Qualities of nucleons, such as the fundamental parameter mass, might be modified in extreme conditions relative to those of isolated nucleons. We show the ratio of the EMC-effect tagged nucleon mass to that of the free one(m*/m);these values are derived from the nuclear structure function ratio between heavy nuclei and deuterium measured in the electron Deep Inelastic Scattering(DIS) reaction in 0.3≤x≤0.7. The increase in m*/mwith A-1/3 is phenomenologically interpreted via the release of a color-singlet cluster formed by sea quarks and gluons in bound nucleons holding high momentum in the nucleus, from which the mass and fraction of non-nucleonic components in nuclei can be deduced. The mass of color-singlet clusters released per short range correlated(SRC) proton in the high momentum region(k > 2 fm-1) is extracted to be 16.890 ±0.016 MeV/c2, which evidences the possibility of a light neutral boson and quantized mass of matter.
In this paper,we examine the hypothesis that the nuclear EMC effect arises merely from the N-N SRC pairs inside the nucleus and that the properties of the N-N SRC pair are universal among the various nuclei,using the conventional x-rescaling model for the EMC effect.With the previously determined effective mass of the short-range correlated nucleon and the number of N-N SRC pairs estimated,we calculated the EMC effect of various nuclei within the x-rescaling approach.According to our calculations,the nuclear EMC effect due to the mass deficits of the SRC nucleons is not sufficient to reproduce the observed EMC effect in experiments.We speculate that the internal structure of the mean-field single nucleon is also clearly modified.Alternatively,there can be more origins of the EMC effect beyond the N-N SRC configuration(such as theαcluster),or the universality of N-N SRC pair is significantly violated from light to heavy nuclei.
The ratio ofγtransition-intensities from the initial capture state to low-lying states may represent the model-independentγ-strength function,which reflects the effects of different neutron-capture reaction mechanisms.The extraordinary quenching of theγ0 transition from the p-wave neutron radiative capture in 57Fe is observed,for the first time,from the pronounced enhancement of theγ-strength function ratios fγ1/fγ0 and fγ2/fγ0.The 2p-1h doorway excitation leads to suppression of theγ0 transition to the ground state and the enhancement of theγ1 andγ2 transitions to the first and second excited states,respectively.The fp sub-shells supply the exact number of spaces required for the 2p-1h configuration,which features the neutron capture mechanism in the vicinity of A=55.
