Gustav Wikström. for the IceCube collaboration

Transcription

1 Results and prospects of Dark Matter searches in IceCube for the IceCube collaboration

2 Direct detection situation: Spin dependent WIMP proton cross section Big gap! 2

3 IceCube 22 string & AMANDA 7 yr limit & IceCube 80+DeepCore sensitivity Published 22 string No gap! result PRELIMINARY IC80+DC sens. 3

4 Neutrinos from dark matter Dark matter in the form of WIMPs could be gravita tionally captured in the potential well of the Sun If WIMPs can annihilate pair wise to SM particles we expect neutrinos in the decay products The neutrinos could exit the Sun, and be detected at Earth 4

5 The IceCube neutrino telescope An array of optical modules embedded in deep ice Digital Optical Module (DOM) 5

6 Photomultipliers in the optical modules detect Cherenkov light and the observed hit times are used to deduce the direction of the muon Light cone from a relativistic muon in ice 6

7 Looking for neutrinos from the Sun During half the year (Austral winter) the Sun is below the horizon at the South Pole SUMMER WINTER ABOVE HORIZON BELOW HORIZON HEAVY Above the horizon there's too much atmospheric muon background ATM. MUON BACKGR. WIMP neutrino WIMP muon SIGNAL MC SOLAR WIMP NEUTRINOS AND MUONS 7

8 The 2007 detector 8

9 IceCube 22 string data taken in 2007 were searched for a WIMP signal from the Sun Used 104 days livetime (Sun below horizon, austral winter) 4.8 billion recorded events By comparing signal simulation and data cuts are placed that reduces the content of atmospheric muon events Analysis blind to Sun's position At the final stage 6946 events are selected Among these events an excess is sought from the direction of the Sun (unblinding) 9

10 Analysis technique: Remove atmospheric muon events until data sample is dominated by atmospheric neutrino events MOSTLY NEUTRINO EVENTS IN FINAL DATA SAMPLE 10

11 The observed events were consistent with the total expected background distribution Cut defining final event sample (chosen such that > 50% neutrino events) SVM output value from signal simulations, data and three background components PRL 102,

12 Effective neutrino area for final event selection PRELIMINARY Derived from signal simulation 12

13 Unblinded data: Events close to the direction of the Sun PRL 102,

14 The observed angle to the Sun is fitted with signal and background pdf:s SIGNAL SIMULATION BACKGROUND Angle between event track and the direc How many signal events can be consistent with the observation? tion of the Sun OBSERVATION 14

15 Limits on the muon flux from the Sun IceCube 22 string b b bar W+W PRL 102,

16 Assuming the number of WIMPs are in equilibrium in the Sun, it is possible to relate muon flux and WIMP nucleon cross section The muon flux is proportional...and the capture rate is to the annihilation rate proportional to the WIMP for a given annihilation channel nucleon cross section With DarkSUSY (and WimpSim) these quantities are calculated and conversion between muon flux and cross section is found JCAP 04(2009)009 16

17 Limits on the SD WIMP proton cross section IceCube 22 string b b bar W+W PRL 102,

18 Kaluza Klein dark matter (LKP) Lightest Kaluza Klein (LKP) particle good WIMP candidate Usually taken as the first excitation of the photon in a universal extra dimension (UED) LKPs could accumulate and annihilate in the Sun similar to neutralinos (Hooper et al. 2003) Branching ratios varies only slightly between different models Neutrino spectrum from annihilation close to neutralino hard channel Limits can be derived from existing WIMP analyses 18

19 Kaluza Klein WIMP dark matter (LKP): Limits on SD WIMP proton cross section IceCube 22 string LKP PRELIMINARY 19

20 Kaluza Klein dark matter (LKP): Limits on the muon flux from the Sun IceCube 22 string PRELIMINARY LKP 20

21 Results from AMANDA AMANDA turned off this year Analysis of complete dataset in progress WIMP results derived from 7 year point source analysis Results for Earth WIMPs in progress AMANDA has a lower energy threshold than IceCube, therefore sensitive to lower WIMP masses DeepCore will improve the low energy capabilities of IceCube 21

22 SD WIMP proton cross section: AMANDA 7 yr limit + IceCube 80+DeepCore sensitivity AMANDA 7y PRELIMINARY IC80+DC sens. 22

23 Summary IceCube has placed limits on WIMPs in the Sun using data from the 22 string detector (published) For spin dependent interactions the converted cross section limits are very competetive Limits have been placed using 7 yr data from AMANDA Limits on Kaluza Klein DM (publication in progress) Earth WIMP searches in progress with both IceCube and AMANDA data 23

24 Back up slides 24

25 Muon flux from the Sun: AMANDA 7 yr limit + IceCube 80+DeepCore sensitivity PRELIMINARY IC80+DC sens. 25

26 Muon flux from the Earth: AMANDA 3 year PRELIMINARY 26

27 The 2009 detector 59 strings out of 86 planned deployed 1 out of 6 planned DeepCore low energy extension strings deployed in between standard strings On the DeepCore strings the DOMs are spaced 7m compared to 17m on standard strings Increased DOM density enhances sensitivity 27

28 Evaluate shape fit with log likelihood rank (Feldman Cousins) to construct confidence regions for the signal content rank = L( ) / L(best fit ) where L is the pdf product over the final sample SIGNAL CONTENT Log of rank GIVES UPPER LIMIT ON as function of #WIMP EVENTS signal content 90% tail of pseudo 90 % confidence interval Example plot experiment distribution 28

29 What is the energy we're looking at? Low mean muon energy > Short tracks, few hits SIGNAL MC Absorption in the Sun becomes important Neutrino interaction in the Sun 29

30 Systematic uncertainties on the effective volume: Neutrino oscillation: 4% Neutrino nucleon cross section: 3% Muon propagation in ice: <1% Photon propagation & absolute OM sensitivity: 17 24% Spread in OM sensitivity: <5% Time & position calibration: <5% 3 5% Signal MC statistics: Total systematic uncertainty: 19 26% 30

31 Detection of neutrinos in ice Neutrinos interact weakly with nucleons in the ice Muon neutrinos create muons Muons can go several kilometers through ice Relativistic muons emit Cherenkov light The neutrino muon deflection angle is small 31

32 LKP and neutralino muon spectra are very similar 32