Heavy quark fragmentation function in 't Hooft Model

We carry out a comprehensive study of the quark-to-meson fragmentation function in the 't Hooft model, i.e., the two-dimensional Quantum Chromodynamics (QCD) in $N_c\to \infty$ limit, following the operator definition pioneered by Collins and Soper. We apply the Hamiltonian approach as well as the diagrammatic approach to construct the functional form of the quark-to-meson fragmentation function in terms of the meson's light-cone wave function. For the sake of comparison, we also investigate the heavy quark fragmentation into quarkonium in two-dimensional QCD within the framework of the nonrelativistic QCD (NRQCD) factorization, at the lowest order in quark velocity. In the heavy quark limit, the quark fragmentation function obtained from the {\it ab initio} method agrees well, both analytically and numerically, with that obtained from the NRQCD approach. This agreement might be regarded as a nontrivial justification for the validity of both field-theoretical approaches to compute the heavy quark fragmentation function.Comment: 23 pages, 4 figures, 1 tabl

Light-cone and quasi generalized parton distributions in the 't Hooft model

We present a comprehensive study of the light-cone generalized parton distribution (GPD) and quasi-GPD of a flavor-neutral meson in the 't Hooft model, {\it i.e.}, two-dimensional QCD (\QCDtw) in the $N_c\to\infty$ limit. With the aid of the Hamiltonian approach, we construct the light-cone GPD in terms of the meson's light-cone wave function in the framework of light-front quantization, and express the quasi-GPD in terms of the meson's Bars-Green wave functions and the chiral angle in the framework of equal-time quantization. We show that, both analytically and numerically, the quasi-GPD does approach the light-cone GPD when the meson is boosted to the infinite momentum frame, which justifies the tenet underlying the large momentum effective theory for the off-forward parton distribution. Upon taking the forward limit, the light-cone and quasi-GPDs reduce to the light-cone and quasi-PDFs. As a bonus, we take this chance to correct the incomplete expression of the quasi-PDFs in the 't Hooft model reported in our preceding work [Y. Jia et al. Phys. Rev. D 98, 054011 (2018)].Comment: 31 pages, 14 figures, 1 tabl

Photoproduction of C-even quarkonia at EIC and EicC

The $\eta_c$ photoproduction in $ep$ collision has long been proposed as an ideal process to probe the existence of odderon. In the current work, we systematically investigate the photoproduction of various $C$-even heavy quarkonia (exemplified by $\eta_{c(b)}$, and $\chi_{c(b)J}$ with $J=0,1,2$) via one-photon exchange channel, at the lowest order in $\alpha_s$ and heavy quark velocity in the context of NRQCD factorization. We find that the photoproduction rates of the $C$-even quarkonia through this mechanism are comparable in magnitude with that through the odderon-initiated mechanism, even in the Regge limit ($s\gg -t$), though the latter types of predictions suffers from considerable theoretical uncertainties. The future measurements of these types of quarkonium photoproduction processes in \texttt{EIC} and \texttt{EicC} are crucial to ascertain which mechanism plays the dominant role.Comment: 16 pages, 9 figure

Hard-scattering approach to strongly hindered electric dipole transitions between heavy quarkonia

The conventional wisdom in dealing with electromagnetic transition between heavy quarkonia is the multipole expansion, when the emitted photon has a typical energy of order quarkonium binding energy. Nevertheless, in the case when the energy carried by the photon is of order typical heavy quark momentum, the multipole expansion doctrine is expected to break down. In this work, we apply the "hard-scattering" approach originally developed to tackle the strongly hindered magnetic dipole ($M1$) transition [Y.~Jia {\it et al.}, Phys. \ Rev. \ D. 82, 014008 (2010)] to the strongly hindered electric dipole ($E1$) transition between heavy quarkonia. We derive the factorization formula for the strongly hindered $E1$ transition rates at the lowest order in velocity and $\alpha_s$ in the context of the non-relativistic QCD (NRQCD), and conduct a detailed numerical comparison with the standard predictions for various bottomonia and charmonia $E1$ transition processes.Comment: 18 pages, 2 figures, 4 table

Enhanced Stem Cell Osteogenic Differentiation by Bioactive Glass Functionalized Graphene Oxide Substrates

An unmet need in engineered bone regeneration is to develop scaffolds capable of manipulating stem cells osteogenesis. Graphene oxide (GO) has been widely used as a biomaterial for various biomedical applications. However, it remains challenging to functionalize GO as ideal platform for specifically directing stem cell osteogenesis. Herein, we report facile functionalization of GO with dopamine and subsequent bioactive glass (BG) to enhance stem cell adhesion, spreading, and osteogenic differentiation. On the basis of graphene, we obtained dopamine functionalized graphene oxide/bioactive glass (DGO/BG) hybrid scaffolds containing different content of DGO by loading BG nanoparticles on graphene oxide surface using sol-gel method. To enhance the dispersion stability and facilitate subsequent nucleation of BG in GO, firstly, dopamine (DA) was used to modify GO. Then, the modified GO was functionalized with bioactive glass (BG) using sol-gel method. The adhesion, spreading, and osteoinductive effects of DGO/BG scaffold on rat bone marrow mesenchymal stem cells (rBMSCs) were evaluated. DGO/BG hybrid scaffolds with different content of DGO could influence rBMSCs’ behavior. The highest expression level of osteogenic markers suggests that the DGO/BG hybrid scaffolds have great potential or elicit desired bone reparative outcome

Heavy quark fragmentation function in two-dimensional QCD in Nc→∞N_c\rightarrow \infty N c → ∞ limit

Abstract We carry out a comprehensive study of the quark-to-meson fragmentation function in the ’t Hooft model, i.e., the two-dimensional quantum chromodynamics (QCD) in $$N_c\rightarrow \infty$$ N c → ∞ limit, following the operator definition pioneered by Collins and Soper. We apply the Hamiltonian approach as well as the diagrammatic approach to construct the functional form of the quark-to-meson fragmentation function in terms of the meson’s light-cone wave function. For the sake of comparison, we also investigate the heavy quark fragmentation into quarkonium in two-dimensional QCD within the framework of the nonrelativistic QCD (NRQCD) factorization, at the lowest order in quark velocity. In the heavy quark limit, the quark fragmentation function obtained from the ab initio method agrees well, both analytically and numerically, with that obtained from the NRQCD approach. This agreement might be regarded as a nontrivial justification for the validity of both field-theoretical approaches to compute the heavy quark fragmentation function

Next-to-next-to-leading-order QCD corrections to e+e− → J/ψηc at B factories

Within the nonrelativistic QCD (NRQCD) factorization framework, we compute the long-awaited O(αs2) corrections for the exclusive double charmonium production process at B factories, i.e., e+e−→J/ψ+ηc at s=10.58 GeV. We confirm that NRQCD factorization does hold at next-to-next-to-leading-order (NNLO) for exclusive double charmonium production. It is found that including the NNLO QCD correction considerably reduces the renormalization scale dependence, and also implies the reasonable perturbative convergence behavior for this process. We also include both O(v2) and O(αsv2) corrections for this process. With all the available corrections lumped together, our most comprehensive prediction is consistent with both the BaBar and Belle measurement within errors

Next-to-next-to-leading-order QCD corrections to J/ψ+χc0,1,2J/\psi+\chi_{c0,1,2} production at BB factory

We compute the next-to-next-to-leading-order (NNLO) perturbative corrections to the exclusive channels $e^+e^-\to J/\psi+\chi_{cJ}$ ($J=0,1,2$) at $\sqrt{s}=10.58$ GeV within the nonrelativistic QCD (NRQCD) factorization framework. The validity of NRQCD factorization at ${\cal O}(\alpha_s^2)$ has been confirmed for these double-charmonium exclusive production processes. We analyze the impact of the NNLO perturbative corrections on the polarized and unpolarized cross sections, as well as the $J/\psi$ angular distributions, which largely reduce the renormalization scale dependence but lower the NLO NRQCD predictions to some extent for $\chi_{c0,1}$. With high numerical accuracy, our NNLO predictions for $\sigma(J/\psi+\chi_{c1,2})$ are compatible with the upper limit of the \texttt{Belle} measurement. Although the finest prediction for $\sigma(J/\psi+\chi_{c0})$ is consistent with both \texttt{Belle} and \texttt{BaBar} measurements within uncertainties, there still exists serious tension between the predicted and the measured profiles for the $J/\psi$ angular distribution. Regarding the bright observation prospect of the $e^+e^-\to J/\psi+\chi_{c1,2}$ channels in \texttt{Belle 2} experiment, it is interesting to compare the future measurements with our NNLO predictions. The more accurate measurement of $e^+e^-\to J/\psi+\chi_{0}$ at \texttt{Belle 2} will also help to clarify the long-standing puzzle of $J/\psi$ angular distribution.Comment: 17 pages, 4 tables, 2 figures. b quark loop contributions explicitly include