arXiv subjects

V. Gaur

Publications and source records attributed to V. Gaur.

At least 199 records · Page 11Linked to original sources

arXiv2018

Observation of $Ξ(1620)^0$ and evidence for $Ξ(1690)^0$ in $Ξ_c^+ \rightarrow Ξ^-π^+π^+$ decays

We report the first observation of the doubly-strange baryon $Ξ(1620)^0$ in its decay to $Ξ^-π^+$ via $Ξ_c^+ \rightarrow Ξ^- π^+ π^+$ decays based on a $980\,{\rm fb}^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The mass and width are measured to be 1610.4 $\pm$ 6.0 (stat) $^{+5.9}_{-3.5}$ (syst)~MeV$/c^2$ and 59.9 $\pm$ 4.8 (stat) $^{+2.8}_{-3.0}$ (syst)~MeV, respectively. We obtain 4.0$σ$ evidence of the $Ξ(1690)^0$ with the same data sample. These results shed light on the structure of hyperon resonances with strangeness $S=-2$.

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arXiv2018

Search for the lepton-flavor-violating decay $B^{0}\to K^{\ast 0} μ^{\pm} e^{\mp}$

We have searched for the lepton-flavor-violating decay $B^{0}\to K^{\ast 0} μ^{\pm} e^{\mp}$ using a data sample of 711 $fb^{-1}$ that contains $772 \times 10^{6}$ $B\bar{B}$ pairs. The data were collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of ${\cal B}(B^{0}\to K^{\ast 0} μ^{+} e^{-})< 1.2\times 10^{-7}$, ${\cal B}(B^{0}\to K^{\ast 0} μ^{-} e^{+})< 1.6\times 10^{-7}$, and, for both decays combined, ${\cal B}(B^{0}\to K^{\ast 0} μ^{\pm} e^{\mp}) < 1.8\times 10^{-7}$. These are the most stringent limits on these decays to date.

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arXiv2018

Measurements of isospin asymmetry and difference of direct $CP$ asymmetries in inclusive $B \to X_s γ$ decays

We report measurements of isospin asymmetry $Δ_{0-}$ and difference of direct $CP$ asymmetries $ΔA_{CP}$ between charged and neutral $B \to X_s γ$ decays. This analysis is based on the data sample containing $772 \times 10^6 B\bar{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric $e^+ e^-$ collider. Using a sum-of-exclusive technique with invariant $X_s$ mass up to 2.8~GeV/$c^2$, we obtain $Δ_{0-} = \bigl[-0.48 \pm 1.49 {\rm (stat.)} \pm 0.97 {\rm (syst.)} \pm 1.15 {(f_{+-}/f_{00})}\bigr]$\% and $ΔA_{CP} = \bigl[+3.69 \pm 2.65 {\rm (stat.)} \pm 0.76{\rm (syst.)}\bigr]$\%, where the last uncertainty for $Δ_{0-}$ is due to the uncertainty on the production ratio of $B^+B^-$ to $B^0\bar{B}^0$ in $Υ(4S)$ decays. The measured value of $Δ_{0-}$ is consistent with zero, allowing us to constrain the resolved photon contribution in the $B \to X_s γ$, and improve the branching fraction prediction. The result for $ΔA_{CP}$ is consistent with the prediction of the SM. We also measure the direct $CP$ asymmetries for charged and neutral $B \to X_s γ$ decays. All the measurements are the most precise to date.

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arXiv2018

Observation of $Ξ_{c}(2930)^0$ and updated measurement of $B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}$ at Belle

We report the first observation of the $Ξ_{c}(2930)^0$ charmed-strange baryon with a significance greater than 5$σ$. The $Ξ_{c}(2930)^0$ is found in its decay to $K^- Λ_{c}^+$ in $B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}$ decays. The measured mass and width are $[2928.9 \pm 3.0(\rm stat.)^{+0.9}_{-12.0}(\rm syst.)]$ MeV/$c^{2}$ and $[19.5 \pm 8.4(\rm stat.) ^{+5.9}_{-7.9}(\rm syst.)]$ MeV, respectively, and the product branching fraction is ${\cal B}(B^{-} \to Ξ_{c}(2930)^0 \barΛ_{c}^{-}) {\cal B}(Ξ_{c}(2930)^0 \to K^- Λ_{c}^{+})=[1.73 \pm 0.45(\rm stat.) \pm 0.21(\rm syst.)]\times 10^{-4}$. We also measure ${\cal B}(B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}) = [4.80 \pm 0.43(\rm stat.) \pm 0.60(\rm syst.)] \times 10^{-4}$ with improved precision, and search for the charmonium-like state $Y(4660)$ and its spin partner, $Y_η$, in the $Λ_{c}^{+}\barΛ_{c}^{-}$ invariant mass spectrum. No clear signals of the $Y(4660)$ nor its spin partner are observed and the 90\% credibility level (C.L.) upper limits on their production rates are determined. These measurements are obtained from a sample of $(772\pm11)\times 10^{6} B\bar{B}$ pairs collected at the $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.

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arXiv2018

Measurements of branching fraction and $CP$ asymmetry of the $\bar{B}^{0}(B^{0})\to K^{0}_{S}K^{\mp}π^{\pm}$ decay at Belle

We report the measurement of the branching fraction and $CP$ asymmetry for the $\bar{B}^{0}(B^{0})\to K^{0}_{S}K^{\mp}π^{\pm}$ decay. The analysis is performed on a data sample of 711 $\rm{fb}^{-1}$ collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We obtain a branching fraction of $(3.60\pm0.33\pm0.15)\times10^{-6}$ and an $\mathcal{A}_{CP}$ of $(-8.5\pm8.9\pm0.2)\%$, where the first uncertainties are statistical and the second are systematic. Hints of peaking structures are also observed in the differential branching fraction as functions of Dalitz variables.

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arXiv2018

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

We report the first observation of the spontaneous polarization of $Λ$ and $\barΛ$ hyperons transverse to the production plane in $e^+e^-$ annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive $Λ/\barΛ$ production, we also report results with subtracted feed-down contributions from $Σ^0$ and charm. This measurement uses a dataset of 800.4 fb$^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the $Λ/\barΛ$ hyperon.

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arXiv2018

Study of charmless decays $B^{\pm} \to K^{0}_{S} K^{0}_{S} h^{\pm}$ ($h=K,π$) at Belle

We report a search for charmless hadronic decays of charged $B$ mesons to the final states $K^{0}_{S} K^{0}_{S} K^{\pm}$ and $K^{0}_{S} K^{0}_{S} π^{\pm}$ . The results are based on a $711 {fb}^{-1}$ data sample that contains $772 \times 10^6$ $B \bar{B}$ pairs, and was collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. For $B^{\pm} \to K^{0}_{S} K^{0}_{S} K^{\pm}$ decays, the measured branching fraction and direct $CP$ asymmetry are $[10.64\pm0.49(stat)\pm 0.44(syst)]\times10^{-6}$ and [$-0.6\pm3.9(stat)\pm 3.4(syst)$] %, respectively. In the absence of a statistically significant signal for $B^{\pm}\to K^{0}_{S} K^{0}_{S} π^{\pm}$, we set the 90 % confidence-level upper limit on its branching fraction at $1.14 \times 10^{-6}$.

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arXiv2018

Measurement of the branching fraction of $B \rightarrow D^{(*)}π\ellν$ at Belle using hadronic tagging in fully reconstructed events

We report a measurement of the branching fraction of the decay $B \rightarrow D^{(*)}π\ellν$. The analysis uses 772$\times 10^6$ $B\bar{B}$ pairs produced in $e^+e^-\rightarrow Υ(4S)$ data recorded by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. The tagging $B$ meson in the decay is fully reconstructed in a hadronic decay mode. On the signal side, we reconstruct the decay $B \rightarrow D^{(*)}π\ellν$ $(\ell=e,μ)$. The measured branching fractions are $\mathcal{B}(B^+ \rightarrow D^-π^+ \ell^+ν)$ = [4.55 $\pm$ 0.27 (stat.) $\pm$ 0.39 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^0 \rightarrow \bar{D}^0π^- \ell^+ν)$ = [4.05 $\pm$ 0.36 (stat.) $\pm$ 0.41 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^+ \rightarrow D^{*-}π^+ \ell^+ν)$ = [6.03 $\pm$ 0.43 (stat.) $\pm$ 0.38 (syst.)]$\times 10^{-3}$, and $\mathcal{B}(B^0 \rightarrow \bar{D}^{*0}π^- \ell^+ν)$ = [6.46 $\pm$ 0.53 (stat.) $\pm$ 0.52 (syst.)]$\times 10^{-3}$. These are in good agreement with the current world average values.

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arXiv2018

Search for $Υ(1S,2S) \to Z^{+}_{c}Z^{(\prime) -}_{c}$ and $e^{+}e^{-} \to Z^{+}_{c}Z^{(\prime) -}_{c}$ at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV

The first search for $Z_{c}$ pair production in $Υ(1S)$ and $Υ(2S)$ decays and in $e^{+}e^{-}$ annihilation at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV is conducted using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant signals are observed in any of the studied modes, and the 90\% credibility level upper limits on their product branching fractions in $Υ(1S)$ and $Υ(2S)$ decays (${\cal B}(Υ(1S,2S)\to Z^{+}_{c}Z^{(\prime) -}_{c})\times{\cal B}(Z^{+}_{c}\toπ^{+}+c\bar c)$ ($c\bar c=J/ψ$, $χ_{c1}(1P)$, $ψ(2S)$)) and the product of Born cross section and branching fraction for $e^{+}e^{-} \to Z^{+}_{c}Z^{(\prime) -}_{c}$ ($σ(e^+e^- \to Z^{+}_{c}Z^{(\prime) -}_{c})\times {\cal B}(Z^{+}_{c} \to π^+ +c\bar c)$) at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV are determined. Here, $Z_{c}$ refers to the $Z_{c}(3900)$ and $Z_{c}(4200)$ observed in the $πJ/ψ$ final state, the $Z_{c1}(4050)$ and $Z_{c2}(4250)$ in the $πχ_{c1}(1P)$ state, and the $Z_{c}(4050)$ and $Z_{c}(4430)$ in the $πψ(2S)$ state.

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arXiv2018

Measurements of the absolute branching fractions of $B^{+} \to X_{c\bar{c}} K^{+}$ and $B^{+} \to \bar{D}^{(\ast) 0} π^{+} $ at Belle

We present the measurement of the absolute branching fractions of $B^{+} \to X_{c\bar{c}} K^{+}$ and $B^{+} \to \bar{D}^{(\ast) 0} π^{+} $ decays, using a data sample of $772\times10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. Here, $X_{c\bar{c}}$ denotes $η_{c}$, $J/ψ$, $χ_{c0}$, $χ_{c1}$, $η_{c}(2S)$, $ψ(2S)$, $ψ(3770)$, $X(3872)$, and $X(3915)$. We do not observe significant signals for $X(3872)$ nor $X(3915)$, and set the 90$\%$ confidence level upper limits: ${\cal B}(B^{+} \to X(3872) K^{+} )<2.7 \times 10^{-4}$ and ${\cal B}(B^{+} \to X(3915) K^{+} )<2.9 \times 10^{-4}$. These represent the most stringent upper limit for ${\cal B}(B^{+} \to X(3872) K^{+} )$ to date and the first measurement for ${\cal B}(B^{+} \to X(3915) K^{+} )$. The measured branching fractions for $η_{c}$ and $η_{c}(2S)$ are the most precise to date: ${\cal B}(B^{+} \to η_{c} K^{+} )=(12.3\pm0.8\pm0.7) \times 10^{-4}$ and ${\cal B}(B^{+} \to η_{c}(2S)K^{+}) =(4.9\pm1.1\pm0.3) \times 10^{-4}$ , where the first and second uncertainties are statistical and systematic, respectively.

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arXiv2018

Observation of an excited $Ω^-$ baryon

Using data recorded with the Belle detector, we observe a new excited hyperon, an $Ω^{*-}$ candidate decaying into $Ξ^0K^-$ and $Ξ^-K^0_S$ with a mass of $2012.4\pm0.7\ {\rm (stat)\pm\ 0.6\ (\rm syst)}\ {\rm MeV}/c^2$ and a width of $Γ=6.4^{+2.5}_{-2.0}\ {\rm(stat)}\pm1.6\ {\rm(syst)}\ {\rm MeV}$. The $Ω^{*-}$ is seen primarily in $Υ(1S), Υ(2S)$, and $Υ(3S)$ decays.

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arXiv2018

Measurement of Time-dependent $CP$ Asymmetries in $B^{0}\to K_S^0 ηγ$ Decays

We report a measurement of time-dependent $CP$ violation parameters in ${B^0 \to K_S^0 ηγ}$ decays. The study is based on a data sample, containing ${772 \times 10^6 B\bar{B}}$ pairs, that was collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We obtain the $CP$ violation parameters of ${{\cal S} = -1.32 \pm 0.77 {\rm (stat.)} \pm 0.36{\rm (syst.)}}$ and ${{\cal A} = -0.48 \pm 0.41 {\rm (stat.)} \pm 0.07{\rm (syst.)}}$ for the invariant mass of the $K_S^0 η$ system up to 2.1 GeV/$c^2$.

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arXiv2018

Observation of $Υ(4S)\to η' Υ(1S)$

We report the first observation of the hadronic transition $Υ(4S)\toη'Υ(1S)$, using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We reconstruct the $η'$ meson through its decays to $ρ^0γ$ and to $π^+π^-η$, with $η\toγγ$. We measure: ${\cal B}(Υ(4S)\toη'Υ(1S))=(3.43\pm 0.88 {\rm(stat.)} \pm 0.21 {\rm(syst.)})\times10^{-5}$, with a significance of 5.7$σ$.

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arXiv2018

Production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation near $\sqrt{s} = 10.52$~GeV

We measure the inclusive production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation using a 800 fb$^{-1}$ data sample taken near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The feed-down contributions from heavy particles are subtracted using our data, and the direct production cross sections are presented for the first time. The production cross sections divided by the number of spin states for $S=-1$ hyperons follow an exponential function with a single slope parameter except for the $Σ(1385)^+$ resonance. Suppression for $Σ(1385)^+$ and $Ξ(1530)^0$ hyperons is observed. Among the production cross sections of charmed baryons, a factor of three difference for $Λ_c^+$ states over $Σ_c$ states is observed. This observation suggests a diquark structure for these baryons.

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arXiv2018

Inclusive study of bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near $Υ(5S)$

We study bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near the $Υ(5S)$, at a center of mass energy of $\sqrt{s}=10.866\,$GeV. The results are based on the $121.4\,$fb$^{-1}$ data sample collected by the Belle experiment at the asymmetric energy KEKB collider. Only the $η$ meson is reconstructed and the missing-mass spectrum of $η$ candidates is investigated. We observe the $e^+e^-\toηΥ_J(1D)$ process and find evidence for the $e^+e^-\toηΥ(2S)$ process, while no significant signals of $Υ(1S)$, $h_b(1P)$, nor $h_b(2P)$ are found. Cross sections for the studied processes are reported.

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arXiv2018

Search for $CP$ violation in the $D^{+}\toπ^{+}π^{0}$ decay at Belle

We search for $CP$ violation in the charged charm meson decay $D^{+}\toπ^{+}π^{0}$, based on a data sample corresponding to an integrated luminosity of $\rm 921~fb^{-1}$ collected by the Belle experiment at the KEKB $e^{+}e^{-}$ asymmetric-energy collider. The measured $CP$ violating asymmetry is $[+2.31\pm1.24({\rm stat})\pm0.23({\rm syst})]\%$, which is consistent with the standard model prediction and has a significantly improved precision compared to previous results.

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arXiv2018

Observation of Excited $Ω_c$ Charmed Baryons in $e^+e^-$ Collisions

Using the entire Belle data sample of 980 ${\rm fb}^{-1}$ of $e^+e^-$ collisions, we present the results of a study of excited $Ω_c$ charmed baryons in the decay mode $Ξ_c^+K^-$. We show confirmation of four of the five narrow states reported by the LHCb Collaboration: the $Ω_c(3000)$ , $Ω_c(3050)$, $Ω_c(3066)$, and $Ω_c(3090)$.

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arXiv2018

Measurement of Branching Fractions of Hadronic Decays of the $Ω_c^0$ Baryon

Using a data sample of 980 ${\rm fb}^{-1}$ of $e^+e^-$ annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the results of a study of the decays of the $Ω_c^0$ charmed baryon into hadronic final states. We report the most precise measurements to date of the relative branching fractions of the $Ω_c^0$ into $Ω^-π^+π^0$, $Ω^-π^+π^-π^+$, $Ξ^-K^-π^+π^+$, and $Ξ^0K^-π^+$, as well as the first measurements of the branching fractions of the $Ω_c^0$ into $Ξ^-\bar{K}^0π^+$, $Ξ^0\bar{K}^0$, and $Λ\bar{K}^0\bar{K}^0$, all with respect to the $Ω^-π^+$ decay. In addition, we investigate the resonant substructure of these modes. Finally, we present a limit on the branching fraction for the decay $Ω_c^0\toΣ^+K^-K^-π^+$.

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