Reanalysis of the GALLEX solar neutrino flux and source experiments

TL;DR

This reanalysis of GALLEX and GNO data leverages enhanced pulse-shape discrimination and improved counter calibrations to refine the solar neutrino flux measurement. The GALLEX-only solar flux is updated to $P_⊙ = 73.4^{+6.1}_{-6.0}$ (stat.)$^{+3.7}_{-4.1}$ (syst.) SNU, with a cross-check via a rise-time analysis; combining GALLEX with GNO yields a consolidated flux of $67.6 \, \pm \, 4.0$ (stat.)$ \pm \, 3.2$ (syst.) SNU. Reanalyzed $^{51}$Cr source experiments indicate a smaller excited-state cross-section contribution than previously assumed, suggesting a reduction of the $^7$Be capture component from 34.8 to ~32.7 SNU. Overall, the results reinforce a consistent, albeit somewhat reduced, solar neutrino signal in gallium experiments and help constrain neutrino oscillation interpretations through improved cross sections and inter-experiment consistency.

Abstract

After the completion of the gallium solar neutrino experiments at the Laboratori Nazionali del Gran Sasso (GALLEX}: 1991-1997; GNO: 1998-2003) we have retrospectively updated the GALLEX results with the help of new technical data that were impossible to acquire for principle reasons before the completion of the low rate measurement phase (that is, before the end of the GNO solar runs). Subsequent high rate experiments have allowed the calibration of absolute internal counter efficiencies and of an advanced pulse shape analysis for counter background discrimination. The updated overall result for GALLEX (only) is (73.4 +7.1 -7.3) SNU. This is 5.3% below the old value of (77.5 + 7.5 -7.8) SNU (PLB 447 (1999) 127-133) with a substantially reduced error. A similar reduction is obtained from the reanalysis of the 51Cr neutrino source experiments of 1994/1995.

Figures (10)

• Figure 1: Proportional counter signal $P(t)$ of a typical multiple event in addition with the 10%-70% rise time levels (above) and the primary current $j(t)$ of the same event derived by deconvolution with the three major peaks (below).
• Figure 2: Distribution of pulse shape parameter $C_1$ for $^{71}\rm Ge$ events (black) and background events (grey) in the L (above) and K (below) energy range.
• Figure 3: All candidate events, divided in early ($t<3 \tau$) and late ($t>3 \tau$) events.
• Figure 4: Single results of the 65 Gallex solar runs (error bars are $\pm 1\sigma$ statistical).
• Figure 5: Distribution of the Gallex single run results in bins of 20 SNU.