山口 敦史*; 村松 はるか*; 林 佑*; 湯浅 直樹*; 中村 圭佑; 滝本 美咲; 羽場 宏光*; 小無 健司*; 渡部 司*; 菊永 英寿*; et al.
Physical Review Letters, 123(22), p.222501_1 - 222501_6, 2019/11
The low-lying isomeric state of Th provides unique opportunities for high-resolution laser spectroscopy of the atomic nucleus. We determine the energy of this isomeric state by measuring the absolute energy difference between two -decays from the 29.2-keV second-excited state. A transition-edge sensor microcalorimeter was used to measure the absolute energy of the 29.2-keV -ray with improved precision. Together with the cross-band transition energy (29.2 keVground) and the branching ratio of the 29.2-keV state measured in a recent study, the isomer energy was determined to be 8.300.88 eV. Our result is in agreement with latest measurements based on different experimental techniques, which further confirms that the isomeric state of Th is in the laser-accessible vacuum ultraviolet range.
Chen, S.*; Lee, J.*; Doornenbal, P.*; Obertelli, A.*; Barbieri, C.*; 茶園 亮樹*; Navrtil, P.*; 緒方 一介*; 大塚 孝治*; Raimondi, F.*; et al.
Physical Review Letters, 123(14), p.142501_1 - 142501_7, 2019/10
Caでは中性子魔法数34が現れると考えられているが、その直接的な実験的証拠を得るため、Caからの中性子ノックアウト反応Ca()Caによって生成される状態を理化学研究所のRI Beam Factoryによって調べた。基底状態および2.2MeVの励起状態が強く生成され、1.7MeVの励起状態の生成量は小さかった。Caの運動量分布から、基底状態および2.2MeVの励起状態は軌道の中性子を叩き出して得られた状態であることが明らかになった。DWIA計算によって得られた分光学的因子から、Caは軌道がほぼ完全に占有された閉殻構造を持つことが明らかになり、中性子魔法数34の出現が確実なものとなった。
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他296名*
Physical Review Letters, 123(12), p.122001_1 - 122001_9, 2019/09
We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively-charged hadrons in polarized , Al and Au collisions at GeV. The measurements have been performed at forward rapidity () over the range of GeV and . We observed a positive asymmetry for positively-charged hadrons in collisions, and a significantly reduced asymmetry in + collisions. These results reveal a nuclear dependence of charged hadron in a regime where perturbative techniques are relevant. These results provide new opportunities to use A collisions as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions and to use TSSA as a new handle in studying small-system collisions.
和田 有希*; 榎戸 輝揚*; 中澤 知洋*; 古田 禄大; 湯浅 孝行*; 中村 佳敬*; 森本 健志*; 松元 崇弘*; 牧島 一夫*; 土屋 晴文
Physical Review Letters, 123(6), p.061103_1 - 061103_6, 2019/08
During a winter thunderstorm on 2017 November 24, a strong burst of gamma-rays with energies up to 10 MeV was detected coincident with a lightning discharge, by scintillation detectors installed at Kashiwazaki-Kariwa Nuclear Power Plant at sea level in Japan. The burst had a sub-second duration, which is suggestive of photoneutron productions. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-frequency radio pulse. These bunches were separated by 0.71.5 ms, with a duration of 1 ms each. Thus, the present burst may be considered as a "downward" terrestrial gamma-ray flash (TGF), which is analogous to up-going TGFs observed from space. Although the scintillation detectors were heavily saturated by these bunches, the total dose associated with them was successfully measured by ionization chambers, employed by nine monitoring posts surrounding the power plant. From this information and Monte Carlo simulations, the present downward TGF is suggested to have taken place at an altitude of 2500500 m, involving avalanche electrons with energies above 1 MeV which is comparable to those in up-going TGFs.
栗田 伸之*; 山本 大輔*; 金坂 拓哉*; 古川 信夫*; 河村 聖子; 中島 健次; 田中 秀数*
Physical Review Letters, 123(2), p.027206_1 - 027206_6, 2019/07
Magnetic excitations of the effective spin =1/2 dimerized magnet BaCoSiOCl have been probed directly via inelastic neutron scattering experiments. We observed five types of excitation, which are all dispersionless within the resolution limits. The scattering intensities of the three low-lying excitations were found to exhibit different -dependences. Detailed analysis has demonstrated that BaCoSiOCl is a two dimensional spin dimer system described only by a single dimer site, where the triplet excitations are localized owing to the almost perfect frustration of the interdimer exchange interactions and the undimerized spins, even in small concentration, make an essential contribution to the excitation spectrum.
Adare, A.*; 長谷川 勝一; 今井 憲一; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他666名*
Physical Review Letters, 123(2), p.022301_1 - 022301_10, 2019/07
The PHENIX collaboration presents first measurements of low-momentum ( GeV/) direct-photon yields from AuAu collisions at =39 and 62.4 GeV. For both beam energies the direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in AuAu collisions at =200. Analyzing the photon yield as a function of the experimental observable reveals that the low-momentum (1,GeV/) direct-photon yield is a smooth function of and can be well described as proportional to with 1.25. This new scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and Large Hadron Collider, for centrality selected samples, as well as for different, collision systems. At a given beam energy the scaling also holds for high (,GeV/) but when results from different collision energies are compared, an additional -dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
Liu, M.-Z.*; Pan, Y.-W.*; Peng, F.-Z.*; Snchez-Snchez, M.*; Geng, L.-S.*; 保坂 淳; Valderrama, M. P.*
Physical Review Letters, 122(24), p.242001_1 - 242001_5, 2019/06
A recent analysis by the LHCb Collaboration suggests the existence of three narrow pentaquarklike states-the (4312), (4440), and (4457)-instead of just one in the previous analysis [the (4450)]. The closeness of the (4312) to the threshold and the (4440) and (4457) to the threshold suggests a molecular interpretation of these resonances. We show that these three pentaquarklike resonances can be naturally accommodated in a contact-range effective field theory description that incorporates heavy-quark spin symmetry. This description leads to the prediction of all the seven possible -wave heavy antimeson-baryon molecules [that is, there should be four additional molecular pentaquarks in addition to the (4312), (4440), and (4457)], providing the first example of a heavy-quark spin symmetry molecular multiplet that is complete. If this is confirmed, it will not only give us an impressive example of the application of heavy-quark symmetries and effective field theories in hadron physics, it will also uncover a clear and powerful ordering principle for the molecular spectrum, reminiscent of the SU(3)-flavor multiplets to which the light hadron spectrum conforms.
山本 慧; Thiang, G. C.*; Pirro, P.*; Kim, K.-W.*; Everschor-Sitte, K.*; 齊藤 英治*
Physical Review Letters, 122(21), p.217201_1 - 217201_5, 2019/05
We propose a topological characterization of Hamiltonians describing classical waves. Applying it to the magnetostatic surface spin waves that are important in spintronics applications, we settle the speculation over their topological origin. For a class of classical systems that includes spin waves driven by dipole-dipole interactions, we show that the topology is characterized by vortex lines in the Brillouin zone in such a way that the symplectic structure of Hamiltonian mechanics plays an essential role. We define winding numbers around these vortex lines and identify them to be the bulk topological invariants for a class of semimetals. Exploiting the bulk-edge correspondence appropriately reformulated for these classical waves, we predict that surface modes appear but not in a gap of the bulk frequency spectrum. This feature, consistent with the magnetostatic surface spin waves, indicates a broader realm of topological phases of matter beyond spectrally gapped ones.
Wo, H.*; Wang, Q.*; Shen, Y.*; Zhang, X.*; Hao, Y.*; Feng, Y.*; Shen, S.*; He, Z.*; Pan, B.*; Wang, W.*; et al.
Physical Review Letters, 122(21), p.217003_1 - 217003_5, 2019/05
We report neutron scattering measurements of single-crystalline YFeGe in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFeGe does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFeGe displays anisotropic stripe-type antiferromagnetic spin fluctuations at (). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector (). These ferromagnetic spin fluctuations are isotropic in the () plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFeGe and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.
Chen, Z. Q.*; Li, Z. H.*; Hua, H.*; 渡邉 寛*; Yuan, C. X.*; Zhang, S. Q.*; Lorusso, G.*; Orlandi, R.; 他60名*
Physical Review Letters, 122(21), p.212502_1 - 212502_6, 2019/05
-delayed -ray spectroscopy of the neutron-rich isotopes Ag was carried out at RIBF, RIKEN. The long predicted 1/2 emitting isomers were identified in both nuclei for the first time. The new experimental results extend the systematic trend of energy spacing between the lowest 9/2 and 1/2 levels in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. The tensor force is found to play a key role in the reduction of the Z=40 sub-shell gap.
Paul, N.*; Obertelli, A.*; Bertulani, C. A.*; Corsi, A.*; Doornenbal, P.*; Rodriguez-Sanchez, J. L.*; Authelet, G.*; Orlandi, R.; 他84名*
Physical Review Letters, 122(16), p.162503_1 - 162503_7, 2019/04
Fifty-five single nucleon removal cross sections from neutron-rich nuclei impinging on a hydrogen target at about 250 MeV/nucleon were measured at the RIKEN RIBF. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons compared to odd-proton number projectiles for the same separation energy, while no even-odd staggering was observed in case of neutron-removal. These observations are linked to paring correlations in the daughter nuclei and the density of bound levels. The effect is particularly strong in loosely bound nuclei.
Li, Y. B.*; 谷田 聖; Belle Collaboration*; 他161名*
Physical Review Letters, 122(8), p.082001_1 - 082001_7, 2019/03
We present the first measurements of absolute branching fractions of decays into , , and final states. The measurements are made using a data set comprising pairs collected at the resonance with the Belle detector at the KEKB collider. We first measure the absolute branching fraction for using a missing-mass technique, the result is . We subsequently measure the product branching fractions , , and with improved precision. Dividing these product branching fractions by the result for yields the following branching fractions: , , and . Our result for can be combined with branching fractions measured relative to to yield other absolute branching fractions.
Kim, S. K.*; 仲田 光樹; Loss, D.*; Tserkovnyak, Y.*
Physical Review Letters, 122(5), p.057204_1 - 057204_6, 2019/02
Guan, Y.*; 谷田 聖; Belle Collaboration*; 他205名*
Physical Review Letters, 122(4), p.042001_1 - 042001_8, 2019/02
We report the first observation of the spontaneous polarization of and hyperons transverse to the production plane in annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive production, we also report results with subtracted feed-down contributions from and charm. This measurement uses a dataset of 800.4 fb 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 hyperon.
住浜 水季*; 谷田 聖; Belle Collaboration*; 他184名*
Physical Review Letters, 122(7), p.072501_1 - 072501_7, 2019/02
We report the first observation of the doubly-strange baryon in its decay to via decays based on a data sample collected with the Belle detector at the KEKB asymmetric-energy collider. The mass and width are measured to be 1610.4 6.0 (stat) (syst) MeV and 59.9 4.8 (stat) (syst) MeV, respectively. We obtain 4.0 evidence of the with the same data sample. These results shed light on the structure of hyperon resonances with strangeness .
Seong, I. S.*; 谷田 聖; Belle Collaboration*; 他191名*
Physical Review Letters, 122(1), p.011801_1 - 011801_8, 2019/01
We report on the first Belle search for a light -odd Higgs boson, , that decays into low mass dark matter, , in final states with a single photon and missing energy. We search for events produced via the dipion transition , followed by the on-shell process with , or by the off-shell process . Utilizing a data sample of 157.3 10 decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges GeV/ and GeV/. We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below 5 GeV/.
立岩 尚之; 芳賀 芳範; 山本 悦嗣
Physical Review Letters, 121(23), p.237001_1 - 237001_6, 2018/12
足立 一郎*; 谷田 聖; Belle Collaboration*; 他421名*
Physical Review Letters, 121(26), p.261801_1 - 261801_11, 2018/12
We present first evidence that the cosine of the -violating weak phase is positive, and hence exclude trigonometric multifold solutions of the CKM Unitarity Triangle using a time-dependent Dalitz plot analysis of with decays, where denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BaBar and Belle experiments collected at the resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain pairs recorded by the BaBar detector and pairs recorded by the Belle detector. The results of the measurement are and . The result for the direct measurement of the angle of the CKM Unitarity Triangle is . The quoted model uncertainties are due to the composition of the decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics data sample. CP violation is observed in decays at the level of standard deviations. The significance for is standard deviations. The trigonometric multifold solution is excluded at the level of standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.
Fulsom, B. G.*; 谷田 聖; Belle Collaboration*; 他197名*
Physical Review Letters, 121(23), p.232001_1 - 232001_8, 2018/12
We report the observation of decay based on analysis of the inclusive photon spectrum of fb of collisions at the center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy collider. We measure a branching fraction of , and derive an mass of MeV/, 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.
Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他362名*
Physical Review Letters, 121(22), p.222301_1 - 222301_8, 2018/11
Asymmetric nuclear collisions of +Al, +Au, +Au, and He+Au at = 200 GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.