The data shown here are from run 1175 at 0 degree rotation angle, taken with sensor D35-S9-43.
The root program "landau1.c" was used to generate the plots (first 4) below.
Only events where used where there is no charge sharing (it was checked that the
charge in the center pixel is at least 20 times larger than the sum of charges in
the surrounding pixels), there for we look at the center region of the pixels.
For each pixel the signal was plotted (ped1-sig1) and then fitted by a landau.
The following 2 pictures are a composite of 20 pixels, while every pixel is
shifted by the center value of it's Landau.
To make sure that we don't get a landau like distribution, just be fitting to it
the following plot was created by shifting the individual pixels by the
center value of a gaussian that was fitted to it. Again we get a landau like distribution.
The following plot shows the charge readout from the center pixel in ADC
one can see that it stays pretty much constant even inbetween 2 pixels.
if the total charge is plotted that is read out from the hit pixel + it's 2
row neighbors, one can see that the total charge increases in between the pixels
where we expect charge sharing.
if we also include the charge from all 5 neighbors(in the double column) we get the following
Note: here the position was calculated using charge sharing, it was earlier shown that the
position that we get from tracking (Si-planes) and from the Charge sharing (pixels) is
approximatly the same.
Conclusion: Even though the signal in the center of the pixel has a landau like shape,
it is clear from the charge versus position plots that the chip is saturating. Since the
collected charge is (nearly) double inbetween 2 pixels it looks like that a saturation of a single
occurs at 10000e.
last up-dated 1-30-01