This is a first report on the result of the survey last week of the primary Brahms detectors. This is not complete, and certain information has still to be extracted by inspection at the IR. The first version of the note deal only with the external survey, and expected internal position in the non-drift direction.

The focus was on

1. MRS with TPM1, TPM2 and the TOFW panels
2. FS in particular T1 that was not surveyed in.
3. In addition a few numbers were extracted to check the position of BB and Multiplicity array.

The first set of results deal with the external position of the TPCs. The surveying was done by sighting all 8 corners of the lucite box; the best that can be done since no reference markers have been put into place. For T2 not all corners were accessible. I sat down with Terry for about an hour in order to understand their nomenclature. The printouts from the programs are stored in the filing cabinet. The main results was transferred from the printout into a spreadsheet, and with a change of coordinate system. The spreadsheets are available upon request. The summary values are given in the table 1.

The coordinate system for TPM1, TPM2 is the global system i.e. origin at IP at nominal height, Z along beam towards 3 o'clock, X-axis down the middle of MRS when at 90 deg.

The Coordinate system for T1 and T2 is in the D2 reference system i.e. z-axis along D2 (the reference ray) and the origin at the D1 pivot point (350cm from IP).

Another important issue is that of possible rotations. To look into that I calculated for each TPC an estimate for units vectors defining the local direction of X<Y and Z for the box. They were made from the possible averages of all appropriate vectors connecting the corners. For each TPC this essentially gives a 3*3 matrix that should be unitary if the boxes are perfectly square and measurement perfect.. The results are given in the following 4 tables.

Several conclusions can be drawn from these tables.

1. Overall all TPCs are pretty well leveled . The exception is T2 where height differences of up to 1.5 mm across the detector is measured. It was though quite difficult to sight the corners. Also the amount of measurements to get good averages of the unit vector is small since two corners could not be sighted
2. The survey re-produce the known physical sizes of the TPC boxes.
3. TPM1. The measurements indicates a small rotation of about +1 mrad in the Z-X plane.
4. TPM2. The measurements indicates a small rotation of about -1.5 mrad in the Z-X plane.
5. MRS. These two rotation and the small offsets from the nominal 90 degree line are consistent with the deviations seen in the track matching. The external measurements do not support the idea of large rotation in the Y-X plane as the matching seems to indicate. At most 1 mrad seems possible in either TPC. It is of course possible that the internal geometry could allow for more. Though in my opinion the track determination should be looked at much more before drawing such conclusions.
6. T1. The TPC is quite parallel to the reference ray. A bit surprising since it was put in following a foil repair and not surveyed. The rotation seen is ~ -1.5 mrad The largest deviation from expected setup is off (farther) from the reference line by 1.0 cm).
7. T2. The rotation matrix i.e. the unit vectors correspond to an angle of ~2.40 degree not 1.90 as was expected from the reference setup. The question is if this indeed is correct. Can be checked again at IR. If correct would imply the stand if off since the .4 degree deviation would translate to 5 mm along the length of the stand - a value not possible from visual inspection . Secondly by matching the T1 T2 tracks from zero field runs and look for d(ax) deviations between T1 and T2.
8. T1,T2 The vertical position implies that the center of the 20 cm active volume (the one referred to in geometry files) which is at 20+18+100 == 138 mm from the bottom is at y=1.05 and y=0.85 for T1 and T2, respectively.

These measurements and tables will then form the basis for the geometry files to be used in the simulations.

The actual setup is slightly different from the one in the geometry definitions. The physical modules are 20 slats interspersed with a single slat (straight light guides). The total number of slats in the 2000 running is 83 and not 84. The survey was done at the edges for slats (1-20), (21-41),(42-62) and (63-83). This is not directly applicable to the geometry setup describing TFP1,TFP2,.. For a first approximation equivalent angle settings have been calculated by conversion to 21slat modules. The values are 17.6, 11.7, 5.4 and -1.4 degrees. The survey put the leftmost slat at (417.97,-0.03, -86.68).

These measurements and tables will then form the basis for the geometry files to be used in the simulations, and any tuned parameters not violate these measurements.