arXiv subjects

M. Iwasaki

Publications and source records attributed to M. Iwasaki.

At least 235 records · Page 13Linked to original sources

arXiv2012

Development of liquid helium-3 target for experimental studies of antikaon-nucleon interaction at J-PARC

A liquid helium-3 target system was developed for experimental studies of kaonic atoms and kaonic nuclei at J-PARC. helium-3 gas is liquefied in a heat exchanger cooled below 3.2 K by decompression of liquid helium-4. To maintain a large acceptance of the cylindrical detector system for decay particles of kaonic nuclei, efficient heat transport between the separate target cell and the main unit is realized using circulation of liquid helium-3. To minimize the amount of material, a vacuum vessel containing a carbon fiber reinforced plastic cylinder having an inside diameter of 150 mm and a thickness of 1 mm was produced. A target cell made of pure beryllium and beryllium-aluminum alloy was developed not only to minimize the amount of material but to obtain also high x-ray transmission. During a cooling test, the target cell was kept at 1.3 K at a pressure of 33 mbar. The total estimated heat load to the components including the target cell and heat exchanger cooled by liquid helium-4 decompression, was 0.21 W, and the liquid helium-4 consumption rate was 50 L/day.

physics.ins-det↗

arXiv2012

Kaonic hydrogen X-ray measurement in SIDDHARTA

Kaonic hydrogen atoms provide a unique laboratory to probe the kaon-nucleon strong interaction at the energy threshold, allowing an investigation of the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. The SIDDHARTA Collaboration has measured the $K$-series X rays of kaonic hydrogen atoms at the DA$Φ$NE electron-positron collider of Laboratori Nazionali di Frascati, and has determined the most precise values of the strong-interaction induced shift and width of the $1s$ atomic energy level. This result provides vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction.

nucl-ex↗

arXiv2011

Kaonic 3He and 4He X-ray measurements in SIDDHARTA

The strong-interaction shift of kaonic 3He and 4He 2p states was measured using gaseous targets for the first time in the SIDDHARTA experiment. The determined shift of kaonic 4He is much smaller than the values obtained in the experiments performed in 70's and 80's. Thus, the problems in kaonic helium (the "kaonic helium puzzle") was definitely solved by our measurements. The first observation of the kaonic 3He X-rays was also achieved. The shift both of kaonic 3He and 4He was found to be as small as a few eV.

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arXiv2011

A New Measurement of Kaonic Hydrogen X rays

The $\bar{K}N$ system at threshold is a sensitive testing ground for low energy QCD, especially for the explicit chiral symmetry breaking. Therefore, we have measured the $K$-series x rays of kaonic hydrogen atoms at the DA$Φ$NE electron-positron collider of Laboratori Nazionali di Frascati, and have determined the most precise values of the strong-interaction energy-level shift and width of the $1s$ atomic state. As x-ray detectors, we used large-area silicon drift detectors having excellent energy and timing resolution, which were developed especially for the SIDDHARTA experiment. The shift and width were determined to be $ε_{1s} = -283 \pm 36 \pm 6 {(syst)}$ eV and $Γ_{1s} = 541 \pm 89 {(stat)} \pm 22 {(syst)}$ eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction.

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arXiv2011

First measurement of kaonic helium-3 X-rays

The first observation of the kaonic 3He 3d - 2p transition was made using slow K- mesons stopped in a gaseous 3He target. The kaonic atom X-rays were detected with large-area silicon drift detectors using the timing information of the K+K- pairs of phi-meson decays produced by the DAFNE e+e- collider. The strong interaction shift of the kaonic 3He 2p state was determined to be -2+-2 (stat)+-4 (syst) eV.

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arXiv2010

Three- and four-nucleon absorption processes observed in the $K^-$-$^4$He reaction at rest

Correlations of back-to-back coincident $Λd$ and $Λt$ pairs from the stopped $K^-$ reaction on $^4$He had been investigated, thereby $Λd$ and $Λt$ branches of non-mesonic three- and four-nucleon absorption processes of antikaon at rest were identified as well-separable processes, respectively. The branching ratio of the three-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λd "n"$, is estimated to be $(0.9 \pm 0.1 (stat) \pm 0.2 (syst)) \times 10^{-3}$ from the normalized $Λd$ spectrum in a $Λd n$ final state, while the fraction of the four-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λt$, is obtained to be $(3.1 \pm 0.4 (stat) \pm 0.5 (syst)) \times 10^{-4}$ per stopped $K^-$.

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arXiv2010

Measurement of CP violating asymmetries in B^0 -> K^+K^- K^0_S decays with a time-dependent Dalitz approach

We report a measurement of $CP$ violating asymmetries in $B^0(\overline{B}^0) \to K^+ K^- K^0_S$ decays with a time-dependent Dalitz approach. This analysis is based on a data sample of $657\times 10^6$ $B\overline{B}$ pairs accumulated at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. As the result of an unbinned maximum likelihood fit to the selected candidates, the mixing-induced and direct $CP$ violation parameters, $ϕ^{\rm eff}_1$ and ${\cal A}_{CP}$ are obtained for $B^0 \to ϕ(1020) K^0_S$, $B^0 \to f_0(980) K^0_S$ and other $B^0 \to K^+ K^- K^0_S$ decays. We find four solutions that describe the data. There are \{eqnarray*} ϕ_1^{\rm eff}(B^0\to ϕ(1020) K^0_S) & = & (32.2 \pm 9.0 \pm 2.6 \pm 1.4)^{\circ}; ϕ_1^{\rm eff}(B^0\to ϕ(1020) K^0_S) & = & (26.2 \pm 8.8 \pm 2.7 \pm 1.2)^{\circ};\\ ϕ_1^{\rm eff}(B^0\to ϕ(1020) K^0_S) & = & (27.3 \pm 8.6 \pm 2.8 \pm 1.3)^{\circ}\; {\rm and}\\ ϕ_1^{\rm eff}(B^0\to ϕ(1020) K^0_S) & = & (24.3 \pm 8.0 \pm 2.9 \pm 5.2)^{\circ}.{eqnarray*}\ The values for the $CP$ violating phase in $B^0\to ϕ(1020) K^0_S$ are similar but other properties of the Dalitz plot are quite different for the four solutions. These four solutions have consistent $ϕ^{\rm eff}_1$ values for all three $B$ meson decay channels and none of them deviates significantly from the values measured in $B \to (c\bar{c}) K^0$ decays with the currently available statistics. In addition, we find no significant direct $CP$ violation.

hep-ex↗

arXiv2009

An Improved Limit on the Muon Electric Dipole Moment

Three independent searches for an electric dipole moment (EDM) of the positive and negative muons have been performed, using spin precession data from the muon g-2 storage ring at Brookhaven National Laboratory. Details on the experimental apparatus and the three analyses are presented. Since the individual results on the positive and negative muon, as well as the combined result, d=-0.1(0.9)E-19 e-cm, are all consistent with zero, we set a new muon EDM limit, |d| < 1.9E-19 e-cm (95% C.L.). This represents a factor of 5 improvement over the previous best limit on the muon EDM.

hep-ex↗

arXiv2007

Detectors and flux instrumentation for future neutrino facilities

This report summarises the conclusions from the detector group of the International Scoping Study of a future Neutrino Factory and Super-Beam neutrino facility. The baseline detector options for each possible neutrino beam are defined as follows: 1. A very massive (Megaton) water Cherenkov detector is the baseline option for a sub-GeV Beta Beam and Super Beam facility. 2. There are a number of possibilities for either a Beta Beam or Super Beam (SB) medium energy facility between 1-5 GeV. These include a totally active scintillating detector (TASD), a liquid argon TPC or a water Cherenkov detector. 3. A 100 kton magnetized iron neutrino detector (MIND) is the baseline to detect the wrong sign muon final states (golden channel) at a high energy (20-50 GeV) neutrino factory from muon decay. A 10 kton hybrid neutrino magnetic emulsion cloud chamber detector for wrong sign tau detection (silver channel) is a possible complement to MIND, if one needs to resolve degeneracies that appear in the $δ$-$θ_{13}$ parameter space.

physics.ins-det↗

arXiv2007

$Λd$ correlations from the $^4$He(stopped-$K^-$,$d$) reaction

We have observed an intense high-energy component in an inclusive $^4$He(stopped $K^-$, $d$) spectrum. For back-to-back $Λd$ pairs a prominent event cluster has been found just below the $m_{^4\textrm{He}}+m_{K^-}-m_{n}$ mass threshold in the $Λd$ invariant mass spectrum of $Λdn$ events, which is evidence for a three-nucleon absorption process of $K^-$ in $^4$He. In addition, an appreciable strength is revealed below $\sim$3220 MeV/$c^2$. Well separated $Σ^0 dn$ events show a peak similar to the case of $Λdn$.

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arXiv2007

$ΛN$ correlations from the stopped $K^-$ reaction on ${}^4$He

We have investigated correlations of coincident $ΛN$ pairs from the stopped $K^-$ reaction on ${}^4$He, and clearly observed $Λp$ and $Λn$ branches of the two-nucleon absorption process in the $ΛN$ invariant mass spectra. In addition, non-mesonic reaction channels, which indicate possible exotic signals for the formation of strange multibaryon states, have been identified.

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arXiv2007

Search for strange tribaryon states in the inclusive ^4He(K^{-}_{stopped}, p) reaction

A search for tribaryon states was performed at KEK-PS. We adopted the $^4$He($K^-_{stopped}, p)$ reaction to populate the states with strangeness -1, charge 0 and isospin 1. No significant narrow structure was observed in the mass region from 3000 to 3200 MeV/c^2 in an inclusive missing mass spectrum. The upper limit of the formation branching ratio was determined to be ($1\sim3)\times 10^{-4}$, ($0.7\sim2)\times 10^{-3}$ and ($2\sim8) \times 10^{-3}$/($stopped K^{-}$) with 95 % confidence level for narrow states with an assumed width of 0, 20 and 40 MeV/c^2, respectively.

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arXiv2007

Precision measurement of the $3d \to 2p$ x-ray energy in kaonic $^4$He

We have measured the Balmer-series x-rays of kaonic $^4$He atoms using novel large-area silicon drift x-ray detectors in order to study the low-energy $\bar{K}$-nucleus strong interaction. The energy of the $3d \to 2p$ transition was determined to be 6467 $\pm$ 3 (stat) $\pm$ 2 (syst) eV. The resulting strong-interaction energy-level shift is in agreement with theoretical calculations, thus eliminating a long-standing discrepancy between theory and experiment.

nucl-ex↗

arXiv2007

Search for a kaonic nuclear state via $^4$He$(K^-, N)$

Very recently, we have performed a couple of experiments, {\it{KEK PS-E549/E570}}, for the detailed study of the strange tribaryon $S^0(3115)$ obtained in {\it{KEK PS-E471}}. These experiments were performed to accumulate much higher statistics with improved experimental apparatusespecially for the better proton spectroscopy of the $^4$He({\it{stopped K}}$^-$, {\it{N}}) reaction. In contrast to the previous proton spectrum, no narrow ($\sim$ 20 MeV) peak structure was found either in the inclusive $^4$He({\it{stopped K}}$^-$, {\it{p}}) or in the semi-inclusive $^4$He({\it{stopped K}}$^-$, {\it{p}}$X^\pm$) reaction channel, which is equivalent to the previous $E471$ event trigger condition. Detailed analysis of the present data and simulation shows that the peak, corresponding to $S^0(3115)$, has been an experimental artifact. Present analysis does not exclude the possible existence of a much wider structure. To be sensitive to such structure and for better understanding of the non-mesonic $K^-$ absorption reaction channel, detailed analysis of the data is in progress.

nucl-ex↗

arXiv2005

Improved Measurement of the Electroweak Penguin Process B->Xsll

We present an improved measurement of the branching fraction for the electroweak penguin process B->Xsll, where l is an electron or a muon and Xs is a hadronic system containing an s-quark. The measurement is based on a sample of 152*10^6 Upsilon(4S) -> BB events collected with the Belle detector at the KEKB energy asymmetric e+e- collider. The Xs hadronic system is reconstructed from one K^{+-} or K^{0}_{S} and up to four pions, where at most one pion can be neutral. Averaging over both lepton flavors, the inclusive branching fraction is measured to be Br(B->Xsll)=(4.11+-0.83(stat)+0.85-0.81(syst))*10^{-6} for M_ll > 0.2GeV/c2.

hep-ex↗

arXiv2005

A search for deeply bound kaonic nuclear states

We have measured proton and neutron energy spectra by stopping negative kaons on liquid helium4. Two distinct peak structures were found on both spectra, which were assigned to the formation of new kinds of strange stribaryons. In this paper, we summarize both results.

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arXiv2004

Indication of a strange tribaryon S^+ from the ^4He(stopped K^-,n) reaction

We measured the neutron time-of-flight spectrum in the ^4He(stopped K^-, n) reaction by stopping negative kaons in a superfluid helium target. A clear enhancement was observed in the neutron spectrum, which indicates the formation of a strange tribaryon of charge +1 with a mass and width of M = 3141 +/- 3 (stat.) +4/-1 (sys.) MeV/c^2 and G < 23 MeV/c^2. This state, denoted as S^+(3140), is about 25 MeV/c^2 higher than the previously observed S^0(3115) T=1.

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arXiv2004

Measurements of Electroweak Penguin Processes b->d,s gamma and b->sl+l- at Belle

We report the measurements of electroweak penguin processes b->d,s gamma and b->sl+l- at the Belle experiment. The analyses are based on 152 million BB-bar events collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e+e- asymmetric-energy collider. The b->d gamma transition is studied through exclusive decays: B0->rho0 gamma, B0->omega gamma and B+ ->rho+ gamma. We apply fully inclusive and semi-inclusive reconstruction to b->s gamma and b->sl+l- processes, respectively. The results on the exclusive b->d gamma and semi-inclusive b->sl+l- measurements are preliminary.

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