Why did the Super-Kamiokande experiment detect half the number of neutrinos emanating from below the earth as from above it?
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2$\begingroup$ Can you please cite the source where you read that? I can't find a statement that that was the case. $\endgroup$– Red ActCommented Sep 25, 2014 at 20:37
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$\begingroup$ This may be a confusion about some basic facts about the super-k measurement. There is a factor of 2,nut between muon and electron flavors in the starting distributions, and the is an up/down difference that depends on the distance traveled. $\endgroup$– dmckee --- ex-moderator kittenCommented Sep 25, 2014 at 21:01
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$\begingroup$ @RedAct Hello, please see ctp.Berkeley.edu/neutrino/neutrino4.html. It mentions that the experiment "discovered that about half of the atmospheric neutrinos from the other side of the Earth were lost, while those from above were not." $\endgroup$– AmygdalaCommented Sep 25, 2014 at 21:10
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$\begingroup$ @dmckee Thank you. Does this mean that the experiment could only detect certain flavours but not all? $\endgroup$– AmygdalaCommented Sep 25, 2014 at 21:12
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$\begingroup$ @Amygdala Thanks for the link. Note that according to that link, Super-Kamiokande is unable to identify tau neutrinos. $\endgroup$– Red ActCommented Sep 26, 2014 at 0:46
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1 Answer
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That is only true if you take a rough look at the number of neutrinos. Actually, a small difference is found when comparing the number of neutrinos during the night (going through the earth) and the day (without having to cross the earth).
This difference is mainly due to the high sensitivity of the detectors on electron neutrinos. When interacting with dense matter (e.g. core of the earth) the neutrinos can oscillate into a different type of neutrino, which explains the small difference in the counting rate. Apart from that, the interaction of neutrinos with matter is in general very low.
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$\begingroup$ Thank you. So there was a bias towards electron neutrino detection? $\endgroup$– AmygdalaCommented Sep 25, 2014 at 21:15
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$\begingroup$ yes, it is indirectly stated for example in this physicsworld-article: "[...] the team found that the flux of solar neutrinos during the night was about 3.2% greater than that measured during the day. In other words, the Earth has caused muon and tau neutrinos to change back to electron neutrinos" $\endgroup$– AlfCommented Sep 26, 2014 at 5:44