Total γ Beam Absorption Cross Section
for TAC and e+e- Runs with Si Target
Runs used:
TAC run 065014 (with Si target)
TAC run 065106 (empty target)
e+e- run 065102 (with Si target and TAC in)
e+e- run 065103 (empty target and TAC in)
For discussion: preliminary results for the following TAC runs:
065063 (with Si target)
065064 (empty target)
Overview
Analyze TAC runs and e+e- runs and compare extracted total
cross sections
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Total γ beam absorption cross section calculations
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Event selections to minimize biases
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Discuss the following items:
- preliminary results on additional TAC runs (Si target)
- TAC ADC spectrum and TAC to Tagger energy ratio for TAC run
065061 (with C target)
- Monte Carlo corrections (Ilya Larin)
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Summarize results and details for future analysis
Difference Between TAC and e+eRuns
TAC Runs 065104 (Si target) and 065106 (empty target):
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B = ~ │0.1643│kG
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Pair Spectrometer Current = │250│A
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Beam Current = 250 pA
e+e- Runs 065102 (Si target) and 065103 (empty target):
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B = ~ │1.980│kG
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Pair Spectrometer Current = │3185│A
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Beam Current = 250 pA
Total γ Beam Absorption Cross Section
σtot = -A/(NAρx)*ln(Nγout/Nγinc)
Nγout= TAC events with Si target
Nγinc= total events with Si target / absolute tagging ratio
absolute tagging ratio = TAC events (empty) / total events (empty)
A = Si atomic mass ( 28.0855 g/mol )
NA = Avogadro's number (6.022e23 mol-1)
ρ = Si target density ( 2.316 g/cm3 )
x = Si target thickness ( 1.0015 cm )
Statistical Errors
Let Nε = NST/ NTT and Nβ = NSE/ NTE
NST= TAC events Si target
NTT= total events Si target
NSE= TAC events empty target
NTE= total events empty target
Let α = Nε / Nβ
σ(Nε) = √ (NTTNε(1-Nε)) with error δ(Nε) = σ(Nε)/NTT
σ(Nβ) = √ (NTENβ(1-Nβ)) with error δ(Nβ) = σ(Nβ)/NTE
propagated error δ(α) = √( (∂α/∂Nε)2(δ(Nε))2 + (∂α/∂Nβ)2(δ(Nβ))2 )
Systematic Errors
Due to an uncertainty in the amount of atoms in the Si
target, there is a systematic error contribution from the
density and thickness of the target.
Information was obtained in PrimEx Notes 69.
Fractional uncertainty for Si target measurements was
found to be ± 0.35%.
It should be noted that more items in systematic error
budget will be added.
TAC TDC counts and TAC ADC
counts for Run 065106
TAC TDC and ADC counts shown for T counter 10
TAC TDC Spectrum Run 065106
TAC TDC spectrum (log scale) shown for T counter 10
Time Difference between TAC and
Tagger
Events were selected if time difference between TAC and Tagger
TDC hits < 3 ns, to minimize accidentals
TAC ADC Spectrum Run 065106
(empty target)
TAC ADC spectrum shown for T counter 10
TAC Energy to Tagger Energy Ratio
(empty target)
Events were selected if calibrated ratio > 0.62, to minimize biases
TAC Energy to Tagger Energy Ratio
(with Si target)
Events were selected if calibrated ratio > 0.62, to minimize biases
Total γ Beam Absorption Cross Section:
TAC 065104 and 065106
e+e- 065102 and 065103
Energy = 5.279 GeV
Energy = 4.373 GeV
*systematic errors not shown
**error not shown on NIST, needs further investigation
Discussion on TAC Runs 065063
and 065064
Further analysis was conducted on the following runs:
TAC run 065063 (with Si target)
TAC run 065064 (empty target)
Total γ Beam Absorption Cross Section:
TAC 065104 and 065106
TAC 065063 and 065064
Energy = 5.279 GeV
For 0651064/065106 Beam current = 250 pA
Energy = 4.373 GeV
For 065063/065064 Beam current = 100 pA
Discussion on TAC run 065061
(with C target)
Comparison between TAC ADC spectrum for T counter 1 and T counter 19
Discussion on TAC run 065061
(with C target)
TAC Energy to Tagger Energy Ratio
Discussion of Monte Carlo Corrections
(Ilya Larin)
Summary
1) The total γ beam absorption cross section was extracted for each T counter (1-19)
using information from TAC runs 065104 (with Si target), 065106 (empty target) and
e+e- runs with TAC in 065102 (with Si target), 065103 (empty target)
2) Results were shown for TAC runs 065063 (with Si target) and 065064 (empty
target), but warrant further investigation due to discrepancies between total γ beam
absorption cross section values for other runs
3) Future analysis will follow a similar process for total cross section extraction from
TAC and e+e- runs with the carbon target. I am currently waiting for exact
measurements on carbon target used in PrimExII to proceed with this item
4) More items in systematic error budget
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Tagging ratio stability will be investigated and added
Systematic contributions related to TAC efficiency and events 'returned' from Bremsstrahlung and Compton