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Pion energy spectra are presented for central collisions of neutron-rich 132Sn+124Sn and neutron-deficient 108Sn+112Sn systems using simulations with Boltzmann-Uehling-Uhlenbeck transport model. These calculations, which incorporate isospin-dependent mean field potentials for relevant baryons and mesons, display a sensitivity to the pion spectra that could allow significant constraints on the density dependence of the symmetry energy and its mean field potential at supra-saturation densities. The predicted sensitivity increases with the isospin asymmetry of the total system and decreases with incident energy.
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The degree of freedom of spin in quantum systems serves as an unparalleled laboratory where intriguing quantum physical properties can be observed, and the ability to control spin is a powerful tool in physics research. We propose a novel method for
controlling spin in a system of rare isotopes which takes advantage of the mechanism of the projectile fragmentation reaction combined with the momentum-dispersion matching technique. The present method was verified in an experiment at the RIKEN RI Beam Factory, in which a degree of alignment of 8% was achieved for the spin of a rare isotope Al-32. The figure of merit for the present method was found to be greater than that of the conventional method by a factor of more than 50.
We have calculated the proton analyzing power A_{y0} of the pion-production reaction from pd collisions for one energy close to threshold and for another in the region of the $Delta$-resonance. A fair reproduction of the experimental data could be obtained in both cases with a model which includes isoscalar and isovector $pi N$ rescatterings in s waves, as well as the p-wave rescattering mechanisms mediated by the $pi NN$ and $pi N Delta$ vertices. For the analyzing power at threshold we found that the initial-state interaction (ISI) is also quite important.
We test the presence of pion-nucleon isoscalar off-shell effects in the $pdto pi^+ t$ reaction around the threshold region. We find that these effects significantly modify the production cross section and that they may provide the missing strength needed to reproduce the data at threshold.
Values of the proton analysing power in the $pdto{}^{3}textrm{He},pi^0/^{3}textrm{H},pi^+$ reactions at 350-360~MeV per nucleon were obtained by using a polarised proton beam incident on a deuterium cluster-jet target and with a polarised deuteron beam incident on a target cell filled with polarised hydrogen. These results have a much larger angular coverage than existing data. First measurements are also presented of the deuteron vector analysing power and the deuteron-proton spin correlations. Data were also obtained on the deuteron-proton spin correlation and proton analysing power at small angles at 600~MeV per nucleon, though the angular coverage at this energy was much more restricted even when using a deuteron beam. By combining the extrapolated values of the spin correlations to the forward or backward directions with published measurements of the deuteron tensor analysing powers, the relative phases between the two non-vanishing amplitudes were evaluated.
The reaction $NN to NN pi$ offers a good testing ground for chiral effective field theory at intermediate energies. It challenges our understanding of the first inelastic channel in nucleon-nucleon scattering and of the charge-symmetry breaking pattern in hadronic reactions. In our previous studies, we presented a complete calculation of the pion-production operator for s-wave pions up-to-and-including next-to-next-to-leading order (NNLO) in the formulation of chiral effective field theory, which includes pions, nucleons and $Delta(1232)$ degrees of freedom. In this paper we calculate the near threshold cross section for the $pp to d pi^{+}$ reaction by performing the convolution of the obtained operators with nuclear wave functions based on modern phenomenological and chiral potentials. The available chiral $NN$ wave functions are constructed with a cutoff comparable with the momentum transfer scale inherent in pion production reactions. Hence, a significant portion of the dynamical intermediate-range physics is thereby cut off by them. On the other hand, the NNLO amplitudes evaluated with phenomenological wave functions appear to be largely independent of the $NN$ model used and give corrections to the dominant leading order contributions as expected from dimensional analysis. The result gives support to the counting scheme used to classify the pion production operators, which is a precondition for a reliable investigation of the chirally suppressed neutral pion production. The explicit inclusion of the $Delta(1232)$ is found to be important but smaller than expected due to cancellations.
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