First Measurements of Spin-Dependent Double-Differential Cross Sections and the Gerasimov-Drell-Hearn Integrand fromH→3e(γ→

Abstract

The first measurement of the three-body photodisintegration of longitudinally-polarized 3 He with a circularly-polarized γ-ray beam was carried out at the High Intensity γ-ray Source (HIγS) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contributions from the three-body photodisintegration to the 3 He GDH integrand are presented and compared with state-of-the-art three-body calculations at the incident photon energies of 12.8 and 14.7 MeV. The data reveal the importance of including the Coulomb interaction between protons in three-body calculations.PACS numbers: 24.70.+s, 25.10.+s, 25.20.Dc, 29.25.Pj, 29.27.Hj, 29.40.Mc, 67.30.ep The study of three-nucleon systems has long been of fundamental importance to nuclear physics [1,2]. Calculations using mainly the machinery of Faddeev [3] and Alt-Grassberger-Sandhas equations (AGS) [4] have been carried out for three-body systems using a variety of nucleon-nucleon (NN) potentials [5,6], and three-nucleon forces (3NFs) like Urbana IX (UIX) [8] or CD Bonn + ∆ [9], with the latter yielding an effective 3NF through the ∆-isobar excitation.Calculations for the three-body photodisintegration of 3 He with double polarizations have been carried out. The calculations by Deltuva et al. are based on AGS equations and employ the CD Bonn + ∆ potential [9] with the corresponding single-baryon and mesonexchange electromagnetic currents (MEC) plus relativistic single-nucleon charge corrections. The results are obtained using the computational technology of Ref. [10]. The proton-proton Coulomb force is included using the method of screening and renormalization [11]. Skibiński et al. solve the Faddeev equations by using the AV18 potential and the UIX 3NF [8] accounting for single nucleon currents and the two most important MEC, the seagull and pion-in-flight terms. Their results are obtained using the methods described in Ref. [12].Recent advances in high intensity polarized beams and polarized 3 He targets allow for tests of new spindependent observables predicted by theory. A polarized 3 He target is often used as an effective polarized neutron target to extract the electromagnetic form factors [13][14][15] and the spin structure functions [16] of the neutron since the nuclear spin of 3 He is carried mostly by the unpaired neutron. To acquire the information about the neutron using a polarized 3 He target, nuclear corrections relying on the state-of-the-art three-body calculations need to be validated by experiments. While data from electrodisintegration of polarized 3 He [17] were used to test three-body calculations [18], data from polarized photodisintegration of 3 He below the pion production threshold did not exist prior to this work.The spin-dependent total cross sections from the threebody photodisintegration of 3 He below pion production threshold are of further importance for the investigation of the Gerasimov-Drell-Hearn (GDH) sum rule [19]. The GDH sum rule relates the energy-weighted di...

Nucleon polarizabilities: From Compton scattering to hydrogen atom

“…Below the pion-production threshold, the dominant channels are the two-and three-body breakup reactions: 3 He ( γ, n) d and 3 He ( γ, n) pp. The latter has been experimentally accessed at HIGS [222]. At MAMI, the helicity-dependent total inclusive 3 He cross section is measured with circularly polarized photons in the energy range: 200 < ν < 500 MeV [223].…”

Spin-dependent cross sections from the three-body photodisintegration ofHe3at incident energies of 12.8 and 14.7 MeV

“…The spin-dependent total cross sections and the first data concerning the contributions from the three-body breakup channel to the GDH integrand were presented in Ref. [35]. The extracted spin-dependent cross sections were averaged and the total unpolarized cross sections were calculated for each incident photon energy.…”

“…The calculations also show that the contribution from the threebody breakup channel to the GDH integral is larger than that from the two-body breakup. Therefore, the measurements of the spin-dependent cross sections of 3 He( γ ,n)pp not only test the dynamics underlying the modern three-body calculations but also represent an important step towards the investigation of the GDH sum rule when one combines the measurements above the pion production threshold from other laboratories [11,34] with our reported measurements below it [35] and upcoming measurements of the two-body breakup channel.…”

Optically polarizedHe3

“…Hence about 87% of the 3 He spin is carried by the lone neutron (Friar et al , 1990; Laskaris et al , 2015, 2013). It is this property of the 3 He nucleus that yields its utility for studies of the spatial distribution of charge, magnetization, (Bernauer, 2012) and spin in the neutron.…”