We present an unquenched quark model for baryons in which the effects of the quark-antiquark pairs ($u\overline{u}$, $d\overline{d}$, and $s\overline{s}$) are taken into account in an explicit form via a microscopic, QCD-inspired, quark-antiquark creation mechanism. In the present approach, the contribution of the quark-antiquark pairs can be studied for any inital baryon and for any flavor of the $q\overline{q}$ pairs. It is shown that, while the inclusion of the $q\overline{q}$ pairs does not affect the baryon magnetic moments, it leads to a sizable contribution of the orbital angular momentum to the spin of the proton and the $\Lambda$ hyperon.

• Received 23 October 2009

DOI:https://doi.org/10.1103/PhysRevC.80.065210