About the sign of ∆m 2 12.

The present status of the problem of identifying the sign of ∆m 12 is discussed in view of the development of new methods of detection of solar neutrinos. The results of solar neutrino experiments [1]-[5] plus KamLAND [6] give strong evidence that neutrinos are massive particles and do oscillate [7]. The important point is that KamLAND experiment allows both signs for ∆m 12 while solar neutrino experiments restrict it only as a positive value. If this is true then one can state that these experiments gave us the very fundamental result that m2 > m1. The impact of this is so great that nearly in all reports and all papers by describing the neutrino mass schemes only the case m2 > m1 is analyzed. Should we accept that this is a firmly established fact? Wise people say “No” [8] because we still have no “a smoking gun evidence” of this. We do have “a smoking gun evidence” from SNO experiment [5] that boron electron neutrinos are attenuated by a factor of about three what is expected from MSW effect [9] and this result is confirmed by a global analyses of all data [7] which prescribes also the attenuation factor of about two for low energy neutrinos observed in a gallium experiment [2], [3]. The agreement is impressive but still this is not enough to make the final conclusion that m2 is really heavier than m1. But what if not? Will this be a total collapse for the solar neutrino experiments? This question was investigated in [10] and it was shown that it is possible to add to a standard Hamiltonian a non standard part which can restore agreement but the mixing angles will be different from what are given now. The introduction of the new free parameters into a theory is of course a costly affair but sometimes it works. What about a mixing angle it appears to be that this point needs some further clarification. And here the new experiments will be very helpful. There are proposals to conduct the new experiments with the reactor antineutrinos [11] which can increase the accuracy of measuring a mixing Corresponding author: Kopylov A.V., Institute for Nuclear Research of Russian Academy of Sciences, Prospect of 60th Anniversary of October Revolution 7A, 117312, Moscow, Russia; telephone (095)3340961, Fax (095)1352268, e-mail: [email protected]