Searcharxiv⌕ Search

arXiv subjects

E. Barberio

Publications and source records attributed to E. Barberio.

At least 73 records · Page 4Linked to original sources

Studies of charmed strange baryons in the $ΛD$ final state at Belle

We report the discovery of $Ξ_{c}(3055)^{0}$, observed by its decay into the final state $ΛD^{0}$, and present the first observation and evidence of the decays of $Ξ_c(3055)^{+}$ and $Ξ_c(3080)^{+}$ into $ΛD^{+}$. We also perform a combined analysis of the $ΛD^{+}$ with the $Σ_{c}^{++}K^{-}$ and $Σ_{c}^{\ast ++}K^{-}$ decay modes to measure the ratios of branching fractions, masses and widths with improved accuracy. We measure the ratios of branching fractions ${\cal B}(Ξ_{c}(3055)^{+} \to ΛD^{+})/{\cal B}(Ξ_{c}(3055)^{+} \to Σ_{c}^{++}K^{-})=5.09\pm1.01\pm0.76$, ${\cal B}(Ξ_{c}(3080)^{+} \to ΛD^{+})/{\cal B}(Ξ_{c}(3080)^{+} \to Σ_{c}^{++}K^{-})=1.29\pm0.30\pm0.15$, and ${\cal B}(Ξ_{c}(3080)^{+} \to Σ_{c}^{\ast ++}K^{-})/{\cal B}(Ξ_{c}(3080)^{+} \to Σ_{c}^{++}K^{-})=1.07\pm0.27\pm0.01$, where the uncertainties are statistical and systematic. The analysis is performed using a 980 fb$^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider.

hep-ex↗

Search for a massive invisible particle $X^0$ in $B^{+}\to e^{+}X^{0}$ and $B^{+}\to μ^{+}X^{0}$ decays

We present a search for a non-Standard-Model invisible particle $X^0$ in the mass range $0.1\textrm{-}1.8 \,{\rm GeV}/{c^2}$ in $B^{+}\to e^{+} X^{0}$ and $B^{+}\to μ^{+} X^{0}$ decays. The results are obtained from a $711~{\rm fb}^{-1}$ data sample that corresponds to $772 \times 10^{6} B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. One $B$ meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner $B$ meson. We find no evidence of a signal and set upper limits on the order of $10^{-6}$.

hep-ex↗

Search for $XYZ$ states in $Υ(1S)$ inclusive decays

The branching fractions of the $Υ(1S)$ inclusive decays into final states with a $J/ψ$ or a $ψ(2S)$ are measured with improved precision to be $\BR(Υ(1S)\to J/ψ+ {\rm anything})=(5.25\pm 0.13(\mathrm{stat.})\pm 0.25(\mathrm{syst.}))\times 10^{-4}$ and $\BR(Υ(1S)\to ψ(2S) + {\rm anything})=(1.23\pm 0.17(\mathrm{stat.})\pm 0.11(\mathrm{syst.}))\times 10^{-4}$. The first search for $Υ(1S)$ decays into $XYZ$ states that decay into a $J/ψ$ or a $ψ(2S)$ plus one or two charged tracks yields no significant signals for $XYZ$ states in any of the examined decay modes, and upper limits on their production rates in $Υ(1S)$ inclusive decays are determined.

hep-ex↗

Observation of the decay $B_s^0\rightarrow K^0\overline{K}^0$

We measure the decay $B_s^0\rightarrow K^0\overline{K}^0$ using data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. The data sample used corresponds to an integrated luminosity of 121.4 ${\rm fb^{-1}}$. We measure a branching fraction $\mathcal{B}(B_s^0\rightarrow K^0\overline{K}^0) = [19.6\,^{+5.8}_{-5.1}({\rm stat.})\,\pm1.0({\rm sys.})\,\pm 2.0(N^{}_{B_s^0\overline{B}_s^0})]\times 10^{-6}$ with a significance of 5.1 standard deviations. This measurement constitutes the first observation of this decay.

hep-ex↗

Angular analysis of $B^0 \to K^\ast(892)^0 \ell^+ \ell^-$

We present a measurement of angular observables, $P_4'$, $P_5'$, $P_6'$, $P_8'$, in the decay $B^0 \to K^\ast(892)^0 \ell^+ \ell^-$, where $\ell^+\ell^-$ is either $e^+e^-$ or $μ^+μ^-$. The analysis is performed on a data sample corresponding to an integrated luminosity of $711~\mathrm{fb}^{-1}$ containing $772\times 10^{6}$ $B\bar B$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the asymmetric-energy $e^+e^-$ collider KEKB. Four angular observables, $P_{4,5,6,8}'$ are extracted in five bins of the invariant mass squared of the lepton system, $q^2$. We compare our results for $P_{4,5,6,8}'$ with Standard Model predictions including the $q^2$ region in which the LHCb collaboration reported the so-called $P_5'$ anomaly.

hep-ex↗

First observation of $γγ\to p \bar{p} K^+ K^-$ and search for exotic baryons in $pK$ systems

The process $γγ\to p \bar{p} K^+ K^-$ and its intermediate processes are measured for the first time using a 980~fb$^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The production of $p \bar{p} K^+ K^-$ and a $Λ(1520)^0~(\barΛ(1520)^0)$ signal in the $pK^-$~($\bar{p} K^+$) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540~MeV/$c^2$, denoted as $Θ(1540)^0$~($\barΘ~(1540)^0$) or $Θ(1540)^{++}$~($Θ(1540)^{--}$), is seen in the $p K^-$~($\bar{p}K^+$) or $pK^+$~($\bar{p} K^-$) invariant mass spectra. Cross sections for $γγ\to p \bar{p} K^+ K^-$, $Λ(1520)^0 \bar{p} K^+ +c.c.$ and the products $σ(γγ\to Θ(1540)^0 \bar{p} K^+ +c.c.)\BR(Θ(1540)^0 \to p K^{-})$ and $σ(γγ\to Θ(1540)^{++} \bar{p} K^- +c.c.)\BR(Θ(1540)^{++}\to p K^{+})$ are measured. We also determine upper limits on the products of the $χ_{c0}$ and $χ_{c2}$ two-photon decay widths and their branching fractions to $p \bar{p} K^+ K^-$ at the 90\% credibility level.

hep-ex↗

Inclusive and exclusive measurements of $B$ decays to $χ_{c1}$ and $χ_{c2}$ at Belle

We report inclusive and exclusive measurements for $χ_{c1}$ and $χ_{c2}$ production in $B$ decays. We measure $\mathcal{B}(B \to χ_{c1} X)$= $(3.03 \pm 0.05(\mbox{stat}) \pm 0.24(\mbox{syst})) \times 10^{-3}$ and $\mathcal{B}(B \to χ_{c2} X)$= $(0.70 \pm 0.06(\mbox{stat}) \pm 0.10(\mbox{syst})) \times 10^{-3}$. For the first time, $χ_{c2}$ production in exclusive $B$ decays in the modes $B^0 \to χ_{c2}π^- K^+$ and $B^+ \to χ_{c2} π^+ π^- K^+$ has been observed, along with first evidence for the $B^+ \to χ_{c2} π^+ K_S^0$ decay mode. For $χ_{c1}$ production, we report the first observation in the $B^+ \to χ_{c1} π^+ π^- K^+$, $B^0 \to χ_{c1} π^+ π^- K_S^0$ and $B^0 \to χ_{c1} π^0 π^- K^+$ decay modes. Using these decay modes, we observe a difference in the production mechanism of $χ_{c2}$ in comparison to $χ_{c1}$ in $B$ decays. In addition, we report searches for $X(3872)$ and $χ_{c1}(2P)$ in the $B^+ \to (χ_{c1} π^+ π^-) K^+$ decay mode. The reported results use $772 \times 10^{6}$ $B\overline{B}$ events collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.

hep-ex↗

Measurement of the branching ratio of $\bar{B}^0 \rightarrow D^{*+} τ^- \barν_τ$ relative to $\bar{B}^0 \rightarrow D^{*+} \ell^- \barν_{\ell}$ decays with a semileptonic tagging method

We report a measurement of ratio ${\cal R}(D^*) = {\cal B}(\bar{B}^0 \rightarrow D^{*+} τ^- \barν_τ)/{\cal B}(\bar{B}^0 \rightarrow D^{*+} \ell^- \barν_{\ell})$, where $\ell$ denotes an electron or a muon. The results are based on a data sample containing $772\times10^6$ $B\bar{B}$ pairs recorded at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. We select a sample of $B^0 \bar{B}^0$ pairs by reconstructing both $B$ mesons in semileptonic decays to $D^{*\mp} \ell^{\pm}$. We measure ${\cal R}(D^*)= 0.302 \pm 0.030({\rm stat)} \pm 0.011({\rm syst)}$, which is within $1.6 σ$ of the Standard Model theoretical expectation, where $σ$ is the standard deviation including systematic uncertainties.

hep-ex↗

First model-independent Dalitz analysis of $B^0 \to DK^{*0}$, $D\to K_S^0π^+π^-$ decay

We report a measurement of the amplitude ratio $r_S$ of $B^0 \to D^0K^{*0}$ and $B^0 \to \bar{D^0}K^{*0}$ decays with a Dalitz analysis of $D\to K_S^0π^+π^-$ decays, for the first time using a model-independent method. We set an upper limit $r_S < 0.87$ at the 68\% confidence level, using the full data sample of $772\times10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. This result is obtained from observables $x_- = +0.4 ^{+1.0 +0.0}_{-0.6 -0.1} \pm0.0$, $y_- = -0.6 ^{+0.8 +0.1}_{-1.0 -0.0} \pm0.1$, $x_+ = +0.1 ^{+0.7 +0.0}_{-0.4 -0.1} \pm0.1$ and $y_+ = +0.3 ^{+0.5 +0.0}_{-0.8 -0.1} \pm0.1$, where $x_\pm = r_S \cos(δ_S \pm ϕ_3)$, $y_\pm = r_S \sin(δ_S \pm ϕ_3)$ and $ϕ_3~(δ_S)$ is the weak (strong) phase difference between $B^0 \to D^0K^{*0}$ and $B^0 \to \bar{D^0}K^{*0}$.

hep-ex↗

Study of $π^0$ pair production in single-tag two-photon collisions

We report a measurement of the differential cross section of $π^0$ pair production in single-tag two-photon collisions, $γ^* γ\to π^0 π^0$, in $e^+ e^-$ scattering. The cross section is measured for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and $|\cos θ^*|$ < 1.0 for the total energy and pion scattering angle, respectively, in the $γ^* γ$ center-of-mass system. The results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The transition form factor of the $f_0(980)$ and that of the $f_2(1270)$ with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.

hep-ex↗

Search for $B^0 \to π^- τ^+ ν_τ$ with hadronic tagging at Belle

We search for the process $B^0 \to π^- τ^+ ν_τ$ using the full Belle data set of $711\,{\rm fb}^{-1}$, corresponding to $772 \times 10^6 B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We reconstruct one $B$ meson in a hadronic decay and search for the $B^0 \to π^- τ^+ ν_τ$ process in the remainder of the event. No significant signal is observed and an upper limit of $\mathcal{B}(B^0 \to π^- τ^+ ν_τ) < 2.5 \times 10^{-4}$ is obtained at the $90\%$ confidence level.

hep-ex↗

Measurement of the decay $B\to D\ellν_\ell$ in fully reconstructed events and determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$

We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ using the decay $B\to D\ellν_\ell$ ($\ell=e,μ$) based on 711 fb$^{-1}$ of $e^+e^-\to Υ(4S)$ data recorded by the Belle detector and containing $772 \times 10^6$ $B\bar{B}$ pairs. One $B$ meson in the event is fully reconstructed in a hadronic decay mode while the other, on the signal side, is partially reconstructed from a charged lepton and either a $D^+$ or $D^0$ meson in a total of 23 hadronic decay modes. The isospin-averaged branching fraction of the decay $B\to D\ellν_\ell$ is found to be $\mathcal{B}(B^0 \to D^- \ell^+ ν_{\ell})=(2.31\pm 0.03(\mathrm{stat})\pm 0.11(\mathrm{syst}))\%$. Analyzing the differential decay rate as a function of the hadronic recoil with the parameterization of Caprini, Lelouch and Neubert and using the form-factor prediction $\mathcal{G}(1)=1.0541\pm 0.0083$ calculated by FNAL/MILC, we obtain $η_\mathrm{EW}|V_{cb}|=(40.12\pm 1.34)\times 10^{-3}$, where $η_\mathrm{EW}$ is the electroweak correction factor. Alternatively, assuming the model-independent form-factor parameterization of Boyd, Grinstein and Lebed and using lattice QCD data from the FNAL/MILC and HPQCD collaborations, we find $η_\mathrm{EW}|V_{cb}|=(41.10 \pm 1.14)\times 10^{-3}$.

hep-ex↗

First Observation of Doubly Cabibbo-Suppressed Decay of a Charmed Baryon: $Λ^{+}_{c} \rightarrow p K^{+} π^{-}$

We report the first observation of the decay $Λ^{+}_{c} \rightarrow p K^{+} π^{-}$ using a 980 $\mathrm{fb^{-1}}$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. This is the first doubly Cabibbo-suppressed decay of a charmed baryon to be observed. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be $\mathcal{B}(Λ^{+}_{c} \rightarrow p K^{+} π^{-})/\mathcal{B}(Λ^{+}_{c} \rightarrow p K^{-} π^{+})=(2.35\pm0.27\pm0.21)\times10^{-3}$, where the uncertainties are statistical and systematic, respectively.

hep-ex↗

First Observation of the Decay B0->psi(2S)pi0

We report a measurement of the $B^0\rightarrowψ(2S)π^0$ branching fraction based on the full $Υ(4S)$ data set of $772\times10^{6}$ $B\bar{B}$ pairs collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain $B(B^0\rightarrowψ(2S)π^0) = (1.17\pm0.17\text{(stat)}\pm0.08\text{(syst)})\times10^{-5}$. The result has a significance of 7.2 standard deviations and is the first observation of the decay $B^0\rightarrowψ(2S)π^0$.

hep-ex↗

Search for the rare decay $D^0\toγγ$ at Belle

We search for the rare radiative decay $D^0\toγγ$ using a data sample with an integrated luminosity of $832{\rm fb^{-1}}$ recorded by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We find no statistically significant signal and set an upper limit on the branching fraction of ${\cal B}(D^0\toγγ)<8.5\times10^{-7}$ at $90\%$ confidence level. This is the most restrictive limit on the decay channel to date.

hep-ex↗

Observation of $B^{0} \rightarrow p\barΛ D^{(*)-}$

We report the first observation of the decays $B^0 \rightarrow p\barΛ D^{(*)-}$. The data sample of $711$ fb$^{-1}$ used in this analysis corresponds to $772$ million $B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We observe $19.8σ$ and $10.8σ$ excesses of events for the two decay modes and measure the branching fractions of $B^0 \rightarrow p\barΛ D^{-}$ and $B^0 \rightarrow p\barΛ D^{*-}$ to be $(25.1\pm2.6\pm3.5)\times10^{-6}$ and $(33.6\pm6.3\pm4.4)\times10^{-6}$, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the di-baryon ($p\barΛ$) system is observed, consistent with that observed in similar $B$ decays.

hep-ex↗

Inclusive cross sections for pairs of identified light charged hadrons and for single protons in $e^+e^-$ at $\sqrt{s}=$ 10.58 GeV

We report the first double differential cross sections of two charged pions and kaons ($e^+e^- \rightarrow hhX$) in electron-positron annihilation as a function of the fractional energies of the two hadrons for any charge and hadron combination. The dependence of these di-hadron cross sections on the topology (same, opposite-hemisphere or anywhere) is also studied with the help of the event shape variable thrust and its axis. The ratios of these di-hadron cross sections for different charges and hadron combinations directly shed light on the contributing fragmentation functions. For example, we find that the ratio of same-sign pion pairs over opposite-sign pion pairs drops toward higher fractional energies where disfavored fragmentation is expected to be suppressed. These di-hadron results are obtained from a $655\,{\rm fb}^{-1}$ data sample collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. Extending the previously published single-pion and single-kaon cross sections, single-proton ($e^+e^- \rightarrow pX$) cross sections are extracted from a $159\,{\rm fb}^{-1}$ data sub-sample.

hep-ex↗

Measurement of the branching ratio of $\bar{B} \to D^{(\ast)} τ^- \barν_τ$ relative to $\bar{B} \to D^{(\ast)} \ell^- \barν_\ell$ decays with hadronic tagging at Belle

We report a measurement of the branching fraction ratios R(D(*)) of Bbar -> D(*) tau- nubar_tau relative to Bbar -> D()* l- nubar_l (where l = e or mu) using the full Belle data sample of 772 x 10^6 BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured values are R(D)= 0.375 +- 0.064(stat.) +- 0.026(syst.) and R(D*) = 0.293 +- 0.038(stat.) +- 0.015(syst.). The analysis uses hadronic reconstruction of the tag-side B meson and purely leptonic tau decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.

hep-ex↗