arXiv subjects

H. J. Kim

Publications and source records attributed to H. J. Kim.

At least 73 records · Page 4Linked to original sources

arXiv2019

Study of cosmogenic radionuclides in the COSINE-100 NaI(Tl) detectors

COSINE-100 is a direct detection dark matter search experiment that uses a 106 kg array of eight NaI(Tl) crystals that are kept underground at the Yangyang Underground Laboratory to avoid cosmogenic activation of radioisotopes by cosmic rays. Even though the cosmogenic activity is declining with time, there are still significant background rates from the remnant nuclides. In this paper, we report measurements of cosmogenic isotope contaminations with less than one year half-lives that are based on extrapolations of the time dependent activities of their characteristic energy peaks to activity rates at the time the crystals were deployed underground. For longer-lived $^{109}$Cd ($T_{1/2}=1.6$ y) and $^{22}$Na ($T_{1/2}=2.6$ y), we investigate time correlations of characteristic $γ$/X-ray peaks. The inferred sea-level production rates are compared with caluclations based on the ACTIVIA and MENDL-2 model calculations and experimental data. For $^{3}$H, which has a long, 12.3 year half-life, we evaluated the activity levels from the exposure times and determined a cosmogenic activation rate that is consistent with other measurements.

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arXiv2019

A Study of NaI(Tl) crystal Encapsulation using Organic scintillators for the Dark Matter Search

Scintillating NaI(Tl) crystals are used for various rare decay experiments, such as dark matter searches. The hygroscopicity of NaI(Tl) crystal makes the construction of crystal detectors in these experiments challenging and requires a tight encapsulation to prevent from air contact. More importantly, in a low radioactivity measurement, identification of external radiations and surface contamination is crucial to characterize the origin of total crystal radioactivities. Studies for NaI(Tl) crystal encapsulation with active organic scintillator vetoes have been performed to mitigate the above-mentioned issues simultaneously. A bare crystal is directly coupled with liquid and plastic scintillators to tag external radiations that penetrate from the outer part of the crystal. We report the pulse shape discrimination for organic scintillator pulses from those of the crystal scintillator in a single detector setup which makes external gammas identifiable and long-term stability tests of the detector setup.

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arXiv2019

First measurements of absolute branching fractions of the $Ξ_c^+$ baryon at Belle

We present the first measurements of the absolute branching fractions of $Ξ_c^+$ decays into $Ξ^- π^+ π^+$ and $p K^- π^+$ final states. Our analysis is based on a data set of $(772\pm 11)\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We measure the absolute branching fraction of $\bar{B}^{0} \to \barΛ_{c}^{-} Ξ_{c}^{+}$ with the $Ξ_c^+$ recoiling against $\barΛ_c^-$ in $\bar{B}^0$ decays resulting in ${\cal B}(\bar{B}^{0} \to \barΛ_{c}^{-} Ξ_{c}^{+}) = [1.16 \pm 0.42(\rm stat.) \pm 0.15(\rm syst.)] \times 10^{-3}$. We then measure the product branching fractions ${\cal B}(\bar{B}^{0} \to \barΛ_c^- Ξ_c^+){\cal B}(Ξ_c^+ \to Ξ^- π^+ π^+)$ and ${\cal B}(\bar{B}^{0} \to \barΛ_c^- Ξ_c^+){\cal B}(Ξ_c^+ \to p K^- π^+)$. Dividing these product branching fractions by $\bar{B}^{0} \to \barΛ_{c}^{-} Ξ_{c}^{+}$ yields: ${\cal B}(Ξ_c^+ \to Ξ^- π^+ π^+) = [2.86 \pm 1.21(\rm stat.) \pm 0.38(\rm syst.)]\%$ and ${\cal B}(Ξ_c^+ \to p K^- π^+)=[0.45 \pm 0.21(\rm stat.) \pm 0.07(\rm syst.)]\%$. Our result for ${\cal B}(Ξ_c^+ \to Ξ^- π^+ π^+)$ can be combined with $Ξ_c^+$ branching fractions measured relative to $Ξ_c^+ \to Ξ^- π^+ π^+$ to set the absolute scale for many $Ξ_c^+$ branching fractions.

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arXiv2019

Search for a Dark Matter-Induced Annual Modulation Signal in NaI(Tl) with the COSINE-100 Experiment

We present new constraints on the dark matter-induced annual modulation signal using 1.7 years, of COSINE-100 data with a total exposure of 97.7 kg$\cdot$years. The COSINE-100 experiment, consisting of 106 kg of NaI(Tl) target material, is designed to carry out a model-independent test of DAMA/LIBRA's claim of WIMP discovery by searching for the same annual modulation signal using the same NaI(Tl) target. The crystal data show a 2.7 cpd/kg/keV background rate on average in the 2--6 keV energy region of interest. Using a $χ$-squared minimization method we observe best fit values for modulation amplitude and phase of 0.0092$\pm$0.0067 cpd/kg/keV and 127.2$\pm$45 d, respectively.

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arXiv2019

A search for solar axion induced signals with COSINE-100

We present results from a search for solar axions with the COSINE-100 experiment. We find no evidence of solar axion events from a data-set of 6,303.9 kg$\cdot$days exposure and set a 90\,\% confidence level upper limit on the axion-electron coupling, $g_{ae}$, at 1.70~$\times$~$10^{-11}$ for an axion mass less than 1\,keV/c$^2$. This limit excludes QCD axions heavier than 0.59\,eV/c$^2$ in the DFSZ model and 168.1\,eV/c$^2$ in the KSVZ model.

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arXiv2019

COSINE-100 and DAMA/LIBRA-phase2 in WIMP effective models

Assuming a standard Maxwellian for the WIMP velocity distribution, we obtain the bounds from null WIMP search results of 59.5 days of COSINE-100 data on the DAMA/LIBRA-phase2 modulation effect within the context of the non-relativistic effective theory of WIMP-nucleus scattering. Here, we systematically assume that one of the effective operators allowed by Galilean invariance dominates in the effective Hamiltonian of a spin-1/2 dark matter (DM) particle. We find that, although DAMA/LIBRA and COSINE-100 use the same sodium-iodide target, the comparison of the two results still depends on the particle-physics model. This is mainly due to two reasons: i) the WIMP signal spectral shape; ii) the expected modulation fractions, when the upper bound on the time-averaged rate in COSINE-100 is converted into a constraint on the annual modulation component in DAMA/LIBRA. We find that the latter effect is the dominant one. For several effective operators the expected modulation fractions are larger than in the standard spin-independent or spin-dependent interaction cases. As a consequence, compatibility between the modulation effect observed in DAMA/LIBRA and the null result from COSINE-100 is still possible for several non-relativistic operators. At low WIMP masses such relatively high values of the modulation fractions arise because COSINE-100 is mainly sensitive to WIMP-sodium scattering events, due to the higher threshold compared to DAMA/LIBRA. A next COSINE analysis is expected to have a full sensitivity for the 5$σ$ region of DAMA/LIBRA.

hep-ph↗

arXiv2019

Search for $Ω(2012)\to KΞ(1530) \to KπΞ$ at Belle

Using data samples of $e^+e^-$ collisions collected at the $Υ(1S)$, $Υ(2S)$, and $Υ(3S)$ resonances with the Belle detector, we search for the three-body decay of the $Ω(2012)$ baryon to $KπΞ$. This decay is predicted to dominate for models describing the $Ω(2012)$ as a $KΞ(1530)$ molecule. No significant $Ω(2012)$ signals are observed in the studied channels, and 90\% credibility level upper limits on the ratios of the branching fractions relative to $K Ξ$ decay modes are obtained.

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arXiv2019

First Results from the AMoRE-Pilot neutrinoless double beta decay experiment

The Advanced Molybdenum-based Rare process Experiment (AMoRE) aims to search for neutrinoless double beta decay (0$νββ$) of $^{100}$Mo with $\sim$100 kg of $^{100}$Mo-enriched molybdenum embedded in cryogenic detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from $^{48}$Ca-depleted calcium and $^{100}$Mo-enriched molybdenum ($^{48\textrm{depl}}$Ca$^{100}$MoO$_4$). The simultaneous detection of heat(phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot $0νββ$ search with a 111 kg$\cdot$d live exposure of $^{48\textrm{depl}}$Ca$^{100}$MoO$_4$ crystals. No evidence for $0νββ$ decay of $^{100}$Mo is found, and a upper limit is set for the half-life of 0$νββ$ of $^{100}$Mo of $T^{0ν}_{1/2} > 9.5\times10^{22}$ y at 90% C.L.. This limit corresponds to an effective Majorana neutrino mass limit in the range $\langle m_{ββ}\rangle\le(1.2-2.1)$ eV.

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arXiv2019

Measurement of branching fraction and final-state asymmetry for the $\bar{B}^{0}\to K^{0}_{S}K^{\mp}π^{\pm}$ decay

We report a measurement of the branching fraction and final-state asymmetry for the $\bar{B}^{0}\to K^{0}_{S}K^{\mp}π^{\pm}$ decays. The analysis is based 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 a final-state asymmetry of $(-8.5\pm8.9\pm0.2)\%$, where the first uncertainties are statistical and the second are systematic. Hints of peaking structures are seen in the differential branching fractions measured as functions of Dalitz variables.

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arXiv2019

Transverse momentum dependent production cross sections of charged pions, kaons and protons produced in inclusive $e^+e^-$ annihilation at $\sqrt{s}=$ 10.58 GeV

We report measurements of the production cross sections of charged pions, kaons, and protons as a function of fractional energy, the event-shape variable called thrust, and the transverse momentum with respect to the thrust axis. These measurements access the transverse momenta created in the fragmentation process, which are of critical importance to the understanding of any transverse momentum dependent distribution and fragmentation functions. The low transverse momentum part of the cross sections can be well described by Gaussians in transverse momentum as is generally assumed but the fractional-energy dependence is non-trivial and different hadron types have varying Gaussian widths. The width of these Gaussians decreases with thrust and shows an initially rising, then decreasing fractional-energy dependence. The widths for pions and kaons are comparable within uncertainties, while those for protons are significantly narrower. These single-hadron cross sections and Gaussian widths are obtained from a $558\,{\rm fb}^{-1}$ data sample collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.

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arXiv2019

First measurements of absolute branching fractions of $Ξ_c^0$ at Belle

We present the first measurements of absolute branching fractions of $Ξ_c^0$ decays into $Ξ^- π^+$, $ΛK^- π^+$, and $p K^- K^- π^+$ final states. The measurements are made using a data set comprising $(772\pm 11)\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We first measure the absolute branching fraction for $B^- \to \barΛ_c^- Ξ_c^0$ using a missing-mass technique; the result is ${\cal B}(B^- \to \barΛ_c^- Ξ_c^0) = (9.51 \pm 2.10 \pm 0.88) \times 10^{-4}$. We subsequently measure the product branching fractions ${\cal B}(B^- \to \barΛ_c^- Ξ_c^0){\cal B}(Ξ_c^0 \to Ξ^- π^+)$, ${\cal B}( B^- \to \barΛ_c^- Ξ_c^0) {\cal B}(Ξ_c^0 \to ΛK^- π^+)$, and ${\cal B}( B^- \to \barΛ_c^- Ξ_c^0) {\cal B}(Ξ_c^0 \to p K^- K^- π^+)$ with improved precision. Dividing these product branching fractions by the result for $B^- \to \barΛ_c^- Ξ_c^0$ yields the following branching fractions: ${\cal B}(Ξ_c^0 \to Ξ^- π^+)= (1.80 \pm 0.50 \pm 0.14)\%$, ${\cal B}(Ξ_c^0 \to ΛK^- π^+)=(1.17 \pm 0.37 \pm 0.09)\%$, and ${\cal B}(Ξ_c^0 \to p K^- K^- π^+)=(0.58 \pm 0.23 \pm 0.05)\%.$ For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for ${\cal B}(Ξ_c^0 \to Ξ^- π^+)$ can be combined with $Ξ_c^0$ branching fractions measured relative to $Ξ_c^0 \to Ξ^- π^+$ to yield other absolute $Ξ_c^0$ branching fractions.

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arXiv2019

The First Direct Search for Inelastic Boosted Dark Matter with COSINE-100

A search for inelastic boosted dark matter (iBDM) using the COSINE-100 detector with 59.5 days of data is presented. This relativistic dark matter is theorized to interact with the target material through inelastic scattering with electrons, creating a heavier state that subsequently produces standard model particles, such as an electron-positron pair. In this study, we search for this electron-positron pair in coincidence with the initially scattered electron as a signature for an iBDM interaction. No excess over the predicted background event rate is observed. Therefore, we present limits on iBDM interactions under various hypotheses, one of which allows us to explore an area of the experimental search for iBDM using a terrestrial detector.

astro-ph.IM↗

arXiv2019

Search for $CP$ violation with kinematic asymmetries in the $D^0 \to K^+ K^- π^+ π^-$ decay

We search for $CP$ violation in the singly-Cabibbo-suppressed decay $D^{0}\rightarrow K^{+}K^{-}π^{+}π^{-}$ using data corresponding to an integrated luminosity of $988\text{ }{\rm fb}^{-1}$ collected by the Belle detector at the KEKB $e^{+}e^{-}$ collider. We measure a set of five kinematically dependent $CP$ asymmetries, of which four asymmetries are measured for the first time. The set of asymmetry measurements can be sensitive to $CP$ violation via interference between the different partial-wave contributions to the decay and performed on other pseudoscalar decays. We find no evidence of $CP$ violation.

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arXiv2019

Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with NaI(Tl) crystal Detectors

Limits on the cross section for weakly interacting massive particles (WIMPs) scattering off nucleons in the NaI(Tl) detectors at the Yangyang Underground Laboratory are obtained with a 2967.4 kg*day data exposure. Nuclei recoiling are identified by the pulse shape of scintillating photon signals. Data are consistent with no nuclear recoil hypothesis, and 90% confidence level upper limits are set. These limits partially exclude the DAMA/LIBRA region of WIMP-sodium interaction with the same NaI(Tl) target detector. This 90% confidence level upper limit on WIMP-nucleon spin-independent cross section is 3.26*10^-4 pb for a WIMP mass at 10 GeV/c^2.

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arXiv2018

Search for the rare decay of $B^+ \to \ell^{\,+} ν_{\ell} γ$ with improved hadronic tagging

We present the result of the search for the rare $B$ meson decay of $B^+ \to \ell^{\,+} ν_{\ell} γ$ with $\ell =e,μ$. For the search the full data set recorded by the Belle experiment of $711 \, \mathrm{fb}^{-1}$ integrated luminosity near the $Υ(4S)$ resonance is used. Signal candidates are reconstructed for photon energies $E_γ$ larger than $1 \, \mathrm{GeV}$ using a novel multivariate tagging algorithm. The novel algorithm fully reconstructs the second $B$ meson produced in the collision using hadronic modes and was specifically trained to recognize the signal signature in combination with hadronic tag-side $B$ meson decays. This approach greatly enhances the performance. Background processes that can mimic this signature, mainly charmless semileptonic decays and continuum processes, are suppressed using multivariate methods. The number of signal candidates is determined by analyzing the missing mass squared distribution as inferred from the signal side particles and the kinematic properties of the tag-side $B$ meson. No significant excess over the background-only hypothesis is observed and upper limits on the partial branching fraction $ Δ\mathcal{B} $ with $E_γ> 1 \, \mathrm{GeV}$ individually for electron and muon final states as well as for the average branching fraction of both lepton final states are reported. We find a Bayesian upper limit of $Δ\mathcal{B}( B^{+} \to \ell^{\, +} ν_{\ell} γ) < 3.0 \times 10^{-6}$ at 90% CL and also report an upper limit on the first inverse moment of the light-cone distribution amplitude of the $B$ meson of $λ_B$ at 90% CL.

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arXiv2018

Measurements of branching fraction and direct $C\!P$ asymmetry in $B^{\pm}\to K^{0}_{S}K^{0}_{S}K^{\pm}$ and a search for $B^{\pm}\to K^{0}_{S}K^{0}_{S}π^{\pm}$

We study charmless hadronic decays of charged $B$ mesons to the final states $K^{0}_{S}K^{0}_{S}K^{\pm}$ and $K^{0}_{S}K^{0}_{S}π^{\pm}$ using 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 $B^{\pm}\to K^{0}_{S}K^{0}_{S}K^{\pm}$, the measured branching fraction and direct $CP$ asymmetry are $[10.42\pm0.43(stat)\pm 0.22(syst)]\times10^{-6}$ and [$+1.6\pm3.9(stat)\pm 0.9(syst)$]%, respectively. In the absence of a statistically significant signal for $B^{\pm}\to K^{0}_{S}K^{0}_{S}π^{\pm}$, we obtain a 90% confidence-level upper limit on its branching fraction as $8.7 \times10^{-7}$.

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arXiv2018

Observation of $B^{+} \rightarrow p\barΛ K^+ K^-$ and $B^{+} \rightarrow \bar{p}ΛK^+ K^+$

We report the study of \OK \ and \SK \ using a $772 \times 10^6$ $B\bar{B}$ pair data sample recorded on the $Υ({\rm 4S})$ resonance with the Belle detector at KEKB. The following branching fractions are measured: $\mathcal{B}$(\OKPHSP) $=$ $(4.22^{+0.45}_{-0.44}\pm 0.51)\times10^{-6}$, $\mathcal{B}$(\SKPHSP) $=$ $(3.81^{+0.39}_{-0.37} \pm 0.45)\times 10^{-6}$, $\mathcal{B}$(\ETACD+c.c.) $=$ $(2.91^{+0.37}_{-0.35}\pm 0.36)\times 10^{-3}$ and $\mathcal{B}$(\PLPHI) $=$ $(8.18 \pm 2.15 \pm 0.79)\times10^{-7}$, where c.c. denotes the corresponding charge-conjugation process. The intermediate resonance decays are excluded in the four-body decay measurements. We also found evidences for $\mathcal{B}$(\ETACS+c.c.) $=$ $(3.59 \pm 1.52 \pm 0.47) \times 10^{-3}$ and $\mathcal{B}$(\LLKO) $=$ $(2.30 \pm 0.65 \pm 0.25) \times 10^{-6}$. No significant signals are found for \JPSIS+c.c. and \LLKS \ ; we set the 90\% confidence level upper limits on their decay branching fractions as $< 1.85\times10^{-3}$ and $< 2.14\times10^{-6}$, respectively.

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arXiv2018

Observation of $Υ(2S)\toγη_{b}(1S)$ decay

We report the observation of $Υ(2S)\toγη_{b}(1S)$ decay based on analysis of the inclusive photon spectrum of $24.7$ fb$^{-1}$ of $e^+ e^-$ collisions at the $Υ(2S)$ center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure a branching fraction of $\mathcal{B}(Υ(2S)\toγη_{b}(1S))=(6.1^{+0.6+0.9}_{-0.7-0.6})\times 10^{-4}$, and derive an $η_{b}(1S)$ mass of $9394.8^{+2.7+4.5}_{-3.1-2.7}$ MeV/$c^{2}$, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.

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