various rupak mahapatra (for angela, joel, mike & jeff) timing cuts
DESCRIPTION
General Idea Nuclear Recoil Band based on Yield Recoil Energy (keV) Z2/Z3/Z5 20 keV 10-40% Z Reduced ionization collection and fast rise timeTRANSCRIPT
Various
Rupak Mahapatra(for Angela, Joel, Mike & Jeff)
Timing Cuts
Different Timing Cuts
• 2-D pminrtc & pdelc: Angela• 2-D pfracc & pdelc: Rupak/Joel• 4-D 2 pfracc, pminrtc, pdelc & y: Rupak/Joel• 2-D Neural Net pfracc & pdelc: Mike A• Technique presentation (2 ): Jeff
General IdeaNuclear Recoil Band based on Yield
Recoil Energy (keV)0 10 20 30 40 50 60 70 80 90 100
1.5
1.0
0.5
0.0
Z2/Z3/Z5
20 keV10-40%
Z
Reduced ionization collection and fast rise time
The Discriminators: Use Combination• Yield = Ionization Energy/ Phonon Recoil Energy
• Surface recoils tend to have lower ionization, mix with NR
• Pfracc = Highest_Phonon_Energy/Opposite_Phonon_Energy
•Surface recoils on phonon side tend to have higher energy partition due to proximity to phonon sensors
• pminrtc = 10%-40% risetime of the largest phonon signal
•Surface recoils tend to have lower risetime than bulk recoils
• pdelc = 20% delay of largest phonon signal wrt to charge st.
•Surface recoils tend to have lower delay than bulk recoils
All discriminators are correlated to some degreeAll discriminators have energy dependence to some degree
Definition of Surface Recoils()• Low Yield events from Ba• R118: reject in 3 NR• R119: Use wider definition
: 0.1 < yic < - 5• More stats for cut defn.• Establish timing cut to
reject all but “n” wide s• Estimate closed leakage
based on allowed leakages in open dataset
QuickTime™ and aTIFF (LZW) decompressor
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2-D cut in pminrtc and pdelc: Angela
•Define delpric and rtpric: energy corrected pdelc and pminrtc •For events between 10 and 100keV in pric, plot pdelc and pminrtc neutrons and betas.•Fit delpric-rtpric distributions for neutrons with gaussian, exclude all events (betas) outside 4 sigma of this distribution.•Define a cut in delpric+rtpric that allows desired beta leakage (set on the sixth event in each detector for this analysis.
Issues associated with timing cutsT2Z5 charge collection: Walter did a study of the timing outliers in T2Z5, which are all clustered at the bottom of the delay plot. He defined several cuts to exclude the affected region. In this analysis, the cut used is a simple ydel>-20 cut.
T1Z1has low efficiency as usual
QuickTime™ and aTIFF (LZW) decompressor
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Results
•Allowed 5 events of leakage in each detector for an exected leakage of 6 events/detector*6Ge detectors =36 betas.•In the WIMP search data, the leakage from these cuts is expected to be on the order of a fraction of an event overall.•Neutron efficiencies for these cuts are around 75% in the higher energy bins and worse at low energies.
N Eff 10-20keV 20-40keV 40-60 keV60-100 keVT1Z1 9.3 30.4 60 51.43T1Z2 45.86 64.73 96.36 70.27T1Z3 48.77 59.38 65.96 77.27T1Z5 56.42 72.27 75 83.33T2Z3 51.61 65.64 73.08 74.07T2Z5 52.56 66.27 83.72 76.19
Leakage by E bin
Low energies and timing
QuickTime™ and aTIFF (LZW) decompressor
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Below 7keV, Long found uncertainty in charge energy, causing leakage from ER toNRBelow 15keV, uncertainty in Qist that affects pdelc. Mostly does not affect the timing cut Below 10keV, ER and NR bands not well separated, hence difficult to define populationBelow 20keV, timing cut efficiency is low ~ around 20% Further work needed to determine where to set our analysis threshold. Probably it should be above 7keV.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
2-D pfracc & pdelc: Rupak/Joel •Reject all in 3 NR
•Found 9 extreme outliers. 3 rejected in T2Z5 by Walter’s cut
•Discovered that flash time cut may be helpful
•Flashtime RQ broken. Joel defined a function that utilizes DAQ gpib log to get flashtime
•Efficiency ~ 70-80% w 6 leakages in open Ba
4-D y,pfracc,pminrtc, pdelc: Rupak/Joel• Similar to Vuk’s rb-rn
method, normalized to 1• Define 4-D space in y,
pfracc, pminrtc & pdelc• Calculate neutron and
centroids from 3 NR• In 4-D space, calculate
dist. of each event from neutron (rn) and (rb)
• Define cut to reject all • Efficiency ~ 70-80% w 1
leakage in open Ba
4-D Cut with 2: Rupak/Joel
• Earlier 4-D cut assumes each discriminator has equal power in discr.
• Assign natural weights to each discriminators based on their accuracy in discrimination
• Calculate combined 2 distance for each event from neutron and
• Efficiency > 80% with 1 leakage in open Ba with WIDE distribution
R119 pfracc & pdelc Timing Cuts using a Neural Network
M. Attisha
• Can create cuts that would be v. tough to parametize by hand
• Easy to experiment with a range of input (RQ) parameters
• Cut must be chosen based on performance upon simulation data
Training Data = Ba open + Cf (even Event#)Simulation Data = Ba closed + Cf (odd Event#)
• Trained on all betas & neutrons within the 3σ NR band
• The cut is calculated in each ZIP for a single energy bin (pric): 10-100 keV
• ~90% rejection below 60keV pric
• Reduced efficiency at higher energies due to low neutron stats
• 6 beta leakage events remain in Z2, Z3, Z5, Z9 & Z11
• Current rejection performed using pdelc and pfracc
• Naïve addition of other parameters such as pminrtc gives little improvement, but plan to study effect of weighting inputs
R119 Timing Cuts using a Neural Network, cont.
M. Attisha
Chi-squared Methods: Jeff
• Our pulse shape and timing parameters show differing discrimination powers and significant correlations– We’d like to figure out the appropriate “metric” on this multi-dimensonal
parameter space.• In the case of gaussian parameters, the optimal metric is provided by the
inverse of the covariance matrix
• Basic Plan:– Preselect samples of neutrons and betas (and perhaps gammas), calculate
mean, cov for each population– Compute
– Make a 1-D cut in
– Reject outliers with large chi-squareds
jijiij xxxx cov
...pdelc
pminrtc where),(cov)( ,
1,,
2, xxx nbnb
Tnbnb
22bn
Chi-Squared Methods
• Do we include yield?– Most rejection power, but
betas clearly non-gaussian
– For now, separate band cut
• Energy dependence– Work in energy bins at
first– Use energy variations in
computed mu, sigma to define energy corrections
– Perform energy-independent cut (or fewer bins, at least)
Status and Plans
• Standard 2-D timing cut looks polished• 4-D timing cut needs refinement to take full
advantage of correlations for better rejection• Not clear whether to include the best discriminator y
in likelihood. Excluding gives easier leakage estimate• Neural Net analysis looks promising• Important to fully exploit all discrimination
parameters provided by our tremendous detectors• Timing cut group needs to formulate an action plan