BUG: fix calculation of background peak
BUG: fix calculation of background peak

SiLab-Bonn/testbeam_analysis,YannickDieter/testbeam_analysis,YannickDieter/testbeam_analysis,YannickDieter/testbeam_analysis,SiLab-Bonn/testbeam_analysis,SiLab-Bonn/testbeam_analysis,YannickDieter/testbeam_analysis,SiLab-Bonn/testbeam_analysis