Is there a problem with low energy SN1987A neutrinos?

Abstract

The observation of several low energy events during the SN1987A burst made by Kamiokande-II is somewhat puzzling when compared with the theoretical expectations and with the observations of IMB, and has an important weight in the attempts to use these data to learn about the properties of the supernova neutrinos. In this paper, we analyze the possibility that a few of the 12 events observed by Kamiokande-II (or 11, neglecting the event number 6) are due to background. The volume distribution of these events is not a uniform distribution at the 3 σ level and this suggests the presence of background events close or at the border of the volume used for the analysis. The theoretical energy distribution is not in perfect agreement with the observations, but the disagreement is not severe, especially when we consider the presence of a peak of low energy background events. The expected energy distribution is used to show that the observation of a supernova neutrino signal has a significance of 8.5 σ and that 2 − 4 background events are plausible. In summary, the distributions of the events in space and in energy support the hypothesis that 3 or 4 of the low energy events-a priori, 2.3 of them-are due to background.In this way, we can argue that there is no actual disagreement between the average energy of the supernova neutrinos seen in Kamiokande-II and the theoretical expectations, the remaining discrepancy being a 1 σ effect. PACS

Improved analysis of SN1987A antineutrino events

“…This definition is different from the one of LL, B i = B(E e )L i (E e )dE e , that has been argued to be inaccurate in [44]. The values of B i that we use for Kamiokande-II are given in Appendix A of [44]. The events of Kamiokande below 7 MeV have a higher background rate than found by LL, those above 9 MeV a lower background rate, while the other ones stay almost unchanged.…”

“…In fact, the events observed by IMB [16,17], Kamiokande-II [18,19] and Baksan [20], represent a historic opportunity to investigate the physics of the collapse and of the explosion. A very extensive literature testifies the effort to extract information from these data with a wide variety of methods [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44]. Usually, a specific characteristic of the SN1987A data is studied, most frequently the energy distribution.…”

“…However, we deem that, in view of the importance of their claim and in the light of various advances in neutrino physics (e.g., in oscillations, [47,48,49,50] and [51,52,53,54,55]), it is necessary to offer a critical discussion of the assumptions of the analysis by Lamb and Loredo. More specifically: 1) the likelihood structure can be enhanced including a more accurate detection cross section [56], the information on the directions of the events, a different treatment of the background [44]; 2) the theoretical model for neutrino emission, required for the data analysis, can be improved and approached as much as possible to the real signal expected from the numerical simulations of neutrino emission. In this respect, a specific criticism was raised by Raffelt and Mirizzi [42], who emphasized that the two-phase parameterization used in LL analysis leads to a sudden jump of the average neutrino energy while passing from accretion to cooling.…”

“…The background distribution differential in time, energy and cosine is B(E e )/2; the factor 1/2 describes a uniform cosine distribution. This definition is different from the one of LL, B i = B(E e )L i (E e )dE e , that has been argued to be inaccurate in [44]. The values of B i that we use for Kamiokande-II are given in Appendix A of [44].…”

Broad-band non-thermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants

“…This would also suppress the electron temperature and the thermal X‐ray emission (Drury et al 2009; Helder et al 2008). A conclusive proof of the hadronic nature of the gamma‐ray emission will possibly come from the detection of neutrinos from SNRs, which are expected to be produced during the same hadronic interactions responsible for the production of gamma rays (Costantini & Vissani 2005; Gabici & Aharonian 2007; Kappes et al 2007). However, since the detection of neutrinos appears challenging even for km 3 ‐scale neutrino telescopes, the search for evidence of CR proton acceleration coming from gamma‐ray or multiwavelength observations is mandatory.…”