[Olympus] Interim report of Olympus test experiment

[Alexander Winnebeck]

Dear colleagues,

let me give you a short report on the things going on at DESY at the moment. There was quite some progress and learning in the last days.
Last Thursday DORIS switched to a 2.0 GeV positron beam and established a smooth operation with a beam current of up to 50 mA. During the nights the machine is switched back to 4.4 GeV for backout. Due to some problems on Friday with 2.0 GeV it was decided to run the weekend at 4.4 GeV and therefore get some extra time next week with 2.0 GeV.

- Target + Vacuum: Behaves as expected, target cell temperature stays below 150K (even at 4.4 GeV and 135 mA), at 2 GeV with 50 mA the temperature is approximately 40 K, clear effect in count rates with gas in the target and without.
- Lead glass calorimeter: Shows high energy peak, which disappears when there is no gas in the target. Trigger threshold might by increased to discard low energy hits and reduce probability of random coincidences.
- Proton arm detector and start detector: Showed time correlations to high energy peak in the calorimeter, After some improvements in the electronics yesterday, operation should be more stable.
- MWPCs: Operate well and see tracks coming from the target, however, efficiency seems to be low, which might be the case when trigger was not released by a positron from the target, but from gammas or particles not passing the acceptance of the tracking detectors (not coming from the target). To verify this a second scintillation counter will be installed in front of the tracking arm.
- GEMs: First signals have been observed, but some fine tuning of the latency is needed. 
- DAQ: Operating smoothly.
- Online monitoring of detectors implemented as well as some first rough cut and correlations to select elastics.

In general our campaign seems to be successful. Count rates in the detectors scale with target density and life time is going down. At 1 sccm flow rate (design is about 0.4 sccm) the life time is approximately 0.4h, what is in good agreement with predictions.
Tomorrow we are supposed to switch from positrons to electrons at 2 GeV.
After seeing again elastic events in the data, the major goals in now to get the tracking detectors ready for operation and collect a good sample of events to analyze.

Cheers,

Alexander

--
Dr. Alexander Winnebeck
winnebeck at mit.edu

Massachusetts Institute of Technology (MIT)
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02139 Cambridge, MA, USA
Tel: +1-617-253-2366

DESY
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Tel: +49-40-8998-6402