PreShower Characterisations Pulse shape study with a cosmic bench Test beam results Set-up Pulse shape characteristics Dependence on pulse height Pedestal stability Photoelectron statistics Dispersion of PMT gains Effects of HV changes Half-channel relative gains Uniformity in a cell Cross talk Additional cross talk studies Cell to cell cross talk Electronic cross talk

Pulse shape study with a cosmic bench Set-up 16 cells of 12 12 cm2 3 m clear fibres Mono-anode R5900 PMT RC = 100   50 pF = 5 ns Results 0 ~ 70 % (i = Si / STOT ) 65-75 % according to channel For maximal 0 : -1 ~ 1-2 % Main exponential decay  ~ 9-11 ns according to channel RC non negligible Affects pulse raising time Small long term component  > 200 ns Perhaps delayed fluorescence Non negligible beyond 50 ns

Test beam set-up 16 cells of 12 12 cm2 80 cm WLS fibres 3 m clear fibres 64 multi-anodes PMT 64 channels VFE prototype Load resistors : R = 150  Readout capacity : C ~ 10 pF RC ~ 1.5 ns 22m Ethernet cables 16 channels FE prototype 1 V  1000 ADC counts First time used in test beam Time jitter of 3.5 ns (min to max)

Pulse shape characteristics 100 GeV Pions / no lead / HV = 800 V Scan integration time from 0 to 24 ns Similar responses for all channels Time position of maximal 0 within ± 1 ns Non zero -1 for maximal 0 Slight discontinuity at replication time Integrator dead time ~ 1 ns Effective integration time ~ 24 ns In Ernest Simulation For maximal 0 0 higher of ~ 7 % 1 in agreement 2 lower of ~ 3 % 3 lower of ~ 2 % Long term component only in data

i distributions ? No peak at 0 for 2 and 3 The 0 photoelectron peak is at 0 in the simulation Not in data : pedestal shift ? ?

i values Compatible with cosmic bench  = 1 / 0  [15.6 % ; 22.5 %] Lower RC  Higher 0  = 1 / 0  [15.6 % ; 22.5 %] Min (%) Max (%) Mean(%) -1 0.2 1.0 0.4 0 68.9 76.7 73.6 1 12.0 15.5 13.8 2 HIGH 4.0 7.6 6.0 2 LOW 2.3 2.9 2.6 3 1.3 2.0 1.7

Long term component : pedestal shift ? < 6 > = 0.83 % 6 distribution : pedestal shift rather than delayed photoelectrons Also seen with LED on one cell Pedestal shift on other channels  here -1 ADC count (worst case) No PM cross talk No PS cross talk Not the same chip

Pulse shape dependence on pulse height Look at  and  variations with pulse height (NADC) To change pulse height Change HV keeping MIP signal  and  are constant Change signal using electrons keeping HV  increases and  decreases (almost linearly) The effect is coming from the PMT Studied as a function of the maximal PMT output current (output current for 100 MIPs) Electron data for various HVs 100 MIPs 100 MIPs

Pulse shape dependence on pulse height (2) The maximal variations of  and  other the full dynamic range are respectively 100 MIPs - MIP 100 MIPs - MIP These maximal variations depends almost linearly on the output current at 100 MIPs Limiting to 1 mA leads to a maximum of 6 % for both  and  Should be lower with the new PMT basis m m

Pedestal Stability 8 hours measurements Mean pedestal ADC counts 8 hours measurements Mean pedestal Stable within  0.1 ADC counts Noise ~ 0.7 ADC counts Stable within  0.05 ADC counts

Photoelectron statistics Measure of the number of photoelectron / MIP Using only MIPs NPE / MIP = (MIP / MIP ) 2 Scaling MIPs to a large LED pulse LED distribution has a gaussian shape NPE / MIP = NPE / LED  (MIP / LED ) Compatible results obtained with the two methods 100 GeV Pions / no lead / HV = 800 V LED / HV = 800 V

Number of photoelectrons and PMT gains < NPE / MIP > = 15. 3 From 10 to 20 PMT gains for the different channels GMAX / GMIN = 2 HV changes The different channels should have the same behaviour (to preserve uniformity) Checked on 4 cells G750V / G650V  7 G650V / G550V  7

Half-channel relative gains Odd/even half-channels Gain differences ~ 5 %

Uniformity in a cell • PS CELL 50 GeV Pions 49 measurement points BEAM 1 2 3 4 5 6 7 8 9 PS CELL 50 GeV Pions HOR  1 cm VER  1.6 cm Muon contamination  1 % (  10 cm) 49 measurement points Each 2cm (horizontal  vertical) RMS of pool distribution = 1.35 Pool distribution with a RMS of 1 introducing a non uniformity of (1.3  0.6) % BEAM

Uniformity in a cell (2) Pool distribution is gaussian No obvious behaviour on a 2D analysis Pool distribution measured assuming 1.3 % of non-uniformity (49 entries) Gaussian ( = 0 ;  = 1 ; 49 entries) 2  cells

Cross talk 100 GeV electrons Beam on cell C12  2.5 % of cell to cell cross talk Total PMT cross talk  18 % Channel repartition depends on mask set up Up to 6.4 % (4.3 %) in June (August) Globally, ¼ of the light is lost by cross talk From 20 to 15 photoelectrons per MIP

Cross talk results PS PMT BEAM June August (August) C13 2.4 C15 1.5 3.4 C14 2.0 C9 1.6 C11 3.7 C12 100 C10 2.2 C6 1.2 C8 C7 C5 0.8 C2 0.1 C4 6.4 C3 0.4 C1 1.8 C13 2.9 C15 1.7 C16 2.5 C14 4.0 C9 1.5 C11 3.2 C12 100 C10 2.4 C6 1.1 C8 1.9 C7 2.2 C5 0.9 C2 0.2 C4 C3 0.4 C1 4.3 PS BEAM June August C7 2.4 C6 1.2 C3 0.4 C2 0.1 C8 C4 6.4 C9 1.6 C11 3.7 C1 1.8 C12 100 C13 C10 2.2 C5 0.8 C14 2.0 C15 1.5 C16 3.4 C7 2.2 C6 1.1 C3 0.4 C2 0.2 C8 1.9 C4 1.7 C9 1.5 C11 3.2 C1 4.3 C12 100 C13 2.9 C10 2.4 C5 0.9 C14 4.0 C15 C16 2.5 PMT (August)

Cell to cell cross talk In Clermont cosmic bench Light coming from a LED Installed very carefully on the cell surface and very well isolated so that there is no light leakage at the LED level Dedicated PMT mask to read only one fibre with the mono-anode R5900 PMT No cross talk at PMT mask ~ 2 % cell to cell cross talk measured Compatible with test beam results

Electronic cross talk Set-up Result Reproduce all the electronic chain from the output of the PMT to the input of the FE board Result Up to 1% cross talk between neighbouring channels at VFE output Where does this cross talk come from exactly ? To be investigated Not from the chip : already measured in standalone mode (cross talk ~ few ‰) Better with the new VFE board ? Perhaps because smaller 10 9 19 17 18 26 25 27 f8 100 f7 0.3 1.0 f6 0.7 f5 f4 f3 f2 f1