PHYS 291 Project: ALPIDE beam test data



Project description


I have analyzed data from a beam test of the ALPIDE sensor, that was performed in Germany in 2018. I want to look at hitmaps/histograms to identify clusters of hits from the beam. The term cluster means a pixel group showing signal above a certain threshold. These can be found either by looking at the hitmaps and identifying maxima(red spots), or by plotting instances of variations above some threshold.
The beam test from which i've been looking at data, is a 50 MeV He-ion beam on an ALPIDE chip with different thickness of material in front. Because of the energy loss given by the Bethe-Bloch formula, the resulting "Bragg-peak" (see figure 1) explains why particle beams are very sensitive to positioning. They deposit most of their energy after traveling a certain distance, and this can be seen from the graphical representation of data presented below.


Fig. 1: Bragg curve for charged particles

Coding


One of the codes I have used, "clustersize_singEvt.C", is generating hit maps from the beam test. It takes the data from an ASCII-file containing x- and y-coordinates, event time signature and number of hits per event. The resulting hit maps display number of hits in the "z-direction", as colors, in a 2-D histogram where x- and y- coordinates corespond to pixels on the sensor.
Next, i wanted to make a plot of clusters. A program that plots every instance of pixels that gets more than a certain number of hits in one event. This is the "clusterplot.C"-code. I wasn't able to finish this one, but I included it to show what I was trying to do.


Results from ALPIDE beam test with 50 MeV Helium ions



Hitmaps from beam test with different thickness material in front:

With 0 cm material:



With 0.5 cm material:



With 1 cm material:



With 1.5 cm material:



With 2 cm material:



Results and conclusion


As we know from Bethe-Bloch, there is a connection between path travelled through a material and the position of the Bragg-peak. This dependence is clear from the hitmaps. The max number of hits (per event, per pixel) is displayed as the color red and as we can see from the color table on the right, these values ranges from 12-14 to more than 2200. Unfortunately i wasn’t able to plot an estimate of how the hits/particle range depends on the material thickness as i had hoped, but the hitmaps demonstrates the point i wanted to make to some extent.






Fredrik M W 2019