Direct Measurement Of The (7)Be Solar Neutrino Flux With 192 Days Of Borexino Data

We report the direct measurement of the 7 Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV (7)Be neutrinos is 49 +/- 3(stat) +/- 4(syst) counts/(day . 100 ton). The hypothesis of no oscillation for (7)Be solar neutrinos is inconsistent with our measurement at the 4 sigma C.L. Our result is the first direct measurement of the survival probability for solar P, in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of (7)Be, pp, and CNO solar v(e) and the limit on the effective neutrino magnetic moment using solar neutrinos.