Observation of Three-Neutron Sequential Emission from ²⁵O

Background: Measurements of neutron-unbound states can test nuclear models in very neutron-rich nuclei that in some cases cannot be probed with other methods. Purpose: Search for highly excited neutron-unbound states of 25O above the three neutron separation energy. Method: The decay energy of 25O was reconstructed using the invariant mass spectroscopy method. A 101.3 MeV/u 27Ne beam collided with a liquid deuterium target. Two-proton removal reactions populated excited 25O that decayed into three neutrons and an 22O fragment. The neutrons were detected by arrays of plastic scintillator bars, while a 4 Tm dipole magnet placed directly after the target redirected charged fragments to a series of charged-particle detectors. The data were compared with detailed Monte Carlo simulations of the reaction process and subsequent decay. Results: The data show evidence of neutron-unbound level(s) in 25O at an excitation energy of about 9 MeV which decay sequentially by the emission of three neutrons to 22O. Conclusion: The observation of resonance strength in 25O at about 9 MeV is consistent with shell-model/eikonal calculations for the two-proton removal reaction from 27Ne.</p

Neutron-unbound states in 31Ne

Background: The Island of Inversion near the N = 20 shell gap is home to nuclei with reordered single-particle energy levels compared to the spherical shell model. Studies of 31 Ne have revealed that its ground state has a halo component, characterized by a valence neutron orbiting a deformed 30 Ne core. This lightly-bound nucleus with a separation energy of only Sn = 170 keV is expected to have excited states that are neutron unbound. Purpose: The purpose of this experiment was to investigate the low-lying excited states in 31 Ne that decay by the emission of a single neutron. Methods: An 89 MeV/nucleon 33 Mg beam impinged on a segmented Be reaction target. Neutron-unbound states in 31 Ne were populated via a two-proton knockout reaction. The 30 Ne fragment and associated neutron from the decay of 31 Ne were detected by the MoNA-LISA-Sweeper experimental setup at the National Superconducting Cyclotron Laboratory. Invariant mass spec-troscopy was used to reconstruct the two-body decay energy (30 Ne + n). Results: The two-body decay energy spectrum exhibits two features: a low-lying peak at 0.30 ± 0.17 MeV and a broad enhancement at 1.50 ± 0.33 MeV, each fit with an energy-dependent asymmetric Breit-Wigner line shape representing a resonance in the continuum. Accompanying shell model calculations using the FSU interaction within NuShellX, combined with cross-section calculations using the eikonal reaction theory, indicate that these peaks in the decay energy spectrum are caused by multiple resonant states in 31 Ne. Conclusions: Excited states in 31 Ne were observed for the first time. Transitions from calculated shell model final states in 31 Ne to bound states in 30 Ne are in good agreement with the measured decay energy spectrum. Cross-section calculations for the two-proton knockout populating 31 Ne states as well as spectroscopic factors pertaining to the decay of 31 Ne into 30 Ne are used to examine the results within the context of the shell model expectations

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

International audienceThis is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection