arXiv subjects

Xin-Yi Zhang

Publications and source records attributed to Xin-Yi Zhang.

6 recordsLinked to original sources

arXiv2026

Polarization and correlation effects in $γγ\to W^-W^+$ at Next-to-Leading-Order Electroweak Accuracy

We study the next-to-leading order (NLO) electroweak (EW) corrections to the polarization and correlation of $W$ boson pairs produced through photon-photon fusion in proton-proton ultra-peripheral collisions at the LHC, with both $W$ bosons decaying leptonically. The azimuthal correlation distributions of the charged leptons, which receive no contribution from anomalous quartic gauge couplings (AQGCs) at linear order, are perturbatively stable at the 0.40\% level, whereas individual correlation coefficient $C_{2,2}$ receives relative corrections of up to $-33.84\%$. Some of correlation coefficients that vanish at leading order (LO) in the Standard Model but are sensitive to AQGCs acquire non-zero one-loop values of order $10^{-4}-10^{-3}$. We quantify the region of the ($a_0/Λ^2,a_c/Λ^2$) plane in which these loop-induced baselines compete with the AQGC contributions and find that, while irrelevant at the current experimental sensitivity, they must be included once the correlation coefficients are measured at the per-mille level.

hep-ph↗

arXiv2026

Spin correlations and quantum entanglement in $γγ\to t\bar t$ at polarized photon colliders with NLO QCD corrections

We study spin correlations and quantum entanglement in the process $γγ\to t\bar t$ with the photons coming from Compton backscattered laser beam. We present predictions for the cross sections and spin observables including next-to-leading order (NLO) QCD corrections under various beam-polarization configurations. The NLO QCD corrections significantly enhance the total cross section while having only a minor impact on spin observables. Using the spin density matrix of the $t\bar t$ system, we further investigate quantum entanglement and Bell nonlocality. We find that the entanglement is the strongest near the $t\bar t$ invariant-mass threshold, while both entanglement and Bell nonlocality are highly sensitive to the initial beam polarization. Our results provide a theoretical basis for future studies of quantum correlations in top-quark pair production at photon colliders.

hep-ph↗

arXiv2026

Study $γγ\to τ^+τ^-$ process including $τ^+ τ^-$ spin information in Pb-Pb ultraperipheral collision and at Lepton collider

We study the $γγ\to τ^+τ^-$ process including full $τ^+ τ^-$ spin information in Pb--Pb ultraperipheral collision and at lepton colliders. We present the predictions for the corresponding cross sections and spin correlations at NLO electroweak precision, and find that the NLO electroweak contributions are numerically small for the observables considered. Additionally, we use the spin correlations obtained in this paper to analyze the quantum entanglement in the $τ^+τ^-$ system of the $γγ\to τ^+τ^-$ process. Our results show that there is a genuine entangled configuration near the $τ^+τ^-$ invariant mass threshold. This work is helpful for studying the $τ$-pair production induced by photon-photon collision at high energy colliders.

hep-ph↗

arXiv2025

NLO EW corrections to tau pair production via photon fusion in Pb-Pb ultraperipheral collision

We study the next-to-leading order (NLO) electroweak (EW) corrections to the $γγ\to τ^+ τ^-$ process in Pb-Pb ultraperipheral collision (UPC). We find that the EW correction $δσ_{\mathrm{EW}}$ decreases the total cross section $σ_{\mathrm{NLO}} = σ_{\mathrm{LO}} + δσ_{\mathrm{EW}}$ by -3\% at Pb-Pb center-of-mass energy $\sqrt{s_{NN}}=5.02$ TeV. The weak correction plays significant role whose contribution is about -4 times of that of QED. The CMS and ATLAS collaborations use the reaction $γγ\to τ^+ τ^-$ in Pb-Pb and proton-proton UPC to constrain tau's anomalous magnetic moment $a_τ$. By parameterizing the $γττ$ vertex with two form factors $F_{1,2}$, the cross section can be written as $σ_{a_τ} = σ_{\mathrm{LO}} + δσ_{a_τ}$, where $δσ_{a_τ}$ is proportional to $a_τ$. The impact of NLO EW corrections on $a_τ$ bounds in Pb-Pb UPC is limited, as the current experimental bounds are loose. We also find that various differential distributions of the two ratios $\mathrm{d} σ_{\mathrm{NLO}}/ \mathrm{d} σ_{\mathrm{LO}}$ and $\mathrm{d} σ_{a_τ}/ \mathrm{d} σ_{\mathrm{LO}}$ have different lineshapes. This work is significant to precisely study the interaction of $γττ$ via $γγ\to τ^+ τ^-$ process.

hep-ph↗

arXiv2023

CP violation in lepton-number-conserving processes through heavy Majorana neutrinos at future lepton colliders

Small neutrino masses confirmed in the neutrino oscillation experiments indicate the need for new physics beyond the standard model. Seesaw mechanism is an interesting way to extend the standard model for explaining the neutrino masses. In a low-scale type-I seesaw mechanism, the tiny masses of neutrinos can be explained by heavy Majorana neutrino masses. Heavy Majorana neutrinos can lead to lepton-number-violating processes and the induced CP violation can contribute to the baryon asymmetry in the Universe. Heavy Majorana neutrinos can also lead to lepton-number-conserving processes and in this paper, we study the CP violation in lepton-number-conserving processes through heavy Majorana neutrinos at future lepton colliders. New possible observations of CP violation can also be connected to evidences of new physics beyond the standard model.

hep-ph↗

arXiv2022

Search for heavy Majorana neutrinos at future lepton colliders

The nonzero neutrino mass can be a signal for new physics beyond the standard model. To explain the tiny neutrino mass, we can extend the standard model with right-handed Majorana neutrinos in a low-scale seesaw mechanism, while the CP violation effect can be induced due to the CP phase in the interference of heavy Majorana neutrinos. The existence of heavy Majorana neutrinos may lead to lepton number violation processes, which can be used as a probe to search for the signal of heavy Majorana neutrinos. In this paper, we focus on the CP violation effect related to two generations of heavy Majorana neutrinos for $15$ GeV $<m_N<$ $70$ GeV in the pair production of W bosons and rare decays. It is valuable to investigate the Majorana neutrino production signals and the related CP violation effects in the W boson rare decays at future lepton colliders.

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