24 Apr 2013
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A view of the LHCb underground area, looking upwards from the cavern floor (Image: Anna Pantelia/CERN)
“The LHCb collaboration at CERN today submitted a paper to Physical Review Letters on the first observation of matter-antimatter asymmetry in the decays of the particle known as the B0s. It is only the fourth subatomic particle known to exhibit such behaviour.
Matter and antimatter are thought to have existed in equal amounts at the beginning of the universe, but today the universe appears to be composed essentially of matter. By studying subtle differences in the behaviour of particle and antiparticles, experiments at the LHC are seeking to cast light on this dominance of matter over antimatter.
Now the LHCb experiment has observed a preference for matter over antimatter known as CP-violation in the decay of neutral B0s particles. The results are based on the analysis of data collected by the experiment in 2011. ‘The discovery of the asymmetric behaviour in the B0S particle comes with a significance of more than 5 sigma – a result that was only possible thanks to the large amount of data provided by the LHC and to the LHCb detector’s particle identification capabilities,’ says Pierluigi Campana, spokesperson of the LHCb collaboration . ‘Experiments elsewhere have not been in a position to accumulate a large enough number of B0s decays.’
Violation of the CP symmetry was first observed at Brookhaven Laboratory in the US in the 1960s in neutral particles called kaons. About 40 years later, experiments in Japan and the US found similar behaviour in another particle, the B0 meson. More recently, experiments at the so-called B factories and the LHCb experiment at CERN have found that the B+ meson also demonstrates CP violation.
All of these CP violation phenomena can be accounted for in the Standard Model, although some interesting discrepancies demand more detailed studies. ‘We also know that the total effects induced by Standard Model CP violation are too small to account for the matter-dominated universe,’ says Campana. ‘However, by studying these CP violation effects we are looking for the missing pieces of the puzzle, which provide stringent tests of the theory and are a sensitive probe for revealing the presence of physics beyond the Standard Model.’”
See the full CERN article here.
And now a different slant from Symmetry Magazine
Strange beauty particle decays boost matter
Photo: CERN via Symmetry Magazine
April 24, 2013
“When the universe was less than a minute old, a tiny difference in the behavior of matter and antimatter led to the matter-dominated existence we experience today.
Today, particle physicists on CERN’s LHCb collaboration announced that, for the first time, they have observed particles called strange beauty mesons, or B0s, contributing to this imbalance.
Scientists found that in strange beauty particles, composed of beauty antiquarks bound with strange quarks, antimatter decays slightly more often than matter. This is called charge-parity, or CP, violation.
When B0s mesons decay to kaons and pions, physicists can determine if the new particles are matter or antimatter by looking at their relative charges. After comparing the number of matter particles with antimatter particles, they were able to confirm the findings.
‘It’s a simple idea, although getting there is quite complicated, says Tara Shears, a physicist on LHCb. ‘We’re looking at a very small discrepancy that reflects the nature of the universe.’
LHCb’s result has a statistical significance exceeding five sigma—the gold standard for declaring a discovery in particle physics.
‘We had about one thousand B0s candidates to measure,’ says Shears. ‘The results unambiguously support predictions that these particles violate CP.’
In the 1960s, James Cronin and Val Fitch observed CP violation in neutral kaons. About 40 years later, another particle, the B0 meson, showed similar behavior in the BaBar and Belle detectors in the United States and Japan. Recently, these experiments and LHCb also observed CP violation effects in B+ meson decays.
However, the Standard Model predicts only a tiny portion of the amount of CP violation needed to explain the huge deficit of antimatter in the universe. While these results help scientists understand the mechanics of CP violation, the case of the missing antimatter remains unsolved.
“We expected a certain amount of CP violation to be found in the strange beauty system,” says Pierluigi Campana, the LHCb spokesperson. “But finding the missing fraction of CP violation in the early universe will be new physics, which the Standard Model can’t predict.”
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