Waveform Analysis for DM-Ice17. Zachary Pierpoint University of Wisconsin - Madison October 21, 2013 Yale Weak Interactions Discussions Group

Transcription

1 Waveform Analysis for DM-Ice17 Zachary Pierpoint University of Wisconsin - Madison October 21, 213 Yale Weak Interactions Discussions Group

2 DM-Ice17 Energy Spectrum counts / day / kev / kg 1 28 Tl+ 214 Bi 6 Co 4 K 214 Bi 28 Tl Alphas Energy (kevee) 2

3 DM-Ice17 Events 5 PMT-1a PMTs PMT-1a PMT-1a

4 Mean Time (τ) Studies of alpha quenching factors and alpha source concentrations are greatly improved by separating the gamma and alpha spectra. Differences in scintillation behavior for electron and nuclear recoils make such separation possible. t t=t ( t t )E t t=t E t Average Gamma Average Alpha 4

5 Mean Time Separation Gammas Gaussian fits separated by 4.84 sigma Alphas 5

6 Other High Energy Events Gammas Mean Time (ns) Alphas Gammas and Alphas are not the only types of high energy waveforms observed in DM-Ice17 Energy (kevee) t 4 PMT-1a

7 Expected Fast Alphas (Thorium Chain) 212 Bi gamma decays to 212 Po 64.5% of the time 212 Po has a half-life of 299 ns Estimated uhz rate based on previous alpha analysis (Uranium Chain) 214 Bi gamma decays to 214 Po 99.98% of the time 214 Po has a half-life of 164, ns Estimated uhz rate based on previous alpha analysis. Accidental coincidence of gammas and alphas Based on alpha event rate, expected at uhz, i.e. small compared to expected rate from the two BiPo contributions 4 PMT-1a

8 BiPo Analysis counts / kg / day 4 PMT-1a 3 Δt Data 212Po (Th Chain) 214Po (U Chain) Summed Contributions -1 Parameter Fit Error Expecta/on 212 Po t 1/2 (ns) Po conc. (uhz) 214 Po conc. (uhz) Great agreement of half-life (i.e. this is dominated by Thorium chain BiPo) Δ t (ns) Good agreement of concentrations for both BiPo processes, though the alpha analysis produces values 5-% higher. 8

9 Low Energy Analysis counts / day / kev / kg Data Simulation Bernabei et al. Int J Mod Phys A (213) PMT-1a Energy (kev) 9

10 4 K 3 kev peak 4 K decay to 4 Ar results in a 3 kev peak due to x-rays and auger electrons. Low energy calibration point. Target line for energy threshold. Multi-crystal coincidence allows for tagging these events. DAMA/LIBRA plot showing coincidence between 1461 kev events in one crystal with 3 kev events in a neighboring crystal. WIDG, 21 Oct 213 Zachary P Pierpoint, UW-Madison C.Cuesta, Status of the ANAIS Experiment 6 th Multidark Consolider Meeting

11 Electromagnetic Interference (EMI) Events Hardware monitoring produces interference that triggers DM- Ice17. Monitoring frequency decreased in March 212 to reduce these events. Pulse shape discrimination used to cut EMI events PMT-1a discriminator = Z 6 ns ( dy dt )2 dt X127 discriminator = ((x i+1 x i ) (x i x i 1 )) 2 i=1 Z 11

12 EMI Cut 1 EMI Counts / day / kev / kg 4 All Data 3 After EMI Cut EMI Events 2 EMI Energy (kev) 12

13 Thin Pulses Interactions within the PMTs or light guides? PMT-1a Plan to use Fermi test site to test origins of these events. For DM-Ice17, pulse shape discrimination required to remove this noise. WIDG, 21 Oct 213 Zachary P Pierpoint, UW-Madison 13

14 Thin Pulses Thin Cut Variable vs. Energy Pulse shape discrimination: discriminator = DM Sum DM1 Sum 128 DM Max DM1 Max Other noise Scintillation Scaling factor for differences in light collection Counts / day / kev / kg 4 After EMI Cut 3 2 Thin Pulses > 4 kev Thin Pulse Extrapolation Thin 1 Below 4 kev, it is not enough to just remove thin peaks! Energy (kev) 14

15 Peak Finding Cut Energy Spectrum after Peak Finding Cut PMT-1a Peak Finding in theory counts the number of photoelectrons in each PMT. In practice, a simple peak finding algorithm is used to count local maxima above a threshold. 5 Cut Requirement : Each PMT sees 5+ peaks WIDG, 21 Oct 213 Zachary P Pierpoint, UW-Madison 15

16 Low Energy Region (After Cuts) counts / day / kev / kg K Data Simulation Noise 15 2 Pb 5 Flat Background : 7.7 counts/day/kev/kg Energy (kev) 16

17 DM-Ice Full Scale 17

18 Conclusions Thanks to high energy analysis, we have a good understanding of the crystal contaminations and low energy backgrounds for DM-Ice17. From cosmogenic activation, we have a strong verification of the DM-Ice17 energy calibration. Studies of the stability of low energy cuts are underway for modulation analysis 18