Evidence for a New Low-Lying Resonance State inH7e

Abstract

Low-lying resonance states in 7He(6He+n), formed after fragmentation reactions of a 227 MeV/nucleon 8He beam on a carbon target, have been studied. Coincidences between 6He nuclei and neutrons, corresponding to the one-neutron knockout channel in 8He, were selected. The relative energy spectrum in the 6He+n system shows a structure, which is interpreted as the 7He ( Ipi = 3/2(-)) ground state, unbound with 0.43(2) MeV relative to the 6He+n system and a width of Gamma = 0.15(8) MeV overlapping with an excited ( Ipi = 1/2(-)) state observed at 1.0(1) MeV with a width of Gamma = 0.75(8) MeV.

Spectroscopy ofHe7using theBe9(HeRenzi1, Raabe2, Randisi3 et al. 2016Phys. Rev. CSelf Cite5010View full textAdd to dashboardCite

“…Its ground state was identified in the 7 Li(t, 3 He) charge-exchange reaction [1,2] as a J π = 3/2 − resonance with a width of 0.16(3) MeV (full width at half maximum; FWHM) at 0.44(3) MeV above the 6 He +n threshold. This observation was further confirmed by other experiments [3][4][5][6][7][8][9][10], although quantitative values slightly differ, as shown in Fig. 1.…”

“…Recently, Aksyutina et al [9] carried out an almost identical experiment to that reported in Ref. [4], replacing the carbon target by a liquid-hydrogen target; the low-lying resonance was not confirmed. Furthermore, no evidence for a state below 1 MeV has been found in five other experiments [5,11,12,14,15] using a variety of techniques.…”

“…For the latter spectrum, three charged-particle coincident events were selected: two α particles from 8 Be g.s. decay and a 4 He or a 6 He in the opposite Lamp sector, as schematically drawn in Fig. 2.…”

“…The convolution of the time resolution of the Si detector and the cyclotron radio frequency was about 4 ns FWHM, while, for instance, the time of flight from the target to LEDA was around 30 ns for 8 MeV α particles. In LEDA the particle identification was achieved by the time-of-flight method, because the mass resolution permitted us to clearly distinguish 4 He from 6 He particles, as evident from separation. In this case the identification of α particles from the 8 Be g.s.…”

“…Meister et al [4] studied 7 He with a beam of 227 MeV/nucleon 8 He on a carbon target. Selecting the one-neutron-knockout channel, they observed a clear deviation of the 6 He +n invariant mass spectrum from the expected R-matrix lineshape.…”