arXiv subjects
Publications and source records attributed to Xiang Liu.
Recently CDF and D0 collaborations observed several bottom baryons. In this work we perform a systematic study of the masses of bottom baryons up to $1/m_Q$ in the framework of heavy quark effective field theory (HQET) using the QCD sum rule approach. The extracted chromo-magnetic splitting between the bottom baryon heavy doublet agrees well with the experimental data.
Babar Collaboration announced two new excited charmed baryons $Ξ_c(3055)^+$ and $Ξ_c(3123)^+$. We study their strong decays assuming they are D-wave states. Some assignments are excluded by comparing our numerical results with the experimental values of the total widths of $Ξ_c(3055)^+$ and $Ξ_c(3123)^+$. We also suggest some possible decay modes, which will be helpful to determine the properties of $Ξ_c(3055)^+$ and $Ξ_c(3123)^+$.
We study whether the broad enhancement X(1576) arises from the final state interaction (FSI) of $ρ(1450,1700)\to ρ^+ρ^-\to K^{+}K^{-}$ decays. We consider both the absorptive and dispersive contribution of the above amplitudes since the intermediate states are very close to $ρ(1450,1700)$. The same mechanism leads to a similar enhancement around 1580 MeV in the $π^{+}π^-$ spectrum in the $J/ψ\to π^{0}π^{+}π^{-}$ channel, which can be used to test whether X(1576) can be ascribed to the FSI effect of $ρ(1450,1700)\to ρ^+ρ^-$.
A new baryonic state $Λ_{c}(2940)^{+}$ has recently been discovered by the Babar collaboration in the $D^{0}p$ channel. Later Belle collaboration also observed this state in the $Σ_c(2455)^{0,++} π^{\pm}\to Λ_{c}^{+}π^{+}π^{-}$ channel. The mass of $Λ_{c}(2940)^{+}$ is just a few MeV below the sum of $D^{*0}$ and $p$ masses suggesting a possibility that this state may be a $D^{*0} p$ molecular state. In this paper we study whether such a molecular state can be consistent with data. We find that the molecular structure can explain data and that if $Λ_c(2940)^+$ is a $D^{*0} p$ molecular state it is likely a $1/2^-$ state. Several other decays modes are also suggested to further test the molecular structure of $Λ_c^+(2940)$.
Assuming $D^*_{sJ}(2317)$ and $D_{sJ}(2460)$ to be the $(0^+,1^+)$ chiral partners of regular $D_{s}(1968)$ and $D^{*}_{s}(2112)$, we calculate the semileptonic decays of $B_s$ to $D_s(1968)$, $D^*_s(2112)$, $D_{sJ}^{*}(2317)$, $D_{sJ}(2460)$ in terms of the Constituent Quark Meson (CQM) model. The large branching ratios of the semileptonic decays of $B_s$ to $D_{sJ}^{*}(2317)$ and $D_{sJ}(2460)$ indicate that those two semileptonic decays should be seen in future experiments.
There has been important experimental progress in the sector of heavy baryons in the past several years. We study the strong decays of the S-wave, P-wave, D-wave and radially excited charmed baryons using the $^3P_0$ model. After comparing the calculated decay pattern and total width with the available data, we discuss the possible internal structure and quantum numbers of those charmed baryons observed recently.
Aims and Methods: We present the results of VLBI observations of nineteen GHz-Peaked-Spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are selected from the Parkes Half Jansky (PHJ) sample (Snellen 2002), 4 others are from our previous observation list. We aimed at imaging the structure of GPS sources, searching for Compact Symmetric Objects (CSOs) and studying the absorption for the convex radio spectra of GPS sources. Results: We obtained total intensity 1.6 GHz VLBI images of 17 sources for the first time. Of them, 80% show mini-double-lobe radio structure, indicating that they are CSOs or candidates, and their host AGNs could be edge-on to us. This result suggests that there is a high incidence of mini double-lobe sources (or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232, J2058+0540, J2123-0112 and J2325-0344 with measured redshift, showing double-lobe structure with sizes of <1 kpc, are classified as CSOs. Three sources J1057+0012, J1600-0037 and J1753+2750 are considered as core-jet sources according to their morphologies and flux variability.
We present images of quasi-simultaneous VLBI observations of the GHz-Peaked-Spectrum radio source OQ 208 with the Very Long Baseline Array at 1.4, 1.7, 2.3, 5.0, 8.4, 15.4 GHz and the European VLBI Network at 6.7 GHz. The low frequency (1.4, 1.7 and 2.3 GHz) observations reveal a weak and extended steep-spectrum component at about 30 mas away in the position angle of $- 110^\circ$ which may be a remnant emission. The radio structure of OQ 208 consists of two mini-lobes at 5.0, 6.7, 8.4 and 15.4 GHz. Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region. By fitting the 8.4 GHz images from 1994 to 2005, we obtain a separation speed of 0.031 $\pm$ 0.006 mas yr$^{-1}$ between the two mini-lobes. This indicates a jet proper motion of 0.105 $\pm$ 0.020 $c$ and a kinematic age of 219 $\pm$ 42 yr for the radio source.
We study whether the broad peak X(1576) observed by BES Collaboration arises from the final state interaction effect of $ρ(1450,1700)$ decays. The interference effect could produce an enhancement around 1540 MeV in the $K^+K^-$ spectrum with typical interference phases. However, the branching ratio $B[J/ψ\to π^{0}ρ(1450,1700)]\cdot B[ρ(1450,1700)\to K^{+}K^{-}]$ from the final state interaction effect is far less than the experimental data.
Recently Babar Collaboration reported a new $c\bar{s}$ state $D_{sJ}(2860)$ and Belle Collaboration observed $D_{sJ}(2715)$. We investigate the strong decays of the excited $c\bar{s}$ states using the $^{3}P_{0}$ model. After comparing the theoretical decay widths and decay patterns with the available experimental data, we tend to conclude: (1) $D_{sJ}(2715)$ is probably the $1^{-}(1^{3}D_{1})$ $c\bar{s}$ state although the $1^{-}(2^{3}S_{1})$ assignment is not completely excluded; (2) $D_{sJ}(2860)$ seems unlikely to be the $1^{-}(2^{3}S_{1})$ and $1^{-}(1^{3}D_{1})$ candidate; (3) $D_{sJ}(2860)$ as either a $0^{+}(2^{3}P_{0})$ or $3^{-}(1^{3}D_{3})$ $c\bar{s}$ state is consistent with the experimental data; (4) experimental search of $D_{sJ}(2860)$ in the channels $D_sη$, $DK^{*}$, $D^{*}K$ and $D_{s}^{*}η$ will be crucial to distinguish the above two possibilities.
We first extract the binding energy $\bar Λ$ and decay constants of the D wave heavy meson doublets $(1^{-},2^{-})$ and $(2^{-},3^{-})$ with QCD sum rule in the leading order of heavy quark effective theory. Then we study their pionic $(π, K, η)$ couplings using the light cone sum rule, from which the parameter $\bar Λ$ can also be extracted. We then calculate the pionic decay widths of the strange/non-strange D wave heavy $D/B$ mesons and discuss the possible candidates for the D wave charm-strange mesons. Further experimental information, such as the ratio between $D_sη$ and $DK$ modes, will be very useful to distinguish various assignments for $D_{sJ}(2860, 2715)$.
We investigate whether the final state interaction (FSI) effect plays a significant role in the large hidden charm decay width of X(3872) and Y(3940) using a model. Our numerical result suggests (1) the FSI contribution to $X(3872)\to J/ψρ$ is tiny; (2) $Γ[ Y(3940)\to D\bar{D}^{*}+\text{h.c.}\to J/ψω]$ from FSI is around several keV, far less than Belle's experimental value 7 MeV.
The branching ratio of $B^-\to h_c+K^-$ is re-evaluated in the PQCD approach. In this theoretical framework all the phenomenological parameters in the wavefunctions and Sudakov factor are priori fixed by fitting other experimental data, and in the whole numerical computations we do not introduce any new parameter. Our results are consistent with the upper bounds set by the Babar and Belle measurements.
Recently the BES collaboration has announced observation of a resonant state in the $π^+π^- η'$ spectrum in $J/ψ\to γπ^+π^-η'$ decay. Fitting the data with a $0^{-+}$ state, the mass is determined to be 1833.7 MeV with $7.7σ$ statistic significance. This state is consistent with the one extracted from previously reported $p \bar p$ threshold enhancement data in $J/ψ\to γp \bar p$. We study the properties of this state using QCD anomaly and QCD sum rules assuming X(1835) to be a pseudoscalar and show that it is consistent with data. We find that this state has a sizeable matrix element $<0|G\tilde G|G_p>$ leading to branching ratios of $(2.61\sim 7.37)\times 10^{-3}$ and $(2.21\sim 10.61)\times 10^{-2}$ for $J/ψ\to γG_p$ and for $G_p \to π^+π^- η'$, respectively. Combining the calculated branching ratio of $J/ψ\to γG_p$ and data on threshold enhancement in $J/ψ\to γp \bar p$, we determine the coupling for $G_p- p-\bar p$ interaction. We finally study branching ratios of other $J/ψ\to γ+ {three mesons}$ decay modes. We find that $J/ψ\to γG_p \to γ(π^+π^- η, K K π^0)$ can provide useful tests for the mechanism proposed.
In this work, we evaluate the contributions of the hadronic loops to the amplitudes of $J/ψ\to PV$ where $P$ and $V$ denote light pseudoscalar and vector mesons respectively. By fitting data of two well measured channels of $J/ψ\to PV$, we obtain the contribution from the pure OZI process to the amplitude which is expressed by a phenomenological quantity $|\mathcal{G}^{PV}_{S}|$, and a parameter $α$ existing in the calculations of the contribution of hadronic loops. In terms of $α$ and $|\mathcal{G}^{PV}_{S}|$, we calculate the branching ratios of other channels and get results which are reasonably consistent with data. Our results show that the contributions from the hadronic loops are of the same order of magnitude as that from the OZI processes and the interference between the two contributions are destructive. The picture can be applied to study other channels such as PP or VV of decays of $J/ψ$.
Recently a $J^{PC}=0^{++}$ (X(1812)) state with a mass near the threshold of $ω$ and $ϕ$ has been observed by the BES collaboration in $J/ψ\to γωϕ$ decay. It has been suggested that it is a $I^G = 0^+$ state. If it is true, this state fits in a mixing scheme based on quarkonia, glueball and hybrid (QGH) very nicely where five physical states are predicted. Together with the known $f_0(1370)$, $f_0(1500)$, $f_0(1710)$, and $f_0(1790)$ states, X(1812) completes the five members in this family. Using known experimental data on these particles we determine the ranges of the mixing parameters and predict decay properties for X(1812). We also discuss some features which may be able to distinguish between four-quark and hybrid mixing schemes.
Recent BES data on $J/ψ\to ϕππ$ indicate that there is a possible new spin-0 state ($f_0(1790)$) with a mass of $m=1790^{+40}_{-30} \mathrm{MeV}/\mathrm{c}^2$. Assuming it to be an iso-singlet $0^+(0^{++})$, we propose a new mixing scheme to describe this and the other three known iso-singlet $f_0(1370)$, $f_0(1500)$, $f_0(1710)$ states by adding iso-singlet hybrid states to the usual basis of two iso-singlet quarkonia and one glueball. Since there are two iso-singlet hybrid states, $(u\bar u+d\bar d)g/\sqrt 2$ and $s\bar sg$, this new basis implies existence of another iso-singlet state $X$. Using known data, we estimate the ranges of the mixing parameters. We find two sets of solutions with X mass predicted to be about 1820 MeV and 1760 MeV, respectively. We also study implications on the decay properties of these new states.
Based on the assumption that $D_{sJ}^{*}(2317)$ and $D_{sJ}(2460)$ are the $(0^+, 1^+)$ chiral partners of $D_{s}$ and $D^*_s$, we evaluate the strong pionic and radiative decays of $D_{sJ}^{*}(2317)$ and $D_{sJ}(2460)$ in the Constituent Quark Meson (CQM) model. Our numerical results of the relative ratios of the decay widths are reasonably consistent with data.