  The muon decay parameter delta characterizes momentum dependence of the
parity-violating muon decay asymmetry. A new measurement of delta has been
performed using the first physics data recorded by the TWIST experiment at
TRIUMF. The obtained value, delta=0.74964+-0.00066(stat.)+-0.00112(syst.), is
consistent with the Standard Model expectation delta=3/4. This is the first
determination of delta performed using a blind analysis technique. Combined
with other data, the measurement sets new model-independent limits on effective
right-handed couplings of the muon. Improved limits on the product of another
muon decay parameter, xi, and the muon polarization in pion decay, Pmu, are
obtained in the form: 0.9960<Pmu*xi<=xi<1.0040, at 90% confidence level.
Implications for left-right symmetric models are discussed.
