Photograph courtesy Maximilien Brice, CERN
Published May 1, 2012
An atom-smashing experiment at the Large Hadron Collider (LHC) has detected a new subatomic particle—and it's a beauty.
Known as Xi(b)* (pronounced "csai bee-star"), the new particle is a baryon, a type of matter made up of three even smaller pieces called quarks. Protons and neutrons, which make up the nuclei of atoms, are also baryons.
The Xi(b)* particle belongs to the so-called beauty baryons, particles that all contain a bottom quark, also known as a beauty quark.
The newfound particle had long been predicted by theory but had never been observed. Although finding Xi(b)* wasn't exactly a surprise, the discovery should help scientists solve the larger puzzle of how matter is formed.
Sorting Through the Mess
Unlike protons and neutrons, beauty baryons are extremely short-lived—Xi(b)* lasted mere fractions of a second before it decayed into 21 other ephemeral particles.
The particle also requires extremely high energies to create, so it's found nowhere on Earth except in the hearts of atom-smashers such as the LHC, operated by the European Center for Nuclear Research (CERN) in Geneva.
The new beauty baryon is a higher energy version of one that was detected last summer by scientists using the Tevatron particle accelerator at Fermilab in Illinois.
LHC scientists didn't detect the new particle directly. Instead they saw evidence of its decay in the messy aftermath of a proton-proton collision captured by the facility's Compact Muon Solenoid (CMS) detector.
"Finding this particle is really very hard," CMS physicist Vincenzo Chiochia, a co-discoverer of the new particle, told Symmetry Breaking magazine.
"Finding this complicated decay in such a messy event makes us confident in our abilities to find other new particles in the future."
The CMS scientists say the new particle's existence has been confirmed to a sigma level of five, which means the researchers are 99.99-percent confident that the result isn't due to chance.
Hunt Still on for Higgs
The discovery is further confirmation that physicists are essentially correct in their understanding of how quarks are bound together, said Fermilab scientist Patrick Lukens, who was not involved in the study.
The particle was predicted by a wildly successful theory in physics known as quantum chromodynamics, which models how quarks combine and are held together to create heavier particles.
However, Lukens said, finding Xi(b)* has no bearing on the hunt for the Higgs boson, a particle that would explain why mass exists in the universe and that's also predicted by quantum chromodynamics.
Cornell's Alexander added that the Higgs "is a huge pivot point for the entire theory" of quantum chromodynamics. "Whether the Higgs is or is not there—everything rests on that."
Details of the new particle's discovery have been submitted for publication in the journal Physical Review Letters.
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