Observation of Lambda H-4 hyperhydrogen by decay-pion spectroscopy in electron scattering

TL;DR

This study used electron scattering at Mainz MAMI to perform high-resolution pion spectroscopy, detecting the decay of Lambda H-4 hyperhydrogen, and precisely measured its binding energy through decay-pion analysis.

Contribution

First high-resolution pion spectroscopy of Lambda H-4 hyperhydrogen via electron scattering, providing precise binding energy measurement of the hypernucleus.

Findings

Detected a monochromatic pion peak at 133 MeV/c indicating hyperhydrogen decay.

Measured the Lambda H-4 binding energy as 2.12 MeV with high precision.

Observed about 1000 hypernuclear decay events.

Abstract

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a Be-9 target in order to study the ground-state masses of Lambda-hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at zero degree forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. In coincidence, negatively charged decay-pions were detected by two independent high-resolution spectrometers. About 10^3 pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at p_pi ~ 133 MeV/c, corresponding to the unique signature for the two-body decay of hyperhydrogen Lambda H-4 -> He-4 + pi-, stopped inside the target. Its binding energy was determined to be B_Lambda = 2.12 +- 0.01 (stat.) +- 0.09 (syst.) MeV with respect to the H-3 + Lambda mass.