arXiv subjects

Xiang Liu

Publications and source records attributed to Xiang Liu.

At least 577 records · Page 32Linked to original sources

arXiv2012

Does the enhancement observed in $γγ\to D\bar{D}$ contain two $P$-wave higher charmonia?

Solved is a new puzzle raised by the observation of an enhancement structure Z(3930) in $γγ\to D\bar{D}$. If categorizing Z(3930) as $χ_{c2}(2P)$ suggested by Belle and BaBar, we must explain why $χ_{c0}(2P)$ dominantly decaying into $D\bar{D}$ is missing in the $D\bar{D}$ invariant mass spectrum. In this work, we propose that the Z(3930) enhancement structure may contain two $P$-wave higher charmonia {$χ_{c0}(2P)$} and $χ_{c2}(2P)$. We show that this assumption is supported by our analysis of the $D\bar{D}$ invariant mass spectrum and $\cosθ^\ast$ distribution of $γγ\to D\bar{D}$. This observation would not only provide valuable information of two P-wave higher charmonia $χ_{c0}(2P)$ and $χ_{c2}(2P)$, but also serve as the crucial test of our novel proposal to the observed enhancement structure Z(3930), especially at the forthcoming BelleII and the approved SuperB.

hep-ph↗

arXiv2012

Exotic B_c-like molecules in QCD Sum Rules

We use the QCD sum rules to study possible $B_c$-like molecular states. We consider isoscalar $J^P = 0^+$ and $J^P = 1^+ D^{(\ast)}B^{(\ast)}$ molecular currents. We consider the contributions of condensates up to dimension eight and we work at leading order in $α_s$ . We obtain for these states masses around 7 GeV.

hep-ph↗

arXiv2012

Few-Body Systems Composed of Heavy Quarks

Within the past ten years many new hadrons states were observed experimentally, some of which do not fit into the conventional quark model. I will talk about the few-body systems composed of heavy quarks, including the charmonium-like states and some loosely bound states.

hep-ph↗

arXiv2012

Interpretation of $Z_b(10610)$ and $Z_b(10650)$ in the ISPE mechanism and the Charmonium Counterpart

The initial single pion emission (ISPE) mechanism is applied to the processes $Υ(5S)\to πB^{(*)}\bar{B}^{(*)}$ whose details have been recently reported at ICHEP2012 and we obtain reasonable agreement with Bell's measurements, i.e., we succeed in reproducing the enhancement structures of $Z_b(10610)$ and $Z_b(10650)$. Inspired by this success, we predict the corresponding enhancement structures in higher charmonia open charm pion decay near the thresholds of $D^\ast \bar{D}$ and $D^\ast \bar{D}^\ast$.

hep-ph↗

arXiv2012

The mass spectrum and strong decays of isoscalar tensor mesons

In this work, we present a systematic study of the observed isoscalar tensor $f_2$ states. With the detailed analysis of the mass spectrum and calculation of the $f_2$ two-body strong decays, we extract information of their underly structures, and try to categorize them into the conventional tensor meson family ($n^{3}P_{2}$ $(n=1,2,3,4)$ and $m^{3}F_{2}$ ($m=1,2$)). We also give predictions for other decay modes of these tensor mesons, which are useful for further experimental investigations.

hep-ph↗

arXiv2012

New structure around 3250 MeV in the baryonic B decay and the $D^*_0(2400)N$ molecular hadron

In this work, we first propose the isovector $nD^{*}_0(2400)^0$ molecular state to explain the enhancement structure around 3250 MeV ($X_c(3250)^0$) in the $Σ_c^{++}π^-π^-$ invariant mass spectrum newly observed by the BaBar Collaboration. Under this molecular state configuration, both the analysis of the mass spectrum and the study of its dominant decay channel can well depict its resonance parameters measured by BaBar. Our investigation also shows that the isovector $nD^{*}_0(2400)^0$ molecular state can decay into $Σ_c^{++}π^-π^-$, which is consistent with the experimental observation. These studies provide the direct support to the isovector $nD^{*}_0(2400)^0$ molecular state assignment to $X_c(3250)^0$.

hep-ph↗

arXiv2012

Revisiting the production of charmonium plus a light meson at PANDA

In this work, we calculate the total cross sections and the center-of-mass frame angular distributions of the charmonium production plus a light meson by the low energy $p\bar{p}$ interaction. The results of $p\bar{p}\to π^0 Ψ$ with and without form factor (FF) indicate that the FF contribution in the calculation cannot be ignored. The obtained cross section of $p\bar{p}\to π^0 J/ψ$ with FF can fit the E760 data well. We also predict the total cross sections and the center-of-mass frame angular distributions of $p\bar{p}\to ωΨ$, which show that these physical quantities are dependent on Pauli ($g_ω$) and Dirac ($κ_ω$) coupling constants of the $ppω$ interaction. Thus, $p\bar{p}\to ωΨ$ can be as the ideal channel to test the different theoretical values of $g_ω$ and $κ_ω$. Applying the formulae of $p\bar{p}\to π^0 Ψ$ and $p\bar{p}\to ωΨ$, we predict the total cross sections of the $p\bar{p}\to ηΨ$ and $p\bar{p}\to ρΨ$ reactions. Our results show a common behavior of the charmonium production with a light meson by the $p\bar{p}$ interaction, where the total cross section of the $η_c$ production is the largest one among all discussed processes. The above observations can be directly tested at the forthcoming $\bar{P}$ANDA experiment.

hep-ph↗

arXiv2012

Two charged strangeonium-like structures observable in the $Y(2175) \to ϕ(1020)π^{+} π^{-}$ process

Via the Initial Single Pion Emission (ISPE) mechanism, we study the $ϕ(1020)π^{+}$ invariant mass spectrum distribution of $Y(2175) \to ϕ(1020)π^{+} π^{-}$. Our calculation indicates there exist a sharp peak structure ($Z_{s1}^+$) close to the $K\bar{K}^\ast$ threshold and a broad structure ($Z_{s2}^+$) near the $K^\ast\bar{K}^\ast$ threshold. In addition, we also investigate the $ϕ(1680) \to ϕ(1020)π^{+} π^{-}$ process due to the ISPE mechanism, where a sharp peak around the $K\bar{K}^\ast$ threshold appears in the $ϕ(1020)π^{+}$ invariant mass spectrum distribution. We suggest to carry out the search for these charged strangeonium-like structures in future experiment, especially Belle II, Super-B and BESIII.

hep-ph↗

arXiv2012

Hadronic molecules with both open charm and bottom

With the one-boson-exchange model, we study the interaction between the S-wave $D^{(*)}/D^{(*)}_s$ meson and S-wave $B^{(*)}/B^{(*)}_s$ meson considering the S-D mixing effect. Our calculation indicates that there may exist the $B_c$-like molecular states. We estimate their masses and list the possible decay modes of these $B_c$-like molecular states, which may be useful to the future experimental search.

hep-ph↗

arXiv2012

The open-charm radiative and pionic decays of molecular charmonium Y(4274)

In this work, we investigate the decay widths and the line shapes of the open-charm radiative and pionic decays of Y(4274) with the $D_s\bar{D}_{s0}(2317)$ molecular charmonium assignment. Our calculation indicates that the decay widths of $Y(4274)\to D^{+}_{s}D^{*-}_{s}γ$ and $Y(4274)\to D^+_{s}D^-_{s}π^0$ can reach up to 0.05 keV and 0.75 keV, respectively. In addition, the result of the line shape of the photon spectrum of $Y(4274)\to D_s^+ {D}_s^{*-} γ$ shows that there exists a very sharp peak near the large end point of photon energy. The line shape of the pion spectrum of $Y(4274)\to D_s^+ {D}_s^{*-} π^0$ is similar to that of the pion spectrum of $Y(4274)\to D_s^+ {D}_s^{*-} γ$, where we also find a very sharp peak near the large end point of pion energy. According to our calculation, we suggest further experiments to carry out the search for the open-charm radiative and pionic decays of Y(4274).

hep-ph↗

arXiv2012

Non-strange partner of strangeonium-like state Y(2175)

Inspired by the observed Y(2175) state, we predict its non-strange partner Y(1915), which has a resonance structure with mass around 1915 MeV and width about $317\sim 354$ MeV. Experimental search for Y(1915) is proposed by analyzing the $ωf_0(980)$ or $ωππ$ invariant mass spectrum of the $e^+e^-\to ωf_0(980), ωππ$ and $J/ψ\to ηωf_0(980)$ processes, which are accessible at Belle, BaBar, BESIII and forthcoming BelleII. Considering similarity between two families, the comparison of the mass spectra of $ω$ and $ϕ$ families can provide important information on the 1D state of $ϕ$ family, $ϕ(1910)$, which has a very broad resonance structure with mass around 1910 MeV regarded as the strangeonium partner of $ω(1650)$. This also answers the question why the 1D state $ϕ(1910)$ is still missing in experiment. This is supported by our former study on the properties of Y(2175), which explains Y(2175) as the 2D strangeonium because our theoretical total width is comparable with the Belle data.

hep-ph↗

arXiv2011

VLBI observations of 10 CSO candidates: expansion velocities of hot spots

Observations of ten Compact Symmetric Objects ({\rm CSO}) candidates have been made with the Very Long Baseline Array at 8.4 GHz in 2005 and with a combined Chinese and European VLBI array at 8.4 GHz in 2009. The 2009 observations incorporate for the first time the two new Chinese telescopes at Miyun and Kunming for international astrophysical observations. The observational data, in combination with archival VLBA data from previous epochs, have been used to derive the proper motions of the VLBI components. Because of the long time baseline of $\sim$16 years of the VLBI data sets, the expansion velocities of the hot spots can be measured at an accuracy as high as $\sim$1.3 $μ$as yr$^{-1}$. Six of the ten sources are identified as CSOs with a typical double or triple morphology on the basis of both spectral index maps and their mirror-symmetry of proper motions of the terminal hot spots. The compact double source J1324+4048 is also identified as a CSO candidate. Among the three remaining sources, J1756+5748 and J2312+3847 are identified as core-jet sources with proper motions of their jet components relating to systemic source expansion. The third source J0017+5312 is likely also a core-jet source, but a robust detection of a core is needed for an unambiguous identification. The kinematic ages of the CSOs derived from proper motions range from 300 to 2500 years. The kinematic age distribution of the CSOs confirm an overabundance of compact young CSOs with ages less than 500 years. CSOs with known kinematic ages may be used to study the dynamical evolution of extragalactic radio sources at early stages.

astro-ph.CO↗

arXiv2011

Estimation and variable selection for generalized additive partial linear models

We study generalized additive partial linear models, proposing the use of polynomial spline smoothing for estimation of nonparametric functions, and deriving quasi-likelihood based estimators for the linear parameters. We establish asymptotic normality for the estimators of the parametric components. The procedure avoids solving large systems of equations as in kernel-based procedures and thus results in gains in computational simplicity. We further develop a class of variable selection procedures for the linear parameters by employing a nonconcave penalized quasi-likelihood, which is shown to have an asymptotic oracle property. Monte Carlo simulations and an empirical example are presented for illustration.

math.ST↗

arXiv2011

Production of charmed baryon $Λ_c(2940)^+$ at PANDA

In this work we evaluate the production rate of the charmed baryon $Λ_c(2940)^+$ at PANDA. For possible assignments of $Λ_c(2940)^+$: $J^P=1/2^\pm$, $3/2^\pm$ and $5/2^\pm$, the total cross section of $p\bar{p}\to \barΛ_c Λ_c(2940)^+$ is estimated, which may exceed 1 nb. With the designed luminosity ($2\times10^{-32}$cm$^{-2}$/s) of PANDA, our estimate indicates that ten thousand events per day if $Λ_c(2940)^+$ is of $J^P=1/2^+$ or $10^8$ per day if it is of $J^P=5/2^+$ can be expected. Those values actually set the lower and upper limits of the $Λ_c(2940)^+$ production. In addition, we present the Dalitz plot and carry out a rough background analysis of the $Λ_c(2940)^+$ production in the $p\bar{p}\to D^0 p\barΛ_c$ and $p\bar{p}\to Σ_c^{0,++}π^{+,-}\barΛ_c$ processes, which would provide valuable information for accurate determination of the $Λ_c(2940)^+$ identity.

hep-ph↗

arXiv2011

Anomalous dipion invariant mass distribution of the $Υ(4S)$ decays into $Υ(1S) π^{+} π^{-}$ and $Υ(2S) π^{+} π^{-}$

To solve the discrepancy between the experimental data on the partial widths and lineshapes of the dipion emission of $Υ(4S)$ and the theoretical predictions, we suggest that there is an additional contribution which was not taken into account in previous calculations. Noticing that the mass of $Υ(4S)$ is above the production threshold of $B\bar B$, the contribution of the sequential process $Υ(4S)\to B\bar B\to Υ(nS)+S\to Υ(nS)+π^+π^-$ ($n=1,2$) may be sizable, and its interference with that from the direct production would be important. The goal of this work is to investigate if a sum of the two contributions with a relative phase indeed reproduces the data. Our numerical results on the partial widths and the lineshapes $dΓ(Υ(4S)\to Υ(2S,1S)π^+π^-)/d(m_{π^+π^-})$ are satisfactorily consistent with the measurements, thus the role of this mechanism is confirmed. Moreover, with the parameters obtained by fitting the data of the Belle and Babar collaborations, we predict the distributions $dΓ(Υ(4S)\to Υ(2S,1S)π^+π^-)/d\cosθ$ which have not been measured yet.

hep-ph↗

arXiv2011

Charged bottomonium-like structures $Z_b(10610)$ and $Z_b(10650)$

The observation of two charged bottomonium-like structures $Z_b(10610)$ and $Z_b(10650)$ has stimulated extensive studies of the properties of $Z_b(10610)$ and $Z_b(10650)$. In this talk, we briefly introduce the research status of $Z_b(10610)$ and $Z_b(10650)$ combined with our theoretical progress.

hep-ph↗

arXiv2011

The possible hidden-charm molecular baryons composed of anti-charmed meson and charmed baryon

With the one-boson-exchange model we have studied the possible existence of the very loosely bound hidden-charm molecular baryons composed of anti-charmed meson and charmed baryon. Our numerical results indicate that there exist $Σ_c\bar{D}^*$ states with $I(J^P)=1/2(1/2^-), 1/2(3/2^-), 3/2(1/2^-), 3/2(3/2^-)$ and $Σ_c\bar{D}$ state with $3/2(1/2^-)$. But the $Λ_c \bar{D}$ and $Λ_c \bar{D}^*$ molecular states do not exist.

hep-ph↗

arXiv2011

Charged bottomonium-like structures in the hidden-bottom dipion decays of $Υ(11020)$

Under the Initial Single Pion Emission mechanism, we study the hidden-bottom dipion decays of $Υ(11020)$, i.e., $Υ(11020)\to Υ(nS)π^+π^-$ $(n=1,2,3)$ and $Υ(11020)\to h_b(mP)π^+π^-$ $(m=1,2)$. We predict explicit sharp peak structures close to the $B\bar{B}^*$ and $B^*\bar{B}^*$ thresholds and their reflections in the $Υ(1S)π^+$, $Υ(2S)π^+$ and $h_b(1P)π^+$ invariant mass spectrum distributions. We suggest future experiment, i.e., Belle, BaBar, and forthcoming BelleII or Super-B, carry out the search for these novel phenomena, which can provide important test to the Initial Single Emission mechanism existing in higher bottomonia.

hep-ph↗