117582931
Study on the mechanism of open-flavor strong decays
Open-flavor strong decays are studied based on the interaction of a potential quark model. The decay process is related to the s-channel contribution of the same scalar confinement and one-gluon-exchange (OGE) interaction in the quark model. After we adopt the prescription of massive gluons in a time-like region from the lattice calculation, the approximation of four-fermion interaction is applied. The numerical calculation is performed to the meson decays in u, d and s light flavor sectors. The analysis of the D/S ratios of b1 → ωπ and a1 → ρπ shows that the scalar interaction should be dominant in the open-flavor decays.
119213233
Hidden-charm tetraquarks and charged Z c states
Experimentally several charged axial-vector hidden-charm states were reported. Within the framework of the color-magnetic interaction, we have systematically considered the mass spectrum of the hidden-charm and hidden-bottom tetraquark states. It is impossible to accommodate all the three charged states $Z_c(3900)$, $Z_c(4025)$ and $Z_c(4200)$ within the axial vector tetraquark spectrum simultaneously. Not all these three states are tetraquark candidates. Moreover, the eigenvector of the chromomagnetic interaction contains valuable information of the decay pattern of the tetraquark states. The dominant decay mode of the lowest axial vector tetraquark state is $J/\psi \pi$ while its $D^*\bar{D}$ and $\bar{D}^*D^*$ modes are strongly suppressed, which is in contrast with the fact that the dominant decay mode of $Z_c(3900)$ and $Z_c(4025)$ is $\bar{D}D^*$ and $\bar{D}^*D^*$ respectively. We emphasize that all the available experimental information indicates that $Z_c(4200)$ is a very promising candidate of the lowest axial vector hidden-charm tetraquark state.
119296933
Probing the XYZ states through radiative decays
In this work, we have adopted the spin rearrangement scheme in the heavy quark limit and extensively investigated three classes of the radiative decays: $\mathfrak{M}\to (b\bar{b})+\gamma$, $(b\bar{b})\to \mathfrak{M}+\gamma$, $ \mathfrak{M} \to \mathfrak{M}^\prime+\gamma$, corresponding to the electromagnetic transitions between one molecular state and bottomonium, one bottomonium and molecular state, and two molecular states respectively. We also extend the same formalism to study the radiative decays of the molecular states with hidden charm. We have derived some model independent ratios when the initial or final states belong to the same spin flavor multiplet. Future experimental measurement of these ratios will test the molecular picture and explore the underlying structures of the $XYZ$ states.
119536600
Study of the heavy molecular states in the quark model with meson exchange interaction
Some charmonium-like resonances such as X(3872) can be interpreted as possible D(*)(*) molecular states. Within the quark model, we study the structure of such molecular states and the similar B(*)(*) molecular states by taking into account the light meson exchange (π, η, ρ, ω and σ) between two light quarks from different mesons.
13990506
Dynamics study of Z+(4430) and X(3872) in molecular picture
In this talk, we review our recent work about the dynamical studies of Z+(4430) and X(3872). Z+(4430) can not be explained as a D1′D* or D1D* molecular state only considering one pion exchange potential without the cutoff, which needs to be confirmed by introducing sigma exchange potential and adding the cutoff in the effective potential. One also excludes the possibility of X(3872) as a DD* molecular state by one pion and one sigma exchanges with the cutoff. Fortunately there exists an S‐wave BB* bound state with JPC = 1++. we suggest future experiment to search this state.
118631198
Fine Splitting in Charmonium Spectrum with Channel Coupling Effect
We study the fine splitting in charmonium spectrum in quark model with the channel coupling effect, including $DD$, $DD^*$, $D^*D^*$ and $D_sD_s$, $D_sD_s^*$, $D_s^*D_s^*$ channels. The interaction for channel coupling is constructed from the current-current Lagrangian related to the color confinement and the one-gluon exchange potentials. By adopting the massive gluon propagator from the lattice calculation in the nonperturbative region, the coupling interaction is further simplified to the four-fermion interaction. The numerical calculation still prefers the assignment $1^{++}$ of X(3872).
118376948
Measuring the beaming angle of GRB 030329 by fitting the rebrightenings in its multiband afterglow
Multiple rebrightenings have been observed in the multiband afterglow of GRB 030329. In particular, a marked and quick rebrightening occurred at about t ∼ 1.2 × 10 5 s. Energy injection from late and slow shells seems to be the best interpreta- tion for these rebrightenings. Usually it is assumed that the energy is injected into the whole external shock. However, in the case of GRB 030329, the rebrightenings are so quick that the usual consideration fails to give a satisfactory fit to the observed light curves. Actually, since these late/slow shells freely coast in the wake of the external shock, they should be cold and may not expand laterally. The energy injection then should only occur at the central region of the external shock. Considering this effect, we numerically re-fit the quick rebrightenings observed in GRB 030329. By doing this, we were able to derive the beaming angle of the energy injection process. Our result, with a relative residual of only 5% - 10% during the major rebrightening, is bet- ter than any previous modeling. The derived energy injection angle is about 0.035. We assume that these late shells are ejected by the central engine via the same mechanism as those early shells that produce the prompt gamma-ray burst. The main difference is that their velocities are much slower, so that they catch up with the external shock relatively late and are manifested as the observed quick rebrightenings. If this were true, then the derived energy injection angle can give a good measure of the beaming angle of the prompt γ-ray emission. Our study may hopefully provide a novel method to measure the beaming angle of gamma-ray bursts.
119113121
Multiple Parton Scattering in Nuclei: Modified DGLAP Evolution for Fragmentation Functions
Within the framework of generalized factorization of higher-twist contributions to semi-inclusive cross section of deeply inelastic scattering off a large nucleus, multiple parton scattering leads to an effective medium-modified fragmentation function and the corresponding medium-modified DGLAP evolution equations. We extend the study to include gluon multiple scattering and induced quarkantiquark production via gluon fusion . We numerically solve these medium-modified DGLAP (mDGLAP) evolution equations and study the scale (Q), energy (E), length (L) and jet transport parameter (q̂) dependence of the modified fragmentation functions for a jet propagating in a uniform medium with finite length (a “brick” problem). We also discuss the concept of parton energy loss within such mDGLAP evolution equations and its connection to the modified fragmentation functions. With a realistic Wood-Saxon nuclear geometry, we calculate the modified fragmentation functions and compare to experimental data of DIS off large nuclei. The extracted jet transport parameter at the center of a large nucleus is found to be q̂0 = 0.024 ± 0.008 GeV /fm.
119201296
Event-by-event generation of electromagnetic fields in heavy-ion collisions
We compute the electromagnetic fields generated in heavy-ion collisions by using the HIJING model. Although after averaging over many events only the magnetic field perpendicular to the reaction plane is sizable, we find very strong electric and magnetic fields both parallel and perpendicular to the reaction plane on the event-by-event basis. We study the time evolution and the spatial distribution of these fields. Especially, the electromagnetic response of the quark-gluon plasma can give non-trivial evolution of the electromagnetic fields. The implications of the strong electromagnetic fields on the hadronic observables are also discussed.
3066888
Global quark polarization in non-central A+A collisions
Partons produced in the early stage of non-central heavy-ion collisionscan develop a longitudinal fluid shear because of unequal local number densities of participant target and projectile nucleons. Under such fluid shear, local parton pairs with non-vanishing impact parameter have finite local relative orbital angular momentum along the direction opposite to the reaction plane. Such finite relative orbitalangular momentum among locally interacting quark pairs can lead to global quark polarization along the same direction due to spin-orbital coupling. Local longitudinal fluid shear is estimated within both Landau fireball and Bjorken scaling model of initial parton production. Quark polarization through quark-quark scatterings with the exchange of a thermal gluon is calculated beyond small-angle scattering approximation in a quark-gluon plasma. The polarization is shown to have a non-monotonic dependence on the local relative orbital angular momentum dictated by the interplay between electric and magnetic interaction. It peaks at a value of relative orbital angular momentum which scales with the magnetic mass of the exchanged gluons. With the estimated small longitudinal fluid shear in semi-peripheral Au+Au collisions at the RHIC energy, the final quark polarization is found to be small left hbar P_q right hbar <0.04 in the weak coupling limit. Possible behavior of the quark polarization in the strong coupling limit and implications on the experimental detection of such global quark polarization at RHIC and LHC are also discussed.
119298308
Suppression of high $p_T$ hadron spectra in $p+A$ collisions
Abstract Multiple hard and semi-hard parton scatterings in high-energy p + A collisions involve multi-parton correlation inside the projectile in both momentum and flavor which will lead to modification of the final hadron spectra relative to that in p + p collisions. Such modification of the final hadron transverse momentum spectra in p + A collisions is studied within HIJING 2.1 Monte Carlo model which includes nuclear shadowing of the initial parton distributions and transverse momentum broadening. Multi-parton flavor and momentum correlation inside the projectile are incorporated through flavor and momentum conservation which are shown to modify the flavor content and momentum spectra of final partons and most importantly lead to suppression of large p T hadron spectra in p + A collisions at both RHIC and LHC energies.