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The cross-section measurement for the 3H(<i>e, e</i>′<i>K</i>+)<i>nn</i>Λ reaction

The small binding energy of hypertrition leads to predictions of non-existence of bound hypernuclei for the isotriplet three-body system such as nn\LambdannΛ. However, invariant mass spectroscopy at GSI reported events that may be interpreted as the bound nn\LambdannΛ state. The nn\LambdannΛ state was searched by missing-mass spectroscopy via the (e, e'K^+)(e, e ′ K + ) reaction at the Jefferson Lab's experimental Hall A. The present experiment has higher sensitivity to the nn\LambdannΛ-state investigation in terms of the better precision by a factor of about three than the previous invariant mass spectroscopy. The analysis shown in this article focuses on the derivation of the reaction-cross section for the ^3{;\rm{;H};}; (\gamma^{;*};, K^+)\textrm{;X}; 3 H(γ ∗ , K + )X reaction. Events that were detected in an acceptance, where a Monte Carlo simulation could reproduce the data well (|\delta p/p| < 4\%∣δp/p∣<4%), were analyzed to minimize the systematic uncertainty. No significant structures were observed with the acceptance cuts, and the upper limit of the reaction-cross section of nn\LambdannΛ state was obtained to be 2121 and 31~\rm{;nb/sr};31 nb/sr at the 90\%90%-confidence level when theoretical predictions of (- B_{;\Lambda};, \Gamma) = (0.25, 0.8)(−B Λ ​ , Γ)=(0.25, 0.8) and (0.55, 4.7)(0.55, 4.7) MeV, respectively, were assumed. The cross-section result provides valuable information to examine the existence of nn\LambdannΛ.

hypertriton, binding energy, hypernucleus, invariant mass spectroscopy

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