Time constant of an LRC circuit

[eljaydub]

I'm having trouble finding an equation for the time constant of an LRC circuit as a function of L, R and C. (In the same way that RC is time constant for an RC circuit) Does anyone know what the equation is?
Thanks!

 

[eljaydub]

Hmm maybe I'll not representing this right...
Say I have an equation of the form
A*exp(-a*x)*cos(b*x+c)
for an LCR where A,a,b,c are parameters. Then 'a' corresonds to 1/(TimeConstant) but there should be a formula similar to 1/RC for an RC circuit to predict the value of that constant.
I'm looking for the formula so that I can justify my guess of the parameter to fit it to my experimental data

 

[eljaydub]

*bump*
No help?