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We investigate the gluonic structure of nuclei within a mean-field model of nuclear structure based upon the self-consistent modification of the structure of a bound nucleon, with the nucleon described by the Nambu--Jona-Lasinio model. This approach has been shown to reproduce the European Muon Collaboration (EMC) effect, involving the ratio of the spin-independent structure functions of a heavier nucleus to that of the deuteron. It also predicts a significant nuclear modification for the spin structure functions, known as the polarized EMC effect. Here we report sizeable nuclear modifications of the gluon distributions (a gluon EMC effect) for the ratios of both the unpolarized and polarized gluon distributions in nuclear matter to those of a free nucleon.
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We estimate the $Upsilon$, $eta_b$ and $B^*$ meson mass shifts in symmetric nuclear matter. The interest is, whether the strengths of the bottomonium-(nuclear matter) and charmonium-(nuclear matter) interactions are similar or different. This is because, each ($J/Psi,Upsilon$) and ($eta_c,eta_b$) meson group is usually assumed to have very similar properties based on the heavy charm and bottom quark masses. The estimate for the $Upsilon$ is made using an SU(5) effective Lagrangian and the anomalous coupling one, by studying the $BB$, $BB^*$, and $B^*B^*$ meson loop contributions for the self-energy. As for the $eta_b$, we include the $BB^*$ and $B^*B^*$ meson loop contributions in the self-energy. The in-medium masses of the $B$ and $B^*$ mesons appearing in the self-energy are calculated by the quark-meson coupling model. An analysis on the $BB$, $BB^*$, and $B^*B^*$ meson loops in the $Upsilon$ mass shift is made by comparing with the corresponding $DD, DD^*$, and $D^*D^*$ meson loops for the $J/Psi$ mass shift. Our prediction for the $eta_b$ mass shift is made including only the lowest order $BB^*$ meson loop. The $Upsilon$ mass shift, with including only the $BB$ loop, is predicted to be -16 to -22 MeV at the nuclear matter saturation density using the $Upsilon BB$ coupling constant determined by the vector meson dominance model with the experimental data, while the $eta_b$ mass shift is predicted to be -75 to -82 MeV with the SU(5) universal coupling constant determined by the $Upsilon BB$ coupling constant. Our results show an appreciable difference between the bottomonium-(nuclear matter) and charmonium-(nuclear matter) interaction strengths. We also study the $Upsilon$ and $eta_b$ mass shifts in a heavy quark (heavy meson) symmetry limit.
We study the medium-induced gluon emission process experienced by a hard jet parton propagating through the dense nuclear matter in the framework of deep inelastic scattering off a large nucleus. We work beyond the collinear rescattering expansion and the soft gluon emission limit, and derive a closed formula for the medium-induced single gluon emission spectrum from a heavy or light quark jet interacting with the dense nuclear medium via transverse and longitudinal scatterings. Without performing the collinear rescattering expansion, the medium-induced gluon emission spectrum is controlled by the full distribution of the differential elastic scattering rates between the propagating partons and the medium constituents. We further show that if one utilizes heavy static scattering centers for the traversed nuclear matter and takes the soft gluon emission limit, our result can reduce to the first order in opacity Djordjevic-Gyulassy-Levai-Vitev formula.
We determine nuclear structure functions and quark distributions for $^7$Li, $^{11}$B, $^{15}$N and $^{27}$Al. For the nucleon bound state we solve the covariant quark-diquark equations in a confining Nambu--Jona-Lasinio model, which yields excellent results for the free nucleon structure functions. The nucleus is described using a relativistic shell model, including mean scalar and vector fields that couple to the quarks in the nucleon. The nuclear structure functions are then obtained as a convolution of the structure function of the bound nucleon with the light-cone nucleon distributions. We find that we are readily able to reproduce the EMC effect in finite nuclei and confirm earlier nuclear matter studies that found a large polarized EMC effect.
We study two- and three-gluon glueballs of $C=+$ using the method of QCD sum rules. We systematically construct their interpolating currents, and find that all the spin-1 currents of $C=+$ vanish. This suggests that the ground-state spin-1 glueballs of $C=+$ do not exist within the relativistic framework. We calculate masses of the two-gluon glueballs with $J^{PC} = 0^{pm+}/2^{pm+}$ and the three-gluon glueballs with $J^{PC} = 0^{pm+}/2^{pm+}$. We propose to search for the $J^{PC} = 0^{-+}/2^{-pm}/3^{pm-}$ three-gluon glueballs in their three-meson decay channels in future BESIII, GlueX, LHC, and PANDA experiments.
Chiral-odd gluon transversity distribution could shed light on a new aspect of hadron physics. Although we had much progress recently on quark transversity distributions, there is no experimental measurement on the gluon transversity. The gluon trasversity does not exist in the spin-1/2 nucleons and it exists in the spin-1 deuteron. Therefore, it could probe new hadron physics in the deuteron beyond the basic bound system of a proton and a neutron because the nucleons cannot contribute directly. Here, we explain that the gluon transversity can be measured at hadron accelerator facilities, such as Fermilab and NICA, in addition to charged-lepton scattering measurements at lepton accelerator facilities by showing cross sections of the proton-deuteron Drell-Yan process as an example.
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