Observation of the Antimatter Hypernucleus ${}_{\bar{\Lambda }}^4\overline{H}$

Abstract

At the origin of the Universe, asymmetry between the amount of created matter and antimatter led to the matter-dominated Universe as we know today. The origins of this asymmetry remain not completely understood yet. High-energy nuclear collisions create conditions similar to the Universe microseconds after the Big Bang, with comparable amounts of matter and antimatter. Much of the created antimatter escapes the rapidly expanding fireball without annihilating, making such collisions an effective experimental tool to create heavy antimatter nuclear objects and study their properties, hoping to shed some light on existing questions on the asymmetry between matter and antimatter. Here we report the first observation of the antimatter hypernucleus \hbox{${}_{\bar{\Lambda }}^4\overline{H}$}, composed of a $\bar{\Lambda }$ , an antiproton and two antineutrons. The discovery was made through its two-body decay after production in ultrarelativistic heavy-ion collisions by the STAR experiment at the Relativistic Heavy Ion Collider. In total, 15.6 candidate \hbox{${}_{\bar{\Lambda }}^4\overline{H}$} antimatter hypernuclei are obtained with an estimated background count of 6.4. The lifetimes of the antihypernuclei \hbox{${}_{\bar{\Lambda }}^3\overline{H}$} and \hbox{${}_{\bar{\Lambda }}^4\overline{H}$} are measured and compared with the lifetimes of their corresponding hypernuclei, testing the symmetry between matter and antimatter. Various production yield ratios among (anti)hypernuclei and (anti)nuclei are also measured and compared with theoretical model predictions, shedding light on their production mechanisms.

28 pages, 5 figures in the main paper; 16 pages, 5 figures in the methods part

References in corpus (4)

• Hypernuclei, dibaryon and antinuclei production in high energy heavy ion collisions: Thermal production vs. Coalescence
• Beam energy dependence of (anti-)deuteron production in Au+Au collisions at RHIC
• Measurements of ${}_{\Lambda }^3\mathrm{H}$ and ${}_{\Lambda }^4\mathrm{H}$ Lifetimes and Yields in Au+Au Collisions in the High Baryon Density Region
• Measurement of the lifetime and $\Lambda$ separation energy of ${}_{\Lambda }^3\mathrm{H}$

Cited by in corpus (6)

• Production of exotic hadrons in $pp$ and nuclear collisions
• Imaging Freeze-out Sources and Extracting Strong Interaction Parameters in Relativistic Heavy-Ion Collisions
• First measurement of A = 4 (anti)hypernuclei at the LHC
• Method to search for the triple-neutron state in an electron scattering experiment
• A Data-Guided Coalescence Model for Light Nuclei and Hypernuclei Production in Relativistic Heavy-Ion Collisions at $\sqrt{s_{\mathrm{NN}}}=3$--200 GeV
• Flavour-Dependent Chemical Freeze-Out of Light Nuclei in Relativistic Heavy-Ion Collisions