Nuclear Experiment

An inelastic excitation and cluster-decay experiment 2 H ( 16 C, 4 He+ 12 Be or 6 He+ 10 Be) 2 H was carried out to investigate the linear-chain clustering structure in neutron-rich 16 C . For the first time, decay-paths from the 16 C resonances to various states of the final nuclei were determined, thanks to the well-resolved Q -value spectra obtained from the three-fold coincident measurement. The close-threshold resonance at 16.5 MeV is assigned as the J π = 0 + band head of the predicted positive-parity linear-chain molecular band with (3/ 2 − π ) 2 (1/ 2 − σ ) 2 configuration, according to the associated angular correlation and decay analysis. Other members of this band were found at 17.3, 19.4, and 21.6 MeV based on their selective decay properties, being consistent with the theoretical predictions. Another intriguing high-lying state was observed at 27.2 MeV which decays almost exclusively to 6 He+ 10 Be(∼6 MeV) final channel, corresponding well to another predicted linear-chain structure with the pure σ -bond configuration.

High-spin states in 84Rb are studied by using the 70Zn(18O, p3n)84Rb reaction at a beam energy of 75 MeV. Three high-lying negative-parity bands are established, whose level spacings are very regular, i.e., there is no signature splitting. The dipole character of the transitions of these three bands is assigned by the gamma-gamma directional correlations of oriented states (DCO) intensity ratios and the multipolarity M1 is suggested by analogy with multiparticle excitations in neighboring nuclei. Strong M1 and weak or no E2 transitions are observed. All these characteristic features show they are magnetic rotational bands.

All existing positive results on two-neutrino double beta decay and two-neutrino double electron capture in different nuclei have been analyzed. Weighted average and recommended half-life values for 48 Ca, 76 Ge, 82 Se, 96 Zr, 100 Mo, 100 Mo - 100 Ru ( 0 + 1 ), 116 Cd, 128 Te, 130 Te, 136 Xe, 150 Nd, 150 Nd - 150 Sm ( 0 + 1 ), 238 U, 78 Kr, 124 Xe and 130 Ba have been obtained. Given the measured half-life values, effective nuclear matrix elements for all these transitions were calculated.

We report high-precision mass measurements of 50−55 Sc isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for 53−55 Sc. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers N=32 and N=34 above proton-magic Z=20 . In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the N=32 isotone, confirming that the empirical neutron shell gap energies peak at the doubly-magic 52 Ca. Moreover, our data, combined with other recent measurements, does not support the existence of closed neutron shell in 55 Sc at N=34 . The results were compared to predictions from both \emph{ab initio} and phenomenological nuclear theories, which all had success describing N=32 neutron shell gap energies but were highly disparate in the description of the N=34 isotone.

The precision measurement of the β− spectrum shape for 210 Bi (historically RaE) have been performed with a spectrometer based on semiconductor Si(Li) detector. This first forbidden non-unique transition has the transition form-factor strongly deviated from unity and knowledge of its spectrum would play an important role in low-background physics in presence of 210 Pb background. The measured transition form-factor could be approximated as S(W)=1+(−0.4363±0.0037)W+(0.0523±0.0010) W 2 , that is in good agreement with previous studies and has significantly increased parameter precision.

The form factor of the electromagnetic excitation of 12 C to its 2 + 1 state was measured at extremely low momentum transfers in an electron scattering experiment at the S-DALINAC. A combined analysis with the world form factor data results in a reduced transition strength B(E2; 2 + 1 → 0 + 1 )=7.63(19) e 2 fm 4 with an accuracy improved to 2.5\%. In-Medium-No Core Shell Model results with interactions derived from chiral effective field theory are capable to reproduce the result. A quadrupole moment Q( 2 + 1 )=5.97(30) efm 2 can be extracted from the strict correlation with the B((E2) strength emerging in the calculations.

We propose a high-statistics measurement of few body nuclear structure and short range correlations in quasi-elastic scattering at 6.6 GeV from 2 H, 3 He and 3 H targets in Hall B with the CLAS12 detector. We will measure absolute cross sections for (e, e ′ p) and (e, e ′ pN) quasi-elastic reaction channels up to a missing momentum p miss ≈1 GeV/c over a wide range of Q 2 and x B and construct the isoscalar sum of 3 H and 3 He. We will compare (e, e ′ p) cross sections to nuclear theory predictions using a wide variety of techniques and NN interactions in order to constrain the NN interaction at short distances. We will measure (e, e ′ pN) quasi-elastic reaction cross sections and (e, e ′ pN)/(e, e ′ p) ratios to understand short range correlated (SRC) NN pairs in the simplest non-trivial system. 3 H and 3 He, being mirror nuclei, exploit the maximum available isospin asymmetry. They are light enough that their ground states are readily calculable, but they already exhibit complex nuclear behavior, including NN SRCs. We will also measure 2 H (e, e ′ p) in order to help theorists constrain non-quasielastic reaction mechanisms in order to better calculate reactions on A=3 nuclei. Measuring all three few body nuclei together is critical, in order to understand and minimize different reaction effects, such as single charge exchange final state interactions, in order to test ground-state nuclear models. We will also measure the ratio of inclusive (e, e ′ ) quasi-elastic cross sections (integrated over x B ) from 3 He and 3 H in order to extract the neutron magnetic form factor G n M at small and moderate values of Q 2 . We will measure this at both 6.6 GeV and 2.2 GeV.

We present measurements of differential cross sections and analyzing powers for the elastic 2H(~d; d)d scattering process. The data were obtained using a 130 MeV polarized deuteron beam. Cross sections and spin observables of the elastic scattering process were measured at the AGOR facility at KVI using two independent setups, namely BINA and BBS. The data harvest at setups are in excellent agreement with each other and allowed us to carry out a thorough systematic analysis to provide the most accurate data in elastic deuteron-deuteron scattering at intermediate energies. The results can be used to confront upcoming state-of-the-art calculations in the four-nucleon scattering domain, and will, thereby, provide further insights in the dynamics of three- and four-nucleon forces in few-nucleon systems.

An experimental overview of anisotropic flow measurements and their ability to probe the properties and the nature of the system created in ultra-relativistic hadron collisions is given in these proceedings. The aim is to discuss the state-of-the-art measurements ranging from small to large systems at different collision energies.

The Facility for Antiproton and Ion Research (FAIR) in Darmstadt will provide unique research opportunities for the investigation of fundamental open questions related to nuclear physics and astrophysics, including the exploration of QCD matter under extreme conditions, which governs the structure and dynamics of cosmic objects and phenomena like neutron stars, supernova explosions, and neutron star mergers. The physics program of the Compressed Baryonic Matter (CBM) experiment is devoted to the production and investigation of dense nuclear matter, with a focus on the high-density equation-of-state (EOS), and signatures for new phases of dense QCD matter. According to the present schedule, the CBM experiment will receive the first beams from the FAIR accelerators in 2025. This article reviews promising observables, outlines the CBM detector system, and presents results of physics performance studies.