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We apply an equal-velocity quark combination model to study the Λ c + / D 0 ratio in the range p T ≲ 10 GeV/c in pp collisions at s = 13 TeV. We decompose the ratio into four parts which are related to quark numbers, light-flavor quark p T spectrum, charm quark p T spectrum, momentum correlation between light and charm quarks, respectively. Their influence on Λ c + / D 0 ratio is individually studied. The curvature property of light-flavor quark p T spectrum is the main reason of the non-monotonic p T dependence of Λ c + / D 0 ratio exhibited in high multiplicity events. Moreover, the multiplicity dependence of Λ c + / D 0 ratio as the function of p T is mainly because of the multiplicity dependence of light-flavor quark p T spectrum. Using the light-flavor quark p T spectrum obtained from experimental data of light-flavor hadrons and charm quark p T spectrum obtained from FONLL and/or PYTHIA calculations, the p T dependence of experimental data of Λ c + / D 0 ratio in high multiplicity events and that in low multiplicity events in pp collisions at s = 13 TeV are reasonably understood. [ABSTRACT FROM AUTHOR]

In this paper, we propose the sterile neutrino portal dark matter in ν THDM. This model can naturally generate tiny neutrino mass with the neutrinophilic scalar doublet Φ ν and sterile neutrinos N around TeV scale. Charged under a Z 2 symmetry, one Dirac fermion singlet χ and one scalar singlet ϕ are further introduced in the dark sector. The sterile neutrinos N are the mediators between the DM and SM. Depending on the coupling strength, the DM can be either WIMP or FIMP. For the WIMP scenario, pair annihilation of DM into NN is the key channel to satisfy various bounds, which could be tested at indirect detection experiments. For the FIMP scenario, besides the direct production of DM from freeze-in mechanism, contributions from late decay of NLOP is also important. When sterile neutrinos are heavier than the dark sector, NLOP is long-lived due to tiny mixing angle between sterile and light neutrinos. Constrains from free-streaming length, CMB, BBN and neutrino experiments are considered. [ABSTRACT FROM AUTHOR]

We apply a quark combination model with equal-velocity combination (EVC) approximation to study the elliptic flow ( v 2 ) of hadrons in heavy-ion collisions in a wide collision energy range ( s NN = 27–5020 GeV). Utilizing the simple relationship between v 2 of hadrons and those of quarks under EVC, we find that v 2 of up/down quarks obtained by experimental data of proton is consistent with that obtained by data of Λ and Ξ . v 2 of strange quarks obtained by data of Ω is consistent with that obtained by data of Λ and Ξ , and at RHIC energies it is also consistent with that obtained by data of ϕ . This means that v 2 of these hadrons have a common quark-level source. Using data of D 0 , we obtain v 2 of charm quarks with p T ≲ 6 GeV/c. We find that under EVC charm quark dominates v 2 of D mesons at low p T but light-flavor quarks significantly contribute to v 2 of D mesons in the range 3 ≲ p T ≲ 8 GeV/c. We predict v 2 of charmed baryons Λ c + and Ξ c 0 which show a significant enhancement at intermediate p T due to the double contribution of light-flavor quarks. The properties of the obtained quark v 2 under EVC are studied and a regularity for v 2 of quarks as the function of p T / m is found. [ABSTRACT FROM AUTHOR]

Radiative transitions between charmonium states offer an insight into the internal structure of heavy quark bound states within QCD. In this work, we systematically investigate the coupled-channel effects of intermediate charmed mesons to charmonium radiative transitions utilizing an effective Lagrangian approach. Our results show that the coupled-channel effects of these decays under the open charm thresholds are relatively weak, while the coupled-channel effects of the excited P-wave states close to the charmed pairs thresholds are relatively important. [ABSTRACT FROM AUTHOR]

Treating the light-flavor constituent quarks and antiquarks whose momentum information is extracted from the data of soft light-flavor hadrons in pp collisions at s=7 TeV as the underlying source of chromatically neutralizing the charm quarks of low transverse momenta (pT), we show that the experimental data of pT spectra of single-charm hadrons D0,+, D∗+Ds+, Λc+ and Ξc0 at mid-rapidity in the low pT range (2≲pT≲7 GeV/c) in pp collisions at s=7 TeV can be well understood by the equal-velocity combination of perturbatively created charm quarks and those light-flavor constituent quarks and antiquarks. This suggests a possible new scenario of low pT charm quark hadronization, in contrast to the traditional fragmentation mechanism, in pp collisions at LHC energies. This is also another support for the exhibition of the soft constituent quark degrees of freedom for the small parton system created in pp collisions at LHC energies. [ABSTRACT FROM AUTHOR]