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Zhi Yang

Publications and source records attributed to Zhi Yang.

At least 127 records · Page 7Linked to original sources
arXiv2017

Note on X(3872) production at hadron colliders and its molecular structure

The production of the X(3872) as a hadronic molecule in hadron colliders is clarified. We show that the conclusion of Bignamini et al., Phys. Rev. Lett. 103 (2009) 162001, that the production of the X(3872) at high $p_T$ implies a non-molecular structure, does not hold. In particular, using the well understood properties of the deuteron wave function as an example, we identify the relevant scales in the production process.

hep-ph↗
arXiv2017

MoS2 Heterostructure with Tunable Phase Stability: Strain Induced Interlayer Covalent Bond Formation

Due to the distinguished properties offered by different structural phases of monolayer MoS2, phase engineering design are urgently required for achieving switchable structural phase. Strain engineering is widely accepted as a clean and flexible method, however, cannot be achieved in engineering monolayer MoS2 phase transition because the critical biaxial strain required (~15%) is much larger than measured elastic limit (~11%). In this study, employing density functional theoretical calculations, it has been found out that with the forming of heterostructure between MoS2 with buckled 2D materials such as silicence, germanene and stanene, only a small strain can trigger the phase transition. As being suggested by the constructed phase stability diagram, biaxial deformation as low as 3% in MoS2/silicene and MoS2/stanene sandwich structure, would be sufficient to induce the structural phase transition in MoS2 lattice. This strain falls well within experimental elastic limit, thus would be feasible to realize in experiment. The origin of such behavior can be understood as strain induced interlayer covalent bond formation, which finally make MoS2 lattice more sensitive to external strain. This theoretical work provides one realistic route for achieving flexible phase stabilities in experimental design.

cond-mat.mtrl-sci↗
arXiv2017

Where does the X(5568) structure come from?

We study the semi-exclusive production of $π^\pm B_s^0$ pairs in hadron colliders which is associated with the $X(5568)$ structure observed by the D0 Collaboration in 2016, but that was not confirmed by LHCb and CMS later. The reason of its appearance in the D0 and absence in LHCb and CMS is discussed in this letter. In a semi-exclusive process, one might miss the third particle which is produced together with the $π^\pm B_s^0$ simultaneously. In the three-body Dalitz plot, once the remaining region is narrow enough after the kinematic cuts, its reflection to another invariant mass distribution will accumulate a large number of events within a specific energy region. If there is an enhancement in the remaining region, it will make the reflection structure more pronounced. The precise line shape of the reflection will depend on the specific interaction form. A combined study of different cone cuts and the low-energy dynamics, e.g. the Landau singularity, demonstrates that the $X(5568)$ structure could come from this kinematic reflection. This conclusion can be checked by both searching for the enhancement in another invariant mass distribution, such as $B_s^0\bar{B}^0$, and the cone cut dependence of the $X(5568)$ mass. Such a combined study can be used to distinguish the effects of the triangle singularity from a genuine state. We also propose how to avoid this kinematic reflection in future experimental analysis.

hep-ph↗
arXiv2016

Remarks on the $P_c$ structures and triangle singularities

It was proposed that the narrow $P_c(4450)$ structure observed by the LHCb Collaboration in the reaction $Λ_b\to J/ψp K$ might be due to a triangle singularity around the $χ_{c1}$--proton threshold at 4.45~GeV. We discuss the occurrence of a similar triangle singularity in the $J/ψp$ invariant mass distribution for the decay $Λ_b\to J/ψp π$, which could explain the bump around 4.45~GeV in the data. More precise measurements of this process would provide valuable information towards an understanding of the $P_c$ structures.

hep-ph↗
arXiv2016

Hindered magnetic dipole transitions between P-wave bottomonia and coupled-channel effects

In the hindered magnetic dipole transitions of heavy quarkonia, the coupled-channel effects originating from the coupling of quarkonia to a pair of heavy and anti-heavy mesons can play a dominant role. Here, we study the hindered magnetic dipole transitions between two $P$-wave bottomonia, $χ_b(n P)$ and $h_b(n^\prime P)$, with $n\neq n^\prime$. In these processes the coupled-channel effects are expected to lead to partial widths much larger than the quark model predictions. We estimate these partial widths which, however, are very sensitive to unknown coupling constants related to the vertices $χ_{b0}(nP)B\bar B$. A measurement of the hindered M1 transitions can shed light on the coupled-channel dynamics in these transitions and hence on the size of the coupling constants. We also suggest to check the coupled-channel effects by comparing results from quenched and fully dynamical lattice QCD calculations.

hep-ph↗
arXiv2016

Invisible QCD as Dark Energy

We account for the late time acceleration of the Universe by extending the QCD color to a $SU(3)$ invisible sector (IQCD). If the Invisible Chiral symmetry is broken in the early universe, a condensate of dark pions (dpions) and dark gluons (dgluons) forms. The condensate naturally forms due to strong dynamics similar to the Nambu--Jona-Lasinio mechanism. As the Universe evolves from early times to present times the interaction energy between the dgluon and dpion condensate dominates with a negative pressure equation of state and causes late time acceleration. We conclude with a stability analysis of the coupled perturbations of the dark pions and dark gluons.

hep-th↗
arXiv2015

How to reveal the exotic nature of the P_c(4450)

The LHCb Collaboration announced two pentaquark-like structures in the $J/ψp$ invariant mass distribution. We show that the current information on the narrow structure at 4.45 GeV is compatible with kinematical effects of the rescattering from $χ_{c1} p$ to $J/ψp$: First, it is located exactly at the $χ_{c1} p$ threshold. Second, the mass of the four-star well-established $Λ(1890)$ is such that a leading Landau singularity from a triangle diagram can coincidentally appear at the $χ_{c1} p$ threshold, and third, there is a narrow structure at the $χ_{c1}\,p$ threshold but not at the $χ_{c0} p$ and $χ_{c2} p$ thresholds. In order to check whether that structure corresponds to a real exotic resonance, one has to measure the process $Λ_b^0\to K^-χ_{c1} p$. If the $P_c(4450)$ structure exists in the $χ_{c1} p$ invariant mass distribution as well, then the structure cannot be just a kinematical effect but is a real resonance, otherwise, one cannot conclude the $P_c(4450)$ to be another exotic hadron. In addition, it is also worthwhile to measure the decay $Υ(1S)\to J/ψp \bar p$: a narrow structure at 4.45 GeV but not at the $χ_{c0} p$ and $χ_{c2} p$ thresholds would exclude the possibility of a pure kinematical effect.

hep-ph↗
arXiv2014

Production of the spin partner of the X(3872) in e^+e^- collisions

We study the production of the spin partner of the X(3872), which is a D^{*}\bar D^{*} bound state with quantum numbers J^{PC}=2^{++} and named X_2(4012) here, with the associated emission of a photon in electron--positron collisions. The results show that the ideal energy region to observe the X_2(4012) in e^+e^- annihilations is from 4.4~GeV to 4.5~GeV, due to the presence of the S-wave \bar D^{*} D_1(2420) and \bar D^{*} D_2(2460) thresholds, respectively. We also point out that it will be difficult to observe the γX(4012) at the e^+e^- center-of-mass energy around 4.26~GeV.

hep-ph↗
arXiv2014

Production of the bottom analogues and the spin partner of the X(3872) at hadron colliders

Using the Monte Carlo event generator tools Pythia and Herwig, we simulate the production of bottom/charm meson and antimeson pairs at hadron colliders in proton-proton/antiproton collisions. With these results, we derive an order-of-magnitude estimate for the production rates of the bottom analogues and the spin partner of the $X(3872)$ as hadronic molecules at the LHC and Tevatron experiments. We find that the cross sections for these processes are at the nb level, so that the current and future data sets from the Tevatron and LHC experiments offer a significant discovery potential. We further point out that the $X_b/X_{b2}$ should be reconstructed in the $γΥ(nS) (n=1,2,3)$, $Υ(1S)π^+π^-π^0$, or $χ_{bJ}π^+π^-$ instead of the $Υ(nS)π^+π^-$ final states.

hep-ph↗
arXiv2014

Unsupervised Spike Sorting Based on Discriminative Subspace Learning

Spike sorting is a fundamental preprocessing step for many neuroscience studies which rely on the analysis of spike trains. In this paper, we present two unsupervised spike sorting algorithms based on discriminative subspace learning. The first algorithm simultaneously learns the discriminative feature subspace and performs clustering. It uses histogram of features in the most discriminative projection to detect the number of neurons. The second algorithm performs hierarchical divisive clustering that learns a discriminative 1-dimensional subspace for clustering in each level of the hierarchy until achieving almost unimodal distribution in the subspace. The algorithms are tested on synthetic and in-vivo data, and are compared against two widely used spike sorting methods. The comparative results demonstrate that our spike sorting methods can achieve substantially higher accuracy in lower dimensional feature space, and they are highly robust to noise. Moreover, they provide significantly better cluster separability in the learned subspace than in the subspace obtained by principal component analysis or wavelet transform.

cs.CV↗
arXiv2014

Application of Multilayer Feedforward Neural Networks in Predicting Tree Height and Forest Stock Volume of Chinese Fir

Wood increment is critical information in forestry management. Previous studies used mathematics models to describe complex growing pattern of forest stand, in order to determine the dynamic status of growing forest stand in multiple conditions. In our research, we aimed at studying non-linear relationships to establish precise and robust Artificial Neural Networks (ANN) models to predict the precise values of tree height and forest stock volume based on data of Chinese fir. Results show that Multilayer Feedforward Neural Networks with 4 nodes (MLFN-4) can predict the tree height with the lowest RMS error (1.77); Multilayer Feedforward Neural Networks with 7 nodes (MLFN-7) can predict the forest stock volume with the lowest RMS error (4.95). The training and testing process have proved that our models are precise and robust.

cs.CE↗
arXiv2014

Production of charm-strange hadronic molecules at the LHC

We explore the inclusive hadroproduction of the D_{s0}^*(2317), D_{s1}(2460) and D_{sJ}(2860) states at the Large Hadron Collider under the assumption that these hadrons are S-wave meson-meson molecules. In addition, the D_{s2}(2910), a predicted bound state of the D_2(2460)K system, is also discussed. We first derive a factorisation formula for the production rates based on effective field theory. Then we make use of two MC event generators, Herwig and Pythia, to simulate the production of pairs of charmed mesons and kaons. Using effective field theory to handle the final state interaction among the meson pairs, we give an estimate of the inclusive production rates for these particles at the order-of-magnitude accuracy. Our results show that the cross sections for the pp --> D_{s0}^*(2317) and pp --> D_{s1}(2460) at the LHC are at O(1 μb) level, while the ones for the pp --> D_{sJ}(2860) and the pp --> D_{s2}(2910) are smaller by about one order of magnitude. Such estimates suggest that these four exotic states could be copiously produced at the LHC. A study of these states at the LHC will thus provide valuable information on hadron spectroscopy as well as hadron interactions.

hep-ph↗
arXiv2014

A Fast, robust algorithm for power line interference cancellation in neural recording

Power line interference may severely corrupt neural recordings at 50/60 Hz and harmonic frequencies. In this paper, we present a robust and computationally efficient algorithm for removing power line interference from neural recordings. The algorithm includes four steps. First, an adaptive notch filter is used to estimate the fundamental frequency of the interference. Subsequently, based on the estimated frequency, harmonics are generated by using discrete-time oscillators, and then the amplitude and phase of each harmonic are estimated through using a modified recursive least squares algorithm. Finally, the estimated interference is subtracted from the recorded data. The algorithm does not require any reference signal, and can track the frequency, phase, and amplitude of each harmonic. When benchmarked with other popular approaches, our algorithm performs better in terms of noise immunity, convergence speed, and output signal-to-noise ratio (SNR). While minimally affecting the signal bands of interest, the algorithm consistently yields fast convergence and substantial interference rejection in different conditions of interference strengths (input SNR from -30 dB to 30 dB), power line frequencies (45-65 Hz), and phase and amplitude drifts. In addition, the algorithm features a straightforward parameter adjustment since the parameters are independent of the input SNR, input signal power, and the sampling rate. The proposed algorithm features a highly robust operation, fast adaptation to interference variations, significant SNR improvement, low computational complexity and memory requirement, and straightforward parameter adjustment. These features render the algorithm suitable for wearable and implantable sensor applications, where reliable and real-time cancellation of the interference is desired.

eess.SY↗
arXiv2013

Heavy Quarkonium Production through the Semi-Exclusive $e^+ e^-$ Annihilation Channels around the $Z^0$ Peak

Within the framework of the non-relativistic QCD, we present a detailed discussion on the heavy quarkonium production at the leading order in $α_s$ at a $e^+ e^-$ collider with the collision energy around the $Z^0$ peak. Quarkonia are produced through the semi-exclusive channels $e^{+}e^{-} \rightarrow |H_{Q\bar{Q}}\rangle +X$ with $X=Q\bar{Q}$ or $gg$, where $Q$ indicates a heavy quark (respectively $b$ or $c$). It is noted that in addition to the color-singlet 1S-level quarkonium states, the 2S and 1P color-singlet states and the color-octet $|(Q\bar{Q})[1^3S_1^{({\bf 8})}]g\rangle$ state also provide sizable contributions. The heavy quarkonium transverse momentum and rapidity distributions for the $e^+ e^-$ collision energy $E_{cm}=m_Z$ are presented. For both charmonium and bottomonium production via the $Z^0$ propagator, there is approximate "spin degeneracy" between the spin-triplet and spin-singlet quarkonium states. Uncertainties for the total cross sections are estimated by taking $m_c=1.50\pm0.15$ GeV and $m_b=4.90\pm0.15$ GeV. Around $E_{cm}=m_{Z}$, due to the $Z^0$-boson resonance effect, total cross sections for the channels via the $Z^0$-propagator become much larger than the channels via the virtual photon propagator. We conclude that, in addition to the $B$ factories as BaBar and Belle and the hadronic colliders as Tevatron and LHC, such a super $Z$-factory will present an excellent platform for studying the heavy quarkonium properties.

hep-ph↗
arXiv2013

BEEC: An event generator for simulating the $B_c$ meson production at an $e^+e^-$ collider

The $B_c$ meson is a doubly heavy quark-antiquark bound state and carries flavors explicitly, which provides a fruitful laboratory for testing potential models and understanding the weak decay mechanisms for heavy flavors. In view of the prospects in $B_c$ physics at the hadronic colliders as Tevatron and LHC, $B_c$ physics is attracting more and more attention. It has been shown that a high luminosity $e^+e^-$ collider running around the $Z^0$-peak is also helpful for studying the properties of $B_c$ meson and has its own advantages. For the purpose, we write down an event generator for simulating $B_c$ meson production through $e^+e^-$ annihilation according to relevant publications. We name it as BEEC, in which the color-singlet $S$-wave and $P$-wave $(c\bar{b})$-quarkonium states together with the color-octet $S$-wave $(c\bar{b})$-quarkonium states can be generated. BEEC can also be adopted to generate the similar charmonium and bottomnium states via the semi-exclusive channels $e^{+}+e^{-}\rightarrow |(Q\bar{Q})[n]\rangle +Q +\bar{Q}$ with $Q=b$ and $c$ respectively. To increase the simulation efficiency, we simplify the amplitude as compact as possible by using the improved trace technology. BEEC is a Fortran programme written in a PYTHIA-compatible format and is written in a modularization structure, one may apply it to various situations or experimental environments conveniently by using the GNU C compiler {\bf make}. A method to improve the efficiency of generating unweighted events within PYTHIA environment has been suggested. Moreover, BEEC will generate a standard Les Houches Event data file that contains useful information of the meson and its accompanying partons, which can be conveniently imported into PYTHIA to do further hadronization and decay simulation.

hep-ph↗
arXiv2012

Excited Heavy Quarkonium Production at the LHC through $W$-Boson Decays

Sizable amount of heavy-quarkonium events can be produced through $W$-boson decays at the LHC. Such channels will provide a suitable platform to study the heavy-quarkonium properties. The "improved trace technology", which disposes the amplitude ${\cal M}$ at the amplitude-level, is helpful for deriving compact analytical results for complex processes. As an important new application, in addition to the production of the lower-level Fock states $|(Q\bar{Q'})[1S]>$ and $|(Q\bar{Q'})[1P]>$, we make a further study on the production of higher-excited $|(Q\bar{Q'})>$-quarkonium Fock states $|(Q\bar{Q'})[2S]>$, $|(Q\bar{Q'})[3S]>$ and $|(Q\bar{Q'})[2P]>$. Here $|(Q\bar{Q'})>$ stands for the $|(c\bar{c})>$-charmonium, $|(c\bar{b})>$-quarkonium and $|(b\bar{b})>$-bottomonium respectively. We show that sizable amount of events for those higher-excited states can also be produced at the LHC. Therefore, we need to take them into consideration for a sound estimation.

hep-ph↗
arXiv2012

$B_c$ Meson Production around the $Z^0$ Peak at a High Luminosity $e^+ e^-$ Collider

Considering the possibility to build an $e^+ e^-$ collider at the energies around the $Z^0$-boson resonance with a planned luminosity so high as ${\cal L}\propto 10^{34}\sim 10^{36}cm^{-2}s^{-1}$ (super $Z$-factory), we make a detailed discussion on the $(c\bar{b})$-quarkonium production through $e^{+}+e^{-}\rightarrow (c\bar{b})[n]+b+\bar{c}$ within the framework of non-relativistic QCD. To simplify the hard-scattering amplitude as much as possible and to derive analytic expressions for the purpose of future events simulation, we adopt the "improved trace technology" to do our calculation, which deals with the hard scattering amplitude directly at the amplitude level other than the conventional way at the squared-amplitude level. Total cross-section uncertainties caused by the quark masses are predicted by taking $m_c=1.50\pm0.30$ GeV and $m_b=4.90\pm0.40$ GeV. If all higher $(c\bar{b})$-quarkonium states decay to the ground state $B_c$ ($|(c\bar{b})_{\bf 1}[^1S_0]>$) with 100% efficiency, we obtain $σ_{e^{+}+e^{-}\rightarrow B_{c}+b+\bar{c}} =5.190^{+6.222}_{-2.419}$ pb, which shows that about $10^5 \sim 10^7$ $B_c$ events per operation year can be accumulated in the super $Z$-factory. If taking the collider energy runs slightly off the $Z^0$-peak, i.e. $\sqrt{S}=(1.00\pm0.05) m_Z$, the total cross-section shall be lowered by about one-order from its peak value. Such a super $Z$-factory shall provide another useful platform to study the properties of $B_c$ meson, or even the properties of its excited $P$-wave states, in addition to its production at the hadronic colliders Tevatron and LHC.

hep-ph↗
arXiv2012

Heavy Quarkonium Production at LHC through $W$ Boson Decays

The production of the heavy $(c\bar{c})$-quarkonium, $(c\bar{b})$-quarkonium and $(b\bar{b})$-quarkonium states ($(Q\bar{Q'})$-quarkonium for short), via the $W^+$ semi-inclusive decays, has been systematically studied within the framework of the non-relativistic QCD. In addition to the two color-singlet $S$-wave states, we also discuss the production of the four color-singlet $P$-wave states $|(Q\bar{Q'})(^1P_1)_{\bf 1}>$ and $(Q\bar{Q'})(^3P_J)_{\bf 1}>$ (with $J=(1,2,3)$) together with the two color-octet components $|(Q\bar{Q'})(^1S_0)_{\bf 8}>$ and $|(Q\bar{Q'})(^3S_1)_{\bf 8}>$. Improved trace technology is adopted to derive the simplified analytic expressions at the amplitude level, which shall be useful for dealing with the following cascade decay channels. At the LHC with the luminosity ${\cal L}\propto 10^{34}cm^{-2}s^{-1}$ and the center-of-mass energy $\sqrt{S}=14$ TeV, sizable heavy-quarkonium events can be produced through the $W^+$ boson decays, i.e. $2.57\times10^6$ $η_c$, $2.65\times10^6$ $J/Ψ$ and $2.40\times10^6$ $P$-wave charmonium events per year can be obtained; and $1.01\times10^5$ $B_c$, $9.11\times10^4$ $B^*_c$ and $3.16\times10^4$ $P$-wave $(c\bar{b})$-quarkonium events per year can be obtained. Main theoretical uncertainties have also been discussed. By adding the uncertainties caused by the quark masses in quadrature, we obtain $Γ_{W^+\to (c\bar{c})+c\bar{s}} =524.8^{+396.3}_{-258.4}$ KeV, $Γ_{W^+\to (c\bar{b})+b\bar{s}} =13.5^{+4.73}_{-3.29}$ KeV, $Γ_{W^+\to (c\bar{b})+c\bar{c}}= 1.74^{+1.98}_{-0.73}$ KeV and $Γ_{W^+\to (b\bar{b})+c\bar{b}}= 38.6^{+13.4}_{-9.69}$ eV.

hep-ph↗