The 3rd Workshop on Perspectives in Nuclear Physics at Intermediate Energies has been held at the... more The 3rd Workshop on Perspectives in Nuclear Physics at Intermediate Energies has been held at the International Centre for Theoretical Physics (ICTP), Trieste, Italy, 18-22 May 1987. It followed the previous ones held in 1983 and 1985 whose focus was on theoretical and experimental activities in the investigation of nucleon and nuclear structure by electromagnetic and hadronic probes at intermediate
ABSTRACT The effect of the nuclear medium on the excitation mechanism of nucleon resonances is in... more ABSTRACT The effect of the nuclear medium on the excitation mechanism of nucleon resonances is investigated in the framework of the constituent quark model (CQM). Calculations of the total strength of the M1 and E1 excitations in a two-nucleon system are performed by means of a two-centre quark potential model in which the intercluster barrier is allowed to vary with the relative distance. The results show that the resonance excitation in the deuteron is not modified with respect to the free nucleon case. In contrast, when the internucleon distance assumes typical nuclear values, the pattern of the quark levels leads to a ~ 10% damping of the D13 resonance, leaving the Δ excitation unaffected, in agreement with the recent photoabsorption measurements.
The general expression of the nucleon-nucleus optical potential has been obtained using Watson... more The general expression of the nucleon-nucleus optical potential has been obtained using Watson's multiple scattering theory and Wolfenstein's parametrization of the nucleon-nucleon scattering amplitude. The resulting theoretical potential is non-local and consists of an energy independent central volume plus surface real and imaginary potential and of a Thomas-like spin-orbit term. The analysis has been restricted to N=Z spherical nuclei, so that neither isospin-isospin nor spin-spin interaction have been included. The widely used Perey-Buck, Greenlees and Watson expressions of the optical potential are easily obtained as particular cases. For practical purposes the non-local potential has been parametrized in the Frahn-Lemmer form, using Woods-Saxon radial form factors and the equivalent local potential (ELP) has been calculated by a Perey-Buck-like transformation. The ELP has a radial behaviour very similar to the original non-local one, but the potential depths and radii ...
The recent values of the proton charge radius obtained by means of muonic-hydrogen laser spectros... more The recent values of the proton charge radius obtained by means of muonic-hydrogen laser spectroscopy are about $4\%$ different from the electron scattering data. It has been suggested that the proton radius is actually measured in different frames and that, starting from a non relativistic quark model calculation, the Lorentz transformation of the form factors accounts properly for the discepancy. We shall show that the relation between the charge radii measured in different frames can be determined on very general grounds by taking into account the Lorentz transformation of the charge density. In this way, the discrepancy between muonic-hydrogen laser spectroscopy and electron scattering data can be removed.
The 3rd Workshop on Perspectives in Nuclear Physics at Intermediate Energies has been held at the... more The 3rd Workshop on Perspectives in Nuclear Physics at Intermediate Energies has been held at the International Centre for Theoretical Physics (ICTP), Trieste, Italy, 18-22 May 1987. It followed the previous ones held in 1983 and 1985 whose focus was on theoretical and experimental activities in the investigation of nucleon and nuclear structure by electromagnetic and hadronic probes at intermediate
ABSTRACT The effect of the nuclear medium on the excitation mechanism of nucleon resonances is in... more ABSTRACT The effect of the nuclear medium on the excitation mechanism of nucleon resonances is investigated in the framework of the constituent quark model (CQM). Calculations of the total strength of the M1 and E1 excitations in a two-nucleon system are performed by means of a two-centre quark potential model in which the intercluster barrier is allowed to vary with the relative distance. The results show that the resonance excitation in the deuteron is not modified with respect to the free nucleon case. In contrast, when the internucleon distance assumes typical nuclear values, the pattern of the quark levels leads to a ~ 10% damping of the D13 resonance, leaving the Δ excitation unaffected, in agreement with the recent photoabsorption measurements.
The general expression of the nucleon-nucleus optical potential has been obtained using Watson... more The general expression of the nucleon-nucleus optical potential has been obtained using Watson's multiple scattering theory and Wolfenstein's parametrization of the nucleon-nucleon scattering amplitude. The resulting theoretical potential is non-local and consists of an energy independent central volume plus surface real and imaginary potential and of a Thomas-like spin-orbit term. The analysis has been restricted to N=Z spherical nuclei, so that neither isospin-isospin nor spin-spin interaction have been included. The widely used Perey-Buck, Greenlees and Watson expressions of the optical potential are easily obtained as particular cases. For practical purposes the non-local potential has been parametrized in the Frahn-Lemmer form, using Woods-Saxon radial form factors and the equivalent local potential (ELP) has been calculated by a Perey-Buck-like transformation. The ELP has a radial behaviour very similar to the original non-local one, but the potential depths and radii ...
The recent values of the proton charge radius obtained by means of muonic-hydrogen laser spectros... more The recent values of the proton charge radius obtained by means of muonic-hydrogen laser spectroscopy are about $4\%$ different from the electron scattering data. It has been suggested that the proton radius is actually measured in different frames and that, starting from a non relativistic quark model calculation, the Lorentz transformation of the form factors accounts properly for the discepancy. We shall show that the relation between the charge radii measured in different frames can be determined on very general grounds by taking into account the Lorentz transformation of the charge density. In this way, the discrepancy between muonic-hydrogen laser spectroscopy and electron scattering data can be removed.
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Papers by Mauro Giannini