Pentaquark (particle physics 101)

Quarks seem to like prime number combinations, two, three, and now five quarks combine into one subatomic particle, Behold the pentaquark.

Physicists have discovered a new class of subatomic particle that will provide unexpected insights into the fundamental building blocks of matter.  The discovery involves quarks - particles that make up the protons and neutrons usually found in the nuclei of atoms.  The new particle is the so-called pentaquark - five quarks in formation. Until now, physicists had only seen quarks packed into two- or three-quark combinations.  They say that the discovery of this new particle should have far-reaching consequences for our understanding of the structure of matter.

More than 99.9% of the mass of everyday objects is contained within the nucleus of atoms. This means that most of your body mass comes from subatomic particles that are made up of quarks.  There are hundreds of subatomic particles known and most are composites of simpler particles. They all fit into two categories - baryons and mesons.  Baryons are made of three quarks and mesons are comprised of two quarks - a quark and an anti-quark.  For a long time scientists have been puzzled as to why only these quark combinations existed. Some predicted other combinations such as the pentaquark which consists of five quarks, including an anti-quark.  The discovery of the pentaquark, also known as a new exotic baryon state, should have far-reaching consequences for our theory of particle interactions that attempt to explain the structure of matter.

Quarks are particles that you never see solo.  You cannot split a two quark particle in half, the force holding the quarks together gets stronger as you try and separate them.  You can smash a pile of particles together and trade quarks between them, but you'll still end up with quarks in twos and threes.  And no-one knows exactly what quarks are made of.  String is one theory

Mesons are hadrons made from an even number of quark-antiquark pairs, baryons are hadrons made from three quarks, like neutrons and protons.  Hadrons are particles made from quarks and/or gluons, which are not sticky (gluons are force-carriers for the strong force like electrons are force-carriers for the electromagnetic force).

The forces that we know of so far are gravity, electromagnetic, strong and weak.  The last two only really show up in atomic or subatomic interactions.  Strong is what hold nuclei together and no-one knows quite how it works, weak is responsible for changing flavour of particles.  Quarks come in six flavours, up, down, top (or true), bottom (or beauty), strange, and charm.  Strange, charm, top, and bottom are pretty rare, and the top quark is a monster heavier than a gold atom.

You also get charged leptons, which are called the electron, muon, and tau, and their respective antiparticles.  Uncharged leptons are called neutrinos, and are a right nuisance to catch because they go straight through most things, including buildings and people.  You need a handy mine shaft, a big tank of ultra pure water, and piles of detectors to spot them.  The Japanese had a good setup, the Super Kamiokande, until it got broken.

The inner physicist has to come out sometimes.