Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Sudbury Neutrino Observatory

  1. May 31, 2008 #1
    I've been reading about this very fascinating experiments there and one thing I can't figure out--either from their literature or that from other places--is how they can be sure that the reactions producing the Cherenkov light are caused by *neutrinos*. That is, how do we know that it's electron-neutrinos that are turning the neutron into the proton and themselves turning into an electron? Is that the only way that reaction could happen? If so, why?

    also, in the second, neutron-current reaction, how, again, do we know that it's neutrinos causing the deuterium to break apart. could not some other particles be causing it?

    btw, I'm a writer, and this information would be very helpful for a story I'm writing.

    Many thanks in advance,

    Eric Grunwald
  2. jcsd
  3. Jun 16, 2008 #2
    I do not usually take it upon myself to interpret standard model theories, however, since no one else has responded to WriterMon's inquiry I will attempt an answer. I believe that most SM theorists would agree that Neutrino theory is not based so much on what we "know" as upon a complex system of "conjectures". Neutrinos as they are commonly defined are very minimally interacting particles and the detection rate therefore is extremely low. Neutrino observatories are based upon the theory that if you isolate a detection system sufficiently from all the more interacting particles you can reasonably hope that the reactions seen in the detector are from Neutrinos. Historically it has been noted that the rate of detection has spiked in these systems just prior to the detection of visible light from new supernovae.
    This is probably the strongest evidence that the detection theory has some validity, however, it is technically not feasible to provide a detection system which is perfectly isolated from all other radiations.

    I studied the commentary by Leon Lederman in his book "The God Particle" and I came away very skeptical of his interpretation of the results on the experiments upon which his team deduced the existence of "electron-neutrinos". I believe he failed to understand what was happening in the system. I believe that pair-bonded electrons were passing through the thick metal walls of the isolation chamber and producing the results that his team observed. However, I do not think that most SM theorists would acknowledge that electrons can bond in both neutral and double charge "transient states".
  4. Jun 24, 2008 #3
    Thanks, Lodestone!

    Here's a reply I received privately to a message I sent directly to SNO:

    Hi Eric,

    Thanks for your interest in SNO.

    There are many different reactions that can occur within the SNO
    detector. Any reaction other than the neutrino interactions that
    produces a neutron or a high-energy electron is a problem for us.
    Some sources are of these "backgrounds" are cosmic rays (high energy
    muons), and decay products from radioactive elements such as uranium,
    thorium and radon in our detector. To reduce these backgrounds as
    much as possible we bury the detector deep underground and keep
    things as clean as possible, including a very elaborate water
    purification system.

    But some backgrounds always remain. Certain types of backgrounds can
    be removed by cuts in the data. For instance, muon-produced neutrons
    can be largely eliminated because they come a short time after a muon
    event, so we simply ignore all events for a certain amount of time
    after each muon. (Muons are easy to spot because they are such high
    energy, and light up the entire detector. We even have outward-
    looking phototubes to catch muons that occur in the water outside the
    detector for this reason.) Any remaining backgrounds must be
    eliminated by statistical analysis of the data.

    The radioactive-element backgrounds are difficult to cope with, and
    some types of these events can not individually be distinguished from
    a neutrino event. So we rely on statistical analysis to determine
    the number of these types of events. Once you have a large number of
    events, the spatial distribution, direction, and energy spectrum of
    the events give you clues as to the number of the various types of
    events. We run Monte Carlo simulations to determine the expected
    characteristics of all event types, and fit the results to the
    observed spectra. This allows us to determine the fraction of
    background events, as well as allowing us to quantify the different
    types of neutrino events. We have to think very carefully about all
    possible backgrounds so we can model them properly in Monte Carlo.
    As I said, this is a statistical analysis. So out of all the events
    we observe, we can say that a certain number are likely to be charge-
    current events, etc, even though we don't know the type of each
    individual event.

    I hope this helps.
  5. Jun 24, 2008 #4

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    WriterMon, I think you got a very good answer from SNOlab.

    Lonestone, deciding based on a popularization that a Nobel-prize winning experiment (and one replicated dozens of times since then) is all wrong is the height of hubris.
  6. Jun 24, 2008 #5
    Hi WriterMon

    Though you're probably looking for more detailed information, below are a couple of links to promotional videos regarding neutrino detecting experiments including the SNO-

    Sudbury Neutrino Observatory (SNO)-


    IceCube Neutrino Observatory AMANDA project-


  7. Jun 25, 2008 #6
    Thanks, guys! Yeah, I'm also using IceCube in my novella!

    stay cool,
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook