Abstract
The orbital angular momentum ($L_q$) of the proton is studied by employing the extended constituent quark model. Contributions from different flavors, namely, up, down, strange, and charm quarks in the proton are investigated. Probabilities of the intrinsic $q\bar{q}$ pairs are calculated using a $^{3}P_{0}$ transition operator to fit the sea flavor asymmetry $I_a=\bar{d}-\bar{u}=0.118\pm0.012$ of the proton. Our numerical results lead to $L_q=0.158 \pm 0.014$, in agreement with $4/3I_a=0.157 \pm 0.016$, and consistent with findings based on various other approaches.
Highlights
In the late 1980’s, the European Muon Collaboration (EMC) published experimental results [2] on the spin asymmetry in polarized deep inelastic scattering, providing unexpected evidence that the sum of the spins of the quarks add up only to a fraction of the proton’s total spin
II, the pentaquark configurations in categories II and IV cannot contribute to the projection of the orbital angular momentum (OAM), since the total angular momentum J4 1⁄4 0 for the four-quark subsystem in category II and J5 1⁄4 0 for the antiquark in category IV
In [26], the nucleon orbital angular momentum is investigated using the unquenched quark model (UQM), within which the effects of the quark-antiquark pairs including uu, dd, and ssare taken into account, and the quark-antiquark pairs creation is assumed to be via a 3P0 mechanism
Summary
In the late 1980’s, the European Muon Collaboration (EMC) published experimental results [2] on the spin asymmetry in polarized deep inelastic scattering, providing unexpected evidence that the sum of the spins of the quarks add up only to a fraction of the proton’s total spin. Alexandrou et al released the results of a calculation [31] of the quark and gluon contributions to the proton spin, using an ensemble of gauge configurations with two degenerate light quarks with a mass fixed to approximately reproduce the physical pion mass. They found the OAM carried by the quarks in the nucleon to be Lq 1⁄4 0.207 Æ 64 Æ 45. In the present work, we study the contributions to the proton’ OAM from different quark flavors, by taking into account all possible five-quark Fock components, based on the results obtained in [32,33].
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