Search for a low-energy resonance in 7He with the 7Li(d, 2He) reaction

Abstract

A search for the J π = 1/2 − spin-orbit partner of the J π = 3/2 − ground state in 7 He has been performed with the 7 Li(d, 2 He) chargeexchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on 7 Li as well as on triton and 4 He clusters in the 7 Li ground state. A possible resonance at an excitation energy E x ≈ 1.45 MeV with a width Γ ≈ 2.0 MeV is suggested when the quasifree charge-exchange process on 7 Li is constrained by a measurement of the 6 Li(d, 2 He) reaction. Gamow-Teller strengths for transitions to the lowest states in 7 He deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations.

Spectroscopy ofHe7using theBe9(HeRenzi1, Raabe2, Randisi3 et al. 2016Phys. Rev. C5010View 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.…”

“…Three other experiments showed a resonance with an excitation energy in good agreement with Ref. [13]: the 9 Be( 15 N , 17 F) 7 He transfer reaction [3], 8 He(p,d) 7 He at 15.6 MeV/nucleon [6] and (d, 3 He) reaction with 8 Li beam of 76 MeV [12]. In the latter two measurements the decay of the 7 He 5/2 − state into α + 3n was also confirmed.…”

“…Since its first observation, the unbound 7 He nucleus has been the focus of numerous works. 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.…”

“…[22] for a review), no excited state was found. Korsheninnikov et al [13] were the first to identified an excited state in 7 He. They investigated the p( 8 He ,d) 7 He reaction at 50 MeV/nucleon observing a resonance at 2.9(3) MeV, with a width = 2.2(3) MeV.…”

“…Korsheninnikov et al [13] were the first to identified an excited state in 7 He. They investigated the p( 8 He ,d) 7 He reaction at 50 MeV/nucleon observing a resonance at 2.9(3) MeV, with a width = 2.2(3) MeV. As decay proceeds mainly into α + 3n, the state was interpreted as a p 3/2 neutron coupled to the unbound 2 + excited state of 6 He, leading to * francesca.renzi@fys.kuleuven.be † Present address: Atys Concept, F-33210 Arcachon, France.…”