What is a hadron in particle physics?
A hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Every hadron must fall into one of the two fundamental classes of particle, bosons and fermions.
Questions about Hadron
Short answers, pulled from the story.
When was the term hadron introduced to science?
The term hadron is a new Greek word introduced by L. B. Okun in a plenary talk at the 1962 International Conference on High Energy Physics at CERN. Experimental confirmations began decades later when a tetraquark state named the Z(4430) was discovered in 2007 by the Belle Collaboration.
How are baryons and mesons classified within the hadron family?
Baryons contain an odd number of valence quarks, usually three, while mesons contain an even number of valence quarks, usually two: one quark and one antiquark. Because they possess an odd number of quarks, all baryons are fermions with half-integer spin, whereas mesons are all bosons with integer spin.
What happened to the Z(4430) tetraquark state after its discovery?
This exotic meson was confirmed as a resonance in 2014 by the LHCb collaboration. Two pentaquark states were discovered in 2015 by the same LHCb team.
Why do most free hadrons decay so quickly?
Hadrons have excited states known as resonances that decay extremely quickly within about 10^-23 seconds via the strong nuclear force. Almost all free hadrons and antihadrons are believed to be unstable and eventually decay into other particles.