# The mass of rho from fitting is lower than that in PDG, why?

First, in my partial wave analysis, I wirte an amplitude, |A|=|A1+A2+A3+A4|, Ai is the amplitude of the i-th resonance, each resonance has four parameters: mass, width, magnitude and angle. The likelihood method is to calculate their probability,|A|^2. I use the RooMinuit to get the minimization of the likelihood value. However, I find that the value of mass from fitting result is lower than that in PDG, such as the the mass of rho is 775.26MeV/c^2 in PDG, my fitting result is 765 +/- 2 MeV/c^2. Could you tell me why? Perhaps there are interferences between different resoncance, I don’t know why. Thanks!

Hi,

this definitively looks like some aspect related to your analysis and no ROOT issue.

Cheers,
Danilo

perhaps you are right, i am a new, when i posted my question, i realized that i made it in an incorrected place. In my analysis, i don’t know how to deal with it. But i really want to make it, could you help me? Thank you!