1. s 1 Summer Student Sessions 13 August 2008 Chew Soo Hoon University Of Malaya, Malaysia (caseycsh@cern.ch) Jan Stark LPSC, Grenoble, France (stark@in2p3.fr)

2. CERN has just announced the start- date for LHC! Unhappy channels in the ATLAS LAr calorimeters One major issue that keeps everyone busy for these few months… 2 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters

3. LAr forward (Fcal) Tile barrel Tile extended barrel LAr electromagnetic barrel LAr electromagnetic end-cap (EMEC ) LAr hadronic end- cap (HEC) 3 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters Hadronic Calorimeter Endcap (Cu-LAr) Electromagnetic Calorimeter Barrel,endcap (Pb-LAr) Forward Calorimeter Endcap (W, Cu-LAr) LAr is the ‘active’ medium and the Pb, Cu and W are absorbers

4. ~ fC ~ µV The signals detected by LAr calorimeters are very small ( ~ fC or ~ µV)…So, huge amplification is needed. 200 kThere are about 200 k readout channels in the LAr calorimeters… Special attention is needed to solve this problem. Lists of unhappy channels have been discussing in many meetings. 4 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters 25nsThe bunch crossing time=25 ns ~ 450 nsBut, the drift time in the LAr gap ~ 450 ns 1 2 3

5. 5 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters Front-end board is read with no input signal to detect noise. Front-end board LAr cell electrodes collect the ionization electrons The preamplifier amplifies the current signal The CR-RC2 shaping filter shapes the amplified signals in 3 gains The SCA stores the signals samples in analogue format The trigger will select the samples to be digitized Ionization signal Shaped signal

6. 6 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters We wrote a program and displayed the rms values for the empty detectors in histograms to hunt for the unhappy channels!

7. 7 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters Icell layer ieta iphi region barrel or ec pos or neg FT slot channel gain ped rms detector 11060 1 116 19 0 0 0 6 3 52 0 974.349 11.2143 0 13202 1 274 17 0 0 0 7 6 18 0 944.784 30.2519 0 31093 1 245 60 0 0 0 17 5 117 0 944.236 13.3464 0 39679 1 63 50 0 0 0 22 2 127 0 983.196 10.7274 0 47604 1 436 42 0 0 0 26 8 116 0 934.201 17.025 0 47605 1 437 42 0 0 0 26 8 117 0 916.555 17.8317 0 47606 1 438 42 0 0 0 26 8 118 0 934.462 17.6548 0 47607 1 439 42 0 0 0 26 8 119 0 951.01 17.2807 0 61640 1 264 5 0 0 1 2 6 72 0 967.332 21.1794 0 68987 1 379 13 0 0 1 6 7 123 0 934.017 17.2334 0 95734 1 310 43 0 0 1 21 6 118 0 965.97 10.401 0 113029 1 5 62 0 0 1 31 2 5 0 952.183 14.8943 0 145444 1 36 46 2 1 0 19 2 36 0 986.41 10.5099 0 153767 1 31 34 3 1 0 24 5 39 0 968.51 11.6612 0 178351 1 63 36 4 1 1 14 7 47 0 992.54 11.8433 0 184619 1 59 44 4 1 1 18 7 43 0 945.703 14.459 0 315531 3 4 29 0 1 0 3 7 11 1 947.216 11.1312 1 315570 2 7 31 0 1 0 3 7 50 1 991.372 12.198 1 326890 2 2 1 0 1 0 10 6 106 1 949.995 13.4252 1 336547 3 6 63 0 1 0 16 7 35 1 992.161 45.2964 1 336551 3 6 62 0 1 0 16 7 39 1 973.108 10.9021 1 336563 3 7 63 0 1 0 16 7 51 1 1012.84 18.8718 1 336655 3 4 52 0 1 0 16 8 15 1 988.347 10.6762 1 346250 2 4 37 0 1 0 22 8 10 1 944.161 13.5916 1 346266 2 5 37 0 1 0 22 8 26 1 952.744 16.1664 1 346302 2 7 36 0 1 0 22 8 62 1 980.425 12.5365 1 355842 2 4 8 0 1 1 3 8 2 1 1001.42 16.2463 1 It agrees well with the list obtained in the meeting!

8. So, we wrote another program and obtained the plots. 8 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters ADC counts Number of events ADC counts Number of events ADC counts two humps???

9. 9 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters ADC counts Number of samples The normal noise signal Look for the noise frequency which has the same pulse pattern… ADC counts Number of samples The abnormal noise signal (from the plot which has two humps) ADC counts Number of samples 10 MHz ADC counts Number of samples 30 MHz ADC counts Number of samples 19.2 MHz

10. ~19.2 MHz We suspected the noise is resulted from the power supply which has a frequency of ~19.2 MHz. 10 S. H. Chew Noise in the Readout of ATLAS LAr Calorimeters The answer is yet to be found out…