$P$--wave quarkonia in jets at the LHC

Abstract

We present the first systematic theoretical study of the production of $P$-wave charmonium states $χ_{cJ}$ and bottomonium states $χ_{bJ}(nP)$ within jets at the LHC using the fragmenting jet function framework at next-to-leading order in $α_s$. Our calculation resums both collinear DGLAP logarithms and threshold double logarithms in the fragmentation functions and accounts for feeddown contributions from higher quarkonium states. We observe a notable contrast between the charmonium and bottomonium sectors. For $χ_{bJ}(nP)$, the normalized momentum-fraction distributions exhibit a nearly universal shape, with remarkably weak dependence on the choice of long-distance matrix element sets, the radial excitation ($n=1,2,3$), and the total angular momentum ($J=0,1,2$). We attribute this universality to the overwhelming dominance of the ${}^3S_1^{[8]}$ fragmentation channel, while feeddown contributions from higher bottomonium states remain small. In contrast, the shape of $χ_{cJ}$ distributions exhibits a stronger dependence on the matrix-element set, reflecting the different relative contributions of the ${}^3S_1^{[8]}$ and ${}^3P_J^{[1]}$ channels. We provide predictions for the $χ_{cJ}$ and $χ_{bJ}(nP)$ distributions for the CMS and LHCb kinematic selections across a range of jet transverse momenta. We also compare our predictions with \textsc{Pythia}~8 simulations for selected $P$-wave quarkonium states.