Transparency of12Cfor protons

Abstract

Existing cross-section data for 1p-shell knockout in the reaction 12 C(e, e ′ p) 11 B -as obtained under different kinematic conditions -are shown to be mutually consistent, apart from a recent measurement performed in Mainz. New data have been collected at the Amsterdam Pulse Stretcher that confirm the normalization of the older measurements. An analysis of the world's 12 C(e, e ′ p) 11 B data has yielded precise values of the spectroscopic factor for 1p-shell and 1s-shell knockout from 12 C. These values have been used to evaluate the transparency of the 12 C nucleus for 1p-shell and 1s-shell protons separately on the basis of recent high-energy 12 C(e, e ′ p) 11 B data taken at a four-momentum transfer squared Q 2 of 1.1 (GeV/c) 2 . As the resulting average value of the nuclear transparency, 0.81 ± 0.04, is considerably higher than the value obtained from previous analyses and theoretical estimates, the high Q 2 data were used instead for an independent determination of the spectroscopic strength for 1p + 1s knockout. Combining these results with the low Q 2 data the spectroscopic factors appear to be momentum-transfer dependent. Possible explanations of these surprising results in terms of reaction-mechanism effects or a possible breakdown of the quasi-particle concept at high Q 2 are discussed as well.PACS number(s): 21.10. Jx, 21.30.Fe, 24.10.Ht, 27.20.+n

Self-consistent Green's function method for nuclei and nuclear matter

“…Clearly an analysis of the data considered in Refs. [254] and [255] will further clarify the validity of the present analysis. It is already encouraging to note that the damping employed in the calculations is adequate to describe the observed absorption in the NE18 experiment [267] as discussed in Ref.…”

“…A serious challenge to the interpretation of (e,e ′ p) experiments was recently published in Refs. [254,255]. This challenge consists in questioning the validity of the constancy of the spectroscopic factor as a function of the four-momentum (squared), Q 2 , transferred by the virtual photon to the knockedout nucleon.…”

Signatures of nucleon disappearance in large underground detectors

“…Theoretical estimates for the spreading width of the s 1/2 hole in infinite nuclear matter [26] gives a value of ∼6 MeV. As another extreme one can use the spreading width of s 1/2 state as determined in proton knock-out exeriments [25]. We adopt what we think is a reasonable compromise here and assumed that the excited level at E * = 23 ± 1 MeV in 11 C has a Lorentzian width of Γ = 7 MeV.…”

“…The excitation energy E * of this state can be calculated by the difference between the binding energy of the s 1/2 neutron level in 12 C and the neutron separation energy of 12 C. While the latter is well known to be S n = 18.72 MeV, no precise experimental or theoretical values exist for the binding energy of the s 1/2 neutron level. In the case of the s 1/2 proton level in 12 C the binding energy and the width have been measured in several electron scattering experiments 12 C(e, e ′ p) [25] and were determined to be E p 1S = 39 ± 1 MeV and Γ p 1S = 12 ± 3 MeV, respectively. Correcting E p 1S for the Coulomb shift of ≈ 2.7 MeV for protons in 12 C gives us E n 1S =41.7 ± 1 MeV for the binding energy of the s 1/2 neutron level in 12 C and, subtracting the neutron separation energy, we get the value E * = 23 ± 1 MeV for the excitation energy in 11 C. Determination of width of the excited state caused by the dis-appearance of s 1/2 nucleon is not that straightforward.…”

Nuclear incoherent photoproduction ofπ0andηfrom 4 to 12 GeV

“…The energy and momentum of the virtual photon are ω and q, respectively. In the plane-wave impulse approximation (PWIA), the fivefold differential (e, e p) cross section can be factorized in the form [42]:…”