Proc. Neutrino Astrophysics - MPP Theory Group

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22 Status of the Radiochemical Gallium Solar <strong>Neutrino</strong> Experiments Michael Altmann Physik Department E15, Technische Universität München, D–85747 Garching and Sonderforschungsbereich 375 Astro-Particle Physics With the successful completion of Gallex after six years of operation and the smooth transition to Gno a milestone in radiochemical solar neutrino recording has been reached. The results from Gallex, 77 ±6±5SNU, and Sage, 74 +11 −10 +5 −7 SNU, both being significantly below all solar model predictions, confirm the long standing solar neutrino puzzle and constitute an indication for non-standard neutrino properties. This conclusion is validated by the results of 51Cr neutrino source experiments which have been performed by both collaborations and 71As doping tests done in Gallex. GALLEX and SAGE: Radiochemical Solar <strong>Neutrino</strong> Recording The radiochemical gallium detectors, Gallex and Sage, have been measuring the integral solar neutrino flux exploiting the capture reaction 71 Ga + νe → 71 Ge + e − . The energy threshold being only 233keV, this reaction allows to detect the pp-neutrinos from the initial solar fusion step which contribute about 90% to the total solar neutrino flux. In a typical run the target, consisting of 30tons of gallium in the form of 101t GaCl3 solution for Gallex and 55t of metallic gallium for Sage, is exposed to the solar neutrino flux for 3-4 weeks. In the following I will mainly focus on Gallex, as for Gallex and Sage the experimental procedure – apart from the chemical extraction of the neutrino produced 71 Ge and the stable germanium carrier which is added at the beginning of each run – is rather similar. Both experiments use the signature provided by the Auger electrons and Xrays associated with the decay 71 Ge + e − → 71 Ga + νe for identification of 71 Ge during a several months counting time. Referring to [4, 5] for a detailed description of the detector setup and experimental procedure I concisely summarize the Gallex experimental program in table 1. Table 1: GALLEX experimental program. It comprises 4 periods of solar neutrino observations (Gallex 1 – Gallex 4), two chromium neutrino source experiments (Source I and Source II) and the arsenic test. date exposure period number of runs result 5/91–4/92 Gallex I 15 solar + 5 blank 81 ± 17 ± 9 SNU 8/92–6/94 Gallex II 24 solar + 22 blank 75 ± 10 +4 −5 SNU 6/94–10/94 Source I ( 51Cr) 11 source runs R = 1.01 +0.11 −0.10 10/94–10/95 Gallex III 14 solar + 4 blank 54 ± 11 ± 3 SNU 10/95–9/96 Source II ( 51Cr) 7 source runs R = 0.84 +0.12 −0.11 9/96–1/97 Gallex IV 12 solar + 5 blank 118 ± 19 ± 8 SNU 1/97–3/97 71As-test 4 arsenic runs Y = 1.00 ± 0.03
The combined result of all 65 Gallex solar runs is 76.4 ± 6.3 +4.5 −4.9 SNU. We note, however, that for the Gallex-IV period pulse shape information is used only for K-peak signals. The present result from Sage, 74 +11 −10 +5 −7 SNU [7], is in perfect agreement with Gallex. The overall results from both experiments are only about 60% of the predictions from solar model calculations, which constitutes an indication for non-standard neutrino properties, even without considering the results from other solar neutrino experiments. The 51 Cr neutrino source experiments In order to validate this conclusion and check the reliability and efficiency of their detectors, both collaborations have prepared intense (≈ 2MCi (Gallex) and 517kCi (Sage)) 51 Cr neutrino sources by neutron irradiating isotopically enriched Cr [3]. 51 Cr decays by EC and emits neutrinos of energy 750keV (decay to g.s., 90%) and 430keV (decay to 320keV excited level, 10%), nicely accommodating the neutrino energies of the solar 7 Be branch. For Gallex, the source has been inserted in the central tube of the target tank. Altogether 18 extractions have been performed with the source in place, divided into two series of measurements with the source being re-activated in between. Figure 1 shows the individual run results. Figure 1: Individual run results of the GALLEX chromium neutrino source experiments, normalized to the known source activity, as a function of time after the end of neutron irradiation of the source. The horizontal bars indicate the durations of the exposures, the exponential curve the expectation from the decay of the source. Source I and Source II runs are represented by circles and diamonds, respectively. An analysis of Source I and Source II yields R = 1.01 +0.11 +0.12 −0.10 and R = 0.84 −0.11 , respectively, where R is the source activity as deduced from the neutrino measurement normalized to the 23
Page 1 and 2: arXiv:astro-ph/9801320v1 30 Jan 199
Page 3: Preface This was the fourth worksho
Page 6 and 7: vi S.J. Hardy Quasilinear Diffusion
Page 8 and 9: viii
Page 11 and 12: History of Neutrino Physics: Pauli
Page 13 and 14: Brief an Oskar Klein, Stockholm, vo
Page 15 and 16: Recent observations with the Hubble
Page 17 and 18: MACHO sample of ∼100,000 light cu
Page 19: Solar Neutrinos
Page 22 and 23: 14 In the depth range where an abun
Page 24 and 25: 16 as follows: (1) All the detector
Page 26 and 27: 18 [3] J.N. Bahcall and H.A. Bethe,
Page 28 and 29: 20 the opacity has a very slowly ch
Page 32 and 33: 24 known true source activity. The
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Page 36 and 37: 28 Events/day/kton/bin 0.3 0.25 0.2
Page 38 and 39: 30 log(Δm 2 (eV 2 log(Δm )) 2 (eV
Page 40 and 41: 32 Table 1: Neutrino event rates in
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Page 44 and 45: 36 Measurements of Low Energy Nucle
Page 46 and 47: 38 Figure 1: The S(E) factor of 3 H
Page 48 and 49: 40 Solar Neutrinos: Where We Are an
Page 50 and 51: 42 [9] B. Pontecorvo, Chalk River R
Page 52 and 53: 44 Figure 2: The difference between
Page 55 and 56: Phenomenology of Supernova Explosio
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Supernova Neutrino Opacities G.G. R
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Quasilinear Diffusion of Neutrinos
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Assuming a saturated thermal distri
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Anisotropic Neutrino Propagation in
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So far the damping rate corresponds
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Cherenkov Radiation by Massless Neu
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on ω so that they are well approxi
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2 2 / meff,e m eff 1.0 0.5 0.0 elec
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Gamma-Ray Burst Observations D.H. H
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Figure 1: The cumulative distributi
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[7] Lilly, S., in Critical Dialogue
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) Phase Transitions in Neutron Star
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after the collapse began (nb., no e
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Models of Coalescing Neutron Stars
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Figure 2: Contour plots of the mass
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From our torus models we find that
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High-Energy Neutrinos
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110 in gamma-rays. However, the acc
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112 Atmospheric Muons and Neutrinos
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114 Today, however, charm productio
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116 Atmospheric Neutrinos in Super-
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118 number of events 300 200 100 (a
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120 Acknowledgements D.K. is suppor
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122 Key signatures for νµ nucleon
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124 (a.u) 0.5 0.4 0.3 0.2 0.1 0 0 1
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126 However, in order to operate th
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128 could be gravitationally captur
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130 Ground-Based Observation of Gam
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132 Figure 2: Sensitivities in unit
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134 Crab flux Figure 4: Gamma-ray f
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136
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Helium Absorption and Cosmic Reioni
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Non-Standard Big Bang Nucleosynthes
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) Non-standard Neutrino Properties
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some heating of the plasma. In cont
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Big Bang Nucleosynthesis With Small
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Neutrinos and Structure Formation i
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Photon and Neutrino Backgrounds The
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The (photon) temperature at aeq is
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spectrum has therefore changed to 1
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Figure 4: Growth of structure in CD
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Future Prospects
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162 Figure 1: Calorimetric β − s
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164 References [1] F. Gatti: Procee
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166 The frequency of Galactic super
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168 Table 1: Comparison of proposed
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170 Neutrinos in Astrophysics José
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172 N eq 7 6.5 6 5.5 5 4.5 4 3.5 3
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174 Figure 4: SN 1987A bounds on FC
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176 [5] A. Joshipura and J. W. F. V
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178 Some Neutrino Events of the 21s
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180 2099: Relic Neutrinos And last
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182
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184 Tuesday, Oct. 21: Supernova Neu
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186 Michael Altmann Technische Univ
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188 Paolo Gondolo Max-Planck-Instit
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190 Patrizia Meunier Max-Planck-Ins
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192 Torsten Soldner Technische Univ
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194 A Experimental Particle Physics
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196 C Astrophysics and Cosmology C1
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