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HBD Commissioning

Itzhak Tserruya

DC meeting, BNL, April 11, 2007

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Outline Noise Gain Response to hadrons: FB vs RB Hadron blindness Event size Gas monitoring Diagnostics and Repair work

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Noise

Was excellent in all 24 modules Recently found large noise in 2 modules

(WN1 and WS3): Noise appears only above ~ 3000 V Does not depend on mesh voltage Induce noise in other 2 modules in same

HV box. Does not look like real sparking or

ground pickup noise. Noise looks like real signals Seems to be coming from inside detector

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Normal module

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One of the two noisy modules

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Tracking, position resolution, gainRun 226502 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

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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

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First look at electrons in FB

Run 226502 ES4 at 3600V FB

Electrons selected in centralarm projected onto HBD

Clear difference with the hadron response. Need much more data for a quantitative analysis.

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Event size The 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. Noise cannot explain this large event size. 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.

Suspicion that there is a large background not track related that dominates the event size.

For the moment we are collecting data with only a few modules such that the DAQ is not affected.

Possible cures of the problem: switch on the HBD gradually as the store luminosity decreases. record only the time samples of interest. Could gain a factor of 2. Not this

year 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.

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Gas monitoring – 2lpm

cell1-input to HBD

ce

ll/m

on

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ell'

/mo

n'

0.4

0.6

0.8

1.0

1.2

wed/ mon (vacuum)wed / mon (HBD CF4)thu / mon (HBD CF4)

cell2- West HBD output

ce

ll/m

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/mo

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0.4

0.6

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cell3- East HBD output

wavelength (nm)

120 130 140 150 160 170 180

ce

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CF4 Scans from HBD Gas Transparency Monitor. 1/29-2/02

~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.

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Gas monitoring – 3.5 lpm

cell1-input to HBD

cell/

mon

/ ce

ll'/m

on'

0.4

0.6

0.8

1.0

1.2

fri pm / fri am (vacuum)fri pm / fri am (HBD CF4) - 30 min after switchfri pm' / fri am (HBD CF4) - 2.5h after switchmon am / fri am (HBD CF4)mon pm / fri am (HBD CF4)

cell2- West HBD output

cell/

mon

/ ce

ll'/m

on'

0.4

0.6

0.8

1.0

1.2

cell3- East HBD output

wavelength (nm)

120 130 140 150 160 170 180

cell/

mon

/ ce

ll'/m

on'

0.4

0.6

0.8

1.0

1.2

CF4 Scans from HBD Gas Transparency Monitor. 3/02/07

1.2

1.9 2.52.0

2.2

2.0

2.20.4

Flow 3.5 lpm

Avg. Trans. of HBD East

0.00

0.20

0.40

0.60

0.80

1.00

1.20

110 130 150 170 190

Wavelength [nm]

Tra

nsm

itta

nce

[%

]

data

FitFitH2O: 59ppmO2: 7ppm

PanametricsH2O: ~8ppmO2: ~3ppm

~29pe

Flow=4slpmMore O2 than Before?

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Why is the gain so high? All modules installed in the HBD show a much higher gain

than previously observed in lab measurements.

A lower HV by approximately 200 V is required to achieve the operating gain of 5000.

3 GEMs randomly selected from the spares were tested recently and show the normal gain curve.

The only differences: CsI Dryness Different gas

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HV problem: facts Frequency of trips much higher than ever observed in the

lab.

Most trips are harmless

Massive trips have caused most of the damage. Mesh to top GEM Negative dI resulting in over-voltage Magnet trip

Sensitivity to magnetic field changes

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Diagnostics of HV problem New endurance test at WIS – done Test CF4 gas from the present batch used in the run at SUNY Check possible effect of magnetic field on the mesh – no

effect Manufacture transparent side cover Before disassembling West detector:

Replace side cover with the transparent one Induce trips Test effectiveness of shadows in preventing massive trips

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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

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Repair work at WI Procurement of GEMs and frames:

order already placed expect first GEMs by the end of the month total delivery time 6 weeks

GEM assembly, test and shipping for first arm:

6 weeks GEM assembly test and shipping for second arm:

6 weeks

Total: 18 weeks

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Repair work at SUNY Diagnostics of HV problem:

6 weeks CsI evaporation, test and assembly West arm:

6 weeks West arm gas flow and CF4 test in the lab.

6 weeks Same for East arm:

6 weeks

Total: 24 weeks

If we want the detectors back at BNL in Nov. 1st for run 8, we must take the West arm out not later than May 1st.

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.