arXiv subjects

Hai-Qing Zhou

Publications and source records attributed to Hai-Qing Zhou.

At least 37 records · Page 2Linked to original sources

arXiv2022

Two-Photon-Exchange effect in $ep\rightarrow enπ^+$ at small $-t$ with the hadronic model and dispersion relation approach

In this work, the two-photon-exchange (TPE) effect in $ep\rightarrow enπ^+$ at small $-t$ is discussed. In the previous work, the TPE contribution with one $π$ intermediate state is estimated numerically within a hadronic model under the pion-dominance approximation. Here we extend the discussion to include one $ρ$ intermediate state. The TPE contribution can be described by one scalar function in the limit $m_e\rightarrow 0$, the dispersion relation (DR) satisfied by this scalar function is analysed. The analytic expressions for the imaginary parts of the TPE contributions from one $π$ or one $ρ$ intermediate state are given within the hadronic model. Combining these analytic expressions and the DR, the corresponding real parts of the TPE contributions can be estimated easily at any available region. This can help the further experimental analysis to include the TPE contributions in a convenient way. The numeric results show that the TPE correction with one $ρ$ intermediate state is much smaller than that with one $π$ intermediate state in the current energy region. These results suggest that the TPE contribution with an elastic state is the main TPE contribution in $ep\rightarrow enπ^+$ at small $-t$.

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arXiv2022

Two-Photon-Exchange effects in $ep\rightarrow enπ^+$ and their corrections to separated cross sections $σ_{\textrm{L,T,LT,TT}}$ at small $-t$

In this work, the two-photon-exchange (TPE) effects in $ep\rightarrow enπ^+$ at small $-t$ are discussed within a hadronic model. Under the pion dominance approximation the TPE contribution to the amplitude can be described by a scalar function in the limit $m_e\rightarrow 0$. The TPE contributions to the amplitude and the unpolarized differential cross section are both estimated when only the elastic intermediate state is considered. We find that the TPE corrections to the unpolarized differential cross section are about from $-4\%$ to $-20\%$ at $Q^2=1$--$ 1.6$ GeV$^2$. After considering the TPE corrections to the experimental data sets of unpolarized differential cross section, we analyze the TPE corrections to the separated cross sections $σ_{\textrm{L,T,LT,TT}}$. We find that the TPE corrections (at $Q^2=1$--$1.6$ GeV$^2$) to $σ_{\textrm{L}}$ are about from $-10\%$ to $-30\%$, to $σ_{\textrm{T}}$ are about $20\%$, and to $σ_{\textrm{LT,TT}}$ are much larger. By these analysis, we conclude that the TPE contributions in $ep\rightarrow enπ^+$ at small $-t$ are important to extract the separated cross sections $σ_{\textrm{L,T,LT,TT}}$ and the electromagnetic magnetic form factor of $π^+$ in the experimental analysis.

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arXiv2021

Exact Relations for Two-Photon-Exchange Effect in Elastic $ep$ Scattering by Dispersion Relation and Hadronic Model

The two-photon-exchange (TPE) effect plays a key role to extract the form factors (FFs) of the proton. In this work, we present some exact properties on the TPE effect in the elastic $ep$ scattering based on four types of typical and general interactions. The possible kinematical singularities, the asymptotic behaviors and the branch cuts of the TPE amplitudes are analyzed. The analytic expressions clearly indicate some exact relations between the dispersion relation (DR) method and the hadronic model (HM) method. It suggests that the two methods should be modified to general forms, respectively. After the modifications the new forms give the same results. Furthermore, they automatically and correctly include the contributions due to the seagull interaction, the meson-exchange effect, the contact interactions and the off-shell effect. To analyze the elastic $e^{\pm}p$ scattering data sets, the new forms should be used.

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arXiv2020

Two-photon exchange effects in $e^+ e^-\rightarrowπ^+π^-$ at small $ \sqrt{s}$

In this work, the two-photon-exchange (TPE) effects in $e^+e^- \rightarrow π^+ π^-$ at small $\sqrt{s}$ are discussed within a hadronic model. In the limit $m_e\rightarrow 0$, the TPE contribution to the amplitude can be described by one scalar function $\overline{c}_{1}^{(2γ)}$. The ratio between this function and the corresponding contribution in one-photon exchange $c_{1}^{(1γ)}$ reflects all the information of the TPE corrections. The numerical results on this ratio are presented and an artificial function is used to fit the numerical results. The latter can be used conveniently in the further experimental data analysis. The numerical results show the asymmetry of the differential cross sections in $e^+e^- \rightarrow π^+ π^-$ is about $-4\%$ at $\sqrt{s}\sim 0.7$ GeV.

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arXiv2020

Decay widthes of $^3 P_J$ charmonium to $DD,DD^,D^D^*$ and corresponding mass shifts of $^3 P_J$ charmonium

In this work, we calculate the amplitudes of the processes $c\bar c({^3P_J}) \rightarrow DD,DD^*, D^*D^* \rightarrow c\bar c({^3P_J})$ in the leading order of the nonrelativistic expansion. The imaginary parts of the amplitudes are corresponding to the branch decay widthes of the charmonium $c\bar c({^3P_J}) \rightarrow DD,DD^*, D^*D^*$ and the real parts are corresponding to the mass shifts of the charmonium $c\bar c({^3P_J})$ due to these decay channels. After absorbing the polynomial contributions which are pure real and include the UV divergences, the ratios between the branch decay widthes and the corresponding mass shifts are only dependent on the center-of-mass energy. We find the decay widthes and the mass shifts of the $^3P_2$ states are exact zero in the leading order. The ratios between the branch decay widthes and the mass shifts for the $^3P_0, {^3P_1}$ states are larger than 5 when the center-of-mass energy is above the $DD,DD^*, D^*D^*$ threshold. The dependence of the mass shifts on the center-of-mass energy is nontrivial especially when the center-of-mass energy is below the threshold. The analytic results can be extended to the $b$ quark sector directly.

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arXiv2020

Electric transitions of the charmed-strange mesons in a relativistic quark model

In the present work, we adopt a relativistic constituent quark model to depict the charmed strange meson spectroscopy, in which $D_{s0}(2317)$ and $D_{s1}(2460)$ are considered as the $1^3P_0$ and $1P_1^\prime$ charmed strange mesons, respectively. By using the wave function obtained from the relativistic quark model, we further investigate the electric transitions between charmed strange mesons. We find the long wave length approximation is reasonable for the charmed strange meson radiative decay by comparing the results with different approximations. The estimated partial widths are all safely under the upper limits of the experimental data. Moreover, we find the branching ratio of $D_{s1}(2536) \to D_s^\ast γ/D_s γ$ are large enough to be detected, which could be searched by further experiments in Belle II and LHCb.

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arXiv2019

Mass shifts of $^3P_J$ heavy quarkonia due to the effect of two-gluon annihilation

In this work, we calculate the nonrelativistic asymptotic behavior of the amplitudes of $q\overline{q}\rightarrow 2g \rightarrow q\overline{q}$ in the leading order of $α_s$ (LO-$α_s$) with $q\overline{q}$ in the $^3P_J$ channels. In the practical calculation we take the momenta of quarks and antiquarks on-shell and expand the amplitudes on the three-momentum of the quarks and antiquarks to order 6 and get three nonzero terms. The imaginary parts of the first term and the second term are the old. The real parts of the results have IR divergence. When applying the results to the heavy quarkonia, the corresponding amplitude of $q\overline{q}\rightarrow1g\rightarrow q\overline{q}$ with $q\overline{q}$ in the color octet $^3S_1$ channel is considered to absorb the IR divergence in a unitary way in the leading order of $v$ (LO-$v$). The finial results can be used to estimate the mass shifts of the $^3P_J$ heavy quarkonia due to the effect of two-gluon annihilation. The numerical estimation shows that the contributions to the mass shifts of $χ_{c0,c1,c2}$ are about $1.23\sim1.58$ MeV, $1.57\sim1.86$ MeV and $5.92\sim5.45$ MeV when taking $α_s\approx 0.25\sim0.35$.

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arXiv2018

Correction to the energy spectrum of $^1S_0$ heavy quarkonia due to two-gluon annihilation effect

In this work, the non-relativistic asymptotic behavior of the transition $q\overline{q}\rightarrow2g\rightarrow q\overline{q}$ in the $^1S_0$ channel is discussed. Different with the usual calculation which expands the physical amplitude around the quark anti-quark threshold, we take the quark anti-quark pairs as off shell and only expand the expression on the three-dimensional momenta of the quarks and anti-quarks. We calculate the results to order 6. The imagine part of the results after applying the on shell conditions can reproduce the non-relativistic QCD (NRQCD) results in leading order of $α_s$. The real part of the results can be used to estimate the mass shift of the $^1S_0$ heavy quark anti-quark system due to the $2g$ annihilation effect. The results can also be used to estimate the energy shifts of the positronium system due to the two-photon annihilation.

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arXiv2018

Two-photon exchange effects in $e^+e^- \rightarrow π^+π^-$ and time-like pion electromagnetic form factor

The two-photon-exchange (TPE) effects in the process $e^+e^- \rightarrow π^+π^-$ at large momentum transfer are discussed within the perturbative QCD (pQCD). The contributions from the twist-2 and twist-3 distribution amplitudes (DAs) of pion are considered in the estimation. Different with the results under the one-photon-exchange (OPE) approximation, the TPE effects result in an asymmetry of the differential cross section on the scattering angle. The precise measurement of this asymmetry by the further experiment is an precise test of pQCD at large momentum transfer. The time-like electromagnetic form factor of pion at the leading order of pQCD is re-discussed and the comparison of our results with those in the references are presented.

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arXiv2017

Two-photon exchange corrections to $γ^*NΔ$ form factors for $Q^2\leq 4 $ (Gev/$c$)$^2$

We evaluate the corrections of the two-photon exchange (TPE) process on the $γ^* NΔ$ transition form factors. The contributions of the TPE process to the $eN\rightarrow eΔ(1232)\rightarrow eNπ$ are calculated in a hadronic model with the inclusion of only the elastic nucleon intermediate states, to estimate its effects on the multipoles $M^{(3/2)}_{1^+}, E^{(3/2)}_{1^+}, S^{(3/2)}_{1^+}$ at the $Δ$ peak. We find that TPE effects on $G^*_M$ is very small. $G^*_E,$ and $ G^*_C$ are also little affected at small $Q^2 $. For $G^*_E$, the TPE effects reach about $3 - 8\%$ near $Q^2\sim 4$ GeV$^2$, depending on the model, MAID or SAID, used to emulate the data. For $G^*_C$, the TPE effects decrease rapidly with increasing $ε$ while growing with increasing $Q^2$ to reach $\sim 6 - 15\%$ with $Q^2 \sim 4$ GeV$^2$ at $ε= 0.2$. Sizeable TPE corrections to $G^*_E$ and $G^*_C$ found here points to the need of including TPE effects in the multipole analysis in the region of high $Q^2$ and small $ε$. The TPE corrections to $R_{EM}$ and $R_{SM}$ obtained in our hadronic calculation are compared with those obtained in a partonic calculation for moderate momentum transfer of $2<Q^2<4$ GeV$^2$.

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arXiv2016

Two-Photon-Exchange Effects and $Δ(1232)$ Deformation

The two-photon-exchange (TPE) contribution in $ep\rightarrow epπ^0$ with $W=M_Δ$ and small $Q^2$ is calculated and its corrections to the ratios of electromagnetic transition form factors $R_{EM} = E_{1+}^{(3/2)}/M_{1+}^{(3/2)} $ and $R_{SM} = S_{1+}^{(3/2)}/M_{1+}^{(3/2)}$, are analysed. A simple hadronic model is used to estimate the TPE amplitude. Two phenomenological models, MAID2007 and SAID, are used to approximate the full $ep\rightarrow epπ^0$ cross sections which contain both the TPE and the one-photon-exchange (OPE) contributions. The genuine the OPE amplitude is then extracted from an integral equation by iteration. We find that the TPE contribution is not sensitive to whether MAID or SAID is used as input in the region with $Q^2<2$ GeV$^2$. It gives small correction to $R_{EM}$ while for $R_{SM}$, the correction is about -10\% at small $ε$ and about $1\%$ at large $ε$ for $Q^2\approx2.5$ GeV$^2$. The large correction from TPE at small $ε$ must be included in the analysis to get a reliable extraction of $R_{SM}$.

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arXiv2016

Two-photon-exchange effects in the unpolarized $μp$ scattering within the hadronic model

In this work, the two-photon-exchange (TPE) effects in the unpolarized $μp$ scattering are discussed within the hadronic model where the intermediate states $N,Δ$ and $σ$ are considered. The contribution from the $N$ intermediate is close to the results given by Ref. \cite{Tomalak2014} at the small $Q$ and there is a sizeable difference when $Q>0.25$GeV (where $Q^2$ is the four momentum transfer). The contributions from the $Δ$ and the $σ$ intermediate states are much smaller than that from the $N$ intermediate at the small $Q$. In the kinematic region with $k_i\subseteq [0.01,0.3]$ GeV and $Q \leq0.4$GeV (where $k_i$ is the three momentum of initial muon at Lab frame), a naive expression for the TPE contributions is given, which can be used directly for other analysis.

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arXiv2016

The $σ$ exchange effect in the Lamb shift of muonic hydrogen by two photons and two pions exchange

Based on the simple phenomenological $σππ$, $σN N$ and $ππγ$ interactions, we estimate the $σ$ exchange effect in the Lamb shift of muonic hydrogen. We at first calculate the effective couplings of $σμμ$ by two photons and two pions exchange, then calculate the corresponding corrections to the energy shift of the 2S/2P states of muonic hydrogen. We find the correction to the energy shift of 2S state is about -14$μ$eV by the current used parameters, which is about $44\%$ of the usual two photons exchange contribution, and is larger than the current experimental precision, and should be considered in the experimental analysis.

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arXiv2015

$Δ(1232)$ Resonance Contribution to Two-Photon Exchange in Electron-Proton Scattering Revisited

We revisit the question of the contributions of two-photon exchange with $Δ(1232)$ excitation to the electron-proton scattering in a hadronic model. Three improvements over the previous calculations are made, namely, correct vertex function for $γN\rightarrowΔ$, realistic $γNΔ$ form factors, and coupling constants. The discrepancy between the values of $R\equiv μ_p G_E/G_M$ extracted from Rosenbluth technique and polarization transfer method can be reasonably accounted for if the data of Andivahis {\it et al.} \cite{Andivahis94} are analyzed. However, substantial discrepancy remains if the data of Qattan {\it et al.} \cite{Qattan05} are used. For the ratio $R^\pm$ between $e^\pm p$ scatterings, our predictions appear to be in satisfactory agreement with the preliminary data from VEPP-3. The agreement between our model predictions and the recent measurements on single spin asymmetry, transverse and longitudinal recoil proton polarizations ranges from good to poor.

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arXiv2015

Could the $X(3915)$ and the $X(3930)$ Be the Same Tensor State?

By using a combined amplitude analysis of the $γγ\rightarrow D\bar{D}$ and $γγ\rightarrow J/ψω$ data, we demonstrate that the $X(3915)$, which is quoted as a $J^{PC}=0^{++}$ state in the Particle Data Group table, is favored by the data to be a $J^{PC}=2^{++}$ state appearing in both channels, which means that the $X(3915)$ and the $X(3930)$ can be regarded as the same $J^{PC}=2^{++}$ state. Meanwhile, the data also prefer a large helicity-0 contribution of this tensor resonance to the amplitudes instead of the helicity-2 dominance assumed by {\it BABAR}, which may indicate a sizable portion of non-$q\bar q$ components in this state. Identifying the $X(3915)$ with the $X(3930)$ and abandoning the helicity-2 dominance for this tensor state are helpful for the further understandings of the properties of this state and also of the mysterious "$XYZ$" charmoniumlike resonances.

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arXiv2015

Nonperturbative numerical calculation of the fine and hyperfine structure of muonic hydrogen by Breit potential including the effects from the proton size

By solving the two-body Schordinger equation in a very high precise nonperturbative numerical (NPnum) way, we reexamine the contributions of fine, hyperfine structure splittings of muonic hydrogen based on the Breit potential. The comparison of our results with those by the first order perturbative theory ($^{1st}$PT) in the literature shows, when the structure of proton is considered, the differences between the results by the $^{1st}$PT and NPnum methods are small for the fine and hyperfine splitting of $2P$ state, while are about $-0.009$ meV and $0.08$ meV for the $F=1$ and total hyperfine splitting of $2S$ state of muonic hydrogen, respectively. These differences are larger than the current experimental precision and would be significant to be considered in the theoretical calculation.

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arXiv2014

Meson exchange effects in elastic $ep$ scattering at loop level and the electromagnetic form factors of the proton

A new form of two-photon exchange(TPE) effect is studied to explain the discrepancy between unpolarized and polarized experimental data in elastic $ep$ scattering. The mechanism is based on a simple idea that apart from the usual TPE effects from box and crossed-box diagrams, the mesons may also be exchanged in elastic $ep$ scattering by two-photon coupling at loop level. The detailed study shows such contributions to reduced unpolarized cross section ($σ_{un}$) and polarized observables ($P_t,P_l$) at fixed $Q^2$ are only dependent on proton's electromagnetic form factors $G_{E,M}$ and a new unknown universal parameter $g$. After combining this contribution with the usual TPE contributions from box and crossed-box diagrams, the ratio $μ_pG_E/G_M$ extracted from the recent precise unpolarized and polarized experimental data can be described consistently.

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arXiv2012

Resonances contribution to two-photon exchange effects and possible large forward-backward asymmetry in $e^+ e^- \rightarrow p \bar{p}$

The resonances ($η_c,χ_{c0,c2}$) contribution to two-photon exchange (TPE) effects in $e^+ e^- \leftrightarrow p \bar{p}$ is calculated in a simple hadronic model. The calculation shows the TPE contributions by resonance $χ_{c2}$, which are dependent on the unknown phases $ϕ_{E,M}$ of proton's time-like form factors $G_{E,M}$, are much larger than the TPE contributions by non-resonance and are comparable with measurement precision of coming PANDA detector at $\sqrt{s} \sim M_{χ_{c2}}$ for most $ϕ_{E,M}$.

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