First results from the NPDGamma experiment at the Spallation Neutron Source

TL;DR

The NPDGamma experiment at SNS aims to measure parity-odd correlations in neutron-proton capture to understand hadronic weak interactions, with initial results from commissioning runs on chlorine, aluminum, and hydrogen targets.

Contribution

This paper reports the first experimental results from the NPDGamma project, demonstrating the setup and initial measurements of parity-violating gamma-ray asymmetries.

Findings

Measured gamma-ray asymmetries for $^{35}$Cl and $^{27}$Al during commissioning.

Assessed systematic effects and backgrounds in initial runs.

Presented preliminary results from hydrogen target measurements.

Abstract

The NPDGamma experiment aims to measure the parity-odd correlation between the neutron spin and the direction of the emitted photon in neutron-proton capture. A parity violating asymmetry (to be measured to 10$^{-8}$) from this process can be directly related to the strength of the hadronic weak interaction between nucleons, specifically the $\Delta$I=1 contribution. As part of the commissioning runs on the Fundamental Neutron Physics beamline at the Spallation Neutron Source (SNS) at ORNL, the gamma-ray asymmetries from the parity-violating capture of cold neutrons on $^{35}$Cl and $^{27}$Al were measured, to check for systematic effects, false asymmetries, and backgrounds. Early this year, the parahydrogen target for the production run of NPDGamma was commissioned. Preliminary results for the commissioning measurements with $^{35}$Cl and $^{27}$Al will be presented as well as first results of the hydrogen run.