arXiv subjects

Xiang Liu

Publications and source records attributed to Xiang Liu.

At least 469 records · Page 26Linked to original sources

arXiv2017

Cooperative Relative Positioning of Mobile Users by Fusing IMU Inertial and UWB Ranging Information

Relative positioning between multiple mobile users is essential for many applications, such as search and rescue in disaster areas or human social interaction. Inertial-measurement unit (IMU) is promising to determine the change of position over short periods of time, but it is very sensitive to error accumulation over long term run. By equipping the mobile users with ranging unit, e.g. ultra-wideband (UWB), it is possible to achieve accurate relative positioning by trilateration-based approaches. As compared to vision or laser-based sensors, the UWB does not need to be with in line-of-sight and provides accurate distance estimation. However, UWB does not provide any bearing information and the communication range is limited, thus UWB alone cannot determine the user location without any ambiguity. In this paper, we propose an approach to combine IMU inertial and UWB ranging measurement for relative positioning between multiple mobile users without the knowledge of the infrastructure. We incorporate the UWB and the IMU measurement into a probabilistic-based framework, which allows to cooperatively position a group of mobile users and recover from positioning failures. We have conducted extensive experiments to demonstrate the benefits of incorporating IMU inertial and UWB ranging measurements.

cs.NI↗

arXiv2017

Low-lying charmed and charmed-strange baryon states

In this work, we systematically study the mass spectra and strong decays of $1P$ and $2S$ charmed and charmed-strange baryons in the framework of nonrelativistic constituent quark models. With the light quark cluster-heavy quark picture, the masses are simply calculated by a potential model. The strong decays are studied by the Eichten-Hill-Quigg decay formula. Masses and decay properties of the well-established $1S$ and $1P$ states can be reproduced by our method. $Σ_c(2800)^{0,+,++}$ can be assigned as a $Σ_{c2}(3/2^-)$ or $Σ_{c2}(5/2^-)$ state. We prefer to interpret the signal $Σ_c(2850)^0$ as a $2S(1/2^+)$ state although at present we cannot thoroughly exclude the possibility that this is the same state as $Σ_c(2800)^0$. $Λ_c(2765)^+$ or $Σ_c(2765)^+$ could be explained as the $Λ_c^+(2S)$ state or $Σ^+_{c1}(1/2^-)$ state, respectively. We propose to measure the branching ratio of $\mathcal{B}(Σ_c(2455)π)/\mathcal{B}(Σ_c(2520)π)$ in future, which may disentangle the puzzle of this state. Our results support $Ξ_c(2980)^{0,+}$ as the first radial excited state of $Ξ_c(2470)^{0,+}$ with $J^P=1/2^+$. The assignment of $Ξ_c(2930)^0$ is analogous to $Σ_c(2800)^{0,+,++}$, \emph{i.e.}, a $Ξ^\prime_{c2}(3/2^-)$ or $Ξ^\prime_{c2}(5/2^-)$ state. In addition, we predict some typical ratios among partial decay widths, which are valuable for experimental search for these missing charmed and charmed-strange baryons.

hep-ph↗

arXiv2017

Understanding the internal structures of the $X(4140)$, $X(4274)$, $X(4500)$ and $X(4700)$

We investigate the newly observed $X(4500)$ and $X(4700)$ based on the diquark-antidiquark configuration within the framework of QCD sum rules. Both of them may be interpreted as the $D$-wave $cs\bar{c}\bar{s}$ tetraquark states of $J^P = 0^+$, but with opposite color structures, which is remarkably similar to the result obtained in Ref.~\cite{Chen:2010ze} that the $X(4140)$ and $X(4274)$ can be both interpreted as the $S$-wave $cs\bar{c}\bar{s}$ tetraquark states of $J^P = 1^+$, also with opposite color structures. However, the extracted masses and these suggested assignments to these $X$ states do depend on these running quark masses where $m_s (2 \mbox{ GeV}) = 95 \pm 5$ MeV and $m_c (m_c) = 1.23 \pm 0.09$ GeV. As a byproduct, the masses of the hidden-bottom partner states of the $X(4500)$ and $X(4700)$ are extracted to be both around 10.64 GeV, which can be searched for in the $Υϕ$ invariant mass distribution.

hep-ph↗

arXiv2017

A review of the open charm and open bottom systems

Since the discovery of the first charmed meson in 1976, many open-charm and open-bottom hadrons were observed. In 2003 two narrow charm-strange states $D_{s0}^*(2317)$ and $D_{s1}(2460)$ were discovered by the BaBar and CLEO Collaborations, respectively. After that, more excited heavy hadrons were reported. In this work, we review the experimental and theoretical progress in this field.

hep-ph↗

arXiv2017

Exploring the $Υ(6S)\to χ_{bJ}ϕ$ and $Υ(6S)\to χ_{bJ}ω$ hidden-bottom hadronic transitions

In this work, we investigate the hadronic loop contributions to the $Υ(6S) \to χ_{bJ} ϕ~(J=0,1,2)$ along with $Υ(6S) \to χ_{bJ} ω~(J=0,1,2)$ transitions. We predict that the branching ratios of $Υ(6S) \to χ_{b0} ϕ$, $Υ(6S) \to χ_{b1} ϕ$ and $Υ(6S) \to χ_{b2} ϕ$ are $(0.68 \sim 4.62) \times 10^{-6}$, $(0.50 \sim 3.43) \times 10^{-6}$ and $(2.22 \sim 15.18) \times 10^{-6}$, respectively and those of $Υ(6S) \to χ_{b0} ω$, $Υ(6S) \to χ_{b1} ω$ and $Υ(6S) \to χ_{b2} ω$ are $(0.15 \sim 2.81) \times 10^{-3}$, $(0.63 \sim 11.68) \times 10^{-3}$ and $(1.08 \sim 20.02) \times 10^{-3}$, respectively. Especially, some typical ratios, which reflect the relative magnitudes of the predicted branching ratios, are given, i.e., for $Υ(6S)\to χ_{bJ}ϕ$ transitions, $\mathcal{R}^ϕ_{10}={\mathcal{B}[Υ(6S) \to χ_{b1} ϕ]}/{\mathcal{B}[Υ(6S) \to χ_{b0} ϕ]} \approx 0.74$, $\mathcal{R}^ϕ_{20}= {\mathcal{B}[Υ(6S) \to χ_{b2} ϕ]}/{\mathcal{B}[Υ(6S) \to χ_{b0} ϕ]} \approx 3.28$, and $\mathcal{R}^ϕ_{21} = {\mathcal{B}[Υ(6S) \to χ_{b2} ϕ]}/{\mathcal{B}[Υ(6S) \to χ_{b1} ϕ]} \approx 4.43$, and for $Υ(6S)\to χ_{bJ}ω$ transitions, $\mathcal{R}^ω_{10}={\mathcal{B}[Υ(6S) \to χ_{b1} ω]}/{\mathcal{B}[Υ(6S) \to χ_{b0} ω]} \approx 4.11$, $\mathcal{R}^ω_{20}= {\mathcal{B}[Υ(6S) \to χ_{b2} ω]}/{\mathcal{B}[Υ(6S) \to χ_{b0} ω]} \approx 7.06$, and $\mathcal{R}^ω_{21} = {\mathcal{B}[Υ(6S) \to χ_{b2} ω]}/{\mathcal{B}[Υ(6S) \to χ_{b1} ω]} \approx 1.72$. With the running of BelleII in the near future, experimental measurement of these two kinds of transitions will be a potential research issue.

hep-ph↗

arXiv2017

Krypton and radon background in the PandaX-I dark matter experiment

We discuss an in-situ evaluation of the $^{85}$Kr, $^{222}$Rn, and $^{220}$Rn background in PandaX-I, a 120-kg liquid xenon dark matter direct detection experiment. Combining with a simulation, their contributions to the low energy electron-recoil background in the dark matter search region are obtained.

astro-ph.IM↗

arXiv2017

Hidden-charm pentaquarks and their hidden-bottom and $B_c$-like partner states

In the framework of the color-magnetic interaction, we have systematically studied the mass splittings of the possible hidden-charm pentaquarks $qqqc\bar{c}$ ($q=u,d,s$) where the three light quarks are in a color-octet state. We find that i) the LHCb $P_c$ states fall in the mass region of the studied system; ii) most pentaquarks should be broad states since their $S$-wave open-charm decays are allowed while the lowest state is the $J^P=\frac12^-$ $Λ$-like pentaquark with probably the suppressed $η_cΛ$ decay mode only; and iii) the $J^P=\frac52^-$ states do not decay through $S$-wave and their widths are not so broad. The masses and widths of the two LHCb $P_c$ baryons are compatible with such pentaquark states. We also explore the hidden-bottom and $B_c$-like partners of the hidden-charm states and find the possible existence of the pentaquarks which are lower than the relevant hadronic molecules.

hep-ph↗

arXiv2017

The hidden-charm multiquark states

Since 2003 many charmonium-like states were observed experimentally. Especially those charged charmonium-like $Z_c$ states and bottomonium-like $Z_b$ states cannot be accommodated within the naive quark model, which are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. In 2015, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this talk, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. We list the puzzles and theoretical challenges of these models when confronted with the experimental data. We also discuss possible future measurements which may distinguish the theoretical schemes on the underlying structures of the hidden-charm multiquark states.

hep-ph↗

arXiv2016

Triply heavy tetraquark states with the $QQ\bar{Q}\bar{q}$ configuration

In the framework of the color-magnetic interaction, we systematically investigate the mass splittings of the $QQ\bar{Q}\bar{q}$ tetraquark states and estimated their rough masses in this work. These systems include the explicitly exotic states $cc\bar{b}\bar{q}$ and $bb\bar{c}\bar{q}$ and the hidden exotic states $cc\bar{c}\bar{q}$, $cb\bar{b}\bar{q}$, $bc\bar{c}\bar{q}$, and $bb\bar{b}\bar{q}$. If a state around the estimated mass region could be observed, its nature as a genuine tetraquark is favored. The strong decay patterns shown here will be helpful to the experimental search for these exotic states.

hep-ph↗

arXiv2016

Enhanced Superconductivity in TiO Epitaxial Thin Films

Titanium oxides have many fascinating optical and electrical properties, such as the superconductivity at 2.0 K in cubic titanium monoxide TiO polycrystalline bulk. However, the lack of TiO single crystals or epitaxial films has prevented systematic investigations on its superconductivity. Here, we report the basic superconductivity characterizations of cubic TiO films epitaxially grown on (0001)-oriented Al2O3 substrates. The magnetic and electronic transport measurements confirmed that TiO is a type-II superconductor and the record high Tc is about 7.4 K. The lower critical field (Hc1) at 1.9 K, the extrapolated upper critical field Hc2(0) and coherence length are about 18 Oe, 13.7 T and 4.9 nm, respectively. With increasing pressure, the value of Tc shifts to lower temperature while the normal state resistivity increases. Our results on the superconducting TiO films confirm the strategy to achieve higher Tc in epitaxial films, which may be helpful for finding more superconducting materials in various related systems.

cond-mat.supr-con↗

arXiv2016

D-wave charmed and bottomed baryons from QCD sum rules

We study the $D$-wave charmed baryons of $SU(3)$ flavor $\mathbf{\bar3}_F$ using the method of QCD sum rule in the framework of heavy quark effective theory (HQET). We find that the $Λ_c(2880)$, $Ξ_c(3055)$ and $Ξ_c(3080)$ can be well described by the $D$-wave $SU(3)$ $\mathbf{\bar 3}_F$ charmed baryon multiplets of $J^P=3/2^+$ and $5/2^+$, which contain two $λ$-mode orbital excitations, i.e., the $Λ_c(2880)$ has $J^P=5/2^+$, and the $Ξ_c(3055)$ and $Ξ_c(3080)$ have $J^P = 3/2^+$ and $5/2^+$, respectively. Our results also suggest that the $Λ_c(2880)$ has a partner state, the $Λ_c(3/2^+)$ of $J^P=3/2^+$. Its mass is around $2.81 ^{+0.33}_{-0.18}$ GeV, and the mass difference between it and the $Λ_c(2880)$ is $28^{+45}_{-24}$ MeV. We also evaluate the masses of their bottom partners.

hep-ph↗

arXiv2016

Chiral corrections to the $1^{-+}$ exotic meson mass

We first construct the effective chiral Lagrangians for the $1^{-+}$ exotic mesons. With the infrared regularization scheme, we derive the one-loop infrared singular chiral corrections to the $π_1(1600)$ mass explicitly. We investigate the variation of the different chiral corrections with the pion mass under two schemes. Hopefully, the explicit non-analytical chiral structures will be helpful to the chiral extrapolation of the lattice data from the dynamical lattice QCD simulation of either the exotic light hybrid meson or tetraquark state.

hep-ph↗

arXiv2016

Revealing the inner structure of the newly observed $D_2^*(3000)$

Stimulated by the recent observation of the $D_2^\ast(3000)$, we study the decay behaviors of the $3P$ and $2F$ charmed mesons in the present work. By comparing the masses and decay properties of the $3^3P_2$ and $2^3F_2$ charmed mesons with the observation of the $D_2^\ast(3000)$, we conclude that the most possible assignment of the $D_2^\ast(3000)$ is the $3^3P_2$ charmed meson, while the assignment of the $2^3F_2$ charmed meson could not be fully exclude. The results of the unobserved $3P$ and $2F$ charmed mesons in this work could provide some fundamental information of searching for these charmed mesons in the further experiments by LHCb and forthcoming Belle II.

hep-ph↗

arXiv2016

Correlation analysis of radio properties and accretion-disk luminosity for low luminosity AGNs

The correlation between the jet power and accretion disk luminosity is investigated and analyzed with our model for 7 samples of low luminosity active galactic nuclei (LLAGNs). The main results are: (1) the power-law correlation index ($P_{jet} \propto L_{disk}^μ$) typically ranges $μ=0.4-0.7$ for the LLAGN samples, and there is a hint of steep index for the LLAGN sample which hosted by a high fraction of elliptical galaxies, and there are no significant correlation between the $μ$ and the LLAGN types (Seyfert, LINER); (2) for $μ\approx$1, as noted in Liu et al., the accretion disk dominates the jet power and the black hole (BH) spin is not important, for the LLAGN samples studied in this paper we find that the $μ$ is significantly less than unity, implying that BH spin may play a significant role in the jet power of LLAGNs; (3) the BH spin-jet power is negatively correlated with the BH mass in our model, which means a high spin-jet efficiency in the `low' BH-mass LLAGNs; (4) an anti-correlation between radio loudness and disk luminosity is found, which is apparently due to the flatter power-law index in the jet-disk correlation of the LLAGNs, and the radio loudness can be higher in the LLAGNs than in luminous AGNs/quasars when the BH spin-jet power is comparable to or dominate over the accretion-jet power in the LLAGNs. The high radio-core dominance of the LLAGNs is also discussed.

astro-ph.GA↗

arXiv2016

Magnetic moments of the hidden-charm pentaquark states

The magnetic moment of a baryon state is an equally important dynamical observable as its mass, which encodes crucial information of its underlying structure. According to the different color-flavor structure, we have calculated the magnetic moments of the hidden-charm pentaquark states with $J^P={\frac{1}{2}}^{\pm}$, ${\frac{3}{2}}^{\pm}$, ${\frac{5}{2}}^{\pm}$ and ${\frac{7}{2}}^{+}$ in the molecular model, the diquark-triquark model and the diquark-diquark-antiquark model respectively. Although a good description for the pentaquark mass spectrum and decay patterns has been obtained in all the three models, different color-flavor structures lead to different magnetic moments, which can be used to pin down their inner structures and distinguish various models.

hep-ph↗

arXiv2016

$X(4140)$, $X(4270)$, $X(4500)$ and $X(4700)$ and their $cs\bar{c}\bar{s}$ tetraquark partners

In the simple color-magnetic interaction model, we investigate possible ground $cs\bar{c}\bar{s}$ tetraquark states in the diquark-antidiquark basis. We use several methods to estimate the mass spectrum and discuss possible assignment for the $X$ states observed in the $J/ψϕ$ channel. We find that assigning the Belle $X(4350)$ as a $0^{++}$ tetraquark is consistent with the tetraquark interpretation for the $X(4140)$ and $X(4270)$ while the interpretation of the $X(4500)$ and $X(4700)$ needs orbital or radial excitation. There probably exist several tetraquarks around 4.3 GeV that decay into $J/ψϕ$ or $η_cϕ$.

hep-ph↗

arXiv2016

Prediction of anomalous $Υ(5S)\toΥ(1^3D_J)η$ transitions

In this work, we study the hadronic loop contribution to the $Υ(5S)\to Υ(1^3D_J)η$ ($J=1,2,3$) transitions. We predict that the branching ratios of $Υ(5S)\to Υ(1^3D_1)η$, $Υ(5S)\to Υ(1^3D_2)η$ and $Υ(5S)\to Υ(1^3D_3)η$ can reach up to $(0.5\sim5.1)\times10^{-3}$, $(0.7\sim7.5)\times10^{-3}$ and $(0.9\sim9.6)\times10^{-4}$, respectively. Since these predicted hadronic transitions of $Υ(5S)$ are comparable with these observed $Υ(5S)\to Υ(nS)π^+π^-$ $(n=1,2,3)$, we suggest future experiment like Belle and BelleII to carry out the search for these anomalous $Υ(5S)\to Υ(1^3D_J)η$ transitions.

hep-ph↗

arXiv2016

Searching for hidden-charm baryonium signals in QCD sum rules

We give an explicit QCD sum rule investigation to hidden-charm baryonium states with the quark content $u\bar u d\bar d c\bar c$, spin $J=0/1/2/3$, and of both positive and negative parities. We systematically construct the relevant local hidden-charm baryonium interpolating currents, which can actually couple to various structures, including hidden-charm baryonium states, charmonium states plus two pions, and hidden-charm tetraquark states plus one pion, etc. We do not know which structure these currents couple to at the beginning, but after sum rule analyses we can obtain some information. We find some of them can couple to hidden-charm baryonium states, using which we evaluate the masses of the lowest-lying hidden-charm baryonium states with quantum numbers $J^P=2^-/3^-/0^+/1^+/2^+$ to be around 5.0 GeV. We suggest to search for hidden-charm baryonium states, especially the one of $J=3^-$, in the $D$-wave $J/ψππ$ and $P$-wave $J/ψρ$ and $J/ψω$ channels in this energy region.

hep-ph↗