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Zhen-Hua Zhang

Publications and source records attributed to Zhen-Hua Zhang.

At least 37 records · Page 2Linked to original sources
arXiv2024

Possible bound states of Heavy Baryonium and Heavy Dibaryon systems

In this work, we systematically study the heavy baryonium and heavy dibaryon systems using the Bethe-Salpeter equation in the ladder and instantaneous approximations for the kernel. Our results indicate that all the heavy baryonium systems, specifically $Λ_Q\barΛ_Q$, $Ξ_Q\barΞ_Q$, $Σ_Q\barΣ_Q$, $Ξ'_Q\barΞ'_Q$, and $Ω_Q\barΩ_Q$ ($Q=c, b$), can form bound states. Among the heavy dibaryon systems, only the $Ξ_QΞ_Q$ system with $I=0$ and the $Σ_QΣ_Q$ systems with $I=0$ and $I=1$ can exist as bound states. Additionally, the $Σ_Q\barΣ_Q$ system with $I=2$ and the $Σ_QΣ_Q$ system with $I=1$ are not deeply bound.

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arXiv2024

Predicting isovector charmonium-like states from X(3872) properties

Using chiral effective field theory, we predict that there must be isovector charmonium-like $D\bar D^*$ hadronic molecules with $J^{PC}=1^{++}$ denoted as $W_{c1}$. The inputs are the properties of the $X(3872)$, including its mass and the ratio of its branching fractions of decays into $J/ψρ^0$ and $J/ψω$. The predicted states are virtual state poles of the scattering matrix, pointing at a molecular nature of the $X(3872)$ as well as its spin partners. They should show up as either a mild cusp or dip at the $D\bar D^*$ thresholds, explaining why they are elusive in experiments. The so far negative observation also indicates that the $X(3872)$ is either a bound state with non-vanishing binding energy or a virtual state, only in these cases the $X(3872)$ signal dominates over that from the $W_{c1}^0$. The pole positions are $3881.2^{+0.8}_{-0.0}- i 1.6^{+0.7}_{-0.9}$ MeV for $W_{c1}^0$ on the fourth Riemann sheet of the $D^0\bar D^{*0}$-$D^+D^{*-}$ coupled-channel system, and $3866.9^{+4.6}_{-7.7}- i (0.07\pm0.01)$ MeV for $W_{c1}^\pm$ on the second Riemann sheet of the $(D\bar D^*)^\pm$ single-channel system. The findings imply that the peak in the $J/ψπ^+π^-$ invariant mass distribution is not purely from the $X(3872)$ but contains contributions from $W_{c1}^0$ predicted here. The states should have isovector heavy quark spin partners with $J^{PC}=0^{++}$, $2^{++}$ and $1^{+-}$, with the last one corresponding to $Z_c$. We suggest to search for the charged $0^{++}$, $1^{++}$ and $2^{++}$ states in $J/ψπ^\pm π^0$.

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arXiv2024

Production of hidden-heavy and double-heavy hadronic molecules at the $Z$ factory of CEPC

With a clean environment and high collision energy, the Circular Electron Positron Collider (CEPC) would be an excellent facility for heavy flavor physics. Using the Monte Carlo event generator Pythia, we simulate the production of the charmed (bottom) hadron pairs in the electron-positron collisions at the $Z$ factory of CEPC, and the inclusive production rates for typical candidates of the hidden/double-charm and hidden/double-bottom $S$-wave hadronic molecules are estimated at an order-of-magnitude level with the final state interactions after the hadron pair production. The predicted cross sections for the hidden-charm meson-meson molecules $X(3872)$ and $Z_c(3900)$ are at $\rm{pb}$ level, which are about two to three orders of magnitude larger than the production cross sections for the double-charm meson-meson molecules $T_{cc}$ and $T_{cc}^{*}$, as the double-charmed ones require the production of two pairs of $c\bar{c}$ from the $Z$ boson decay. The production cross sections for the hidden-charm pentaquark states $P_{c}$ and $P_{cs}$ as meson-baryon molecules are a few to tens of fb, which are about one magnitude larger than those of the possible hidden-charm baryon-antibaryon and double-charm meson-baryon molecules. In the bottom sector, the production cross sections for the $Z_b$ states as $B^{(*)}\bar{B}^{*}$ molecules are about tens to hundreds of fb, indicating $10^6$ - $10^7$ events from a two-year operation of CEPC, and the expected events from the double-bottom molecules are about 2 - 5 orders of magnitude smaller than the $Z_b$ states. Our results shows great prospects of probing heavy exotic hadrons at CEPC.

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arXiv2024

Nuclear charge radius predictions by kernel ridge regression with odd-even effects

The extended kernel ridge regression (EKRR) method with odd-even effects was adopted to improve the description of the nuclear charge radius using five commonly used nuclear models. These are: (i) the isospin dependent $A^{1/3}$ formula, (ii) relativistic continuum Hartree-Bogoliubov (RCHB) theory, (iii) Hartree-Fock-Bogoliubov (HFB) model HFB25, (iv) the Weizsäcker-Skyrme (WS) model WS$^\ast$, and (v) HFB25$^\ast$ model. In the last two models, the charge radii were calculated using a five-parameter formula with the nuclear shell corrections and deformations obtained from the WS and HFB25 models, respectively. For each model, the resultant root-mean-square deviation for the 1014 nuclei with proton number $Z \geq 8$ can be significantly reduced to 0.009-0.013~fm after considering the modification with the EKRR method. The best among them was the RCHB model, with a root-mean-square deviation of 0.0092~fm. The extrapolation abilities of the KRR and EKRR methods for the neutron-rich region were examined and it was found that after considering the odd-even effects, the extrapolation power was improved compared with that of the original KRR method. The strong odd-even staggering of nuclear charge radii of Ca and Cu isotopes and the abrupt kinks across the neutron $N=126$ and 82 shell closures were also calculated and could be reproduced quite well by calculations using the EKRR method.

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arXiv2024

Decay-angular-distribution correlated $CP$ violation in heavy hadron cascade decays

$C\!P$ violation in baryon decay processes is still undiscovered to date. We present a general analysis of the decay-angular-distributions and the corresponding $C\!P$ asymmetries in cascade decays of the type $\mathbb{H}\to R(\to ab) c$, where $\mathbb{H}$ is a heavy hadron that decays through weak interactions $\mathbb{H}\to R c$, and the resonance $R$ decays strongly via $R\to ab$. Based on the analysis, we propose to search for $C\!P$ violation in the decay-angular-distributions in the cascade decay processes ${\mathbb{B}}\to \mathcal{B} M$, with $\mathcal{B}$ or $M$ subsequently decaying through strong interactions, where ${\mathbb{B}}$ is the mother baryon, $\mathcal{B}$ or $M$ are the daughter baryon and meson, respectively, and $M$ has to be spin-nonzero. We also present some typical decay channels in which the search for such kinds of $C\!P$ asymmetries can be performed.

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arXiv2024

Hunting for $X_b$ via hidden bottomonium decays $X_b\to ππχ_{bJ}$

In this work, we investigate the isospin breaking decay $X_b \to π^0χ_{bJ}$ and the isospin conserved decay $X_b \to ππχ_{bJ}$, where $X_b$ is taken to be the heavy quark flavor symmetry counterpart of $X(3872)$ in the bottomonium sector as a $B^*\bar B$ molecule candidate. Since the mass of this state may be far below the $B {\bar B}^*$ threshold and the mass difference between the neutral and charged bottom meson is small compared to the binding energy of the $X_b$, the isospin-violating decay channel $X_b \to π^0 χ_{bJ}$ would be highly suppressed. The calculated partial width of $X_b \to ππχ_{b1}$ is found to be about tens of $\rm{keVs}$, $1\sim 2$ order(s) of magnitude larger than those of $X_b \to ππχ_{b2}$ and $X_b \to ππχ_{b0}$. Taking into account the fact that the total width of $X_b$ may be smaller than a few MeV like $X(3872)$, the calculated branching ratios $X_b\to ππχ_{b1}$ may reach to orders of $10^{-2}$, which makes it a possible channel for the experimental searching of the $X_b$.

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arXiv2023

How to measure the transverse polarization of the produced hadrons in a symmetric collider?

In this paper, some subtleties in the measurement of the transverse polarization of the produced hadrons on symmetric colliders -- such as the Large Hadron Collider when conducting the $pp$ collisions -- are revealed. It can be proved that the transverse polarization of the produced particles with opposite pseudorapidity takes exactly opposite values if the normal vector of the production plane is defined in a convention-dependent way, regardless of whether parity is conserved or not in the production process. The analysis shows that, due to the symmetry of the initial state, the $Λ_b$ transverse polarization measured by the CMS collaboration in Phys. Rev. D 97, 072010 (2018) should be exactly equal to zero. A modified measurement of the $Λ_b$ polarization for CMS and ATLAS is proposed, the result of which can be compared to the LHCb measurement.

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arXiv2023

Radiative decays of the heavy-quark-spin molecular partner of $T_{cc}^+$

With the assumptions that the $T_{cc}^+$ discovered at LHCb is a $D^{*}D$ hadronic molecule, using a nonrelativistic effective field theory we calculate the radiative partial widths of $T_{cc}^* \to D^*Dγ$ with $T_{cc}^*$ being a $D^{*}D^{*}$ shallow bound state and the heavy-quark-spin partner of $T_{cc}^+$. The $I=0$ $D^*D$ rescattering effect with the $T_{cc}$ pole is taken into account. The results show that the isoscalar $D^{\ast} D$ rescattering can increase the tree-level decay width of $T_{cc}^{\ast +}\rightarrow D^{*+}D^0γ$ by about $50\%$, while decrease that of $T_{cc}^{\ast +}\rightarrow D^{*0}D^+γ$ by a similar amount. The two-body partial decay widths of the $T_{cc}^{*+}$ into $T_{cc}^+γ$ and $T_{cc}^+π^0$ are also calculated, and the results are about $6~\rm{keV}$ and $3~\rm{keV}$, respectively. Considering that the $D^*$ needs to be reconstructed from the $Dπ$ or $Dγ$ final state in an experimental measurement, the four-body partial widths of the $T_{cc}^{*+}$ into $DDγγ$ and $DDπγ$ are explicitly calculated, and we find that the interference effect between different intermediate $D^*Dγ$ states is small. The total radiative decay width of the $T_{cc}^*$ is predicted to be about $24~\rm{keV}$. Adding the hadronic decay widths of $T_{cc}^* \to D^*Dπ$, the total width of the $T_{cc}^*$ is finally predicted to be $(65\pm2)$ keV.

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arXiv2023

Hadronic decays of the heavy-quark-spin molecular partner of $T_{cc}^+$

Starting from the hypothesis that the $T_{cc}^+$ discovered at LHCb is a $D^{\ast+} D^0/D^{\ast 0}D^+$ hadronic molecule, we consider the partial width of its heavy quark spin partner, the $T_{cc}^{\ast +}$ as a $D^{\ast +} D^{\ast 0}$ shallow bound state, decaying into the $D^{\ast}Dπ$ final states including the contributions of the $D^{\ast} D$ and $D^{\ast} π$ final state interaction by using a nonrelativistic effective field theory. Because of the existence of the $T_{cc}^+$ pole, the $I=0$ $D^{\ast} D$ rescattering can give a sizeable correction up to about $40\%$ to the decay widths considering only the tree diagrams, and the $D^{\ast} π$ rescattering correction is about $10\%$. The four-body partial widths of the $T_{cc}^{*+}$ into $D Dππ$ are also explicitly calculated, and we find that the interference effect between different intermediate $D^*Dπ$ states is small. The total width of the $T_{cc}^{*+}$ is predicted to be about 41 keV.

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arXiv2023

Analysis of angular distribution asymmetries and the associated $C\!P$ asymmetries in three-body decays of bottom baryons

We introduce a set of observables representing angular distribution asymmetries, which can be viewed as a generalization of the forward-backward asymmetry of angular distributions, and can be used as an effective tool to search for $C\!P$ violation in three-body decays of bottom and charmed baryons. We propose to search for such $C\!P$ asymmetries (1) in decays with $Λ^0$, $Σ^\pm$, or $Λ_c^+$ involved, such as $Λ_b\to Λ^0 D$ and $Λ_b\toΛ^0ρ(770)^0$; and (2) in three-body decays of bottom baryons with opposite parity intermediate resonances involved. Typical examples include $Ξ_b^-\to p K^- K^-$, $Λ_b^0\to p K_Sπ^-$ and $Λ_b^0\to p π^0π^-$, in which the last decay channel is used as a toy model to illustrate of the basic idea.

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arXiv2022

Searching for $C\!P$ violation through two-dimensional angular distributions in four-body decays of bottom and charmed baryons

It is proposed to search for $C\!P$ violation through the two-fold angular distributions in the four-body decays of bottom and charmed hadrons. The two polar angles in the two-fold angular distributions are correlated, to which the interferences of intermediate resonances are one important origin. These interferences will leave tracks in the two-fold angular distributions, with which the $C\!P$ violation can be studied. Special attention is paid to the case when all the intermediate resonances are different, which is unique to four-body decays. It is suggested to look for $C\!P$ violation in four-body decays such as $Λ_b^0\to p π^-π^+π^-$ through the analysis of the two-fold angular distributions. The method proposed in this paper is also widely applicable to other four-body decays processes.

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arXiv2022

Forward-backward asymmetry induced $CP$ asymmetry of $B^{\pm}\rightarrow π^{\pm}π^{+}π^{-}$

$CP$ violation of the decay $B^{\pm}\rightarrow π^{\pm}π^{+}π^{-}$ in the $f_{0}(500)-ρ(770)^{0}$ interfering region is analyzed. The forward-backward asymmetries (FBAs) and the corresponding $CP$ asymmetries FB-$CP$As are particularly investigated. To isolate the $CP$V caused by the interference of different partial wave more cleanly, we also introduce the direct-$CP$V-subtracted FB-$CP$A. Based on the LHCb data, we extract the FBAs, FB-$CP$As, direct-$CP$V-subtracted FB-$CP$A, as well as the regional $CP$As with invariant mass of the $π^{+}π^{-}$ pair in the range 0.2 GeV/$c^{2}<\sqrt{s_{\text{low}}}<1.8$ GeV/$c^{2}$. It is found that the (direct-$CP$V-subtracted) FB-$CP$As are quite large in the $f_{0}(500)-ρ(770)^{0}$ interfering region, which confirms that the interference of the intermediate resonances $f_{0}(500)$ and $ρ(770)^{0}$ plays an important role for the $CP$ violation of the three-body decay channel $B^{\pm}\rightarrow π^{\pm}π^{+}π^{-}$.

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arXiv2022

Data-based analysis of Forward-Backward Asymmetry in $B^\pm \to K^\pm K^\mp K^\pm$

An analysis of the Forward-Backward Asymmetry (FBA) in the decay $B^\pm \to K^\pm K^\mp K^\pm$ is carried out based on the LHCb data. It is found that the large FBA observed for the invariant mass of the $K^+ K^-$ pair around 1.5 GeV can be explained by the interference of the amplitudes between the resonances with even and odd spins, where the former can be the spin-0 $f_0(1500)$ resonance plus a non-resonance $s$-wave, while the latter is a spin-1 resonance which is probably $ρ^0 (1450)$. The analysis shows the existence of the decay channel $B^\pm\to ρ^0(1450) K^\pm$, with $C\!P$ asymmetry of $A_{CP}(B^\pm\to ρ^0(1450) K^\pm)=(-3.4\pm3.0)\%$. This is in contradiction with the conclusion of BaBar in Phys. Rev. D 85, 112010, according to which the analysis showed no signal of the spin-1 resonance $ρ^0(1450)$. We suggest our experimental colleagues to perform a closer analysis to this channel. We also suggest to perform the measurements of the FBAs (as well as the FB-$C\!P$As) in other three-body decay channels of beauty and charmed mesons, as it is helpful for resonance analysis.

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arXiv2022

Improved phenomenological nuclear charge radius formulae with kernel ridge regression

The kernel ridge regression (KRR) method with Gaussian kernel is used to improve the description of the nuclear charge radius by several phenomenological formulae. The widely used $A^{1/3}$, $N^{1/3}$ and $Z^{1/3}$ formulae, and their improved versions by considering the isospin dependence are adopted as examples. The parameters in these six formulae are refitted using the Levenberg-Marquardt method, which give better results than the previous ones. The radius for each nucleus is predicted with the KRR network, which is trained with the deviations between experimental and calculated nuclear charge radii. For each formula, the resultant root-mean-square deviations of 884 nuclei with proton number $Z \geq 8$ and neutron number $N \geq 8$ can be reduced to about 0.017~fm after considering the modification of the KRR method. The extrapolation ability of the KRR method for the neutron-rich region is examined carefully and compared with the radial basis function method. It is found that the improved nuclear charge radius formulae by KRR method can avoid the risk of overfitting and have a good extrapolation ability. The influence of the ridge penalty term on the extrapolation ability of the KRR method is also discussed. At last, the nuclear charge radii of several recently observed K and Ca isotopes have been analyzed.

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arXiv2022

$D^+D^-$ hadronic atom and its production in $pp$ and $p\bar{p}$ collisions

There must be Coulomb bound states of a pair of hadrons, which are stable against the strong interaction, with opposite electric charges. Such bound states are hadronic atoms. We study the properties and the production of the ground-state $D^+D^-$ hadronic atom $A_{D^+D^-}$, called dionium, with quantum numbers $J^{PC}=0^{++}$. Using a nonrelativistic effective field theory for the $D^0\bar{D}^0$-$D^+D^-$ coupled-channel system, the mass of the ground-state dionium is predicted to be $(3739.3 \pm 0.1)~\text{MeV}$, with the binding energy reduced by about 10% compared to the Coulomb binding energy due to the strong interaction. Its width for the decay into the neutral $D^0\bar D^0$ channel is predicted to be $1.8^{+1.4}_{-0.6}$ keV using lattice inputs for the $D\bar D$ strong interaction. The cross section for the inclusive prompt production of the dionium at CMS and LHCb and that for the direct production $p\bar p\to A_{D^+D^-}$ at PANDA are estimated at an order-of-magnitude level. In particular, we expect that $\mathcal{O}(10^3\sim 10^5)$ events of the reaction chain $p\bar p\to A_{D^+D^-}\to D^0\bar D^0 \to K^-π^+K^+π^-$ can be collected at PANDA, and valuable information on the charmed meson interaction and on understanding charmoniumlike states will be obtained.

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arXiv2021

The pollution to the $Kπ$-puzzle from the isospin-breaking $π^0-η-η'$ mixing effect

The influence of the isospin-breaking $π^0\!\!-\!η\!-\!η'$ mixing effect on the $CP$-asymmetries of $B\to Kπ$ processes is examined for the first time. It is found that this mixing effect brings a large uncertainty both to the $CP$-asymmetry sum rule of $B\to Kπ$ processes and the $CP$-asymmetry difference of the $B^+\to K^+π^0$ and $B^0\to K^+π^-$, obscuring the significance of the $Kπ$-puzzle. This uncertainty can be so large that it is even possible to explain the $Kπ$-puzzle by the $π^0\!\!-\!η\!-\!η'$ mixing effect {\it alone}.

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arXiv2021

Possible antimagnetic rotation bands in $^{100}$Pd: a particle-number conserving investigation

The particle-number conserving method based on the cranked shell model is adopted to investigate the possible antimagnetic rotation bands in $^{100}$Pd. The experimental kinematic and dynamic moments of inertia, together with the $B(E2)$ values are reproduced quite well. The occupation probability of each neutron and proton orbital in the observed antimagnetic rotation band is analyzed and its configuration is confirmed. The contribution of each major shell to the total angular momentum alignment with rotational frequency in the lowest-lying positive and negative parity bands is analyzed. The level crossing mechanism of these bands is understood clearly. The possible antimagnetic rotation in the negative parity $α=0$ branch is predicted, which sensitively depends on the alignment of the neutron ($1g_{7/2}$, $2d_{5/2}$) pseudo-spin partners. The two-shears-like mechanism for this antimagnetic rotation is investigated by examining the closing of the proton hole angular momentum vector towards the neutron angular momentum vector.

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arXiv2021

Systematic investigation of the high-spin structures in the odd-odd nuclei $^{166, 168, 170, 172}$Re by a particle-number conserving method

The recently observed two and four-quasiparticle high-spin rotational bands in the odd-odd nuclei $^{166, 168, 170, 172}$Re are investigated using the cranked shell model with pairing correlations treated by a particle-number conserving method. The experimental moments of inertia and alignments can be reproduced well by the present calculation if appropriate bandhead spins and configurations are assigned for these bands, which in turn confirms their spin and configuration assignments. It is found that the bandhead spins of those two rotational bands observed in $^{166}$Re~[Li {\it et al.}, Phys. Rev. C 92 014310 (2015)] should be both increased by $2\hbar$ to get in consistent with the systematics of the experimental and calculated moments of inertia for the same configurations in $^{168, 170, 172}$Re. The variations of the backbendings/upbendings with increasing neutron number in these nuclei are investigated. The level crossing mechanism is well understood by analysing the variations of the occupation probabilities of the single-particle states close to the Fermi surface and their contributions to the angular momentum alignment with rotational frequency. In addition, the influence of the deformation driving effects of the proton $1/2^-[541]$ ($h_{9/2}$) orbtial on the level crossing in $^{172}$Re is also discussed.

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