Breakthrough in Matter-Antimatter Asymmetry: CERN’s CP Violation Discovery, Japan’s Uranium Battery Innovation, and Donanemab Setback

New piece from CERN in the matter-antimatter asymmetry puzzle 

ON March 24, at the annual Rencontres de Moriond conference in Italy, the international LHCb collaboration at CERN reported a finding that could be rightly termed as a new milestone in the understanding of the subtle yet profound differences between matter and antimatter.

In its analysis of huge amount of data from the Large Hadron Collider (LHC), the team found definitive evidence of violation of a symmetry, called the “charge-parity (CP) symmetry” among particles known as baryons—to which family protons and neutrons belong—causing matter and antimatter to behave differently. The results have been posted as a preprint in the online repository arXiv.

CP-symmetry implies that the laws of physics should be the same if a particle is interchanged with its antiparticle (C-symmetry) while its spatial coordinates are inverted (mirror, or P-symmetry). The discovery provides further insights into why the universe after the big bang is made overwhelmingly of matter as against antimatter.

“CP violation” was first observed in the 1960s among particles called mesons, which are made up of a quark-antiquark pair. Over the past decades, CP violation has been observed in the decays of K mesons, B mesons, and D mesons. However, despite intense searches in several experiments, the effect, though expected, was hitherto not seen among the main class of particles, the baryons, which are made of three quarks.

In the present LHCb study, researchers observed subtle differences between the decay rates of a particle called the beauty-lambda baryon (in which one of the three quarks is a “beauty” quark) and its antimatter counterpart.

The team first sifted through data collected by the LHCb detector during the first and second runs of the LHC (which lasted from 2009 to 2013 and from 2015 to 2018, respectively) in search of the decay of beauty-lambda into a proton, a kaon, and a pair of oppositely charged pions, as well as the corresponding decay of its antimatter counterpart. They then counted the numbers of the observed decays of each and took the difference between the two.

The analysis showed that the difference in the numbers of beauty-lambda and anti-beauty-lambda decays was away from zero by 5.2 standard deviations, which is above the statistical threshold required to claim an experimental discovery. The LHCb team had seen hints of CP violation in the decay of beauty-lambda into a proton and three pions in 2017 but only at a 3.3 standard deviation level, which did not improve in a subsequent 2020 study.

Similarly, about two weeks before this latest result, the LHCb had reported in Physical Review Letters CP violating decay of the beauty-lambda baryons through another mode, where the particle decayed into a lambda particle and a pair of K mesons. However, the matter-antimatter asymmetry in this mode was only at the level of 3 standard deviations, below the gold standard to mark a discovery.

“The reason why it took longer to observe CP violation in baryons than in mesons is down to the size of the effect and the available data,” explained LHCb spokesperson Vincenzo Vagnoni. “We needed a machine like the LHC capable of producing a large enough number of beauty baryons and their antimatter counterparts…. It took over 80,000 baryon decays for us to see matter-antimatter asymmetry with this class of particles for the first time.”

With this new result, CP violation has now been observed across multiple types of particles, strengthening the framework of the standard model of particle physics while also hinting at potential new physics as the amount of CP violation predicted by the standard model is many orders of magnitude too small to account for the matter-antimatter asymmetry observed in the universe.

Japan develops world’s first ‘uranium rechargeable battery’

THE Japan Atomic Energy Agency (JAEA) has developed what it says is the world’s first “uranium rechargeable battery” and says that tests have verified its performance in charging and discharging.

The uranium storage battery utilises depleted uranium (DU) as the negative electrode active material and iron as the positive one. The single-cell voltage of this rechargeable battery is 1.3 volts, nearly that of a common alkaline battery (1.5 V). When the battery was charged and discharged 10 times, its performance was almost unchanged, indicating relatively stable cycling characteristics, according to the JAEA.

“To utilise DU as a new resource, the concept of rechargeable batteries using uranium as an active material was proposed in the early 2000s,” the JAEA said. “However, no studies were reporting the specific performance of the assembled uranium rechargeable batteries.”

According to the JAEA, there is currently about 1.6 million tonnes DU stored worldwide. So, if uranium rechargeable batteries are increased in capacity and put to practical use, this large amount of DU will become a new resource for output controls in the electricity supply grid derived from renewable energy, thereby contributing to the realisation of a decarbonised society, the JAEA noted.

JAEA proposes to increase the capacity of uranium storage batteries by circulating the electrolyte and increasing the concentration of uranium and iron and by looking at optimal materials for the electrodes and membranes that make up the storage battery.

Early Alzheimer’s drug donanemab gets thumbs down from European regulator

THE much-touted drug donanemab to treat early symptomatic Alzheimer’s disease (AD) has got a thumbs down from the European Medicines Agency, which recommended against the drug being granted market authorisation. The agency’s Committee for Medicinal Products for Human Use said that the benefits of the medicine were not sufficient to outweigh the risk of potentially fatal events.

Donanemab, which was approved by the US Food and Drug Administration in July last year, is a monoclonal antibody against amyloid beta, a key component of the amyloid plaques found in the brains of people with AD. The drug slows the progression of AD in adults with mild cognitive impairment or mild dementia by reducing amyloid plaques in the brain. Administered as a monthly infusion, it often causes amyloid-related imaging abnormalities (ARIA) due to swelling and potential bleedings in the brain.

While this does not usually cause any symptoms and is usually a temporary effect, more extensive bleeding and serious symptoms, including headache, dizziness, nausea, difficulty in walking, confusion, vision changes, and seizures, can occur. In severe cases, ARIA can be fatal, and according to the committee, this risk outweighed the potential benefits of the drug.

Marketing approval for the drug had been sought on the basis of the positive results from the TRAILBLAZER-ALZ 2 clinical trial, which compared donanemab with a placebo in 1,736 patients with early symptomatic AD and demonstrated brain amyloid beta plaques. The committee noted that ARIA emerged as the most important safety concern in the TRAILBLAZER trial, occurring in 36.8 per cent of the active group compared with 14.9 per cent of the placebo arm. Serious ARIA events occurred in 1.6 per cent of the donanemab-treated patients, resulting in death in three cases.