Sigma of the crystal ball

Roofit and RooStats
1

Hi

I’m using a crystall ball to fit a dataset. How to get the sigma of the gaussian part only ? I am trying to do someting with the Half Witdh at Half Maximum and the formula which gives the sigma:
HWHM = 1,178*sigma.

Or maybe, there is a link between the sigma of the crystall, the sigma of the gaussian part ?

Any idea ?

Thanks.