arXiv subjects

Tianhong Wang

Publications and source records attributed to Tianhong Wang.

At least 55 records · Page 3Linked to original sources

arXiv2021

Nonlinear Conversion of Orbital Angular Momentum States of Light

We investigate the second harmonic generation of light field carrying orbital angular momentum in bulk $χ^{(2)}$ material. We show that due to conservation of energy and momentum, the frequency doubled beam light has a modified spatial distribution and mode characteristics. Through rigorous phase matching conditions, we demonstrate efficient mode and frequency conversion based on three wave nonlinear optical mixing.

physics.optics↗

arXiv2021

Sub-femtosecond wakefield injector and accelerator based on an undulating plasma bubble controlled by a laser phase

We demonstrate that a long-propagating plasma bubble executing undulatory motion can be produced in the wake of two co-propagating laser pulses: a near-single-cycle injector and a multi-cycle driver. When the undulation amplitude exceeds the analytically derived threshold, highly-localized injections of plasma electrons into the bubble are followed by their long-distance acceleration. While the locations of the injection regions are controlled by the carrier-envelope phase (CEP) of the injector pulse, the mono-energetic spectrum of the accelerated sub-femtosecond high-charge electron bunches is shown to be nearly CEP-independent

physics.plasm-ph↗

arXiv2021

CP violation in non-leptonic $B_c$ decays to excited final states

We study the CP violation in two-body nonleptonic decays of $B_c$ meson. We concentrate on the decay channels which contain at least one excited heavy meson in the final states. Specifically, the following channels are considered: $B_c\to c\bar c(2S, 2P)+\bar cq(1S, 1P)$, $B_c\to c\bar c(1S)+\bar cq(2S, 2P)$, $B_c\to c\bar c(1P)+\bar cq(2S)$, $B_c\to c\bar c(1D)+\bar cq(1S, 1P)$, and $B_c\to c\bar c(3S)+\bar cq(1S)$. The improved Bethe-Salpeter method is applied to calculate the hadronic transition matrix element. Our results show that some decay modes have large branching ratios, which is of the order of $10^{-3}$. The CP violation effect in $B_c \rightarrow η_c(1S)+D(2S)$, $B_c \rightarrow η_c(1S)+D_0^{*}(2P)$, and $B_c \rightarrow J/ψ+D^{*}(2S)$ are most likely to be found. If the detection precision of the CP asymmetry in such channels can reach the $3σ$ level, at least $10^7$ $B_c$ events are needed.

hep-ph↗

arXiv2020

Spin-$1/2$ invisible particles in heavy meson decays

The flavor-changing neutral current decay processes of the $B$ and $B_c$ mesons with the final states involving spin-$1/2$ particles are investigated. By considering the background of the Standard Model where $ν\barν$ contributes the missing energy and the experimental upper bounds for the branching fractions, we get the constraints of the coupling constants of the quark-antiquark and the assumed invisible particles $χ\barχ$. The constraints of the coupling constants are then used to study the similar processes of the $B_c$ meson. At some specific region of $m_χ$, the upper limit of BR($B_c\to D_{(s)}χ\barχ$) is of the order of $10^{-6}$, while for BR($B_c\to D^\ast_{(s)}χ\barχ$), it is $10^{-5}$. The possibility of distinguishing $χ$ to be a Majorana or Dirac fermion by the differential branching fractions is also discussed.

hep-ph↗

arXiv2020

Laser-Ion Lens and Accelerator

Generation of highly collimated monoenergetic relativistic ion beams is one of the most challenging and promising areas in ultra-intense laser-matter interactions because of the numerous scientific and technological applications that require such beams. We address this challenge by introducing the concept of laser-ion lensing and acceleration (LILA). Using a simple analogy with a gradient-index lens, we demonstrate that simultaneous focusing and acceleration of ions is accomplished by illuminating a shaped solid-density target by an intense laser pulse at ~10^22 W/cm^2 intensity, and using radiation pressure of the laser to deform/focus the target into a cubic micron spot. We show that the LILA process can be approximated using a simple deformable mirror model, and then validate it using three-dimensional particle-in-cell simulations of a two-species plasma target comprised of electrons and ions. Extensive scans of the laser and target parameters identify the stable propagation regime where the Rayleigh-Taylor (RT)-like instability is suppressed. Stable focusing are found at different laser powers (from few- to multi-petawatt). Focused ion beams with the focused density of order 10^23 cm^-3, energies in access of 750MeV, and energy density up to 2*10^13 J/cm^3 at the focal point are predicted for future multi-petawatt laser systems.

physics.plasm-ph↗

arXiv2020

Laser-Pulse and Electron-Bunch Plasma Wakefield Accelerator

Propagation distances of intense laser pulses and high-charge electron beams through the plasma are, respectively, limited by diffraction and self-deceleration. This imposes severe constraints on the performance of the two major advanced accelerator concepts: laser and plasma wakefield accelerators. Using numerical simulations, we demonstrate that when the two beams co-propagate in the plasma, they can interact synergistically and extend each other's travel distances. The key interactions responsible for the synergy are found to be laser channeling by the electron bunch, and direct laser acceleration of the bunch electrons by the laser pulse. Remarkably, the amount of energy transferred from the laser pulse to the plasma can be increased by several times by the guiding electron bunch despite its small energy content. Implications of such synergistic interactions for the high-gradient acceleration of externally injected witness charges are discussed, and a new concept of a Laser-pulse and Electron-bunch Plasma Accelerator (LEPA) is formulated.

physics.plasm-ph↗

arXiv2020

The study of two quasi-degenerate heavy sterile neutrinos in rare meson decays

In this work, we study the lepton-number-violating processes of $K^\pm$ and $D^\pm$ mesons. Two quasi-degenerate sterile neutrinos are assumed to induce such processes. Different with the case where only one sterile neutrino involves, here, the CP phases of the mixing parameters could give sizable contribution. This, in turn, would affect the absolute values of the mixing parameters determined by the experimental upper limits of the branching fractions. A general function which express the difference of the mixing parameters for two-generation and one-generation is presented. Special cases with specific relations of the parameters are discussed. Besides, we also thoroughly investigate the CP violation effect of such processes. It is shown that generally $\mathcal A_{CP}$ is a function of the sterile neutrino mass.

hep-ph↗

arXiv2020

The weak $B$, $B_s$ and $B_c$ decays to radially excited states

Recently, many new excited states of heavy mesons, especially the radially excited states, are discovered. The study of the production processes of these states from the ground b-flavored mesons is of interest. In this paper, we use the improved Bethe-Salpeter method to study the semi-leptonic and non-leptonic decays of $B$, $B_s$, and $B_c$ mesons, where the final states are focused on the radial excited $2S$ and $3S$ states. We find that many channels have branching ratios up to $10^{-4}$, which are within the detection accuracy of current experiments.

hep-ph↗

arXiv2019

Isgur-Wise function in $B_c$ decays to charmonium with the Bethe-Salpeter method

The Isgur-Wise function vastly reduces the weak-decay form factors of hadrons containing one heavy quark. In this paper, we extract the Isgur-Wise functions from the instantaneous Bethe-Salpeter method, and give the numerical results for the $B_c$ decays to charmonium where the final states include $1S$, $1P$, $2S$ and $2P$. The overlapping integral of the wave functions for the initial and final states is the Isgur-Wise function, as the heavy quark effective theory does. In the case of accurate calculation, describing form factors need to introduce more relativistic corrections which are the overlapping integrals with the relative momentum between the quark and antiquark to Isgur-Wise function. The relativistic corrections to Isgur-Wise function provide greater contributions especially involving the excited state, and therefore are necessary to be adopted.

hep-ph↗

arXiv2019

Mixing angle and decay constants of $J^P=1^+$ heavy-light mesons

The mass spectra, mixing angle and decay constants of the $J^P=1^+$ heavy-light mesons are systematically studied within the framework of the Bethe-Salpeter equation (BSE). The full $1^+$ Salpeter wave function is given for the first time. The mixing between the $1^{+-}$ and $1^{++}$ in the $1^+$ heavy-light systems are automatically determined by the dynamics in the equation without any man-made mixing. The results indicate that in a rigorous study there exists the phenomenon of mixing angle inversion or mass inversion within $1^{+}$ heavy-light doublet, which is sensitive to the $s$-quark mass for the charmed mesons and $u$- or $d$-quark masses for the bottomed mesons. This inversion phenomenon can answer the question of why we have confused mixing angles in the literature and partly explain the lower mass of $D_{s1}(2460)$ compared to that of $D_{s1}(2536)$. The decay constants are also presented and can behave as a good quantity to distinguish the $1^+$ doublet in heavy-light mesons. This study indicates that the light-quark mass may play an important role in deciding the mass order, mixing angle, and decay constant relation between the $\ket{j_l=\frac{3}{2}}$ and $\ket{j_l=\frac{1}{2}}$ heavy-light mesons.

hep-ph↗

arXiv2019

Study of the dilepton electromagnetic decays of $χ_{cJ}(1P)$

In this paper, the dilepton electromagnetic decays $χ_{cJ}(1P) \to J/ψe^+e^-$ and $χ_{cJ}(1P) \to Jψμ^+μ^-$, where $χ_{cJ}$ denotes $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$, are calculated systematically in the improved Bethe-Salpeter method. The numerical results of decay widths and the invariant mass distributions of the final lepton pairs are given. The comparison is made with the recently measured experimental data of BESIII. It is shown that for the cases including $e^+e^-$, the gauge invariance is decisive and should be considered carefully. For the processes of $χ_{cJ}(1P) \to J/ψe^+e^-$, the branching fraction are: $\mathcal{B}[χ_{c0}(1P) \to J/ψe^+e^-]=1.06^{+0.16}_{-0.18} \times 10^{-4}$, $\mathcal{B}[χ_{c1}(1P) \to J/ψe^+e^-]=2.88^{+0.50}_{-0.53} \times 10^{-3}$, and $\mathcal{B}[χ_{c2}(1P) \to J/ψe^+e^-]=1.74^{+0.22}_{-0.21} \times 10^{-3}$. The calculated branching fractions of $χ_{cJ}(1P)\to J/ψμ^+μ^-$ channels are: $\mathcal{B}[χ_{c0}(1P) \to J/ψμ^+μ^-]=3.80^{+0.59}_{-0.64} \times 10^{-6}$, $\mathcal{B}[χ_{c1}(1P) \to J/ψμ^+μ^-]=2.04^{+0.36}_{-0.38} \times 10^{-4}$, and $\mathcal{B}[χ_{c2}(1P) \to J/ψμ^+μ^-]=1.66^{+0.19}_{-0.19} \times 10^{-4}$.

hep-ph↗

arXiv2019

Rates of $D^{}_{0}(2400)$, $ D_J^(3000) $ as the $D^{}_{0}(2P)$ and $D^{}_{0}(3P)$ in $B$ Decays

In this paper, we use the instantaneous Bethe-Salpeter method to calculate the semi-leptonic and non-leptonic production of the orbitally excited scalar $ D_0^* $ in $ B $ meson decays. When the final state is $ 1P $ state $ D_0^*(2400) $, our theoretical decay rate is consistent with experimental data. For $ D_J^*(3000) $ final state, which was observed by LHCb collaboration recently and here treated as the orbitally excited scalar $D^{*}_{0}(2P)$, its rate is in the order of $ 10^{-4} \sim 10^{-6}$. We find the special node structure of $D^{*}_{0}(2P)$ wave function possibly results in the suppression of its branching ratio and the abnormal uncertainty. The $3P$ states production rate is in the order of $ 10^{-5}$.

hep-ph↗

arXiv2019

The study of light invisible particles in $B_c$ decays

In this paper, we study the light scalar and pseudoscalar invisible particles in the flavor changing neutral current processes of the $B_c$ meson. Effective operators are introduced to describe the couplings between quarks and light invisible particles. The Wilson coefficients are extracted from the experimental results of the $B$ and $D$ mesons, which are used to predict the upper limits of the branching fractions of the similar decay processes for the $B_c$ meson. The hadronic transition matrix element is calculated with the instantaneously approximated Bethe-Salpeter method. The upper limits of the branching fractions when $m_χ$ taking different values are presented. It is found that at some region of $m_χ$, the channel $B_c\to D_s^{(\ast)}χχ$ has the largest upper limit which is of the order of $10^{-6}$, and for $B_c\to D_s^\astχχ^\dagger$, the largest value of the upper limits can achieve the order of $10^{-5}$. Other decay modes, such as $B_c\to D^{(*)}χχ^{(\dagger)}$ and $B_c\to B^{(*)}χχ^{(\dagger)}$, are also considered.

hep-ph↗

arXiv2018

Direct laser acceleration of electrons by tightly focused laser pulses

We present an analytical theory that reveals the importance of the longitudinal laser electric field in the resonant acceleration of relativistic electrons by the tightly confined laser beam. It is shown that this field always counterworks to the laser transverse component and effectively decreases the final energy gain of electrons through direct laser acceleration mechanism. This effect is demonstrated by carrying out the particle-in-cell simulations in the setup where the wakefield in the plasma bubble is compensated by the longitudinal laser electric field experienced by the accelerated electrons. The derived scalings and estimates are in good agreement with numerical simulations.

physics.plasm-ph↗

arXiv2018

Semi-leptonic decays of $B^\ast$, $B_s^\ast$, and $B_c^\ast$ with the Bethe-Salpeter method

In this paper we study the semileptonic decays of $B^\ast$, $B_s^\ast$, and $B_c^\ast$ by using the Bethe-Salpeter method with instantaneous approximation. Both the $V\to Pl^-\barν_l$ and $V\to Vl^-\barν_l$ cases are considered. The largest partial width of these channels is of the order of $10^{-14}$ GeV. The branching ratios of these semileptonic decays are also estimated by using the partial width of the one photon decay channel to approximate the total width. For $B^{\ast-}\to D^{(\ast)0}e^-\barν_e$ and $B_s^{\ast0}\to D_s^{(\ast)+}e^-\barν_e$, the branching ratios are of the order of $10^{-8}$ and $10^{-7}$, respectively. For $B_c^{\ast-}$, the $J/ψe^-\barν_e$ and $B_s^{\ast0}e^-\barν_e$ channels have the largest branching ratio, which is of the order of $10^{-6}$.

hep-ph↗

arXiv2018

Relativistic effects in the semileptonic $B_c$ decays to charmonium with the Bethe-Salpeter method

Relativistic effects are important in the rigorous study of heavy quarks. In this paper, we study the relativistic corrections of semileptonic $B_c$ decays to charmonium with the instantaneous Bethe-Salpeter method. Within the Bethe-Salpeter framework, we use two methods to study the relativistic effects. One of them is to expand the transition amplitude in powers of $\vec{q}$ which is the relative momentum between the quark and antiquark, and the other is to expand the amplitude base on the wave functions. In the level of decay width, the results show that, for the transition of $B_c\to η_c$, the relativistic correction is about $22\%$; for $B_c\to J/ψ$, it is about $19\%$; the relativistic effects of $1P$ final states are about $14\sim46\%$ larger than those of $1S$ final states; for $2S$ final states, they are about $19\sim 28\%$ larger than those of $1S$ final states; for $3S$ final states, they are about $12\sim13\%$ larger than those of $2S$ final states; for $2P$ final states, they are about $10\sim14\%$ larger than those of $1P$ final states; for $3P$ final states, they are about $7\sim12\%$ larger than those of $2P$ final states. We conclude that the relativistic corrections of the $B_c$ decays to the orbitally or radially excited charmonium (2S, 3S, 1P, 2P, 3P) are quite large.

hep-ph↗

arXiv2018

Strong Decays of the Orbitally Excited Scalar $D^{*}_{0}$ Mesons

We calculate the two-body strong decays of the orbitally excited scalar mesons $D_0^*(2400)$ and $D_J^*(3000)$ by using the relativistic Bethe-Salpeter (BS) method. $D_J^*(3000)$ was observed recently by the LHCb Collaboration, the quantum number of which has not been determined yet. In this paper, we assume that it is the $0^+(2P)$ state and obtain the transition amplitude by using the PCAC relation, low-energy theorem and effective Lagrangian method. For the $1P$ state, the total widths of $D_0^*(2400)^{0}$ and $ D_0^*(2400)^+$ are 226 MeV and 246 MeV, respectively. With the assumption of $0^+(2P)$ state, the widths of $D_J^*(3000)^0$ and $D_J^*(3000)^+$ are both about 131 MeV, which is close to the present experimental data. Therefore, $D_J^*(3000)$ is a strong candidate for the $2^3P_0$ state.

hep-ph↗

arXiv2018

Doubly-charged scalar in four-body decays of neutral flavored mesons

In this paper, we study the four-body decay processes of neutral flavored mesons, including $\bar K^0$, $D^0$, $\bar B^0$, and $\bar B_s^0$. These processes, which induced by a hypothetical doubly-charged scalar particle, violate the lepton number. The quantity $Br\times\left(\frac{s_Δh_{ij}}{m_Δ^2}\right)^{-2}$ of different channels are calculated, where $s_Δ$, $h_{ij}$, and $M_Δ$ are parameters related to the doubly-charged scalar. For $\bar K^0\rightarrow h_1^+h_2^+l_1^-l_2^-$, $D^0\rightarrow h_1^-h_2^-l_1^+l_2^+$, and $\bar B_{d,s}^0\rightarrow h_1^+h_2^+l_1^-l_2^-$, it is of the order of $10^{-13}\sim 10^{-11}$ ${\rm GeV^4}$, $10^{-17}\sim 10^{-10}$ ${\rm GeV^4}$, and $10^{-17}\sim 10^{-10}$ ${\rm GeV^4}$, respectively. Based on the experimental results for the $D^0\rightarrow h_1^-h_2^-l_1^+l_2^+$ channels, we also set the upper limit for $\frac{s_Δh_{ij}}{M_Δ^2}$.

hep-ph↗