A search for the analogue to Cherenkov radiation by high energy neutrinos at superluminal speeds in ICARUS

Abstract

The OPERA Collaboration (2011) [1] has reported evidence of superluminal νμ propagation between CERN and the LNGS. Cohen and Glashow (2011) [2] argued that such neutrinos should lose energy by producing photons and e+e− pairs, through Z0 mediated processes analogous to Cherenkov radiation. In terms of the parameter δ ≡ (v2ν −v2 c )/v2 c , the OPERA result corresponds to δ ≈ 5 · 10−5. For this value (note that (vν − vc)/vc ≈ δ2 ≈ 2.5 · 10−5) of δ, a very significant deformation of the neutrino energy spectrum and an abundant production of photons and e+e− pairs should be observed at LNGS. We present an analysis based on the 2010 and part of the 2011 data sets from the ICARUS experiment, located at Gran Sasso National Laboratory and using the same neutrino beam from CERN. We find that the rates and deposited energy distributions of neutrino events in ICARUS agree with the expectations for an unperturbed spectrum of the CERN neutrino beam, as also reported by OPERA. Our results therefore refute a superluminal interpretation of the OPERA result according to the Cohen and Glashow (2011) prediction [2] for a weak current analog to Cherenkov radiation. In a dedicated search, no superluminal Cherenkov-like e+e− pair or γ emission event has been directly observed inside the fiducial volume of the “bubble chamber-like” ICARUS TPC-LAr detector, setting the much stricter limit of δ < 2.5 · 10−8 at the 90% confidence level,comparable with the one due to the observations from the SN1987a (M.J. Longo, 1987 [4]). The observations of high energy neutrino events by Super-Kamiokande and IceCube are also pointing to a much stricter limit on δ.