SAMURAI International Collaboration Workshop 2017

The invariant mass spectroscopy of the unbound oxygen isotopes 27O and 28O was carried out by the SAMURAI+NeuLAND+MINOS setup. I will show a progress report on the analysis of the SAMURAI21 experiment.

The most recent developments in the analysis of the data acquired for the SAMURAI04 experiment will be presented. In particular, the decay energy spectra for the most neutron-rich unbound isotopes of B, C and N will be presented. The possibility of employing charge exchange to reach beyond the dripline will also be briefly discussed. By way of conclusion we will present the motivations for the SAMURAI36 experiment, which was run at the end of 2016, and discuss briefly the expected outcome.

I will report on the status of the exclusive Coulomb breakup of neutron drip-line nuclei, 19B and 22C. (SAMURAI-03).

Obtaining direct information on neutron-proton (np) correlations in nuclei is a long-sought goal in nuclear physics. Two-nucleon knockout reactions offer a powerful tool as the reaction cross section is a direct probe of nucleon correlations. The available experimental data with 12C incident on a C target at 1.05 and 2.10 GeV/u shows that the inclusive cross sections from np removal channel is 5~8 times greater than those for 2n (to 10C) and 2p pairs (to 10Be) [1,2], in excess of the ratio 16/6~2.7 from simple pair counting in 12C. Such enhancement however could not be described by the calculations using eikonal reaction dynamics and structure from the effective-interaction shell model and the no-core shell model (NCSM) [3]. To further investigate the nature of nucleon correlations and the origin of discrepancy between the observations and theories, we have performed the first final-state exclusive np-removal cross section measurements using DALI2 gamma-detection array and SAMURAI spectrometer at RIKEN. By the gamma-residue and gamma-residue-neutron coincidence technique, the partial cross sections to 10B and 10Be T=0 and T=1 final sates following np and pp removal from 12C at 190 MeV/u were extracted. The large ratio (5~8) of the np- to pp-removal cross section mentioned above was found to be mis-interpreted due to the ignorance of the particle-evaporation channels in the data. Our work reveals that the ratio is only 3.5(3) and could be well described by the NCSM approach with the inclusion of 3N forces. In addition, the NCSM calculations also provide an overall good agreement with the measured exclusive cross sections to both T=0 and T=1 states of 10B and 10Be, at variance with the conventional p-shell shell-model calculations which systematically underestimate the cross sections to the T=0 states. This study (i) reveals significant particle-evaporation contribution to the reaction yield of 10B, (ii) gains new insight into the importance of the 3N forces, and (iii) suggests insufficient treatment of the T=0 np correlations in the adopted p-shell shell model. References [1] D. L. Olson et al., Phys. Rev. C. 28, 1602 (1983) [2] J. M. Kidd et al., Phys. Rev. C. 37, 6 (1988) [3] E. Simpson P. Navrátil, R. Roth, and J. A. Tostevin, Phys. Rev. C 86, 054609 (2012).

We will report on the progress of the SAMURAI08 experiment. In this experiment, alpha-cluster levels in 16C were investigated with a 200 MeV/u 16C beam and a liquid He target. The four momenta of decay particles (alpha particle, neutrons and residuals) were measured by the SAMURAI spectrometer. The gamma-rays from the decay particles were also detected by DALI2. We will report the results of some important decay channels such as 12Be + alpha and 11Be + alpha + n. We will also discuss the future perspective of invariant-mass spectroscopy with alpha particle. In terms of analysis, tracks of two charged particles in single event are needed to reconstruct their four momenta. The analysis method to obtain the two tracks in FDC1 and FDC2 is mainly reported.

Neutron-neutron correlation in Borromean nuclei have been investigated by measuring the momentum distribution via the quasi-free (p,pn) reaction. We will report the result on 11Li.

The first kinematically complete measurement for the quasi-free (p,pn) reaction on Borromean nuclei 11Li, 14Be, and 17,19B was performed at RIBF in order to study dineutron correlation. Preliminary results on the dineutron correlation in 14Be and the spectroscopy of the unbound 13Be will be presented.

I will present the status report of SAMURAI17 experiment and future (p,n) studies and required developments in SAMURAI.

The density dependence of the nuclear symmetry energy governs important aspects of very neutron rich systems such as heavy nuclei and neutron stars. Many observables and experiments have been employed to probe the symmetry energy in regions below saturation density and constraints are emerging. At RIKEN, the SπRIT TPC and SAMURAI collaborations have completed a first campaign to extend these constraints to supra-saturation densities. I will discuss some of the scientific ideas to be explored in future campaigns with this powerful new device. This work is supported by the U.S. DOE under Grant Nos. DE-SC0004835, DE-SC0014530, DENA0002923, US NSF Grant No. PHY-1565546, the Japanese MEXT KAKENHI grant No. 24105004.

We measured the elastic scattering of polarized proton from 6He at 200 A MeV in June 2016 as SAMURAI13 experiment. Polarized proton target was used for the measurement. Status of the analysis will be presented.

We have performed the Coulomb excitation of 50,52Ca at around 240 AMeV. In this talk, the experimental setup and the status of the ongoing analysis will be given.

In November 2016, we performed the SAMURAI27 experiment. The aim is to search for unbound excited states of 31Ne, a deformed p-wave halo nuclei in the "island of inversion." So far its deformation properties have not been experimentally studied with direct methods. In the present study, we applied the invariant mass method to study the unbound states of 31Ne in the inelastic scattering reaction C(31Ne,30Ne+n) and one neutron removal reaction C(32Ne,30Ne+n) to produce the excited states. In addition, we performed the Coulomb breakup reaction Pb(31Ne,30Ne+n) to obtain further properties of the ground state. In this talk, the experimental setup and the analysis result will be reported.

The measurement methode, following the ideas outlined in a recently published paper [Kahlbow et al] will be presented. Furthermore a short summary on the performed experiment will be given as well as a brief analysis report.

Production cross section of neutron-rich nuclei has been measured with a deuterium operation of the MINOS setup at the SAMURAI. Secondary beams, consisting mainly of 58Ti, 57Sc, 51K, were irradiated on the liquid deuterium target and their fragments were identified with the SAMURAI spectrometer. Cross sections for one and two proton removal and charge exchange reactions will be reported in the workshop.

Short report about the SAMURAI 19 experiment

We have measured (p,2p) reaction on 8He this July with SAMURAI spectrometer to study multi-neutron systems 7H and 4n. Vertex-tracking MINOS target, NeuLAND+NEBULA neutron detector array, and large-coverage recoil proton calorimeter are also used in the current measurement.

The tetraneutron has attracted a lot of experimental and theoretical attention in recent years. The observation of a 4-neutron ground state resonance could deliver information about a three nucleons interaction and may contribute to further understanding of the equation of state in neutron stars. The 4n ground state resonance is created by using the 8He(p,p alpha)4n knock-out reaction. Three layers of silicon detectors determine the position of the reaction vertex in a liquid hydrogen target. The energy of the resonance is determined through the missing mass method using the four momenta of the scattered charged particles, which are measured in full kinematics with the SAMURAI spectrometer at the RIKEN facility in Japan. We developed a new setup of highly segmented 100 μm thin silicon detectors for vertex reconstruction in a 5 cm LH2 target. The detectors concept, its implementation and performance during the experiment will be presented. This work is supported by the SFB1245 of TU Darmstadt (DFG) and the DFG Cluster of Excellence "Origin and Structure of the Universe“.

I will report on the parasitic test experiment of the HIME detector performed at SAMURAI in Nov.-Dec., 2016. HIME (HIgh resolution detector array for Multi neutron Events) is a new-type high resolution neutron detector designed to detect multi neutrons at 100-300 MeV in coincidence with high resolution. High granularity of HIME enables us to track the recoil protons to distinguish the multi neutrons and to enhance the position and timing resolutions. I will also present about the tracking algorithm we have developed. Note that the proposal to use HIME to measure the correlation in the barely unbound nucleus has recently approved as grade-A at RIKEN NP-PAC meeting in Dec. 2016.

A high resolution particle telescope based on HPGe detectors was tested during the first part of the 18O campaign in a parasitic mode at the end of the fragment arm. Some preliminary results on its performance will be discussed.

10He is an unique quantum many-body system which has the largest N/Z ratio in the nuclear chart. Measuring the properties of 10He can provide a stringent test of shell-model and ab initio calculations. Starting from the pioneering work of Korsheninnikov et al. [1], several experiments have been carried out to study the resonance states in 10He. However, up to now, the energy of 10He ground state resonance is still under debate. The results from the 11Li(-p) [1, 2] and 14Be(-2p2n) [3] knockout reactions, provide a ground-state resonance lying at 1.2(3) MeV [1], 1.54(11) MeV [2] and 1.60(25) MeV [3], respectively, while the results from 3H(8He, p)10He transfer reaction suggest a much higher ground state at 2.1(2) MeV [4]. Recently, the inconsistency between these two methods has been investigated by theoretical calculations considering sudden removal of a proton from 11Li populating a three-body 10He continuum [5]. It has been discussed that the strong initial-state-structure (ISS) effects in 11Li knockout reaction altered the excitation spectrum of 10He, and the final state interaction (FSI) was found to play a minor role. It is evident that more exclusive measurements with higher statistics are needed to clarify the deviations between different methods. Therefore, we performed a new 11Li(p, 2p) knockout reaction at 250 AMeV at RIBF, RIKEN, using the MINOS device and SAMURAI spectrometer. A recoil proton detector (RPD), covering 30-65 degrees of polar angle, was used to measure the recoil and knocked-out protons. The invariant mass of 10He was reconstructed by the momentum of fragments and neutrons. In this talk, the preliminary results will be discussed. References [1] A. A. Korsheninnikov et al., Phys. Lett. B 326, 31 (1994). [2] H. T. Johansson et al., Nucl. Phys. A842, 15 (2010). [3] Z. Kohley et al., Phys. Rev. Lett. 109, 232501 (2012). [4] S. I. Sidorchuk et al., Phys. Rev. Lett. 108, 202502 (2012). [5] P. G. Sharov et al., Phys. Rev. C 90, 024610 (2014).

Current status and near-future perspectives of the experimental program with proton-rich nuclei will be presented with a particular focus on the ongoing development of the dual-gain preamplifiers for the silicon trackers and on the possible setup configuration for the campaign-type experiments.

Beta-delayed multiple-neutron emission of neutron-rich nuclei is crucial for studying the structure of n-rich nuclei as well as the origin of heavy elements. We propose a new experimental method to study this process via (p,n) charge-exchange reactions of n-rich nuclei in inverse kinematics. It decouples the beta-delayed neutron emissions into two parts: beta-decay and neutron emissions, and can be used to determine precisely the beta-delayed neutron emission branching ratios and furthermore to identify new beta-delayed multiple-neutron emitters. We propose to make the first proof-of-principle experiment using the well-known beta-delayed neutron emitters 29-31Na, then seek for about 5 new beta-delayed two-neutron and three-neutron emitters including 31-34Na (or others) and determine the branching ratios. The high-resolution and large-acceptance SAMURAI spectrometer coupled with the WINDS detector and the standard beam tracking detector system, is the ideal facility to perform such experiments. In this presentation, the principle of the new method and some details on the proposed experiment will be discussed.

Short review (~15min) of analysis techniques and procedures (DC tracking, particle and neutron identifications, etc) used for analyzing SAMURAI data on- and off-line. This presentation will also be the occasion to discuss needs for recently carried-out or future experiments (for example: multiple tracking in DCs, online analysis...)

I will present my work on calibrating the setup in the S21 experiment and show some first preliminary results from the analysis of the data. The focus will be on problems encountered during and possible remaining issues with the calibration. My first aim of the analysis is to find signatures of any unbound states in 30Ne, hence the focus is on particle identification and the neutron multiplicity in NeuLAND/NEBULA.

In recent years, shell evolution of Ne isotopes from N=20 to N=32 is emerging topic of interest [1]. Especially, the ground state of 33Ne known as an unbound state has not yet been measured [2]. The spectroscopic research of the 33Ne can help to establish the mass of the ground state as well as to study the shell evolution by comparing with the theoretical calculation. The experiment was carried out at the RIBF facility in RIKEN. The 34Na secondary beam with 268 MeV/nucleon was provided by BigRIPS [3] and directed towards the secondary carbon target before SAMURAI magnet. After the one proton knockout reaction, 33Ne which decays into 32Ne and neutron immediately was produced. The invariant mass spectrum was reconstructed by measurement data of fragments from several detectors with SAMURAI spectrometer. In this presentation, details of analysis and very preliminary results of the invariant mass spectrum of 32Ne + n will be reported. References [1] P. Doornenbal et al., Phys. Rev. Lett. 103, 032501 (2009). [2] T. Baumann, A. Spyrou, and M. Thoennessen, Rep. Prog. Phys. 75, 036301 (2012). [3] T. Kubo, Nucl. Instr. Meth. B 204, 97 (2003).

Revealing few aspects of analysis of S21 experiment.

I propose to present some calibration steps of the s021 experiment and possibly some preliminary results depending on the advances that will be made before the workshop. So far the calibrations for NeuLAND, NEBULA, BDCs, FDCs have been done and the calibrations for the HOD are in progress. If available, I will present the preliminary results for the structure of the 28F populated from both the 29F and the 29Ne.

The report on the ongoing analysis on the SAMURAI09 experiment will be given. It will include the analysis on the incoming beams and the outgoing charged particles. The result of calibrations for the gamma detectors CATANA and LaBr3 will also be given.

NeuLAND is the neutron detector for the R3B experiment at the FAIR facility. It is a fully active detector composed of plastic scintillator bars. Neutrons are detected by the production of charged particles in the scintillators through hadronic scattering. These charged particles are then detected by their scintillation light. Due to the highly granular design of NeuLAND, the primary neutron interaction points can be accurately reconstructed. These reconstructed points allow for kinematically complete reconstruction of reactions with relativistic heavy-ions beams, the goal of the R3B experiment. A demonstrator version of NeuLAND has been used in several experiments of the SAMURAI collaboration, including the recent tetraneutron experiment carried out in June and July 2017. For this tetraneutron experiment, an analysis tool called the NeuLANDConverter was developed. The NeuLANDConverter covers the full analysis procedure from raw TDC and QDC data to the reconstructed primary neutron interaction points. Moreover, it filters out the background by using the information from the NeuLAND VETO wall. The NeuLANDConverter provides output in the R3BRoot data format. This output was also added to the SAMURAI Merger, a program developed by the SAMURAI analysis team to gather the analysis results of all detectors in the setup. In this contribution, a complete overview of all analysis performed by the NeuLANDConverter is given.

NeuLAND analysis for EOS experiment is discussed.

The nuclear equation of state is a fundamental property of nuclear matter that describes relationships between energy, pressure, temperature, density, and isospin asymmetry in a nuclear system. The asymmetric part of EoS, which is originated by the isospin asymmetry, has not been well constrained yet above the saturation density, contrary to the symmetric part of EoS. Transport model calculations predict that pions generated by the heavy-ion collisions are sensitive probe to constrain the symmetry energy above the saturation density. The SπRIT Time Projection Chamber and ancillary trigger detectors were specifically designed and constructed to constraint the symmetry energy at above the saturation density using the radioactive isotope beams produced by the Radioactive Isotope Beam Factory (RIBF) at RIKEN by measuring pions as well as light ions. In this talk, I will present the progress of the analysis of the first experimental campaign ran in Spring 2016. Data was collected for the four collision systems: 132Sn+124Sn, 112Sn+124Sn, 124Sn+112Sn, and 108Sn+112Sn with beam energy of 270 AMeV. This work is supported by the U.S. DOE under Grant Nos. DE-SC0004835, DE-SC0014530, DE-NA0002923, US NSF Grant No. PHY-1565546, and by the Japanese MEXT KAKENHI grant No. 24105004.