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Cake day: June 9th, 2023

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  • The deep sea detector in the news uses Cherenkov radiation to detect the neutrino.

    A neutrino can interact with the nuclei in water molecules (so hydrogen and oxygen nuclei) and produce a charged particle like an electron or a muon. The outgoing particles carry the energy of the incident neutrino, so they can be emitted at a speed greater than the speed of light in the liquid medium.

    Note this is much less than the speed of light in a vacuum, so this isn’t breaking any physics. When charged particles (electrons, muons) pass through a medium at speeds greater than light in that medium, they emit Cherenkov light in a forward cone.

    The Cherenkov light is analogous to the shockwave formed when breaking the sound barrier. Since it points in the direction the particle was traveling, you can detect the shape of the light cone with a large array of photon detectors and reconstruct the direction of the neutrino.














  • My interpretation is you’re both saying the same thing. In regards to what the other person wrote: during Trump’s first term, often people in his administration were worried that something he asked/ordered them to do was against the law. So they’d try to find a legal way to accomplish some part of his request, or just slow walk the order and never really do it. Trump was notorious for having very little follow through on making sure things actually got done. Now trump’s people will do what he asks without worrying about the legality.






  • macarthur_park@lemmy.worldtoScience Memes@mander.xyzCat
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    1 month ago

    Actually we haven’t observed a difference between the speed of neutrinos and light, which sets an upper limit on their mass based on the precision of those measurements. The evidence of mass is much weirder, in the observation of neutrino flavor oscillation.

    Neutrinos come in 3 flavors: electron, tau, and muon. We’ve observed that the flavor oscillates as a function of time, or equivalently as a function of distance from the neutrino source. The data is quite precise, and is perfectly explained by there being 3 neutrino mass states that are distinct from the flavor state. So a neutrino with a well defined flavor will have a superposition of the 3 mass states, with each flavor corresponding to a different admixture of mass states.

    The flavor oscillations allow us to measure the difference in the mass values, but not the absolute masses. Technically it’s possible that the “lightest” neutrino is massless, and the other 2 mass states are nonzero. Without an absolute value for the masses we can’t rule this out.