Monday 22 August 2005, 4.15 pm
(Refreshments available at 4pm)
Location HEPL Conference Room
Christopher D. Bass
Indiana University / IUCF
“Measurement of the Parity-Odd Neutron Spin Rotation in Liquid-4He”
Non-leptonic weak interactions among u and d quarks at low energy are not yet understood because they are trapped within hadrons where strong QCD takes over. In the nucleon-nucleon (NN) system, quark-quark weak interactions produce tiny (10−7) parity-odd (PV) effects. These weak interactions can be described by a meson exchange model, where the exchange of virtual mesons between the nucleons is parameterized by a set of NN weak interaction amplitudes. The strengths of these amplitudes from theoretical calculations are not well known, and experimental measurements of PV observables in different nuclear systems have not yet constrained their values. These PV effects are important to understand because (1) NN weak interactions are in principle a new probe of strong QCD and (2) knowledge of NN weak couplings can aid the interpretation of many nuclear and atomic observations.
In forward elastic nuclear scattering, the most prominent PV observable is the rotation of the neutron spin of transversely polarized neutrons propagating through a medium. We are preparing an experiment to make a precision measurement of the PV neutron spin rotation in a liquid-4He target. We describe our apparatus and detail our efforts to reduce systematic effects in order to reach a sensitivity goal of 10−7 rad/m during a run at NIST during 2005/2006.
Christopher Bass is a graduate student at Indiana University.
rev 14 Aug 2005 NC