A "four-flavoured" quark is the newest elementary particle on the scene, detected at Fermilab by physicists of Indiana University. The new tetraquark has been dubbed X(5568) owing to its mass of 5568 Megaelectronvolts, making it 5.5 times heavier than a proton. This one follows the pentaquark discovered last year at the Cern collider.
Particle physics has raced deep into the realms of particles since Dalton first proposed the atom in early 19th century. For some time now, it has been accepted that all particles are made of a quark and antiquark or three quarks. Protons and neutrons are each composed of three quarks.
In all, there are six "flavours" of quarks to pick from. These have been named, strangely as: up, down, strange, charm, bottom and top. All have an antiquark complement. The latest discovery is the first to show a particle made of four distinct quarks.
Research led by Daria Zieminska , a senior scientist in the IU Bloomington College of Arts and Sciences' Department of Physics, led to the detection at the U.S. Department of Energy's Fermi National Laboratory last month.
The paper describing the observation has been submitted to Physics Review Letters.
"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," said Zieminska. The results can help scientists understand "quark matter," the hot, dense material that existed immediately after the Big Bang, believed to still exist in the super-dense interior of neutron stars.
While a tetraquark or group of four quarks has been recorded by Japanese scientists in 2008, the latest discovery is the first quark quartet to contain four different quark flavors: up, down, strange and bottom.
Four-quark states are rare and not as well understood as two- and three-quark states. Zieminska and colleagues now plan to measure various properties of the particle, such as the ways it decays or how much it spins on its axis.
Currently, Zieminska leads the "heavy flavor" group of the DZero experiment, meaning all particles containing one or more "heavy quarks". The DZero experiment was behind the first observation of the elusive Higgs boson particle decaying into 'bottom' quarks at Fermilab.
In addition to flavours, another property of quarks is referred to as "colours" with three types detected. With flavours, they gove rise to 18 quarks. Then there are the six leptons, which include neutrinos and electrons. Together the quarks and leptons add up to 24 matter constituents. Alongwith their antiparticle counterparts, we then have 48 particles.
Add up the gluons (binding stuff) and bosons (like photons, and hence not matter particles) and we have a total 61 elementary particles in the Standard Model of physics today. Life is not as simple as mere atoms that Dalton proposed.