arXiv subjects

Tianhong Wang

Publications and source records attributed to Tianhong Wang.

At least 37 records · Page 2Linked to original sources

arXiv2024

Acceleration and focusing of multispecies ion beam using a converging laser-driven shock

We demonstrate an ion acceleration scheme capable of simultaneously focusing and accelerating a multispecies ion beam with monoenergetic spectra to a few micron radius. The focal length and ion mean energy can be independently controlled: the former by using a different front-surface shape and the latter by tuning the laser-plasma parameters. We interpret the results using simple models and validate the results using first-principles simulations. The scheme is applicable to different laser transverse profiles and multi-ion species target, and limiting factors for the ion focusing are delineated. The generated ion beam exhibits high charge, low emittance, and high energy flux and is of interest to various applications including Inertial Confinement Fusion (ICF), high flux neutron generation, and biomedical applications.

physics.plasm-ph↗

arXiv2024

Radiative transitions of $χ_{_{cJ}}\toψγ$ and $χ_{_{bJ}}\toΥγ$

In the framework of instantaneous Bethe-Salpeter equation, according to the $J ^ {PC}$ of quarkonia, we find that their wave functions all contain multiple partial waves, rather than pure waves. In the radiative electromagnetic transitions $χ_{_{cJ}}$$\rightarrow$$γψ$ and $χ_{_{bJ}}$$\rightarrow$$γΥ$ ($J=0,1,2$), the main wave of quarkonium gives the non-relativistic contribution, while other waves provide the relativistic corrections. Our results indicate that the relativistic effect of charmonium, especially highly excited states, is significant. Such as the relativistic effects of $χ_{_{cJ}}(2P)\toγψ(1S)$ ($J=0,1,2$) are $\{49.7\%,~30.9\%,~37.5\%\}$, much larger than the corresponding $\{17.8\%,~7.08\%,~12.9\%\}$ of $χ_{_{bJ}}(2P)\rightarrowγΥ(1S)$. The decay of $χ_{_{cJ}}(2P)\toγψ$ can be used to distinguish between $χ_{_{c0}}(3860)$ and $χ_{_{c0}}(3915)$, which particle is the charmonium $χ_{_{c0}}(2P)$. Although our result of $χ_{_{c1}}(3872)$$\rightarrow$$γψ(2S)$ is consistent with data, but the one of $χ_{_{c1}}(3872)$$\rightarrow$$γψ(1S)$ is much larger than data, so whether $χ_{_{c1}}(3872)$ is the conventional $χ_{_{c1}}(2P)$ remains an open question. The undiscovered $Υ(1D)$ and $Υ(2D)$ have large production rates in decays of $χ_{_{b0}}(2P)\rightarrowγΥ(1D)$ and $χ_{_{bJ}}(3P)\rightarrowγΥ(2D)$ ($J=0,1$), respectively. To search for $χ_{_{bJ}}(3P)$ $(J=0,1,2)$, the most competitive channels are the decays $χ_{_{bJ}}(3P)\rightarrowγΥ(3S)$. And the best way to find $χ_{_{b2}}(1F)$ is to search for the decay of $χ_{_{b2}}(1F)\rightarrowγΥ(1D)$.

hep-ph↗

arXiv2024

Kinetic energy and speed powers $v^n$ of a heavy quark inside $S$ wave and $P$ wave heavy-light mesons

Based on the instantaneous Bethe-Salpeter equation method, we calculate the average values $\overline{|\vec{q}|^n}\equiv q^n$ and speed powers $\overline{|\vec{v}|^n} \equiv v^n$ ($n=1,2,3,4$) of a heavy quark inside $S$ wave and $P$ wave heavy-light mesons, where $\vec{q}$ and $\vec{v}$ are the three dimensional momentum and velocity of the heavy quark, respectively. We obtain the kinetic energy $μ^2_{_π}=0.455$ GeV$^2$ for the $B$ meson, which is consistent with the experimental result $0.464\pm 0.076$ GeV$^2$. For the $B_{s}$, $D$ and $D_{s}$ mesons, the $μ^2_{_π}$ are $0.530$ GeV$^2$, $0.317$ GeV$^2$ and $0.369$ GeV$^2$, respectively. And $v^2=0.0185$, $0.0215$, $0.121$, and $0.140$ for $B$, $B_{s}$, $D$, and $D_{s}$. We obtain some relationships, for example, $q^n_{_{0^-}}(mS)\approx q^n_{_{1^-}}(mS)$, $q^n_{_{0^+}}(mP)\approx q^n_{_{1^{+'}}}(mP^{'})> q^n_{_{1^+}}(mP)\approx q^n_{_{2^+}}(mP)$, and $q^n(mS)< q^n(mP)$ ($m=1,2,3$), etc.

hep-ph↗

arXiv2024

Production of $D_{s0}(2590)^+$ in $B$ nonleptonic decays

In 2021, a new charm-strange meson, $D_{s0}(2590)^+$, has been discovered, it is believed to be the $D_s^+(2^1S_0)$. However, its low mass and wide width are challenged by theoretical results. Given the small branching ratio of the current production channel, resulting in a small number of events and large errors. We suggest to search for the $D_{s0}(2590)^+$ in the $B$ meson nonleptonic decays, $B_q\rightarrow D^{(*)}_qD_{s0}(2590)^+$ ($q=u,d$), followed by $D_{s0}(2590)^+\to D^*K$. We find $Br(B_q\rightarrow D^{(*)}_qD_{s0}(2590)^+)\times Br(D_{s0}(2590)^+\to D^{*}K)=(2.16\sim2.82)\times 10^{-3}$ is very large, and the result is not sensitive to the mass of $D_{s0}(2590)^+$. Due to large branching ratio, large amount of $D_{s0}(2590)^+$ events are expected. This study is based on the framework of instantaneous Bethe-Salpeter equation, and the used relativistic wave functions for mesons contain different partial waves. The contributions of different partial waves are also studied.

hep-ph↗

arXiv2024

Semirelativistic study on the semileptonic decays of $B_q$ mesons to orbital excited heavy Tensors

Based on the method of solving the complete Salpeter equation, we study the semileptonic decays of a $0^-$ heavy meson to $1P$, $2P$, or $3P$ heavy tensor mesons, $B_q \to (\bar c q)(nP) \ell^+ ν_\ell$ $(q=u,d,s,c;n=1,2,3)$. The obtained branching ratio of $\mathcal{B} (B \rightarrow D_2^{\star}(2460)\ell^{+} ν_{\ell})$ agrees with the experimental data. We predict $\mathcal{B}\left(B_s^{0} \rightarrow D_{s2}^{\star-}(1P) \ell^{+} ν_{\ell}\right)$$=$$3.76\times 10^{-3}$ and $\mathcal{B}\left(B_c^+ \rightarrow χ_{c2}(1P)\ell^{+} ν_{\ell}\right)$$=$$1.82\times 10^{-3}$. The branching ratios of decays to $2P$ and $3P$ final states are found to be very small. The ratios $\mathcal{R}(\bar{D}_{2}^{\star 0})=0.045$, $\mathcal{R}({D}_{s2}^{\star})=0.048$ and $\mathcal{R}(χ_{c2})=0.059$ are also obtained. This study focuses on the contribution of relativistic corrections. The wave function of the pseudoscalar includes non-relativistic $S$-wave and relativistic $P$-wave. While for a tensor, it contains non-relativistic $P$-wave and relativistic $P$, $D$ and $F$ waves in its wave function. We find the individual contributions of relativistic partial waves are significant in the decay $B \to D_2^{\star }(2460)\ell^{+} ν_{\ell}$, but the overall contribution of the relativistic effect is $24.4\%$, which is small due to cancellation. Similarly, for the decay $B_s^{0} \rightarrow D_{s2}^{\star-}(1P) \ell^{+} ν_{\ell}$, the contribution of the relativistic effect is $28.8\%$. While for $B_c^+ \rightarrow χ_{c2}(1P)\ell^{+} ν_{\ell}$, the individual contributions of relativistic partial waves and the overall relativistic correction are both small, the later of which is $22.1\%$.

hep-ph↗

arXiv2024

The decay property of the $X(3842)$ as the $ψ_{_3}(1^3D_{_3})$ state

In this paper, the new particle $X(3842)$ discovered by the LHCb Collaboration is identified to be the $ψ_{_3}(1^3D_{_3})$ state. We study its strong decays with the combination of the Bethe-Salpeter method and the $^3P_{_0}$ model. Its electromagnetic (EM) decay is also calculated by the Bethe-Salpeter method within Mandelstam formalism. The strong decay widths are {$Γ[X(3842)\rightarrow D^{0}\bar{D}^{0}]=1.28$ MeV}, $Γ[X(3823)\rightarrow D^{+}D^{-}]=1.08$ MeV, and the ratio ${\cal B}[X(3842)\rightarrow D^{+}D^{-}]/{\cal B}[X(3823)\rightarrow D^{0}\bar{D}^{0}]=0.84$. The EM decay width is $Γ[X(3842)\rightarrowχ_{_{c2}}γ]=0.29$ MeV. We also estimate the total width to be 2.87 MeV, which is in good agreement with the experimental data $2.79^{+0.86}_{-0.86}$ MeV. Since the used relativistic wave functions include different partial waves, we also study the contributions of different partial waves in electromagnetic decay.

hep-ph↗

arXiv2023

Partial wave effects in the heavy quarkonium radiative electromagnetic decays

In a previous paper \cite{Bc}, it was pointed out that the wave functions of all particles are not pure waves, besides the main partial waves, they all contain {other partial waves}. It is very interesting to know what role these different partial waves play in particle transitions. Therefore, by using the Bethe-Salpeter equation method, we study the radiative electromagnetic decays $ψ\rightarrowγχ_{_{cJ}}$ and $Υ\rightarrowγχ_{_{bJ}}$ ($J=0,1,2$). We find that for the $S$ and $P$ wave dominated states, like the $ψ(2S)$, $Υ(2S)$, $χ_{_{cJ}}(1P)$, and $χ_{_{bJ}}(1P)$ etc., the dominant $S$ and $P$ waves provide main and nonrelativistic contrition to the decays; other partial waves mainly contribute to the relativistic correction. For the states like the $ψ(1D)$, $Υ(2D)$, $χ_{c2}(1F)$, and $χ_{b2}(1F)$ etc., they are the $S-P-D$ mixing state dominated by $D$ wave or the $P-D-F$ mixing state dominated by $F$ wave. Large decay widths are found in the transitions $ψ(2D)\to χ_{c2}(1F)$, $Υ(1D)\to χ_{bJ}(1P)$, and $Υ(2D)\to χ_{bJ}(2P)$ etc., which may be helpful to study the missing states $χ_{c2}(1F)$, $Υ(1D)$, and $Υ(2D)$.

hep-ph↗

arXiv2023

The electromagnetic decays of $X(3823)$ as the $ψ_2(1^{3}D_{2})$ state and its radial excited states

We study the electromagnetic (EM) decays of $X(3823)$ as the $ψ_2(1^{3}D_{2})$ state by using the relativistic Bethe-Salpeter method. Our results are $Γ[X(3823)\rightarrowχ_{_{c0}}γ]=1.2$ keV, $Γ[X(3823)\rightarrowχ_{_{c1}}γ]=265$ keV, $Γ[X(3823)\rightarrowχ_{_{c2}}γ]=57$ keV and $Γ[X(3823)\rightarrowη_{_c}γ]=1.3$ keV. The ratio ${\cal B}[X(3823)\rightarrowχ_{_{c2}}γ]/{\cal B}[X(3823)\rightarrowχ_{_{c1}}γ]=0.22$, agrees with the experimental data. Similarly, the EM decay widths of $ψ_{_2}(n^{3}D_{_2})$, $n=2,3$, are predicted, and we find the dominant decays channels are $ψ_{_2}(n^{3}D_{_2})\rightarrowχ_{_{c1}}(nP)γ$, where $n=1,2,3$. The wave function include different partial waves, which means the relativistic effects are considered. We also study the contributions of different partial waves.

hep-ph↗

arXiv2023

Strong decays of $P_ψ^N(4312)^+$ to $J/ψ(η_c) p$ and $\bar D^{(*)}Λ_c$ within the Bethe-Salpeter framework

Based on the effective Lagrangian in the heavy quark limit, we calculate the one-boson-exchange interaction kernel of $P_ψ^N(4312)^+$ as the $\bar DΣ_c$ molecular state in isospin-$\frac12$. We present the Bethe-Salpeter equation and wave function for the constituent particles to be a (pseudo)scalar meson and a $\frac12$ baryon. By solving the Bethe-Salpeter equation, we obtain $P_ψ^N(4312)^+$ as the $\bar DΣ_c$ molecular state with $J^P=(\frac{1}{2})^-$. Combining the effective Lagrangian and the obtained BS wave function, the partial decay widths of $P_ψ^N(4312)^+$ to $J/ψp$, $η_c p$, $\bar D^{*0}Λ_c^+$ and $\bar D^0Λ_c^+$ are calculated to be $0.17$, $0.085$, $8.8$, and $0.026$ MeV, respectively, which are roughly consistent with the LHCb experimental measurements and some other theoretical researches. The obtain results indicate the fraction of $\bar D^{*0}Λ_c^+$ channel amounts to $\sim90\%$ of $P_ψ^N(4312)^+$, and is a highly promising channel to be discovered in the near future experiments. Our results favor the interpretation of $P_ψ^N(4312)^+$ as the $\bar DΣ_c$ molecular state with $J^P=(\frac{1}{2})^-$ and isospin $I=\frac12$.

hep-ph↗

arXiv2022

The solution to the `$1/2$ vs $3/2$' puzzle

Using an almost complete relativistic method based on the Bethe-Salpeter equation, we study the mixing angle $θ$, the mass splitting $\bigtriangleup M$, the strong decay widths $Γ(D^{({\prime})}_1)$ and the weak production rates $Br(B\to D^{({\prime})}_1\ellν_{\ell})$ of the $D_1(2420)$ and $D_1^{\prime}(2430)$. We find there is the strong cancellation between the $^1P_1$ and $^3P_1$ partial waves in $D_1^{\prime}(2430)$ with $θ\sim-35.3^{\circ}$, which leads to the `$1/2$ vs $3/2$' puzzle. The puzzle can not be overcome by adding only relativistic corrections since in a large parameter range where $\bigtriangleup M$ is linear varying and not small, the $θ$, $Γ(D^{({\prime})}_1)$ and $Br(B\to D^{({\prime})}_1\ellν_{\ell})$ remain almost unchanged but conflict with data. While in a special range around the mass inverse point where $\bigtriangleup M=0$ and $θ=\pm 90^{\circ}$, they change rapidly but we find the windows where $\bigtriangleup M$, $Γ(D^{({\prime})}_1)$ and $Br(B\to D^{({\prime})}_1\ellν_{\ell})$ are all consistent with data. The small $\bigtriangleup M$ confirmed by experiment, is crucial to solve the `$1/2$ vs $3/2$' puzzle.

hep-ph↗

arXiv2022

Polarization control of electron injection and acceleration in the plasma by a self steepening laser pulse

We describe an interplay between two injection mechanism of background electrons into an evolving plasma bubble behind an intense laser pulse: one due to the overall bubble expansion, and another due to its periodic undulation. The two mechanisms occur simultaneously when an intense laser pulse propagating inside a plasma forms a shock like steepened front. Periodic undulations of the plasma bubble along the laser propagation path can either inhibit or conspire with electron injection due to bubble expansion. We show that Carrier Envelope Phase (CEP) controlled plasma bubble undulation induced by the self steepening laser pulse produces a unique electron injector: Expanding Phase controlled Undulating Bubble (EPUB). The longitudinal structure of the electron bunch injected by the EPUB can be controlled by laser polarization and power, resulting in high-charge (multiple nano Coulombs) high-current (tens of kilo Amperes) electron beams with ultra short (femtosecond scale) temporal structure. Generation of high energy betatron radiation with polarization and CEP controlled energy spectrum and angular distribution is analyzed as a promising application of EPUB produced beams.

physics.acc-ph↗

arXiv2022

Strong decays of excited $ 2^+ $ charmed mesons

The new charmed resonance $ D_2^*(3000) $ was observed by the LHCb Collaboration in $ B $ decays. In this paper, by assigning it as four possible excited states of the $ 2^+ $ family, we use the instantaneous Bethe-Salpeter method to calculate their Okubo-Zweig-Iizuka-allowed two-body strong decays. The results of $ 1^3F_2 $ and $ 3^3P_2 $ states deviate from the present experimental observation while $ 2^3P_2 $ and $ 2^3F_2 $ are in the error range. Our study also reveals that the widths of these states depend strongly on the masses. Due to the large uncertainties and different mass input, variable models get inconsistent conclusions at the moment. The analysis in this work can provide essential assistance for future measurements and investigations.

hep-ph↗

arXiv2022

WAND-PIC: an accelerated three-dimensional quasi-static particle-in-cell code

We introduce a quasi-static particle-in-cell (PIC) code -- WAND-PIC -- which does not suffer from some of the common limitations of many quasi-static PICs, such as the need for a predictor-corrector method in solving electromagnetic fields. We derive the field equations under quasi-static (QS) approximation and find the explicit form of the "time" derivative of the transverse plasma current. After that, equations for the magnetic fields can be solved exactly without using the predictor-corrector method. Algorithm design and code structure are thus greatly simplified. With the help of explicit quasi-static equations and our adaptive step size, plasma bubbles driven by the large beam charges can be simulated efficiently without suffering from the numerical instabilities associated with the predictor-corrector method. In addition, WAND-PIC is able to simulate the sophisticated interactions between high-frequency laser fields and beam particles through the method of sub-cycling. Comparisons between the WAND-PIC and a first-principle full PIC code (VLPL) are presented. WAND-PIC is open-source, fully three-dimensional, and parallelized with the in-house multigrid solver. Scalability, time complexity, and parallelization efficiency up to thousands of cores are also discussed in this work.

physics.plasm-ph↗

arXiv2022

Multiple feedback based wavefront shaping method to retrieve hidden signal

We present an optical wavefront shaping approach that allows tracking and localization of signal hidden inside or behind a scattering medium. The method combines traditional feedback based wavefront shaping together with a switch function, controlled by two different signals. A simple, in transmission imaging system is used with two detectors: one monitors the speckle signature and the other tracks the fully hidden signal (e.g., fluorescent beads). The algorithm initially finds the optimal incident wavefront to maximize light transmission to generate a focus in the scattering medium. This modulation process redirects the scattered input signal inducing instantaneous changes in both monitored signals, which in turn locates the hidden objects. Once the response from the hidden target becomes distinct, the algorithm switches to use this signal as the feedback. We provide experimental demonstrations as a proof of concept of our approach. Potential applications of our method include extracting information from biological samples and developing non-invasive diagnosis methods.

physics.optics↗

arXiv2022

Femtosecond Filament Coupled with Structured Light for Free Space Optical Communication

The generation of a laser filament through clouds produces a shockwave which displaces the small water droplets from the air to create a quasi-transparent channel through which, information can be transmitted. We present a robust method that utilizes the channel for free-space optical communication using structured light beams coupled with a femtosecond filament. Vortex beams based on their spatial profiles and non-diffractive characteristics are perfectly suited to propagate around the filament. We have also developed a 4-bit communication channel using these structured light beam. We introduce a method dubbed segmented space division multiplexing. Our system demonstrates resilience to noise and is unaffected by the filament. This method can improve the scalability, robustness, and capacity of the free optical channel.

physics.optics↗

arXiv2021

Positron Acceleration in an Elongated Bubble Regime

A new concept is proposed for accelerating positrons in a nonlinear plasma wakefield accelerator. By loading the wakefield (back of the plasma bubble) with a short electron bunch, an extended area of excessive plasma electron accumulation is created after the first bubble, resulting in a favorable region with simultaneous focusing and accelerating fields for positrons. Scaling laws for optimized loading parameters are obtained through extensive parameters scans. Owing to the good quality of the focusing field, positron acceleration with emittance preservation can be achieved in this new regime and it has been demonstrated in the three-dimensional particle-in-cell simulations.

physics.plasm-ph↗

arXiv2021

Mass spectra and wave functions of $T_{QQ\bar Q\bar Q}$ tetraquarks

The compact tetraquark states with fully heavy quark contents $QQ\bar Q\bar Q$ are studied as the bound states of the diquark-antidiquark within the Bethe-Salpeter framework. The (anti)diquark masses and form factors used are the same as we calculated the doubly heavy baryons in a previous work. Under the instantaneous approximation, the three-dimensional (Bethe-)Salpeter equation of the tetraquarks is derived and solved numerically to obtain the corresponding mass spectra and wave functions of the tetraquarks with $J^{PC}=0^{++}$, $1^{+-}$, and $2^{++}$. Our results show that the three ground states of $cc\bar c\bar c$ locate in the mass range of $6.4\sim6.5$GeV, and the $bb\bar b\bar b$ states in mass range of $19.2\sim19.3$GeV. The obtained relativistic wave functions naturally include the mixing effects from the possible $D$\,(or $G$) partial waves, and then can be further used to do precise calculations of the tetraquark decays. Based on the obtained results, the LHCb's observation $X(6900)$ is less likely to be the ground states of compact $cc\bar c\bar c$ tetraquarks but might be the first or second excited states. In addition, a widely used propagator-like form factor is also investigated and discussed.

hep-ph↗

arXiv2021

The light invisible boson in FCNC decays of $B$ and $B_c$ mesons

In this paper, we study the FCNC decay processes of $B$ and $B_c$ meson, in which one invisible particle is emitted. Both the spin-0 and spin-1 cases are considered. The model-independent effective Lagrangian is introduced to describe the coupling between the light invisible boson and quarks. The constraints of the coupling coefficients are extracted by experimental upper limits of the missing energy in $B$ meson decays. The bounds are used to predict the upper limits of branching fractions of corresponding $B_c$ decays, which are of the order of $10^{-6}$ or $10^{-5}$ when final meson is pseudoscalar or vector, respectively. The maximum branch ratios are achieved when $m_χ\approx3.5- 4$~GeV, where $m_χ$ is the mass of the invisible particle.

hep-ph↗