Physicists Discover a New “Four-Flavored” Particle

March 7, 2016 | Joanne Kennell

Diagram representing a tetraquark
Photo credit: Fermilab

It’s the “birth of a new paradigm” in our view of elementary particles.

Scientists, led by Indiana University physicist Daria Zieminska and using the DZero Collaboration at the US Department of Energy’s Fermi National Laboratory, have detected a new form of elementary particle: the “four-flavored” tetraquark.

Quarks are the building blocks that form subatomic particles, including protons and neutrons, each composed of three quarks.  However, there are six types, or “flavors,” of quarks: up, down, strange, charm, bottom and top, and each has its own antimatter counterpart.

“For most of the history of quarks, it's seemed that all particles were made of either a quark and an antiquark, or three quarks; this new particle is unique — a strange, charged beauty,” Zieminska, who has been a member of the DZero experiment since the project's establishment in 1985, said in a press release.

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A tetraquark is a group of four quarks, and the first evidence of one was recorded by scientists in Japan in 2008.  What makes this new particle unique is that it is the first quark quartet to contain four different quark flavors: up, down, strange and bottom.

“It's the birth of a new paradigm. Particles made of four quarks — specifically, two quarks and two antiquarks — is a big change in our view of elementary particles,” explained Zieminska.

As with many scientific discoveries in the field of physics, the unearthing of the tetraquark was a surprise, according to Zieminska.  

Alexey Drutskoy, a colleague at Russia's National Research Nuclear University, spotted a tetraquark signal in the summer 2015, after which Zieminska joined his search for the particle.  After performing numerous cross-checks in collaboration with Alexey Popov, another Russian colleague, the team confirmed they were observing evidence of a new particle.

Even though nature does not forbid the formation of a tetraquark, four-quark states are so rare that they are not as well understood as two- and three-quark states.  The team will begin measuring various properties of the particle, including how it decays and how much it spins on its axis, in order to get a better understanding of it.

They hope that these results will also help them understand what is known as quark matter or quark-gluon plasma — the hot, dense material that existed just moments after the Big Bang, and which could exist within the interior of superdense neutron stars.

The discovery of the tetraquark comes shortly after the first observation of a pentaquark, a five-quark particle, announced last year by CERN's LHCb experiment at the Large Hadron Collider.

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