Observation of antihypertriton in $pp$ collisions with LHCb

The first observation at the LHCb experiment of hypertritons and antihypertritons is reported. The dataset consists of $pp$ collisions at $\sqrt{s}=13{\rm \,Te\kern -0.1em V}$, collected between 2016 and 2018 and corresponding to an integrated luminosity of $5.5\,{\rm fb}^{-1}$. The hypertritons are reconstructed via the two-body decay $^3_{\it \Lambda}\text{H}\rightarrow{}^3\text{He}\pi^{-}$ and its charge conjugate. The helium nuclei are identified with an innovative technique at LHCb that exploits ionisation losses in the silicon detectors, as well as information from the Outer Tracker and RICH detectors. By requiring such helium tracks to form a well-defined vertex together with a pion, a total of $107\pm11$ hypertriton decays are found. This observation opens the door to a rich programme of precise measurements of QCD and astrophysics interest to be performed on the available data.