Quantum correlations in high-energy collisions provide a novel perspective on both fundamental physics and hadron structure. We calculate the quantum information observable in spin-1/2 particle-antiparticle systems produced in $e^+e^-$ annihilation. Starting from the two-qubit density operator, we calculate the Bell variable, concurrence and negativity as functions of the scattering angle and collision energy for the $\Lambda\bar{\Lambda}$, $\Sigma^+\bar{\Sigma}^-$, and $\Lambda^+_c\bar{\Lambda}^-_c$ systems in the process $e^+e^-\rightarrow B\bar{B}$ at BESIII experiments. Unlike elementary particle-antiparticle systems, the hyperon-antihyperon system exhibits non-vanishing transverse polarization for $B$ and $\bar{B}$ with respect to the production plane, which significantly restrict the kinematic region where the CHSH inequality is violated while leaving the entanglement largely unaffected. We also extend our analysis to the general case of spin-1/2 particle-antiparticle production, and explore the potential of using quantum correlations as probes to hadron structure, particularly to the parton-level entanglement inside heavy-flavored mesons.
We study quantum spin correlations in top-quark pair production at future lepton colliders in the presence of a neutral gauge boson from anomaly-free general $U(1)$ extensions of the Standard Model. The process $\ell^+\ell^-\to t\bar t$, with $\ell=e,\mu$, is analyzed through the spin-density matrix including $\gamma$, $Z$ and $Z^\prime$ exchange and their interference. We focus on quantum-information observables such as the sufficient entanglement marker $\mathcal{D}_{\min}$, concurrence, purity and the maximal Clauser-Horne-Shimony-Holt (CHSH) parameter, and compare their behavior with conventional rate information. Within the $U(1)_X$ framework, we consider several representative charge assignments to investigate how different chiral structures influence these observables, with particular emphasis on the $Z^\prime$ resonance region and polarized $e^-e^+$ collisions, where the two allowed initial-state helicity configurations can be selectively enhanced. We show that electron-beam polarization provides a direct handle on the left- and right-handed lepton charges of various $U(1)_X$ scenarios. These results demonstrate that quantum spin observables provide information complementary to cross sections and angular distributions in searches for chiral neutral gauge interactions.
ShivaSankar K. A., Arindam Das, Sanjoy Mandal· 0 citations
We present a partial wave analysis of the process $e^+e^- \rightarrow D^0 D^- \pi^++c.c.$ using a data sample collected with the BESIII detector at a center-of-mass energy of 4682~MeV. A charged structure, referred to as the $X(3790)^-$ near the $D^0D^-$ mass threshold with a significance of $5.3\sigma$, which includes systematic uncertainties and the look-elsewhere effect. Assuming a Flatt\'e description of the structure, the quantum numbers of the $X(3790)^-$ are found to be $J^{P}=1^{-}$, and its mass and coupling strength to the $D^0D^-$ channel are determined to be $(3794.7 \pm 6.0 \pm 8.7)$~MeV/$c^2$ and $(1.6 \pm 0.2 \pm 0.2)$~GeV, respectively, where the first uncertainties are statistical and the second systematic. In addition, we also report measurements of the masses and widths of the $D_{2}^{*}(2460)$, $D_{1}^{*}(2600)$, and $D_{1}^{*}(2760)$ charmed mesons.
We study radiative double-charmonium production, $e^+e^-\to HH\gamma$ with $H=J/\psi$ and $\eta_c$, at $\sqrt{s}=10.58~{\rm GeV}$, including a possible tensor contribution from the fully charmed state $X(6900)$. The nonresonant amplitudes are calculated within the color-singlet non-relativistic QCD framework, while the $J^{PC}=2^{++}$ resonance is combined coherently with the continuum. We find that continuum--resonance interference significantly modifies the invariant-mass distributions near $M_{HH}\simeq M_X$. The $J/\psi J/\psi\gamma$ channel exhibits a pronounced phase-dependent resonant structure, with a near-resonance cross section of $0.038$--$0.111~{\rm fb}$. In contrast, the $\eta_c\eta_c\gamma$ channel is continuum dominated and shows only a localized interference effect with an extremely suppressed production rate, rendering its experimental observation extremely challenging. These channel-dependent features arise from the different effective decay structures and demonstrate the importance of an amplitude-level treatment of the $X(6900)$ contribution.
Meng Jia, Yi-Jie Li, Guanghua Xu et al.· 1 citation
We characterize several quantum resources carried by the spins of the $\tau^{+}\tau^{-}$ pair produced in $e^{+}e^{-}$ annihilation. At the Belle-II energy, $\sqrt{s}=10.579\,\mathrm{GeV}$, Bell nonlocality, steerability, entanglement of formation, and coherence are governed by the production angle and are largest for transverse emission, $\vartheta=\pi/2$. Their common kinematic origin is exposed by expressing the spin state as a velocity and angle-dependent mixture of a separable contribution and a maximally entangled component. Within the physical production domain, this representation connects the weakly correlated threshold state at $\sqrt{s}=2m_{\tau}$ to the Bell-state limit approached at ultrarelativistic energies. We then propagate the two-spin state through a phenomenological correlated-dephasing channel to determine how environmental memory and inter-channel classical correlations affect the available resources. Memory effects generate collapses and revivals that are absent from the monotonic Markovian evolution. The analysis therefore separates the kinematic mechanism that creates the spin correlations from the noise properties that control their subsequent survival.
Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector operating at the BEPCII collider, the Dalitz decay $\Sigma^0 \rightarrow \Lambda e^+e^-$ is studied experimentally for the first time. The $\Sigma^0$ hyperons are produced through the process $J/\psi \rightarrow \Sigma^0\bar{\Sigma}^0$ and analyzed using a double-tag method. The absolute branching fraction is measured to be $\mathcal{B}(\Sigma^0 \rightarrow \Lambda e^+e^-) = (6.34 \pm 0.25_{\rm stat.} \pm 0.23_{\rm syst.}) \times 10^{-3}$. This result shows a $2\sigma$ discrepancy from the theoretical calculation quoted in the PDG, where the uncertainties are statistical and systematic, respectively. In addition to the branching fraction, the transition magnetic moment $\mu$ is determined to be $(1.74 \pm 0.03_{\rm stat.} \pm 0.09_{\rm syst.})\,\mu_N$, where $\mu_N=e/(2m_p)$ represents the nucleon magnetic moment, providing valuable insight into the intrinsic structure of the $\Sigma^0$ hyperon.
B. C. M. Ablikim, M. N. Achasov, P. Adlarson et al.· 0 citations
In the hadronic molecular picture, an isoscalar $S$-wave $D\bar{D}$ molecule is naturally expected as the spin-0 partner of $X(3872)$. Assuming this state, denoted by $X_0$, to be a pure $D\bar D$ molecule with quantum numbers $J^{PC}=0^{++}$, we investigate its radiative decays $X_0\to\gamma V (V=\rho^0,\omega)$ within an effective Lagrangian framework. The decay amplitudes are generated by intermediate charmed-meson loops, with electromagnetic gauge invariance consistently maintained throughout the calculation. We evaluate the partial decay widths and examine their dependence on the $X_0$ mass and the cutoff. Although the individual decay widths exhibit a sizable dependence on the cutoff, their ratio is remarkably stable. In particular, we obtain that the ratio for the decays $X_0\to\gamma\rho^0$ and $X_0\to\gamma\omega$ is approximately 2.26, which is insensitive to the variation of the cutoff. This robust ratio provides a useful model-insensitive signature of the molecular structure of $X_0$.
Yuan Gao, Gang Li, Shidong Liu et al.· 0 citations
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