We develop a quantum-tomographic framework for determining whether possible CP-odd effects in $t\bar t$ events originate in production, in decay, or in both. In the narrow-width approximation, the process $I\to t\bar t\to b\ell^+\nu\,\bar b\ell^-\bar\nu$ factorises into a production density matrix and top and antitop decay density matrices. We extend the standard tomography procedure to a general anomalous $Wtb$ vertex and derive the corresponding angular distributions. Polar-angle distributions retain their usual tomographic form, up to modifications of the spin-analysing powers, and can therefore be used to reconstruct the production density matrix and test its CP properties. By contrast, dedicated azimuthal observables involving the $b$--lepton decay planes contain characteristic sine modulations that provide linear probes of possible new CP-violating interactions in the decay vertex. Combining the two classes of observables gives a systematic strategy for separating sources of CP violation in production and in decay. We illustrate the resulting angular signatures for representative $t\bar t$ production scenarios at hadron and lepton colliders.
We investigate how possible new CP-violating top-quark interactions are encoded in the quantum state of a produced $t\bar t$ pair. We derive analytic expressions for the production density matrix in several benchmark channels relevant to hadron, lepton and photon colliders. In a common spin basis, we identify two characteristic CP-odd structures in the Fano--Bloch decomposition: a difference between the top and antitop polarisation vectors and an antisymmetric component of the spin-correlation matrix. We construct observables that directly probe these structures and study how quantum information measures, including discord, concurrence, magic and trace distance, respond to CP-even and CP-odd SMEFT contributions. Finally, using current measurements and future collider projections, we assess the sensitivity of these observables to possible new sources of CP violation in top-quark production. This establishes the production-level framework whose experimental reconstruction is developed in a companion paper.
P. Lamba, F. Maltoni, Olimpia Miniati et al.· 1 citation
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
Tests of fundamental symmetries, such as $C\!PT$ and Lorentz invariance, provide sensitive probes of physics beyond the standard quantum-field-theory framework. Possible violations of these symmetries are investigated through interference effects in decays of $B_s^0$ mesons to $D_s^-\pi^{+}$ states. The analysis uses proton-proton collision data collected with the LHCb detector in 2015-2018 at a centre-of-mass energy of $13~\mathrm{TeV}$, corresponding to an integrated luminosity of $6~\mathrm{fb}^{-1}$. The results are interpreted within the Standard Model Extension framework, yielding sensitivities to the Lorentz-violating parameter $\Delta a_{\mu}$ at the ${\cal O}(10^{-14})\,\mathrm{GeV}$ level. Without assuming Lorentz-invariance violation, the $C\!PT$-violating parameter $z$ in the $B_s^0$ system is measured to be $\mathcal{R}e(z) = 0.018 \pm 0.016 \pm 0.003$ and $\mathcal{I}m(z) = 0.003 \pm 0.004 \pm 0.002$, where the first uncertainties are statistical and the second systematic. These results represent the most precise constraints on $C\!PT$ violation in the $B_s^0$ system.
L. C. R. Aaij, M. Abdelfatah, A. Abdelmotteleb et al.· 0 citations
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.
Wenyu Zhang, Yang Li, Xiao-Rong Zhou et al.· 0 citations
To circumvent the severe numerical cancellations in the standard integrated CP asymmetry ($A_{CP}$) near the $\omega$ mass $m_\omega$, we propose a modified CP-violating observable, $A_{CP}^{\Re}$, which explicitly highlights the contribution of the real part of the interference term. Subsequently, we employ the three-body hadronic decay $B^{-} \rightarrow \pi^{+} \pi^{-} \pi^{-}$ within the Perturbative QCD (PQCD) approach as a primary case study to validate this theoretical framework. Furthermore, this method naturally eliminates the smooth, sign-preserving continuum background originating from broad scalar resonances like the $f_0(500)$. This generalized framework provides clean and robust theoretical guidance for recovering localized CP-violation signals that might otherwise be masked by coarse experimental binning at future high-luminosity colliders.
Jin-Zhao Guo, Gang Lu, Zhen-Hua Zhang· 0 citations
The rare decays $K^+\to\pi^+\nu\bar\nu$ and $K_L\to\pi^0\nu\bar\nu$ are among the most precisely predicted flavor observables, enabling determinations of the CKM matrix and its CP-violating phase, as well as providing sensitivity to new physics at scales far beyond the reach of colliders. We propose a dedicated rare-kaon program at Fermilab, exploiting the high-intensity proton complex currently under construction for its neutrino programs and potential collider R&D. In this letter, we estimate the achievable kaon flux and project the sensitivity to the aforementioned kaon golden modes, as well as the reach on new dynamics in the UV with an EFT framework. Such a program could measure both modes with unprecedented precision, probe new physics up to $\mathcal{O}(100)$ TeV, and determine the unitarity triangle from kaon processes alone. All this can be achieved while sharing infrastructure with other frontier programs.
C. Cesarotti, S. Homiller· 0 citations
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