Session 2WA: Science and Next Generation Experiments at FRIB and RIBF II

SCRIT electron scattering facility

Electron scattering is the most powerful and reliable tool to investigate the nuclear structure because this reaction has the great advantage that the electron is structureless particle and its interaction is well described by the quantum electrodynamics. As is well known, the charge density distributions of many stable nuclei were determined by elastic electron scattering. Recently, many efforts for studies of unstable nuclei have been made, and the precise information of the structure of unstabe nuclei have been strongly desired. However, due to the difficulty of preparing a short-lived unstable nuclear target, there is no electron scattering on unstable nuclei with a few important exceptions, such as on ${}^{3}$H, ${}^{14}$C and so on. Under these circumstances, we have established a completely new target-forming technique, namely SCRIT (Self-Confining Radioactive isotope Ion Target) which makes electron scattering on unstable nuclei possible. A Dedicated electron scattering facility at RIKEN consists of an electron accelerator with the SCRIT system, an ERIS (Electron-beam-driven RI separator for SCRIT), and a WiSES (Window-frame Spectrometer for Electron Scattering). Feasibility test of the SCRIT and ERIS system have been successfully carried out using the stable nuclei, and more than 10${}^{26}$ [cm${}^{-2}$s${}^{-1}$] luminosity was already achieved. Furthermore, ${}^{132}$Sn, which is one of the important target at the beginning of this project, was also successfully separated in the ERIS. The WiSES with momentum resolution of $\Delta$p/p $\sim$ 10${}^{-3}$ consisting of the wide acceptance dipole magnet, two set of drift chambers together with trigger scintillation hodoscope is under construction. Electron scattering on unstable nuclei will start within a year. In this talk, the introduction of our project and the progress of the preparation status will be presented.   

Advanced Gamma-ray Detectors: Science with GRETINA/GRETA

In 2007 the NSAC Rare Isotope Beam Task force introduced 17 ``benchmark experimental programs'' to provide a measure of facility performance capabilities for rare-isotope research and to characterize the physics that can be pursued at FRIB. A majority of these topics, and hence the FRIB program and current RIBF programs, will rely on high-resolution, high-efficiency in-flight $\gamma$-ray detection. Toward that end, GRETA is proposed to be a high-resolution, high-efficiency 4$\pi$ $\gamma$-ray spectrometer, consisting of highly segmented germanium detectors grouped in quad-crystal modules. Using pulse shape analysis, the array will be capable of reconstructing the individual interaction points of incident $\gamma$-rays. When combined with tracking algorithms, this provides a large increase in sensitivity and resolving power over existing arrays. GRETA, with 30 quad-crystal modules, will allow maximization of the physics opportunities at FRIB, and will play a central role in the science program both with fast-fragmentation and reaccelerated beams. The technology of GRETA, and the capabilities in terms of science have already been demonstrated through the performance of the 1$\pi$ spectrometer, GRETINA. Consisting of 7 quad-crystal modules, GRETINA has proven its capabilities in fast-beam experiments at NSCL, a campaign which saw 24 successful experiments which would not have been possible with previous detector technologies. The capabilities of the array in the energy regime of reaccelerated beams is being put to a similar test in the physics campaign currently underway at ANL. The performance and physics accomplishments to date of GRETINA, and a description and path forward to GRETA, the full 4$\pi$ tracking array will be discussed. Emphasis will be placed on the role of GRETA or a similar device at facilities like FRIB and RIBF, in terms of experimental capabilities and physics reach.   

Mass Measurement with Rare-RI Rin

Mass measurement with Rare-RI Ring in RIKEN RI Beam Factory (RIBF) will be presented. The main purpose of Rare-RI Ring is to measure the mass for very neutron-rich nuclei, the production rate of which is very small (rare RI) and the life-time of which is predicted to be very short (less than 10 ms). In Rare-RI Ring, mass measurements will be performed based on isochronous mass spectrometry. There are two innovative apparatus in Rare-RI Ring: individual injection, which can realize the injection of 200 A MeV rare RI one-by-one, and a cyclotron-like storage ring, which allows high isochronous magnetic fields with large angular and momentum acceptances ($\sim$1{\%}). By these apparatus, we will achieve a 10$^{-6}$ mass resolution, and will be able to access rare RI, the production rate of which is down to 1 event/day/pnA in RIBF. Construction of Rare-RI Ring has started from the 2012 fiscal year. Construction of the storage ring itself was almost completed. In this fiscal year, we succeeded to store alphas from 241Am source and to check the production of isochronous fields in the storage ring. In this talk, present status of Rare-RI Ring and the possible mass measurement there will be presented.   

Active Targets for Experiments with Rare Isotopes

Experimental studies of un-bound nuclear states and nuclear reaction rates relevant for astrophysical processes are an important area of research with rare isotope beams. Both topics require the development of specialized experimental methods to study resonant reactions. The so-called active target approach, where the target material becomes part of the detection process, promises to combine high yields from thicker targets and low background with high resolution. This presentation will describe the implementation of the active-target technique in the ANASEN detector, which was developed by researchers from Louisiana State University and Florida State University. ANASEN was used in a number of stable and rare iosotope experiments in $\alpha$-- and proton scattering, as well as $(\alpha,p)$ and $(d,p)$ reactions at FSU's in-flight radioactive beam facility RESOLUT. ANASEN also was used to perform the first experiment, proton scattering off a $^{37}$K beam at the ReA3 facility. Another active-target detector with a very different approach is found in the Active Target Time-Projection Chamber, which was developed by a collaboration between researchers from MSU, the University of Notre Dame, Western Michigan University, LLNL, LBNL, and St. Mary's University (Canada). First experiments with an AT-TPC prototype have been reported [1]. The talk will summarize the results from the first experiments with these systems, describe further development and future research projects. \\[4pt] [1] D. Suzuki {\it et al.} Physical Review {\bf C 87} 054301 (2013).   

Science with SLOWRI

High precision optical spectroscopy of radioactive ions played important roles in comprehensive studies of the ground state properties of nuclei. Such experiments have been carried out almost exclusively at conventional ISOL facilities where available nuclides were limited by the chemical properties of the elements and the life-time of the nuclei. A universal stopped and low-energy RI-beam facility (SLOWRI) is being installed at RIKEN RIBF. It will convert relativistic RI-beams from the inflight separator BigRIPS to low-energy, low-emittance, high-purity RI beams using two different gas catcher cells: RF-carpet gas cell for universal RI-beams using main beams from BigRIPS and PALIS gas cell for parasitic RI-beams using those nuclei abandoned in the 2nd focal plane slit of BigRIPS. The extracted RI-beams from the gas cells will be mass separated and merged into a single beam line leading to the experimental room where various devices such as a MRTOF mass spectrograph, ion traps and a collinear laser spectroscopy apparatus will be placed and users can always access the room. Many experiments and tuning the spectrometers can be conducted daily using the parasitic beam; the main beam will be required only when very rare isotopes are studied. Possible experiments will be discussed.   

Rare Isotope Traps and Prospects for Fundamental Interaction Studies

A number of useful tests of the standard model exhibit greatly enhanced sensitivities to new physics when performed with unstable nuclei, especially Schiff moment (electric dipole moment) and parity violation measurements. Other tests, such as beta decay correlation experiments must by necessity be performed on unstable species. By combining techniques of nuclear and atomic physics, it is possible to execute experiments of exquisite sensitivity on these unstable isotopes, and search for physics beyond the standard model even in a low energy setting. Many of these experiments are limited by atom number and so greatly benefit from intense sources of rare isotopes. A brief overview of the topic is presented, with special focus on Schiff moment searches.