A new look at the particle interactions that may occur in the cores of neutron stars

Alice detector. credit: CERN

The ALICE International Collaboration at the Large Hadron Collider (LHC) has just released the most accurate measurements yet of two properties of hypernuclei that may exist in the cores of neutron stars.

Atomic nuclei and their antimatter counterparts, known as antinuclei, are often produced in the LHC in high-energy collisions between heavy ions or protons. On a less frequent but still regular basis, unstable nuclei called hypernuclei are also formed. In contrast to normal nuclei, which consist only of protons and neutrons (i.e. neutrons), hypernuclei are also made up of hyperons—unstable particles It contains strange quarks.

It has been nearly 70 years since it was first observed in cosmic rays، Hypernuclearity continues to fascinate physicists because it is rarely produced in natural world Although they have traditionally been made and studied in low-energy nuclear physics experiments, their properties are extremely difficult to measure.

At the Large Hadron Collider, hypernuclei are created in large quantities in heavy ion collisions, but the only hypernuclear observed in the collider so far is the lightest nucleus, the hypertriton, which consists of a proton, neutron, and lambda – a hypernuclear containing one strange quark.

In their new study, the ALICE team examined a sample of about a thousand hypertetons resulting from lead and lead collisions that occurred at the Large Hadron Collider during its second round. Once formed in these collisions, the hypertritons fly a few centimeters inside the ALICE experiment before decomposing into two particles, a helium-3 nucleus and a charged pion, that ALICE detectors can pick up and identify. The ALICE team investigated these nascent particles and the pathways they leave in the detectors.

Alice writes down the properties of hypermatter

Hypertriton lifetime measurements were made using various techniques over time, including the new ALICE measurement (in red). The horizontal lines and boxes indicate the statistical and regular uncertainties, respectively. The dashed lines represent different theoretical predictions. Credit: Alice Collaboration

By analyzing this sample of hypertritons, one of the largest available for these “alien” nuclei, ALICE researchers were able to obtain the most accurate measurements yet of two properties of the hypertriton: its lifespan (how long it takes to decay) and the energy needed to separate the hypertriton, Lambda , for the remaining components.

These two properties are fundamental to understanding the internal structure of this hypernucleus and, as a consequence, the nature of the strong force that holds nucleons and hyperrons together. Studying this force is not only interesting in its own right, but can also provide insight into the particle interactions that may occur in the inner cores of neutron stars. It is expected that these nuclei, which are very dense, favor the creation of hyperons over purely nuclear matter.

New ALICE measurements indicate that the interaction between Hyperon and its nucleon is very weak: the Lambda separation energy is just a few tens of kiloelectronvolts, similar to the X-ray energy used in Medical ImagingThe hypertriton lifetime is compatible with the free lambda lifetime.

In addition, since the substance and antihypertensive are produced in approximately equal amounts in the LHC, the ALICE collaboration was also able to study and determine their antihypertensive life. The team found that within the experimental uncertainty of the measurements, antihypertensives and hypertritons have the same lifespan. Finding a slight difference between the two lifetimes could indicate a break in nature’s basic symmetry, CPT symmetry.

With the data from the LHC’s third round, which began in earnest in July of this year, ALICE will not only investigate further the properties of the haptitron, but will also expand its studies to include heavier hypernuclei.


The light nucleus is expected to be stable despite the presence of two strange quarks


more information:
ALICE Collaboration, Age Measurement and Separation Energy 3Thee. arXiv: 2209.07360v1 [nucl-ex]And the arxiv.org/abs/2209.07360

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