M E M B R A N E T H E O R Y
'The barman said, "We don't serve Nutrinos."' A Neutrino walked into a bar.
QUANTUM HUMOUR
QUANTUM HUMOUR
"As you say, the way string theory requires all these extra dimensions and this comes from certain consistency requirements about how string should behave and so on."
ROGER PENROSE
ROGER PENROSE
"Individual events. Events beyond law. Events so numerous and so uncoordinated that, flaunting their freedom from formula, they yet fabricate firm form."
JOHN WHEELER
JOHN WHEELER
Quantum foam, also referred to as spacetime foam, is a concept in quantum mechanics, devised by John Wheeler in 1955. The foam is supposed to be the foundations of the fabric of the universe. Additionally, it can be used as a qualitative description of subatomic spacetime turbulence at extremely small distances (of the order of the Planck length). At such small scales of time and space the uncertainty principle allows particles and energy to briefly come into existence, and then annihilate, without violating conservation laws. As the scale of time and space being discussed shrinks, the energy of the virtual particles increases. According to Einstein's theory of general relativity, energy curves spacetime. So, this suggests that at sufficiently small scales the energy of the fluctuations would be large enough to cause significant departures from the smooth spacetime seen at larger scales - giving spacetime a 'foamy' character.
Hey, this is really cool. Some brainiacs in a room buried under a mountain in Italy measured the distance between themselves and colleagues at CERN in Switzerland to an incredibly fine tolerance (something like 20cm). Then they measured the time it took for elementary particles to travel the distance. And, would you believe, they got there fractionally faster than the speed of light. If that's possible then the whole basis of physics is going to be dramatically revised. And so far the science standing up pretty well to peer scrutiny.
There's a really elegant idea called 'Brane (short for membrane) Theory' which neatly reconciles the obvious contradiction of particles traveling at superluminal velocity without exceeding the speed of light; here's how it works. 'Brane Theory' is a logical extension of 'string theory' which suggests that we live in a four dimensional universe consisting of 'strings'. On this membrane elementary particles (and our physical reality) are simply manifestations of the the rate of vibration of these strings. 'Brane Theory' operates by positing the existence of between ten and eleven other universes which are parallel to ours and arranged like a sliced loaf. This collection of universes 'Brane Theorists' term 'The Bulk'.
The explanation for the superluminal particles that don't breach the speed of light is now simple. They take a shortcut across the nearest parallel 'brain'. In other words they cheat. And in doing so they arrive at their destination before they are supposed to. So 'speed of light' is a physical limitation on the 'brane' (Einstein can stop spinning in his grave) but does not apply between the 'branes'. The irreconcilable neatly reconciled; see what I mean by elegant.
My feelings, for what they're worth, are that we are at a truly pivotal point in the history of physics; maybe the history of everything. And to my ears the detractors of these new revelations are starting to sound a bit embarrassing. Just like Lord Kelvin when he rung the death knell of Newtonian physics by announcing that there's nothing left to discover.
In theory we have been living with the possibility of faster than light particles for a while now. Neutrinos (someone called them the bad boys of the particle zoo) seem to be pretty speedy too. In some theories of quantum gravity, such as the superfluid vacuum theory, superluminal propagation of particles, including neutrinos, is allowed. According to this theory, at very high velocities the behavior of the particles becomes distinct from the relativistic one - they can reach the speed of light limit at finite energy; also the faster-than-light propagation is possible without requiring moving objects to have imaginary mass.
The central idea is that the visible, four-dimensional universe is restricted to a brane inside a higher-dimensional space, called the "bulk". If the additional dimensions are compact, then the observed universe contains the extra dimensions, and then no reference to the bulk is appropriate. In the bulk model, at least some of the extra dimensions are extensive (possibly infinite), and other branes may be moving through this bulk. Interactions with the bulk, and possibly with other branes, can influence our brane and thus introduce effects not seen in more standard cosmological models.
Why gravity is weak
SEE: FLAT UNIVERSE Now this is just me here, an airhead artist interjecting amongst all this heavyweight science, but I've always visualised the big bang as an explosion. That is central point from which everything moves away from in every possible direction; an expanding and ever thinning ball of matter. Then I learn that the universe is in fact flat and to me, whatever the cause or origin, flatness is not what I see when I hear big bang. So I think that as the nature of an explosion (if that is what I am still to take the 'big bang' to be) is explosive; that being so there must have been something constraigning the explosion which limited its direction to a level plane. And that's where I see the membrane as becoming very plausable. The 'big bang' had no where else to go. Like honey combs in a hive.
The model can explain the weakness of gravity relative to the other fundamental forces of nature, thus solving the so-called hierarchy problem. In the brane picture, the other three forces (electromagnetism and the weak and strong nuclear forces) are localized on the brane, but gravity has no such constraint and so much of its attractive power "leaks" into the bulk. As a consequence, the force of gravity should appear significantly stronger on small (subatomic or at least sub-millimetre) scales, where less gravitational force has "leaked". Various experiments are currently underway to test this.
Models of brane cosmology
One of the earliest documented attempts on brane cosmology is dated by 1983.[2] The authors discussed the possibility that the Universe has (3 + N) + 1 dimensions, but ordinary particles are confined in a potential well which is narrow along N spatial directions and flat along three others, and proposed a particular five-dimensional model.
In 1998/99 Merab Gogberashvili published on Arxiv a number of articles where he showed that if the Universe is considered as a thin shell (a mathematical synonym for "brane") expanding in 5-dimensional space then there is a possibility to obtain one scale for particle theory corresponding to the 5-dimensional cosmological constant and Universe thickness, and thus to solve the hierarchy problem.[3][4][5] It was also shown that four-dimensionality of the Universe is the result of stability requirement since the extra component of the Einstein equations giving the confined solution for matter fields coincides with the one of the conditions of stability.
In 1999 there were proposed the closely related Randall-Sundrum (RS1 and RS2; see 5 dimensional warped geometry theory for a nontechnical explanation of RS1) scenarios. These particular models of brane cosmology have attracted a considerable amount of attention.
Later, the pre-big bang, ekpyrotic and cyclic proposals appeared. The ekpyrotic theory hypothesizes that the origin of the observable universe occurred when two parallel branes collided.
There's a really elegant idea called 'Brane (short for membrane) Theory' which neatly reconciles the obvious contradiction of particles traveling at superluminal velocity without exceeding the speed of light; here's how it works. 'Brane Theory' is a logical extension of 'string theory' which suggests that we live in a four dimensional universe consisting of 'strings'. On this membrane elementary particles (and our physical reality) are simply manifestations of the the rate of vibration of these strings. 'Brane Theory' operates by positing the existence of between ten and eleven other universes which are parallel to ours and arranged like a sliced loaf. This collection of universes 'Brane Theorists' term 'The Bulk'.
The explanation for the superluminal particles that don't breach the speed of light is now simple. They take a shortcut across the nearest parallel 'brain'. In other words they cheat. And in doing so they arrive at their destination before they are supposed to. So 'speed of light' is a physical limitation on the 'brane' (Einstein can stop spinning in his grave) but does not apply between the 'branes'. The irreconcilable neatly reconciled; see what I mean by elegant.
My feelings, for what they're worth, are that we are at a truly pivotal point in the history of physics; maybe the history of everything. And to my ears the detractors of these new revelations are starting to sound a bit embarrassing. Just like Lord Kelvin when he rung the death knell of Newtonian physics by announcing that there's nothing left to discover.
In theory we have been living with the possibility of faster than light particles for a while now. Neutrinos (someone called them the bad boys of the particle zoo) seem to be pretty speedy too. In some theories of quantum gravity, such as the superfluid vacuum theory, superluminal propagation of particles, including neutrinos, is allowed. According to this theory, at very high velocities the behavior of the particles becomes distinct from the relativistic one - they can reach the speed of light limit at finite energy; also the faster-than-light propagation is possible without requiring moving objects to have imaginary mass.
The central idea is that the visible, four-dimensional universe is restricted to a brane inside a higher-dimensional space, called the "bulk". If the additional dimensions are compact, then the observed universe contains the extra dimensions, and then no reference to the bulk is appropriate. In the bulk model, at least some of the extra dimensions are extensive (possibly infinite), and other branes may be moving through this bulk. Interactions with the bulk, and possibly with other branes, can influence our brane and thus introduce effects not seen in more standard cosmological models.
Why gravity is weak
SEE: FLAT UNIVERSE Now this is just me here, an airhead artist interjecting amongst all this heavyweight science, but I've always visualised the big bang as an explosion. That is central point from which everything moves away from in every possible direction; an expanding and ever thinning ball of matter. Then I learn that the universe is in fact flat and to me, whatever the cause or origin, flatness is not what I see when I hear big bang. So I think that as the nature of an explosion (if that is what I am still to take the 'big bang' to be) is explosive; that being so there must have been something constraigning the explosion which limited its direction to a level plane. And that's where I see the membrane as becoming very plausable. The 'big bang' had no where else to go. Like honey combs in a hive.
The model can explain the weakness of gravity relative to the other fundamental forces of nature, thus solving the so-called hierarchy problem. In the brane picture, the other three forces (electromagnetism and the weak and strong nuclear forces) are localized on the brane, but gravity has no such constraint and so much of its attractive power "leaks" into the bulk. As a consequence, the force of gravity should appear significantly stronger on small (subatomic or at least sub-millimetre) scales, where less gravitational force has "leaked". Various experiments are currently underway to test this.
Models of brane cosmology
One of the earliest documented attempts on brane cosmology is dated by 1983.[2] The authors discussed the possibility that the Universe has (3 + N) + 1 dimensions, but ordinary particles are confined in a potential well which is narrow along N spatial directions and flat along three others, and proposed a particular five-dimensional model.
In 1998/99 Merab Gogberashvili published on Arxiv a number of articles where he showed that if the Universe is considered as a thin shell (a mathematical synonym for "brane") expanding in 5-dimensional space then there is a possibility to obtain one scale for particle theory corresponding to the 5-dimensional cosmological constant and Universe thickness, and thus to solve the hierarchy problem.[3][4][5] It was also shown that four-dimensionality of the Universe is the result of stability requirement since the extra component of the Einstein equations giving the confined solution for matter fields coincides with the one of the conditions of stability.
In 1999 there were proposed the closely related Randall-Sundrum (RS1 and RS2; see 5 dimensional warped geometry theory for a nontechnical explanation of RS1) scenarios. These particular models of brane cosmology have attracted a considerable amount of attention.
Later, the pre-big bang, ekpyrotic and cyclic proposals appeared. The ekpyrotic theory hypothesizes that the origin of the observable universe occurred when two parallel branes collided.
OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran SassoGeneva, 23 September 2011.
The OPERA result is based on the observation of over 15000 neutrino events measured at Gran Sasso, and appears to indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature’s cosmic speed limit. Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny. The collaboration’s result is available on the preprint server arxiv.org: http://arxiv.org/abs/1109.4897.
The OPERA measurement is at odds with well-established laws of nature, though science frequently progresses by overthrowing the established paradigms. For this reason, many searches have been made for deviations from Einstein’s theory of relativity, so far not finding any such evidence. The strong constraints arising from these observations makes an interpretation of the OPERA measurement in terms of modification of Einstein’s theory unlikely, and give further strong reason to seek new independent measurements.
“This result comes as a complete surprise,” said OPERA spokesperson, Antonio Ereditato of the University of Bern. “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.”
“When an experiment finds an apparently unbelievable result and can find no artefact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice,” said CERN Research Director Sergio Bertolucci. “If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane, explanations. That will require independent measurements.”
In order to perform this study, the OPERA Collaboration teamed up with experts in metrology from CERN and other institutions to perform a series of high precision measurements of the distance between the source and the detector, and of the neutrinos’ time of flight. The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 20 cm over the 730 km travel path. The neutrinos’ time of flight was determined with an accuracy of less than 10 nanoseconds by using sophisticated instruments including advanced GPS systems and atomic clocks. The time response of all elements of the CNGS beam line and of the OPERA detector has also been measured with great precision.
"We have established synchronization between CERN and Gran Sasso that gives us nanosecond accuracy, and we’ve measured the distance between the two sites to 20 centimetres,” said Dario Autiero, the CNRS researcher who will give this afternoon’s seminar. “Although our measurements have low systematic uncertainty and high statistical accuracy, and we place great confidence in our results, we’re looking forward to comparing them with those from other experiments."
“The potential impact on science is too large to draw immediate conclusions or attempt physics interpretations. My first reaction is that the neutrino is still surprising us with its mysteries.” said Ereditato. “Today’s seminar is intended to invite scrutiny from the broader particle physics community.”
The OPERA experiment was inaugurated in 2006, with the main goal of studying the rare transformation (oscillation) of muon neutrinos into tau neutrinos. One first such event was observed in 2010, proving the unique ability of the experiment in the detection of the elusive signal of tau neutrinos.
The OPERA result is based on the observation of over 15000 neutrino events measured at Gran Sasso, and appears to indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature’s cosmic speed limit. Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny. The collaboration’s result is available on the preprint server arxiv.org: http://arxiv.org/abs/1109.4897.
The OPERA measurement is at odds with well-established laws of nature, though science frequently progresses by overthrowing the established paradigms. For this reason, many searches have been made for deviations from Einstein’s theory of relativity, so far not finding any such evidence. The strong constraints arising from these observations makes an interpretation of the OPERA measurement in terms of modification of Einstein’s theory unlikely, and give further strong reason to seek new independent measurements.
“This result comes as a complete surprise,” said OPERA spokesperson, Antonio Ereditato of the University of Bern. “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.”
“When an experiment finds an apparently unbelievable result and can find no artefact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice,” said CERN Research Director Sergio Bertolucci. “If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane, explanations. That will require independent measurements.”
In order to perform this study, the OPERA Collaboration teamed up with experts in metrology from CERN and other institutions to perform a series of high precision measurements of the distance between the source and the detector, and of the neutrinos’ time of flight. The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 20 cm over the 730 km travel path. The neutrinos’ time of flight was determined with an accuracy of less than 10 nanoseconds by using sophisticated instruments including advanced GPS systems and atomic clocks. The time response of all elements of the CNGS beam line and of the OPERA detector has also been measured with great precision.
"We have established synchronization between CERN and Gran Sasso that gives us nanosecond accuracy, and we’ve measured the distance between the two sites to 20 centimetres,” said Dario Autiero, the CNRS researcher who will give this afternoon’s seminar. “Although our measurements have low systematic uncertainty and high statistical accuracy, and we place great confidence in our results, we’re looking forward to comparing them with those from other experiments."
“The potential impact on science is too large to draw immediate conclusions or attempt physics interpretations. My first reaction is that the neutrino is still surprising us with its mysteries.” said Ereditato. “Today’s seminar is intended to invite scrutiny from the broader particle physics community.”
The OPERA experiment was inaugurated in 2006, with the main goal of studying the rare transformation (oscillation) of muon neutrinos into tau neutrinos. One first such event was observed in 2010, proving the unique ability of the experiment in the detection of the elusive signal of tau neutrinos.
THURSDAY, JUNE 3, 2010
Opera Project Observes Muon Neutrino Transmute Into Tau Neutrino for First Time
After over two years of data taking, in all likelihood the first tau neutrino has been observed in the Opera detector. Launched in 1997, the Opera project in the Gran Sasso underground laboratory is searching for tau neutrinos from neutrino oscillations of muon neutrinos.
On May 31, several organizations involved in the Opera experiment, including Cern in Geneva and the Istituto Nazionale di Fisica Nucleare (INF) in Italy, proudly announced that they were 98 percent sure they had detected the tau neutrino. The Opera project was launched in 1997 with the aim of directly observing so-called neutrino oscillation, the transmutation of a muon neutrino into a tau neutrino, for the first time. The team of André Rubbia, professor of particle physics at ETH Zurich, is also involved in the initiative.
Journey through the Earth’s crust
The experiment launched in 2006 is set to run for five years. “We’ve only really had measurement data since 2008, though”, explains ETH-Zurich physicist Andreas Badertscher, a member of Rubbia’s team involved in the experiment in Gran Sasso in Abruzzo, Italy. That’s where the almost 5,000-ton detector is set up to detect the reactions of neutrinos coming from Cern – a 730-kilometer journey which the neutrinos complete in 2.4 milliseconds traveling through the Earth’s crust.
Side view of the Opera detector
Photo credit: Opera website
Some muon neutrinos supposedly transmutate into tau neutrinos en route; this was what scientists concluded when they noticed a discrepancy between the number of neutrinos sent out from an accelerator, for instance, and those registered by a remote detector, says physicist Badertscher. The transmutation of the muon neutrino into a tau neutrino was deemed the cause.
Ten particles in five years
The fact that neutrinos of a particular flavor can disappear has already been proved in so-called disappearance experiments; this led the scientists to suspect that one neutrino flavor might transform into another. They described the process as “neutrino oscillation”; however, the neutrino produced by the transmutation could never directly be detected.
The Opera project, a so-called appearance experiment, is the first – and so far only – project which has most likely identified the newly created neutrino through neutrino oscillation – the proverbial needle in a haystack. In fact, the physicists estimate that in five years of data taking about 10 tau neutrino reactions will be found in the Opera detector.
Discovering new physics
Up until now, only a fraction of the data collected has been analyzed; however, the physicists are convinced that the phenomenon observed is a tau neutrino reaction: “Judging by the data we’ve analyzed, there really isn’t any other explanation for it; however, we need to find more events like this if we are to establish the neutrino-oscillation hypothesis”, says Badertscher.
That said, the physicists are excited about the first observation of a tau neutrino reaction in a muon neutrino beam. Neutrino oscillation is an indication of new, fascinating physics that goes beyond the Standard Model as it is known today. This is because oscillating neutrinos – contrary to the previous assumption of massless neutrinos – have to have mass.
Scientists have been hot on the trail of the three neutrino “generations” since the fifties. Until a few years ago, it was assumed that neutrinos were massless and stable; it wasn’t until the end of the nineties that it was discovered that one neutrino flavor can transmutate into another, which is only possible if not all neutrinos are massless. Other experiments, such as the T2K experiment at the new J-PARC accelerator in Japan, are only just starting the first measurements that should detect the electron neutrino from the transmutation of a muon neutrino.
The Opera detector in Hall C of the underground lab at Gran Sasso[6]
OPERA tunes into first-ever tau neutrinos
by anil
The OPERA experiment in the underground Gran Sasso Laboratory in Italy has likely seen the first tau neutrino, making it the first time that a neutrino type may have been seen “appearing” rather than “disappearing”.
Before we dig further into this strange statement and why it’s important, here’s a bit of background on neutrino appearances and disappearances. Neutrinos come in three flavours: electron, muon and tau. During the 1960s, neutrino detectors showed that there was a deficit of neutrinos coming from the sun. This came to be called the mystery of the missing solar neutrinos. Eventually, physicists figured out that the neutrinos were morphing from one type to another on their journey from the sun to the Earth. So if a detector was sensitive to only one type of neutrino, then it would see less of that type than was being emitted by the sun, since that particular neutrino type had changed into another type along the way, and hence could not be seen by the detector. This phenomenon is called neutrino oscillation.
This “disappearance” of a neutrino type has been detected by various detectors worldwide.
But how about detecting the reverse process? Say a neutrino source is spewing out muon neutrinos, and some of them are changing to tau neutrinos on their way to the detector. How about detecting the “appearance” of the neutrino which was not produced at the source?
That’s exactly what OPERA has done. A neutrino source at the CERN Accelerator Complex has been generating muon neutrinos. These neutrinos travel 730 kilometres to the OPERA detector (in about 2.4 milliseconds). Now, OPERA has most likely found one tau neutrino from among the many billions of muon neutrinos produced at CERN. This tau neutrino “appeared”—it is of course equivalent to a muon neutrino disappearing. But still, it’s a first.
Why is all this important? It turns out that neutrino oscillations require neutrinos to have mass, something which is not allowed in the standard model of particle physics. New physics is required to explain the process, and the more we study neutrino oscillations, the clearer the new physics will become.
Hitoshi Murayama, a theoretical physicist at the University of California, Berkeley, wrote about the announcement of the discovery of neutrino oscillations in Japan in 1998 (quoted in The Edge of Physics): “It was a moving moment. Uncharacteristically for a physics conference, people gave the speaker a standing ovation. I stood up too. Having survived every experimental challenge since the late 1970s, the Standard Model had finally fallen. The results showed that at the very least the theory is incomplete.”
by anil
The OPERA experiment in the underground Gran Sasso Laboratory in Italy has likely seen the first tau neutrino, making it the first time that a neutrino type may have been seen “appearing” rather than “disappearing”.
Before we dig further into this strange statement and why it’s important, here’s a bit of background on neutrino appearances and disappearances. Neutrinos come in three flavours: electron, muon and tau. During the 1960s, neutrino detectors showed that there was a deficit of neutrinos coming from the sun. This came to be called the mystery of the missing solar neutrinos. Eventually, physicists figured out that the neutrinos were morphing from one type to another on their journey from the sun to the Earth. So if a detector was sensitive to only one type of neutrino, then it would see less of that type than was being emitted by the sun, since that particular neutrino type had changed into another type along the way, and hence could not be seen by the detector. This phenomenon is called neutrino oscillation.
This “disappearance” of a neutrino type has been detected by various detectors worldwide.
But how about detecting the reverse process? Say a neutrino source is spewing out muon neutrinos, and some of them are changing to tau neutrinos on their way to the detector. How about detecting the “appearance” of the neutrino which was not produced at the source?
That’s exactly what OPERA has done. A neutrino source at the CERN Accelerator Complex has been generating muon neutrinos. These neutrinos travel 730 kilometres to the OPERA detector (in about 2.4 milliseconds). Now, OPERA has most likely found one tau neutrino from among the many billions of muon neutrinos produced at CERN. This tau neutrino “appeared”—it is of course equivalent to a muon neutrino disappearing. But still, it’s a first.
Why is all this important? It turns out that neutrino oscillations require neutrinos to have mass, something which is not allowed in the standard model of particle physics. New physics is required to explain the process, and the more we study neutrino oscillations, the clearer the new physics will become.
Hitoshi Murayama, a theoretical physicist at the University of California, Berkeley, wrote about the announcement of the discovery of neutrino oscillations in Japan in 1998 (quoted in The Edge of Physics): “It was a moving moment. Uncharacteristically for a physics conference, people gave the speaker a standing ovation. I stood up too. Having survived every experimental challenge since the late 1970s, the Standard Model had finally fallen. The results showed that at the very least the theory is incomplete.”
For other uses of "Gran Sasso", see Gran Sasso (disambiguation).
Laboratori Nazionali del Gran Sasso (LNGS) is a particle physics laboratory of the INFN, situated near the Gran Sasso mountain in Italy, between the towns of L'Aquila and Teramo, about 120 km from Rome. In addition to a surface portion of the laboratory, there are extensive underground facilities beneath the mountain. The first large experiments at LNGS ran in 1989; the facilities were later expanded. According to its official website, the Gran Sasso lab is, as of 2006, the largest underground particle physics laboratory in the world.
The lab is located within the Gran Sasso and the Monti della Laga National Park. The underground facilities are located next to a freeway tunnel, the 10km long Traforo del Gran Sasso. The experimental halls are covered by about 1400m of rock, protecting the experiments from cosmic rays.
The mission of the laboratory is to host experiments that require a low background environment in the field of astroparticle physics and nuclear astrophysics and other disciplines that can profit of its characteristics and of its infrastructures. The LNGS is, like the three other European underground astroparticle laboratories, Laboratoire Souterrain de Modane, Laboratorio subterráneo de Canfranc, and Boulby Underground Laboratory, a member of the coordinating group ILIAS.
Since late August 2006, CERN has directed a beam of muon neutrinos from the CERN SPS accelerator to the Gran Sasso lab, 730 km away, where they will be detected by the OPERA and ICARUS detectors, in a study of neutrino oscillations that will improve on the results of the Fermilab to MINOS experiment.
In May 2010, Lucia Votano, Director of the Gran Sasso laboratories, announced that "[t]he OPERA experiment has reached its first goal: the detection of a tau neutrino obtained from the transformation of a muon neutrino, which occurred during the journey from Geneva to the Gran Sasso Laboratory."[1] This finding indicates a deficiency in the Standard Model of particle physics, as neutrinos would have to have mass for this change to occur.
An effort to determine the mass of the neutrino, called CUORE (Cryogenic Underground Observatory for Rare Events), is scheduled to begin in 2011. The detector will be shielded with lead recovered from an ancient Roman shipwreck, due to the ancient lead's lower radioactivity than recently minted lead. The artifacts are being given to CUORE from the National Archaeological Museum in Cagliari.[2]
In September 2011, Dario Autiero of the Institut de Physique Nucléaire de Lyon presented findings that indicated neutrinos were arriving at OPERA about 60 ns earlier than they would if they were travelling at the speed of light. These results are as yet unexplained.[3][4]
Roman ingots to shield particle detector
Lead from ancient shipwreck will line Italian neutrino experiment.
Nicola Nosengo
The Roman lead was discovered by a scuba diver in 1988.INFN/Cagliari Archeological Superintendence
Around four tonnes of ancient Roman lead was yesterday transferred from a museum on the Italian island of Sardinia to the country's national particle physics laboratory at Gran Sasso on the mainland. Once destined to become water pipes, coins or ammunition for Roman soldiers' slingshots, the metal will instead form part of a cutting-edge experiment to nail down the mass of neutrinos.
The 120 lead ingots, each weighing about 33 kilograms, come from a larger load recovered 20 years ago from a Roman shipwreck, the remains of a vessel that sank between 80 B.C. and 50 B.C. off the coast of Sardinia. As a testimony to the extent of ancient Rome's manufacturing and trading capacities, the ingots are of great value to archaeologists, who have been preserving and studying them at the National Archaeological Museum in Cagliari, southern Sardinia. What makes the ingots equally valuable to physicists is the fact that over the past 2,000 years their lead has almost completely lost its natural radioactivity. It is therefore the perfect material with which to shield the CUORE (Cryogenic Underground Observatory for Rare Events) detector, which Italy's National Institute of Nuclear Physics (INFN) is building at the Gran Sasso laboratory.
CUORE, which will begin operations next year, will investigate neutrinos: fundamental particles with no electronic charge and long thought to have no mass. Researchers have confirmed that neutrinos do have a mass, but have been unable to pin down a figure for it1. The aim is to use the detector to try to observe a theoretical atomic event called neutrinoless double-beta decay — a radioactive process whereby an atomic nucleus releases two electrons and no neutrinos. 'Standard' double-beta decay is accompanied by the release of two neutrinos. By observing this predicted but so far unseen event, physicists hope to estimate the neutrino's mass and to establish whether neutrinos and their antimatter counterparts, antineutrinos, are different particles. Some believe the two to be one and the same.
Sunken treasure
CUORE scientists will wait for neutrinoless double-beta decay to happen in a 750-kilogram cube of tellurium dioxide placed under 1,400 metres of rock at the Gran Sasso laboratory. But to successfully observe this rare event, they will need to shield their experiment from external radioactivity.
A curator at the National Archaeological Museum in Cagliari checks the ingots after they were retrieved from a Roman shipwreck.INFN/Cagliari Archeological Superintendence
This is where the shipwrecked lead comes into the picture. Lead is, in principle, a shield against radiation, but freshly mined lead is itself slightly radioactive because it contains an unstable isotope, lead-210. "We could never use it for our experiment, which is exactly about keeping background radioactivity to a minimum," says Ettore Fiorini, a physicist at the University of Milan-Bicocca and coordinator of the CUORE experiment. After it is extracted from the ground, however, lead-210 decays into more stable isotopes, with the concentration of the radioactive isotope halving every 22 years. The lead in the Roman ingots has now lost almost all traces of its radioactivity.
The ingots arrived at Gran Sasso thanks to an agreement dating back to 1991. In 1988, a scuba diver discovered the ship's remains at a depth of 28 metres, a mile and a half from Oristano, just over 1 mile from the Sardinian coast. Fiorini recalls reading about the finding in a newspaper, and immediately foreseeing its value to physicists.
"It is not unusual for particle physicists to go hunting for low-radioactivity lead," he says. "Metal extracted from roofs in antique churches or from keels of wrecked ships has often been used in experiments." But the Sardinian finding was unprecedented, both in terms of the age and the abundance of the material.
Painful parting
The ship was in fact a navis oneraria magna, a specialized cargo vessel often used to transport heavy loads such as lead or other metals. It carried more than 1,000 ingots, or 33 tonnes of metal. Given that civil war was raging in Rome at the time it sank and that the ship was loaded with slingshot ammunition, archaeologists believe that much of the ship's lead may have been destined to end up as shot. They also think that the ship was deliberately sunk on the orders of its captain to prevent it from being seized by enemy forces: it was still anchored, and close enough to the coast for the crew to swim to shore.
Only the inscriptions on the lead ingots will be preserved.INFN/Cagliari Archeological Superintendence
When Fiorini learned that the Archeological Superintendence, a government office that oversees heritage projects, in Cagliari did not have enough funds to retrieve all the ingots, he convinced INFN managers to contribute 300 million lira (US$210,000) to the operation, which was completed in 1991. In exchange, a proportion of the recovered lead would become available for physicists. Some ingots were used in experiments during the 1990s, but Fiorini says that CUORE is what he had in mind when he first proposed the deal.
At Gran Sasso, the ingots will be melted into a 3-centimetre-thick lead lining that will surround the cubic CUORE detector. Before the ingots are melted down, the inscriptions on each one will be removed and sent back to Cagliari for preservation. "They are trademarks, bearing the names of various firms that extracted and traded lead," explains Donatella Salvi, an archaeologist at the Cagliari museum.
Salvi says that parting with the ingots has been "painful". The ones given to INFN are the worst-preserved, but are still of exceptional historical value. However, she says she is happy with the collaboration, because physicists are performing important analyses on the lead. For example, Fiorini's team has helped archaeologists to settle a debate about the ship's route. It had first been proposed that its lead could come from Sardinian ores, but Salvi was skeptical. "Romans at that time preferred to preserve Italian ores, which they considered strategic, and instead extracted most of their lead from Northern Africa, Spain and Britain," she says. By studying the particular mix of isotopes in the lead — a signature of its origin — INFN physicists have confirmed that Salvi was right. The ingots came from Sierra de Cartagena, in southern Spain.