البروتون يكشف خيوطه الخفية سريع

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2602.14271

A first measurement of beam spin asymmetries for $$\pi^+\pi^0$$ and $$\pi^-\pi^0$$ pairs in semi-inclusive deep inelastic scattering is reported. The asymmetries in the dihadron angular distributions were measured from the scattering of a 10.6 GeV longitudinally polarized electron beam off a proton target, using the CLAS12 detector at Jefferson Lab. A photon classifier using a Gradient Boosted Trees (GBTs) architecture was trained with Monte Carlo simulations to reduce the amount of false combinatorial background $$\pi^0$$s, increasing statistics by up to five-fold compared to previous CLAS12 $$\pi^0$$ analyses. A nonzero $$\sin\phi_{R_\perp}$$ asymmetry is observed. This measurement is sensitive to the underexplored collinear twist-3 PDF $$e(x)$$, which encodes quark-gluon correlations in the proton, and presents a new avenue for its point-by-point extraction. The asymmetries also provide the first experimental evidence for the isospin-dependence of the helicity-dependent dihadron fragmentation function $$G_1^\perp$$, revealed by a sign-difference between the $$\pi^+\pi^0$$ and $$\pi^-\pi^0$$ channels in the $$\sin(\phi_h-\phi_{R_\perp})$$ modulation. In contrast, a large, same-sign enhancement near the $$\rho$$ mass for the $$\sin(2\phi_h-2\phi_{R_\perp})$$ modulation is observed, matching spectator model predictions in $$\pi^+\pi^-$$ pairs.