Damping of neutrino oscillations, decoherence and the lengths of neutrino wave packets

Abstract

Spatial separation of the wave packets (WPs) of neutrino mass eigenstates leads to decoherence and damping of neutrino oscillations. Damping can also be caused by finite energy resolution of neutrino detectors or, in the case of experiments with radioactive neutrino sources, by finite width of the emitted neutrino line. We study in detail these two types of damping effects using reactor neutrino experiments and experiments with radioactive 51Cr source as examples. We demonstrate that the effects of decoherence by WP separation can always be incorporated into a modification of the energy resolution function of the detector and so are intimately entangled with it. We estimate for the first time the lengths σx of WPs of reactor neutrinos and neutrinos from a radioactive 51Cr source. The obtained values, σx = (2 × 10−5 − 1.4 × 10−4) cm, are at least six orders of magnitude larger than the currently available experimental lower bounds. We conclude that effects of decoherence by WP separation cannot be probed in reactor and radioactive source experiments.

Decoherence effects in reactor and Gallium neutrino oscillation experiments -- a QFT approach

“…The formalism naturally allows a distinction of "quantum decoherence" (at the amplitude level) compared to "classical averaging" (at the probability level), which are, however, indistinguishable observationally. Our work is complementary to the recent paper by Akhmedov & Smirnov [27], who base their argumentation on the neutrino wave packet approach, reaching very similar conclusions as we do. A somewhat different approach has been pursued by Jones, Marzec & Spitz [43] whose results for the decoherence parameters differ quantitatively from ours.…”

“…First we need to estimate the momentum spreads σ of all involved particles, as well as their velocities v. Similar estimates have been performed recently in [27] in the context of neutrino wave packets. The momentum spread is calculated via the spatial localization δ x , assuming the uncertainty principle δ x σ = 1/2.…”

“…For the initial state nucleus we assume a thermal velocity v = k B T /m, where the temperature in the nuclear fuel ranges from 700 K at the outer egde to 2000 K in the center [52]. This is justified, as the fission products termalize on time scales much faster than their beta decay lifetimes [27]. For nuclei with mass numbers in the range of 80 to 160, the velocity of fission products lies in the range of 6.3×10 −7 to 1.5×10 −6 .…”

“…For early papers on the topic see [1][2][3][4][5][6][7][8][9][10][11], some examples of further investigations are e.g., [12][13][14][15][16][17]. Recently, this discussion received further attention in the context of short-baseline reactor [18][19][20][21] and radioactive source Gallium experiments [22][23][24][25] searching for sterile neutrino oscillations [26][27][28][29][30]. These papers discuss the question whether quantum decoherence could help to reduce tension in the data [26,30] which arises in standard sterile neutrino explanations, see e.g., [31][32][33][34].…”

On neutrino-mediated potentials in a neutrino background

“…reactor neutrinos, estimates are more uncertain, ranging from ∼ 20 MeV to ∼ 1 eV [34][35][36][37][38], with corresponding suppression of the potential from neutrinos of 1 MeV over distances larger than ∼ 10 −14 m to ∼ m.…”