BM@N Data Analysis Aimed at Studying SRC Pairs: One-Step Single Nucleon Knockout Measurement in Inverse Kinematics Out of a 48 GeV/c12^{12}C Nucleus

International audienceNucleon knockout reactions with high energy probes are widely used to reveal the inner structure of nuclei, however, they cannot be applied to study unstable nuclei. We recently demonstrated the feasibility to access single particle and short-range correlation (SRC) properties in nuclei with hadronic probes in inverse kinematics, opening the pathway for such studies in short-lived nuclei at upcoming accelerator facilities. The experiment was carried out using the BM@N setup at JINR. A $^{12}$C beam at 4 GeV/c/u impinged on a liquid hydrogen target using a kinematically complete reaction. We show that by selecting the fragment in the $^{{12}}$C($p$,$2p$)$^{{11}}$B reaction, limitations posed by final-state interactions are overcome and single nucleon properties are probed in a single-step knockout reaction. The ground-state distributions are in agreement with theoretical calculations. We probe SRCs in the same way by the break up of SRC pairs in $^{{12}}$C($p$,$2pN$)$^{{10}}$B/$^{{10}}$Be reactions. We not only identify SRCs in such kinematical conditions for the first time but also deduce factorization and other pair properties from direct measurements. The ongoing analysis continues with the study of multi-fragmentation following quasielastic and SRC pair removal, and with 4-fold coincidence events including the recoil neutron being detected. We are also conducting studies to optimize the experimental conditions for the next scheduled beam time in 2021

Unperturbed inverse kinematics nucleon knockout measurements with a carbon beam

From superconductors to atomic nuclei, strongly-interacting many-body systems are ubiquitous in nature. Measuring the microscopic structure of such systems is a formidable challenge, often met by particle knockout scattering experiments. While such measurements are fundamental for mapping the structure of atomic nuclei, their interpretation is often challenged by quantum mechanical initial- and final-state interactions (ISI/FSI) of the incoming and scattered particles. Here we overcome this fundamental limitation by measuring the quasi-free scattering of 48 GeV/c 12C ions from hydrogen. The distribution of single protons is studied by detecting two protons at large angles in coincidence with an intact 11B nucleus. The 11B detection is shown to select the transparent part of the reaction and exclude the otherwise large ISI/FSI that would break the 11B apart. By further detecting residual 10B and 10Be nuclei, we also identified short-range correlated (SRC) nucleon-nucleon pairs, and provide direct experimental evidence for the separation of the pair wave-function from that of the residual many-body nuclear system. All measured reactions are well described by theoretical calculations that do not contain ISI/FSI distortions. Our results thus showcase a new ability to study the short-distance structure of short-lived radioactive atomic nuclei at the forthcoming FAIR and FRIB facilities. These studies will be pivotal for developing a ground-breaking microscopic understanding of the structure and properties of nuclei far from stability and the formation of visible matter in the universe.Comment: Accepted for publication in Nature Physics. 28 pages, 19 figures, and 1 table including main text, Methods, and Supplementary material