2016/11/23 by Emanuele R. Nocera, Nocera, Emanuele R., E. Santopinto +1
Earth and Planetary Sciences · Physics and Astronomy · #FOS: Physical sciences #Geophysics and Gravity Measurements #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Pulsars and Gravitational Waves Research #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.1611.07980
openalex publication_date 2016/11/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
A striking prediction of several extensions of the constituent quark model,\nincluding the unquenched quark model, the pion cloud model and the chiral quark\nmodel, is a proportionality relationship between the quark sea asymmetry and\nthe orbital angular momentum of the proton. We investigate to which extent a\nrelationship of this kind is corroborated by the experiment, through a\nsystematic comparison between expectations based on models and predictions\nobtained from a global analysis of hard-scattering data in perturbative Quantum\nChromodynamics. We find that the data allows the angular momentum of the proton\nto be proportional to its sea asymmetry, though with a rather large range of\nthe optimal values of the proportionality coefficient. Typical values do not\nenable us to discriminate among expectations based on different models. In\norder to make our comparison conclusive, the extrapolation uncertainties on the\nproportionality coefficient should be reduced, hopefully by means of accurate\nmeasurements in the region of small proton momentum fractions, where the data\nis currently lacking. Nevertheless, the unquenched quark model predicts that\nquarks account for a proton spin fraction much larger than that accepted by the\nconventional wisdom. We explicitly demonstrate that such a discrepancy can be\nreabsorbed in the unknown extrapolation region, without affecting the\ndescription of current data, by imposing the unquenched quark model expectation\nas a boundary condition in the analysis of the data itself. We delineate how\nthe experimental programs at current and future facilities may shed light on\nthe region of small momentum fractions.\n