Solar neutrino flux measurements by the Soviet-American gallium experiment (SAGE) for half the 22-year solar cycle

We present measurements of the solar neutrino capture rate on metallic gallium in the Soviet-American gallium experiment (SAGE) over a period of slightly more than half the 22-year solar cycle. A combined analysis of 92 runs over the twelve-year period from January 1990 until December 2001 yields a capture rate of 70.8(-5.2)(+5.3)(stat)(-3.2)(+3.7)(sys) SNU for solar neutrinos with energies above 0.233 MeV. This value is slightly more than half the rate predicted by the standard solar model, 130 SNU. We present the results of new runs since April 1998 and analyze all runs combined by years, months, and bimonthly periods beginning in 1990. A simple analysis of the SAGE results together with the results of other solar neutrino experiments gives an estimate of (4.6 +/- 1.2) x 10(10) neutrinos cm(-2) s(-1) for the flux of the electron pp neutrinos that reach the Earth without changing their flavor. The flux of the pp neutrinos produced in thermonuclear reactions in the Sun is estimated to be (7.6 +/- 2.0) x 10(10) neutrinos cm(-2) s(-1), in agreement with the value of (5.95 +/- 0.06) x 10(10) neutrinos cm(-2) s(-1) predicted by the standard solar model. (C) 2002 MAIK "Nauka/Interperiodica".