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Register a new userModelling nucleon-nucleon scattering above 1 GeV
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Motivated by the recent measurement of proton-proton spin-correlation parameters up to 2.5 GeV laboratory energy, we investigate models for nucleon-nucleon (NN) scattering above 1 GeV. Signatures for a gradual failure of the traditional meson model with increasing energy can be clearly identified. Since spin effects are large up to tens of GeV, perturbative QCD cannot be invoked to fix the problems. We discuss various theoretical scenarios and come to the conclusion that we do not have a clear phenomenological understanding of the spin-dependence of the NN interaction above 1 GeV.
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Deuteron-deuteron elastic scattering and transfer reactions in the energy regime above four-nucleon breakup threshold are described by solving exact four-particle equations for transition operators. Several realistic nuclear interaction models are used, including the one with effective many-nucleon forces generated by the explicit $Delta$-isobar excitation; the Coulomb force between protons is taken into account as well. Differential cross sections, deuteron analyzing powers, outgoing nucleon polarization, and deuteron-to-neutron polarization transfer coefficients are calculated at 10 MeV deuteron energy. Overall good agreement with the experimental data is found. The importance of breakup channels is demonstrated.
Magnetic field effects on free nucleons are studied in peripheral collisions of $^{197}$Au + $^{197}$Au at energies ranging from 600 to 1500 MeV/nucleon by utilizing an isospin-dependent quantum molecular dynamics (IQMD) model. With the help of angular distributions and two-particle angular correlators, the magnetic field effect at an impact parameter of 11 fm is found to be more obvious than at an impact parameter of 8 fm. Moreover, the results suggest that with an increase in the number of peripheral collisions, protons are more easily condensed with the magnetic field. Magnetic field effects are further investigated by the ratio of free neutrons to free protons as functions of a two-particle correlator $C_{2}$, four-particle correlator $C_{4}$ and six-particle correlator $C_{6}$ of angle $phi$, rapidity $Y$ and transverse momentum $p_{T}$. The results show that weak magnetic field effects could be revealed more clearly by these multiple-particle correlators, with the larger number of particle correlators demonstrating a clear signal. The results highlight a new method to search for weak signals using multi-particle correlators.
We review the major progress of the past decade concerning our understanding of the nucleon-nucleon interaction. The focus is on the low-energy region (below pion production threshold), but a brief outlook towards higher energies is also given. The items discussed include charge-dependence, the precise value of the $pi NN$ coupling constant, phase shift analysis and high-precision NN data and potentials. We also address the issue of a proper theory of nuclear forces. Finally, we summarize the essential open questions that future research should be devoted to.
The one-pion and two-pion production in the p(alpha, alpha prime)X reaction at an energy of E{alpha} = 4.2 GeV has been studied by simultaneous registration of the scattered alpha particles and the secondary pion or proton. The obtained results demonstrate that the inelastic alpha-particle scattering on the proton at the energy of the experiment proceeds either through excitation and decay of Delta resonance in the projectile or through excitation in the target proton of the Roper resonance, which decays mainly on a nucleon and a pion or a nucleon and a sigma meson - system of two pions in the isospin I = 0, S-wave.
Energy-dependent and single-energy fits to the existing nucleon-nucleon database have been updated to incorporate recent measurements. The fits cover a region from threshold to 3 GeV, in the laboratory kinetic energy, for proton-proton scattering, with an upper limit of 1.3 GeV for neutron-proton scattering. Experiments carried out at the COSY-WASA and COSY-ANKE facilities have had a significant impact on the partial-wave solutions. Results are discussed in terms of both partial-wave and direct reconstruction amplitudes.
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