^-$ ($n$ = 1, 2, 3) and $e^+e^-\to b\bar b$ from a high-luminosity fine scan of the region $\sqrt{s} = 10.63$-$11.05$ GeV with the Belle detector. We observe that the $Υ(n{\rm S})π^+π^-$ spectra have little or no non-resonant component and extract from them the masses and widths of $Υ(10860)$ and $Υ(11020)$ and their relative phase. We find $M_{10860}=(10891.1\pm3.2^{+0.6}_{-1.7})$ MeV/$c^2$ and $Γ_{10860}=(53.7^{+7.1}_{-5.6}\,^{+1.3}_{-5.4})$ MeV and report first measurements $M_{11020}=(10987.5^{+6.4}_{-2.5}\,^{+9.0}_{-2.1})$ MeV/$c^2$, $Γ_{11020}=(61^{+9}_{-19}\,^{+2}_{-20})$ MeV, and $ϕ_{\rm 11020}-ϕ_{\rm 10860} = (-1.0\pm0.4\,^{+1.4}_{-0.1})$ rad.

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arXiv2016

Evidence for the decay $B^{0}\to ηη$

We report a search for $B^{0}\to ηη$ with a data sample corresponding to an integrated luminosity of $698 \,{\rm fb}^{-1}$ containing $753 \times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The branching fraction is measured to be $\mathcal{B}(B^{0} \to ηη) = (7.6^{+2.7 +1.4}_{-2.3 -1.6}) \times 10^{-7}$ at the level of 3.3 standard deviations above zero, which provides the first evidence for the decay $B^{0} \to ηη$.

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