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Journal ArticleDOI

Charge symmetry breaking in the neutron-proton system

20 Oct 1980-Nuclear Physics (North-Holland)-Vol. 348, Iss: 4, pp 365-387

AbstractTwo consequences of charge symmetry breaking (CSB) in the n-p system are examined. In n-p elastic scattering, CSB nuclear forces cause a difference between the polarizations of the neutron and the proton scattered in opposite directions in the center of mass system. The expected differences in polarizations due to one-boson exchanges, particularly a photon exchange, isospin mixed mesons, and a pion (with the n-p mass difference taken into account), are computed. The calculated polarization difference is typically of the order of several tenths of a percent. In np → dπ0, the CSB of nuclear forces can be tested by measuring the asymmetry of the angular distribution of deuterons about 90° in the center of mass frame. The expected asymmetry is calculated for one-boson exchange CSB mechanisms, as in the elastic scattering. The asymmetry caused by the mixed η−π0 exchange is dominant, but all of the mechanisms contribute asymmetries with similar angular dependences. The maximum asymmetry is about 0.8 % at 0°; the average is about 0.2 %.

Topics: Asymmetry (58%), Elastic scattering (55%), Symmetry breaking (54%), Nuclear force (53%), Isospin (53%)

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Journal ArticleDOI
Abstract: Nuclear forces can be systematically derived using effective chiral Lagrangians consistent with the symmetries of QCD. I review the status of the calculations for two- and three-nucleon forces and their applications in few-nucleon systems. I also address issues like the quark mass dependence of the nuclear forces and resonance saturation for four-nucleon operators.

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Journal ArticleDOI
Abstract: Charge symmetry breaking (CSB) in particle and nuclear physics is reviewed. The data and theory relevant to understand CSB in hadronic mass spittings, interactions and decay rates; nucleon-nucleon interactions; nuclear reactions; and binding energies of mirror nuclei are examined. This vast information is consistent with the hypothesis that the difference between the masses of the up and down quarks plus electromagnetic interactions amongst quarks causes all CSB.

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Abstract: A method is developed for treating the effect of the neutron-proton mass difference in isospin-violating nuclear forces. Previous treatments utilized an awkward subtraction scheme to generate these forces. A field redefinition is used to remove that mass difference from the free Lagrangian (and hence from asymptotic nucleon states) and replace its effect by effective interactions. Previous calculations of static class II charge-independence-breaking and class III charge-symmetry-breaking potentials are verified using the new scheme, which is also used to calculate class IV nuclear forces. Two-body forces of the latter type are found to be identical to previously obtained results. A three-body force is also found. Problems involving Galilean invariance with class IV one-pion-exchange forces are identified and resolved.

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Abstract: The asymmetry in the angular distribution of np->dpi{sup 0} attributable to charge symmetry breaking is calculated using heavy baryon chiral perturbation theory. Recent developments in power counting have proven successful in describing total cross sections, and we apply them to the asymmetry calculation. Reducibility in one of the leading-order diagrams is examined. We compare the updated theory with experimental results for a range of physically reasonable parameters and find overprediction for the entire range.

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References
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Journal ArticleDOI
Abstract: An energy independent nucleon-nucleon potential model is described. The model represents the two-nucleon data below 315 MeV more faithfully than any other potential model known to date. The data include the effective range expansion parameters and the deuteron properties as well as the scattering data at higher energies. It is of special significance that the n-p data have been represented by the energy independent potential model in a satisfactory manner for the first time. For this purpose a quadratic LS potential was found essential in the T = 0 state. The T = 1 potential differs little from those previously proposed by several authors. The phase shifts predicted by the model are in fair agreement with the solutions YLAM ( T = 1) and YLAN3M ( T = 0) recently found by the Yale group.

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Journal ArticleDOI
Abstract: Electromagnetic nucleon form factors have been determined from Rosenbluth plots and, independently, by fitting a dispersion ansatz to electron-nucleon scattering cross sections, allowing for a renormalization of the data in both cases. The ϱ-exchange contribution was taken from a Frazer-Fulco-type analysis based on new π N. Pole terms with adjustable parameters were used for the other parts of the spectral functions. Only the Dirac isoscalar and the Pauli isovector spectral function show a pronounced dipole- like bump-dip structure. The bumps belong to ω- and ϱ-exchange and the dips presumably to o- and ω′(1250)-exchange in the first case and to ϱ′(1250)-exchange in the second case. The results for vector meson-nucleon coupling constants are compared with predictions from SU(3). Values for the nucleon radii are given which are only weakly model dependent.

448 citations