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Re: [Phys-l] Neutrinos going faster than speed of light?



-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of Jack Uretsky
Sent: Saturday, September 24, 2011 5:40 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Neutrinos going faster than speed of light?

There were no light rays involved in the experiment. The
experimenters calculated the equivalent light arrival time using the
defined value of the speed of light (in vacuo). The experimentally
measured quantities (which could, of course, be subject to error) were
(1) the distance from the target at CERN to the Gran Sasso detector,

[Bill Nettles] From the paper: "The measurement also relies on
a high-accuracy geodesy campaign that allowed measuring the 730 km CNGS baseline with a
precision of 20 cm."
So, that measurement was made in house, it seems. The reference given for this measurement is [26] G. Colosimo, M. Crespi, A. Mazzoni, M. Jones and D. Missiaen, “Determination of the CNGS global geodesy”, OPERA public note 132 (2011). That's a measurement that needs to be retaken.

Two statements concern me. "Mesons decay in flight into neutrinos in a 1000 m long vacuum tunnel.” At the top of page 5. Then, "The point where the parent meson produces a neutrino in the decay tunnel is unknown.
However, this introduces a negligible inaccuracy in the neutrino time of flight measurement,
because the produced mesons are also travelling with nearly the speed of light." I don't completely follow their subsequent argument as to why this 1000 m distance produces "negligible inaccuracy." The "superluminal" neutrinos could be produced anywhere in that 1000 m, and the superluminal distance delta is only 20 m. I follow their timing method, somewhat, but this 1000 m decay tube is bothersome.

(2) The time between the clicker pulse (putting the proton beam on
target)
and the event in the deetector signifying a neutrino hit.
[Bill Nettles] If you read the paper, the timing is a statistical pattern matching with GPS time stamps, not a single packet-to-neutrino-event start/stop. There are "bunches" of smaller "packets" of proton-on-target events so the GPS time stamps help them correlate the data. It's really ingenious if it's done correctly. I still don't understand why the unknown decay location in a 1000 m tube is "negligible."

Regards,
Jack

"Trust me. I have a lot of experience at this."
General Custer's unremembered message to his men,
just before leading them into the Little Big Horn Valley