Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos R. S. Raghavan Virginia Tech XII...

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Transcript of Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos R. S. Raghavan Virginia Tech XII...

  • Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos

    R. S. RaghavanVirginia Tech

    XII Neutrino TelescopesVenice March 9 2007

  • BeBeginnings: Important influences:

    Zero Threshold Reactions (ZTR)Weinberg Paper 1962: Inference:

    All weak interaction reactions (EC, , +) are affected by the CRN. Their normal decay rates are modified by additionalMode of decay induced by CRN species anti to that emitted in normal decayCRNNormal DecayA(Z) A(Z+1) + e- + eRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • II. Long interest in e reactionswith thresholds
  • Cross section for IEC---Resonance reactionApply Resonance Theory contains all weak interaction properties (IEC) 0 unless E(e) = Q(EC).within very difficult since very very narrow for weak decays

    No progress since 1968 since no sourceof resonant e could be found

    RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Idea III. Bahcall 1963 Bound state beta decayTake source of beta decaynot 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 e energy is at exactly I mean Exactly at resonanceEmission & Absorption areExact time-reversed processesResonant capture of antineutrinosExact resonance is still impossible unless thee is emitted and absorbed WITHOUT RECOIL (RSR 2005)Moessbauer neutrinos ! (still --many solid state problems now in technical development )

    2005 (RSR)Yes there is ! RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Induced Decay?What happens when eis applied not to the daughter to excite it but to the radioactive PARENT to persuadeit to decay?

    Same formula can be appliedIn this case the reaction threshold is ZEROAny neutrino can induce decaycosmic relic nu of ultra-low energyRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Radiative EC decay induced by CRNCompetes with normalradiative EC (Internal BremmstrahlungKnown since 1940Morrison & Schiff))RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • CRN induced Radiative EC / K radiative fraction of K-EC decayphoton coupling is the same as in normal IB emission / EC = (/12) Q2 (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 9 2007

  • This formula displays new general physical insights for CRN-induced decay Every nu in beam can induce decay (spectral density for interaction/incident nu = 1/eV if (in eV) determined by the deBroglie wavelength of incident CRNkey pointMomentum of CRN are very small smallest of known Nus (CRN effect) is largest for CRN than for any other known Nu !

    Nature provides a rare break for nu physics & cosmology

    = h / (s)RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Rates, background.

    CRN Source: number density, motion of earth in galaxy

    Assume mc2 = 1 eV: N is only for eFor earth v = 10-3 cRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • K [m c2 / (v/c)] fK

    RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Signal: Monoenergetic line just above endpoint

    Background:

    Unavoidable background Internal Bremmstrahlung just below end point(in mc2 units)RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Illustration: EC decay of 37ArTarget factor is fK = ft / tRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Typical experimental numbers for 37Ar andImplications for nu massRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • Exactly same considerations for + and - decaysexcept: Drop the photon coupling factorK improves by x103 Mainly because 10-4 photon factor is absent Positron Decay:RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • mc2 sensitivity a few meVRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • tTritium case very unfavorable because f is so low (v low energy ~18 keV) for T decayRSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • For better case, go to high energy decaysshort lifetimesCan apply continuous beams of radioactive speciesExample: 6He Q~ 3.5 MeV t1/2 ~1 s: production e.g. 9Be(n,)In a powerful nuclear reactorexctract beam by boiling off He.Mass sensitivity few meV

    6He beams (100 amp, 1018 He/year ( mega Curie Equivalents) are being produced in beta-beam development. Technology available now.RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007

  • New: Signatures for CRN effect

    For a given target, size of effect depends on the Neutrino Momentum in the experiment. If the momentumIs controllable, the effect can be controlled.Example: Ar source experimentVearth in galaxy 300 km/sVearth rotation 30 km/sec10% 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 9 2007

  • Additional Signatures:kinematic control in beam experiments

    Precision velocity control necessary< 1 keV (~ galaxy motion)v

  • 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 (E~0.2 eV)Target selection is not very restrictiveMany possibilitiesBeams 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 9 2007

    H