# Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton

## TL;DR

This study measures the mass difference and binding energy of hypertriton and antihypertriton to test CPT symmetry in strange nuclear matter, providing new insights into hyperon-nucleon interactions and neutron star composition.

## Contribution

It provides the first precise comparison of hypertriton and antihypertriton masses, testing CPT symmetry in a strange nucleus with improved constraints on hyperon-nucleon interactions.

## Key findings

- No deviation from CPT symmetry observed.
- Hypertriton binding energy differs from previous values.
- Results constrain hyperon-nucleon interaction models.

## Abstract

According to the CPT theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. This hypernucleus is the lightest one yet discovered and consists of a proton, a neutron, and a $\Lambda$ hyperon. With data recorded by the STAR detector{\cite{TPC,HFT,TOF}} at the Relativistic Heavy Ion Collider, we measure the $\Lambda$ hyperon binding energy $B_{\Lambda}$ for the hypertriton, and find that it differs from the widely used value{\cite{B_1973}} and from predictions{\cite{2019_weak, 1995_weak, 2002_weak, 2014_weak}}, where the hypertriton is treated as a weakly bound system. Our results place stringent constraints on the hyperon-nucleon interaction{\cite{Hammer2002, STAR-antiH3L}}, and have implications for understanding neutron star interiors, where strange matter may be present{\cite{Chatterjee2016}}. A precise comparison of the masses of the hypertriton and the antihypertriton allows us to test CPT symmetry in a nucleus with strangeness for the first time, and we observe no deviation from the expected exact symmetry.