Analysis of spectral modification of mesons at finite density using a transport approach in 12 GeV pA reactions

市川 真也; Gubler, P.; 成木 恵; KEK-PS E325 Collaboration*; 他25名*

Progress of Theoretical and Experimental Physics (Internet), 2025(9), p.093D01_1 - 093D01_21, 2025/08

https://doi.org/10.1093/ptep/ptaf108

The hadron spectrum at finite density is an important observable for exploring the origin of hadron masses. In the KEK-PS E325 experiment, the di-electron decays of mesons inside and outside nuclei were measured using 12 GeV pA reactions. In the previous analysis, a significant excess was observed on the low-mass side of the meson peak in the data for slow-moving mesons ( = / 1.25) with the Cu target, and in-medium vector meson spectral modification was verified. We newly employed the PHSD transport approach to take into account the time evolution of spatial density distribution of the target nuclei. Consistent with the previous analysis, a significant excess was observed in the present analysis as well. It was found that incorporating momentum dependence into the spectral modification leads to better agreement with the experimental results. For the slow-moving mesons with the Cu target, the newly obtained modification parameters are consistent with those from the previous analysis within the uncertainties.

First high-precision direct determination of the atomic mass of a superheavy nuclide

Schury, P.*; 伊藤 由太; 小浦 寛之; 他25名*

Physical Review C, 104(2), p.L021304_1 - L021304_7, 2021/08

https://doi.org/10.1103/PhysRevC.104.L021304

We present the first direct measurement of the atomic mass of a superheavy nuclide. Atoms of Db (Z=105) were produced online at the RIKEN Nishina Center for Accelerator-Based Science using the fusion-evaporation reaction Pb(V, 2n)Db. The gas-filled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and some transfer products, prior to delivering the energetic beam of Db ions to a helium gas-filled ion stopping cell wherein they were thermalized. Thermalized Db ions were then transferred to a multireflection time-of-flight mass spectrograph for mass analysis. An alpha particle detector embedded in the ion time-of-flight detector allowed disambiguation of the rare Db time-of-flight detection events from background by means of correlation with characteristic decays. The extreme sensitivity of this technique allowed a precision atomic mass determination from 11 events. The mass excess was determined to be 100063(231)(132) keV/c. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as Z=105 and should allow similar evaluations for heavier species in future work.

Monte Carlo simulations and n-p differential scattering data measured with Proton Recoil Telescopes

Terranova, N.*; Aberle, O.*; Alcayne, V.*; 木村 敦; 他125名*

EPJ Web of Conferences, 239, p.01024_1 - 01024_5, 2020/09

https://doi.org/10.1051/epjconf/202023901024

The U(n,f) cross section from 20 MeV up to about 1 GeV has been measured relative to the H(n,n)H reaction. The neutron flux impinging on the U sample has been obtained by detecting recoil protons originating from n-p scattering in a CH sample. Two Proton Recoil Telescopes (PRT), consisting of several layers of solid-state detectors and fast plastic scintillators, have been set at proton scattering angles of 25.07 and 20.32. Extensive Monte Carlo simulations were performed to characterize proton transport through the PRTs. In this work we compare measured data collected with the PRTs with a full Monte Carlo simulation based on the Geant-4 toolkit.

Measurements of at forward rapidity in collisions at GeV

Aidala, C.*; 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425名*

Physical Review D, 95(9), p.092002_1 - 092002_18, 2017/05

AA2017-0101.pdf:1.49MB

https://doi.org/10.1103/PhysRevD.95.092002

We report the first measurement of the fraction of mesons coming from -meson decay () in collisions at GeV. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of due to -meson decays from prompt . The measured value of is for with transverse momenta GeV/ and rapidity . The measured fraction at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The cross section per unit rapidity extracted from the obtained and the PHENIX inclusive cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean hadron rapidity in 510 GeV collisions, is b. It is consistent with the fixed-order-next-to-leading-logarithm calculations.

Summary of physical properties of rocks collected during the IODP Exp.402 in the back-arc Tyrrhenian Basin

Filina, I. Y.*; 安邊 啓明; 他25名*

no journal, , 

The IODP Expedition 402 occurred from February to April of 2024 in the Tyrrhenian Sea with the primary objective of sampling the transition between the continental and oceanic tectonic domains. We have drilled two sites on the conjugate Cornaglia and Campania terraces, and four sites in the Vavilov basin. In this paper, we summarize different rock types recovered during the IODP expedition 402 that range from felsic to ultramafic composition. We present the average values of bulk density, porosity, grain density, compressional velocity, magnetic susceptibility, gamma-radiation, and thermal conductivity for different types of rocks. In particular, we report physical properties for shales and muds of the post-Messinian section including ach intervals and volcaniclastic gravel encountered in all holes, evaporites (halite, gypsum and anhydrite) of Messinian interval, and pre-Messinian shales in the continental domains, as well as basalts and diorites, granitoids/gneisses and peridotites recovered from the Vavilov basin. The data gathered from the 6 sites drilled by Expedition 402 will allow us to study the origin, formation, evolution and tectonic history of the Tyrrhenian Sea and uncover the geological processes that were active in the area at different times. The physical properties reported in this paper provide mandatory constraints for all kinds of geomodelling, such as geological, geophysical, geochemical and geodynamical studies, as well as tectonic reconstructions, which eventually will shed light on the complex tectonics of this important region.