arXiv subjects

Xiang Liu

Publications and source records attributed to Xiang Liu.

At least 595 records · Page 33Linked to original sources

arXiv2011

Radio observations of the first three-month Fermi-AGN at 4.8 GHz

Using the Urumqi 25m radio telescope, sources from the first three-month Fermi-LAT detected AGN catalog with declination >0 were observed in 2009 at 4.8 GHz. The radio flux density appears to correlate with the gamma-ray intensity. Intra-day variability (IDV) observations were performed in March, April and May in 2009 for selected 42 gamma-ray bright blazars, and 60% of them show evident flux variability at 4.8 GHz during the IDV observations, the IDV detection rate is higher than that in previous flat-spectrum AGN samples. The IDV appears more often in the VLBI-core dominant blazars, and the non-IDV blazars show relatively `steeper' spectral indices than the IDV blazars. Pronounced inter-month variability has been found in two BL Lac objects: J0112+2244 and J0238+1636.

astro-ph.CO↗

arXiv2011

$Z_b(10610)$ and $Z_b(10650)$ structures produced by the initial single pion emission in the $Υ(5S)$ decays

We propose an unique mechanism called {\it Initial Single Pion Emission} existing in the $Υ(5S)$ decays, and further study the line shapes of $dΓ(Υ(5S\to Υ(nS)π^+π^-))/dm_{Υ(nS)π^+}$ ($n=1,2,3$) and $dΓ(Υ(5S\to h_b(mP)π^+π^-))/dm_{h_b(mP)π^+}$ ($m=1,2$). We find sharp structures around 10610 MeV and 10650 MeV in the obtained theoretical line shapes of $dΓ(Υ(5S\to Υ(nS)π^+π^-))/dm_{Υ(nS)π^+}$ and $dΓ(Υ(5S\to h_b(mP)π^+π^-))/dm_{h_b(mP)π^+}$ distributions, which could naturally correspond to the $Z_b(10610)$ and $Z_b(10650)$ structures newly observed by Belle.

hep-ph↗

arXiv2011

Charged bottomonium-like states $Z_b(10610)$ and $Z_b(10650)$ and the $Υ(5S)\to Υ(2S)π^+π^-$ decay

Inspired by the newly observed two charged bottomonium-like states, we consider the possible contribution from the intermediate $Z_b(10610)$ and $Z_b(10650)$ states to the $Υ(5S)\to Υ(2S)π^+π^-$ decay process, which naturally explains Belle's previous observation of the anomalous $Υ(2S)π^+π^-$ production near the peak of $Υ(5S)$ at $\sqrt s=10.87$ GeV [K.F. Chen {\it et al}. (Belle Collaboration), Phys. Rev. Lett. {\bf 100}, 112001 (2008)]. The resulting $dΓ(Υ(5S)\to Υ(2S)π^+π^-)/dm_{π^+π^-}$ and $dΓ(Υ(5S)\to Υ(2S)π^+π^-)/d\cosθ$ distributions agree with Belle's measurement after inclusion of these $Z_b$ states. This formalism also reproduces the Belle observation of the double-peak structure and its reflection in $Υ(2S)π^+$ invariant mass spectrum of $Υ(5S)\to Υ(2S)π^+π^-$ decay.

hep-ph↗

arXiv2011

Dipion invariant mass distribution of the anomalous $Υ(1S) π^{+} π^{-}$ and $Υ(2S) π^{+} π^{-}$ production near the peak of $Υ(10860)$

Considering the defects of the previous work for estimating the anomalous production rates of $e^+e^-\to Υ(1S)π^+π^-,\,Υ(2S)π^+π^-$ near the peak of the $Υ(5S)$ resonance at $\sqrt s=10.87$ GeV [K.F. Chen {\it et al}. (Belle Collaboration), Phys. Rev. Lett. {\bf 100}, 112001 (2008)], we suggest a new scenario where the contributions from the direct dipion transition and the final state interactions interfere to result in not only the anomalously large production rates, but also the lineshapes of the differential widths consistent with the experimental measurement when assuming the reactions are due to the dipion emission of $Υ(5S)$. At the end, we raise a new puzzle that the predicted differential width $dΓ(Υ(5S)\toΥ(2S)π^+π^-)/d\cosθ$ has a discrepant trend from the data while other predictions are well in accord with the data. It should be further clarified by more accurate measurements carried by future experiments.

hep-ph↗

arXiv2011

The Pseudoscalar Meson and Heavy Vector Meson Scattering Lengths

We have systematically studied the S-wave pseudoscalar meson and heavy vector meson scattering lengths to the third order with the chiral perturbation theory, which will be helpful to reveal their strong interaction. For comparison, we have presented the numerical results of the scattering lengths (1) in the framework of the heavy meson chiral perturbation theory and (2) in the framework of the infrared regularization. The chiral expansion converges well in some channels.

hep-ph↗

arXiv2011

Predicted charged charmonium-like structures in the hidden-charm dipion decay of higher charmonia

In this work, we predict two charged charmonium-like structures close to the $D^\ast\bar{D}$ and $D^\ast\bar{D}^\ast$ thresholds, where the Initial Single Pion Emission mechanism is introduced in the hidden-charm dipion decays of higher charmonia $ψ(4040)$, $ψ(4160)$, $ψ(4415)$ and charmonium-like state Y(4260). We suggest BESIII to search for these structures in the $J/ψπ^+$, $ψ(2S)π^+$ and $h_b(1P)π^+$ invariant mass spectra of the $ψ(4040)$ decays into $J/ψπ^+π^-$, $ψ(2S)π^+π^-$ and $h_b(1P)π^+π^-$. In addition, the experimental search for these structures in the $J/ψπ^+$, $ψ(2S)π^+$ and $h_c(1P)π^+$ invariant mass spectra of the $ψ(4260)$ hidden-charm dipion decays will be accessible at Belle and BaBar.

hep-ph↗

arXiv2011

$Z_b(10610)^\pm$ and $Z_b(10650)^\pm$ as the $B^\bar{B}$ and $B^\bar{B}^{*}$ molecular states

In the framework of the one-boson-exchange model, we have studied the interaction of the $B^*\bar{B}$ and $B^*\bar{B}^{*}$ system. After considering the S-wave and D-wave mixing, we notice that both $Z_b(10610)^\pm$ and $Z_b(10650)^\pm$ can be interpreted as the $B^*\bar{B}$ and $B^*\bar{B}^{*}$ molecular states quite naturally. Within the same framework, there also exist several molecular charmonia including X(3872) and several other molecular bottomonia, which are the partners of $Z_b(10610)$ and $Z_b(10650)$. The long-range one-pion-exchange force alone is strong enough to form these loosely bound molecular states, which ensures the numerical results quite model-independent and robust.

hep-ph↗

arXiv2011

Categorizing resonances X(1835), X(2120) and X(2370) in the pseudoscalar meson family

Inspired by the newly observed three resonances X(1835), X(2120) and X(2370), in this work we systematically study the two-body strong decays and double pion decays of $η(1295)/η(1475)$, $η(1760)/X(1835)$ and $X(2120)/X(2370)$ by categorizing $η(1295)/η(1475)$, $η(1760)/X(1835)$, X(2120) and X(2370) as the radial excitations of $η(548)/η^\prime(958)$. Our numerical results indicate the followings: (1) The obtained theoretical strong decay widths of three pseudoscalar states $η(1295)$, $η(1475)$ and $η(1760)$ are consistent with the experimental measurements; (2) X(1835) could be the second radial excitation of $η^\prime(958)$; (3) X(2120) and X(2370) can be explained as the third and fourth radial excitations of $η(548)/η^\prime(958)$, respectively.

hep-ph↗

arXiv2011

QCD sum rule calculation for the charmonium-like structures in the J/psi phi and J/psi omega invariant mass spectra

Using the QCD sum rules we test if the charmonium-like structure Y(4274), observed in the $J/ψϕ$ invariant mass spectrum, can be described with a $D_s\bar{D}_{s0}(2317)+h.c.$ molecular current with $J^{PC}=0^{-+}$. We consider the contributions of condensates up to dimension ten and we work at leading order in $α_s$. We keep terms which are linear in the strange quark mass $m_s$. The mass obtained for such state is $m_{D_s{D}_{s0}}=(4.80\pm 0.55)$ GeV. We also consider a molecular $0^{-+}$ $D\bar{D}_{0}(2400)+h.c.$ current and we obtain $m_{D{D}_0}=(4.61\pm 0.71)$ GeV. Our study shows that the newly observed Y(4274) in the $J/ψϕ$ invariant mass spectra can be, considering the uncertainties, described using a molecular charmonium current.

hep-ph↗

arXiv2011

Novel charmonium-like structures in the $J/ψϕ$ and $J/ψω$ invariant mass spectra

Stimulated by the new evidence of Y(4274) observed in the $J/ψϕ$ invariant mass spectrum, we first propose the charmonium-like state Y(4274) as the S-wave $D_s\bar{D}_{s0}(2317)+h.c.$ molecular state with $J^P=0^-$, which is supported well by dynamics study of the system composed of the pseudoscalar and scalar charmed mesons. The S-wave $D\bar{D}_{0}(2400)+h.c.$ molecular charmonium appears as the molecular partner of Y(4274), which is in accord with the enhancement structure appearing at 4.2 GeV in the $J/ψω$ invariant mass spectrum from B decays. Our study shows that the enhancement structures, $i.e.$, the newly observed Y(4274) and the previously announced $Y(4140)/Y(3930)$ in the $J/ψϕ$ and $J/ψω$ invariant mass spectra, can be understood well under the uniform framework of the molecular charmonium, which can be tested by future experiments.

hep-ph↗

arXiv2011

A novel explanation of charmonium-like structure in $e^+e^-\to ψ(2S)π^+π^-$

We first present a non-resonant description to charmonium-like structure $Y(4360)$ in the $ψ(2S)π^+π^-$ invariant mass spectrum of the $e^+e^-\to ψ(2S)π^+π^-$ process. The $Y(4360)$ structure is depicted well by the interference effect of the production amplitudes of $e^{+} e^{-} \to ψ(2S) π^+ π^-$ via the intermediate charmonia $ψ(4160)/ψ(4415)$ and direct $e^+e^-$ annihilation into $ψ(2S)π^+ π^-$. This fact shows that $Y(4360)$ is not a genuine resonance, which naturally explains why $Y(4360)$ was only reported in its hidden-charm decay channel $ψ(2S)π^+π^-$ and was not observed in the exclusive open-charm decay channel or $R$-value scan.

hep-ph↗

arXiv2011

Nonresonant explanation for the Y(4260) structure observed in the $e^+e^-\to J/ψπ^+π^-$ process

In this work, we proposed a nonresonant explanation for the Y(4260) structure observed in the $e^+e^-\to J/ψπ^+π^-$ process, i.e., Y(4260) is not a genuine resonance. Our result indicates that the Y(4260) structure can be reproduced by the interference of production amplitudes of the $e^+e^-\to J/ψπ^+π^-$ processes via direct $e^+e^-$ annihilation and through intermediate charmonia $ψ(4160)/ψ(4415)$. Besides describing Y(4260) line shape in $e^+e^-\to J/ψπ^+π^-$ well, such a nonresonant explanation for the Y(4260) structure naturally answers why there is no evidence of Y(4260) in the exclusive open-charm decay channel and $R$-value scan.

hep-ph↗

arXiv2010

The observed charmed hadron $Λ_c(2940)^+$ and the $D^*N$ interaction

In this work, we systematically study the interaction of $D^*$ and nucleon, which is stimulated by the observation of $Λ_c(2940)^+$ close to the threshold of $D^*p$. Our numerical result obtained by the dynamical investigation indicates the existence of the $D^*N$ systems with $J^P=1/2^\pm,\,3/2^\pm$, which not only provides valuable information to understand the underlying structure of $Λ_c(2940)^+$ but also improves our knowledge of the interaction of $D^*$ and nucleon. Additionally, the bottom partners of the $D^*N$ systems are predicted, which might be as one of the tasks in LHCb experiment.

hep-ph↗

arXiv2010

\textsc{MaGe} - a {\sc Geant4}-based Monte Carlo Application Framework for Low-background Germanium Experiments

We describe a physics simulation software framework, MAGE, that is based on the GEANT4 simulation toolkit. MAGE is used to simulate the response of ultra-low radioactive background radiation detectors to ionizing radiation, specifically the MAJORANA and GERDA neutrinoless double-beta decay experiments. MAJORANA and GERDA use high-purity germanium detectors to search for the neutrinoless double-beta decay of 76Ge, and MAGE is jointly developed between these two collaborations. The MAGE framework contains the geometry models of common objects, prototypes, test stands, and the actual experiments. It also implements customized event generators, GEANT4 physics lists, and output formats. All of these features are available as class libraries that are typically compiled into a single executable. The user selects the particular experimental setup implementation at run-time via macros. The combination of all these common classes into one framework reduces duplication of efforts, eases comparison between simulated data and experiment, and simplifies the addition of new detectors to be simulated. This paper focuses on the software framework, custom event generators, and physics lists.

nucl-ex↗

arXiv2010

Newly observed D(2550), D(2610), and D(2760) as 2S and 1D charmed mesons

We study three newly observed D(2550), D(2610), and D(2760) by the BaBar Collaboration utilizing the mass spectra and investigating the strong decays. Our calculation indicates that D(2610) is an admixture of $2^3S_1$ and $1^3D_1$ with $J^P=1^-$. $D(2760)$ can be explained as either the orthogonal partner of D(2610) or $1^3D_3$. Our estimate of the decay width for $D(2550)$, assuming it as $2^1S_0$, is far below the experimental value. the threshold effect because the strong decay of $D(2550)\to D_0^*π$ is forbidden.} The decay behavior of the remaining two 1D charmed mesons, i.e., $^3D_2$ and $^1D_2$ ($J^P=2^-$) states, is predicted, which will help future experimental search for these missing $D$-wave charmed mesons.

hep-ph↗

arXiv2010

Long-distant contribution and $χ_{c1}$ radiative decays to light vector meson

The discrepancy between the PQCD calculation and the CLEO data for $χ_{c1}\to γV$ ($V=ρ^0,\,ω,\,ϕ$) stimulates our interest in exploring extra mechanism of $χ_{c1}$ decay. In this work, we apply an important non-perturbative QCD effect, i.e., hadronic loop mechanism, to study $χ_{c1}\to γV$ radiative decay. Our numerical result shows that the theoretical results including the hadronic loop contribution and the PQCD calculation of $χ_{c1}\to γV$ are consistent with the corresponding CLEO data of $χ_{c1}\to γV$. We expect further experimental measurement of $χ_{c1}\to γV$ at BES-III, which will be helpful to test the hadronic loop effect on $χ_{c1}$ decay.

hep-ph↗

arXiv2010

$B^{()}\bar B^{()}$ intermediate state contribution to $Υ(4S,5S)\to η_b+γ$ radiative decay

In this work, we investigate the re-scattering effects in the radiative decay $Υ(5S)\toη_b+γ$, which were suggested to be crucially important for understanding the anomalous largeness of the branching ratios $B(Υ(5S)\to Υ(1S)+ππ)$ and $B(Υ(5S)\to Υ(1S)+η)$. Our calculations show that the re-scattering effects may enhance $Γ(Υ(10860)\to η_b+γ)$ by four orders, but the tetraquark structure does not. Recently the BaBar and CLEO collaborations have measured the mass of ${η_b}$ and the branching ratios $\mathcal{B}(Υ(2S)\rightarrowη_b+γ)$, $\mathcal{B}(Υ(3S)\rightarrowη_b+γ)$. We hope that very soon, $Υ(10860)\to η_b+γ$ will be measured and it would be an ideal opportunity for testing whether the re-scattering or the tetraquark structure is responsible for the anomaly of $\mathcal{B}\big(Υ(5S)\rightarrowΥ(nS)π^+π^- (n=1,2,3)\big)$, $i.e.$, the future measurements on the radiative decays of $Υ(5S)$ might be a touchstone of the two mechanisms.

hep-ph↗

arXiv2010

$D\bar{D}$ production and their interactions

S and P wave $D\bar{D}$ scatterings are studied in a meson exchange model with the coupling constants obtained in the heavy quark effective theory. With the extracted P wave phase shifts and the separable potential approximation, we include the $D\bar{D}$ rescattering effect and investigate the production process $e^+e^-\to D\bar{D}$. We find that it is difficult to explain the anomalous line shape observed by the BES collaboration with this mechanism. Combining our model calculation and the experimental measurement, we estimate the upper limit of the nearly universal cutoff parameter to be 1.7 GeV. With this number, the upper limits of the binding energies of the S wave $D\bar{D}$ and $B\bar{B}$ bound states are obtained. Assuming that the S wave and P wave interactions rely on the same cutoff, our study provides a way of extracting the information about S wave molecular bound states from the P wave meson pair production.

hep-ph↗