SMASHING protons together in search of strange particles, scientists at the Large Hadron Collider near Geneva say they have discovered signs of particle decays that have long been predicted, but have never before been seen.
The decay pattern of the two B mesons, described in the journal Nature, could help researchers test the limits of the standard model of particle physics and probe unexplained cosmic phenomena, including the existence of dark matter and the dearth of antimatter in the universe.
Three years after the dramatic discovery of the Higgs boson—a find that earned the theorists who predicted its existence a Nobel Prize—CERN’s Large Hadron Collider has been retrofitted and upgraded to search for particles at even higher energies than before.
“From the scientific standpoint, this is big, heady stuff. All the puzzles of physics could fall into place or they could just remain mysteries based on what we learn from these decays,” said study co-author Joel Butler, a member of the collider’s Compact Muon Solenoid experiment and an experimental particle physicist at Fermilab in Illinois. “This is kind of a fantastic time in physics, where many mysteries might get resolved.”
That’s because while the Higgs boson fits neatly into the standard model, scientists know that the model does not truly explain the reality around us. It cannot account for dark matter—the invisible, untouchable stuff that can’t be directly detected but whose gravitational influence defines the structure of the cosmos. Nor does it describe dark energy, the strange repulsive force that is causing the universe to expand at a faster and faster rate.
It certainly can’t explain what happened to all the antimatter in the universe. If antimatter was created in equal or near-equal amounts to matter, then all (or at least most) of the matter and antimatter should have annihilated each other by now. The stuff we’re made of should not have survived—or at least, not in such high amounts.
The standard model also “makes a worrisome warning that the universe is probably unstable, ready to collapse in a ‘big crunch,’” Daria Zieminska of Indiana University in Bloomington wrote in a commentary on the paper. So scientists smash protons together to watch the shower of decaying particles that result. Like detectives probing the holes in a suspect’s alibi, they’re trying to find discrepancies that don’t match the standard model’s story.
Some particles are easier to interrogate than others. The scientists decided to examine neutral B mesons, short-lived particles that quickly decay into other products. Just like more well-known particles, such as protons and neutrons, mesons are composed of quarks, which come in six flavors: up, down, strange, charm, top and bottom. Different mesons have different combinations of quarks.
Since the standard model makes some pretty clear predictions about these B mesons’ behavior, they’re a good place to start looking for discrepancies. The scientists used data from the proton-smasher taken in 2011 and 2012. They searched through the resulting subatomic rubble for signs of two neutral B mesons: the strange B meson, which is made of a bottom antiquark and a strange quark; and a nonstrange B meson, which is made of a bottom antiquark and a down quark.
B mesons haven’t been directly seen, but their fingerprints can be lifted from the particular shower of particles into which they decay.
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