DM- Ice Simula.on Summary. Walter C. Pe8us UW- Madison June 22, 2010

Transcription

1 DM- Ice Simula.on Summary Walter C. Pe8us UW- Madison June 22, 2010

2 Sta.s.cal tests of the DAMA signal DAMA/LIBRA background spectrum: Background range over 2 6 kev: cpd/kg/kev (extracted from plot) Eur. Phys. J. C. 56, (2008), 333

3 DAMA Sta.s.cs If DAMA error bars were 1- σ Poisson- based dominated by background For 2-6 kev range: Expected error (cpd/kg/kev) Plo3ed error (cpd/kg/kev) DAMA/LIBRA (232.8 kg) DAMA/NaI (87.3 kg) * All values approximated from graph, as DAMA does not release raw data * Does not take into account detector down.me. Based on reported exposure and run dates, DAMA/LIBRA had less than 60% live.me (Eur. Phys. J. C. 56 (2008), 333)

4 DAMA Sta.s.cs Live.me Can calculate exact live.me for DAMA/LIBRA: Period Run dates Exposure (kg*day) For DAMA/LIBRA 1-4, live.me is Using live.me to correct error bar es.mates: Expected error (cpd/kg/kev) Plo3ed error (cpd/kg/kev) Frac>on Live>me DAMA/LIBRA- 1 Sept. 9, 2003 July 21, DAMA/LIBRA- 2 July 21, 2004 Oct. 28, DAMA/LIBRA- 3 Oct 28, 2005 July 18, DAMA/LIBRA- 4 July 19, 2006 July 17, Eur. Phys. J. C. 56, (2008), 333 Discrepancy DAMA/LIBRA (232.8 kg) DAMA/NaI (87.3 kg)

5 DAMA Error Bars Graphical representa.on of error bar mismatch for 2-6 kev range Data points are DAMA values 0.08 Red: expected Poisson error (*not corrected for live.me) Blue: reported error 0.04 Residual (cpd/kg/kev) Day

6 DM- Ice Projec.ons Assuming DAMA signal modula.on is correct, we can simulate what our signal may look like Error generated to be purely Poisson Assuming background of NAIAD crystals (with no addi.onal contribu.on from cosmogenic ac.va.on), 7.5 cpd/kg/kev Assuming data can be taken across en.re 2-6 kev range (and constant background across range)

7 NAIAD limita.on NAIAD has significantly higher background than DAMA (~7.5 cpd/kg/ kev) Cannot apply pulse shape discrimina.on below 4 kev for NaI Phys. Lett. B. 616, (2005), 17

8 DM- Ice Prototype Simula.on kev 0.16 Residuals (cpd/kg/kev) kev 17.0 kg of NAIAD crystal cpd/kg/kev background Time (day) 0.16 Residuals (cpd/kg/kev) Time (day)

9 0.08 DM- Ice Experiment Simula.on 2-4 kev Residuals (cpd/kg/kev) kev 100 kg of NAIAD crystal cpd/kg/kev background Time (day) Residuals (cpd/kg/kev) Time (day)

10 Energy Range What if we are stuck with only 4-6 kev energy range? Taking fit parameters from combined DAMA: Energy Range Count Rate (cpd/kg/kev) Count Rate (cpd/kg) 2-4 kev kev Leaving cpd/kg in the 4-6 kev range cpd/kg/kev 85% of signal is in 2-4 kev range

11 DAMA CL Based on reported CL for DAMA/NaI and DAMA/LIBRA: CL scales approximately with sqrt(exposure) 2 4 kev: σ/sqrt(ton*yr) 2 5 kev: σ/sqrt(ton*yr) 2 6 kev: σ/sqrt(ton*yr) Also scale CL by 1/sqrt(count rate) for NAIAD crystals with higher background Eur. Phys. J. C. 56, (2008), 333

12 Projected DM- Ice CL Assuming the DM- Ice CLs will scale exactly as DAMA, and seing the count rate at 7.5 cpd/kg/ kev (as in NAIAD, no ac.va.on) 2-4 kev 2-5 kev 2-6 kev 2 NAIAD NAIAD size DAMA size Years 17.0 kg 44.5 kg 250 kg * Years of running include no down.me, unlike the DAMA experiment Exposure (kg*day) Years 17.0 kg 44.5 kg 250 kg

13 Low Background CLs Looking at only the 2-4 kev range (lowest CL), the effect of improved crystals with lower backgrounds would be to give CLs of: NAIAD background 50% NAIAD background Double DAMA background DAMA background 1/10 DAMA background 2 NAIAD NAIAD size DAMA size Years 17.0 kg 44.5 kg 250 kg

14 Muons Muon rates have been measured at Gran Sasso laboratory by both MACRO and LVD experiments Both experiments observed similar peaks in the muon flux MACRO: mid- July LVD: July 4

15 Muon Modula.on at Gran Sasso MACRO (4 yrs) Astropart. Phys. 7, (1997), 109 LVD (8 yrs) Selvi, Proc. 31 st ICRC. (2009)

16 Muon Modula.on at South Pole Opposite Muon modula.on at the South Pole: Tilav, Proc. 31 st ICRC. (2009) LVD: Selvi, Proc. 31 st ICRC. (2009)

17 LNGS Muon Signal from LVD Data fi8ed to I µ = I µ 0 +δi µ cos 2π T t t 0 ( ) From all eight cycles: I 0 µ = 3.31± 0.03 From data averaged into one cycle: 1.5% signal modula.on * (No fit data available for MACRO) ( ) 1 ( ) 10 4 m 2 s T = ( 367 ±15) days ( ) 10 6 m 2 s δi µ = 5.0 ± 0.2 t 0 = ( 185 ±15) days Selvi, Proc. 31 st ICRC. (2009) ( ) 1

18 Muon Modula.on Can we exclude poten.al muon- related background at the South Pole? Overlay of expected dark matter and muon modulation Signal (arbitrary units) DAMA DM modulation LVD muon modulation at LNGS IceCube muon modulation at South Pole Time (day)

19 Muon Modula.on Fi8ed phase of combined DAMA/NaI + DAMA/LIBRA data aner DAMA/LIBRA- 4: Energy Range t 0 (day) (2-4) kev 138 ± 7 (2-5) kev 145 ± 7 (2-6) kev 144 ± 8 (LVD phase was 185 ± 15 days) Thus, the [2-6 kev DAMA phase] is 5σ far from the? muon modula.on phase measured at LNGS by the large surface apparata MACRO and LVD. Bernabei, SciNeGHE 2009

20 Muon Modula.on Combining uncertain.es in LVD fit with DAMA fit should give: Uncertainty Δt 0 (day) Sigma