1. CMS Week Muon Alignment
James N. Bellinger
University of Wisconsin at Madison
5-December-2006
DCOPS Data from MTCC2

2. CMS Week Muon Alignment
General notes
With a better understanding of disk deformation and more time available we were able to align the lasers better for MTCC2.
Although disk deformation results in a laser position change larger than the DCOPS aperture, COCOA can use lasers from opposite sides to reconstruct positions.

3. CMS Week Muon Alignment
Review of the structure of single SLM
A typical SLM has 10 DCOPS along its line, with a crosshair laser pointing into the line from each end. This line is not perfectly radial.
Each DCOPS has 4 CCDs arranged in a square. CCD numbers 1 and 3 measure something like “Rphi” and 2 and 4 measure “CMS Z.”

4. CMS Week Muon Alignment
What happens when the field is on
The center of the disk is pulled inward and the rim of the disk pushed outward.
This tilts the lasers backwards, so that the beam is redirected about 2 mrad inward towards the solenoid.
For the DCOPS near the laser, the pull of the disk inward approximately compensates for the laser tilt, and we don’t see large deflections in Z. We see a large effect in DCOPS far from the laser.

5. CMS Week Muon Alignment
When the field is on
Because the laser lines don’t go through the center of the disk, the laser tilt causes deflections in the “Rphi” as well as the “Z” measurements, so both are required to reconstruct the true rphi and z.
Because the DCOPS are now in new locations with respect to each other and the laser, the CCD for one can shadow a downstream CCD and reduce the signal it sees.

6. CMS Week Muon Alignment
Field Off data:
laser positions in
2 CCDs in DCOPS
along an SLM 9
CCD3
Rphi 5
Laser
Background of
glare from laser 10 9 8 7 6
The laser position
does not change much
from position 1 to 5,
but once past the
midpoint it quickly
goes offscale in Z.
The “Rphi” variation
is well contained.
CCD4 Z 5 4 3 2 1
Laser
This reflection is unique:
rarely a problem

7. CMS Week Muon Alignment
Data Quality observations
The double peak is a unique local reflection.
The DCOPS next to the laser sees a substantial background due to glare.
Some CCDs show a reasonable profile but have low signal strength (CCD 3 set, #9).
Some show no signal (CCD 3 set, #5).
Most profiles are perfectly useable.

8. CMS Week Muon Alignment
Field On
Same SLM as
before
The changes in
“Z” are easy to
see, and there
are changes
in “Rphi” also.
CCD3
Rphi
Saturation
Position
offscale
in other
direction 6
CCD4 Z

9. CMS Week Muon Alignment
Deviations
in Rphi
Beam off – Beam on “Rphi” position in mm
ME+2/SLM1
The trend of the
deviations is
consistent with
the tilting of
the laser.
Relative position along the SLM in mm
CCD has bad signal.
Fit should have failed.

10. CMS Week Muon Alignment
Field Off
Laser
CCD3
RPhi
This is the same
SLM as before,
but with the laser
at the opposite end.
The profiles are
generally clean,
and COCOA
will be able to
link together
the measurements. 9 8 7 6 10
CCD4 Z
Laser 5 4 3 2 1

11. CMS Week Muon Alignment
Field On 9 8 7 6 10
Laser
CCD3
RPhi
Same SLM as before.
There appears to be
some shadowing in
CCD3 data, but the
peaks are still
detectable. 3 1 5 4 2
CCD4 Z
Laser

12. CMS Week Muon Alignment
As you can see here
the fit result is decent
even when the profile
has some saturation,
as in CCD3 (lower
left plot).
I restrict the fit to a
range around the peak.
This is the DCOPS I
numbered ’10’ in the
previous sets of plots.

13. CMS Week Muon Alignment
This shows the
Z-position of the laser
peak as a function of
field for 4 different
Layer 2 chambers at
ME+1.
The overall deflection is
O(.5mm): small because
the disk bending and
laser deflection are in
the same direction.

14. CMS Week Muon Alignment
COCOA reconstruction of
CSC center positions, from
Gyongyi Baksay at FIT
CMS Z position of the CSC center
In mm, arbitrary origin
Position along the SLM in mm

15. CMS Week Muon Alignment
CMS RPhi position of CSC Center
In mm, arbitrary origin
COCOA reconstruction of
CSC center positions, from
Gyongyi Baksay at FIT
The error bars are smaller
than the symbols.
Position along SLM in mm

16. CMS Week Muon Alignment
Running Experience
At irregular intervals a random terminal server port would lose connection with the DCOPS, and remain offline until the power was cycled at the LV crate. (This required a reboot of the analog system, as we belatedly discovered).
3 times during the month a telnet access to a terminal server port wedged, and ran in an infinite loop.
We did not recover any instances of data corruption.

17. CMS Week Muon Alignment
The majority of the DCOPS data is available online in text form via the address above. It includes the fit information and the raw profiles.

18. CMS Week Muon Alignment
Near-term Plans
Finish rewriting the core of the DAQ to get better speed. It isn’t complete, but I estimate that a full readout cycle will take less than 15 minutes. It addresses the hung port problem.
Integrate the DAQ into the DCS/PVSS system. I think I can use DIM protocols, but need advice.
Finish the code to retrieve and assemble DCOPS data from the database.

19. CMS Week Muon Alignment
Old Readout Scheme
A bash script looped over the laser lines and submitted scripts which would telnet to the port for each DCOPS, issue the commands, and read back the raw profile.
Another short program fit the profiles, if possible, and another shell script accumulated the resulting fit information and committed it to the omds database.
Since this was sequential, the time required to complete a cycle for the +side was over an hour and a half, and a hanging process could stall the readout.

20. CMS Week Muon Alignment
New Readout Scheme
A C++ program loops over the SLM Lines, forking a job to manage each Line and fork off subtasks to read out particular ports. The lowest level forked task is still a telnet invocation. I estimate that this part of the readout will take 9 minutes for all the SLMs, not just the +side ones.
When the SLM jobs have completed or timed out, the Transfer Lines will be read.
Then the profiles will be fit, data committed to the database, and the DIM service updated with the new results.