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DRS-II results on electron energy scan (Signal integration method)

DRS-II results on electron energy scan (Signal integration method). F.Bedschi, R. Carosi, M.Incagli, F.Scuri. - A summary of what we learned on features and limits of the DRS chip version II by looking at the Cherenkov and the Scintillation electron signals from the

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DRS-II results on electron energy scan (Signal integration method)

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  1. DRS-II results on electron energy scan (Signal integration method) F.Bedschi, R. Carosi, M.Incagli, F.Scuri - A summary of what we learned on features and limits of the DRS chip version II by looking at the Cherenkov and the Scintillation electron signals from the Dream fiber detector during the 1st week of the 2008 test beam. - A detailed study of the electron energy scan. - A quick look on single pion events as a function of energy. Dream Collaboration meeting, Rome, March 16-17, 2009 DRS-II results on electron energy scan

  2. Energy scale calibration done on run 592 – 50 GeV electrons Typical DRS event shape and definition of the integration ranges Peak_cell + 40 Peak_cell + 40 Peak_cell - 15 Peak_cell - 20 Cherenkov signal window = 27.5 ns Scintillation signal window = 30 ns mV x 10 mV x 10 Peak_cell + 80 (Excluding neutron signal window (20 ns) to be used in hadron analysis) Drs cell number Drs cell number } } Peak_cell - 35 20 ns wide window for baseline calculation Peak_cell - 30 20 ns wide window for baseline calculation Peak_cell - 75 Peak_cell - 70 DRS-II results on electron energy scan

  3. Time profile comparison: run 592 – 50 GeV electrons, event 5 Black: Cherenkov Red: Scintillation mV x 10 10%-90% rise time: 5 ns 10%-90% rise time: 7 ns Drs cell number DRS-II results on electron energy scan

  4. Cherenkov vs Scintillation: run 592 – 50 GeV electrons Cut for energy resolution/linearity measurements isol_Ch > 0.9 && isol_Sc > 0.9 DRS-II results on electron energy scan

  5. run 591/592 (50 GeV e-) to set the energy scale ref. for the DRS int’d charge output Gaussian fit Gaussian- Landau convolution fit Entries per GeV Entries per GeV GeV GeV Entries per GeV Entries per GeV DRS-II results on electron energy scan GeV GeV

  6. run 599 (30 GeV e-): Gaussian+Landau fit has a better c2/ndf at lower energies (S) Gaussian fit Gaussian- Landau convolution fit Entries per GeV Entries per GeV GeV GeV Entries per GeV Entries per GeV DRS-II results on electron energy scan GeV GeV

  7. run 601 (100 GeV e-): Gau+Landau and single Gaussian fit return values within 1% Gaussian fit Gaussian- Landau convolution fit Entries per GeV Entries per GeV GeV GeV Entries per GeV Entries per GeV DRS-II results on electron energy scan GeV GeV

  8. Additional remarks for electron runs: - Position scan with 50 GeV electrons – run 313 to run 331 – used for equalization of the single tower response (Q and S) - Electron energy scan with electrons – run 591 to run 623 – used for energy linearity/resolution checks warning ! a) runs at 150 GeV removed because bad beam file was loaded b) runs at 200 GeV removed because of full signal saturation (missing attenuator !) - Electron runs (50 GeV) 589 to 592 used to measure the attenuation on Q1 and S1 (attenuation factor measured to be exactly the nominal 3 dB value) …however: 50 GeV e- in runs 589592 gave a 10% less signal (both C and S) w.r.t 50 e- GeV in run 333 (position scan); attenuation box (with cables) left in the line during data taking at 0 nominal attenuation? (see below) DRS-II results on electron energy scan

  9. Linearity plots Blue : Gaussian fit Red : Gaussian + Landau fit Cherenkov Scintillation Average signal per GeV Average signal per GeV GeV GeV (%) (%) GeV GeV DRS-II results on electron energy scan

  10. Linearity results vs Dream published ones 10-15% non linearity for Scintillation signal almost compatible with published results 8-10% non linearity for Cherenkov signal NOT compatible with published results (tilted calorimeter) NIM A 536 (2005) DRS-II results on electron energy scan

  11. Energy resolution plots 20 GeV 20 GeV 30 GeV 30 GeV 50 GeV 50 GeV 100 GeV 100 GeV Q sideS side Blue: Gaussian-Landau fit Red : Single Gaussian fit NIM A536(2005) 19-51 Table 2 Resolution results NOT compatible with DREAM published values DRS-II results on electron energy scan

  12. Studies on some “features” of the DRS-II response • Several study were done to understand what can be ascribed to the DRS-II • limits/characteristics in order to explain why TB08 electron results do not reproduce • DREAM published performances. • Here are listed the main DRS-II bad characteristics we observed, potentially • dangerous for good energy measurements: • Cherenkov signals always show a decay tail much longer than expected • Baseline average value in pedestal events always significantly lower than • baseline average value in “physics” events with sizable charge accumulation • in the sampling capacitors (even at raw data level) • Baseline average value in “physics” events at the spill start always sizably higher • w.r.t the spill average DRS-II results on electron energy scan

  13. DRS-II problems analysis (1) Issue a): 100 cells = 50 ns t = 5 ns mV x10 mV x10 Log scale t = 30 ns DRS cell number DRS cell number Explanation: according to the Pisa Magic group, the long decay term contribution should be due to the non optimal coupling of the DRS-II chip out of the sampling capacitor/switch system to the ADC in the lines of the mezzanine we used at the TB • Potential source of limitation in measuring the “slow” neutron contribution • Only possible solution we investigated: use a “time profile template” method to subtract/correct for the effect (see F. Bedeschi talk) DRS-II results on electron energy scan

  14. DRS-II problems analysis (2) Issue b) Issue b) Average event baseline always > 10 (1 mV) after subtraction of the average value in the of the pedestal event baseline (baseline spread of ped. events is 5) See issue c) Av. baseline value before signal (mVx10) Progressive event number in the spill Explanation: “physics” events are taken in “bursts” inside the spill at an instantaneous rate which can be much higher than the typical KHz average trigger rate; in this conditions, a not complete cell refresh occurs  partial solution: correct of offline by subtracting, event by event, the average baseline value measured in the cells before the signal rise edge (slide 2) DRS-II results on electron energy scan

  15. Run 599, 20 GeV electrons DRS-II problems analysis (3) Issue c) Events with higher average baseline (>60) concentrate at the spill begin (evt. spill num. < 100) Same behavior in all studied runs (electron and pion energy scan) Av. baseline value before signal (mVx10) • Explanation:(given by all experts – Magic, • Meg, S. Ritt - separately contacted) • When activated at relatively high frequency, • chip internal local temperature slowly grows • and fluctuates around a dynamic equilibrium • Calibration curve changes with temperature, • we did only one calibration at the TB start. • Possible solution, make calibration at dif- ferent temperatures and at each run start • (not practical, very long procedure); store • board temperature during data acquisition • (not done during 2008 TB !) Progressive event number in the spill Run 599, 20 GeV electrons Av. baseline value before signal (mVx10) DRS-II results on electron energy scan Progressive event number in the spill

  16. DRS-II calibrations curves Typical shapes: linear region  200 – 700 mV ADC counts T- T+ (after off-set - 2048 – subtraction) DAQ input level (mV) Pedestal values fall in a non-linear region, difficult to correct for temperature drifts…. DRS-II results on electron energy scan

  17. Electron energy scan: linearity vs event category Scintillation CherenkoV Average signal per GeV Average signal per GeV GeV GeV Red : all eventsBlue: first events in the spill • Just a slight improvement in the scintillation case when selecting events • at the spill begin (progressive event number in the spill < 100) • The average signal is almost systematically lower for the first events in the • spill, consistent with a shift to higher values of the chip internal temperature • after the spill start …. A much more sizable effect seen on the energy resolution (next slide…) DRS-II results on electron energy scan

  18. Electron energy scan: resolution vs event category 20 GeV 20 GeV 30 GeV 30 GeV 50 GeV 50 GeV 100 GeV 100 GeV 100 GeV 50 GeV 30 GeV 20 GeV Q sideS side Blue: all events Red: only events with ave. baseline value > 60 NIM A536(2005) 19-51 Table 2 DRS-II results on electron energy scan

  19. Then I started to look at pions …. …and I met other problems! As a first exercise I have analyzed just one run per energy point: - Run 431 : 20 GeV pi- - Run 406 : 50 GeV pi- - Run 381 : 100 GeV pi- - Run 343 : 200 GeV pi+ DRS-II results on electron energy scan

  20. Q and S measurements… 100 GeV p- No leakage correction NIM A537 Q/S ratio DRS Leakage corrected 10% average S correction due to leakage <S>DRS: +10% <Q>DRS: + 7% DRS-II results on electron energy scan

  21. Something is changed just before the electron energy scan! (maybe some attenuation left for the S and Q central towers) <Q>333 +4% Entries per GeV Entries per GeV Run 333 Run 591 GeV GeV <S>333 +9% Entries per GeV Entries per GeV Run 591 Run 333 GeV GeV DRS-II results on electron energy scan

  22. Use 50 GeV electron run 333 (position scan) for Q and S response equalization in hadron run instead of run 591/592 (50 GeV electrons, energy scan) !! +2.5% Entries per em GeV +4% Signal (em GeV) DRS, TB 2008 100 GeV p- NIM A537 DRS-II results on electron energy scan

  23. Pion energy resolution before applying any correction DRS TB 2008 10% events saturated DRS NIM A537 Blue: Cherenkov Red : Scintillator 300 GeV pions, all runs: 100% events saturated No attenuator !! Events at the spill begin tend to give better resolutions as In the electron case. Check with the full statistics DRS-II results on electron energy scan

  24. Some check before applying the Q/S method….. S = c Q + (c-1) E P0 = (c -1) E, P1 = c 100 GeV p- <Scorr > (GeV) • = P1 = 0.57 c = P0/E – 1 = 0.47 Cherenkov signal (GeV) c Dream published (NIM A537) DRS-II results on electron energy scan

  25. Leakage correction works, more or less, as in NIM A537 +10% correction on the average in both cases, higher R.M.S for DRS… DRS, TB 2008 Which h/e (c) values should I use to compute fe.m. and to apply the Q/S method? Entries per GeV NIM A537 DRS-II results on electron energy scan

  26. Moving to the (Q+S)/E method… NIM A537 Good agreement in this case! <S> DRS-II results on electron energy scan

  27. …..I WILL STOP HERE WITH PIONS. TOO MANY THINGS I HAVE NOT YET UNDERSTOOD….. (see Franco’s talk for pions) DRS-II results on electron energy scan

  28. Conclusions from electron (and pion) energy scan analysis • - DRS version II confirmed many limits, partially already known… •  Strong non linear response •  calibration high sensitivity to chip internal temperature drift •  not complete cell refresh at relatively high (>1 KHz) trigger frequency • By isolating event categories less sensitive to the temperature drift (spill begin) • and by off-line correcting for non linearity and baseline fluctuations:  energy linearity and resolution results with electrons approach the Dream published performances - Analysis of the energy scan with pions shows problems others than DRS limits (see also F. Bedeschi talk) - The DAQ system used at 2008 TB and based on MAGIC mezzanines hosting the DRS-II chips was operationally reliable, however….  The relatively long tail observed also for the Cherenkov signal decay (not optimi- zed coupling of the DRS capacitor outs to the ADC) required careful treatment in the measure of the scintillation signal (see F. Bedeschi and M.Incagli talks) • Non-linearity, sensitivity to the temperature drift, and cell incomplete refresh should • have been moderated in the version IV of the DRS chip; it should be useful to prove • it in a next Dream T.B. (see F. Scuri talk) DRS-II results on electron energy scan

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