# Breit-Wigner distribution

Hi,

I just wondered how the Breit-Wigner distribution correctly looks like.
T tought that it woud look like

(1/2Pi) gammagamma/((x-mean)(x-mean) + gamma*gamma/4)

but in TMath:BreitWigner I found

(1/2Pi) gamma/((x-mean)(x-mean) + gammagamma/4)
–> only gamma and not gamma^2 in the numerator.
Which form is the right one?

Cheers & Thanks for a hint,
Thomas

Hi,

what is in TMath and in MathCore, see

seal.web.cern.ch/seal/MathLibs/M … 996d046f73

is correct ! It should be Gamma and not Gamma**2 in the numerator.

You can also check on MathWorld, where you find the definition of the Cauchy distribution (it is the same as the Breit Wigner but with b = Gamma/2) :

mathworld.wolfram.com/CauchyDistribution.html

Best Regards

Lorenzo