New strategies for new physics search with ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\nu \overline{\nu }$ decays

Journal Article · Tue Apr 08 00:00:00 EDT 2025 · Physical Review. D.

DOI:https://doi.org/10.1103/PhysRevD.111.075005· OSTI ID:2550699

Altmannshofer, Wolfgang; Gadam, Sri Aditya; Toner, Kevin

We examine the new physics sensitivity of the rare decay ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\nu \overline{\nu }$ , which can be accessible at future $Z$ -pole machines like Future Circular Collider and Circular Electron Positron Collider. We find that the longitudinal polarization of ${\mathrm{\Lambda }}_b$ baryons produced in $Z$ decays introduces a novel observable, the forward-backward asymmetry $A_{\mathrm{FB}}^{\uparrow }$ in the angle between the outgoing $\mathrm{\Lambda }$ momentum and the ${\mathrm{\Lambda }}_b$ spin. We provide Standard Model predictions for the ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\nu \overline{\nu }$ branching ratio and $A_{\mathrm{FB}}^{\uparrow }$ , and show that future precision measurements of these observables are complementary and probe new physics scales comparable to other $b\to s\nu \overline{\nu }$ and $b\to s{\ell }^{+}{\ell }^{-}$ processes. We also show that the zero crossing of the forward-backward asymmetry offers a robust test of form factor calculations independent of new physics.

Published by the American Physical Society 2025

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0010107
• OSTI ID: 2550699
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 7 Vol. 111; ISSN PRVDAQ; ISSN 2470-0010
• Publisher: American Physical Society
• Country of Publication: United States
• Language: English