2. 1 Cosmic Ray Test Stand with Scintillating Cells for Digital Hadron Calorimeter 06/23/2003 Kurt Francis - Northern Illinois University

3. 2 Introduction At NICADD we studying technology for the design of a Digital Hadron Calorimeter using scintillating cells As a first step we built a cosmic ray test stand with 2 layers of 7 hexagonal scintillating cells (9.4 cm 2 x 5mm thick BC408 with sigma groove, painted white) Light from the 14 cells is fed through optical fibers into a 16 channel PMT The analog electrical output of the PMT is digitized with a VME bus QDC and then read into a PC

4. 3 Multi-Channel PMT Cosmic Ray Test Stand 14 Hexagonal Cells and Optical Fibers connected to 16 channel Hamamatsu H6568 Multichannel-PMT Multi-Channel PMT Top view Side view

5. 4 COSMIC RAY TEST STAND TRIGGER COUNTER #1-set of 7 cells ganged to one single channel PMT TRIGGER COUNTER #2 TRIGGER COUNTER #3 14 cells connected to 16 channel PMT to collect comic ray data under investigation BLOCK OF PASSIVE ABSORBER MATERIAL (STEEL, BRASS, LEAD) NUCLEAR INTERACTION LENGTH ~ 1.5 LIGHT PROOF BOX

6. 5 Software Used National Instruments LabView to create software to collect data from 32 channel VME QDC Data is dumped into a flat data file Wrote my own software to view and analyze data –used Microsoft Visual Basic –displays histograms or scatter plots –plots can be arranged by cell or by PMT channel Also used Excel, Origin, JAS, and PAW

7. 6

8. 7 First Layer of CellsSecond Layer of Cells SCATTER PLOTS

9. 8 First Peak: Crosstalk? Initial Observations: Data collected has two curves to right of pedestal. What is first peak?

10. 9 Channel 4 Not Isolated First step isolate a channel Channel 4 isolated from other channels by black paper between cells and by covering all but ch4 photocathode with black paper

11. 10 Crosstalk Isolating a single channel from others reduces the first peak - indicates the first peak is caused by crosstalk from the other cells / channels Crosstalk can be: –Optical crosstalk between cells –Optical crosstalk at PMT due to photocathode cover –Electrical crosstalk at PMT

12. 11 3 6 2 4 8 7 5 14% 10% 11% 15% 5% 10% 5% 13%8% 6% 8% 7% Standard Configuration with no black paper Cells 5,8,6 covered by black paper and layers separated by paper Crosstalk at cells evaluated by covering some of cells with black paper. Note: this apparently weak cell (#5) was later found to be due to the ADC channel Cell numbering scheme Number on cell is percent of total events in first peak -->Suggests Optical crosstalk at cells can be reduced by isolating cells with black paper

13. 12 Scatter plot of all PMT channels with Channel 4 stimulated by several fibers driven by LED -Other channels are not connected -Cells are not connected -->Suggests crosstalk at PMT Crosstalk at PMT evaluated by covering all but one channel.

14. 13 Another way to view crosstalk at PMT In this case only channel 4 is connected to a cell collecting cosmic ray data - all other channels have crosstalk from channel 4

15. 14 Summary of crosstalk issues Part of crosstalk is optical crosstalk between cells –Initially used cells painted in white paint to reflect light back into scintillator –We can reduce optical crosstalk by covering cells with black paper –Another option would be to paint cells with black paint A greater part of crosstalk occurs at the PMT –Probably due to optical diffusion in the photo-cathode cover –This crosstalk is significant only on adjacent channels

16. 15 Finding the single photo-electron peak for a single channel Use 2,3,4,5 layers of neutral density gelatin filter material –(Kodak No.96 N.D. 0.20 = 63% transmission) Stimulate with an LED channeled through optical fiber Start with 2 layers of filter -> get peak far from pedestal Increase filter layers -> pedestal appears and grows, Position of peak moves closer to pedestal, shrinks and merges with pedestal When the position of the peak stops changing as filter layers are added then moving closer top pedestal then we have found the single photo- electron peak

17. 16 Example using channel 4/20

18. 17 --> plots with 4 - 8 filter layers is approximately flat and linear - expected for the single photo electron peak

19. 18 --> Indication of ‘gain’ for that particular channel Single Photo-Electron Map Single Photo-electron peak

20. 19 Light Yield Map The light yield for the cell/channel combination is equal to the ADC Counts from the pedestal of the MIP peak (determined from cosmic ray data sets) divided by the ADC Counts from pedestal of the S.P.E peak (determined from the LED with filter layer tests as described on the previous slides)

21. 20 Range of a factor of 2

22. 21 Summary NICADD has developed a cosmic ray test stand using scintillating cells to prepare for DHC The test stand reveals crosstalk –Optical crosstalk between cells - can be reduced by isolating cells with black paper or paint = 30 to 40% of total crosstalk –Crosstalk at PMT (probably optical) = 60 to 70 % of total Can use LED driven by pulse generator and layers of filter material to find Single photo-electron peak (S.P.E.) S.P.E. and M.I.P. average can be used to determine light yield cells The light yield has a range of 8 to 17 P.E.