In the context of protons, the spin is indeed carried by the quarks and gluons within the proton. Quarks are elementary particles that possess intrinsic angular momentum or spin, while gluons are the carriers of the strong nuclear force within the theory of quantum chromodynamics (QCD).
The proton is composed of three quarks: two up quarks and one down quark. Each quark has a spin of 1/2, which means that the total spin of the three quarks in a proton adds up to 1/2 + 1/2 + 1/2 = 3/2.
The gluons, on the other hand, also carry spin. In QCD, the gluons themselves have a spin of 1. They can interact with the quarks inside the proton and contribute to the overall spin of the proton.
The detailed mechanism of how the spin of the quarks and gluons combine to give the total spin of the proton is a complex aspect of QCD and is still an active area of research. This phenomenon is referred to as the "spin crisis" because the naive sum of the quark spins does not account for the full spin of the proton.
Experimental studies, such as deep inelastic scattering and proton spin structure measurements, provide insights into the distribution of the proton's spin among its constituents. However, a complete understanding of the precise role of quark and gluon spins in determining the total spin of the proton is still an ongoing area of investigation in particle physics.