Posts Tagged ‘Opera experiment’
ICARUS: Neutrinos Travel At Light Speed. Period.
By Tommaso Dorigo
Little less than one year ago the world of fundamental physics was shaken by the bold claim of the OPERA collaboration, which produced a measurement of the time of flight of neutrinos traveling underground from Geneva to the Gran Sasso mine in central Italy. The beam of neutrinos, produced by the CERN SpS proton synchrotron, was observed to produce interactions in the large mass of the OPERA detector with about 60 nanosecond anticipation with respect to what would be expected for a particle traveling at exactly the speed of light (2439096.1+-0.3 nanoseconds, since the flight path is of 731221.95+-0.09 meters).
Following the CERN announcement of the OPERA result physicists around the world busied themselves with pointing out several issues with the measurement, among which the statistical analysis of the data, the precise measurement of several delays in the detection process, and other hardware components, and remained generally quite cold….
Read more: science20.com
Error Undoes Faster-Than-Light Neutrino Results
OPERA detector
by Edwin Cartlidge
It appears that the faster-than-light neutrino results, announced last September by the OPERA collaboration in Italy, was due to a mistake after all. A bad connection between a GPS unit and a computer may be to blame.
Physicists had detected neutrinos travelling from the CERN laboratory in Geneva to the Gran Sasso laboratory near L’Aquila that appeared to make the trip in about 60 nanoseconds less than light speed. Many other physicists suspected that the result was due to some kind of error, given that it seems at odds with Einstein’s special theory of relativity, which says nothing can travel faster than the speed of light. That theory has been vindicated by many experiments over the decades.
According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer. After tightening the connection and then measuring the time it takes data to travel the length of the fiber, researchers found that the data arrive 60 nanoseconds earlier than assumed. Since this time is subtracted from the overall time of flight, it appears to explain the early arrival of the neutrinos. New data, however, will be needed to confirm this hypothesis.
Read more: news.sciencemag.org
(updated) Read also:
1. ‘Faster than light’ measurement blamed on loose cable
Are OPERA neutrinos faster than light because of non-inertial reference frames?
Distribution of timing corrections. Top: Distribution calculated over a typical OPERA run (April to November 2010). It would imply an overall miss-synchronization of ∼ -80 ns. Middle: Distribution over an entire year. Bottom: Distribution from January 1 to March 31. It would imply an overall miss-synchronization of ∼ +50 ns.
Claudio Germana
ABSTRACT
Recent results from the OPERA experiment reported a neutrino beam traveling faster than light.
The experiment measured the neutrino time of flight (TOF) over a baseline from the CERN to the Gran Sasso site.
The neutrino beam arrives 60 ns earlier than a light ray would do.
Because the result has an enormous impact on science, it might be worth double-checking the time definitions with respect to the non-inertial system in which the neutrino travel time was measured.
Potential problems in the OPERA data analysis connected with the definition of the reference frame and time synchronization are emphasized. We aim to investigate the synchronization of non-inertial clocks on Earth by relating this time to the proper time of an inertial observer at Solar System Barycenter(SSB).
The Tempo2 software was used to time-stamp events observed on the geoid with respect to the SSB inertial observer time. Neutrino results from OPERA might carry the fingerprint of non-inertial effects.
The CERN-Gran Sasso clock synchronization is accomplished by applying corrections that depend on special and general relativistic time dilation effects at the clocks, depending on the position of the clocks in the solar system gravitational well.
As a consequence, TOF distributions are centered on values shorter by tens of ns than expected, integrating over a period from April to December, longer if otherwise.
It is worth remarking that the OPERA runs have always been carried out from April/May to November.
If the analysis by Tempo2 holds for the OPERA experiment, the excellent measurement by the OPERA collaboration will turn into a proof of the General Relativity theory in a weak field approximation.
The analysis presented here is falsifiable because it predicts that performing the experiment from January to March/April, the neutrino beam will be detected to arrive 50 ns later than light.
Read more: http://arxiv.org/pdf/1201.4147v1.pdf
Neutrinos still faster than light in latest version of experiment
OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso
UPDATE 18 November 2011
Following the OPERA collaboration’s presentation at CERN on 23 September, inviting scrutiny of their neutrino time-of-flight measurement from the broader particle physics community, the collaboration has rechecked many aspects of its analysis and taken into account valuable suggestions from a wide range of sources. One key test was to repeat the measurement with very short beam pulses from CERN. This allowed the extraction time of the protons, that ultimately lead to the neutrino beam, to be measured more precisely.
The beam sent from CERN consisted of pulses three nanoseconds long separated by up to 524 nanoseconds. Some 20 clean neutrino events were measured at the Gran Sasso Laboratory, and precisely associated with the pulse leaving CERN. This test confirms the accuracy of OPERA’s timing measurement, ruling out one potential source of systematic error. The new measurements do not change the initial conclusion. Nevertheless, the observed anomaly in the neutrinos’ time of flight from CERN to Gran Sasso still needs further scrutiny and independent measurement before it can be refuted or confirmed.
On 17 November, the collaboration submitted a paper on this measurement to the peer reviewed Journal of High Energy Physics (JHEP). This paper is also available on the Inspire website.
press.web.cern.ch
More data shows neutrinos still faster than light
One of the most staggering results in physics – that neutrinos may go faster than light – has not gone away with two further weeks of observations. The researchers behind the jaw-dropping finding are now confident enough in the result that they are submitting it to a peer-reviewed journal.
“The measurement seems robust,” says Luca Stanco of the National Institute of Nuclear Physics in Italy. “We have received many criticisms, and most of them have been washed out.”
Stanco is a member of the OPERA collaboration, which shocked the world in September with the announcement that the ghostly subatomic particles had arrived at the Gran Sasso mine in Italy about 60 nanoseconds faster than light speed from the CERN particle accelerator in Switzerland 730 kilometres away.
Tighter bunches
Theorists are struggling to reconcile the result with the laws of physics. Einstein’s theory of special relativity posits that nothing can travel faster than light, and many physicists believe the result could disappear in a puff of particles.
The result also unsettled those within the OPERA collaboration. Stanco was one of 15 team members who did not sign the original preprint of the paper because they thought the results were too preliminary.
One of the main concerns was that it was difficult to link individual neutrino hits at Gran Sasso to the particles that left CERN. To double check, the team ran a second set of measurements with tighter bunches of particles from 21 October to 6 November.
In that time, they observed 20 new neutrino hits – a piddling number compared to the 16,000 hits in the original experiment. But Stanco says the tighter particle bunches made those hits easier to track and time: “So they are very powerful, these 20 events.”
More checks
The team also re-checked their statistical analysis, confirming that the error on their measurements was indeed 10 nanoseconds. Some team members, including Stanco, had worried that the true error was larger. What they found was “absolutely compatible” with the original announcement, Stanco says.
That was enough for Stanco to sign his name to the paper, although he says six or seven team members are still holding out. The team was planning to submit the paper to a European physics journal on Thursday.
The team is still running other tests, including measuring the length of a fibre-optic cable that carries information from the underground lab at Gran Sasso to a data-collection centre on the surface. The team is also trying to do the same test using another detector at the lab called RPC. That test will take another several months.
Even though he agreed to sign the paper, Stanco says: “I’m not so happy. From a theoretical point of view, it is not so appealing. I still feel that another experiment should make the measurement before I will say that I believe this result.” newscientist.com
Measurement of the neutrino velocity with the OPERA detector in the CNGS beam
The OPERA Collaboraton, last revised 17 Nov 2011
Summary of the results for the measurement of δt. The left plot shows δt as a function of the energy for νµ CC internal events. The errors attributed to the two points are just statistical in order to make their relative comparison easier since the systematic error (represented by a band around the no-effect line) cancels out. The right plot shows the global result of the analysis including both internal and external events (for the latter the energy cannot be measured). The error bar includes statistical and systematic uncertainties added in quadrature.
The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos.
The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011.
Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies.
An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (57.8 ± 7.8 (stat.)+8.3-5.9 (sys.)) ns was measured.
This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.37 ± 0.32 (stat.) (sys.)) x 10-5.
The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 {\mu}s long extractions, was confirmed by a test performed using a beam with a short-bunch time-structure allowing to measure the neutrino time of flight at the single interaction level.
Read more: http://arxiv.org
Testing the Special Relativity Theory with Neutrino interactions
P.W. Cattaneo
Abstract
A recent report of superluminal neutrinos from the OPERA experiment appears in contradiction with prediction of energy loss of superluminal neutrino via the pair creation process ν → νe+e−.
The same process should result in isolated e+e− pairs in detectors with good tracking capability traversed by a large flux of high energy neutrino like NOMAD.
In the past different physical arguments motivated NOMAD to search for similar topologies.
These results can be reinterpreted to provide stringent limits on
special relativity violating parameters for all ν species.
…………………………
Detector characteristics
Conclusions
We set strong bounds on special relativity violating processes involving neutrinos
and anti-neutrinos of all species based on previous search of isolated e+e− pairs in the NOMAD detector.
This translates in strong limits on possible superluminal behaviours of neutrinos of all species for extensions of the special relativity theory with ’broken’ Lorentz invariance.
We strongly encourage the NOMAD collaboration to perform a dedicated analysis to optimize these limits…..
Read more: arxiv.org
Read also: A Bound On Neutrino Speeds From Nomad
Faster-than-light neutrino experiment to be run again
The neutrinos are fired deep under the Italian Apennines to the Gran Sasso lab
Scientists who announced that sub-atomic particles might be able to travel faster than light are to rerun their experiment in a different way.
This will address criticisms and allow the physicists to shore up their analysis as much as possible before submitting it for publication.
Dr Sergio Bertolucci said it was vital not to “fool around” given the staggering implications of the result.
So they are doing all they can to rule out more pedestrian explanations.
Physicists working on the Opera experiment announced the perplexing findings last month.
Neutrinos sent through the ground from Cern (the home of the Large Hadron Collider) in Geneva toward the Gran Sasso laboratory 732km away in Italy seemed to show up a tiny fraction of a second earlier than light would have.
“It’s like sending a series of loud and isolated clicks instead of a long blast on a horn”
Prof Matt Strassler
Rutgers University
The speed of light is widely regarded as the Universe’s ultimate velocity limit. Outlined first by James Clerk Maxwell and then by Albert Einstein in his theory of special relativity, much of modern physics relies on the idea that nothing can travel faster than light.
For many, the most comforting explanation is that some repeated “systematic error” has so far eluded the experimenters.
Since September, more than 80 scientific papers about the finding have been posted to the arXiv pre-print server. Most propose theoretical solutions for the observation; a few claim to find problems.
Dr Bertolucci, the director of research at Cern, told BBC News: “In the last few days we have started to send a different time structure of the beam to Gran Sasso.
“This will allow Opera to repeat the measurement, removing some of the possible systematics.”
The neutrinos that emerge at Gran Sasso start off as a beam of proton particles at Cern. Through a series of complex interactions, neutrino particles are generated from this beam and stream through the Earth’s crust to Italy.
Read also: A Test for Neutrinos: Put Up or Shut Up
Neutrino watch
… Speed claim baffles CERN theoryfest
Typical event recorded in ICARUS. Evidence for a pair of γ’s from a π_o (tracks 16a and 16b) with a momentum of 912 MeV/c pointing at the primary vertex, showing the typical behavior of γ conversions in the TPCN LAr Imaging chamber.
Even a meeting of elite minds at Europe’s top particle physics lab couldn’t do it: reconciling neutrinos that appear to break the cosmic speed limit with the laws of physics is still beyond us. However, a paper on the speeding neutrinos has been accepted for publication and the first preliminary results from a comparable experiment are out.
“For the moment, there is no explanation that works,” says physicist Ignatios Antoniadis, who helped to organise the meeting at CERN near Geneva, Switzerland, last Friday. It was three weeks to the day after physicists in the OPERA collaboration at Gran Sasso, Italy, announced that neutrinos travelling from CERN had apparently moved faster than light.
Frantic calculation, speculation and debate have followed in the wake of the announcement. The meeting’s goal was to “review the situation and discuss whether it is possible [that neutrinos broke the speed of light]” , says Antoniadis.
The biggest challenge yet to the OPERA result comes from Nobel laureate Sheldon Glashow and his Boston University colleague Andrew Cohen in a paper posted online a few weeks ago.
First publication
Physical Review Letters has agreed to publish the paper, making it the first scientific journal to accept work on the OPERA result.
In the paper, Glashow and Cohen point out that if neutrinos can travel faster than light, then when they do so they should sometimes radiate an electron paired with its antimatter equivalent – a positron – through a process called Cerenkov radiation, which is analogous to a sonic boom. Each electron-positron pair should carry away a large chunk of the neutrinos’ energy: Cohen and Glashow calculated that at the end of the experiment, the neutrinos should have had energies no higher than about 12 gigaelectronvolts. But OPERA saw plenty of neutrinos with energies upwards of 40 GeV.
“It doesn’t correspond to the energies measured at all,” says CERN physicist Christophe Grojean.
Another strike against the speedy neutrinos comes from the fact that neutrinos are linked to certain other particles – electrons, muons and tau particles – via the weak nuclear force. Because of that link, neutrinos can’t travel faster than light unless electrons do too – although electrons needn’t travel as fast as the neutrinos.
Speedy electrons
CERN physicist Gian Giudice, who spoke at the seminar, and colleagues looked into what would happen if electrons travelled faster than light by one part in 100,000,000, a speed consistent with the OPERA neutrino measurement. Such speedy electrons should emit a cone of Cerenkov radiation in empty space – but previous experiments show that they don’t.
The only way out, theorists at the meeting decided, was to break another supposedly fundamental law of nature – the conservation of energy. But that suggestion seems even more ludicrous than breaking the speed of light.
“At the moment, there is no concrete model that really avoids all these theoretical constraints,” Grojean says. “That’s why it’s so interesting. We cannot explain it in terms of known physics.”
Despite the care the OPERA researchers took to rule out errors in the measurement, that possibility remains. Another unpublished paper on the arxiv.org physics preprint server has attracted attention with its explanation. Ronald van Elburg at the University of Groningen in the Netherlands has calculated that special relativity could have messed up the synchronisation of the clocks at CERN and Gran Sasso. This would make neutrinos appear to arrive 64 nanoseconds early – almost exactly what the OPERA experiment observed.
Icarus test
If this argument holds up, rather than breaking Einstein’s theory of special relativity, the faster-than-light neutrinos would actually end up reaffirming it. But it’s unclear whether the result has legs. “In general, the feeling of theorists is that one should repeat the experiment,” Antoniadis says.
CERN plans to provide a new neutrino beam to do this. Meanwhile, the first glimpses from another detector at the Gran Sasso laboratory don’t look good for the faster-than-light hypothesis. An experiment there called ICARUS (Imaging Cosmic And Rare Underground Signals) has been catching neutrinos travelling from CERN since last year. The 100 or so it has seen do not seem to travel faster than light. ICARUS also doesn’t see any evidence of the Cerenkov-like radiation Glashow and Cohen predicted.
The case is far from closed, however. “For the moment, we don’t have an answer,” Antoniadis says. “That doesn’t mean an answer doesn’t exist.”
References: Glashow and Cohen: arxiv.org/abs/1109.6562; van Elburg: arxiv.org/abs/1110.2685; ICARUS:arxiv.org/abs/1110.3763
http://www.newscientist.com
physics4me 