Download - Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos R. S. Raghavan Virginia Tech
Zero Threshold Reactions for Detecting Cosmic Relic Neutrinos
R. S. RaghavanVirginia Tech
XII Neutrino TelescopesVenice March 9 2007
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 additionalMode of decay induced by CRN species anti to that emitted in normal decay
CRN
Normal Decay
A(Z) A(Z+1) + e- + νe
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
II. Long interest in νe 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(νe) = Q(EC).
Resonance Reaction
A(Z)
A(Z-1)
ECIEC
QEC
Γ
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
Resonance Density= No of nu’s in beamPer unit energyAt the resonance energy
Width of final stateh / τ = mean life
= deBroglieWavelength ofIncidentneutrino = h/p
Cross section for IEC---Resonance reaction—Apply Resonance Theory
Γ contains all weak interaction properties
σ (IEC) ≈ 0 unless E(νe) = Q(EC).within Γ very difficult sinceΓ very very narrow for weak decays
No progress since 1968 since no sourceof resonant νe could be found
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
Idea III. Bahcall 1963 Bound state beta decayTake 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 νe energy is at exactly –I mean Exactly at resonance—Emission & Absorption areExact time-reversed processesResonant capture of antineutrinos—Exact resonance is still impossible unless theνe 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- + νe
A(Z)
IECQEC
Γ
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
νe
A(Z)
A(Z-1)
EC QEC
Γ
Induced Decay?What happens when νe
is 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 energy
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
Radiative EC decay induced by CRN
νe
A(Z)
A(Z-1)
EC QEC
Γ
γ
Competes with normalradiative EC (Internal BremmstrahlungKnown since 1940—Morrison & Schiff))
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
CRN induced Radiative EC
ωγ / ωK radiative fraction of K-EC decay—photon coupling is the same as in normal IB emissionωγ / ωEC = (α/12π) 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 decayρ (spectral density for interaction/incident nu = 1/eV if Γ (in eV)σ determined by λ the deBroglie wavelength of incident CRN—key pointMomentum of CRN are very small –smallest of known Nu’sσ (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 9 2007
Rates, background….
• CRN Source: number density, motion of earth in galaxy
Assume mνc2 = 1 eV: Nν is only for νe
For earth v = 10-3 c
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 37Ar
Target factor is fK = ft / t
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
Typical experimental numbers for 37Ar andImplications for nu mass
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
Exactly same considerations for β+ and β- decaysexcept: Drop the photon coupling factor
K improves by x103 Mainly because 10-4 photon factor is absent
Positron Decay:
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
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 9 2007
For better case, go to high energy decays—short lifetimesCan apply continuous beams of radioactive species
Example: 6He —Q~ 3.5 MeV t1/2 ~1 s: production e.g. 9Be(n,α)In a powerful nuclear reactor—exctract beam by boiling off He.
Mass sensitivity few meV
6He beams (100 μamp, 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 experiment
Vearth in galaxy 300 km/s
Vearth 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 9 2007
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 neutrinoThe e-flavor is present in different proportions in each mass eigenstate that move with different momentaThe size of the CRN effect will increase and decreaseAs the correct velocity is scannedcomplete PMNS matrix ( is there a θ13 ? Since m3
is much more separated than 1 and 2.Heavier neutrinos of any kind (sterile?)
Earth motions completely cancelled –natural CRN FD spectrumAbsolute energies from absolute beam velocities
RSRaghavan Virginia Tech: XII Nu telescopes Venice Match 9 2007
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 9 2007