Plans for the Study of the Spin Properties of the $\Lambda_b$ Baryon Using the Decay Channel $\Lambda_b \to J\psi(\mu^+ \mu^-) \Lambda(p\pi^{-})$

This note summarizes the results of a study of the feasibility of measuring certain spin properties of $\Lambda_b$ baryon in the ATLAS experiment. We present an assessment of approaches for extracting the inclusive $\Lambda_b$ polarization and the parity violating $\alpha_{\Lambda_b}$ parameter for the decay $\Lambda_b \to J\psi(\mu^+ \mu^-) \Lambda(p\pi^{-})$ from the reconstructed four final state charged particles. As a key test, we generated Monte Carlo samples of $\Lambda_b$ events of fixed polarization in the ATLAS detector and evaluated our ability to precisely extract the input polarization from the reconstructed events. The physics motivation for the planned measurements in ATLAS include the search for an explanation of the anomalous spin effects in hyperon inclusive production observed at lower energies, tests of various decay models based on HQET, tests of CP in an area not yet directly explored, and the development of $\Lambda_b$ polarimetry as a possible tool for spin analysis in future SUSY and other studies.