CERN finds neutrinos faster than light - Page 43

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.

On November 20 2011 23:04 Onioncookie wrote:
Wow ... so in short they proved , that they were right? o.O

On November 20 2011 23:05 Telcontar wrote:

It still has to go through peer scrutiny again, but it looks likely that the results are accurate. We'll see though.

On November 21 2011 01:10 Suisen wrote:
Given that the measurements are both precise and accurate, almost no one believes what is measured is actually neutrinos violating the speed of light. In that case they must have some trick or loophole. There might be 7 spacial dimensions. Maybe neutrinos take shortcuts through dimensions unlike any other matter known so far. This is pure speculation just meant to give an idea.

An international team of scientists in Italy studying the same neutrino particles colleagues say appear to have travelled faster than light rejected the startling finding this weekend, saying their tests had shown it must be wrong.

They argue, on the basis of recently published studies by two top US physicists, that the neutrinos pumped down from CERN, near Geneva, should have lost most of their energy if they had travelled at even a tiny fraction faster than light.

But in fact, the ICARUS scientists say, the neutrino beam as tested in their equipment registered an energy spectrum fully corresponding with what it should be for particles travelling at the speed of light and no more.