1 HBD Commissioning Itzhak Tserruya DC meeting, BNL, April 11, 2007

2 Outline nNoise nGain nResponse to hadrons: FB vs RB nHadron blindness nEvent size nGas monitoring nDiagnostics and Repair work

3 Noise nWas excellent in all 24 modules nRecently found large noise in 2 modules (WN1 and WS3): u Noise appears only above ~ 3000 V u Does not depend on mesh voltage u Induce noise in other 2 modules in same HV box. u Does not look like real sparking or ground pickup noise. u Noise looks like real signals u Seems to be coming from inside detector

4 Normal module

5 One of the two noisy modules

6 Tracking, position resolution, gain Run ES4 at 3600V FB Hadrons selected in central arm projected onto HBD Position resolution as expected of the order of a cm dictated by the pad size Mostly single pad response as expected Gas gain: (assuming a primary charge of 19e in the 1.5mm drift gap and a conversion of 10 ADC counts/fC) G = 2900 Much larger than expected

7 Hadron Blindness- FB vs RB response Spectra Comparison in FB and RB (for the same number of central tracks) Results very similar to those previously obtained in lab tests or beam tests

8 First look at electrons in FB Run ES4 at 3600V FB Electrons selected in central arm projected onto HBD Clear difference with the hadron response. Need much more data for a quantitative analysis.

9 Event size nThe event size is too large and limits the DAQ archiving rate at least in the first half of the store when the luminosity is large. n Noise cannot explain this large event size. n We observe the expected decrease of PH, and consequently of the rate, while operating in RB mode. But this is not reflected in the overall event size. n Suspicion that there is a large background not track related that dominates the event size. nFor the moment we are collecting data with only a few modules such that the DAQ is not affected. nPossible cures of the problem: u switch on the HBD gradually as the store luminosity decreases. u record only the time samples of interest. Could gain a factor of 2. Not this year u use one fiber per module instead of one fiber per 2 modules. We could operate as many as 12 modules which is close to the number of operational modules.

10 Gas monitoring – 2lpm ~30 % Loss ~30-40 % Loss HBD IN HBD W HBD E Flow 2lpm 30% loss should correspond to 80 ppm of water. However, according to the hygrometer the detector is at app. 12 ppm. Origin of discrepancy not understood. Working assumption: the gas monitoring results are correct. At the present flow of 2lpm we are loosing 25% of the UV photons. We asked Rob to increase the gas flow by a factor of two.

11 Gas monitoring – 3.5 lpm Flow 3.5 lpm

12 Why is the gain so high? nAll modules installed in the HBD show a much higher gain than previously observed in lab measurements. n A lower HV by approximately 200 V is required to achieve the operating gain of n 3 GEMs randomly selected from the spares were tested recently and show the normal gain curve. nThe only differences: uCsI uDryness uDifferent gas

13 HV problem: facts nFrequency of trips much higher than ever observed in the lab. nMost trips are harmless nMassive trips have caused most of the damage. uMesh to top GEM uNegative dI resulting in over-voltage uMagnet trip nSensitivity to magnetic field changes

14 Diagnostics of HV problem nNew endurance test at WIS – done nTest CF 4 gas from the present batch used in the run at SUNY nCheck possible effect of magnetic field on the mesh – no effect nManufacture transparent side cover nBefore disassembling West detector: uReplace side cover with the transparent one uInduce trips uTest effectiveness of shadows in preventing massive trips

15 New Endurance Test exactly the same powering scheme used in the installed HBD no sparks in almost 2 weeks gain curve very similar to those measured in many previous tests Very different from gain curves of the modules installed in the HBD

16 Repair work at WI n Procurement of GEMs and frames: u order already placed uexpect first GEMs by the end of the month u total delivery time 6 weeks nGEM assembly, test and shipping for first arm: 6 weeks nGEM assembly test and shipping for second arm: 6 weeks Total: 18 weeks

17 Repair work at SUNY n Diagnostics of HV problem: 6 weeks nCsI evaporation, test and assembly West arm: 6 weeks nWest arm gas flow and CF 4 test in the lab. 6 weeks n Same for East arm: 6 weeks Total: 24 weeks If we want the detectors back at BNL in Nov. 1 st for run 8, we must take the West arm out not later than May 1 st. Working hypothesis: access on April 25 is the target date to take out HBD west, pending progress on the preparations at SUNY and collecting enough data with the two arms.