arXiv subjects

Jun He

Publications and source records attributed to Jun He.

At least 361 records · Page 20Linked to original sources

arXiv2010

Understanding the branching ratios of χ_{c1}\toϕϕ, ωω, ωϕobserved at BES-III

In this work, we discuss the contribution of the mesonic loops to the decay rates of $χ_{c1}\to ϕϕ,\,ωω$ which are suppressed by the helicity selection rules and $χ_{c1}\to ϕω$ which is a double-OZI forbidden process. We find that the mesonic loop effects naturally explain the clear signals of $χ_{c1}\to ϕϕ,\,ωω$ decay modes observed by the BES collaboration. Moreover, we investigate the effects of the $ω-ϕ$ mixing which may result in the order of magnitude of the branching ratio $BR(χ_{c1} \to ωϕ)$ being $10^{-7}$. Thus, we are waiting for the accurate measurements of the $BR(χ_{c1} \to ωω)$, $BR(χ_{c1} \to ϕϕ)$ and $BR(χ_{c1} \to ωϕ)$, which may be very helpful for testing the long-distant contribution and the $ω-ϕ$ mixing in $χ_{c1}\toϕϕ,\,ωω,\,ωϕ$ decays.

hep-ph↗

arXiv2009

Discovery potential for charmonium-like state Y(3940) by the meson photoproduction

In this work, we investigate the discovery potential for Y(3940) by the photoproduction process $γp\to Y(3940)p$. The numerical result shows that the upper (lower) limit of the total cross section for $γp\to Y(3940)p$ is up to the order of 1 $nb$ (0.1 $μb$). Additionally, the background analysis and the Dalitz plot relevant to the production of Y(3940) are studied. The Dalitz plot analysis of Y(3940) production indicates that Y(3940) signal can be distinguished from the background clearly. The lower limit of the number of events of Y(3940) reaches up to 10/0.02GeV$^2$ for one billion collisions of $γp$ by studying the invariant mass spectrum of $J/ψω$. Experimental search for Y(3940) by the meson photoproduction is suggested.

hep-ph↗

arXiv2009

Toward an automaton Constraint for Local Search

We explore the idea of using finite automata to implement new constraints for local search (this is already a successful technique in constraint-based global search). We show how it is possible to maintain incrementally the violations of a constraint and its decision variables from an automaton that describes a ground checker for that constraint. We establish the practicality of our approach idea on real-life personnel rostering problems, and show that it is competitive with the approach of [Pralong, 2007].

cs.AI↗

arXiv2009

The contributions of $qqqq\bar{q}$ components to the axial charges of proton and its resonances

We calculate the axial charges of the proton and its resonances in the framework of the constituent quark model, which is extended to include the $qqqq\bar{q}$ components. If 20% admixtures of the $qqqq\bar{q}$ components in the proton are assumed, the theoretical value for the axial charge in our model is in good agreement with the empirical value, which can not be well reproduced in the traditional constituent quark model even though the $SU(6) \bigotimes O(3)$ symmetry breaking or relativistic effect is taken into account. We also predict an unity axial charge for $N^{*}(1440)$ with 30% $qqqq\bar{q}$ components constrained by the strong and electromagnetic decays.

nucl-th↗

arXiv2009

Combined study of gamma p to eta p and pi-p to eta n in a chiral constituent quark approach

Within a chiral constituent quark model approach, $η$-meson production on the proton {\it via} electromagnetic and hadron probes are studied. With few parameters, differential cross-section and polarized beam asymmetry for γp \to ηp$ and differential cross section for $π^- p\to ηn$ processes are calculated and successfully compared with the data in the center-of-mass energy range from threshold up to 2 GeV. The five known resonances $S_{11}(1535)$, $S_{11}(1650)$, $P_{13}(1720)$, $D_{13}(1520)$, and $F_{15}(1680)$ are found to be dominant in the reaction mechanisms in both channels. Possible roles plaied by new resonances are also investigated and in the photoproduction channel, significant contribution from $S_{11}$- and $D_{15}$-resonances, with masses around 1715 MeV and 2090 MeV, respectively, are deduced. For the so-called missing resonances, no evidence is found within the investigated reactions. The helicity amplitudes and decay widths of $N^* \to πN, ηN$ are also presented, and found consistent with the PDG values.

nucl-th↗

arXiv2008

Study of $η$ photoproduction on the proton in a chiral constituent quark approach via one-gluon-exchange model

A formalism based on a chiral quark model ($χ$QM) approach complemented with a one-gluon exchange model, to take into account the breakdown of the $SU(6)\otimes O(3)$ symmetry, is presented. The configuration mixing of wave functions for nucleon and resonances are derived. % With few adjustable parameters, differential cross-section and polarized beam asymmetry for the $γp \to ηp$ process are calculated and successfully compared with the data in the centre-of-mass energy range from threshold up to 2 GeV. The known resonances $S_{11}(1535)$, $S_{11}(1650)$, $P_{13}(1720)$, $D_{13}(1520)$, and $F_{15}(1680)$, as well as two new $S_{11}$ and $D_{15}$ resonances are found to be dominant in the reaction mechanism. Besides, connections among the scattering amplitudes of the $χ$QM approach and the helicity amplitudes, as well as decay widths of resonances are established. Possible contributions from the so-called "missing resonances" are investigated and found to be negligible.

nucl-th↗

arXiv2008

Automated and robust population transfer method for three-level system using oscillating dark states

An automated and robust method for adiabatic population transfer and the preparation of an arbitrary quantum superposition state in atomic system using the oscillating dark states (ODS) is presented. Quantum state of a three-level $Λ$ configuration atomic system oscillates periodically between two ground levels, when two pairs of classical detuning laser fields driving the system into the ODS under evolving adiabatic conditions. The decoherence of the ODS evolution is greatly suppressed, and the oscillation is very stable, therefore adiabatic population transfer and the preparation of an arbitrary quantum superposition state of atomic system can be completed accurately and conveniently.

quant-ph↗

arXiv2008

Active Quantum Memory Using Oscillating Dark States

An active method for long time storage of quantum superposition state in atomic system using the Oscillating Dark States (ODS) is presented. Quantum state of a three-level $Λ$ configuration atomic system oscillates periodically between two ground levels, when two pairs of classical detuning laser fields driving the system into the ODS under evolving adiabatic conditions. When considering another uploading/unloading adiabatic conditions and applying the oscillation of the ODS to quantum state storage, surprisingly, we can obtain the greatly suppressed decoherence of the system and high fidelity of the retrieved state, even if decay factor of coherence term of the system density matrix $γ_{21}$$\cdot$ $t$$ \gg$1. The storage time is not limited by coherence decay time of the atomic system any longer, and can be thousands of times longer than that in those passive schemes without additional laser fields.

quant-ph↗

arXiv2007

Study of π^{-}p \to ηn at low energies in a chiral constituent quark model

A chiral quark model approach is extended to the study of the $πN$ scattering at low energies. The process of $π^{-}p \to ηn$ near threshold is investigated. The model is successful in describing the differential cross sections and total cross section near the $η$ production threshold. The roles of the resonances in $n\leq 2$ shells are clarified. Near threshold, the $S_{11}(1535)$ dominates the reactions, while the interferences from the $S_{11}(1650)$ turn out to be destructive around $W\lesssim 1.6$ GeV. The $D_{13}(1520)$ is crucial to give correct shapes of the differential cross sections. The nucleon pole term contributions are significant. The $P_{11}(1710)$ plays an important role around the c.m. energy $W=1.7$ GeV, it is crucial to produce an enhancement in the region of $W>1.6$ GeV as suggested by the data for total cross section. The $t$-channel is negligible in the reactions.

nucl-th↗

arXiv2007

Chiral constituent quark model study of the process $γp \to ηp$

A constituent quark model is developed for the reaction, allowing us to investigate all available data for differential cross sections as well as single polarization asymmetries (beam and target) by including {\it all} of the PDG, one to four star, nucleon resonances ($S_{11}$, $P_{11}$, $P_{13}$, $D_{13}$, $D_{15}$, $F_{15}$, $F_{17}$, $G_{17}$, $G_{19}$, $H_{19}$, $I_{1,11}$, and $K_{1,13}$). Issues related to the missing resonances are also briefly discussed by examining possible contributions from several new resonances ($S_{11}$, $P_{11}$, $P_{13}$, $D_{13}$, $ D_{15}$, and $H_{1,11}$).

nucl-th↗

arXiv2007

$πN\to ηN$ process in a $χ$QM approach

A chiral quark model approach is used to investigate the $π^{-}p \to ηn$ process at low energies. The roles of the most relevant nucleon resonances in $n\leq 2$ shells are briefly discussed.

nucl-th↗

arXiv2006

Three-photon absorption in water-soluble ZnS nanocrystals

We report on large three-photon absorption (3PA) in glutathione-capped ZnS semiconductor nanocrystals (NCs), determined by both Z-scan and transient transmission techniques with 120-fs laser pulses. The monodispersed, water-soluble ZnS NCs are synthesized by a modified protocol with a mean diameter of 2.5 nm. Their 3PA cross-section is determined to be around 2.7x10^-78 cm^6s^2photon^-2 at an optimal wavelength of commercial Ti:sapphire femtosecond lasers. This value is nearly one order of magnitude greater than that of CdS NCs, and four to five orders of magnitude higher than those of the previously reported common UV fluorescent dyes.

cond-mat.mtrl-sci↗

arXiv2005

Zero Modes in Electromagnetic Form Factors of the Nucleon in a Light-Cone Diquark Model

We use a diquark model of the nucleon to calculate the electromagnetic form factors of the nucleon described as a scalar and axialvector diquark bound state. We provide an analysis of the zero-mode contribution in the diquark model. We find there are zero-mode contributions to the form factors arising from the instantaneous part of the quark propagator, which cannot be neglected compared with the valence contribution but can be removed by the choice of wave function. We also find that the charge and magnetic radii and magnetic moment of the proton can be reproduced, while the magnetic moment of the neutron is too small. The dipole shape of the form factors, $G^p_M(Q^2)/μ_p$ and $G^n_M(Q^2)/μ_n,$ can be reproduced. The ratio $μG^p_E/G^p_M$ decreases with $Q^2,$ but too fast.

hep-ph↗

arXiv2005

Three photon absorption in ZnO and ZnS crystals

We report a systematic investigation of both three-photon absorption (3PA)spectra and wavelength dispersions of Kerr-type nonlinear refraction in wide-gap semiconductors. The Z-scan measurements are recorded for both ZnO and ZnS with femtosecond laser pulses. While the wavelength dispersions of the Kerr nonlinearity are in agreement with a two-band model, the wavelength dependences of the 3PA are found to be given by (3Ephoton/Eg-1)5/2(3Ephoton/Eg)-9. We also evaluate higher-order nonlinear optical effects including the fifth-order instantaneous nonlinear refraction associated with virtual three-photon transitions, and effectively seventh-order nonlinear processes induced by three-photon-excited free charge carriers. These higher-order nonlinear effects are insignificant with laser excitation irradiances up to 40 GW/cm2. Both pump-probe measurements and three-photon figures of merits demonstrate that ZnO and ZnS should be a promising candidate for optical switching applications at telecommunication wavelengths.

cond-mat.mtrl-sci↗

arXiv2005

Observation of Interband Two-Photon Absorption Saturation in CdS Nanocrystals

We report the observation of interband two-photon absorption (TPA) saturation in cadmium sulfide nanocrystals (CdS NCs) under intense femtosecond laser excitation with 1.6-eV photon energy. The observation has been compared to interband TPA saturation in bulk CdS under the same experimental conditions. By using both Z-scan technique and transient absorption measurement, the saturation intensity has been determined to be 190 GW/cm^2 for CdS NCs of 4-nm diameter, which shows two orders of magnitude greater than that for CdS bulk crystal. The results are in agreement with an inhomogeneously-broadened, saturated TPA model.

cond-mat.mtrl-sci↗

arXiv2005

Electroweak properties of the $π$, $K$ and $K^*(892)$ in the three forms of relativistic kinematics

The electromagnetic form factors, charge radii and decay constants of pion, K and K*(892) are calculated using the three forms of relativistic kinematics: instant form, point form and (light) front form. Simple representations of the mass operator together with single quark currents are employed with all the forms. Making use of previously fixed parameters, together with the constituent quark mass for the strange quark, a reasonable reproduction of the available data for form factors, charge radii and decay constants of pion, rho, K and K*(892) is obtained in front form. With instant form a similar description, but with a systematic underestimation of the vector meson decay constants is obtained using two different sets of parameters, one for pion and rho and another one for K and K*(892). Point form produces a poor description of the data.

hep-ph↗

arXiv2004

Electromagnetic form factors of pion and rho in the three forms of relativistic kinematics

The electromagnetic form factors of the $π$ and the $ρ$ are obtained using the three forms of relativistic kinematics, instant form, point form and (light) front form. Simple representations of the mass operator together with single quark currents are employed with all the forms. The Poincaré covariant current operators are generated by the dynamics from single-quark currents that are covariant under the kinematic subgroup. Front and instant forms allow to reproduce the available data for the pion form factor. On the other hand point form is not able to reproduce qualitatively the experimental data with reasonable values for the wave function parameters. For the $ρ$ electromagnetic form factors, instant and front forms provide a consistent picture. The obtained results do not depend appreciably on the wave function used.

hep-ph↗

arXiv2004

Magnetic moments and electromagnetic radii of nucleon and $Δ(1232)$ in an extended GBE model

We derive the exchange currents of pseudoscalar, vector, and scalar mesons from Feynman diagrams, and use them to calculate the magnetic form factors of nucleon and $Δ(1232)$. The magnetic moments and electromagnetic radii are obtained by using those form factors and the parameters determined from the masses of nucleon and $Δ(1232)$. We find the magnetic moments and electromagnetic radii of nucleon and $Δ(1232)$ can be produced very well in the extended Goldstone-boson-exchange model (GBE) in which all of pseudoscalar, vector and scalar meson nonet are included. The magnetic moments of $Δ(1232)$ are closer to experiment values and results from lattice calculation than the results obtained by the model without other mesons except for pion and sigma.

nucl-th↗