Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos R. S. Raghavan Virginia Tech XII Neutrino Telescopes Venice March

Be Beginnings: Important influences: Zero Threshold Reactions (ZTR) Weinberg Paper 1962: Inference: All weak interaction reactions (EC, β −, β + ) are affected by the CRN. Their normal decay rates are modified by additional Mode of decay induced by CRN species anti to that emitted in normal decay CRN Normal Decay A(Z)  A(Z+1) + e - + ν e RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

II. Long interest in ν  e reactions with thresholds << 1.8 MeV (geoneutrinos etc) In particular the 1 MeV addition due to positron emission L Mikaelyan (1968) showed the way…. Induced Electron Capture-- IEC σ (IEC) ≈ 0 unless E(ν e ) = Q(EC). Resonance Reaction A(Z) A(Z-1) EC IEC Q EC Γ RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Resonance Density = No of nu’s in beam Per unit energy At the resonance energy Width of final state h / τ = mean life = deBroglie Wavelength of Incident neutrino = h/p Cross section for IEC- --Resonance reaction—Apply Resonance Theory Γ contains all weak interaction properties σ (IEC) ≈ 0 unless E(νe) = Q(EC). within Γ  very difficult since Γ very very narrow for weak decays  No progress since 1968 since no source of resonant ν e could be found RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Idea III. Bahcall 1963  Bound state beta decay Take source of beta decay—not normal one where e goes into thecontinuum but is captured in a bound orbit— bound state beta decay !(0.5% in tritium) In this case the ν e energy is at exactly –I mean Exactly at resonance—Emission & Absorption are Exact time-reversed processes  Resonant capture of antineutrinos— Exact resonance is still impossible unless the ν e is emitted and absorbed WITHOUT RECOIL (RSR 2005)  Moessbauer neutrinos ! (still --many solid state problems now in technical development ) 2005 (RSR)—Yes there is ! A(Z)  A(Z+1) + e - + ν e  A(Z) IEC Q EC Γ RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

ν e A(Z) A(Z-1) EC Q EC Γ Induced Decay? What happens when ν e is applied not to the daughter to excite it but to the radioactive PARENT to persuade it to decay?  Same formula can be applied  In this case the reaction threshold is ZERO  Any neutrino can induce decay  cosmic relic nu of ultra-low energy RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Radiative EC decay induced by CRN ν e A(Z) A(Z-1) EC Q EC Γ γ Competes with normal radiative EC (Internal Bremmstrahlung Known since 1940—Morrison & Schiff)) RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

CRN induced Radiative EC ω γ / ω K radiative fraction of K-EC decay— photon coupling is the same as in normal IB emission ωγ / ωEC = (α/12π) Q 2 (Bambynek et al RMP 49, 77, 1977) We have now everything to understand rates of the CRN effect and the unshieldable background due to internal bremmstrahlung RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

This formula displays new general physical insights for CRN-induced decay Every nu in beam can induce decay  ρ (spectral density for interaction/incident nu = 1/eV if Γ (in eV)  σ determined by λ the deBroglie wavelength of incident CRN—key point  Momentum of CRN are very small –smallest of known Nu’s  σ (CRN effect) is largest for CRN than for any other known Nu ! Nature provides a rare break for nu physics & cosmology = h / τ (s) RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Rates, background…. CRN Source: number density, motion of earth in galaxy Assume m ν c 2 = 1 eV: N ν is only for ν e For earth v = c RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

K  [m ν c 2 / (v/c)] f K RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Signal: “Monoenergetic” line just above endpoint Background: Unavoidable background —Internal Bremmstrahlung just below end point (in mc 2 units) RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Illustration: EC decay of 37Ar Target factor is f K = ft / t RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Typical experimental numbers for 37Ar and Implications for nu mass RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Exactly same considerations for β + and β - decays except: Drop the photon coupling factor K improves by x10 3 Mainly because photon factor is absent Positron Decay: RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

 m ν c 2 sensitivity a few meV RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

t Tritium case very unfavorable because f is so low (v low energy ~18 keV) for T decay RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

For better case, go to high energy decays—short lifetimes Can apply continuous beams of radioactive species Example: 6He —Q~ 3.5 MeV t 1/2 ~1 s: production e.g. 9 Be(n,α) In a powerful nuclear reactor—exctract beam by boiling off He. Mass sensitivity  few meV 6He beams (100 μamp, He/year (  mega Curie Equivalents) are being produced in beta-beam development. Technology available now. RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

New: Signatures for CRN effect For a given target, size of effect depends on the Neutrino Momentum in the experiment. If the momentum Is controllable, the effect can be controlled. Example: Ar source experiment V earth in galaxy 300 km/s V earth rotation 30 km/sec ±10% daily sinusoidal variation of p  20% max variation Of signal every day with time of day  Easily detectable RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Additional Signatures:  kinematic control in beam experiments Precision velocity control necessary— < 1 keV (~ galaxy motion) Δv << 1 keV  May be possible to explore mass structure of neutrino  The e-flavor is present in different proportions in each mass eigenstate that move with different momenta  The size of the CRN effect will increase and decrease  As the correct velocity is scanned  complete PMNS matrix ( is there a θ 13 ? Since m 3  is much more separated than 1 and 2.  Heavier neutrinos of any kind (sterile?)  Earth motions completely cancelled –natural CRN FD spectrum  Absolute energies from absolute beam velocities RSRaghavan Virginia Tech: XII Nu telescopes Venice Match

Conclusions Experiments (Ar, O, He) are all within reach of state of the art Technology Nuclear Physics (beams, source production, beta spectrometers,Ge detectors (GammaSpheres), Bent Crystal Spectrometers ( ΔE~0.2 eV)…… Target selection is not very restrictive—Many possibilities Beams of Light nuclei easily produced and manipulated Cautious view of ONE experimentalist: Future for CRN science and spectroscopy appears not so dim! RSRaghavan Virginia Tech: XII Nu telescopes Venice Match