Experimental search for the “LSND anomaly” with the ICARUS detector in the CNGS neutrino beam

A search for a nu_e signal, due to a LSND anomaly, with ICARUS at LNGS exposed at the CNGS neutrino beam, is hereby presented. At a distance of 730 km and with the 0-30 GeV energy interval, such anomaly is characterised by fast energy oscillations with probability averaging to 0.5*sin^2(2 theta_new). This is compared with the small but significant backgrounds due to conventional neutrino sources. The ionization along the early part of e.m. showers, has been examined wire by wire to tag the presence of an electron emitted from the vertex of the neutrino event. This is powerful eliminator of gamma converting pairs, which are generally separated from the vertex and are double minimum ionizing. In order to simulate the LSND anomaly, Montecarlo nu_e events have been generated with the nu_mu energy spectrum. These events have been used to estimate the electron identification efficiency due to visibility cuts, found to be ~74%. The present ICARUS experimental sample is based on 1091 neutrino events, about 50% of the data collected up to now. Two events with a clear electron have been found, compared with the expectation of 3.7 events from conventional sources. Within the range of observations, the result is compatible with the absence of LSND anomaly. At 90 and 99% CL this corresponds to 3.41 and 7.13 events with oscillation probabilities 5.4 10^-3 and 1.1 x 10^-2 respectively. This result strongly limits the window for the LSND anomaly, reducing to a narrow region around Dm2=0.5 eV2 and sin^2(2 theta)=0.05, where there is an overall agreement (90 % CL) between the ICARUS limit, the published limit of KARMEN and the published positive signals of LSND and MiniBooNE collaborations. To complete the search of an LSND-like anomaly, especially in the surviving region, we intend to move the ICARUS detector to a much closer distance and to collect new data from a lower energy neutrino.