void peaksum(const TH1F *trace, Int_t t0, Int_t t1, Int_t base)
{
   Double_t sum = 0;
   Double_t peak = 0;
   for (int n=t0; n<t1; ++n) {
      Double_t val = trace->GetBinContent(n)-base;
      peak = (peak > val)? peak : val;
      sum += val;
   }
   Double_t width = sum*4/peak;
   std::cout << "average pulse width is " << width << " ns" << std::endl;
}