https://home.cern/news/news/physics/alice-finds-first-ever-evidence-antimatter-partner-hyperhelium-4 Skip to main content CERN Accelerating science * + Sign in * Directory home Toggle navigation * About CERN At CERN, we probe the fundamental structure of particles that make up everything around us. We do so using the world's largest and most complex scientific instruments. Know more + Who we are o Our Mission o Our Governance o Our Member States o Our History o Our People + What we do o Fundamental research o Contribute to society o Environmentally responsible research o Bring nations together o Inspire and educate o Fast facts and FAQs + Key Achievements Key achievements submenu + The Higgs Boson + The W boson + The Z boson + The Large Hadron Collider + The Birth of the web + Antimatter * News Featured news, updates, stories, opinions, announcements CLOUD experiment resolves puzzle of new aeros... Physics Press release 4 December, 2024 CERN signs long-term solar power agreements Engineering News 29 November, 2024 CERN launches Resonance, a new arts collabora... At CERN News 28 November, 2024 CERN Council selects Mark Thomson as next Dir... At CERN Press release 6 November, 2024 Latest news + News o Accelerators o At CERN o Computing o Engineering o Experiments o Knowledge sharing o Physics + Events + CERN Community o News and announcements o Official communications o Events + Scientists o News + Press Room Press Room submenu + Media News + Resources + Contact * Science Science img The research programme at CERN covers topics from kaons to cosmic rays, and from the Standard Model to supersymmetry Know more + Physics o Antimatter o Dark matter o The early universe o The Higgs boson o The Standard Model o + More + Accelerators o CERN's accelerators o The Antiproton Decelerator o The Large Hadron Collider o High-Luminosity LHC o + More + Engineering o Accelerating: radiofrequency cavities o Steering and focusing: magnets and superconductivity o Circulating: ultra-high vacuum o Cooling: cryogenic systems o Powering: energy at CERN o + More + Computing o The CERN Data Centre o The Worldwide LHC Computing Grid o CERN openlab o Open source for open science o The birth of the web o + More + Experiments o ALICE o ATLAS o CMS o LHCb o + More * Resources Featured resources CERN Courier Sep/Oct 2024 Courier Physics 9 January, 2024 High-Luminosity LHC images Image Accelerators 20 June, 2018 LHC Facts and Figures Brochure Knowledge sharing 10 May, 2022 See all resources + By Topic o Accelerators o At CERN o Computing o Engineering o Experiments o Knowledge sharing o Physics + By format o 360 image o Annual report o Brochure o Bulletin o Courier o Image o Video o + More + By audience o CERN community o Educators o General public o Industry o Media o Scientists o Students o + More * search E.G. BIRTH OF WEB, LHC PAGE 1, BULLETIN... E.G. BIRTH OF WEB, LHC... Search [ ]Search * | en + o en o fr News News Topic: Physics --------------------------------------------------------------------- ALICE finds first ever evidence of the antimatter partner of hyperhelium-4 The finding also represents the first evidence of the heaviest antimatter hypernucleus yet at the LHC 9 December, 2024 | By ALICE collaboration ALICE,Event,ALICE GeneralIllustration of the production of antihyperhelium-4 (a bound state of two antiprotons, an antineutron and an antilambda) in lead-lead collisions. (Image: Janik Ditzel for the ALICE collaboration) Collisions between heavy ions at the Large Hadron Collider (LHC) create quark-gluon plasma, a hot and dense state of matter that is thought to have filled the Universe around one millionth of a second after the Big Bang. Heavy-ion collisions also create suitable conditions for the production of atomic nuclei and exotic hypernuclei, as well as their antimatter counterparts, antinuclei and antihypernuclei. Measurements of these forms of matter are important for various purposes, including helping to understand the formation of hadrons from the plasma's constituent quarks and gluons and the matter-antimatter asymmetry seen in the present-day Universe. Hypernuclei are exotic nuclei formed by a mix of protons, neutrons and hyperons, the latter being unstable particles containing one or more quarks of the strange type. More than 70 years since their discovery in cosmic rays, hypernuclei remain a source of fascination for physicists because they are rarely found in nature and it's challenging to create and study them in the laboratory. In heavy-ion collisions, hypernuclei are created in significant quantities, but until recently only the lightest hypernucleus, hypertriton, and its antimatter partner, antihypertriton, have been observed. A hypertriton is composed of a proton, a neutron and a lambda (a hyperon containing one strange quark). An antihypertriton is made up of an antiproton, an antineutron and an antilambda. Following hot on the heels of an observation of antihyperhydrogen-4 (a bound state of an antiproton, two antineutrons and an antilambda), reported earlier this year by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC), the ALICE collaboration at the LHC has now seen the first ever evidence of antihyperhelium-4, which is composed of twoantiprotons, an antineutron and an antilambda. The result has a significance of 3.5 standard deviations and also represents the first evidence of the heaviest antimatter hypernucleus yet at the LHC. The ALICE measurement is based on lead-lead collision data taken in 2018 at an energy of 5.02 teraelectronvolts (TeV) for each colliding pair of nucleons (protons and neutrons). Using a machine-learning technique that outperforms conventional hypernuclei search techniques, the ALICE researchers looked at the data for signals of hyperhydrogen-4, hyperhelium-4 and their antimatter partners. Candidates for (anti)hyperhydrogen-4 were identified by looking for the (anti)helium-4 nucleus and the charged pion into which it decays, whereas candidates for (anti)hyperhelium-4 were identified via its decay into an (anti)helium-3 nucleus, an (anti)proton and a charged pion. In addition to finding evidence of antihyperhelium-4 with a significance of 3.5 standard deviations, as well as evidence of antihyperhydrogen-4 with a significance of 4.5 standard deviations, the ALICE team measured the production yields and masses of both hypernuclei. For both hypernuclei, the measured masses are compatible with the current world-average values. The measured production yields were compared with predictions from the statistical hadronisation model, which provides a good description of the formation of hadrons and nuclei in heavy-ion collisions. This comparison shows that the model's predictions agree closely with the data if both excited hypernuclear states and ground states are included in the predictions. The results confirm that the statistical hadronisation model can also provide a good description of the production of hypernuclei, which are compact objects with sizes of around 2 femtometres (1 femtometre is 10^-15 metres). The researchers also determined the antiparticle-to-particle yield ratios for both hypernuclei and found that they agree with unity within the experimental uncertainties. This agreement is consistent with ALICE's observation of the equal production of matter and antimatter at LHC energies and adds to the ongoing research into the matter-antimatter imbalance in the Universe. ALICEheavy ionquark-gluon plasma Related Articles ALICE probes the strong interaction three-bod... Physics News 25 September, 2024 ALICE does the double slit Physics News 12 August, 2024 ALICE honours its 2024 Thesis Award winners Experiments News 9 August, 2024 View all news Also On Physics CLOUD experiment resolves puzzle of new aeros... Physics Press release 4 December, 2024 ATLAS observes top quarks in lead-lead collis... Physics News 15 November, 2024 CMS uses photons to probe the structure of nu... Physics News 25 October, 2024 Decoding top quarks with precision Physics News 16 October, 2024 Particle physicists chart a course to the fut... Physics Press release 11 October, 2024 ALICE probes the strong interaction three-bod... Physics News 25 September, 2024 NA62 experiment at CERN observes ultra-rare p... Physics Press release 25 September, 2024 LHC experiments at CERN observe quantum entan... Physics Press release 18 September, 2024 CMS experiment at CERN weighs in on the W bos... Physics Press release 17 September, 2024 View all news Follow Us Facebook icon Instagram icon TikTok icon X icon LinkedIn icon Youtube icon More Social Media Accounts Find us * Contact us * Getting here * CERN * Esplanade des Particules 1 * P.O. Box * 1211 Geneva 23 * Switzerland CERN & You * Doing business with CERN * Knowledge transfer * CERN's neighbours * CERN & Society Foundation * Partnerships * Alumni General Information * Careers * Visits * Privacy policy * Cookie Management Copyright (c) 2024 CERN