Physicists are Alice Collaboration. Evidence of antihyperhelium-4 has been seen for the first time at CERN’s Large Hadron Collider (LHC). Antihyperhelium-4 consists of two antiprotons, an antineutron, and an antilambda. New results are also the first evidence of the heaviest antimatter hypernuclear still at the LHC.
Illustration of the production of antihyperhelium-4 in a lead-lead collision. Image credit: AI-assisted J. Ditzel.
Collisions between heavy ions at the LHC created quark-gluon plasma, a hot, dense state of matter that is thought to have filled the universe about a millionth of a second after the Big Bang.
Heavy ion collisions also create conditions suitable for the production of atomic nuclei, exotic hypernuclei, and their antimatter counterparts, antinuclei and antihypernuclei.
Measuring these forms of matter is important for a variety of purposes, including helping to understand the formation of hadrons from quarks and gluons, the building blocks of plasma, and the matter-antimatter asymmetry seen in the modern universe.
Hypernuclei are exotic atomic nuclei formed by a mixture of protons, neutrons, and hyperons, the latter of which are unstable particles containing one or more strange types of quarks.
More than 70 years after their discovery in cosmic rays, hypernuclei continue to be a source of fascination for physicists. This is because hypernuclei are rarely found in nature and are difficult to create and study in the laboratory.
Collisions of heavy ions produce large numbers of hypernuclei, and until recently, the lightest hypernuclei, hypertriton (composed of protons, neutrons, and lambda), and its antimatter partner, antihypertriton, have been observed.
Following recent observations of antihyperhydrogen-4, ALICE physicists have detected antihyperhelium-4.
This result has a significance of 3.5 standard deviations and is also the first evidence of the heaviest antimatter hypernucleus ever at the LHC.
The ALICE measurements are 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).
The researchers examined data for the signals of hyperhydrogen-4, hyperhelium-4, and their antimatter partners using machine learning techniques that go beyond traditional hypernuclear search techniques.
Candidates for (anti)hyperhydrogen-4 were identified by looking for an (anti)helium-4 nucleus and a charged pion with which it decays; identified by. -Three atomic nuclei, an (anti)proton, and a charged pion.
In addition to finding evidence for antihyperhelium-4 with a significance of 3.5 standard deviations and evidence for antihyperhydrogen-4 with a significance of 4.5 standard deviations, the ALICE team found that the production yields of both hypernuclei and measured the mass.
“For both hypernuclei, the measured masses are consistent with current global average values,” the scientists said.
“The measured production yields were compared with predictions from a statistical hadronization model that adequately accounts for the formation of hadrons and nuclei in heavy ion collisions.”
“This comparison shows that the model's predictions closely match the data when both the excited hypernuclear state and the ground state are included in the prediction.”
“This result confirms that the statistical hadronization model can also adequately explain the production of hypernuclei, which are compact objects about 2 femtometers in size.”
The authors also determined the antiparticle-to-particle yield ratios for both hypernuclei and found that they agreed within experimental uncertainties.
“This agreement is consistent with ALICE's observation that matter and antimatter are produced equally at LHC energy and further strengthens ongoing research into the matter-antimatter imbalance in the Universe.” concluded.
Source: www.sci.news
