Straw tube measurements Sebastian Bablok, Øystein Djuvsland, Per Thomas Hille

The Detector A model of the straw tube detector used for the Outer Tracker in LHCb A model of the straw tube detector used for the Outer Tracker in LHCb 16 channels 16 channels 1500 V bias 1500 V bias Gas mixture: 75% Ar, 15% CH 4, 10% CO 2 Gas mixture: 75% Ar, 15% CH 4, 10% CO 2

The straw tube 1500 V Cathode tube, (5 mm Ø) Anode wire, Au-plated tungsten (0,025mm Ø) Gas: 75 % Ar 15 % CH 4 10 % CO 2

Testing Test setup for testing the 16 channels one by one Test setup for testing the 16 channels one by one “Only” 2 dead channels “Only” 2 dead channels Nice soldering points!

The Final setup

Scope trace (average) of output voltage from straw tube 15.

Hypotesis The gas amplification gain depends on the bias voltage of the straw tubes. The gas amplification gain depends on the bias voltage of the straw tubes. The gain increases at higher voltages The gain increases at higher voltages

Test of hypotesis Measure the output signal from the straw tubes for different values of the HV. Measure the output signal from the straw tubes for different values of the HV.

Results

Conclusion (preliminary) Our observations contradicts the Hypotesis. The gain is independent of the bias voltage. Our observations contradicts the Hypotesis. The gain is independent of the bias voltage.

Discussion We dont believe in these results, gain shoud depend on HV. We dont believe in these results, gain shoud depend on HV. Implication: We need an ad-hoch hypotesis Implication: We need an ad-hoch hypotesis Ad hock hypotesis: We used wrong type of radioactive source (strontium). Ad hock hypotesis: We used wrong type of radioactive source (strontium). We should repeat the measurements again with a monocromatic source (Fe55). We should repeat the measurements again with a monocromatic source (Fe55).

New Gain measurements The output voltage of the straw tubes was measured for 1350, 1400, 1450, 1500, 1550 Volt. The output voltage of the straw tubes was measured for 1350, 1400, 1450, 1500, 1550 Volt. At 1550 V we could also se the escape peak. At 1550 V we could also se the escape peak V 1400 V 1450 V 1500 V 1550 V

Escape peak, enlarged view

Results All measuremnts fitted with an exponential Function. Only the 4 highest measuremts fitted with an exponential Function.

Conclusion The output signal from the straw tubes depends on the bias voltage. The output signal from the straw tubes depends on the bias voltage. The dependence is exponential between 1400 and 1550 Volt The dependence is exponential between 1400 and 1550 Volt

Noise measurement We measured the number of fake trigger as a function of the trigger treshold. We measured the number of fake trigger as a function of the trigger treshold. Without radioactive (upper figure). Without radioactive (upper figure). With radioactove source (bottom figure). The source was sentered abowe straw 8 With radioactove source (bottom figure). The source was sentered abowe straw 8