1. A High Rigidity Spectrometer for FRIB Remco Zegers for the HRS working group HRS whitepaper – 2014 1 st FRIB-China Workshop on Physics of Nuclei and Hadrons May 28-30, 2015 https://www.phy.anl.gov/nsac-lrp/Whitepapers/HRS%20white%20paper.pdf

2. Whitepaper contributors & Users 2 Argonne National LaboratoryHope CollegeTexas A&M University Augustana CollegeIndiana UniversityUniversity of Notre Dame Bucknell UniversityKalamazoo CollegeUniversity of Tennessee Central Michigan University Lawrence Berkeley National LaboratoryUniversity of Washington Florida State University Los Alamos National LaboratoryUrsinus College Gettysburg CollegeMichigan State UniversityWabash College Hampton UniversityOhio UniversityWestmont College Users from the following US institutions contributed to the white paper In addition, researchers from institutions in Canada (TRIUMF), Europe (GSI and FAIR) and Japan (RIBF, RIKEN) and their users, were involved and contributed to the whitepaper. Based on the experiences with the S800/Sweeper and the size of the FRIB users community, a user community of over 500 scientists for the HRS is expected

3. Endorsements 2014 Town Meetings In the resolution of the 2014 APS Division of Nuclear Physics Town Meeting on Nuclear Structure, timely construction of the HRS as a state-of-the-art instrument for FRIB was recommended. In the resolution of the 2014 APS Division of Nuclear Physics Town Meeting on Nuclear Astrophysics, the HRS was listed as a critical piece of equipment, and the development and implementation was recommended. 3 The FRIB Scientific Advisory Committee (SAC) has continuously endorsed the scientific need for the HRS in its assessments of the plans presented by the HRS Working Group: “The SAC viewed the science addressed in your submission as having the highest scientific priority and this was communicated to the FRIB Laboratory Director…The SAC views the activity of your group as central to the FRIB mission and encourages your continued actions…The HRS is one of the flagship projects at FRIB. To facilitate the fast beam programs, the HRS is designed to be coupled with detectors necessary for experiments enabling techniques such as missing-mass, in-beam gamma and invariant mass in inverse reactions…The HRS is necessary to conduct the scientific mission of FRIB.”

4. Spectrometers for fast beams at NSCL The magnetic rigidity of the S800 and Sweeper are limited to ~4 Tm.

5. Ancillary detectors used at S800 & Sweeper enable a very diverse scientific program 5 SeGACAESAR GRETINA PLUNGER HiRA LENDA LH 2 /LD 2 target Diamond Tracking About half of all NSCL experiments are with S800 spectrograph or Sweeper

6. Optimizing the scientific opportunities at FRIB FRIB will produce the most exotic isotopes at unprecedented intensities by fast fragmentation of heavy-ion beams To minimize losses, experiments with the most exotic species are best performed at the energy at which maximum production rate is achieved Available spectrometers at NSCL lack necessary bending power – the proposed HRS overcomes this serious limitation 6

7. The magnetic rigidity (B  ) required for achieving the maximum rare-isotope beam intensity is larger than 4 Tm for almost all species produced at FRIB, and ranges up to 8 Tm for the most neutron-rich species S800 and sweeper spectrometers currently available at NSCL have bending limits of 4 Tm The High Rigidity Spectrometer at FRIB 7

8. The gains are strongest for the most neutron-rich systems. Luminosity gains are more than a factor of 10 for neutron-rich isotopes: same effect as having 4000 kW primary beam power instead of 400 kW Tremendous increase of the discovery potential of FRIB, including at early operations when beam power is not yet maximal The HRS will increase the luminosity for experiments with fast rare-isotope beams for the vast majority of nuclei available at FRIB 8

9. Luminosities at the HRS 1) The rare-isotope beam delivery rate to the experimental station is up to 5 times higher when beams are produced at the optimal beam energy compared to the rate when slowed down to match currently available rigidities at NSCL. The gains are highest for the most neutron-rich species. 9 2) Luminosities at optimum rigidity are further increased by significant factors because thick reaction targets can be used 60 Ca on 9 Be for fixed d  of 5% to ensure energy resolutions ~ 2% (FWHM) for experiments with GRETA@HRS optimum rigidity for production x4 luminosity

10. 3) At higher beam energies, charge- state production is reduced, increasing yields and simplifying experiments; Most important for experiments with heavier nuclei 10 Luminosities at the HRS Luminosity gains with the HRS exceed a factor of 10 for experiments with neutron-rich rare isotopes for which the potential for scientific discovery is highest

11. 11 NoProgram 1Study of Shell Structure 2Superheavy Elements 3Neutron Skins 4Pairing 5Nuclear Symmetries 6Equation of State 7r-process 8 15 O( α, γ ) 9 59 Fe s-process 10Medical Isotopes 11Stewardship 12Atomic EDM 13Limits of Stability 14Halo Nuclei 15Mass Surface 16rp-process 17Weak Interactions Scientific program of the HRS: Is responsive to 12 of 17 NSAC RIB Task Force benchmarks Covers all four overarching questions of the NRC decadal study How did visible matter come into being and how does it evolve? How does subatomic matter organize itself and what phenomena emerge? Are the fundamental interactions that are basic to the structure of matter fully understood? How can the knowledge and technological progress provided by nuclear physics best be used to benefit society?

12. Evolution of nuclear structure Study the modification of the nuclear potential, the impact of the nucleon- nucleon interaction on single-particle energies and increased many-body correlations far some stability to generate a complete description of nuclei, with applications in stewardship science and astrophysics Tools: invariant mass spectroscopy (at the dripline) in-beam  -ray spectroscopy with intermediate-energy Coulomb excitation inelastic proton scattering and nucleon removal reactions inelastic and charge-exchange reactions recoil-distance Doppler-shift measurements isomer and fission studies commensal decay spectroscopy … S. Suchyta et al., PRC89, 021301(R) (2014)

13. Gretina  -detection S800 Spectrograph+Gretina first campaign 2012-2013 Gamma-Ray Energy Tracking In-beam Nuclear Array S800 Spectrograph Highly successful science campaign with 24 experiments

14. Proposed by the GRETINA/GRETA community 14 Efficiency (~40% at 1 MeV) 4 π Coverage: Angular distributions/correlations. High-energy efficiency by proper summing of scattered γ -rays, no solid angle lost to Compton shields Position resolution ( σ x,y,z = 2 mm) Position of 1 st interaction  Excellent Doppler reconstruction, in-beam energy resolution Excellent peak-to-background ratio Tracking  Reject partial-energy events, maintaining good spectral quality https://www.phy.anl.gov/nsac-lrp/Whitepapers/GRETA_WP_LE_TM_Full.pdf

15. Understanding the nuclear force – Changes in the nuclear shell structure 15 The neutron-rich Ca isotopes beyond 48 Ca provide textbook examples of shell evolution Microscopic calculations suggest a sensitivity of the detailed structure to the inclusion of a variety of many-body correlations, including 3N forces GRETA@HRS (simulated) 9 Be( 61 Sc, 60 Ca+  ) 50 Ca -> 49 Ca GRETINA @ NSCL GEANT4 simulation 57 Ca -> 56 Ca γ-γ Detailed studies of single particle structure, provide a critical test of effective interactions and 3N forces The structure around 60 Ca informs the location of the drip line at Z = 20 GRETA@HRS will have superior sensitivity for fast-beam experiments compared to any other γ -ray detector

16. Nuclear structure beyond the neutron drip line – Invariant mass spectroscopy 16 Highly successful program at NSCL will be extended along the neutron drip line to heavier systems: excellent discovery potential for: Evolution of shell-structure away from stability; the discovery of new magic numbers New phenomena, such as the recently discovered two-neutron radioactivity of 26 O Decay properties reveal many-body correlations in nuclei and connect to open quantum systems Layout of HRS is optimized to detect neutrons at forward angles for invariant mass spectroscopy

17. Nuclear Astrophysics Nuclear Astrophysics: understand the nuclear reactions and processes that drive stellar evolution and nucleosynthesis, provide the nuclear physics input to interpret astronomical observation with complete simulations of astrophysical phenomena and objects Some of the experimental tools available at HRS Heavy-ion collisions and projectile multifragmentation charge-exchange reactions/weak reactions proton and alpha decay branching ratios measurements time-of-flight mass measurements invariant-mass spectroscopy … SN 1994D ESA/Hubble Müller, E. and Janka, H.-T. A&A 317, 140–163, (1997)

18. Time-of-flight mass measurements reaching the r-process Masses can be deduced from the simultaneous measurement of an ion's time-of- flight, charge, and magnetic rigidity thorough a magnetic system of a known flight path With the HRS at FRIB, this will approach can reach a large fraction of the r process nuclei up to N=100 and comes close to the r-process path beyond Masses are crucial for modeling the r process and so finally unraveling its site 18 65m flight path to the end of the HRS, ~400ns flight time at FRIB energies and anticipated TOF and position detector resolutions allow for 0.2 MeV precision for masses around N=100

19. Weak reaction rate for nuclear astrophysics 19 Supernovae are considered as major sources of nucleosynthesis and their shockwaves drive galactic chemical evolution Understanding the evolution of core-collapse and thermonuclear supernovae, as well as crustal processes in neutron stars requires an accurate knowledge of reaction rates mediated via the weak force (e-capture/  -decay/neutrino-induced) on medium-heavy nuclei Charge-exchange reactions at intermediate energies in are the best way to measure relevant weak-interaction strengths distributions and benchmark theoretical models Inverse kinematics (10 4 pps needed) – ( 7 Li, 7 Be+ γ ) – HRS+GRETA – (d, 2 He) – HRS and Active Target TPC – (p,n) – HRS+LENDA Recent result with LENDA@S800 56 Ni(p,n) in inverse kinematics

20. Scope 1.A high-rigidity, large-acceptance beam line to transport the rare isotopes with minimal losses from the FRIB fragment separator to the HRS spectrometer 2.A sweeper dipole behind the reaction target for diverting charged particles 3.A focusing beam line that transports the diverted particles from the sweeper dipole to two spectrometer dipoles for analysis 4.Two spectrometer dipoles for identifying and analyzing charged particles 5.Charge-particle detectors that are i) placed in the beam lines for tracking rare-isotopes that are impinged on the reaction target, and ii) placed in the focusing beam line and final focal plane to analyze the particles emerging from reactions in the target 6.Civil infrastructure to house the HRS 20 1 2 3 4 5 6

21. High Rigidity Spectrometer Pre-conceptual (first order) ion-optical design 21 Spectrometer Magnetic bending power: up to 8 Tm Large momentum (10% dp/p) and angular acceptances (80x80 mrad) Particle identification capabilities extending to heavy masses (~200) Momentum resolution 1 in 5000; intermediate image after sweeper Dispersion: 7cm/% Invariant mass spectroscopy:  6 o opening in sweeper dipole for neutrons Beam transport Dispersion-matching capability Beam line from fragment separator designed to optimize transmission to HRS

22. HRS Project Notional Budget 22 EquipmentLaborTotal* Including contingency Beam line $3.9M$4.8M$8.7M$11.4M HRS $4.1M$8.3M$12.4M$17.8M Total $8.0M$13.1M$21.1M$29.1M *Excludes civil infrastructure Because of the high impact on the FRIB science program, completion of the HRS by ~2024 is envisioned

23. Summary The fast-beam program with the High Rigidity Spectrometer (HRS) will optimize the discovery potential of FRIB by enabling experiments at the highest intensities with the most neutron-rich isotopes. Gain factors in luminosity of factors of 10 or more can be achieved, with the largest gains for the most exotic species. The HRS will increase the scientific reach from other state-of- the-art and community-priority devices, such as the Gamma-Ray Energy Tracking Array (GRETA) and the Modular Neutron Array (MoNA-LISA), in addition to other ancillary detectors. There are many opportunities to collaborate on the HRS and the associated science program, and this is a good time to consider such opportunities. 23