Polarized tau decay and CP violation in ultraperipheral heavy-ion collisions
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arXiv
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| Format: | Preprint |
| Veröffentlicht: |
2025
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| _version_ | 1866915914285318144 |
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| author | Jaiswal, Amaresh |
| author_facet | Jaiswal, Amaresh |
| contents | We investigate the role of $τ$-lepton polarization in ultraperipheral heavy-ion collisions (UPCs) as a novel application of the intense electromagnetic fields generated in such processes. In particular, we analyze the decay distributions of polarized $τ$-leptons produced via photon-photon fusion, focusing on both leptonic and semi-leptonic channels. We show that the external magnetic field present in UPCs induces a preferred spin quantization axis, which modifies the angular and energy distributions of $τ$ decay products relative to the standard helicity frame. By formulating the spin polarization along the magnetic field direction, we derive modified polarization-sensitive observables and demonstrate how kinematic selections can retain nonvanishing polarization signals even after ensemble averaging. Furthermore, we propose that the relative polarization of $τ^-$ and $τ^+$, accessible through complementary angular ranges of their decay products, serves as a sensitive observable for potential CP-violating effects. This framework provides a pathway for future experimental studies at the LHC and future colliders to exploit polarized $τ$ decays in UPCs as an application of the strong electromagnetic fields to probe new sources of CP violation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_02228 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Polarized tau decay and CP violation in ultraperipheral heavy-ion collisions Jaiswal, Amaresh High Energy Physics - Phenomenology High Energy Physics - Theory Nuclear Theory We investigate the role of $τ$-lepton polarization in ultraperipheral heavy-ion collisions (UPCs) as a novel application of the intense electromagnetic fields generated in such processes. In particular, we analyze the decay distributions of polarized $τ$-leptons produced via photon-photon fusion, focusing on both leptonic and semi-leptonic channels. We show that the external magnetic field present in UPCs induces a preferred spin quantization axis, which modifies the angular and energy distributions of $τ$ decay products relative to the standard helicity frame. By formulating the spin polarization along the magnetic field direction, we derive modified polarization-sensitive observables and demonstrate how kinematic selections can retain nonvanishing polarization signals even after ensemble averaging. Furthermore, we propose that the relative polarization of $τ^-$ and $τ^+$, accessible through complementary angular ranges of their decay products, serves as a sensitive observable for potential CP-violating effects. This framework provides a pathway for future experimental studies at the LHC and future colliders to exploit polarized $τ$ decays in UPCs as an application of the strong electromagnetic fields to probe new sources of CP violation. |
| title | Polarized tau decay and CP violation in ultraperipheral heavy-ion collisions |
| topic | High Energy Physics - Phenomenology High Energy Physics - Theory Nuclear Theory |
| url | https://arxiv.org/abs/2509.02228 |