Opera

[pamela]

arxiv.org

 

The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (60.7 \pm 6.9 (stat.) \pm 7.4 (sys.)) ns was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.48 \pm 0.28 (stat.) \pm 0.30 (sys.)) \times 10-5.

[phision]

arxiv.org

I have tried to find out as much as possible about the, "high precision geodesy measurements", as I feel any error which may have happened, is likely to have occurred in the "baseline" calculation. I have saw the accuracy of the baseline measurement quoted as, +/- 20cm, but have, as yet, failed to find out how this accuracy was achieved! Could anyone involved in this measurement or who knows details of how the measurement was taking, PLEASE, point me in the direction of this information?

[JMJones0424]

Here's a link to the pdf

 

Determination of the CNGS global geodesy

 

http://operaweb.lngs.infn.it/Opera/publicnotes/note132.pdf

[phision]

Here's a link to the pdf

 

Determination of the CNGS global geodesy

 

http://operaweb.lngs.infn.it/Opera/publicnotes/note132.pdf

Thank you, for the above link, exactly the kind of information I was looking for.

 

May I ask, if you randomly knew of this link or are you more intimately involved in it's content?

[JMJones0424]

No, my random knowledge tends to be far more esoteric and less useful than particle physics. If you need to know the ideal breech points on a structure, or the air order of battle for Haeju, I'm your man.

 

I don't want to end up being guilty of over promotion of an off-site blog, but I regularly read the blog Starts With a Bang, written by a theoretical astrophysicist, Ethan Siegel. I find his explanations to be very understandable, which is rare amongst physicists.

 

Comment number 96 in the post Are We Fooling Ourselves With FTL Neutrinos is where I first learned of the OPERA report on their distance measurements.

 

Before anyone is continuing to speculate over superliminal velocities, I would like to point

out something interesting...

 

Determination of the CNGS global geodesy

http://operaweb.lngs.infn.it/Opera/publicnotes/note132.pdf

 

To get the exact point on the surface of earth, we need to know the position

of the GPS satellites for a given time and their distance from us. No problem so far,

GPS is able to provide us with that information.

 

The authors used the Bernese software which is available under

http://www.bernese.unibe.ch/

 

There are some kinds of problems which will be further points of investigation

if my first suspicion is incorrect.

One problem: You will normally compile Bernese yourself and it is a known problem

that FORTRAN compilers are very different in their quality to numerical

problems. The second problem is that FORTRAN constants are stored in REAL

precision (6-7 digits) if you are not declaring them. Anyway...

 

Lets imagine a programmer did the marginal error of not using the correct

reference ellipsoid value of 6 378 137 m, but the abbreviated version

6 378 000 m.

 

What will be the influence on the GPS precision ? Practically *NOTHING* because

the satellites are symmetrically around the earth and position accuracy is very insensitive against

height changes if the distance between sender and receiver is long enough.

For example, to get a 18 m change for a distance of 730 km you need a height difference of

5 km !

So the values are in fact accurate concerning the position and noone will see a problem,

the software is reliable.

 

But what if you want to know the *distance* between two points on earth ? Having a slightly

smaller value has the effect that the calculated distance is smaller than the actual distance.

 

How much ?

 

730534.610 km * ( (6 378 137 /6 378 000)-1.0) = 15.7 m

 

15.7 m / 299 792 458 m/s = 52.3 ns

 

Opera difference: 53.1 and 67.1 ns

 

Strange coincidence, isnt it ?

 

The conversation immediately following that comment may be of interest to you as well.

[phision]

Thank you JMJones0424 :D