Results from a preliminary analysis of the MWPC test at the GIF

Test set-up hodoscope finger Muon beam S3 & S4 S5 S1 & S2 radioactive source MWPC lead walls Concrete wall The source radiation could be shielded with several absorbers with different thickness The trigger signal was given by the coincidence of the scintillators S1, S2, S3 and S4; The hodoscope data have been used off-line to select muon illuminating only two chamber pads; We decided not to use finger data for the analisys: - too poor muon rate on it: 20 hits per spill (i.e. each 14 sec) - it was irradiated

Set-up performance We tried to evaluate the trigger time-resolution. The finger and S5 signals were sent to a constant fraction discriminator. finger time (ns) S5 time (ns) No visible correlation between the finger and S5 times was found The rms of the chamber time w.r.t. S5 is even worst (4.44 ns) than the one w.r.t. the trigger (4.37 ns). We concluded that the trigger time resolution was better than 0.9 ns which is the one of S5.

Test outlook We tested an M3R3 final chamber built in Frascati; The chamber was fully equipped with final electronics: - 12 CARDIAC boards: 192 physical ch -> 96 output logical ch; - 2 I2C long lines chains and 1 service board controlled via OPC CANBUS by a PVSS program developped in Roma 1; An Ar/CO2/CF4 40/40/20 gas mixture was used; We studied the efficiency and time proporties as a function of the gain in different rate conditions (source OFF, source ON, source ON with different absorbers) for: - the quadri-gap - the “double mono-gap” -> two gaps going into two front-end electronics (M1 like) OR-ed by the dialog - the “single bi-gap” -> two gaps hardware OR-ed going into one front-end electronics

Gamma rate studies Region Rate/cm2 Rate/chan Gap number M1R2 43 kHz Expected particle rates in the muon system (without safe factor). Rate at the GIF as measured with the quadri-gap M2R1 Rate/channel (kHz) Rate/(cm2 x gap) (kHz) M2R1 M1R2 M3R3 M3R3 Dead time effect HV (kV) HV (kV) Space-charge effect

Dead time expectations (for GIF!) Muons give correlated signals in all the 4 gaps. Photons give signals completely uncorrelated in the 4 gaps. The rate seen by each CARIOCA is half of the total rate seen by the DIALOG. Moreover, the CARIOCA output is about 50 ns long, the DIALOG one is 25 ns.  hit a pad 0 25 50 t (ns) CARIOCA 1 output After about 25 ns the dialog is ready to axcept a signal from CARIOCA 2 CARIOCA 2 output DIALOG output At 2750 V (for a rate of 250 kHz/chan in each gap), we expect: Quadri-gap 2.5% dead time Double mono-gap 2.5% dead time Single bi-gap 5% dead time

Currents studies We measured the current drawn by each gap by using the HV supply (the nanoamperometer induced noise in the FE electronics) At the max rate (10 kHz /cm2) : 100 A/gap -> 25 nA/cm2 This means than each  produces a current of 2.5 pC (while a mip produces about 1 pC) Current/gap (A) Current/cm2 (nA) HV (kV)

Data analysis method In the classical analysis method, the chamber time spectra are filled with the first hit in the region illuminated by the beam in each event. First hit spectrum with source OFF First hit spectrum with source ON Hits due to photons first hit time (ns) first hit time (ns) In order to clean the time spectra from the photon hits we changed the classical analysis method Confrontare il numero di entries con l’hodoscopio

The “nearest” hit method One could take the larger time (first) lower than a time_max value evaluated in the run with source OFF. The time spectra result cut and time r.m.s. are dominated by the photon hits. Or one can choose the time nearest to a time_mean evaluated in the run with source OFF. first hit time (ns) The spectra are not cut and it is possible to see the photon hits which have given a dead time. The time r.m.s. results the same found with source OFF. 65 counts (1.1% of entries) nearest hit time (ns) nearest hit time (ns)

Comparison between the methods We made the analysis of the scan without source with the two methods in order to evaluate the difference between the results obtained. In the scan with source OFF: the efficiency found is the same - the time r.m.s. has a little bias of about 200 ps time r.m.s. (ns) Efficiency in 20 ns (%) High voltage (V) High voltage (V) In the scan with source ON: the efficiency found is slightly higher (the spectra are no cut) the r.m.s. are better because of a better rejection of the photon hit.

Quadri-gap: efficiency in 20 ns Rate/chan = 1.2 MHz Dead time expected about 2.0 % Rate/chan = 450 kHz Dead time expected about 0.8% Efficiency in a 20 ns (%) Efficiency in a 20 ns corrected (%) High Voltage (V) The efficiency can be corrected with dead time values. We used directly the rates found in the TDC for the illuminated by the beam High Voltage (V) rate of 3 kHz/cm2 rate of 8.5 kHz/cm2

Quadri-gap: time resolution The r.m.s. of the time specra don’t show visible deterioration because of the high rate Time r.m.s. (ns) High voltage (V) Up to a  rate of 8.5 kHz/cm2 (70% of the one expected in R1M2), the only visible effect is due to the electronics dead time. No evidence of other effects spoiling the chamber properties.

Double monogap: efficiency We studied the behavior of a M1 like chamber by shutting down the high voltage in the gaps A and C Rate/chan = 500 kHz Dead time expected about 1.25 % Efficiency in 20 ns (%) Corrected efficiency in 20 ns (%) High voltage (V) Also in this case we can correct by the dead time effect High voltage (V) rate of 3 kHz/cm2 rate of 8.5 kHz/cm2

Double monogap: time resolution Time r.m.s. (ns) The time properties of the M1 like chamber don’t seem to change in high rate conditions High voltage (V) Up to a  rate of 8.5 kHz/cm2 (the rate expected in M1R4), the only visible effect is due to the electronics dead time. No evidence of other effects deteriorating the chamber properties.

Single bi-gap: efficiency We also studied he single bigap by turning off the high voltage in the gap C and D Rate/chan = 500 MHz Dead time expected about 2.5 % Rate/chan = 250 kHz Dead time expected about 1.25 % Efficiency in 20 ns (%) Corrected efficiency in 20 ns (%) High voltage (V) Also in this case we can correct by the dead time effect High voltage (V) rate of 3 kHz/cm2 rate of 8.5 kHz/cm2

Single bi-gap: time resolution The time properties of the M1 like chamber don’t seem to change in high rate conditions. Something strange appears at high rate, maybe due to the high dead time Time r.m.s. (ns) High voltage (V)

Comparison: source OFF In the quadrigap and in the single bi-gap the analog signals are added before going to the CARIOCA. The effective gain of the double mono-gap results then to be lower. As we could expect the quadrigap is the best. Time r.m.s. (ns) Efficiency in 20 ns (%) High voltage (V) High voltage (V)

Conclusions Electronics The CARDIAC didn’t shown any strange behavior up to 1.2 MHz/channel which is two times the highest rate/channel expected in LHCb (M2R1) She system controlling the electronics chain worked rather well. MWPC In quadrigap mode: - the quadrigap chamber reach 99% efficiency in 20 ns at 2550 V - up to a  rate of about 10 kHz/cm2 (70% of the M2R1 rate/cm2) no visible efficiency and time performance loss due to space-charge effect. In double monogap mode (M1 like): - 99 % of efficiency in 20 ns is reached at 2650 V (100 V higher than quadri-gap); - for high gain values up to a  rate of about 10 kHz/cm2 (the M1R4 rate/cm2) no visible efficiency loss due to space-charge effect.