arXiv subjects

A. B. Kaliyar

Publications and source records attributed to A. B. Kaliyar.

At least 55 records · Page 3Linked to original sources

arXiv2022

The Silicon Vertex Detector of the Belle II Experiment

In 2019 the Belle II experiment started data taking at the asymmetric SuperKEKB collider (KEK, Japan) operating at the Y(4S) resonance. Belle II will search for new physics beyond the Standard Model by collecting an integrated luminosity of 50~ab$^{-1}$. The silicon vertex detector (SVD), consisting of four layers of double-sided silicon strip sensors, is one of the two vertex sub-detectors. The SVD extrapolates the tracks to the inner pixel detector (PXD) with enough precision to correctly identify hits in the PXD belonging to the track. In addition the SVD has standalone tracking capability and utilizes ionization to enhance particle identification in the low momentum region. The SVD is operating reliably and with high efficiency, despite exposure to the harsh beam background of the highest peak-luminosity collider ever built. High signal-to-noise ratio and hit efficiency have been measured, as well as the spatial resolution; all these quantities show excellent stability over time. Data-simulation agreement on cluster properties has recently been improved through a careful tuning of the simulation. The precise hit-time resolution can be exploited to reject out-of-time hits induced by beam background, which will make the SVD more robust against higher levels of background. During the first three years of running, radiation damage effects on strip noise, sensor currents and depletion voltage have been observed, as well as some coupling capacitor failure due to intense radiation bursts. None of these effects cause significant degradation in the detector performance.

physics.ins-det↗

arXiv2022

Measurement of the branching fraction and $CP$ asymmetry for $B\to\bar{D}^{0} π$ decays

We measure the branching fractions and $CP$ asymmetries for the decays $B^{0}\to \bar{D}^{0}π^{0}$ and $B^{+}\to \bar{D}^{0}π^{+}$, using a data sample of $772\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The branching fractions obtained and direct $CP$ asymmetries are $\mathcal{B}(B^{0}\to \bar{D}^{0}π^{0}) = [2.70 \pm 0.06~ \text{(stat.)} \pm 0.10~ \text{(syst.)}] \times 10^{-4}$, $\mathcal{B}(B^{+}\to \bar{D}^{0}π^{+}) = [4.53 \pm 0.02~ \text{(stat.)} \pm 0.15~ \text{(syst.)}] \times 10^{-3}$, $ {\cal A}_{CP}(B^{0}\to \bar{D}^{0}π^{0}) = [+0.42 \pm 2.05~ \text{(stat.)} \pm 1.22~ \text{(syst.)}]\%$, and $ {\cal A}_{CP}(B^{+}\to \bar{D}^{0}π^{+}) = [+0.19 \pm 0.36~ \text{(stat.)} \pm 0.57~ \text{(syst.)}]\%$. The measurements of $\mathcal{B}$ are the most precise to date and are in good agreement with previous results, as is the measurement of ${\cal A}_{CP}(B^{+}\to \bar{D}^{0}π^{+})$. The measurement of ${\cal A}_{CP}$ for $B^{0}\to \bar{D}^{0}π^{0}$ is the first for this mode, and the value is consistent with Standard Model expectations.

hep-ex↗

arXiv2022

Search for $B^{0} \to K_S^{0}K_S^{0}γ$ decays at Belle

We report the first search for the penguin-dominated process $B^0 \rightarrow K_S^0 K_S^0 γ$ using the full data sample of $772\times 10^6$ $B\bar{B}$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We do not observe any statistically significant signal yield in the $K_S^0$-pair invariant mass range 1 GeV/$c^2 < M_{K_S^0 K_S^0} < $ 3 GeV/$c^2$, and set the following upper limits at 90% confidence level: $\mathcal{B}(B^0 \to K_S^0 K_S^0 γ) < 5.8\times10^{-7}$, $\mathcal{B}(B^0 \to f_2 γ)\times \mathcal{B}(f_2 (1270) \to K_S^0 K_S^0 ) < 3.1\times10^{-7}$, and $\mathcal{B}(B^0 \to f_2^{\prime} γ)\times \mathcal{B}(f_2^{\prime} (1525) \to K_S^0 K_S^0 ) < 2.1\times10^{-7}$. Further, 90% confidence upper limits have also been set in the range of [0.7-2.9]$\times10^{-7}$ on the $B^0 \rightarrow K_S^0 K_S^0 γ$ branching fraction in bins of $M_{K_S^0 K_S^0}$.

hep-ex↗

arXiv2022

First Measurement of the $Λ_c^+ \to p η'$ decay

We present the first measurement of the branching fraction of the singly Cabibbo-suppressed (SCS) decay $Λ_c^+ \to p η'$ with $η' \to ηπ^+π^-$, using a data sample corresponding to an integrated luminosity of 981 $\rm fb^{-1}$, collected by the Belle detector at the KEKB $e^{+}$$e^{-}$ asymmetric-energy collider. A significant $Λ_c^+$ signal is observed for the first time with a signal significance of 5.4$σ$. The relative branching fraction with respect to the normalization mode $Λ_c^+ \to pK^-π^+$ is measured to be \begin{equation*} \frac{{\cal B}(Λ_c^+ \to p η')}{{\cal B}(Λ_c^+ \to p K^-π^+)} = (7.54 \pm 1.32 \pm 0.75) \times 10^{-3}, \end{equation*} where the uncertainties are statistical and systematic, respectively. Using the world-average value of ${\cal B}(Λ_c^+ \to p K^-π^+) = (6.28\pm0.32)\times10^{-2}$, we obtain \begin{equation*} {\cal B}(Λ_c^+ \to p η') = (4.73 \pm 0.82 \pm 0.47 \pm 0.24)\times 10^{-4}, \end{equation*} where the uncertainties are statistical, systematic, and from ${\cal B}(Λ_c^+ \to pK^-π^+)$, respectively.

hep-ex↗

arXiv2022

Search for a light Higgs boson in single-photon decays of $Υ(1S)$ using $Υ(2S) \to π^+ π^- Υ(1S)$ tagging method

We search for a light Higgs boson ($A^0$) decaying into a $τ^+τ^-$ or $μ^+μ^-$ pair in the radiative decays of $Υ(1S)$. The production of $Υ(1S)$ mesons is tagged by $Υ(2S)\to π^+ π^- Υ(1S)$ transitions, using 158 million $Υ(2S)$ events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant $A^0$ signals in the mass range from the $τ^+τ^-$ or $μ^+μ^-$ threshold to 9.2 GeV/$c^2$ are observed. We set the upper limits at 90\% credibility level (C.L.) on the product branching fractions for $Υ(1S)\to γA^0$ and $A^0\to τ^+τ^-$ varying from $3.8\times10^{-6}$ to $1.5\times10^{-4}$. Our results represent an approximately twofold improvement on the current world best upper limits for the $Υ(1S)\to γA^0(\to τ^+τ^-)$ production. For $A^0\to μ^+μ^-$, the upper limits on the product branching fractions for $Υ(1S)\to γA^0$ and $A^0\to μ^+μ^-$ are at the same level as the world average limits, and vary from $3.1\times10^{-7}$ to $1.6\times10^{-5}$. The upper limits at 90\% C.L. on the Yukawa coupling $f_{Υ(1S)}$ and mixing angle ${\rm sin}θ_{A^0}$ are also given.

hep-ex↗

arXiv2022

Search for tetraquark states $X_{cc\bar{s}\bar{s}}$ in $D_{s}^{+}D_{s}^{+}~(D_{s}^{+}D_{s}^{+})$ final states at Belle

A search for double-heavy tetraquark state candidates $X_{cc\bar{s}\bar{s}}$ decaying to $D_{s}^{+}D_{s}^{+}$ and $D_{s}^{*+} D_{s}^{*+}$ is presented for the first time using the data samples of 102 million $Υ(1S)$ and 158 million $Υ(2S)$ events, and the data samples at $\sqrt{s}$ = 10.52~GeV, 10.58~GeV, and 10.867~GeV corresponding to integrated luminosities of 89.5~fb$^{-1}$, 711.0~fb$^{-1}$, and 121.4~fb$^{-1}$, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. The invariant-mass spectra of the $D_{s}^{+}D_{s}^{+}$ and $D_{s}^{*+} D_{s}^{*+}$ are studied to search for possible resonances. No significant signals are observed, and the 90\% confidence level upper limits on the product branching fractions [${\cal B}(Υ(1S,2S) \to X_{cc\bar{s}\bar{s}} + anything) \times {\cal B}(X_{cc\bar{s}\bar{s}} \to D_{s}^{+}D_{s}^{+}(D_{s}^{*+} D_{s}^{*+}))$] in $Υ(1S,2S)$ inclusive decays and the product values of Born cross section and branching fraction [$σ(e^+e^- \to X_{cc\bar{s}\bar{s}} + anything ) \times {\cal B}(X_{cc\bar{s}\bar{s}} \to D_{s}^{+}D_{s}^{+}(D_{s}^{*+} D_{s}^{*+}))$] in $e^+e^-$ collisions at $\sqrt{s}$ = 10.52~GeV, 10.58~GeV, and 10.867~GeV under different assumptions of $X_{cc\bar{s}\bar{s}}$ masses and widths are obtained.

hep-ex↗

arXiv2022

Study of $\overline{B}{}^0\rightarrow D^{+}h^{-} (h=K/π)$ decays at Belle

We present a measurement of the branching fractions of the Cabibbo favored $\overline{B}{}^0\rightarrow D^{+}π^{-}$ and the Cabibbo suppressed $\overline{B}{}^0\rightarrow D^{+}K^{-}$ decays. We find $\mathcal{B}(\overline{B}{}^0\rightarrow D^{+}π^{-}) = (2.48 \pm 0.01 \pm 0.09 \pm 0.04) \times 10^{-3}$ and $\mathcal{B}(\overline{B}{}^0\rightarrow D^{+}K^{-})= (2.03 \pm 0.05 \pm 0.07 \pm 0.03) \times 10^{-4}$ decays, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the $D^{+} \rightarrow K^{-}π^{+}π^{+}$ branching fraction. The ratio of branching fractions of $\overline{B}{}^0\rightarrow D^{+}K^{-}$ and $\overline{B}{}^0\rightarrow D^{+}π^{-}$ is measured to be $R^{D} = [8.19 \pm 0.20(\rm stat) \pm 0.23(\rm syst)] \times 10^{-2} $. These measurements are performed using the full Belle data set, which corresponds to $772 \times 10^{6} B\overline{B} $ pairs.

hep-ex↗

arXiv2022

Measurement of ${\mathcal B}$($B_s \rightarrow D_s X$) with $B_s$ Semileptonic Tagging

We report the first direct measurement of the inclusive branching fraction ${\mathcal B}(B_s \rightarrow D_s X)$ via $B_s$ tagging in $e^+e^-\toΥ$(5S) events. Tagging is accomplished through a partial reconstruction of semileptonic decays $B_s \rightarrow D_s X \ell ν$, where $X$ denotes unreconstructed additional hadrons or photons and $\ell$ is an electron or muon. With 121.4 fb$^{-1}$ of data collected at the $Υ$(5S) resonance by the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider, we obtain ${\mathcal B}(B_s \rightarrow D_s X)$ = $(60.2 \pm 5.8 \pm 2.3)$\%, where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2022

Search for the decay $B_s^0 \to η^\prime K_S^0$

We report the results of the first search for the decay $B_s^0 \to η^\prime K_S^0$ using $121.4\,{\rm fb}^{-1}$ of data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe no signal and set a 90\% confidence-level upper limit of $8.16 \times 10^{-6}$ on the $B_s^0 \to η^\prime K_S^0$ branching fraction.

hep-ex↗

arXiv2022

Measurement of Two-Particle Correlations of Hadrons in $e^{+}e^{-}$ Collisions at Belle

The measurement of two-particle angular correlation functions in high-multiplicity $e^+e^-$ collisions at $\sqrt{s}=10.52$ GeV is reported. In this study, the $89.5~{\text{fb}}^{-1}$ of hadronic $e^+e^-$ annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle ($Δϕ$) and three units of pseudorapidity ($Δη$), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime.

hep-ex↗

arXiv2021

Search for the decay $B_s^0\rightarrowηη$

We report results from a search for the decay $B_s^0\rightarrowηη$ using 121.4 fb$^{-1}$ of data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We do not observe any signal and set an upper limit on the branching fraction of $14.3\times 10^{-5}$ at $90\%$ confidence level. This result represents a significant improvement over the previous most stringent limit.

hep-ex↗

arXiv2021

Measurements of the branching fractions of $Ξ_c^0 \to ΛK_S^0$, $Ξ_c^0 \to Σ^0 K_S^0$, and $Ξ_c^0 \to Σ^+ K^-$ decays at Belle

Using the entire data sample of $980\mathrm{~fb}^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we present measurements of the branching fractions of the Cabibbo-favored decays $Ξ_c^0 \to ΛK_S^0$, $Ξ_c^0 \to Σ^0 K_S^0$, and $Ξ_c^0 \to Σ^+ K^-$. Taking the decay $Ξ_c^0 \to Ξ^- \pip$ as the normalization mode, we measure the branching fraction ratio ${\cal B}(Ξ_c^0 \to ΛK_S^0)/{\cal B}(Ξ_c^0 \to Ξ^- π^+) = 0.229\pm0.008\pm0.012$ with improved precision, and measure the branching fraction ratios ${\cal B}(Ξ_c^0 \to Σ^0 K_S^0)/{\cal B}(Ξ_c^0 \to Ξ^- π^+) = 0.038\pm0.006\pm0.004$ and ${\cal B}(Ξ_c^0 \to Σ^+ K^-)/{\cal B}(Ξ_c^0 \to Ξ^- π^+) = 0.123\pm0.007\pm0.010$ for the first time. Taking into account the branching fraction of the normalization mode, the absolute branching fractions are determined to be ${\cal B}(Ξ_c^0 \to ΛK_S^0) = (3.27\pm0.11\pm0.17\pm0.73) \times 10^{-3}$, ${\cal B}(Ξ_c^0 \to Σ^0 K_S^0) = (0.54\pm 0.09\pm 0.06\pm 0.12) \times 10^{-3}$, and ${\cal B}(Ξ_c^0 \to Σ^+ K^-) = (1.76\pm 0.10\pm0.14\pm 0.39) \times 10^{-3}$. The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty of the branching fraction of $Ξ_c^0 \to Ξ^- π^+$.

hep-ex↗

arXiv2021

Measurements of $q^2$ Moments of Inclusive $B \rightarrow X_c \ell^+ ν_{\ell}$ Decays with Hadronic Tagging

We present the measurement of the first to fourth order moments of the four-momentum transfer squared, $q^2$, of inclusive $B \rightarrow X_c \ell^+ ν_{\ell}$ decays using the full Belle data set of 711 $\mathrm{fb}^{-1}$ of integrated luminosity at the $Υ(4S)$ resonance where $\ell = e, μ$. The determination of these moments and their systematic uncertainties open new pathways to determine the absolute value of the CKM matrix element $V_{cb}$ using a reduced set of matrix elements of the heavy quark expansion. In order to identify and reconstruct the $X_c$ system, we reconstruct one of the two $B$-mesons using machine learning techniques in fully hadronic decay modes. The moments are measured with progressively increasing threshold selections on $q^2$ starting with a lower value of 3.0 $\mathrm{GeV}^2$ in steps of 0.5 $\mathrm{GeV}^2$ up to a value of 10.0 $\mathrm{GeV}^2$. The measured moments are further unfolded, correcting for reconstruction and selection effects as well as QED final state radiation. We report the moments separately for electron and muon final states and observe no lepton flavor universality violating effects.

hep-ex↗

arXiv2021

Search for $B^{0} \to τ^\pm \ell^\mp$ ($\ell=e,μ$) with a hadronic tagging method at Belle

We present a search for the lepton-flavor-violating decays $B^{0} \to τ^\pm \ell^\mp$, where $\ell=(e,\,μ)$, using the full data sample of $772 \times 10^6$ $B \overline{B}$ pairs recorded by 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. The $τ^\pm$ lepton is reconstructed indirectly using the momentum of the reconstructed $B$ and that of the $\ell^\mp$ from the signal decay. We find no evidence for $B^{0} \to τ^\pm \ell^\mp$ decays and set upper limits on their branching fractions at 90% confidence level of $\cal B$($B^{0} \to τ^\pm μ^{\mp}$)$ < 1.5 \times 10^{-5}$ and $\cal B$($B^{0} \to τ^\pm e^{\mp}$)$ < 1.6 \times 10^{-5}$.

hep-ex↗

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.

hep-ex↗

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 $Λ_c^+ \to p K^- π^+$.

hep-ex↗

arXiv2021

Measurement of the Masses and Widths of the $Σ_c(2455)^+$ and $Σ_c(2520)^+$ Baryons

Using 980 ${\rm fb}^{-1}$ of data {collected} with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the measurements of the masses, and the first measurements of the instrinsic widths, of the $Σ_c(2455)^+$ and $Σ_c(2520)^+$ charmed baryons. We find $M(Σ_c(2455)^+)-M(Λ_c^+) = 166.17\pm 0.05^{+0.16}_{-0.07}\ {\rm MeV}/c^2$, $Γ(Σ_c(2455)^+) = 2.3 \pm 0.3 \pm 0.3\ {\rm MeV/c^2}$, $M(Σ_c(2520)^+)-M(Λ_c^+) = 230.9 \pm 0.5 ^{+0.5}_{-0.1}\ {\rm MeV}/c^2$, and $Γ(Σ_c(2520)^+) = 17.2^{+2.3\ +3.1}_{-2.1\ -0.7}\ {\rm MeV}/c^2$, where the uncertainties are statistical and systematic, respectively. These measurements can be used to test models of the underlying quark structure of the $Σ_c$ states.

hep-ex↗

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.

hep-ex↗