from ROOT import *
import math
import glob

def cos2phi(var, par):
   return par[0] * (1 + par[1] * math.cos(2 * (var[0] - par[2])))

def fasym():
   f = TF1("fasym", cos2phi, -2 * math.pi, 2 * math.pi, 3)
   f.SetParameter(0, 100)
   f.SetParameter(1, 0.2)
   f.SetParameter(2, 0.1)
   return f
   
ch = TChain("epairXS")
for f in glob.glob("triplets_*.root"):
   ch.Add(f)