Neutron-deuteron breakup experiment atEn=13MeV: Determination of the1

Abstract

We report on results of a kinematically complete neutron-deuteron breakup experiment performed at Triangle Universities Nuclear Laboratory using an E n = 13 MeV incident neutron beam. The 1 S 0 neutron-neutron scattering length a nn has been determined for four production angles of the neutron-neutron final-state interaction configuration. The absolute cross-section data were analyzed with rigorous three-nucleon calculations. Our average value of a nn = −18.7 ± 0.7 fm is in excellent agreement with a nn = −18.6 ± 0.4 fm obtained from capture experiments of negative pions on deuterons. We also performed a shape analysis of the final-state interaction cross-section enhancements by allowing the normalization of the data to float. From these relative data, we obtained an average value of a nn = −18.8 ± 0.5 fm, in agreement with the result obtained from the absolute cross-section measurements. Our result deviates from the world average of a nn = −16.7 ± 0.5 fm determined from previous kinematically complete neutron-deuteron breakup experiments, including the most recent one carried out at Bonn. However, this low value for a nn is at variance with theoretical expectation and other experimental information about the sign of charge-symmetry breaking of the nucleon-nucleon interaction. In agreement with theoretical predictions, no evidence was found of significant three-nucleon force effects on the neutron-neutron final-state interaction cross sections.

He6nucleus in halo effective field theory

“…The nn interaction is dominated by an s-wave virtual state, where the scattering length, a 0 = −18.7 fm [52], is approximately one order of magnitude larger than the corresponding effective range, r 0 = 2.75 fm [53]. According to the effective-range expansion at low energies, the nn t matrix for elastic scattering can be written up to second order in the expansion in powers of M lo /M hi as…”

Radiative pion capture in H2 , He3 , and Golak1, Skibiński2, Topolnicki3 et al. 2018Phys. Rev. CSelf Cite

“…Since then many theoretical efforts [14][15][16][17][18][19][20][21] combined with more and more precise measurements [22][23][24][25][26][27][28][29][30][31][32] have contributed decisively to our present day knowledge about a nn . Detailed information about this rich field can be found in the review by Šlaus, Akaishi, and Tanaka [33] and in the more recent review by Gårdestig [34], where also complementary efforts [35,36] to determine a nn from the 2 H(n, np)n reaction were reported.…”

Effective-range dependence of resonantly interacting fermions

“…In 6 Li cold-atom experiments (see [9] for details), a s ≈ ∞ can be tuned using the wide magnetic Feshbach resonance at 834.1(15) G [10] with an effective range of r e ≈ 4.7 nm, while the gas can be cooled at densities of 1/k F ≈ 400 nm so that k F r e ≈ 0.01. In dilute neutron matter a nn ≈ −18.9(4) fm [11] and r nn ≈ 2.75(11) fm [12], while densities are on the order of 1/k F ∼ 1 fm: thus, k F r e ≈ 3 is several orders of magnitude larger than in cold-atom systems.…”