Introduction

As beam line is fixed, the response for different locations on the detector is measured by moving the large scissor table on which the experiment is installed. The controls for this is located just outside the test beam radiation zone allowing a visual view of the full setup while moving the table.

Coordinate system and scan points

The FASER coordinator system is defined by the center of the tracker station with the calorimeter center offset by about 4cm from the middle of that.

To be added - how this relates to the coordinate system of the scissor table, i.e. the sign of those measurements.

As shown above, a set of nominal scan points have been defined. The scan point for each measurement is defined in the spreadsheet and in most cases only one coordinate will need to be changed from measurement to measurement. Precision positioning of the scissor table is difficult, particularly in the vertical decision and an accuracy of 5mm is considered sufficient given the large beam spot size. The actual beam position should be monitored at the start of each measurement in the online tracker monitoring (link to plot to be added) and the precise scissor table position recorded in the spreadsheet.

Conversion between scan point, tracker position and scissor table is given here:

	Tracker Position		Scissor table position
Scan point	x	y	Horizontal	Vertical
1	-100mm	+80mm
2	-60mm	+80mm
3	0mm	+80mm
4	+60mm	+80mm
5	+100mm	+80mm
6	-100mm	+20mm
7	-60mm	+20mm
8	0mm	+20mm
9	+60mm	+20mm
10	+100mm	+20mm
11	-100mm	-40mm
12	-60mm	-40mm
13	0mm	-40mm
14	+60mm	-40mm
15	+100mm	-40mm
16	-100mm	-100mm
17	-60mm	-100mm
18	0mm	-100mm
19	+60mm	-100mm
20	+100mm	-100mm
21	-30mm	+50mm
22	+30mm	+50mm
23	-30mm	-10mm
24	+30mm	-10mm

Operation of the scissor table

• in order to find out in which direction one needs to move the table, you can use the hitmap_track in the IFTMonitoring and the position panel in Grafana EHN1/IFT Tracker
• keep in mind: beam is fixed, we move the detector!
• horizontal direction: if the measured mean x value is too large, you have to move the table/detector in the forward (Saleve) direction, otherwise back (Jura)
• vertical direction: if the measured mean y value is too large, you have to move the table/detector up, otherwise down

-- BrianPetersen - 2021-07-24