Analysis of the Nab Commissioning Data

From the beta decay of free neutrons, the Nab experiment aims to test the Standard Model with a high precision measurement of the beta-antineutrino angular correlation coefficient, a, and the Fierz Interference term, b, respectively probing the unitarity of Cabbibo-Kobayashi-Maskawa (CKM) matrix and search for exotic Scalar and Tensor couplings. The angular correlation coefficient is extracted from the differential decay rate as a function of proton momentum and beta energy, and to detect the beta and the proton in coincidence, the Nab experiment utilizes a pair of highly segmented silicon detectors installed at opposite ends of a 7 m long superconducting magnet, which provides the guiding field for the charged decay products.

With the goal of measuring a to a relative precision of 0.1% and b to a absolute precision of 0.003, Nab commissioning began at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory (ORNL) during the 2023 Summer beam cycle. I will present an analysis of the commissioning data, exploring systematics of key experimental components.