Prospects for the Direct Detection of the Cosmic Neutrino Background

Transcription

1 Prospects for the Direct Detection of the Cosmic Neutrino Background Andreas Ringwald ringwald DESY PANIC 2008 November 9 14, 2008, Eilat, Israel

2 Prospects for the Direct Detection of the CNB 1 0. Introduction Progress in observational cosmology Cosmic recipe emerged: Material Particles E or m N ρ /ρc Obs. Radiation γ 0.1 mev % CMB Hot Dark > 0.04 ev > 0.1 % BBN Matter Neutrinos CMB < 0.6 ev < 2 % LSS Ordinary BBN Matter p, n, e MeV-GeV % CMB Cold Dark WIMPs? > 100 GeV < LSS Matter 25 % CMB Axions? < mev > Dark SN Energy? ev? 70 % CMB [Connecting quarks... cosmos] Direct, weak interaction based detection of the Cosmic Neutrino Background (CNB)?

3 Prospects for the Direct Detection of the CNB 2 Indirect evidence for CNB from cosmological probes: BBN prefers N ν > 0 (expansion rate during BBN He-4 abundance) CMB and LSS prefer N ν > 0 (matter/radiation eq. fluctuation power spectra) CNB has not been detected directly in laboratory: neutrinos interact only weakly smallness of neutrino mass small momentum-transfer Design of direct, weak interaction based detection experiment need phase space distribution of relic neutrinos theoretically known better than ever! Further content: 1. How many, how fast? 2. How to detect? 3. Conclusions

4 Prospects for the Direct Detection of the CNB 3 1. How many, how fast? Relic neutrinos decoupled at t 1 s Predictions (for small degeneracy): n νi 0 = n νi 0 ßÞ Ð CνB = 3 22 n γ ßÞÐ 0 CMB = 56 cm 3 # relic neutrinos # relic photons p νi 0 = p νi 0 ßÞ Ð CνB 4 1/3 = 3 Tγ 0 11 ßÞÐ CMB = ev At least two neutrino mass eigenstates nonrelativistic (m νi ev) Gravitational clustering on CDM Density enhanced in galactic halos

5 Prospects for the Direct Detection of the CNB 4 1. How many, how fast? Relic neutrinos decoupled at t 1 s Predictions (for small degeneracy): n νi 0 = n νi 0 ßÞ Ð CνB = 3 22 n γ ßÞÐ 0 CMB = 56 cm 3 # relic neutrinos # relic photons p νi 0 = p νi 0 ßÞ Ð CνB 4 1/3 = 3 Tγ 0 11 ßÞÐ CMB = ev At least two neutrino mass eigenstates nonrelativistic (m νi ev) Gravitational clustering on CDM Density enhanced in galactic halos

6 Prospects for the Direct Detection of the CNB 5 1. How many, how fast? Relic neutrinos decoupled at t 1 s Predictions (for small degeneracy): n νi 0 = n νi 0 ßÞ Ð CνB = 3 22 n γ ßÞÐ 0 CMB = 56 cm 3 # relic neutrinos # relic photons p νi 0 = p νi 0 ßÞ Ð CνB 4 1/3 = 3 Tγ 0 11 ßÞÐ CMB = ev At least two neutrino mass eigenstates nonrelativistic (m νi ev) Gravitational clustering on CDM Density enhanced in galactic halos

7 Prospects for the Direct Detection of the CNB 6 1. How many, how fast? Relic neutrinos decoupled at t 1 s Predictions (for small degeneracy): n νi 0 = n νi 0 ßÞ Ð CνB = 3 22 n γ ßÞÐ 0 CMB = 56 cm 3 # relic neutrinos # relic photons p νi 0 = p νi 0 ßÞ Ð CνB 4 1/3 = 3 Tγ 0 11 ßÞÐ CMB = ev At least two neutrino mass eigenstates nonrelativistic (m νi ev) Gravitational clustering on CDM Density enhanced in galactic halos [archive.ncsa.uiuc.edu]

8 Prospects for the Direct Detection of the CNB 7 Relic neutrinos in neighbourhood of Earth (r 8 kpc): Overdensity 1 20 Momentum distribution: almost isotropic flat at low momenta turning point at p esc m ν v esc m ν 2 φ(r ) matches Fermi-Dirac at high momenta [AR,Wong 04]

9 Prospects for the Direct Detection of the CNB 8 Relic neutrinos in neighbourhood of Earth (r 8 kpc): Overdensity 1 20 Momentum distribution: almost isotropic flat at low momenta turning point at p esc m ν v esc m ν 2 φ(r ) matches Fermi-Dirac at high momenta [AR,Wong 04]

10 Prospects for the Direct Detection of the CNB 9 2. How to detect? Some possibilities of direct detection: mechanical force through coherent scattering of relic neutrinos neutrino capture on β decaying nuclei Pauli blocking effects near thresholds for atomic neutrino pair emission enhanced by laser irradiation scattering of accelerator beams off the relic neutrinos

11 Prospects for the Direct Detection of the CNB 10 Mechanical force based detection Low average momentum of relic neutrinos corresponds to a (reduced) de Broglie wavelength of macroscopic dimension, λ = 1/ p = 0.12 cm/ y Envisage scattering processes in which many target atoms act coherently over a macroscopic volume λ 3 elastic scattering rate enhanced by N A A ρ t λ ( )( ) ( 100 ρt λ A g/cm cm ) 3 compared to case where neutrinos are elastically scattered coherently only on the individual nuclei of the target [Shvartsman et al. 82; Smith,Lewin 83]

12 Prospects for the Direct Detection of the CNB 11 Test body will experience neutrino wind force through random neutrino scattering: a t ν, ν [Shvartsman et al. 82; Smith,Lewin 83;...; Duda et al. 01] n ν v ßÞ rel Ð flux 4π 3 N2 A ρ t r 3 t σ νn 2 m ν v ßÞ rel Ð mom. transfer nν 10 3 c ρt rt n ν v rel g/cm 3 λ Majorana neutrinos: suppressed by factor (v rel /c) 2 s 2 3 cm At present, smallest measurable acceleration > cm/s 2, using conventional Cavendish-type torsion balance. Improvements to > cm/s 2 proposed [Hagmann 99] Detection possible in years, if neutrinos are Dirac particles [Smith 03]

13 Prospects for the Direct Detection of the CNB 12 Test body will experience neutrino wind force through random neutrino scattering: a t ν, ν [Shvartsman et al. 82; Smith,Lewin 83;...; Duda et al. 01] n ν v ßÞ rel Ð flux 4π 3 N2 A ρ t r 3 t σ νn 2 m ν v ßÞ rel Ð mom. transfer nν 10 3 c ρt rt n ν v rel g/cm 3 λ s 2 3 cm Majorana neutrinos: suppressed by factor (v rel /c) 2 Laser Resonator At present, smallest measurable acceleration > cm/s 2, using conventional Cavendish-type torsion balance. Improvements to > cm/s 2 proposed [Hagmann 99] Detection possible in years, if neutrinos are Dirac particles [Smith 03] A B Neutrino Target [Hagmann 99] Persistent Magnet Suspension Magnet Balancing Mass

14 Prospects for the Direct Detection of the CNB 13 Test body will experience neutrino wind force through random neutrino scattering: a t ν, ν [Shvartsman et al. 82; Smith,Lewin 83;...; Duda et al. 01] n ν v ßÞ rel Ð flux 4π 3 N2 A ρ t r 3 t σ νn 2 m ν v ßÞ rel Ð mom. transfer nν 10 3 c ρt rt n ν v rel g/cm 3 λ s 2 3 cm Majorana neutrinos: suppressed by factor (v rel /c) 2 At present, smallest measurable acceleration > cm/s 2, using conventional Cavendish-type torsion balance. Improvements to > cm/s 2 proposed [Hagmann 99] Detection possible in years, if neutrinos are Dirac particles [Smith 03] MWnow mν = nν nν λ = 1 p v 0.6 ev cm ev cm ev cm ev cm NFWhalo mν = 0.6 ev cm ev cm ev cm ev cm

15 Prospects for the Direct Detection of the CNB 14 Neutrino capture of radioactive nuclei based detection [Irvine,Humphrey 83; Cocco,Mangano,Messina 07; Lazauskas,Vogel,Volpe 08; Blennow 08] Consider neutrino capture on e.g. tritium, Capture rate of CNB neutrinos, ν i + 3 H e + 3 He N i, CNB 6.5 yr 1 ( 100 g 3 H ) 1 Uei 2 n ν i n νi Signature: monoenergetic electrons with kinetic energy T kin = Q β + m νi where Q β = 18.6 kev is the energy release in 3 H β-decay for m νi = 0

16 Prospects for the Direct Detection of the CNB 15 Main challenge: Separation of signal electrons from overwhelming background of electrons from 3 H β-decay Need very good energy resolution < 0.5 ev (degenerate masses), 0.05eV (inverted hierarchy), ev (normal hierarchy) 200 = 0.03 ev = 0.06 ev 1000 Mixed neutrinos Single unmixed neutrino Rate [events/(ev year)] 100 Rate [events/(ev year)] T e - Q [ev] T e - Q [ev] [Blennow 08] Opportunity for KATRIN ( 0.5eV) and future 3 H β decay campaigns

17 Prospects for the Direct Detection of the CNB 16 Pauli blocking of atomic neutrino pair emission [Yoshimura 07;Takahashi,Yoshimura 07] Laser irradiated neutrino pair emission from metastable ions or atoms, γ + I I + ν i ν i j I ** i! ji * i jni º i {º j Signature: detection of I ; rate resonantly enhanced by tuning ω In presence of CNB, rate reduced near threshold due to Pauli blocking

18 Prospects for the Direct Detection of the CNB 17 Accelerator beam based detection For center-of-mass energies below W- and Z-resonances, cf. 2mν E 4.5 ( mν ) ( ) 1/2 1/2 E MeV ev 10 TeV weak interaction cross sections grow rapidly with energy Exploit a flux of extremely energetic particles accelerator beams from cosmic rays [Weiler 82;...;Fodor,Katz,AR;...;Eberle,AR,Song,Weiler;...;L.Schrempp,AR;...] for scattering on relic neutrinos as target

19 Prospects for the Direct Detection of the CNB 18 Exploit accelerator beams: Scattering rate [B. Müller 87; Melissinos 99, Weiler 01] R ν A Z N ν, ν n ν σ ν A Z N L I/(Z e) nν mν A 2 n ν ev Z Too small to give rise to an observable effect in the foreseeable future (LHC, VLHC) Need Ultimate Large Hadron Collider Few elastic scattering events per year; hard to detect, due to small momentum transfers ( 1 GeV at E N 10 7 TeV) Alternative: exploit inverse beta decay A Z N + ν e A Z+1 N + e detect A Z+1N on exit of machine EN 10 TeV L 100 km I 0.1 A [Melissinos 99; Zavattini unpubl] yr 1 R accel. N E N L I νa n ν nν m ν ev [TeV] [km] [A] [yr 1 ] p LHC Pb VLHC p Pb ULHC p

20 Prospects for the Direct Detection of the CNB Conclusions BBN, CMB, and LSS provide presently the only evidence for the CNB Roadmap for direct CNB detection A more more direct, weak interaction based detection of the big bang relic neutrinos may proceed by measuring neutrino capture in β decaying nuclei Remarks: current technology 1-2 orders of magnitude off coherent elastic scattering of relic ν s off nucleons in terrestrial detector Remarks: current technology 3 orders of magnitude off Pauli blocking effects in laser induced atomic neutrino pair emission Remarks: needs more study to estimate discovery potential interactions of very high energy particles from terrestrial accelerator beams with the relic neutrinos as target Remarks: needs design of specialized accelerator (beyond our lifetime?)