Sudbury Neutrino Observatory

  • Thread starter WriterMon
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  • #1
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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
Boston
 

Answers and Replies

  • #2
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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".
 
  • #3
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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.
 
  • #4
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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
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Thanks, guys! Yeah, I'm also using IceCube in my novella!

stay cool,
eRic
 

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