Histograms of C_p (Eq. (10)) using two different backgrounds, BG1 and BG2. The mean, median and the most probable values of C_p with BG1 are 5.90, 4.29, and 2.39, respectively and the mean, median, and the most probable value of C_p with BG2 are 4.76, 3.02, and 1.64, respectively. The mean value for each histogram is marked by a vertical line. The maximum value shown on the x axis is limited to 24.5 in order to zoom in on the histogram peaks.