Damped neutrino oscillations

Transcription

1 Damped neutrino oscillations Erroneous measurements of neutrino oscillation parameters? Based on hep-ph/ Mattias Blennow Division of Mathematical Physics Department of Physics Royal Institute of Technology (KTH) Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.1/17

2 Outline Standard neutrino oscillations Sub-leading effects and damping factors Implications for experimental measurements Outlook Summary and conclusions Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.2/17

3 Neutrino oscillations Prime candidate for neutrino flavor conversion Pure quantum mechanical effect Requires neutrinos to be massive and mix Physics beyond the SM? Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.3/17

4 Standard oscillation formulas The probability of an α flavor neutrino to convert to a β flavor neutrino is given by P αβ = 3 i,j=1 J ij αβ exp( i2 ij), where ij = m 2 ij L/(4E), J ij αβ = U βiu αiu βju αj, and U is the leptonic mixing matrix. Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.4/17

5 The leptonic mixing matrix The standard way of parameterizing the leptonic mixing matrix in the case of three neutrino flavors is: U = c 13 c 12 c 13 s 12 s 13 e iδ s 12 c 23 c 12 s 23 s 13 e iδ c 12 c 23 s 12 s 23 s 13 e iδ s 23 c 13 s 12 s 23 c 12 c 23 s 13 e iδ c 12 s 23 s 12 c 23 s 13 e iδ c 23 c 13 s ij = sin(θ ij ), c ij = cos(θ ij ) Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.5/17

6 Oscillations vs. other effects MeV prompt analysis threshold KamLAND data best-fit oscillation best-fit decay best-fit decoherence Ratio L 0 /E νe (km/mev) KamLAND Collaboration, Phys. Rev. Lett. 94, (2005) Possible other effects: Neutrino decay Neutrino quantum decoherence Neutrino wave-packet decoherence etc... Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.6/17

7 Damping factors Even if not leading, other effects may still contribute Introduce damping factors into the neutrino oscillation formulas: P αβ = 3 i,j=1 D ij J ij αβ exp( i2 ij), where D ij = exp ( α ij m 2 ij ξ L β E γ ) Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.7/17

8 Damping factors (2) The parameters α ij, ξ, β, and γ are characteristic for the type of effect The number of free parameters can often be reduced to one or two for specific effects Examples: Damping type β γ ξ Wave packet decoherence Decay Oscillations to ν s Absorption Quantum decoherence I Quantum decoherence II 1 or Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.8/17

9 Two classes of damping Most types of damping falls into one of two categories Decoherence-like damping damps only the interference terms: D ii = 1 α ii = 0 β P αβ = 1 Includes: Neutrino wave-packet decoherence, neutrino quantum decoherence Decay-like damping acts independently on the mass eigenstates: D ij = A i A j α ij = α i + α j β P αβ < 1 Includes: Neutrino decay, neutrino absorption Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.9/17

10 Damped probabilities (2f) The effect of damping on the neutrino survival probability P αα : Pure oscillation Oscillation + decoherence Oscillation + decay I Oscillation + decay II Survival probability Oscillation phase ( ) Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.10/17

11 Implications for experiments Damping effects modify the neutrino oscillation probabilities Will give erroneous measurements of the oscillation parameters if not taken into account Higher dimension of the parameter space Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.11/17

12 Example: θ 13 at CHOOZ For neutrino wave packet decoherence at a reactor experiment: Pēē = c 4 13 { 1 1 } 2 sin2 (2θ 12 )[1 D 21 cos(2 21 )] sin2 (2θ 13 )[D 31 c 2 12 cos(2 31 ) +D 32 s 2 12 cos(2 32 )] + s The effect of the damping terms could counter a θ 13 effect If the damping parameters are allowed to vary, the bound on θ 13 may become weaker Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.12/17

13 Example: θ 13 at CHOOZ (2) 10 sin 2 2Θ 13 Σ E sensitivity for Reactor I 5 sin 2 2Θ 13 Σ E sensitivity for Reactor II 8 4 3Σ Fit value of ΣE MeV 6 4 1Σ 2Σ 3Σ Fit value of ΣE MeV 3 2 1Σ 2Σ Fit value of sin 2 2Θ Fit value of sin 2 2Θ 13 Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.13/17

14 Which type of damping? How to identify the specific effect? Baseline length fixed no information on β Energy dependence is a better candidate: Decoherence Decay Oscillations PΜΜ 0.4 PΜΜ 0.4 PΜΜ Σ E 0,1,2,3,4,5 GeV 0.2 Α 0,2,4,6,8, GeV km 0.2 Ε 0,1,2,3,4, ev E GeV E GeV E GeV Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.14/17

15 Outlook Effects that may not be described by damping factors Hamiltonian level effects (e.g., matter effects) Alters the effective neutrino oscillation parameters directly Work in progress Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.15/17

16 Summary and conclusions Sub-leading mechanism treated in a common framework May alter the precision determination of neutrino oscillation parameters Distinguishing different types of effects Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.16/17

17 Damped formulas (2f) Decoherence-like damping: P αβ = δ αβ (1 2δ αβ) sin 2 (2θ)[1 D cos(2 )] Decay-like damping (only one decaying mass eigenstate): P αα = [ (c 2 + As 2 ) 2 A sin 2 (2θ) sin 2 ( ) ], P ββ = [ (Ac 2 + s 2 ) 2 A sin 2 (2θ) sin 2 ( ) ], P αβ = 1 4 sin2 (2θ)[1 + A 2 2A cos(2 )], Damped neutrino oscillations Mattias Blennow, KTH Partikeldagarna 2005 i Lund p.17/17