Gluon shadowing and nuclear entanglement entropy

Relying on previous results, that link entanglement entropy and parton distribution functions in deep inelastic scattering, and focusing on the small Bjorken scaling region we present here indications that gluon shadowing might indeed be explained as due to a depletion of the entanglement entropy, between observed and unobserved degrees of freedom, per nucleon within a nucleus, with respect to the free nucleon. We apply to gluon shadowing the general Page approach to the calculation of the entanglement entropy in bipartite systems, giving physical motivations of the results.

Z-boson production in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV and Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

Measurement of Z-boson production in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 8.16 TeV and Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity −4 < ημ< −2.5 and transverse momentum $$ {p}_{\mathrm{T}}^{\mu } $$ p T μ > 20 GeV/c in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass 60 < mμμ< 120 GeV/c2 and rapidity 2.5 <$$ {y}_{\mathrm{cms}}^{\mu \mu} $$ y cms μμ < 4. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward (−4.46 <$$ {y}_{\mathrm{cms}}^{\mu \mu} $$ y cms μμ < −2.96) and forward (2.03 <$$ {y}_{\mathrm{cms}}^{\mu \mu} $$ y cms μμ < 3.53) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a 3.4σ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.

The role of transverse momentum on the nuclear valence and sea quark distribution functions

We investigate the transverse momentum dependence of valence and sea quark distribution functions of light asymmetric nuclei ($$^{3}He$$3He and $$^{7}Li$$7Li). To this end, we first calculate the valence and sea distributions of these nuclei applying a parametrization method in which the parton distribution functions (PDFs) of nucleus are related to those of free nucleon via a weight function that contains the nuclear modifications. Then we obtain the unpolarized transverse momentum dependent (TMD) PDFs of the nucleus using the covariant parton model (CPM) approach. We also compute the valence and sea quark distributions ratios of $$^{3}He$$3He and $$^{7}Li$$7Li to those of deuteron and present the results with respect to x (Bjorken variable) at fixed values of transverse momentum. It is found that these ratios shift to the larger values of x by increasing the transverse momentum value as expected and they are not transverse momentum dependent in large x region.

Analysis of the flow systematics in Au+Au collisions

The new implementation of the Boltzmann-Uhling-Uhlenbeck equation, the VdWBUU simulation (with EoS-dependent in-medium nucleon-nucleon cross sections) appears to reproduce the flow observables in the Au+Au collisions in the energy range from 400 AMeV to 10 AGeV. The range of the feasible stiffness of the EoS can be identified, based on the analysis presented here, as encompassing compressibilities starting from 250-260 MeV and above, and thus consistent with the results of re-analysis of the giant monopole resonance data (250-310 MeV). Using that additional constraint, the range of feasible values of the stiffness of density dependence can be set as γ=1−1.25, with the value γ=1 appearing as as a global value of stiffness of the symmetry energy feasible over the whole range of constrained compressibilities. The implementation of BUU with the free nucleon-nucleon cross sections can not describe correctly the global trends of flow observables.

Electron and Muon production cross-sections in quasielastic ν(ν̄)-Nucleus scattering for Eν < 1GeV

In this paper, we have studied (anti)neutrino induced charged current quasielastic (CCQE) scattering from some nuclear targets in the energy region of [Formula: see text]. Our aim is to confront electron and muon production cross-sections relevant for [Formula: see text] or [Formula: see text] oscillation experiments. The effects due to lepton mass and its kinematic implications, radiative corrections, second class currents (SCCs) and uncertainties in the axial and pseudoscalar form factors are calculated for (anti)neutrino induced reaction cross-sections on free nucleon as well as the nucleons bound in a nucleus where nuclear medium effects influence the cross-section. For the nuclear medium effects, we have taken some versions of Fermi gas model (FGM) available in the literature. The results for (anti)neutrino–nucleus scattering cross-section per interacting nucleons are compared with the corresponding results in free nucleon case.

The role of quark exchange in the structure function of Lithium nucleus

The quark exchange formalism is formulated to calculate the quark momentum distribution in the iso-scalar Lithium nucleus. Then by boosting the nucleus to an infinite momentum frame, the Lithium structure function is evaluated at different nucleon "sizes", i.e., b = 0.7, 0.8, 0.9 and 1 fm and the Bjorken scale (x) values. It is shown that the Lithium structure function becomes narrower, and it is pushed to the smaller x values, as the nucleon size is increased. Similar to our previous works for three nucleon systems, the Lithium nucleus European muon collaboration (EMC) ratio decreases, as we increase the x and b values and it shows larger effect, with respect to the free nucleon and three nucleons iso-scalar nucleus. On the other hand, present calculation of the EMC ratio for Lithium nucleus shows a good agreement with the corresponding NMC data, which is available for 1.4 × 10-4 ≤ x ≤ 0.65. Since the atomic number is still small (A = 6), in this work as usual, we ignore the possibility of simultaneous exchange of quarks between more than two nucleons, which can be important as one moves to the heavy nuclei. Although, according to Hen et al., in the neutron rich nuclei the protons have a greater probability than neutrons to have momentum greater than the Fermi momentum, the three-body contribution may be suppressed.

GROUND STATE MAGNETIC PROPERTIES OF ODD NEUTRON DY ISOTOPES

Using the quasiparticle phonon nuclear model (QPNM) and taking into account the spin–spin interaction, the effects of the spin polarization on spin gyromagnetic factors (gs) as well as the intrinsic magnetic moments (gK) of the deformed odd neutron155-165Dy isotopes were studied. The calculated values of gsand gKare in fair agreement with the experiment as well as with other microscopic calculations. Our calculations indicated that because of the core polarization, the gsfactors of the nucleons in the nucleus reduce noticeably from its free nucleon value and the spin–spin interactions play an important role in the explanation of the quenching of the gsfactors. A very good reproduction of the phenomenological quenching of gsfactor from its free values [Formula: see text] is obtained for155-165Dy .

DUALITY OF DYNAMICAL AND THERMAL DESCRIPTIONS IN PARTON DISTRIBUTION FUNCTIONS

We suggest a duality between the standard (dynamical) and statistical distributions of partons in the nucleons. The temperature parameter entering into the statistical form for the quark distributions is estimated. It is shown that the freeze-out temperature in central heavy-ion collisions at zero chemical potential or the effective width of the energy distribution of pions has a similar value which was estimated in this paper for the valence massless quarks in a free nucleon.

MESONS IN THE MEDIUM: EXPERIMENTS WITH CLAS AT JEFFERSON LAB

In this article, we report on on investigations of the in-medium meson-nucleon interaction for the ω, ɸ, and [Formula: see text] mesons. Their in-medium cross sections and collisional widths can be measured by their absorption in a nucleus. In Hall B at the Thomas Jefferson National Accelerator Facility (JLab), the CLAS detector was used to study these long-lived mesons in nuclei. All of the mesons were produced by a photon beam with E γ < 4 GeV in targets of 2 H , C , Fe , and Pb . The vector mesons were reconstructed through their decay into e+e-. The [Formula: see text] mesons were measured with their dominant π+π- decay. The in-medium widths of the ω and ɸ mesons are found to be substantially larger than their values from the elementary reaction with a free nucleon. The analysis with the [Formula: see text] is preliminary, and its status will be discussd in this paper.