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EPD vertex analysis, x-y plain with different z cut selections, with 3 different zooms on the x-y plain

Updated on Fri, 2018-05-11 05:26. Originally created by rolandp on 2018-05-08 14:19.

First of all, I replotted the plots of Mate, and fixed the scaling of the z axis, since there it was not ranged from 1 in all cases.
Mate's plots can be found here: https: //drupal.star.bnl.gov/STAR/blog/mcsanad/track-vertices-epd-hits-various-z-values

I. The x-y plane at various z values, with 3 different zooms

(I.1.) Zoom 0: x-y ranges from -10..10 centimetres:


Above +/-2000 centimetres, there is not any entry.

(I.2.) Zoom 1: x-y ranges from -100..100 centimetres:


Above +/-2000 centimetres, there is not any entry.

(I.3.) Zoom 2: x-y ranges from -450..450 centimetres:

 
Above +/-2000 centimetres, there is not any entry.

As it can be seen from the Zoom 2 section, the mysterious rectangle shape appears at +/- z = 1800..2000 centimetres sections, where the x-y plain ranges from -400 centimetres to 400 centimetres.
To further investigate this rectangle, I made 1D histograms, in which I plotted the vertex z distribution for the left, right, top, bottom side of the rectangle.

II. Analysing the rectangle

(II.1) Rectangle, vertex z 1D distributions

(II.1.1.) For negative z values, between 0...-2100 centimetres


(II.1.2.) For positive z values, between 0...2100 centimetres



To see these plots better, I plotted them to a single 1D distribution, where z ranges from -2100 centimetres to 2100 centimetres.

(II.2.) Z values between -2100 centimetres and 2100 centimetres

 +/- means in the legend that for that side of the rectangle, I plotted the values for both positive and negative z values. The rectangle is where the z of the 4 sides (left, right, top, bottom) are the same. 
Since it's a back-scattering to the EPD, what we see is reasonable. It's clearly visible that this rectangular shape "appears" around +/- 800 centimetres at vertex z, and from that point, it decreases.

III. Fixed target scattering

Mate informed me about the fact that in the beam pipe, there is a fixed target holder around +2.1 metres in the z axis, and relatively close to the beam in the x-y plain. Consequently, I have made 2 plots, between z = +/- 1.8 metres ... +/- 2.4 metres and in the x-y plain from x,y = -3 centimetres .... +3 centimetres. Theoretically, we should see a semicircle, or some kind of curve on the positive z one. 

As mentioned, we should see a semicircle or a curve on the positive z plot, but on these 2 pictures, we can see nothing.
The reason why I plotted the negative z side as well is that I was hoping maybe we could see something there too.



IV. Conclusions

(1) As we investigated the vertex x-y plain on 3 different zoom ranges, with different vertex z selections, we can see some typical shapes.

(2) For the fixed target holder, which is at around 2.1 metres in the beam pipe, we should have seen a semicircle or a curve as plotting the vertex x-y plain with vertex z limited at +180... +240, while x-y ranges between  -3...+3 centimetres (at 4.5 there is the inner circle of the EPD), but there is not any semicircle or curve as expected.
I've plotted both positive and negative sides, hoping that maybe we could find something on the negative z side as well, but this was not successful.


(3) By taking a closer look at the rectangular shape, we can see on my unified plot that the rectangle is where the vertex z of the 4 sides (left, right, top, bottom; both + and -) are the same. Since it's an inward-scattering in the EPD, what we see is reasonable. It's clearly visible that this rectangular shape "appears" around +/- 700 centimetres at vertex z, and from that point, it decreases.


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