[ntp:questions] Accuracy of NTP - Advice Needed

Danny Mayer mayer at ntp.org
Wed Dec 28 00:39:10 UTC 2011


On 12/24/2011 1:11 PM, unruh wrote:
> On 2011-12-24, John Hasler <jhasler at newsguy.com> wrote:
>> I wrote:
>>> An upcoming experiment at Fermilab will observe neutrinos at both ends
>>> (the far end will be in Minnesota).
>>
>> unruh writes:
>>> Well, no. At best the electrons or muons at one end.
>>
>> At best the electrical pulse produced by a photomultiplier when struck
>> by a photon generated when a muon or electron emitted as a result of a
>> neutrino collision interacts with the detector medium (there are a
>> variety of detector designs but photomultipliers are almost always
>> involved).
>>
>> However, the use of similar or identical neutrino detectors at both ends
>> means that systemic errors in delay estimation will tend to cancel.  I
>> assume that they will try to match up the timing equipment at both ends
>> as well.
> 
> Just saying, it is not the same neutrino that is being detected at both
> ends. The detection probability is just too small. Thus again there is
> the same inference that the timing at one end measures the same class of
> things as teh timing at the other. 
> 
> Yes, the timing equipment is a worry. They require ns accuracy in the
> timing and m accuracy in the distance. And the timing is not simply gps
> ( although they could have gotten that wrong) but then that timing has
> to be brought down into the mine a km or so below ground and
> horizontally and that also has to be surveyed for the distance.

You need a very good atomic clock at both ends that are synchronized to
each other. Chances are very good that they have a number of them at
each end. Nothing less than an atomic clock will do.

Now what has this to do with the original question?

Danny


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