The LHCb detector at CERN.
For the first time ever, the physicists in the world’s biggest atom smasher have observed differences in the decay of particles and antiparticles with a fundamental building block of matter, called the charm quark.
The discovery may help to explain the mystery of why matter exists at all.
“It is a historic milestone,” said Sheldon Stone, professor of physics at the University of Syracuse and one of the employees to the new research.
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Every particle of matter has an antiparticle, which is identical in mass but with opposite electric charge. When matter and antimatter meet, they annihilate each other. That is a problem. The Big Bang should have created an equal amount of matter and antimatter, and all those particles must have destroyed each other in quick succession, so that there is nothing behind it but pure energy. [Strange Quarks and Muons, Oh My! Nature’s Tiniest icles Dissected]
Clearly, that has not happened. Instead, about 1 in a billion quarks (elementary particles of which protons and neutrons) have survived. So, the universe exists. What that means is that particles and antiparticles must not behave completely identical, Stone told Live Science. They must instead decay at slightly different rates, causing a disruption of the balance between matter and antimatter. Physicists call that the difference in behavior of the charge-parity (CP) violation.
The notion of CP-violation was from the Russian physicist Andrei Sakharov, who proposed in 1967 as an explanation for why matter survived the Big Bang.
“This is one of the criteria that are necessary for our existence,” Stone said, “so it is important to understand what the origin of CP-violation is.”
There are six different types of quarks, each with their own features: up and down, top and bottom and charm and strange. In 1964, physicists first observed the CP violation in real life, in strange quarks. In 2001, they saw it happen with particles among the quarks. (Both discoveries led to Nobel prizes for the researchers involved.) Physicists have long had a theory that it happened with the particles of the charm of the quarks, too, but no one had ever seen.
Charmed, I’m sure of that
Stone is one of the researchers on the Large Hadron Collider (LHC), the beauty experiment, which makes use of the CERN Large Hadron Collider, the 16.5 mile (27-km) ring on the French-Swiss border that will send subatomic particles careening into each other to re-create the flashes of mind-boggling energy that followed the Big Bang. As the particles smash together, they break into their constituent parts, which then decay within fractions of a second to more stable particles.
The last sighting involved combinations of quarks called mesons, in particular the D0 (“d-zero”) meson and the anti-D0-meson. The D0 meson consists of a charm quark and an anti-up quark (the antiparticle of the up quark). The anti-D0 meson is a combination of an anti-charm quark and an up quark.
Both of these mesons decay in many ways, but what small percentage of them end up as mesons called kaons, or pawns. The researchers measured the difference in decay rates between the D0 and anti-D0 mesons, a process that is taking indirect measurements to ensure that they not only measure a difference in the initial production of the two mesons, or differences in how well their equipment can detect several subatomic particles.
The bottom line? The ratios of decay differed by a tenth of a percent.
“It means that the D0 and anti-D0 not decay at the same rate, and that is what we call CP-violation,” Stone said.
And that makes things interesting. The differences in the void is probably not large enough to explain what happened after the Big Bang to leave behind as much out, Stone said, but it is big enough to be surprising. But now, he said, physics theorists will get their turn with the data. [Big Bang to Civilization: 10 Amazing Origin Events]
Physicists rely on the Standard Model to explain, well, everything at the subatomic scale. Now the question is, Stone said, is the question of whether the predictions of the Standard Model can explain the charm-quark measurement of the team just made, or if it requires a type of new physics that Stone said, would be the most exciting result.
“If this can only be explained by new physics, the new physics could include the idea of where this CP violation comes from,” he said.
Researchers announced the discovery in a webcast from CERN and published a preprint of a paper describing the results online.
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Originally published on Live Science.