LONG TERM MUON STABILITY AT CALDET

Aim: Measure and compare the MIP values per strip end at two points separated in time.

Why?: To investigate MIP value stability over calibration timescales at FarDet, (~month)

Previously: CalDet 3 GeV runs show ~2% decrease in muon-induced light output over 1 month

Procedure:

Drift point correct hits
Find tracks in CalDet data
Demand double-ended readout
Angle correct hits
Histogram deposits per strip end
Use truncated mean at 90% level to get MIP values

Difficulties in making a new measurement:

No data to do this simply!!
No cosmic runs with LI from before the end of the test beam
Only one cosmic run taken after test-beam that has useful LI data
Only thing to compare this run with is cosmics in the test-beam data...

Looking only for muons out of spill, the angular distributions look as follows:

There is a significant contribution from PS muons. Need to cut them out for a valid comparison with the pure cosmic run.

Cutting on vertical angle: Only accept events with >20degrees or <-20degrees

Then, the angular distributions for the beam runs become:

compared with the cosmic run with the same cuts:

Final difficulty:

No data (currently) to use pins to relate gains from before and after CalDet move.
Instead use mean/sigma method to obtain gains from LI drift point data.

Results:

First look at the gains from the drift point data for the two runs:

There is a ~16% increase in gains between the two runs. (Not the HV change).

Sanity check: do the cosmic muons from the beam run follow the same temperature pattern as the beam muons?

Added complication - less cosmics than beam muons => fewer data points....

They agree well and show the pattern expected due to overnight temperature shifts.
(Plot of observed temperature shift vs muon stability for a different cosmic run.)

Looking at the cosmic run:

Larger shifts are observed, in the right direction to be temperature related, but there is no temp. data for this run.
Behaviour after 5.00am not understood.

Long term stability: Looking at the change in MEU between the two runs

There is a ~6% drop in light output between the two runs.
The red/magenta dots show the expected shift due to average monthly temperature changes.

(eps version)

Improvements:

Use cosmic counters as cosmic muon event trigger
Use low light level gains to compare data from before and after CalDet move
Take data with better drift point information