1. The Surface Rejection with Position Information Gensheng Wang California Institute of Technology CDMS Collaboration Meeting, UCBS Feb. 11, 2005

2. Overview Do we need to improve the beta rejection efficiency? How? Position information based beta rejection Summary

3. Surface Event Rejection with Timing Surface electron recoils could be low yield, but have fast timing Near neighbor low yield double scatterings as ejectrons minimum risetime rejects the surface recoils phonon delay rejects the surface recoils

4. Phonon Timing Distribution Ejectron at a big radius is most likely to fail flat surface rejection timing cuts

5. 1 2 3 Geometry Parameter Because of phonon traveling distance, solid angle and side reflection, therefore But pfrac behaves in the central area of the detector

6. Separating Betas and Neutrons Phonon starttime Radius

7. Opposite Quadrant Phonon Energy Distribution A DC B shared phonon energy is expected to increase at big radius choose the radius cutoff value (between 2 and 3 cm) to allow pfrac behave in a reasonable fashion

8. A Handle of Discrimination R- phonon partition partition=(pa+pb- pc+pd)/pt for event in quadrant A Phonon partition is a symmetrical parameter between the phonon sensors, but pfrac is not Ejectrons can be discriminated in phonon partition and starttime two dimensional plane. RQ - no position correction neutrons (blue dots) and ejectrons (green crosses) R118 Z5

9. Red: ejectrons at the top of the detector Green: ejectrons at the bottom Circles: ejectrons in 3  nuclear recoil band Blue dots: neutrons 10-20 keV ejectrons 20-100 keV ejectrons phonon partition--pdelc

10. Ejectron at A Small Radius Phonon timing discrimination parameters are generally very good, only care should go to the exact centre area of the detector with phonon starttime and local quadrant phonon risetime. Luke phonons go away then are reflected back for surface events at phonon sensor side, but Luke phonons hit the phonon sensors directly for surface event at charge side. Phonon flux distribution as a function of time. Can we discriminate surface event at phonon side and surface event at charge electrode side? risetime ratio: (PAr50-PAr20)/(PAr80-PAr50) for an event in quadrant A Look at the data

11. Red: ejectrons at the top of the detector Green: ejectrons at the bottom Circles: ejectrons in 3  nuclear recoil band Blue dots: neutrons 10-20 keV ejectrons20-100 keV ejectrons risetime ratio--pdelc

12. Using Run 119 Calibration Data All open Ba calibration data except 140615_1252 Neutron calibration data cQin_119 & cChiSq_119 & cQThresh_119 & ~cVT gband_qi_arov119, yband_qi_arov119

13. Red: 10-20 keV ejectrons at the top of the detector Black: 10-20 keV ejectrons at the bottom Cyan: 10-20 keV ejectrons not near doubles Magenta: 20-100 keV ejectrons at the top of the detector Green: 20-100 keV ejectrons at the bottom Yellow: 20-100 keV ejectrons not near doubles Circles: ejectrons in 3  nuclear recoil band Blue dots: neutrons Surface Events Rejection at Small Radius

14. Surface Events Rejection at Big Radius Red: 10-20 keV ejectrons at the top of the detector Black: 10-20 keV ejectrons at the bottom Cyan: 10-20 keV ejectrons not near doubles Magenta: 20-100 keV ejectrons at the top of the detector Green: 20-100 keV ejectrons at the bottom Yellow: 20-100 keV ejectrons not near doubles Circles: ejectrons in 3  nuclear recoil band Blue dots: neutrons

15. Surface Event Cuts for Ge Detectors c119 – defined in risetime ratio-pdelc plane (R<2.5cm, transformation parameter) or phonon partition-pdelc plane (R  2.5 cm, transformation parameter). Defined c119 is R119 ebook 104. crt—defined as pminrtc > the mean of pminrtc of ejectrons in 3  NR and ptrtc > the mean of ptrtc of ejectrons in 3  NR, it’s a safety guard Events that pass both c119 and crt are selected as nuclear recoils.

16. T1Z1T1Z2T1Z3T1Z5T2Z3T2Z5 2  NR before 47545789010075 2  NR after 100010 3  NR before 8247384134148117 3  NR after 300011 Beta1 before 1976734601791799553 Beta1 after 2171343 Beta2 before -323602667748418 Beta2 after -11332 Beta Rejection in Ba calibration Data (10-100 keV)

17. The Leakage Event in T2Z3 ~cVT ~nearest double In 2  NR band pric=12.2 keV pdelc=14.5  s pminrtc=10.6  s ptrtc=17.0  s R=1.82 cm Small risetime ratio

18. T1Z1T1Z2T1Z3T1Z5T2Z3T2Z5 2  NR before 1821711 6 2  NR after 400311 3  NR before 6042818 1410 3  NR after 1000411 Beta1 before 36438653918 Beta1 after 012931 Beta2 before -12143213- Beta2 after -0050- Beta Rejection in Ba Calibration Data (5-10 keV)

19. The Neutron Selection Efficiency of c119 and crt Cuts Only

20. Summary Enhanced surface event rejection efficiency is achieved with radius parameter, phonon risetime ratio and phonon partition The original features of phonon parameters and position corrected phonon timing parameters are used together The optimizations of R and ejectron rejection efficiency could be done

21. The Outliers in the Open Ba Data

22. T2Z3

25. Reconstructed x and y Charge Inner and Outer Share Event (R118 BKGD) Z5, 40 ~ 80 keV, charge inner events and charge share events Conventional delay plotReconstructed x and y plot