Fe55 Longitudinal Measurements In Straw Tracker Prototype Tom-Erik Haugen, David Brown, Richard Bonventre, Andrew Edmonds.
Straw Tracker • 5mm straw made of 15µm thick aluminum • Filled with ArCO2 and held at high voltage 2
Straw Tracker • 5mm straw made of - + - - 15µm thick aluminum + + -- + + • Filled with ArCO2 and - + - + - - + + held at high voltage • Signal amplified in gas 𝑓 − 3
Straw Tracker • 5mm straw made of 15µm thick aluminum • Filled with ArCO2 and held at high voltage • Earlier signal Signal amplified in gas Later signal propagation • Signal sent through propagation integrating amplifiers then to TDC and ADC • End result of gain and time difference 4
Prototype Setup • 8 straw prototype with a preamp on each side • Straws 0 and 1 preamps don’t work • Particle crosses straw, signal travels down to each end of straw • Time difference from each end gives longitudinal position of track through straw 5
Longitudinal Measurements Measuring along z-axis (z = 0 at center of straw). Measure signal from Fe55 source with straws at 1250 Volts Signal size using Fe55 at 1250V is the same as MIPs at 1425V Measurements along z axis should show attenuation and resolution effects 6
Fe55 Signal Peak Minus Pedestal Signal is recorded once it passes threshold. Both ends of straw are summed It is recorded in 16 samples, the first 4 are presamples. Peak of signal minus pedestal (average of presamples) forms this characteristic shape. 7
Means from Gaussian fit Plotting the mean of the gaussian shows outliers on all straws except for straw 3 and 7 8
Asymmetric Signal Measuring peak minus pedestal from only +z side (HV side) and -z side (cal side) of straw. This is physical and expected that signal is larger when measured closer to event Using the difference of the means and the sum of the means we can calculate the attenuation 9
Attenuation Sum of signals Difference of signals Subtracting the mean value from the positive z side from the negative z side The sum of signals shows a clear dip at z = 0 is potentially from straw aging. Sum is expected to be independent of z to first order. Straw 3 and Straw 7 show very clear linear difference, straw 5 shows outlier at 87.5 10
Attenuation Length 𝑀 2 +𝑨 𝐵 𝑑𝑏𝑚 𝑨 = 𝐵 0 𝑑𝑏𝑚 𝑓 − 𝜇 Modeling Attenuation as an exponential 𝑀 2−𝑨 Dividing the sum of both ends divided 𝐵 𝐼𝑊 𝑨 = 𝐵 0 𝐼𝑊 𝑓 − 𝜇 by the slope of the difference gives the attenuation length. Straw 3: 4.84 ± 0.20 meters Σ𝐵 𝜇 = 𝜖 𝜖𝑨 Δ𝐵 Straw 5: 4.97 ± 0.21 meters Straw 7: 4.33 ± 0.14 meters 11
One straw deltaT Plot of the time difference between both ends of the straw. Taking the gaussian fit provides a mean and sigma 12
One straw deltaT Plot of the time difference between both ends of the straw. Taking the gaussian fit provides a mean and sigma Straw 4 showed much worse resolution than all of the other straws 13 13
Gaussian Mean Plotting the z position versus the gaussian mean acts linearly Slope of line is half of effective propagation velocity Data shown was taken at 1250V v eff = 193.64 ± 39.24 mm/ns or 0.65c with 6.5% RMS variation between straws 14
Effective velocity Running the same analysis at other voltages shows very different propagation velocities (variations up to 50%). v eff = 0.43c v eff = 0.67c v eff = 0.76c 15
Signal Spread + Threshold Reduces V eff D Z V eff = < V prop Original current pulse D Z V prop + T thresh V prop Broadened pulse HV Cal Straw Threshold Threshold T Thresh 55 Fe source 16
Changes in Velocity Effective velocity versus gain shows a clear drop off effect. Signal is expected between 400 and 500 peak - pedestal counts, in the region where variation is small. 17 17 17
Z resolution Multiplying deltaT sigma by the velocity gives the longitudinal position resolution This does not accommodate asymmetric tails or any effect of slewing 18
Resolution vs Voltage Plots of the core resolution: Black = 1425V Cyan = 1250V Red = 1200V Blue = 1150V All straws except straw 4 show better resolution at higher voltage We have not had time to study these variations in detail
Backup Slides 20
Tracker Design Individual straw Prototype panel of 98 straws 6 panels to a plane 18 stations in tracker 21
Sum of both signals and difference of signals 22
5 Positions Along z Measurement of peak minus pedestal at 5 positions along straw. Small variations in straw 3 are expected due to attenuation Straw 5 shows a clear outlier at Z = 87.5mm 23
Mapping out Straw 5 at z = 87.5mm Measuring with 10 mm intervals around 85mm Anomalous region has length of about 40mm 24
Reducing Source Rate at z = 85mm Moving the Fe55 source further away to reduce the rate from 187 kHz to 1.1kHz Peak minus pedestal returns to normal shape Rate dependent gain 187 51 21 11 3.5 1.1 rate (kHz) loss is consistent with charge accumulation inside the straw 25
G4 charge accumulation Andrew Edmonds: Using Fe55 at 50kHz rate gives a current of 0.18 μA/cm Blue histogram shows full range of currents expected from backgrounds in Mu2e experiment 38% of straw-cms have large enough currents to produce significant gain losses 26
Loss of Metalization Second batch of straws produced showed loss of metalization. According to Bob Wagner the straws used in the LBL prototype were from batch 2 Batch 3 did not show this problem of metalization inner liner from PPG batch 2 straw showing traces of metal removed from the straw inner wall (photo courtesy of Bob Wagner) 27
Calculating velocity Δt = t 1 − t 2 Δt = 𝑒 1 − 𝑒 2 𝑒 1 𝑒 2 𝑤 𝑓𝑔𝑔 𝑤 𝑓𝑔𝑔 Δ𝑢 = 𝑨 𝑓𝑜𝑒 − 𝑨 − 𝑨 − 𝑨 𝑓𝑜𝑒 𝑤 𝑓𝑔𝑔 𝑤 𝑓𝑔𝑔 𝑨 −𝑨 𝑓𝑜𝑒 𝑨 = 0 +𝑨 𝑓𝑜𝑒 𝑤 𝑓𝑔𝑔 = 2 ∗ 𝑨 Δ𝑢 28
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