REVIEW
Coherence of neutrino oscillations in the wave packet approach
High Energy Physics - Phenomenology · Submitted 18 Nov 1997 · 13 references
Pith's verdict: A useful, compact extension of the wave-packet formalism with a real algebra slip in Eq. (13) that shifts, but does not kill, the new coherence bound.
T0 · AI review
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Referee report
The paper
The paper claims
Precise measurement of the particles that detect a neutrino can stretch the distance over which its mass states still interfere, but a wave-packet calculation puts a ceiling on that stretch, set by the neutrino energy and the mass-squared差距
The reading
What carries the argument
The load-bearing device is the overlap integral between two gaussian wave packets: the propagating state produced at the source and a separate gaussian state representing the neutrino the detector is able to absorb. Their widths add in quadrature, $1sigma_x^2 = 1sigma_{xP}^2 + 1sigma_{xD}^2$, which is what lets the detection process enter the coherence length at all. The second device is the average of the probability over the detection time $T$, which is not measured in real experiments. That average converts the packet-separation gaussian into the damping factor $1exp[-(L/L_{1mathrm{coh}}^{ab})^2]$ multiplied by $F_{ab} = 1exp[-2pi^2(1-1xi)^2 (1sigma_x/L_{1mathrm{osc}}^{ab})^2]$, where $1xi$ parametrizes how the mass eigenstate energies are fixed by production kinematics. The interplay of these two exponentials is what produces both the claimed gain and the claimed ceiling.
Extended reading notes
Core claim
The paper's central claim is that the coherence length of neutrino oscillations has an upper bound. Working in the wave-packet formalism, the authors write the flavor-changing amplitude as the overlap $A_{1D0}(L,T) = 1int dx 1langle1 u_1beta(x-L)|1 u_1alpha(x,T)1rangle$ of the propagating neutrino state with a detection state that carries its own momentum width $1sigma_{pD}$, so that the width controlling coherence is $1sigma_x^2 = 1sigma_{xP}^2 + 1sigma_{xD}^2$ rather than the production width alone. Averaging the resulting probability over the unmeasured detection time $T$ gives the standard oscillation phase together with a damping factor $1exp[-(L/L_{1mathrm{coh}}^{ab})^2]$ and an extra factor $F_{ab}$, with $L_{1mathrm{coh}}^{ab} = 4sqrt{2}1sigma_x E^2/|1Delta m_{ab}^2|$. Because a precise energy measurement in the detector means a small $1sigma_{pD}$ and hence a large $1sigma_{xD}$, the coherence length can indeed be increased, as Kiers, Nussinov and Weiss had observed. But once $1sigma_x$ exceeds the oscillation length, the phase of the interference term depends sensitively on the unmeasured $T$, and the time average erases the interference. That yields the ceiling $L_{1mathrm{coh}}^{ab} 1lesssim E,(L_{1mathrm{osc}}^{ab})^2 = 16pi^2 E^3/(1Delta m_{ab}^2)^2$, beyond which the coherence length stops being a meaningful quantity because coherence is lost at every distance.
Load-bearing premise
The derivation treats the detected neutrino as a gaussian wave packet sharing the propagating states' average momenta and averages the probability over all detection times from minus to plus infinity, an approximation the authors themselves note gives the detector an unphysical response before the neutrino arrives.
Editorial extensions
If this is right
- Coherence lengths quoted for oscillation experiments should be computed from the larger of the production and detection coherence widths, not from the production width alone.
- An experiment that measures the recoil particles' energies very precisely gains coherence length only up to $16pi^2 E^3/(1Delta m^2)^2$; beyond that the gain does not translate into visible oscillations.
- In the opposite regime, where the effective packet width exceeds the oscillation length, the observable transition probability flattens to the averaged value $1sum_a |U_{1alpha a}|^2|U_{1beta a}|^2$ with no oscillatory term.
- The same washout logic applies when the source distance $L$ rather than the time $T$ is unknown, which the authors note is the situation relevant to neutrino oscillations in the early universe.
Reading between the lines
- The ceiling is a statement about the unmeasured time, not about the neutrino itself: if a detection scheme could time-stamp the interaction to within the oscillation period, the interference the paper says is washed out would in principle be recoverable.
- Because the bound scales as $E^3/(1Delta m^2)^2$, the loss of coherence is most severe for low-energy neutrinos with large mass splittings, which is the regime of solar and reactor neutrinos rather than accelerator beams.
- The authors' own footnote concedes that the gaussian detection packet lets the detector respond before the neutrino arrives; a retarded, causal packet would likely soften rather than remove the ceiling, and checking whether the bound survives that replacement is a concrete calculational target.
Original abstract
The temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of neutrino oscillations, confirming the observation of Kiers, Nussinov and Weiss that an accurate measurement of the energies of the particles participating in the detection process can increase the coherence length. However, the wave packet treatment presented here shows that the coherence length has an upper bound, determined by the neutrino energy and the mass-squared difference, beyond which the coherence of the oscillation process is lost.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
The temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of neutrino oscillations, confirming the observation of Kiers, Nussinov and Weiss that an accurate measurement of the energies of the particles participating in the detection process can increase the coherence length. However, the wave packet treatment presented here shows that the coherence length has an upper bound, determined by the neutrino energy and the mass-squared difference, beyond which the coherence of the oscillation process is lost.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of neutrino oscillations, confirming the observation of Kiers, Nussinov and Weiss that an accurate measurement of the energies of the particles participating in the detection process can increase the coherence length. | contribution 0.50 | 0.27 | 0.11 | asserted 0.98 |
| s1 | However, the wave packet treatment presented here shows that the coherence length has an upper bound, determined by the neutrino energy and the mass-squared difference, beyond which the coherence of the oscillation process is lost. | result 0.98 | 0.90 | 0.79 | asserted 1.00 |
What was examined, and what was not
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References
How the literature uses it
36 arXiv papers cite this in 59 sentences
Papers citing it · 35 sentences without a confident label
Contests it 1 paper
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This differs from statements frequently found in the literature, e.g., Refs. [ref] , where it is said that all neutrino mass eigenstates are produced at the moment the source decays, and the different mass eigenstates propagate with different velocities in the lab frame.
Neutrino Oscillation Measurements Computed in Quantum Field Theory · Discussion and Conclusions · contest 0.79
Uses its method or tool 5 papers
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Localization is implemented by assigning Gaussian wave packets to all external lines and performing the calculation accordingly [ref] .
Real and Virtual Propagation in Neutrino Oscillations · External Wave Packet Model · 0.85
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In this section we present a simple one-dimensional quantum-mechanical wave-packet model [ref] in which the momentum uncertainties of the states which describe the produced and detected massive neutrinos are approximated by Gaussian distributions.
Neutrino Flavor States and the Quantum Theory of Neutrino Oscillations · Quantum-Mechanical Wave-Packet Model · 0.82
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We do this using the wave-packet formalism for neutrino propagation [ref] and by properly investigating the kinematical constraints imposed by the neutrino production process.
Beyond $\Delta m^2$: Absolute Mass Sensitivity in Neutrino Oscillations · Neutrino Oscillations Beyond Leading Order · 0.98
Compares with it 2 papers
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We can also use the fact that $Δv=Δm^2/2E_ν^2$ to find: [equation] It is notable that the wavepacket separation term obtained in this limit corresponds precisely to the one obtained through a treatment that ignores the entangled recoil altogether, for example Ref. [ref] .
The Width of a Beta-decay-induced Antineutrino Wavepacket · From parent localization scale to neutrino coherence distance · 0.99
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While intriguing, results consistent with ours have been found in the literature [ref] .
Beyond $\Delta m^2$: Absolute Mass Sensitivity in Neutrino Oscillations · Production kinematics and the next-to-leading-order phase · 0.81
Cites it as background 13 papers
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From a theoretical perspective, the wave-packet formulation in quantum field theory (WPQFT) provides one of the most fundamental frameworks for describing neutrino oscillations, and the basics of the formalism were established in [ref] .
Real and Virtual Propagation in Neutrino Oscillations · Introduction · 0.91
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That the finite width of the wavepacket has implications for neutrino oscillation phenomenology has been long recognized and widely studied theoretically [ref] .
The Width of a Beta-decay-induced Antineutrino Wavepacket · Introduction · 0.99
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The microscopic layer relates to the theories in the literature [ref] , which can be represented by either the Fock-PS or the Wigner-PS on which Fock states and the Wigner quasi-probability distribution are represented, respectively.
Microscopic and Macroscopic Effects in the Decoherence of Neutrino Oscillations · Introduction · 0.85
Discussion
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