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CERN boss targets linear collider

The boss of CERN wants the next big experiment in particle physics after the Large Hadron Collider (LHC) to be built at the Geneva lab. Speaking in an interview with physicsworld.com, Rolf-Dieter Heuer said that CERN should host the experiment, which would collide electrons and positrons in a linear accelerator. Although a design for the machine has not been finalized by the international particle-physics community, Heuer is keen to bring the collider to CERN.

“I would be a bad director-general if I did not push for CERN at least bidding for the next global project,” Heuer told physicsworld.com. “CERN is a fantastic place. [It] has proven that it can host such a project and therefore I think CERN should do it.” However, Heuer is aware that it is far from certain that CERN will host the facility – Fermilab in the US is likely to be a contender – and the CERN chief is looking forward to bids from rival labs. “Competition is always welcome,” he says.

Heuer’s desire to host the linear collider is part of his plan to make CERN a much more global laboratory. Although CERN was set up in 1954 as a European facility, its convention does not prevent countries from outside Europe from becoming members. Several thousand physicists from the US have already helped to build the LHC and its detectors, and Heuer is keen for links with non-European nations to become more permanent.

“Why not involve some of the nations from the Americas or Asia as members [of CERN]?” he asks. “This would enable us to start the next global project as a global project from the very beginning – be it at CERN or elsewhere.” CERN is already developing a blue-print for a future linear collider, known as CLIC, while a rival design known as the International Linear Collider is being drawn up by a team led by Barry Barish of the California Institute of Technology. The precise energy at which such a collider should operate will depend in part on what the LHC discovers.

Switch-on schedule

In his interview, Heuer also confirmed the timetable for switching the LHC back on following the electrical fault that occurred on 19 September last year and led to 53 magnets having to be repaired or replaced. As CERN announced last month, beams will be injected into the 27 km long circular accelerator in mid-November with collisions taking place a few weeks later. “I am pretty confident that we will have the first collisions this year,” says the CERN boss.

CERN engineers will begin by colliding protons at an energy of 450 GeV per beam, before attempting collisions at 3.5 TeV per beam. “We will stay there for several months, depending on what experiments find and on running experience,” says Heuer. “Then in the course of the next year we will go up to 10 TeV in the centre of mass [i.e. 5 TeV per beam]”. The LHC will be kept going until the end of 2010 before it is shut down to prepare the way for collisions at a maximum energy of 14 TeV (i.e. 7 TeV per beam) at some point in 2011. “But if we find something interesting at 10 TeV, we will continue running at 10 TeV,” Heuer added.

Challenges and opportunities

Heuer, who replaced Robert Aymar as CERN’s director-general in January this year, admitted in his interview that one of his challenges as lab boss has been to motivate staff following last year’s accident. He revealed that his tactic has been to get staff involved in technical and scheduling decisions, which “brought the spirit up very quickly”, and to bring the LHC’s users – non-CERN staff from universities around the world – in contact with machine staff.

By the time he steps down as director-general at the end of 2013, Heuer hopes that the LHC will have been running at 14 TeV “for a long time” and that physicists will have been able to make their first discoveries. Although he is cautious not to reveal what those discoveries will be, they are likely to include the Higgs boson, which would be the icing on the cake for the Standard Model, and possibly, exotic new “sparticles” that would reveal a new symmetry of nature called supersymmetry and hint at physics beyond the Standard Model.

The discoveries made with the LHC – particularly the mass of the Higgs boson – will influence the nature of any future linear collider and the energy at which it operates. Although the linear collider will have a lower energy than the LHC, it will be able to make measurements more accurately because electron-positron collisions are “cleaner” than those between protons. “I would hope that I am able to shape the future of particle physics with the discoveries made at the LHC during my mandate,” says Heuer. “That’s at least Heuer’s wishful thinking.”

A question of hype

Meanwhile, in a separate interview with physicsworld.com, CERN’s head of communications James Gillies rejected suggestions that the laboratory was guilty of over-hyping the switch-on of the LHC last year, which saw some 340 journalists from over 100 nations attending the opening. “We didn’t over-hype it,” he says. “The hype was there and we lived with it.” Gillies puts the media interest in the LHC down to three factors: fears that the collider would create black holes; Dan Brown’s novel Angels and Demons, part of which is set at CERN; and the lab’s deliberate attempts to tell the world about the LHC.

But with the LHC soon to start running again and taking real data for the first time, Gillies reiterated that CERN wants to improve how it manages the flow of information from the lab to the wider world. In the past, CERN tended to hold onto sensitive information for too long and then was caught out by rumours spreading, particularly from blogs written by particle physicists. “Our whole approach to information is now to be quick [and] honest and to put it out as fast as we can.”

However, Gillies denied that rules imposed by particle-physics collaborations about what bloggers can and cannot say amount to censorship. “The guidelines are not very restraining at all,” he says. “All the guidelines say is follow your collaboration’s internal peer-review guidelines and make sure the information is of sufficient quality to be published before you start talking about it. That’s not over restraining in my opinion – it’s perfectly reasonable.”

Vox pops: life at the frontier

From the canteen to the control room, seven CERN insiders describe what life is really like in the build-up to the switch-on of the LHC in November 2009. Find out their roles in the world’s biggest physics experiment, in which thousands of researchers from around the world are unearthing nature’s secrets, playing with cathedral-sized detectors and drinking lots of coffee too.

Big science: managing the information

James Gillies has been head of communications at CERN since 2003. He trained as a particle physicist and was a member of the OPAL collaboration at CERN until 1993. After a spell as head of science with the British Council in Paris, he returned to CERN in 1995, initially as a science writer. In 2000 he co-authored the book How the Web was Born.

Creating ‘Schrödinger’s virus’ in the lab

In 1935 Erwin Schrödinger devised his famous thought experiment – in which a cat is both alive and dead at the same time – to highlight the paradoxical nature of quantum mechanics. Now, a group of physicists in Germany and Spain believe that it should be possible to build an experiment in which an actual living creature such as a virus is held in a superposition of quantum states.

Schrödinger imagined a cat being held in an opaque box that also contained a glass vial of cyanide. Next to the vial there were a radioactive source, a Geiger counter and a hammer, set up so that decay would lead to the smashing of the vial and the poisoning of the cat. However, the radioactive source would be so weak that within an hour, say, there would only be a 50:50 chance that decay could take place. Before an observer opens the box and looks inside, quantum mechanics tells us that the radioactive material would be in a quantum superposition of both having experienced a decay and not, and that the cat would therefore also exist in a quantum superposition – of being simultaneously alive and dead.

Schrödinger’s scenario illustrates the seeming irreconcilability between the indeterminate quantum realm and our everyday world of concrete – and living – objects. However, physicists have started to probe the boundary between the quantum and the classical and are finding that relatively large objects can be held in superposition states. Such objects include molecules like fullerene carbon-70, as well as hoops of superconducting material that contain currents circulating in opposite directions at the same time.

Superposition of living creatures?

Now, researchers hope to observe superpositions of even larger “optomechanical” systems – objects, such as tiny mirrors or cantilevers, which respond mechanically when exposed to laser light. It is one such system that Oriol Romero-Isart of the Max Planck Institute for Quantum Optics in Garching and colleagues say could be used to demonstrate the superposition of living creatures.

Their plan is to trap an organism inside an optical cavity using “optical tweezers” – a laser beam tightly focused on a tiny region in space that can confine objects in three dimensions. The radiation pressure of a second laser would then slow down the organism’s centre-of-mass motion so that it exists in its motional ground state. Finally, a single-photon pulse from the second laser would put the organism into a superposition of its ground state and an excited motional state.

The German-Spanish group points out that an organism must satisfy three basic requirements if it is to be placed in a superposition in this way. First, they say, it must approximate a dielectric object so that it is very transparent but still refracts light. This means that when the organism moves, the properties of the optical cavity change, varying the light intensity inside the cavity and therefore the force on the organism, which is what cools it. Second, the organism must be smaller than the wavelength of light used, about 500 nm, so that it can be confined between the peaks and troughs in the light wave. Finally, the organism must be able to withstand extremely low pressures, because the merest trace of air molecules would rapidly lead to the decoherence of its quantum states.

Common flu a candidate

The researchers say that the common influenza virus would be a good candidate for the experiment because it is about 100 nm long and can exist in a vacuum. Alternatively they might use the Tobacco Mosaic Virus, which is 50 nm wide and can also withstand very low pressures. Both viruses are good approximations of dielectric objects.

Romero-Isart and colleagues believe that studying organisms in this way could have profound implications. “We expect these proposed experiments to be a first step to experimentally address fundamental questions,” they write in their paper, “such as the role of consciousness in quantum mechanics, and to make distinctive many-world and Copenhagen interpretations.”

Good news for cats

Maciej Lewenstein of the Institute of Photonic Sciences in Barcelona believes that the experiment is feasible using existing technology and agrees that it could have exciting implications. “Proving that quantum-mechanical phenomena exist at this large scale would open the road to studying the role of quantum mechanics in biology,” he says. However, he cautions that it may be some time before we can understand the relationship between consciousness and quantum mechanics. He also doubts that it will ever be possible to carry out Schrödinger’s experiment as applied to actual cats, which, he adds, “is probably good news for cats”.

UPDATE 11 March 2010: A peer-reviewed version of the paper describing this work has been published at New Journal of Physics 12 033015.

More physics on the silver screen…

atlas.jpg
A charming little film from Phil Owen

By Hamish Johnston

I happened to be looking at the ATLAS experiment web page at CERN and came across a series of videos on the particle physics that ATLAS will be exploring once the LHC is up and running.

The six films are all winners of the “ATLAS Multimedia Contest and Intern Program”. There isn’t much information on the site about the contest — I’m assuming that the videos were made by interns who perhaps spent the summer at CERN?

The overall winner is Phil Owen — congratulations Phil — and his video is called Origin of Mass. Runner-up titles include ATLAS Rising and Eye on the Answers.

The rest of the winning videos can be viewed here.

Astronomers confirm rocky nature of new exoplanet

Astronomers have obtained the best evidence yet that a planet orbiting a star 400 light years away from Earth is a solid, rocky world just like our own.

The extrasolar planet (or exoplanet), known as CoRoT-7b, was discovered earlier this year by the French CoRoT space telescope, which established that the body has a radius less than twice that of Earth and orbits extremely close to its parent star. Temperatures on the planet are expected to be as high as 2000 °C, which led astronomers to assume that it was comprised of molten and solid rock, rather than frozen gases, because the latter would boil away under such conditions.

Density a mystery

This assumption could not, however, be confirmed because CoRoT measures the shadow cast by the exoplanet as it crosses between Earth and its star, giving the radius of the exoplanet, but not its mass and density.

Now, though, an international team of astronomers led by Didier Queloz of Switzerland’s Geneva Observatory has used the HARPS spectrograph at La Silla Observatory in Chile to measure the mass of CoRoT-7b. HARPS makes very accurate measurements of the velocity of the planet’s parent star, which allows astronomers to observe the “wobble” induced on the star by the orbiting planet.

By observing this wobble for a total of 70 hours over several months, the team concluded that CoRoT-7b has a mass about five times that of Earth. The density is therefore about the same as Earth, suggesting that the exoplanet has a similar rocky composition.

All in a wobble

However, some other astronomers are not as certain. Suzanne Aigrain at the University of Exeter in the UK told physicsworld.com that the parent star is particularly active (covered in spots), which results in apparent changes to its velocity that are greater than those induced by CoRoT-7b. These variations had to be removed from the HARPS data, leading to uncertainties in the mass of CoRoT-7b that may “have been seriously underestimated”.

However, Aigrain, who was involved in the discovery of CoRoT-7b, says that some degree of controversy is unavoidable when researchers are trying to push back the limits of what can be done with state-of-the-art instruments. “Now it is very important that the entire community works towards the consolidation of this result by re-analysing the data with a variety of techniques and by continuing to gather data on this very interesting object,” she says.

Although the exoplanet may bear some resemblance to Earth, Queloz does not expect it to harbour life, comparing the exoplanet to Dante’s Inferno, with the probable temperature plummeting from above 2000 °C during the day to –200 °C at night. “Theoretical models suggest that the planet may have lava or boiling oceans on its surface,” he says. “With such extreme conditions this planet is definitively not a place for life to develop.”

The research will be published next month in Astronomy and Astrophysics.

Laser…the film

By Hamish Johnston

laser.jpg
Light is red, atoms are blue…

If light and atoms were people, what colour t-shirts would they wear?

Red and blue respectively — at least in a new educational video about the inner workings of the laser from physics blogger Clifford Johnson.

The video is called Laser and you can watch it on Johnson’s Asymptotia blog. However, Johnson recommends viewing it on YouTube, where a high definition version is also available.

Johnson uses a group of people to represent the atoms and photons inside a laser — and how population inversion and stimulated emission result in the emission of coherent light. It could come in handy if you are teaching an introductory atomic physics or optics course.

The video is the second in a series by Johnson and funded by the US National Science Foundation. The first film is called Shine a light and is also on YouTube.

Heavy water could add weight to climate models

An international collaboration of researchers has produced the most detailed map to date of water content in the lower atmosphere. This is the first such map to be made with satellite data and could lead to improvements in weather forecasting and climate modelling.

Water is a powerful greenhouse gas that is expected to contribute significantly to global warming. As global temperatures rise, the quantity of water in the atmosphere will increase exponentially – due to increased global evaporation – which will lead to even higher temperatures.

To gain a clearer picture of how the changing water distribution across the Earth is impacting on the climate, researchers need to develop a more sophisticated understanding of the hydrological cycle. That is, the budgeting of water between the Earth’s surface and atmosphere via evaporation and condensation.

Heavy water

One way of achieving this is to look at the abundance of deuterated, or “heavy”, water (HDO), in relation to standard water (H2) in the atmosphere. These data can yield valuable information about prevailing atmospheric conditions because the amount of heavy water in water vapour is related to prevailing temperatures.

Over the past few years, researchers have started to trace the distribution of heavy water in the upper atmosphere using a number of space-borne interferometers. These projects, however, have struggled to generate an accurate picture of how heavy water is distributed closer to the Earth’s surface, because the infrared detection technique does not reach the lower troposphere in which most atmospheric water resides.

Now, Christian Frankenberg at SRON-Netherlands Institute for Research and his colleagues have carried out a new series of measurements using a different technique, to incorporate this important zone in the lower atmosphere. Their technique involves a form of spectroscopy that is capable of resolving thermal emissions in the short-wave infrared, called SCIAMACHY or scanning imaging absorption spectrometer for atmospheric cartography.

Using an instrument on board the European Space Agency (ESA)’s Environmental Satellite (ENVISAT) the researchers monitored the changing global distribution of heavy water between 2003 and 2005.

Clearer picture

The researchers say that their findings can now be fed into climate models to give a more accurate representation of the hydrological cycle. “The potential to retrieve water isotopes from SCIAMACHY has been either overlooked or underestimated,” Frankenberg told physicsworld.com.

Fred Taylor, the Haley Professor of Physics at the University of Oxford is impressed by the latest work. “It has a lot of potential for clarifying the contributions of different processes within a complicated climate system and it is likely to lead to better regional climate models,” he said. However, Taylor believes that the data will not be as beneficial to weather forecasters. “I doubt it will make any difference to global mean forecasts, which probably reached the limit of their potential several years ago.”

The next challenge for the researchers is to further explore the relationship between temperature and water isotope ratios. “It is generally accepted that not only temperature but also dynamics impacts the variability of isotopes in ice-cores,” said Frankenberg. “Atmospheric circulation models are needed in order to understand this variability and to disentangle temperature from dynamics effects.”

Adam Scaife, a climate scientist at the UK Met Office believes that there may be other climate issues that need to be addressed before this research can be valuable. “It is clear that the fraction of deuterated water is dependent on several climate processes,” he said. “While this research may help to provide a tighter constraint on climate models, it will be difficult to untangle the causes of the differences between models and observations.”

Michelson–Morley experiment is best yet

Physicists in Germany have performed the most precise Michelson-Morley experiment to date, confirming that the speed of light is the same in all directions. The experiment, which involves rotating two optical cavities, is about 10 times more precise than previous experiments – and a hundred million times more precise than Michelson and Morley’s 1887 measurement.

The laws of physics appear to be the same for all processes occurring in laboratories moving at constant speed and for any orientation – a fundamental concept known as Lorentz symmetry. It takes its name from the Dutch physicist Hendrik Antoon Lorentz, who was attempting to explain the null result of Albert Michelson and Edward Morley’s famous experiment. Then in 1905, Albert Einstein used Lorentz symmetry as a postulate of his special theory of relativity.

Lorentz symmetry has so far withstood the tests of time, but in recent years physicists have begun to question whether it is indeed an exact symmetry of nature. They are motivated primarily by the development of string and loop quantum gravity theories, which try to make gravity compatible with quantum physics and allow for the possibility that Lorentz symmetry might not hold exactly.

In order to develop these and other theories, physicists need to know if and when the speed of light is different in different directions. Michelson and Morley tackled this problem by splitting light into two beams that travel at right angles to each other, are reflected by mirrors and then recombined with each other to produce an interference pattern, which depends on different lengths of the two paths. A change in this pattern as the interferometer is rotated would suggest that the speed of light is different in different directions.

Floating on air

In the past 120 years physicists have improved the Michelson-Morley experiment – and its latest incarnation can be found in Stephan Schiller’s lab at the Heinrich-Heine University in Düsseldorf. The apparatus floats on a thin cushion of air above a 1.3 tonne granite table. It comprises two optical cavities – essentially pairs of mirrors that reflect light back and forth – that are both about 8.4 cm long and at right angles to each other. Because the cavities are slightly different in length, they have slightly different resonant frequencies.

In the experiment, a laser beam is split into two beams, one for each cavity. The frequencies of the beams are then tuned to that of their respective cavities using “acousto-optic modulators”. The two beams – which now have different frequencies – are then recombined to produce a beat signal. If the speed of light were different in different directions, it would affect the resonant frequencies of the two cavities in an out-of-step manner, which could then be detected as a shift in the beat frequency as the apparatus is rotated.

Schiller and colleagues Christian Eisele and Alexander Nevsky gathered data as they rotated their experiment about 175,000 times over about 13 months, with each rotation taking 90 seconds. To investigate whether Lorentz symmetry had been violated, the team analysed their time series of beat frequency measurements in terms a simplified version of the Standard Model Extension (SME) – a mathematical framework that describes violations to Lorentz symmetry in terms of 19 measurable parameters.

100 million times better

Schiller’s experiment is sensitive to eight of these parameters and the team was able to show that four are zero to about two parts in 1017; one is zero to about one part in 1016; and three are zero to about two parts in 1013. According to Schiller, this represents a factor of more than 10 improvement over previous measurements of these parameters and a factor of about 100 million better than Michelson and Morley’s original experiment.

Ben Varcoe at the University of Leeds in the UK told physicsworld.com that Schiller’s experiment appears to be the most precise Michelson-Morley experiment to date. He also pointed out that if Schiller and colleagues were able to boost the precision of their experiment by a few more orders of magnitude, it could become sensitive to the effects of dark energy on the propagation of light.

The idea is that if the Earth is moving in a specific direction through stationary dark energy, the latter could be detected as a Lorentz violation. (Michelson and Morley were looking for a similar violation due to luminiferous aether, which we now know does not exist.)

Sensitivity boost

According to Schiller, it should be feasible to boost the sensitivity of the experiment by as much as a factor of 1000 over the next 10 years by introducing major improvements to the apparatus.

However, most current theories of quantum gravity leqad one to expect Lorentz violations at levels of about 10–30 – a precision that has already been reached in some astrophysical measurements of other SME parameters. How to reach such levels with Michelson-Morley experiments “is a tremendous challenge for the future,” said Schiller.

The work is described in Physical Review Letters.

Physicist to advise UK on energy and climate change

The physicist David MacKay has been appointed chief scientific adviser to the UK government’s Department of Energy and Climate Change. MacKay is a professor of physics at the University of Cambridge and author of the book Sustainable Energy – Without the Hot Air, which offers numerical estimates of the UK’s future energy production and consumption after fossil fuels run out.

Speaking shortly after his appointment was announced, MacKay described climate change and secure energy as “two of the most urgent issues facing the UK and the global community” and added that “the solutions must be rooted firmly in science”.

Known for his no-nonsense approach to outlining the challenges of reducing the UK’s carbon footprint, MacKay told the BBC this morning that “we need to move the conversation on from the Punch and Judy show of anti-wind and anti-nuclear to a quantitative discussion”. He added that “people need to understand the numbers and the choices.”

As aging coal-fired and nuclear plants go offline in the UK, MacKay is also worried that the country could be short of electricity by 2016. “My guess is the market might fix the problem by building more gas power stations, which is not the direction we want to be going,” he told the BBC.

Industrialization of the countryside

MacKay believes that the UK can achieve energy sustainability in two ways. The first is the “industrialization” of the British countryside – covering it with vast numbers of wind turbines, for example – or the industrialization of someone else’s countryside – solar cells in the Sahara, for example. The other option is to build lots of new nuclear reactors and possibly “clean coal” power plants that capture the carbon dioxide that they release and bury it underground.

However, MacKay believes that any solution is going to be a tough sell. “The public is anti everything,” he told the BBC. “There is a strong anti-wind movement, a strong anti-nuclear movement, people are against the [tidal power] barrage in the Severn, they’re against waste incinerators and they’re not that keen on electric cars and insulating houses. We have to stop saying no to these things and understand that we have a serious building project on our hands.”

MacKay takes over his new role on 1 October and will be seconded from Cambridge for four days a week. A review of MacKay’s book is to appear in the October issue of Physics World magazine.

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