ZDC Time Measurements

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# ZDC Time Measurements - PowerPoint PPT Presentation

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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Presentation Transcript
ZDC Time Measurements

Signal alignment:

(PHOS4, 1 ns step)

A. Poblaguev ZDC Meeting

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

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

A1/A2vs A2

A. Poblaguev ZDC Meeting

Signal “saturation” ?

PMT

PMT

A. Poblaguev ZDC Meeting

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

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

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

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

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

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