Observation of antihelium and antihypertriton in pp collisions with LHCb

The first observation at the LHCb experiment of hypertritons and antihypertritons is reported. The used dataset consists of $pp$ collisions at √s = 13\,Te -0.1em V, collected between 2016 and 2018, and corresponds to an integrated luminosity of 5.5\,fb⁻¹. The hypertriton candidates are reconstructed via the two-body decay into helium-3 and a charged pion. The corresponding helium nuclei are identified with a technique that is innovative at the LHCb experiment and mainly exploits ionisation losses in the LHCb silicon sensors. A total of 1.1×10⁵ prompt helium and antihelium candidates are identified with negligible background contamination and 107±11 hypertriton candidates are found, paving the way for a rich programme of precise measurements of QCD and astrophysical interest to be performed on the available data.