Walter C. Pettus on behalf of the DM- ICE collaboration University of Wisconsin Madison. APS April Meeting Session D11: Dark Matter II 13 April 2013

Transcription

1 Walter C. Pettus on behalf of the DM- ICE collaboration University of Wisconsin Madison APS April Meeting Session D11: Dark Matter II 13 April 2013

2 Before running a dark matter experiment at the South Pole... Sandiviken, SWE DM- ICE17 Component Sources Crystals: Boulby, UK Steel: Sandviken, SWE DM- ICE17 Construction Madison, WI, USA Polar Program Waypoints Christchurch, NZ McMurdo Station South Pole Station Christchurch, NZ McMurdo Station Madison, WI Boulby, UK South Pole Station APS April Meeting 2013 Walter C. Pettus, UW Madison 1

3 Commercial flights at ~35,000+ ft Location Relative Neutron Rate (to sea level) Madison, WI 1.26 South Pole 9.7 Commercial Flight 130 Madison, WI Sandiviken, SWE Boulby, UK Polar program flights Storage at 9,301 ft South Pole Station Christchurch, NZ McMurdo Station Low geomagnetic rigidity APS April Meeting 2013 Walter C. Pettus, UW Madison 2

4 Activity of cosmogenic isotopes simulated by: COSMO code for NaI Literature values for Steel and Copper Breakdown of crystal activation by travel stage: Christchurch (25 days) Wisconsin (60 days) Flight: MCM NPX (3 hrs) Flight: CHC MCM (5 hrs) South Pole (15 days) Flight: MSN CHC (16 hrs) Crystal APS April Meeting 2013 Walter C. Pettus, UW Madison 3 Steel 3 H 7 Be 7 Be 46 Sc 22 Na 48 V 113 Sn 51 Cr 121m 123m 125m 127m 52 Mn 54 Mn 56 Co 56 Ni 125 I 58 Co 127 Xe

5 Long- lived cosmogenic isotopes from crystal and pressure vessel are expected to persist into data taking 1 st Data Month: Simulated Spectrum Crystal Steel 3 H 7 Be 7 Be 46 Sc 22 Na 48 V counts/kg/kev/day 113 Sn 51 Cr 121m 123m 125m 127m 52 Mn 54 Mn 56 Co 56 Ni 125 I 58 Co 127 Xe APS April Meeting 2013 Walter C. Pettus, UW Madison 4

6 * (6.5 months after deployment, first month of data run) NaI Crystal Still expect clear peaks from multiple isotopes Steel Pressure Vessel 54 Mn is only significant isotope counts/kg/kev/day NaI Crystal Cosmogenics: All in Crystal 113 Sn in Crystal 121m in Crystal 123m in Crystal 125m in Crystal 127m in Crystal 125 I in Crystal counts/kg/kev/day Pressure Vessel Cosmogenics: APS April Meeting 2013 Walter C. Pettus, UW Madison 5

7 125 I (t 1/2 = 59.4 days) is good candidate for search in early data months Low- Energy Spectra from 2011: counts (arb) Geant4 125 I Energy Deposited counts/kg/kev/day 125 I Full Energy 125 I X- rays 1 st Data Month 5 th Data Month APS April Meeting 2013 Walter C. Pettus, UW Madison 6

8 Residual between two months of data reveals clean 125 I peaks: 4 Month Data Residual counts (arb) Geant4 125 I Energy Deposited counts/kg/kev/day APS April Meeting 2013 Walter C. Pettus, UW Madison 7

9 λ = ± month - 1 t 1/2 = ± 2.66 days (59.4 days) Deploy activity: 1151 ± 118 cpd/kg Integrated Peak Area (counts/kg/day) 125 I Peak Decay Month (since July 2011) APS April Meeting 2013 Walter C. Pettus, UW Madison 8

10 γ- line expected from 54 Mn E γ = 835 kev t 1/2 = days counts/kg/kev/day 54 Mn Peak Finding Fit Expectation ± Sigma (kev) 36.9 ± Deploy Rate (decays/day) 51,700 ± 6, ,800 APS April Meeting 2013 Walter C. Pettus, UW Madison 9

11 Time on surface at South Pole can be most damaging stage for cosmogenics: Christchurch Wisconsin Flight: MCM NPX Flight: CHC MCM South Pole Flight: MSN CHC South Pole is topographically flat and station buildings provide minimal overburden APS April Meeting 2013 Walter C. Pettus, UW Madison 10

12 40-50 ft firn overburden ~ 10 m.w.e. ~ 30% of surface muon rate APS April Meeting 2013 Walter C. Pettus, UW Madison 11

13 Muon spectra comparison of South Pole sites with Christchurch and Madison data Count Rate (/MeV/min) MCA1 Compiled Average Data South Pole - Surface South Pole - ICL South Pole - Tunnel Christchurch, NZ Madison, WI, USA Energy (MeV) APS April Meeting 2013 Walter C. Pettus, UW Madison 12

14 Location Elevation (ft) Relative Intensity* South Pole - Surface South Pole ICL South Pole Tunnel Christchurch, NZ Madison, WI, USA South Pole Tunnels (15 days) Christchurch (25 days) Wisconsin (60 days) Flight: MCM NPX (3 hrs) Flight: CHC MCM (5 hrs) *Relative to Christchurch approximately sea level Flight: MSN CHC (16 hrs) APS April Meeting 2013 Walter C. Pettus, UW Madison 13

15 Cosmogenic activation is a significant concern for running a low- background detector at the South Pole Mitigation strategies can significantly reduce activation levels Cosmogenic lines can also be helpful in calibration of remote detector See Antonia Hubbard s talk, (D ) APS April Meeting 2013 Walter C. Pettus, UW Madison 14