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Brian Dorney | USLHC | USA

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The OPERA Measurement & the Peer-Review Process

An article posted on engadget.com [1] regarding the OPERA Neutrino measurement has been making its way through the internet and various social network sites recently.  I’ve had several discussions on Facebook regarding this article, the most recent was on the Society of Physics Students Facebook Page.  And it looks like I’m starting yet another discussion regarding this article.

The article references a recent paper published on arXiv, which can be found here [2].  This arXiv reference states that the OPERA Collaboration have not properly accounted for relativistic effects [2] when calculating the time of flight of the neutrino’s in their recent pre-print (also published on arXiv, [3]).  But, let me be very explicit in this, the OPERA Collaboration has correctly taken into account relativistic effects in their calculation [3].

So why discuss this engadget.com article and the source it references?  Well, my goal with this post is to illustrate reasons why one should always remain skeptical regarding scientific news, and the importance of doing your own search for sources when a new result is presented.

The Argument

But let’s get back to talking about this engadget article.  I was immediately skeptical of this article, the source engadget.com referenced was a paper published solely on arXiv (which has NOT been submitted to a peer-review journal).

Now arXiv is a fantastic resource, which is used by scientists all over the world, and publishes world class research.  However, arXiv is not a peer-review journal, and anyone is able to submit to it.  As a result, arXiv is a resource that needs to be used with care, much like Wikipedia; arXiv’s own disclaimer reads:

Papers will be entered in the listings in order of receipt on an impartial basis and appearance of a paper is not intended in any way to convey tacit approval of its assumptions, methods, or conclusions by any agent (electronic, mechanical, or other). We reserve the right to reject any inappropriate submissions [4].

Meaning anyone is free to submit to arXiv, however if a document is published on arXiv it does not mean that the material covered in the document has been accepted by the scientific community.  Most documents that hit arXiv are also published in peer-review journals.  Which is what makes arXiv great, it provides free access to scientific publications, but not all papers on arXiv have been “published” in a peer-review journal.

But what does it mean to be published in a peer-review journal?  Well, it means that your research has been accepted, or at least acknowledge, by the scientific community.  This gives your research merit since other scientists reviewed your work (i.e. the peer-reviewers).  The peer-review process is often intense, and many publications submitted  to a journal are rejected, or asked to provide additional material to support their claims before they are published.  However, after your results have been published other scientists are still free to dispute your results/conclusions; but they must do so by submitting  their own work to the same (or other) peer-review journals.

Now Ref. [2] uses what I would call overly simplified model of a satellite in orbit.  The author makes use of only special relativity, and assumes the satellite moves in a straight line parallel to the earth’s surface.  Using this model of satellite motion the author claims that the OPERA Collaboration has miscalculated the time of flight for the neutrinos by 64 nanoseconds [2].  This discrepancy, if it was true, would mean that the neutrino’s did not travel faster than light.

Example of a typical elliptical orbit

However, if you know anything about orbital mechanics, you should already be raising your eyebrow.  When an object with very little mass, like a satellite, orbits another object with a lot of mass, like the earth, the small object makes an elliptical path.  The ellipse created by the small object’s orbit has one of its foci centered on the large object; take a look at the figure I’ve added for a graphical interpretation.  Now other types of orbits exist, but this orbit is one of the simplest types that is easiest to achieve.  Suffice to say in an elliptical orbit, a satellite is not moving parallel to the ground.

Also, if you want to talk about relativistic motion for objects in orbit, you need to worry about general relativity, and not just special relativity.  The reason for this is you need to be concerned with gravitational fields that cause “reference” frames to undergo uniform acceleration.

But in case you were wondering the OPERA Collaboration has correctly accounted for general relativity in their calculations [3].

So the assumptions made in Ref. [2] regarding satellite motion are not a very accurate representation of reality.

Additionally, Some criticism of the analysis used Ref. [2] was published by Dr. Ted Bunn, an associate professor of physics at Richmond University.  Dr. Bunn points out an error in the analysis performed in Ref. [2].   With Dr. Bunn’s correction, the OPERA Collaboration’s time of flight measurement is off by zero nanoseconds, and not 64 nanosecond [5]. e.g. the OPERA Collaboration did not make a mistake.

I should point out that Dr. Bunn’s paper has also yet to be published in a peer-review journal, however I cite him as a credible source due to his position within Richmond University.  Now some you may disagree with my decision to use Dr. Bunn’s paper as a credible source since it wasn’t published in a peer-review journal…

…and that is exactly what I would like you to do!  Be skeptical of what you read online and look for credible information on your own! The OPERA Collaboration has yet to even submit their measurement to a peer-review journal, but they plan to do so in the future.

Some Scientific Concerns

However, everything above being said, their are plenty of scientific concerns regarding the OPERA measurement.  Additionally, the measurement needs to be repeated by another neutrino beamline before it will be accepted by the scientific community.


But one of the major concerns of the community surrounding the OPERA measurement is that the proton beam used to make the muon-neutrino beam was 10.5 micro-seconds long [3].  Meaning, if you started a stop-watch the moment the first proton reached you, and stopped it the moment the last proton went past, this time interval would be 10.5 micro-seconds (hope you have good reflexes!!!).

Now why is this fact important?  The OPERA Collaboration at this time is unable to determine from which proton a muon-neutrino which struck the OPERA detector originated from [3].  To counteract this the OPERA Collaboration employs a widely accepted statistical technique, outlined in Ref [3], to determine the time of flight of the neutrino’s.  But as a result of the length of the proton beam, the reported excess of 60 nanoseconds in favor the neutrino’s over the photons has been met with skepticism.

If you are interested in additional concerns of the peer-review community regarding the OPERA measurement I can point you to Aidan’s live coverage of the CERN Press-Release on the OPERA measurement:

http://www.quantumdiaries.org/2011/09/23/live-blog-neutrinos/

 

The Future of FTL Neutrino’s

You may have read on Jonathan’s blog that CERN plans to decrease the proton waveform from 10.5 microseconds to 1-2 nanosecond pulses separated by 500 nanosecond delays.  If the neutrinos were then found to travel faster than light by 60 nanoseconds it really would be something!

But in the spirit of this post, Jonathan and I are referencing a recent article published on the BBC’s science page, which can be found here:

http://www.bbc.co.uk/news/science-environment-15471118

This BBC article discusses the plans of the OPERA Collaboration to reduce the proton beam time as I mentioned above.  Additionally, this BBC article states that two additional neutrino beamlines plan on repeating the OPERA measurement.  These two beamlines are  these are Japan’s T2K experiment, and FermiLab’s MINOS experiment.

Once the OPERA Collaboration conducts their experiment using a shorter timed proton beam they plan to publish their results in a peer-review journal.  I should point out that OPERA will publish regardless of  their findings.  So even if they find that the neutrino’s don’t travel faster than light they will still publish; as they should!

With these new plans of the OPERA, T2K and the MINOS Collaborations we will really be able to say if the preliminary measurement published by OPERA (on arXiv) was a statistical fluke, or a real phenomenon.

Until then I will remain skeptical, but it will be a very interesting day if we find out that the neutrino’s really did go faster than light….

 

Before closing I would like to take the time to acknowledge and congratulate all scientific journalists.  These individuals do a truly fantastic job of bringing attention to exciting new research.  I myself rely on many scientific journalists (and my colleagues here at Quantum Diaries!)  to keep me informed about what happens in the scientific community; and for this I must extend my sincere gratitude to all of them.

 

Until Next Time,

-Brian

 

Reference

[1]  Sharif Sakr, “Remember those faster-than-light neutrinos? Great, now forget ‘em,” Engadget.com, Oct 17th 2011, http://www.engadget.com/2011/10/17/remember-those-faster-than-light-neutrinos-great-now-forget-e/.

[2] Ronald A. J. van Elburg, “Time-of-flight between a Source and a Detector observed from a Satellite,” arXiv:1110.2685v3 [physics.gen-ph], http://arxiv.org/abs/1110.2685.

[3] OPERA Collaboration, “Measurement of the neutrino velocity with the OPERA detector in the CNGS beam,” arXiv:1109:4897v1 [hep-ex], http://arxiv.org/abs/1109.4897.

[4] arXiv, “General Information About arXiv,” http://arxiv.org/help/general.

[5] Ted Bunn, “Critique of ‘Time of flight between a sourceand a detector observed from a satellite’ (arxiv:1110.2685v3),” https://facultystaff.richmond.edu/~ebunn/vanelburg.pdf.

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7 Responses to “The OPERA Measurement & the Peer-Review Process”

  1. [...] Brian Dorney “The OPERA Measurement & the Peer-Review Process“ [...]

  2. helmingstay says:

    For all the discussion of peer-reviewed literature, there is not a single peer-reviewed article referenced in this blog post. It seems like an odd argument to invoke when the argument boils down to “believe me and not those guys over there”, does it not?

    • Brian Dorney says:

      helmingstay,

      Update: Just now realized this was not my post giving an update on the OPERA measurement, please see this post regarding the issue: http://www.quantumdiaries.org/2011/11/18/an-update-from-opera/

      The purpose of this blog post was to publicize the latest update from the OPERA Collaboration regarding their recent muon-neutrino time of flight measurement. If you’ll look in the press release quote I posted above, you’ll see that the OPERA Collaboration has indeed submitted their manuscript to a peer review journal, the Journal of High Energy Physics, just this past week. I anticipate the reviewers at JHEP will be in correspondence with the OPERA Collaboration in the near future (i.e. we will know if it is published soon).

      Additionally, large scientific collaborations such as OPERA, CMS, DZero, etc… all conduct their own internal peer-review process before releasing any results to the public, or the rest of the scientific community. This is an additional level of the peer-review process that ensures top quality results are published by scientific experiments.

      Hope this helps.

      Best,
      -Brian

  3. Debbie Diktiz says:

    “the neutrino’s did not travel faster than light.”
    What possession of the neutrinos did not travel faster than light? Where and what is this unreferenced object?

  4. Derek says:

    I’m not even remotely a scientist, but the one thing that struck me (although it may be extremely trivial and a non-issue) is knowing the exact distance between source and receiver. I am assuming that the original finding of ~1.000025 times the speed of light is determined by comparing the actual time it took the neutrinos (which can pass through the Earth’s crust) to travel the distance and dividing the distance by the speed of light to determine how long a photon (which cannot pass through the Earth’s crust) would have done so. What if the distance they are assuming is incorrect?

    • Brian Dorney says:

      Derek,

      An excellent question! If you look in Section 4 of OPERA’s manuscript (the arXiv link above), they describe their measurement of the distance between the origin of the Neutrino Beam and the OPERA Detector (they even take into account continental drift!). This distance is measured with a precision of 20 centimeters. The OPERA team acknowledges this 20 centimeter uncertainty has an affect on their measurement, and takes this into account by attributing what’s known as a “systematic uncertainty” to their measurement. Light would take 0.67 nanoseconds to travel this distance. So the OPERA Collaboration adds, in quadrature, these 0.67 nanoseconds as a systematic uncertainty on their time of flight measurement; as can be seen in Table 2 on page 24 of the OPERA Manuscript (again see arXiv Link above).

      So yes, the distance used in OPERA’s Calculation could be off by 20 centimeters at most. But the uncertainty in time due to this is only 0.67 nanoseconds. Since this time is two orders of magnitude less than OPERA’s Results, we can say that this 20 centimeter uncertainty in the path length does not affect the result significantly.

      Hope this helps,
      -Brian

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