Unquenched quark model for baryons: Magnetic moments, spins, and orbital angular momenta

We present an unquenched quark model for baryons in which the effects of the quark-antiquark pairs (uu, dd, and ss) 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 qq pairs. It is shown that, while the inclusion of the qq 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.