# A New MINOS measurement of neutrinos speed through earth

1. Jul 17, 2015

### Enoy

Most presice measurement to date done by MINOS of neutrino time of flight through earth published two days ago, once again found neutrinos slightly faster than light speed within statistical errors. Only when they extend the band with systematic errors doesn't neutrinos surpass light speed. Here is the MINOS arxiv publication of this new result:
http://arxiv.org/abs/1507.04328

2. Jul 17, 2015

### Orodruin

Staff Emeritus
They make no claim of FTL discovery. In fact, the abstract clearly states (1±1.1)×10^-6.

3. Jul 17, 2015

### Enoy

Here is a quote from the conclusion in MINOS paper that concludes about their measurement within the statistical error-band:

"
Combining the contained and partially reconstructed samples, the time-of-flight between the RWCM and FD is found to be (2 453 935.0 ± 0.1) ns, considering only statistical errors. Subtracting the measured time-of- flight (using GPS) between RWCM and ND of 4621.1 ns we obtain the time-of-flight between ND and FD as (2 449 313.9 ± 0.1) ns (statistical error only): the most precise measurement of the neutrino time-of-flight ever achieved, and the only one obtained directly using two neutrino detectors. The time required to traverse the distance between the front face of the Near and Far de- tectors at the speed of light, including the Sagnac cor- rection, is (2 449 316.3 ± 2.3) ns"

Neutrinos faster than speed of light through earth in this "most precise measurement of the neutrino time-of-flight ever achieved" could not be ruled out here. In fact the direct measurement shows neutrinos slightly faster. Only when the band is extended to include systematic error the result is that the neutrinos is just belove the speed of light.

This is a very interesting measurement of the issues concerning testing the theory of relativity.

4. Jul 17, 2015

### jerromyjon

From the paper: "The 0.98 kton ND is located 1.04 km downstream of the production target and 104 m underground. The 5.4 kton FD is approximately 735 km downstream of the target and 705 m underground." They are pretty much estimating the time dilation difference from ND to FD?

5. Jul 17, 2015

### Staff: Mentor

@Enoy You are blatantly misrepresenting the results of the experiment.

The statistical errors described apply only to the time-of-flight for neutrinos between the two detectors. This is the quantity that is measured with more precision than any previous measurement, but it is only a measurement of the time-of-flight for neutrinos between these two specific detectors, not for the speed of neutrinos. There is no "direct measurement" of the speed at all in this experiment (nor is one claimed).

The only way to estimate the speed of the neutrinos is to divide the distance by the measured time. The distance measurement itself is subject to systematic errors, and therefore the speed measurement is subject to these same errors. The systematic errors in the distance cannot be neglected in any comparison with c. The authors do not attempt to neglect such errors and your attempt to do so is a misrepresentation of the experiment.

Last edited: Jul 17, 2015
6. Jul 17, 2015

### jerromyjon

"The time required to traverse the distance between the front face of the Near and Far detectors at the speed of light, including the Sagnac correction, is (2 449 316.3 ± 2.3) ns, where the dominant uncertainty comes from the inertial survey of the FD location"
What's the "inertial survey"?

7. Jul 17, 2015

### PAllen

Just to focus on the amazing precision of these experiments: the systematic error in the speed determination corresponds to an uncertainty in distance between the Far Detector and Fermilab of 2 feet over 735 km!!

8. Jul 17, 2015

### Staff: Mentor

In order to measure the distance they had to use some accelerometers and gyroscopes, commonly called an "inertial measurement unit" or "inertial guidance unit".

9. Jul 17, 2015

### PAllen

From the paper:

"For the FD however, there is no direct plumb line down
the sloped shaft and issues with atmospheric stratication
prohibit optical surveys. Therefore, a Honeywell Inertial
Navigation Unit (INS) containing three gyroscopes
and three accelerometers was utilized to connect the surface
and underground control networks. The INS was
mounted in the elevator cage and traveled multiple times
up and down the mine shaft, stopping each time at four
approximately equal distance positions to reset accumulated
velocity errors in the INS. Limiting factors of the
accuracy include: the relatively high vibration rate of the
elevator cage; the fact that the cage stops at slightly different
places each time; and residual oscillations as the
cage came to a stop. The INS measurement is detailed
in Ref. [23]."

Note, unless one accuses the team of unethical behavior, this systematic error was estimated before data analysis. As I mentioned previously, they compute that this uncertainty amounts to about +-2 feet in distance from the far detector and Fermilab 735 km away! (and deep underground).

This is amazing confirmation of neutrino's traveling at c, not suspicion of violation. Note the their prior measurement was an order of magnitude less accurate, and its error bars also spanned both sides of c. When we see an tenfold increase in precision, with the c remaining within the error bars, the logical thing to conclude is greatly increased confidence that neurtinos travel effectively, at c, not DECREASED CONFIDENCE.

10. Jul 17, 2015

### jerromyjon

It is amazing by itself that neutrinos travel through earth roughly nearly as fast as light... to such great certainty is well done!

11. Jul 17, 2015

### Orodruin

Staff Emeritus
In this context, I think it is worth noting the expectation for the neutrino speed at MINOS. The neutrino energy is roughly in the GeV range and the upper bounds on neutrino masses are in the eV range. The speed is given by:
$$v = \frac pE = \sqrt{1 - \frac{m^2}{E^2}} \simeq 1 - \frac{m^2}{2E^2} \Longrightarrow 1 - v \lesssim 0.5 \cdot 10^{-18}$$
Essentially undistinguishable from the speed of light compared to the $10^{-6}$ precision.

12. Jul 17, 2015

Staff Emeritus
I agree. "Statistical errors only" makes the same amount of sense as "Errors beginning with the letters A-M only". You have to include all uncertainties in an analysis. Indeed, it's not even always clear in which column an uncertainty should be assigned to: imagine a potential systematic effect that is constrained by the same data that's being taken.

The paper says that the position of the far detector relative to the near detector is known to about 2 feet. That's about a part per million. That's pretty good. One might think "GPS is better", but GPS tells you where your antenna is. That's not so helpful when your experiment is 2000 feet below your antenna - and a couple hundred feet across.

13. Jul 18, 2015