Feature #1724

Tracker to solenoid alignment

Added by Rogers, Chris almost 7 years ago. Updated over 6 years ago.

Start date:
29 July 2015
Due date:
% Done:


Estimated time:


Desire to understand the alignment of the tracker to the solenoid, based on data taken on Thursday 23rd July. Plan is to:

a. Run modified pattern recognition in order to get a first estimate of alignment
b. Probably find a better way to do it using "some fancy algorithm" which might include Kalman fits
c. Throw tracks from upstream tracker to downstream tracker and wiggle the magnets until tracking agrees with data


theta_residuals.png (38.8 KB) theta_residuals.png Rogers, Chris, 29 July 2015 16:02
residuals.png (34.1 KB) residuals.png Rogers, Chris, 29 July 2015 16:02
residuals.tar (74.7 MB) residuals.tar Rogers, Chris, 29 July 2015 18:54
2015-08-13_tracker-to-solenoid-alignment.pdf (1.01 MB) 2015-08-13_tracker-to-solenoid-alignment.pdf Rogers, Chris, 13 August 2015 13:06
34.png (89.5 KB) 34.png Rogers, Chris, 23 September 2015 12:14

Updated by Rogers, Chris almost 7 years ago

Analysis based on run 07290 only. For cuts I require exactly 5 space points in TKD but I have no other cuts included so far (not TOF nor number of clusters per space point). I make a linear least squares fit, allowing the linear least squares to make a track by track adjustment to the fit proportional to distance along the tracker (i.e. tilt the helix). I histogram those track-by-track tilt angles (theta_residuals.png). I note a mean of the fit of 2.8 mrad +/- 1 mrad (I have cut the tails in a statistically suspect way, however).

I also attach the residuals of the least squares fit; they look okay - I note tracker_1_station_3 has a slightly significant residual (about 1 RMS).

Compare with JHC,

penultimate slide (32), which shows (roughly)

The physical bore:

x0, z0 = -3.9, 17650
x1, z1 = 2.3, 20300
gives tilt 2.3 mrad

The magnetic axis:

x0, z0 = -8.3, 17400
x1, z1 = -8.7, 20300
gives tilt -0.1 mrad (not significant I expect)

So the two numbers are consistent. Note that I need to check the sign...


Updated by Rogers, Chris almost 7 years ago

I attach data for run 07288, 07289, 07290.

I added requirement that we have exactly three clusters per space point and exactly one space point in TOF1 and one space point in TOF2. I looked at making a TOF cut but it doesn't seem necessary.

07288 and 07290 are consistent with the result outlined in note 1. 07289 shows a theta y (nb this is the rotation angle around the y axis) of 4 mrad +- 1 mrad. I will try making a chi2 cut next (with luck tomorrow) - I hope this will remove events in the tails, which are e.g. not small angles any more so the fit is incorrect.

I also note the feature that in all instances the downstream plane, station 4 (and to a lesser extent station 3) has worse residuals than the others. I don't understand this, will mull it over tonight.


Updated by Rogers, Chris almost 7 years ago

Attached current status of the analysis; note also (historical) slides from 2015-07-30 analysis meeting


Updated by Rogers, Chris over 6 years ago

pdf updates attached to following wiki pages:

PC-2015-09-03a - and presented at VC


Updated by Rogers, Chris over 6 years ago

We took more data last night and the night before, with SSU only. Note M1 currents were screwed up last night, see attached plot.

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