Posts Tagged ‘Opera experiment

ICARUS Refutes Opera’s Superluminal Neutrinos

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a picture of ICARUS in the LNGS cavern

The saga of the superluminal neutrinos took a dramatic turn today, with the publication of a very simple yet definitive study by ICARUS, another neutrino experiment at the Gran Sasso Laboratories, who has looked at the neutrinos shot from CERN since 2010.

The ICARUS team jumped on the chance to test the Opera result based on the article recently published by Cohen and Glashow. The latter argue that superluminal neutrinos should lose energy through  neutral-current weak-interaction radiation -the analogue of Cherenkov radiation for a neutral particle. Given a neutrino moving at a speed v>c as the one measured by Opera, and given the distance traveled to the Gran Sasso cavern, one can relatively easily compute the energy spectrum of observable neutrinos at the cavern, given the production energy spectrum.

The physics is a bit more complicated than I summarized it in the paragraph above, but really, you need not squeeze your brains: there is nothing much to know. What is important is that there is a clean and simple relationship between the superluminal speed and the rate of decrease of the neutrino energy. Neutrinos at CERN are produced with an average energy of 28.2 GeV, and neutrinos at the receiving end – the LNGS where Opera and ICARUS both sit – should have an average energy of only 12.1 GeV for neutrinos detected via charged-current interaction.

Incidentally, a charged-current neutrino interaction occurs when the neutrino “exchanges” a unit of electric charge, along with weak quantum numbers, with a nucleus. The neutrino thus turns into a muon, while the nucleus breaks apart in a shower of light hadrons. The muon is then very easy to detect and measure.

I can imagine the ICARUS team brainstorming all together at a meeting. Everybody brings about their favourite objections to the timing measurement of Opera. Some argue whether they can redo the Opera measurement. Others pass along the tray of donuts. Then somebody brings up the Cohen-Glashow paper: “Look, it is quite easy: we take neutrino interactions, measure their energy, and compare with various hypotheses for the superluminal speed. All based on known physics and hard facts. Can we do it ? Can we ? OMG wait… We have already those neutrino interactions!”

So off they go, and do their homework. And a very good homework it is: in less than three weeks from the appearance of the Cohen-Glashow paper -yesterday evening-, they publish a preprint. Kudos to them for their speed and focus. True, ICARUS is not flooded with neutrino statistics these days -I could not help chuckling at their honest but a bit vintage description of why they lost this or that event, ending up with a statistics of less than 100 interactions (OPERA has 16000, although they’ve run for much longer so far). But those less-than-100 neutrinos do kick ass.

In fact, what do they find ?

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October 18, 2011 at 4:26 pm

Two exercises about neutrino departure times at CERN

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Bernd A. Berg, Peter Hoeflich

Two simple exercises are solved, which educators can use to awake interest of their students in subtleties of the CERN Neutrino beam to Grand Sasso (CNGS) experiment. The first one is about the statistical error of the average departure time of neutrinos from CERN. The second one about a hypothetical bias in the departure times…..
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October 15, 2011 at 9:50 pm


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Faster-Than-Light Neutrino Puzzle Claimed Solved by Special Relativity

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The relativistic motion of clocks on board GPS satellites exactly accounts for the superluminal effect, says physicist
It’s now been three weeks since the extraordinary news that neutrinos travelling between France and Italy had been clocked moving faster than light. The experiment, known as OPERA, found that the particles produced at CERN near Geneva arrived at the Gran Sasso Laboratory in Italy some 60 nanoseconds earlier than the speed of light allows.

The result has sent a ripple of excitement through the physics community. Since then, more than 80 papers have appeared on the arXiv attempting to debunk or explain the effect. It’s fair to say, however, that the general feeling is that the OPERA team must have overlooked something.

Today, Ronald van Elburg at the University of Groningen in the Netherlands makes a convincing argument that he has found the error.

First, let’s review the experiment, which is simple in concept: a measurement of distance and time.

Results of the OPERA experiment

The distance is straightforward. The location of neutrino production at CERN is fairly easy to measure using GPS. The position of the Gran Sasso Laboratory is harder to pin down because it sits under a kilometre-high mountain. Nevertheless, the OPERA team says it has nailed the distance of 730 km to within 20 cm or so.

The time of neutrino flight is harder to measure. The OPERA team says it can accurately gauge the instant when the neutrinos are created and the instant they are detected using clocks at each end.

But the tricky part is keeping the clocks at either end exactly synchronised. The team does this using GPS satellites, which each broadcast a highly accurate time signal from orbit some 20,000km overhead. That introduces a number of extra complications which the team has to take into account, such as the time of travel of the GPS signals to the ground.

But van Elburg says there is one effect that the OPERA team seems to have overlooked: the relativistic motion of the GPS clocks.

It’s easy to think that the motion of the satellites is irrelevant. After all, the radio waves carrying the time signal must travel at the speed of light, regardless of the satellites’ speed.

But there is an additional subtlety. Although the speed of light is does not depend on the the frame of reference, the time of flight does. In this case, there are two frames of reference: the experiment on the ground and the clocks in orbit. If these are moving relative to each other, then this needs to be factored in.

So what is the satellites’ motion with respect to the OPERA experiment? These probes orbit from West to East in a plane inclined at 55 degrees to the equator. Significantly, that’s roughly in line with the neutrino flight path. Their relative motion is then easy to calculate.

So from the point of view of a clock on board a GPS satellite, the positions of the neutrino source and detector are changing. “From the perspective of the clock, the detector is moving towards the source and consequently the distance travelled by the particles as observed from the clock is shorter,” says van Elburg.

By this he means shorter than the distance measured in the reference frame on the ground.

The OPERA team overlooks this because it thinks of the clocks as on the ground not in orbit.

How big is this effect? Van Elburg calculates that it should cause the neutrinos to arrive 32 nanoseconds early. But this must be doubled because the same error occurs at each end of the experiment. So the total correction is 64 nanoseconds, almost exactly what the OPERA team observes.

That’s impressive but it’s not to say the problem is done and dusted. Peer review is an essential part of the scientific process and this argument must hold its own under scrutiny from the community at large and the OPERA team in particular.

If it stands up, this episode will be laden with irony. Far from breaking Einstein’s theory of relatively, the faster-than-light measurement will turn out to be another confirmation of it.

Ref: Times Of Flight Between A Source And A Detector Observed From A GPS Satellite

Written by physicsgg

October 14, 2011 at 2:46 pm

The neutrino song

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“Toor a loo, toor a loo, toor a loo, toor-a-lino, is light now slower than a neutrino?”  is the question of Corrigan Brothers….

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October 12, 2011 at 4:41 pm

New theories emerge to disprove OPERA faster-than-light neutrinos claim

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— It’s been just two weeks since the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) team released its announcement claiming that they have been measuring muon neutrinos moving faster than the speed of light, causing an uproar in the physics community. Since that time, many papers (perhaps as many as 30 to the preprint server arXiv alone) have been published seeking ways to discredit the findings. Thus far though, only two seem credible.

The first is by Carlo Contaldi of Imperial College London. He says that it’s likely the OPERA team failed to take gravity into their math equations and its effect on the clocks used to time the experiment. This because the degree of gravity at the two stations involved in the experiment (Gran Sasso National Laboratory in Italy and the CERN facility in Geneva) were different, thus one of the clocks would have been running slightly faster than the other, resulting in faulty timing. If this turns out to be the case, the OPERA team will most certainly be embarrassed to have overlooked such a basic problem with their study.

The second is by Andrew Cohen and Sheldon Glashow, who together point out that if the neutrinos in the study were in fact traveling as fast as claimed, they should have been radiating particles as they went, leaving behind a measurable trail; this due to the energy transfer that would occur between particles moving at different speeds. And since the OPERA team didn’t observe any such trail (or at least didn’t report it) it follows that the neutrinos weren’t in fact traveling as fast as were claimed and the resultant speed measurements would have to be attributed to something else.

New Constraints on Neutrino Velocities
Andrew G. Cohen, Sheldon L. Glashow
The OPERA collaboration has claimed that muon neutrinos with mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about 7.5 km/s or 25 ppm. However, we show that such superluminal neutrinos would lose energy rapidly via the bremsstrahlung of electron-positron pairs (νμ→νμ+e++e). For the claimed superluminal neutrino velocity and at the stated mean neutrino energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. Thus we refute the superluminal interpretation of the OPERA result. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of high-energy neutrinos.

Neither of these papers actually disproves the results found by the OPERA team of course, the first merely suggests there may be a problem with the way the measurements were taken, the second takes more of a “it can’t be true because of…” approach which only highlight the general disbelief in the physics community regarding the very possibility of anything, much less the speed of neutrinos traveling faster than the speed of light, messing with Einstein’s most basic theories. The first can be addressed rather easily by the OPERA team if it so desires, and the second, well, if the neutrinos did in fact travel faster than the speed of light and did so without leaving a trail, a lot of physics theory will have to be rethought. Though that may not necessarily be a bad thing, physics is supposed to be about finding answers to explain the natural world around us after all, even if it means going back to the drawing board now and then.
© 2011

Read also: “Is the OPERA Speedy Neutrino Experiment Self-Contradictory?

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October 6, 2011 at 9:07 pm

Live Chat: Have Neutrinos Broken the Speed Limit of Light?

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Nothing can go faster than light, right? Einstein said so. But last week a group of researchers in Italy announced that they’d measured the speed of thousands of neutrinos (tiny, almost massless particles that were fired at their detector from the CERN particle physics lab 730 kilometers away) and found they were traveling slightly faster than light. Is this the beginning of the end for Einstein’s theory of relativity? Have the researchers simply made a mistake in their measurements? Or are the neutrinos, as some versions of string theory allow, taking a shortcut through a higher dimension and arriving in Italy in double-quick time?
Join us for a live chat on this page at 3 p.m. EDT on Thursday, 29 September, to discuss these and other questions with two experts in the field. You can leave your questions in the comments section below before the chat starts.
Upcoming Event:  Have Neutrinos Broken the Speed Limit of Light?

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September 28, 2011 at 4:52 pm

Saving both super-luminal and SN1987A neutrinos?

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Inconsistence of super-luminal Opera neutrino speed with SN1987A neutrinos burst and with flavor neutrino mixing

Recent news from Cern Opera experiment seem to hint for a muon neutrino faster than light, maybe tachyon in nature. If all neutrino are just tachyon their arrival (at 17 MeV) will be even much faster than 17 GeV Opera neutrino, nearly 2.5 times faster than c, coming back nearly 100000 years ago. If all the neutrino velocity, independently on their energy, were frozen at a Opera speed 2.5 10^{-5} times faster than c, than Supernova 1987A had not to be observed (as it is well known to be) on February 23th 1987, but just 4.2 years before. Possibly in late 1982 early 1983, miraculously hidden in oldest IMB records. In such tuned new physics no explanation will be on the same neutrino burst found on February 23 1987. A more consistent scenario is the one where electron neutrinos (and antineutrino) fly at velocity c, while muon neutrino are super-luminal: than SN1987A electron neutrino may be in agreement with observed signals; nevertheless even in this ideal scenario one should also find a coexisting precursor neutrino burst signal in early 1982-1983 inside IMB records, signal due to a muon neutrino conversion in flight nearby the Earth. To find such a 8-16 event cluster in IMB will be a true miracle (for me, now unrealistic). Mostly because any different electron neutrino speed respect muon ones strongly disagree with near distance low energy neutrino flavor mixing and with the same Solar neutrino flavor solution. In conclusion SN 1987A strongly constrain any ad hoc super luminal neutrino signal. OPERA-CERN neutrino speed measure must be indebt to some miss-leading time calibrations….
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September 27, 2011 at 4:20 pm

Apparent Lorentz violation with superluminal Majorana neutrinos at OPERA?

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F. Tamburini , Μ. Laveder
From the data release of OPERA – CNGS experiment, and publicly announced on 23 Septem- ber 2011, we cast a phenomenological toy model based on a Majorana neutrino state carrying an imaginary mass term, already discussed by Majorana in 1932. This imaginary term can be a fictious term induced by the interaction with the matter of the Earth’s crust during the 735 Km travel or it could represent a proof of a particular real solution representing a Majorana neutrino propagating in a medium. Possible violations to Lorentz invariance due to quantum gravity effect have been considered…..

Based on the recent data released by OPERA experiment, where is suggested a superluminal propagation of muonic neutrinos in the Earth’s crust that might be ascribed to an apparent violation of Lorentz invariance, we suggest a simple toy model that describe these neutrino states as a Majorana-like particles with an imaginary mass component lower limit on the order of 10−13 eV and, for p ≤ kc, in the limit p ∼ kc, an imaginary mass of 1.19 × 10eV, if the data interpretation and Montecarlo simulations of OPERA results are correct.
This solution, already discussed by Majorana in 1932, has here the meaning of a phenomenological description of what has been observed without invoking Lorentz invariance violations due to quantum gravity effects, discarded by the most recent results present in the literature.
This apparent tachyonic propagation, also supposed in SN1987a data [4] can be due either because of an actual Majorana property of neutrinos or induced by the structured material present in the Earth’s crust through MSW mixing, sterile neutrino states and acquisition of orbital angular momentum states.
We argue that this superluminal effect is expected only in the presence of neutrino interacting with matter, acting as a metamaterial for photons [7].
In vacuum, instead, neutrinos are expected to propagate at speed less or equal than the speed of light, otherwise the anticipation observed in the SN1987a would have been of years.
This superluminal effect in astrophysical scenarios of high energy neutrinos is expected to occur only in the inner core of the star when the supernova is starting its catastrophic state and matter is dense and widely structured [30].
Neutrinos might be held responsible for the starting of supernova explosion because of their superluminality.
Moreover, neutrinos might have played a crucial role in the early universe scenario differently than thought before.
As already said, in this case relativity is not violated, because this propagation occurs only in the presence of media and SN1987a data confirm both the equivalence principle [31] and test of relativity [30].
Whether MSW mixing in a medium and sterile neutrinos might be interpreted as a superposition of neutrino flavors carrying OAM, in a different mass superposition, or parametric resonance change their mobility is matter of future investigations.
A deeper investigation could solve the still unsolved quest for Majorana neutrinos and use these results as preliminary test. In any case, these new neutrino properties would not only revolutionize the standard model of particles [32] and its extensions to Lorentz-violating phenomenologies [33], but would have a deep impact in the astrophysics of supernova core explosions, of compact objects, and cosmology.
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September 27, 2011 at 9:13 am