CDC run 2551 drift time fits

Fit function: 
  TF1 *g2 = new TF1("g2","[0] * (1 + [1]*exp(([3]-x)/[2]) + [7]*exp(([3]-x)/[8]) ) / ( (1+exp(([3]-x)/[5])) * (1+exp((x-[4])/[6])) )");

  [0] overall height
  [1] amplitude of 1st exp contrib to peak
  [2] first exp fall-off
  [3] t0
  [4] tmax
  [5] slope up of t0 edge
  [6] slope down of tmax edge
  [7] amplitude of 2nd exp contrib to peak
  [8] second exp fall-off

Drift time fit t0

Drift time fit tmax

Drift time fit tmax vs parameter 6

Drift time fit tmax vs parameter 8

Drift time fit parameter 6 vs parameter 8