We show that the rate of charged-current ν_μ events with a hard internal bremsstrahlung photon is consistent with the excess ν_e candidate events reported by the MiniBoone and LSND (decay in flight) experiments. [See Apparent Low-energy Discrepancy] Hard photons radiated by the muon leg in charged-current neutrino interactions (ν_μ N → μ γ N) are a significant source of background that should be considered by current and future ν_μ → ν_e neutrino oscillations appearance experiments (e.g. LSND, MiniBoone, SuperK, MINOS, T2K and NOVA).

[Q] Didn't MiniBoone include the process in their MC simulation? GEANT-type simulation should have included this type of background.

[Arie's Answer] GEANT only does external bremstrahlung. The internal bremstrahlung is part of the cross section radiative corrections. There is no way that GEANT can do it. It has to be part of the cross section model. So it is not included unless one includes it in the cross section Monte Carlo.

[Q] Does MiniBooNE's estimate include "muon internal bremsstrahlung"?

[Janet's Answer] No but we have limited the effect with our own data to a level and can show it is negligible. We are going to put a paper up on the webserver soon. Only about 20% of out numu CCQE events fail to have a michel electron. So if the 200 event execss in our single subevent were due to numu CCQE were due to misidentifying muons with hard bremsstranhlung plus failing to find the michel, then in the 2 subevent sample we would have 5 times that excess or 1000 events! I assure you there is no 1000 event excess and we will post the plots soon.

Ref. 1: astro-ph/0409064.pdf
Ref. 2: astro-ph/0607179.pdf