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1. Optical potentials for the rare-isotope beam era

   https://doi.org/10.1088/1361-6471/acc348  

   Hebborn, C.; Nunes, F. M.; Potel, G.; Dickhoff, W. H.; Holt, J. W.; Atkinson, M. C.; Baker, R. B.; Barbieri, C.; Blanchon, G.; Burrows, M.; et al (April 2023, Journal of Physics G: Nuclear and Particle Physics)

   Abstract We review recent progress and motivate the need for further developments in nuclear optical potentials that are widely used in the theoretical analysis of nucleon elastic scattering and reaction cross sections. In regions of the nuclear chart away from stability, which represent a frontier in nuclear science over the coming decade and which will be probed at new rare-isotope beam facilities worldwide, there is a targeted need to quantify and reduce theoretical reaction model uncertainties, especially with respect to nuclear optical potentials. We first describe the primary physics motivations for an improved description of nuclear reactions involving short-lived isotopes, focusing on its benefits for fundamental science discoveries and applications to medicine, energy, and security. We then outline the various methods in use today to build optical potentials starting from phenomenological, microscopic, andab initiomethods, highlighting in particular, the strengths and weaknesses of each approach. We then discuss publicly-available tools and resources facilitating the propagation of recent progresses in the field to practitioners. Finally, we provide a set of open challenges and recommendations for the field to advance the fundamental science goals of nuclear reaction studies in the rare-isotope beam era. This paper is the outcome of the Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program ‘Optical Potentials in Nuclear Physics’ held in March 2022 at FRIB. Its content is non-exhaustive, was chosen by the participants and reflects their efforts related to optical potentials. 

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2. Design and construction of a novel energy-loss optical scintillation system (ELOSS) for heavy‐ion particle identification

   https://doi.org/10.1063/5.0124846  

   Cortesi, M.; Dziubinski, S.; Gade, A.; Zegers, R.; Pereira, J.; Asciutto, J.; Lidia, S.; Bazin, D. (December 2022, Review of Scientific Instruments)

   We present the development of a novel heavy-ion particle-identification (PID) device based on an energy-loss measurement to be implemented in the focal plane of the S800 spectrograph of the Facility for Rare Isotope Beams (FRIB). The new instrument consists of a multi-segmented optical detector [energy-loss optical scintillation system (ELOSS)] that is filled with xenon at pressures ranging from 400 to 800 Torr. The gas volume is surrounded by arrays of photomultiplier tubes and placed along the direction of the beam for recording the prompt scintillation light. The number of detected photons, which is proportional to the energy deposited by the beam particle along its track in the detector volume, allows one to identify the corresponding atomic number (Z). The ELOSS technology is expected to provide high-resolution ΔE measurements (≤0.6% σ) at a high counting rate (>50 kHz). In addition, it has the capability of providing timing information with around 150 ps resolution (σ) compared to the lack of useable timing information of the conventional ionization chamber relying on drifting charges. The development of fast, accurate ΔE measurement techniques for present and future nuclear science facilities will have a high impact on the design and implementation of rare-isotope beam experiments at FRIB and their scientific outcome. As such, ELOSS also represents a prototype for the development of PID detector systems of other planned and future spectrometers, such as the high rigidity spectrometer at FRIB. 

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3. Machine learning enabled measurements of astrophysical ( $p,n$ ) reactions with the SECAR recoil separator

   https://doi.org/10.1103/PhysRevResearch.7.013074  

   Tsintari, P; Dimitrakopoulos, N; Garg, R; Hermansen, K; Marshall, C; Montes, F; Perdikakis, G; Schatz, H; Setoodehnia, K; Arora, H; et al (January 2025, Physical Review Research)

   The synthesis of heavy elements in supernovae is affected by low-energy $(n,p)$and $(p,n)$reactions on unstable nuclei, yet experimental data on such reaction rates are scarce. The SECAR (SEparator for CApture Reactions) recoil separator at FRIB (Facility for Rare Isotope Beams) was originally designed to measure astrophysical reactions that change the mass of a nucleus significantly. We used a novel approach that integrates machine learning with ion-optical simulations to find an ion-optical solution for the separator that enables the measurement of $(p,n)$reactions, despite the reaction leaving the mass of the nucleus nearly unchanged. A new measurement of the ${}^{58}\mathrm{Fe}(p,n){}^{58}\mathrm{Co}$reaction in inverse kinematics with a $3.66\pm 0.12$MeV/nucleon ${}^{58}\mathrm{Fe}$beam (corresponding to $3.69\pm 0.12$MeV proton energy in normal kinematics) yielded a cross-section of $20.3\pm 6.3$ mb and served as a proof of principle experiment for the new technique demonstrating its effectiveness in achieving the required performance criteria. This novel approach paves the way for studying astrophysically important $(p,n)$reactions on unstable nuclei produced at FRIB. Published by the American Physical Society2025 

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4. Formation of negative-ion resonance and dissociative attachment in collisions of NO ₂ with electrons

   https://doi.org/10.1088/1361-6455/ac2c8b  

   Liu, Hainan; Jiang, Xianwu; Yuen, Chi-Hong; Kokoouline, Viatcheslav; Ayouz, Mehdi (September 2021, Journal of Physics B: Atomic, Molecular and Optical Physics)

   Abstract The process of electron attachment to the NO 2 molecule is investigated theoretically using an approach based on a study by O’Malley (1966 Phys. Rev. 150 14). The approach combines the normal mode approximation for representation of vibrational dynamics of NO 2 and one-dimensional treatment, along each normal mode, of the attachment process as in O’Malley’s theory, such that only a modest computational effort is required to compute the attachment cross section. Taking into account the survival probability of the formed resonant state of N O 2 − , the cross section for dissociative electron attachment to NO 2 is also estimated. To compare with available experimental data, the theoretical cross section is convoluted with energy distribution of NO 2 –e − collisions with uncertainties reported in experimental studies. Peak values of the convoluted theoretical cross section are found to be about a factor of 2–10 larger than the experimental results. 

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5. Molecular Polaritonics:Chemical Dynamics Under Strong Light–Matter Coupling

   Tao E. Li, Bingyu Cui (December 2021, Annual review of physical chemistry)

   Chemical manifestations of strong light–matter coupling have recently been a subject of intense experimental and theoretical studies. Here we review the present status of this field. Section 1 is an introduction to molecular polaritonics and to collective response aspects of light–matter interactions. Section 2 provides an overview of the key experimental observations of these effects, while Section 3 describes our current theoretical understanding of the effect of strong light–matter coupling on chemical dynamics. A brief outline of applications to energy conversion processes is given in Section 4. Pending technical issues in the construction of theoretical approaches are briefly described in Section 5. Finally, the summary in Section 6 outlines the paths ahead in this exciting endeavor. 

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