Searching for the Dark Matter Wind: a Novel Approach to Dark Matter - PowerPoint PPT Presentation

Searching for the Dark Matter Wind: a Novel Approach to Dark Matter Detection Jocelyn Monroe, MIT Imperial College HEP Seminar November 8, 2007

Outline The Dark Matter Wind Dark Matter Search Strategy Directionality Where We Are Now: DMTPC Detector Development Jocelyn Monroe November 8, 2007

Dark Matter is ~25% of the energy density of the universe. Jocelyn Monroe November 8, 2007

1 st Dark Matter Evidence Fritz Zwicky Vera Rubin Jocelyn Monroe November 8, 2007

Properties density ~ 0.3 GeV/cm 3 optically dark cold mass: ~unconstrained interactions: < weak σ dust-like, collisionless v RMS ~ 230 km/s we are rotating relative to the halo: a dark matter wind Jocelyn Monroe November 8, 2007

Properties density ~ 0.3 GeV/cm 3 optically dark cold mass: ~unconstrained interactions: < weak σ dust-like, collisionless v RMS ~ 230 km/s we are rotating relative to the halo: a dark matter wind Jocelyn Monroe November 8, 2007

Candidates SUSY dark matter (neutralinos, gravitinos, sneutrinos, axinos) axions, simpzillas, light scalar dark matter, little Higgs dark matter, Kaluza-Klein dark matter, CHAMPS, D-matter, Cryptons, SWIMPS, Mirror particles, Brane world dark matter, Q-balls, sterile model neutrinos, etc. Jocelyn Monroe November 8, 2007

Direct Detection Signal: χ N ➙ χ N’ χ χ Backgrounds: γ e - ➙ γ e - ’ n N ➙ n N’ N ➙ N’ + α , e - ν N ➙ ν N’ γ γ Jocelyn Monroe November 8, 2007

χ χ WIMP Scattering kinematics : β D ~ 8E-4! Z E D = 1 2 m D v 2 A A E recoil = E D r ( 1 − cos θ ) 2 4 m D m T r = Spin Independent: ( m D + m T ) 2 χ scatters coherently off of the entire nucleus A: σ ~A 2 q 2 = 2 m T E recoil Spin Dependent: coherent interactions, only unpaired nucleons contribute very low recoil energies to scattering amplitude: σ ~ J(J+1) D. Z. Freedman, PRD 9, 1389 (1974) Jocelyn Monroe November 8, 2007

Measurement Recoil Nucleus χ Kinetic Energy χ N ~ Jocelyn Monroe November 8, 2007

Spin-Independent Cross Section Limits current experiments larger detectors Jocelyn Monroe November 8, 2007

The Wind: Annual Modulation June-December event rate asymmetry ~2-10% Drukier, Freese, Spergel, Phys. Rev. D33:3495 (1986) Dama positive result: 6.1 σ excluded by other experiments Jocelyn Monroe November 8, 2007

Spin-Dependent Cross Section Limits current direct detection experiments 10 7 x larger upper limits than SI cross sections Jocelyn Monroe November 8, 2007

The Wind: Directionality Cygnus Daily direction modulation: asymmetry ~ 20-100% in forward-backward event rate. Spergel, Phys. Rev. D36:1353 (1988) a dark matter source! Jocelyn Monroe November 8, 2007

Dark Matter Search Strategy Expected WIMP Interaction Cross Section Backgrounds The Zero-Background Paradigm Jocelyn Monroe November 8, 2007

Signal SUSY+ collider limits: σ ( χ A) may be as small as 10 -48 cm 2 Shrimps, not WIMPS: 1 pb = 10 -36 cm 2 σ (weak) ~ 10 -3 pb σ (DM el) ~ 10 -10 pb ~10 4 below current expt’l sensitivity J. R. Ellis, et al., PRD 71 , 095007 (2005) Jocelyn Monroe November 8, 2007

10 4 is a lot of σ 10 -28 cm 2 : σ (total inelastic pp at TeVatron) 10 -35 cm 2 : σ (gg ➔ H) at LHC (Standard Model) 10 -37 cm 2 : σ (gg ➔ H) at TeVatron (Standard Model) 10 -39 cm 2 : σ (single top) at TeVatron Not to Scale 10 -40 cm 2 : σ ( ν QE) at MiniBooNE (E ν = 1 GeV) 10 -43 cm 2 : σ ( ν NC Elastic) for geo- ν (E ν = 2 MeV) 10 -45 cm 2 : σ ( ν -e Elastic) for solar ν σ (DM coherent scattering)? 10 -48 cm 2 Jocelyn Monroe November 8, 2007

EM Backgrounds (D. McKinsey) Gamma ray interaction rate is proportional to (# of electrons in detector) x (gamma ray flux) Typical count rate = 100 events/s/kg = 10,000,000 events/day/kg in a good lead shield, rate drops to 100 events/day/kg Best dark matter detectors: sensitive to 0.01 events/day/kg ( σ ~1E-44 cm 2 ) Jocelyn Monroe November 8, 2007

μ μ Neutron Backgrounds γ N* N n (A. Heim/D. M. Mei) eg. Study for CDMS-II Cosmic muons Detector spall neutrons: ~10 -4 neutrons/ (100 GeV μ )/ gm/cm 2 Boulby, neutron flux: 10 -8 - 10 -10 /cm 2 /s (range for depth) Homestake Caverns Jocelyn Monroe November 8, 2007

U and Th Decay Backgrounds can’t shield a detector from U and Th inside, recoiling progeny and associated betas can fake nuclear recoils Jocelyn Monroe November 8, 2007

ν Backgrounds can’t shield a detector from ν coherent elastic scattering of ν solar neutrinos Φ (B 8 ) = 5.86 x 10 6 cm -2 s -1 Z N N 100 events/ton-year = ~ 10 -46 cm 2 limit unless you measure the direction! JM, P. Fisher, PRD76:033007 (2007) Jocelyn Monroe November 8, 2007

Setting a Limit 1. The theoretical dark matter interaction rate is: E R = nuclear recoil energy, � c 1 R 0 � � − c 2 E R � dR exp = E 0 = dark matter particle energy dE R E 0 r E 0 r 2. Experiments measure: �� 2 v 0 �� N 0 ( ρ D / m D ) �� R 0 = σ 0 × exposure √ π A σ A = σ 0 F 2 ( E R , A ) I c , , I c = A 2 F 2 ( E R , A ) = nuclear form factor 3. vary until (90% of the time) theory predicts observed rate σ A 4. Normalize to to compare limits: σ W − N � µ 1 � 2 � 1 � 2 m D m target µ = σ W − N = σ A µ A A ( m D + m target ) Jocelyn Monroe November 8, 2007

... in the Presence of Background step 3: vary until (90% of the time) σ A theory predicts observed maximum gap between background events S. Yellin, Phys. Rev. D66:032005 (2002) Yellin gap method: a way to make a “zero-background” measurement over a restricted range of an experiment’s acceptance (zero signal too) Jocelyn Monroe November 8, 2007

Directionality Expected Signal Limit Sensitivity Discovery Potential Jocelyn Monroe November 8, 2007

Directional Signal Expectation �� R 0 d 2 R � − ( v E cos ψ − v min ) 2 � 1 � � dE R d ( cos ψ ) = exp v 2 2 E 0 r 0 Cygnus 0.18 Events /kg / day 0.16 0.14 0.12 0.1 0.08 0.06 D. N. Spergel, 0.04 Phys. Rev. D37 1353 (1988) 0.02 0 020406080 Recoil Kinetic Energy (keV) -0.20 0.20.40.60.8 1 ) B A L 100 � ( 120 s o C 140 -0.4 160 -0.6 180 -1-0.8 200 Jocelyn Monroe November 8, 2007

Forward-Backward Asymmetry Define coordinate system with respect to direction to Cygnus (F) (B) Compare integral of cos( ϴ CYGNUS ) above 90% 90 o with below: A = ( forward − backward ) ( forward + backward ) Asymmetry increases with increasing recoil kinetic energy, ~maximal by 100 keV Jocelyn Monroe November 8, 2007