The cross-section measurement for the H-3(e, e ' K (+))nn Lambda reaction

The small binding energy of the hypertriton leads to predictions of the non-existence of bound hypernuclei for isotriplet three-body systems such as nn Lambda. However, invariant mass spectroscopy at GSI has reported events that may be interpreted as the bound nn Lambda state. The nn Lambda state was sought by missing-mass spectroscopy via the (e, e'K+) reaction at Jefferson Lab's experimental Hall A. The present experiment has higher sensitivity to the nnA-state investigation in terms of better precision by a factor of about three. The analysis shown in this article focuses on the derivation of the reaction cross-section for the H-3(gamma*, K+)X reaction. Events that were detected in an acceptance, where a Monte Carlo simulation could reproduce the data well (vertical bar delta p/p vertical bar < 4%), were analyzed to minimize the systematic uncertainty. No significant structures were observed with the acceptance cuts, and the upper limits of the production cross-section of the nnA state were obtained to be 21 and 31 nb sr(-1) at the 90% confidence level when theoretical predictions of (-B-Lambda, Gamma) = (0.25, 0.8) MeV and (0.55, 4.7) MeV, respectively, were assumed. The cross-section result provides valuable information for examining the existence of nn Lambda.