CERN finds neutrinos faster than light - Page 42

On November 07 2011 07:28 Eishi_Ki wrote:


This was my line of thinking as well, 'If it's something I can come up with, that's not the reason'

On November 07 2011 08:42 aksfjh wrote:

It's all still up for debate. This is a long and arduous process of peer review and repeating the same experiment. While the single result opens up the debate, the general consensus won't be reached for at least a year.

On November 07 2011 12:39 Cyro wrote:
Wait, i thought this was confirmed to be caused by the GPS satellite moving at a different speed relative to the earth through space or something? I forgot what it was, i read an article on it like a month ago but it was pretty much written off

On November 07 2011 12:44 Belisarius wrote:


Escapist wrote it off. Unfortunately, Escapist doesn't actually speak for the scientific consensus. As far as I know, the real jury is still out, which is why a number of major groups are spending quite a lot of time and money setting up to reproduce OPERA's test.

On November 07 2011 15:19 Wampaibist wrote:
My dad works at Michigan state university in nuclear physics and he was telling me about a star that went super nova not to far back, and the neutrinos were not detected before the light reached the earth.

On November 07 2011 21:14 rubio91 wrote:

Guys, i know it's not possible to read 40+ pages of comments, but you should give a quick read of at least the OP and the last 1-2 pages, just to don't repeat the same 2 things ad infinitum. Please read my post in the previous page.

On November 08 2011 05:06 Alay wrote:
Somewhat related to the discussion, but a question;
If motion is relative, how can a "speed limit" like the speed of light exist? Take for example, if you're standing on a bus that's drive at 25mph, and you throw a plastic ball towards the front of the bus. Inside the bus, relative to the environment, the ball moves at 10mph--but to someone standing on the street outside the bus, the ball would be moving 35mph, no?

Throw in bending of space and other wonky crap that gravity causes, how can the speed of light actually be measured accurately--is it based on a common view point? I assume our sun is moving through our galaxy at a high rate--if it's moving and throwing off light, would that light going in the direction it's already moving not "move faster"?

Can someone give me a link or explain this? It's always puzzled me =]

On November 08 2011 05:06 Alay wrote:
Somewhat related to the discussion, but a question;
If motion is relative, how can a "speed limit" like the speed of light exist? Take for example, if you're standing on a bus that's drive at 25mph, and you throw a plastic ball towards the front of the bus. Inside the bus, relative to the environment, the ball moves at 10mph--but to someone standing on the street outside the bus, the ball would be moving 35mph, no?

Throw in bending of space and other wonky crap that gravity causes, how can the speed of light actually be measured accurately--is it based on a common view point? I assume our sun is moving through our galaxy at a high rate--if it's moving and throwing off light, would that light going in the direction it's already moving not "move faster"?

Can someone give me a link or explain this? It's always puzzled me =]

On November 08 2011 05:06 Alay wrote:
Somewhat related to the discussion, but a question;
If motion is relative, how can a "speed limit" like the speed of light exist? Take for example, if you're standing on a bus that's drive at 25mph, and you throw a plastic ball towards the front of the bus. Inside the bus, relative to the environment, the ball moves at 10mph--but to someone standing on the street outside the bus, the ball would be moving 35mph, no?

Throw in bending of space and other wonky crap that gravity causes, how can the speed of light actually be measured accurately--is it based on a common view point? I assume our sun is moving through our galaxy at a high rate--if it's moving and throwing off light, would that light going in the direction it's already moving not "move faster"?

Can someone give me a link or explain this? It's always puzzled me =]

OPERA scientists will measure neutrino velocity over the same baseline without using statistics, by using a new CERN beam which provides proton pulses of 1 to 2 nanoseconds each with 500 nanosecond gaps. They expect to be done before November 21, 2011.[6]

Following OPERA and CERN's request for confirmation, both Fermilab and the T2K experiment have announced they intend to test the OPERA result in coming months.[19] Fermilab has stated that the detectors for the MINOS project are being upgraded, and new results are not expected until at least 2012.[20] A result based on already recorded data should be available in 4 to 6 months. But this result can only possibly refute OPERA's original result; it cannot confirm faster-than-light speeds because the accuracy would not be high enough.[21] Nobel laureate Martin Perl is skeptical of how reanalyzing data will clarify the situation.[22]

The Borexino and ICARUS experiments (both located at Gran Sasso) will begin independent cross-checks of OPERA's results in 2012.[18]

The OPERA Collaboration sent to the Cornell Arxiv a new preprint today, where they summarize the results of their analysis, expanded with additional statistical tests, and including the check performed with 20 additional neutrino interactions they collected in the last few weeks. These few extra timing measurements crucially allow the ruling out of some potential unaccounted sources of systematic uncertainty, notably ones connected to the knowledge of the proton spill time distribution.

These benefits come from CERN, where proton bunches have been made much shorter: down to three nanosecond long pulses. That means that OPERA can measure the speed of each detected neutrino separately! Of course, with such short pulses, the statistics of protons on target is "only" of 4x10^16, but this is still enough to reach meaningful results from the additional data.
The figure below show the timing structure of the proton bunches. The black arrow spans 20 nanoseconds to size up the horizontal scale.



As a sidebar to the improvements yielded by the reduction in the pulse duration, and the related checks that were performed on the source, apparently allowed CERN to spot some less than perfect sinchronisms in the apparatus responsible for the creation of the beam. In particular, the horns that focalize the beam are brought to the right magnetic field by currents that are ramped up before the particles pass through them. It transpired that due to some imperfect arrangement, the currents might still have been ramping up during the passage of the particles, with the result that the focusing of the beam could be less good than predicted.

This might bring into the Opera speed measurement some systematics due to the fact that the neutrinos produced later -the trailing ones from the spill- woud be better focused (field closer to plateau in the horns). However, this potential issue is made irrelevant by working with very narrow proton pulses (however ramping, the current is practically constant during a very narrow proton spill).

So what does OPERA find ? Their main result, based on the 15,233 neutrino interactions collected in three years of data taking, is unchanged from the September result. The most interesting part of the new publication is instead that the find that the 20 new neutrino events (where neutrino speeds are individually measured, as opposed to the combined measurement done with the three-year data published in September) confirm the earlier result: the arrival times appear to occur about 60 nanoseconds before they are expected.

The figure below, taken from the paper, shows the individual timing measurements of the neutrino interactions from the narrow spills taken between end of October and beginning of November. The red line indicates the average of the 20 measurements.



It is necessary here to note that since distance from source to detector and time offsets necessary to determine the travel time of neutrinos have not been remeasured, the related systematics (estimated as well as -possibly- underestimated ones) are unchanged. The measurement therefore is only a "partial" confirmation of the earlier result: it is consistent with it, but could be just as wrong as the other.

Just to make an example, I will reiterate here the doubts I have on one of the time offsets necessary to obtain the timing measurement in Gran Sasso: an 8-km-long light guide brings in a 40,000+-1 ns offset: in order to determine a "delta t" of 60 nanoseconds, a subtraction of that large number has to be made. This offset was measured three years ago, and could have changed if the refraction index had changed even very slightly (e.g. due to aging of the plastic material). This offset was not remeasured in the new analysis, and the possible associated systematic uncertainty remains in my mind an issue.