Up quark

 Up quarks are one of the six flavours of quarks⁽¹⁾. they are fundimental particles like electrons (and other leptons); which means that they cannot be broken down any further ^{(1) (2)}. They have a charge of +2/3 and a baryon number of 1/3 ⁽¹⁾. They are the smallest quarks and are the main constiuents of protons and neutrons alongside the down quark ⁽¹⁾.

References

1. HyperPhysics. Quarks. [cited 05/12/2017]. Availiable from: http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html

2. The New York Times. Fundimental particles. [cited 05/12/2017]. Availiable from: http://topics.nytimes.com/top/news/science/topics/fundamental_particles/index.html