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ZDC Time Measurements

ZDC Time Measurements. Signal alignment: (PHOS4, 1 ns step). What time do we measure?. In ideal case: t = 0 (collisions and readout are synchronized with clocks) . t = t beam + t clock + t ZDC + t calibrations. IP fluctuations t beam = τ 0 + τ z

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ZDC Time Measurements

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  1. ZDC Time Measurements Signal alignment: (PHOS4, 1 ns step) A. Poblaguev ZDC Meeting

  2. What time do we measure? In ideal case: t = 0 (collisions and readout are synchronized with clocks) t = tbeam + tclock + tZDC + tcalibrations IP fluctuations tbeam = τ0 + τz (τz=z/c – time of flight effect) tAbeam = τ0 + τz tCbeam = τ0 - τz Clock fluct. in PPM generally: tPPM1 ≠ tPPM2 <tPPM1tPPM2> ≠ 0 Actual ZDC contribution: tZDC = tPMT+Cable + t digitization Ampitude → Time Conversion Can not distinguish t = tarm + tchn <tarmtchn>= 0 → σ2 = σ2arm + σ2chn A. Poblaguev ZDC Meeting

  3. Signal Shape Mean = <An/A2> Slope = d <An/A2> /dt = Mean(t=1 ns)-Mean(t=0 ns) High Gain Channels. 400 < A2 < 980 (cnts) A. Poblaguev ZDC Meeting

  4. A1/A2vs A2 A. Poblaguev ZDC Meeting

  5. Bad small PMT channels Signal “saturation” ? PMT PMT Readout Error A. Poblaguev ZDC Meeting

  6. Time Correlations t77vs t73 Chn 73 – ZDC A, HM1, Big PMT, High Gain Chn 77 – ZDC A, HM2, Big PMT, High Gain Time resolution is better than signal time fluctuation! σ2t73-t77 = 0.30 ns (two big PMT’s in one arm) σ2t73-t101 = 0.31 ns (big PMT vs small PMT in one arm) σ2t73 -t9 = 0.38 ns (two big PMT’s in different arms) ? Expected σbeam σclock ? σarm ≈ 0.35 ns ≈ 0.20 + 0.30 σchn ≈ 0.20 ns A. Poblaguev ZDC Meeting

  7. ZDC Signal Time Correlations t77vs t73 The following high gain channels where tested: Chn 9 – ZDC C, HM1, Big PMT Chn 13 – ZDC C, HM2, Big PMT Chn 73 – ZDC A, HM1, Big PMT Chn 77 – ZDC A, HM2, Big PMT Chn 101 – ZDC A, HM1, Small (coordinate) PMT Signal Energy Range 250 – 600 GeV Assumptions: t1,2 = T1,2 + τ1,2, where Ti actual signal time , and τi is error of measurements < Tiτi > = 0, <T1T2> = Σ2, < τiτi > = σ2i T1 = T2 (ΣT1-T2 = <T1T2>will be estimated for correlation between arms) t– = (t2 – t1) / √2 → σ– ≈σ1,2 A. Poblaguev ZDC Meeting

  8. Estimation of Time Resolution Ch73 -Ch77 Ch73 -101 Ch 9 –Ch13 Ch 9 -Ch73 σZDC≈ 0.20-0.25 ns Σ≈ 0.35 ns ΣT1-T2≈ 0.10 ns A. Poblaguev ZDC Meeting

  9. ZDC A. Gain Calibration. 3.5 TeV ? Big PMT, Low Gain calibration C1 = 6.0 GeV/cnt C2< 7 GeV/cnt C3< 35 GeV/cnt A. Poblaguev ZDC Meeting

  10. ZDC C. Gain Calibration. 3.5 TeV ? Big PMT, Low Gain calibration C1 = 6.3 GeV/cnt C2< 18 GeV/cnt C3< 23 GeV/cnt A. Poblaguev ZDC Meeting

  11. Summary • All channels are aligned with accuracy ≈ 1 ns. • Time calibration was tested. • Actual ZDC time resolution is ≈ 0.2 ns. • Gains in both HM1 are equal. • ZDC has reasonable setting (gains, delays, pedestals). • Do we need delayed PMT channels ? • We have to find all “bad” channels. • Why A1/A2 depends on A2 (if A2>200 cnts in Low Gain channel) ? • Is amplitude measurement linear? • How to calibrate gains in HM2 and HM3? • Where 0.3 ns time fluctuations come from? A. Poblaguev ZDC Meeting

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