Measurement of $\rm ^{6}H$ ground state energy in an electron scattering experiment at MAMI-A1

Tianhao Shao, Jinhui Chen, Josef Pochodzalla, Patrick Achenbach, Mirco Christmann, Michael O. Distler, Luca Doria, Anselm Esser, Julian Geratz, Christian Helmel, Matthias Hoek, Ryoko Kino, Pascal Klag, Yu-Gang Ma, David Markus, Harald Merkel, Miha Mihovilovič, Ulrich Müller, Sho Nagao, Satoshi N. Nakamura, Kotaro Nishi, Ken Nishida, Fumiya Oura, Jonas Pätschke, Björn Sören Schlimme, Concettina Sfienti, Daniel Steger, Marcell Steinen, Michaela Thiel, Andrzej Wilczek, Luca Wilhelm

Published 2025-01-02Version 1

For the first time the neutron-rich hydrogen isotope $\rm ^{6}H$ was produced in an electron scattering experiment in the reaction $\rm ^{7}Li(e,~e'p\pi^{+})^{6}H$ using the spectrometer facility of the A1 Collaboration at the Mainz Microtron accelerator. By measuring the triple coincidence between the scattered electron, the produced proton, and $\pi^{+}$, the missing mass spectrum of $\rm ^{6}H$ was obtained. A clear peak above $^3$H+n+n+n energy threshold was seen resulting in a ground state energy of $\rm ^{6}H$ at $2.3\pm0.5({\rm stat.})\pm0.4({\rm syst.})$ MeV with a width of $1.9\pm1.0({\rm stat.})\pm0.4({\rm syst.})$ MeV. This work challenges the understandings of multi-nucleon interactions and presents a new method to study light neutron-rich nuclei with electron scattering experiments.