New signals and old backgrounds in dark matter direct detection - PowerPoint PPT Presentation

New signals and old backgrounds in dark matter direct detection Josef Pradler Perimeter Institute with Spencer Chang and Itay Yavin , Phys.Rev.D 85 063505 (2012) with Maxim Pospelov , arXiv:1203.0545 CERN, March 16, 2012 Friday, 16 March, 12

PLAN Part I • signal modulation in dark matter direct detection experiments • DAMA & CoGeNT and the “muon-hypothesis” • new signatures from dark matter modulation Part II • dark matter vs. neutrinos from the sun • “baryonic” neutrinos ν b • direct detection experiments as observatories? ν b Friday, 16 March, 12

one species - three signals? • DAMA : 250 kg of scintillating NaI crystals, running since 1995, exposure in excess of 1 ton x year, no discrimination • CoGeNT : 440 g Ge crystal, 442 live days; ionization only, no discrimination • CRESST : scintillation and phonons; 730 kg days, multi-target Friday, 16 March, 12

one species - three signals? [Angloher et al., 2011] • DAMA : 250 kg of scintillating NaI crystals, running since 1995, exposure in excess of 1 ton x year, no discrimination • CoGeNT : 440 g Ge crystal, 442 live days; ionization only, no discrimination • CRESST : scintillation and phonons; 730 kg days, multi-target Friday, 16 March, 12

Part I “take away message” • cosmic muons as origin for DAMA modulation strongly disfavoured - different in phase - different in correlation - possibly different in power - possibly different in amplitude • similar conclusions hold for CoGeNT modulation • there is more than “one modulation” Friday, 16 March, 12

signal modulation in direct detection dR d 3 v vf LAB ( v ) d σ Z = N T n DM [cpd/kg/keV] dE R dE R v ≥ v min f GAL ( v obs + v ) see e.g. [Druiker et al, 1986; Freese et al, 1988; Savage et al, 2009] Friday, 16 March, 12

signal modulation in direct detection dR d 3 v vf LAB ( v ) d σ Z = N T n DM [cpd/kg/keV] dE R dE R v ≥ v min f GAL ( v obs + v ) v obs = v � + V � [ ε 1 cos ω ( t − t 1 ) + ε 2 sin ω ( t − t 1 )] | v obs | = | v � | + 1 2 V � cos ω ( t − t 0 ) t 0 ' 152 days (June 2nd) see e.g. [Druiker et al, 1986; Freese et al, 1988; Savage et al, 2009] Friday, 16 March, 12

signal modulation in direct detection annual modulation Z ∞ dR ( t ) f ( v ) dv ' c 0 ( v min ) + c 1 ( v min ) cos [ ω ( t � t 0 )] / dE R v v min 10 − 2 . c 0 10 − 3 c 1 ✓ m N E R ◆ 1 + δ v min = 10 − 4 √ 2 m N E R µ N χ | c n | (km / s) − 1 10 − 5 10 − 6 10 − 7 10 − 8 10 − 9 t 0 ' 152 days (June 2nd) 10 − 10 0 100 200 300 400 500 600 700 800 v min (km / s) [using f(v) from Lisanti et al, 2010] Friday, 16 March, 12

∼ 3% DAMA/LIBRA 0.87 ton × yr • scintillation from 0.04 NaI-crystals 0.02 0 -0.02 • residuals (cpd/kg/keV) (2–4 keV) 8 σ + modulation -0.04 • 0.04 phase consistent 0.02 0 as expected from -0.02 (2–5 keV) WIMPs -0.04 0.04 t 0 ' 2 June 0.02 0 -0.02 = 152 . 5 days (2–6 keV) -0.04 3500 4000 4500 5000 days since Jan 1, 1995 [Bernabei et al. 2010] Friday, 16 March, 12

Muon Flux underground --- modulates too --- • underground flux sourced mainly by primary meson decays (pions, kaons,...) => muons need to be TeV-like to reach underground • competition between secondary meson interactions vs. decay depends on air-density => muon flux correlated with temperature Z ∞ ∆ I µ ∆ T e ff T e ff = dX T ( X ) W ( X ) = α T I 0 T e ff µ 0 • flux peaks in Summer (on northern hemisphere) Friday, 16 March, 12

Muon Flux underground • many measurements available, correlation with firmly established T e ff • LNGS: Macro, LVD, T e ff Borexino (DAMA location) • Soudan Mine: MINOS φ µ (CoGeNT location) • South Pole: Amanda, Icecube [Borexino 2011] Friday, 16 March, 12

LVD and DAMA • Large Volume liquid scintillator Detector (LVD) reports underground muon-flux at LNGS => temporal overlap with DAMA data [Selvi, 2009] @ DAMA site I µ ∼ 30 / day / m 2 Friday, 16 March, 12

LVD and DAMA muon flux (10 − 7 cm − 2 s − 1 ) 0.37 (digitized from LVD data) 0.36 0.35 0.34 0.33 0.32 0.31 0.3 0 500 1000 1500 2000 2500 t (days) • renewed interest in muons as DAMA background, see e.g. [Ralston, 2010], [Nygren, 2011], [Blum, 2011] • very recent response by DAMA [Bernabei, 2012] Friday, 16 March, 12

LVD and DAMA . 6 percent residuals 4 2 0 -2 2–4 keV -4 muons -6 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 days since Jan 1, 2001 • renewed interest in muons as DAMA background, see e.g. [Ralston, 2010], [Nygren, 2011], [Blum, 2011] • very recent response by DAMA [Bernabei, 2012] Friday, 16 March, 12

LVD and DAMA • muons can either directly hit the detector or indirectly, by spallation of nuclei which leads to neutron flux => guaranteed source of background (especially if un-vetoed) • in this talk we will base our analysis exclusively on the time-series of events in both data sets => we are ignorant to how the signal formation process concretely happens => but if we can make firm statements already it means that this approach is very model-independent and thus conservative Friday, 16 March, 12

detecting periodicities • evenly spaced data discrete FT d i = d ( t i ) 2 ! 2 3 2 ! 2 � � X X � � X P ( ω ) ∝ d i exp( − i ω t i ) = d i cos( ω t i ) + d i sin( ω t i ) � � 4 5 � � � � i i i • unevenly spaced data: Lomb-Scargle Periodogram • invariant to shifts in 8 # 2 "X LS( ω ) = 1 1 < ω ˜ � � d i cos time origin t i ω ˜ i cos 2 � � 2 P t i : i • if is pure noise (with # 2 9 d i "X 1 = ω ˜ � � unit variance) + d i sin t i ω ˜ i sin 2 � � P t i ; i Pr( P > p ) = e − p ˜ t i ≡ t i − τ Friday, 16 March, 12

detecting periodicities LVD muons DAMA/LIBRA 500 50.0 T = 365 days T = 365 days 99 % H any freq L 100 10.0 50 5.0 99 % H one freq L Power Power 99 % H any freq L 10 1.0 5 99 % H one freq L 0.5 1 100 150 200 300 500 700 1000 1500 2000 50 100 200 500 1000 2000 Period H days L Period H days L no power on timescales > 1yr Friday, 16 March, 12

detecting periodicities LVD muons DAMA/LIBRA 500 50.0 T = 365 days T = 365 days 99 % H any freq L 100 10.0 50 5.0 99 % H one freq L Power Power 99 % H any freq L 10 1.0 5 99 % H one freq L 0.5 1 100 150 200 300 500 700 1000 1500 2000 50 100 200 500 1000 2000 Period H days L Period H days L adopting DAMA’s procedure of no power on timescales > 1yr subtracting baseline on each cycle suppresses power on timescales longer BUT than 1 yr (see also Blum, 2011) Friday, 16 March, 12

detecting periodicities DAMA/LIBRA, 2012 Normalized Power 22.5 20 17.5 15 12.5 6 years period 10 7.5 5 2.5 0 0 0.001 0.002 0.003 0.00 Frequency (d -1 ) LS of baselines O(10) data points, no significant power! Friday, 16 March, 12

detecting periodicities LVD muons DAMA/LIBRA, 2012 Normalized Power 22.5 20 100 17.5 15 99 % H one freq L 10 LS 12.5 6 years period 10 1 7.5 0.1 5 1000 1500 2000 T H days L 2.5 0 0 0.001 0.002 0.003 0.00 Frequency (d -1 ) LS of baselines LS of muon baselines O(10) data points, no O(10) data points significant power! no significant power neither! Friday, 16 March, 12

detecting periodicities DAMA/LIBRA, 2012 • Normalized Power with a small dataset it is hard to 22.5 achieve statistical significance 20 17.5 => normalized power 15 12.5 6 years period 10 P ( ω ) = LS ( ω ) / σ 2 7.5 5 • power spectrum of baselines 2.5 alone does NOT convincingly 0 0 0.001 0.002 0.003 0.00 Frequency (d -1 ) show that there is indeed no long term modulation in DAMA => DAMA should provide baseline rates Friday, 16 March, 12

The phase of DAMA vs the “phase” of LVD A × cos [ ω ( t − t 0 )] • interpret data as sinusoidal variations LVD 200 • DM phase of DAMA/LIBRA incompatible with muons 150 Phase H days L ω = 2 π / 1yr : @ 100 68 % DAMA ê LIBRA 90 % t 0 (DAMA) = (131 ± 13) days 50 99 % t 0 (LVD) = (187 ± 2) days 0 340 350 360 370 380 390 400 Period H days L Friday, 16 March, 12

The phase of DAMA vs the “phase” of LVD • two studies suggest that phase can potentially in agreement 1. Selvi for LVD collaboration finds − 3 10 × − 1 0.37 s) 2 Muon intensity (m 0.36 t 0 (LVD) LVD − collab = (185 ± 15) days 0.35 0.34 χ 2 /dof = 577 / 362 0.33 0.32 0.31 adopting this procedure we find 0.3 0 50 100 150 200 250 300 350 Progressive day in year ! [Selvi for LVD, 2009] t 0 (LVD) = (186 ± 2) days Friday, 16 March, 12

The phase of DAMA vs the “phase” of LVD • two studies suggest that phase can potentially in agreement 1. Selvi for LVD collaboration finds − 3 10 × − 1 0.37 s) ↯ 2 Muon intensity (m 0.36 t 0 (LVD) LVD − collab = (185 ± 15) days 0.35 0.34 χ 2 /dof = 577 / 362 0.33 0.32 0.31 adopting this procedure we find 0.3 0 50 100 150 200 250 300 350 Progressive day in year ! [Selvi for LVD, 2009] t 0 (LVD) = (186 ± 2) days χ 2 suspecting that Selvi used reduced for construction of confidence region => confidence interval overestimated Friday, 16 March, 12