A scientist discovered an elementary particle paired with another particle. It has a positive charge equal to two-thirds of the charge of an electron. How should the scientist categorize the particle?

A.) Boson

B.) Lepton

C.) Photon

D.) Quark

W boson has + 1e or - 1e charge, Z boson has 0 charge.

Leptons have + 1e, - 1e or 0 charge.

Photons have 0 charge.

Only quarks have a charge of + 2/3e or - 1/3e of an electron charge.

To be exact, only up-type quarks (Up, Down and Top quarks) have a + 2/3e or two thirds of an electron charge.

So the correct answer is D) Quark.