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Graphane makes its debut

The “wonder material” graphene burst onto the scene five years ago — and the sheet of carbon just one atom thick continues to wow physicists with its growing list of remarkable properties. Now, a team including the UK-based research group that discovered graphene has created a new material called graphane by adding hydrogen atoms to their original discovery.

As well as being an insulator that could prove useful for creating graphene-based electronic devices, graphane might also find use as a hydrogen-storage medium that could help hydrogen-powered vehicles travel further before refuelling.

Despite being extremely thin, graphene has great physical strength as well as being an excellent conductor of both heat and electricity. What’s more, it is a semiconductor with electronic properties that can be adjusted by simply applying a voltage across a region of a graphene sheet — rather than by introducing chemical impurities as in silicon. As a result, some researchers believe that it could be used to create transistors that are smaller and faster than silicon-based devices.

Further on a tank of graphane?

Thanks to its low mass and large surface area, graphane has also been touted as an an ideal material for storing hydrogen fuel on vehicles. Finding an economical way of storing enough hydrogen for a reasonably long journey is a major challenge because liquefying the gas (as is done with propane)is prohibitively expensive in terms of both money and energy.

However, making graphane had proven to be difficult. The problem is that the hydrogen molecules must first be broken into atoms and this process usually requires high temperatures that could alter or damage the crystallographic structure of the graphene.

Now, a team led by Andre Geim and Kostya Novoselov at the University of Manchester has worked out a way to make graphane by passing hydrogen gas through an electrical discharge. This creates hydrogen atoms, which then drift towards a sample of graphene and bond with its carbon atoms.

The team studied both the electrical and structural properties of graphane and concluded that each carbon atom is bonded with one hydrogen atom. It appears that alternating carbon atoms in the normally-flat sheet are pulled up and down — creating a thicker structure that is reminiscent of how carbon is arranged in a diamond crystal. And, like diamond, the team found that graphane is an insulator — a property that could be very useful for creating carbon-based electronic devices.

Fine tuning graphene’s properties

“This is the first step in being able to fine tune the electronic properties of graphene by attaching various species to its scaffolding,” said Novoselov. “It is a new look at graphene, if you like, with far reaching and promising consequences.”

The next step would be to learn how to control the electronic properties by adding other chemicals, with perhaps different arrangements of these species on graphene’s surface, according to Novoselov.

“The modern semiconductor industry makes use of the whole periodic table, from insulators to semiconductors to metals. But what if a single material could be modified so that it covers the entire spectrum needed for electronic applications?” added Geim. “Imagine a graphene wafer with all interconnects made from highly conductive, pristine graphene whereas other parts are modified chemically to become semiconductors — and work as transistors — or become insulators.”

And that’s not all: the team also showed that reaction is reversible because graphane can be converted back into graphene by heating it up so that the hydrogen is removed. This property, plus the high hydrogen density and low mass of graphane, could make it a candidate for hydrogen storage.

Bloggers versus journalists

By Hamish Johnston

…is it hype or reporting a neat idea?

Sorry for the navel gazing but I thought I would point out an interesting discussion of one of our news stories over on Chad Orzel’s Uncertain Principles blog.

The article in question is about a proposal for using ultracold atoms to make precise measurements of neutrino mass.

The question that Chad asks is whether it is appropriate for us to report as “news” what is really just an interesting idea that may or may not ever come to fruition? By doing so, are we guilty of hyping the importance of the proposal?

We decided to go with the story for two reasons — the first is that this experiment is a very clever way of using developments in one field of physics (ultracold atoms) to solve a fundamental problem in a seemingly unrelated field (particle physics).

The second reason — perhaps a bit more woolly — is that this proposal comes from a respected experimental physicist, which suggests to me that there is at least a chance that it could be realized.

Chad alludes to the idea that a blogger with expertise in the field of ultracold atoms would probably take a more cautious approach to reporting this proposal because they would have a better understanding of the technical challenges involved.

However, I’m guessing that if you asked a circa 1970 semiconductor physicist whether it would be possible to mass-produce CMOS devices with 32 nm features, you would be given a list of seemingly insurmountable technical challenges.

I suppose what I’m saying is that there’s nothing wrong with reporting on what a reputable group of physicists thinks may be possible, without getting too caught up in the nitty gritty of why it might never come to pass.

Indeed, coming up with such ideas (and having them shot down) is an important part of the scientific process, so I don’t think that we should shy away from reporting on informed speculation.

So should we have taken a more cautious approach? I don’t think so — we did after all make it clear that this was a proposal and that it would be difficult to implement.

However, I do agree with Chad that we perhaps should have toned down the headline a bit. I like one of the suggestions put forward in the comments on Chad’s blog: put a question mark at the end of the headline.

Plot thickens for iron-arsenide superconductors

Since they were discovered a little more than a year ago, iron-arsenide superconductors have raised hopes that physicists will soon crack the difficult problem of explaining why certain materials remain superconducting at relatively high temperatures, while others do not. Now, a team of physicists in the US and China has shown that the superconductivity in a specific iron-arsenide material does not depend on the orientation of an applied magnetic field. The finding could challenge a long-standing belief among some physicists that high-temperature superconductivity only occurs when electrons are confined to move in two directions.

Superconductivity occurs when a material is cooled below a certain temperature and its conduction electrons form a condensate that can flow without any resistance. In a conventional, low-temperature superconductor, such as lead, this process (which involves electron pairs) is described by BCS theory, developed in 1957 by John Bardeen, Leon Cooper and Robert Schrieffer. However, BCS theory cannot explain why superconductivity persists in certain cuprate materials, some of which remain superconductors at temperatures above 100 K.

The new family of iron-arsenide-based high-temperature superconductors that were discovered last year do not, however, appear to fit either the BCS or cuprate models. Some physicists think that the mystery of why the cuprates are superconductors at such high temperatures could be cracked by comparing the physical properties of these new materials to known superconductors.

Now, Huiqiu Yuan and colleagues at Los Alamos National Laboratory in the US and the Chinese Academy of Science in Beijing have added an important piece to the puzzle by measuring the electrical resistivity of Ba_0.6K_0.4Fe₂As₂ by placing a single crystal of it in a strong magnetic field that could be varied between 0 and 60 T (Nature 457 565).

2D or not 2D

In all types of superconductors, the critical temperature (Tc) at which a material ceases to be a superconductor falls as the magnetic field is increased. In conventional superconductors only the strength of the field matters, not its direction. In cuprates, both the strength and direction of the field relative to the crystal lattice will affect superconductivity — suggesting that the superconductivity occurs in special 2D planes in the material.

The researchers found that the Tc of Ba_0.6K_0.4Fe₂As₂ fell from 28K as the field was increased from zero. Surprisingly, however, the material’s Tc did not depend much on the orientation of the magnetic field relative to material — in other words the superconductivity is 3D. It appears therefore that the iron arsenides are more like conventional superconductors in this respect.

Directionality in the cuprates suggests that the electrons move without resistance through planes of copper and oxygen atoms, which has led some physicists to conclude that the “quasi-2D” nature of these electrons is necessary for high-Tc superconductivity. But because the material studied by Yuan’s team contains planes of iron-arsenide — yet does not have the directionality of the cuprates — the link between high-Tc superconductivity and two-dimensionality could be a “red herring”, according to Jan Zaanen of Leiden University in the Netherlands.

Not very high-Tc

Others, however are more cautious in how they interpret Yuan’s data. Nigel Hussey of the University of Bristol, UK, points out that with a Tc of 28K, Ba_0.6K_0.4Fe₂As₂ cannot really be compared to the cuprates as is not really a high-temperature superconductor. Instead, he points out that such a Tc is more in line with other “3D” superconductors such as the perovskite Ba_0.6K_0.4BiO₃ and the fulleride superconductors, which have Tc values as high as 30K.

Hussey adds that some iron-arsenide superconductors similar to Yuan’s sample, but with Tc values as high as 56K, appear to be more 2D in nature.

So the plot thickens for iron-arsenide superconductors and the mystery of high-Tc superconductivity lives on.

Japanese mega-lab nears completion

The massive $1.5bn Japan Proton Accelerator Research Complex (J-PARC) in Tokai-Mura moved a step closer to completion after researchers successfully accelerated proton beams to 30 GeV at the facility’s 50 GeV synchrotron. The protons are then sent to the Hadron Experimental Facility (HEL), where they can be smashed against a target to produce a variety of subatomic particles, including muons, neutrinos and kaons.

The HEL will have room for five experiments, the first of which will be a study of how neutral kaons decay. Other planned experiments include a study of hyper nuclei — nuclei that contain strange quarks.

In April the 50 GeV synchrotron will also send its first stream of neutrinos to the SuperKamiokande detector located in the Kamioka mine, 295 km away.

J-PARC also contains a neutron-scattering facility, which is the country’s only neutron “spallation” source and replaces the KENS facility at the KEK particle-physics lab in Tsukuba. The neutrons are produced when protons are accelerated to 3 GeV in a synchrotron and then smashed into a mercury target. They are then guided guided to J-PARC’s Materials and Life Science Facility, where researchers can carry out experiments in biology and condensed-matter physics.

Can geoengineering cool the climate?

The first numerical study to compare different geoengineering schemes and determine how good they might be at reversing manmade climate change has been released by researchers at the University of East Anglia (UEA) in the UK.

They say that injecting the skies with aerosols to reflect incoming sunlight might offer great short-term potential but that such a plan also carries large risks. The team recommends instead that land-based carbon storage is the most effective solution over the long term. (ACPD 9 2559).

“What we’ve created is a clear, analytical framework for comparing different geoengineering options; hopefully this can be a guide future research,” said lead author Tim Lenton of UEA’s School of Environmental Sciences.

From Hollywood to East Anglia

The idea of controlling local weather conditions by the large-scale engineering of the environment came to prominence during the Cold War when the US and the Soviet Union both researched the concept for military ends. In the past few years global climate engineering has started to move out of the realm of science fiction as atmospheric carbon dioxide (CO₂) levels continue to rise despite international emission reduction targets. Proposals have been eclectic in characteristic and scale: from increasing the Earth’s reflectivity or “albedo”, to deploying large-scale shields between the Earth and the Sun.

John Latham of the National Center for Atmospheric Research in Boulder, US said, “The geoengineering community believes the chance of achieving the necessary reductions in CO₂ to avert likely catastrophe are virtually zero, so it is necessary and responsible to examine alternative ways of stabilizing global temperature.”

“If we failed to keep the process [geoengineering] going — perhaps due to political unrest — we would leave the planet open to the Sun’s full force” Tim Lenton, University of East Anglia

The trouble with the geoengineering at the moment, according to the UEA researchers, is the lack of quantitative framework for evaluating projects. What’s more, they suggest that the enthusiasm of certain proponents has created a skewed view, where a handful of schemes are surrounded by bold but unsubstantiated claims.

Quick fix

At the most basic level, Earth’s surface temperature is governed by a balance between incoming solar radiation and outgoing terrestrial radiation. For a series of different geoengineering schemes, the UEA researchers calculate the impact on this radiative balance by considering the global energy balance and the climate’s response to rapid changes in CO₂ levels.

The researchers find that increasing the reflectivity or “albedo” of the atmosphere offers by far the greatest potential to cool the climate by 2050. One mechanism for doing this — put forward last year — is to spray low-lying clouds with sea salt to act as condensation nuclei and enhance cloud cover. According to this latest research, a more effective measure is to aim higher by firing aerosols into the stratosphere, in the same process as volcanic activity.

Steven Salter of the University of Edinburgh, who was involved in the “cloud-salting” proposal, told physicsworld.com, “I welcome this new study as it is represents a much needed aspect of geoengineering; the more rigid testing our idea receives, the more we can develop it.”

The major risk, however, with these short term “Sun block” approaches is that failure to keep engineering projects in good repair would expose Earth to a rapid jump in temperature. “You are effectively masking the effect of a warming climate system,” Lenton told physicsworld.com, “if we failed to keep the process going — perhaps due to political unrest — we would leave the planet open to the Sun’s full force.”

Century scale

Over longer timeframes, the researchers suggest removing CO₂ from the atmosphere through schemes like planting trees, carbon capture and storage, and fertilizing the oceans. Perhaps surprisingly, existing activities that add phosphorus to the ocean may have greater carbon sequestration potential than running expensive schemes to add iron or nitrogen.

The most favoured solution is bioenergy, described by Lenton as a “win-win” option. Carbon from the burning of bio-waste is converted into “biochar” before being returned to the soil. Lenton told physicsworld that he will take this research forward by comparing their predictions with the established climate models of the Hadley Centre.

This year the School of Environmental Sciences at UEA will be launching a new centre to bridge the gap between their research and national policy. These results will also be feeding into a Royal Society study to be published later in the year.

David Mitchell, a researcher at the Desert Research Institute, US, said, “Geoengineering should not viewed as an alternative to mitigation, but as a means of buying time. If geoengineering is seriously considered by any government, this may affect other countries and perhaps a new committee by the UN is needed to regulate this new capability.”

Is science elitist?

By Hamish Johnston

…and if so, is that a bad thing?

There was lots of talk this morning on various BBC outlets about whether the “elitist image” of science is putting off the public. The debate was inspired by a campaign launched today by the UK government that aims to get the public more interested in science.

The campaign seems to have chosen a rather odd group of people to argue that science is not elitist. According to the BBC they include mathematician Marcus du Sautoy (Oxford), chef Hugh Fearnley-Whittingstall (Eton, Oxford) and TV naturalist David Attenborough (Cambridge).

Granted, the programme has also enlisted the self-taught chef Heston Blumenthal and author Bill Bryson – both of whom have achieved great success (partly thanks to science) without a university degree.

But is science elitist? I suppose it is in the sense that one must study hard to become a scientist — and someone from an elite background is more likely to have the resources and parental backing to succeed academically.

Also, the practice of science is elitist in the sense that we all know who the top scientists in our fields are — and these individuals are often treated with great reverence.

But let’s not forget that whatever their background, members of the scientific elite worked hard for their success — indeed, science is one of few professions where it is very difficult to be a fraud.

That’s why I was a bit annoyed by Kathy Sykes of the University of Bristol, who declared on BBC TV this morning “You don’t have to be a genius to be a scientist”. I suppose she is technically correct, but I think her statement is rather flippant given the high degree of intellectual rigour displayed by scientists.

Do the public think science is elitist? The UK’s science minister Paul Drayson has said so. But according to a poll commissioned by one of his departments, only 3% of Britons believe scientists have “the most influence on our daily lives”. So if science is an elite, it is an impotent one.

Finally, one needs to ask if people eschew science because they perceive it as elitist? I think we only need to look at lawyers — perhaps the most elitist of professions — who as fictional characters permeate popular literature, film and television. And law schools seem to have no trouble attracting students from a wide variety of backgrounds.

So maybe elitism is not such a bad thing?

China builds super-sized radio telescope

Construction has begun on a massive new 500 m diameter radio telescope in Guizhou province, China, that will allow astronomers to detect galaxies and pulsars at unprecedented distances. The $102m facility, known as the Five-hundred-meter Aperture Spherical Telescope (FAST), will boast a collecting area equal to 30 football fields — more than twice as big as the 305 m diameter radio telescope at Arecibo Observatory in Puerto Rico, which has been the world’s largest since it opened in 1964.

The geography and remoteness of FAST’s site — located some 170 km by road from the provincial capital Guiyang, near the village of Dawodang — make it unusually radio-quiet, says Nan Rendong, FAST chief scientist and a researcher from the National Astronomical Observatories at the Chinese Academy of Sciences. Like Arecibo, the new telescope will sit in a natural karst depression that mimics the shape of the collecting surface, simplifying the support structure and shielding the telescope from stray human-generated radio waves.

The site’s potential for long, uninterrupted observations — coupled with the telescope’s huge size, which will give it twice the sensitivity of Arecibo — means that researchers there will be able to detect objects like weak, fast-period pulsars that are too faint to be measured accurately by smaller instruments. The team also expects to discover the first pulsar outside the Milky Way, according to Nan.

‘Extraordinary’ impact on astronomy

“The FAST science impact on astronomy will be extraordinary,” Nan told physicsworld.com, adding that although the telescope is located in China, once it is completed in 2014 it will be open to astronomers from around the world.

Giant dish in a natural hollow

In addition to being big, FAST is designed to be flexible: a system of motors attached to its 4600 panels will allow astronomers to change its shape from a sphere to a paraboloid, making it easier to move the position of the telescope’s focus. This will allow the south-pointing telescope to cover a broad swathe of the sky — up to 40 degrees from its zenith, compared to the 20-degree-wide strip covered by Arecibo.

“Arecibo points straight up, and it’s a real chore to move more than 20 degrees,” says Murray Lewis, head of the radio astronomy group at Arecibo. “In that respect, they definitely have an advantage.” However, he notes that in its initial phase, FAST will only be sensitive to low-frequency (less than 3 GHz) radio waves. This range includes the commonly observed 1.4 GHz hyperfine transition in atomic hydrogen, the universe’s most abundant element and an important marker for a variety of stellar objects. Arecibo’s bandwidth, by contrast, stretches up to 10 GHz, allowing astronomers to collect data on molecular transitions in this region of the spectrum.

A planned second phase of construction will extend FAST’s range to 5 GHz, but a date for the upgrade has not yet been set.

CERN: the view from inside

James Gillies

How do you get a billion people excited about a giant superconducting proton collider?

Thinking about how to communicate the start-up of the LHC was the focus of everything we were doing since 2004. We saw a huge opportunity to put CERN and particle physics on the map. So we started saying to journalists: “Wanna see this? Well you’d better come soon because it’s going to be closed up — and it’s impressive.” Until 2004 we’d have about 200 visits per year, but in 2007 we had 600.

It’s now clear that 10 September was the only day the LHC was functioning long enough to get protons around in both directions. Does it unnerve you that so much luck was involved when the world was watching?

We took the decision to show people the reality of doing science at this level, and that carries risk. It could have gone wrong, but on the other hand I know the people who run these machines and they’re just an amazing bunch.

How did you feel when you woke up on 10 September?

Slightly terrified. Plan B was for me to stand up in the Globe [where the media were corralled] and tell 340 journalists who had come to CERN that it ain’t going to happen today. As it was, a minor cryogenic outage added a bit of drama, but that drove home to people that the event was live. We hadn’t rehearsed it, and that openness was appreciated.

And by the time you went to bed?

Well, fantastic. It was just the most amazing day. It was amazing to see how much emotion there was in witnessing this big machine coming to life. The event was huge. Eurovision [the broadcast service which beamed footage to television networks and cost CERN about 50,000 CHF] estimated we had exposure to 1bn people. The result now is that the LHC is mentioned without explanation in contexts that have nothing to do with science.

Rumour was that the switch-on date was arranged around BBC presenter Andrew Marr’s holiday plans?

It’s hilarious. The BBC did ask if we could put the date back if Andrew couldn’t make it, and we said “no”. But on the other hand, BBC Radio 4 pulled out all the stops and decided to do something unprecedented in science by devoting a day to the event, so in return we gave them a room just off the CERN Control Centre to use as a studio. The fact that Radio 4 went so big on CERN drove it out to the rest of the BBC, culminating in “Big Bang Day”, and then out to the rest of the UK media and the world.

Did the black-hole Armageddon frenzy aid or hinder your communication efforts?

Ultimately it helped us by generating interest, but it also worried an awful lot of people and that makes me somewhat angry. People were phoning us up genuinely worried about the end of the world and demanding to know who CERN is accountable to. Of course we’re accountable — 20 countries have to say “yes” before we do anything! We ran a strict press accreditation procedure and there was heightened security on the day.

People were phoning us up genuinely worried about the end of the world and demanding to know who CERN is accountable to.

Did CERN handle the issue well?

With hindsight I would have treated the black hole stuff in exactly the same way we dealt with Angels and Demons [the Dan Brown novel in which antimatter is stolen from CERN to destroy the Vatican]. We were very proactive with that — we put up a webpage and had fun with it — but we didn’t envisage the black hole story going as far as it did. On one hand we didn’t want to engage with the scaremongers, but the particle physics community worldwide was slow to pick up and say “this is nonsense”. It’s one thing for CERN to say everything is safe, but we needed other voices, which have since surfaced.

How did you feel when you realized the full extent of the damage caused by the electrical fault on 19 September?

I was genuinely sad, and I think a lot of people at CERN felt the same. When you’ve been so intimately involved with something for such a long time, and when the start up went so well, the incident was a huge shock. But there’s a story to tell here: mishaps like this are part of life when working at the cutting edge of technology and research.

Wouldn’t it have made more sense to test all the LHC circuits before the media event on the 10th?

I don’t think it would have been any easier to live with what happened. In fact, it may have been less easy because at least now we know that the LHC works extremely well.

So the incident wasn’t the result of pressure to switch on before the machine was ready?

No. The timetable was driven by [LHC project director] Lyn [Evans] and the machine operators. The plan was to get some collision data at low energies, then finish testing the hardware to run at higher energies. Had an electrical transformer not broken down three days after the 10th, we would have had that collision data and the incident would have happened later.

We knew the warm up and cool down would take two months minimum so we quickly put that out in a statement, although with hindsight we should have been more cautious.

CERN’s new director general [Rolf-Dieter Heuer] told staff on 12 January, that from now on people would hear about events first from him, not the press. Was there a lack of communication internally following the incident?

It wasn’t organized in a way that it needs to be now that there is such a huge demand for information. We knew the warm up and cool down would take two months minimum so we quickly put that out in a statement, although with hindsight we should have been more cautious because we soon realized there was no way the LHC was going to be back up that year. Internally, people from the machine and management side were giving talks to the experiments, but we could have used our intranet, website and the CERN Bulletin better.

Did CERN try to withhold information from the media?

There’s a great quote in a Salman Rushdie book: whenever information is tightly controlled, rumour becomes a valued source of news. That was happening at CERN. All the way through, the then director-general [Robert Aymar] genuinely wanted to put out factually accurate information as soon as it was available, but CERN probably tried too hard to keep tight control. Although we were quick off the mark with releasing official statements there were long gaps in between. Even though there wasn’t very much to say, there was stuff that could have been said which would have capped those rumours.

Why was the LHC logbook modified retrospectively on the day of the incident?

There’s nothing sinister about it. The person on shift that morning just wrote down what had happened, then someone came along and said: “Everybody can see that, let’s take it away!” It was a wrong decision made in the heat of the moment, but it was naivety rather than anything systematic. It’s an issue we’re probably going to look at. A logbook should be somewhere people can write down whatever they feel, but that’s not necessarily something that should be visible to the whole world.

[Modifying the log book] was a wrong decision made in the heat of the moment, but it was naivety rather than anything systematic.

Were the long awaited official photos of the damage chosen because they were taken after the tunnel had been cleaned up?

No. They were specifically chosen because they showed where the damage was worse, at the end of the helium-induced pressure wave. I think the rumours had led people to expect something more dramatic.

Who ordered links to photos and some presentations to be password protected after they appeared on blogs?

[Aymar] wanted the CERN community to receive the news from him before it was made more widely available, so access to slides was temporarily restricted. People just hadn’t realized how much in the spotlight we are now.

Is it true that people were being threatened with disciplinary action if they circulated pictures of the tunnel before they had been officially released?

It’s true that the former DG wanted to be the one issuing the information. Look, we have to be more effective in the way that we communicate at CERN both internally and externally. The world is watching this. We’ve created what we’ve created, there is a demand for information and we need to provide it. That’s something that the new management is very aware of.

How are the repairs going?

They’re going well, but there’s a lot to do. We need to increase the LHC’s capacity to vent helium in the event of another leak, so already on all the sectors that are warmed up (half the machine) we are changing the valves on all the quadrupole magnets and putting new ones on the dipoles.

Where’s the logic in making only half of the machine safer?

What we’re doing is about as conservative as you can get. The LHC will now be able to vent ten times as much helium as before, and on top of that we’ve got lots of extra monitoring which will allow us to see a similar electrical fault coming.

CERN has a history of overly optimistic LHC timetables. Isn’t the current schedule of first-beam in July/August rather aggressive?

I’m pretty confident there will be collisions this year. There’s a great determination, but caution is the guiding principle. There will be a meeting in Chamonix in early February after which a realistic schedule will be announced.

Does the world have the appetite for “Big Bang Day II”?

It won’t be as big as 10 September. We’re not going to be inviting anyone back for first-beam this year. Journalists are keen to see first collisions even though it may involve camping out with us for a week. The whole process will be webcast. CERN was unwilling to invest in bandwidth before the 10th so the webcast fell over very early in the morning, but we’ve since had companies offering us bandwidth in exchange for having their logo displayed.

This year CERN won’t be chasing the media or the blogs. We’ll be the primary source of news about [the lab].

What do you think the LHC will find and when?

Well, you should probably ask the people who are working on it.

Come on, you’ve got a PhD in physics!

We’re going to find the Higgs particle if it exists, and I can’t think of any reason why it doesn’t. But that will take a year’s worth of good data. What I would really like to see, although it would be a nightmare from a communications point of view, is a flood of supersymmetric particles as soon as we switch on. Some models say that could happen, and if so we’ll have a group of people saying “wait!” and another group saying “look, this is a signal!”

How are you going to manage information when data arrive and rumours spread?

We’ve got protocols in place for the experiments so that if they really feel they are ready to make an announcement then we move very fast and organize a seminar here very quickly. One thing you’ll see this year is that CERN’s official communications won’t be chasing the media or the blogs. We’ll be the primary source of news about CERN.

Is that realistic, given that bloggers can brain-dump a post in a matter of minutes?

I think we’ve got to try. If there’s someone who’s blogging about a “three sigma” effect [meaning there is less than 1% chance it is a statistical fluke] that’s been verified, then there’s no reason why we wouldn’t talk about it as well. But if someone is blogging about a three sigma effect in their own particular analysis which hasn’t gone through the official verification process in their experiment then we will deny it, which may come to releasing a statement.

Are you planning to implement rules on blogging, as the CDF collaboration at Fermilab has done in response to rumours about Higgs sightings?

Yes. Some of the experiments have them already as a result of what happened there.

Isn’t that an attempt to censor information?

It’s an attempt to stop blogs fuelling rumour. Nobody wants to clamp down on people releasing information about results that have passed through official quality control in an experiment.

What’s the best question you’ve ever been asked about the LHC?

Visitors often ask first whether they can ask a really stupid question, and then come out with something profound and unanswerable that goes straight to the core of what we’re doing here.

Chilly solution to neutrino mass problem

Physicists in the US have put forward a new way of measuring one of the most important but elusive quantities in particle physics — the mass of the neutrino. The proposed experiment borrows techniques from atomic physics to lower the temperature of tritium atoms to nearly absolute zero and then study their beta decay.

A more precise measurement of neutrino mass is important because it will tell physicists what sort of theory is needed to extend the Standard Model of particle physics. A better value could also help astrophysicists work out how much of the universe’s dark matter can be accounted for by neutrinos.

The Standard Model itself assumes that neutrinos have zero mass. However several different experiments have proven that neutrinos oscillate between three different types or “flavours” — which can only happen if neutrinos have mass. Unfortunately, oscillation measurements are only sensitive to differences between the squares of the masses of different flavours, not absolute mass.

Physicists do know that the neutrino mass is less than 2.2 eV because of two independent experiments involving beta-decay — whereby a neutron in a tritium nucleus turns into a proton, emitting an electron and an antineutrino. Careful measurements of the energies of a large number of such electrons gives an upper limit on neutrino mass. A larger version of these experiments called KATRIN switches on in Germany in 2012 and should be able to further constrain the neutrino mass to 0.2 eV.

Nature does not easily reveal the secrets of the neutrino mass Guido Drexlin, KATRIN project

Other experiments, meanwhile, will measure neutrino mass by studying a very rare form of beta decay in which two neutrons inside a nucleus transform into protons at the same time, emitting two electrons but no neutrinos. The half-life of this process depends on the value of neutrino mass. Neutrino mass can also be deduced from measurements of the cosmic microwave background — the current upper limit is 1 eV — but this result depends on certain assumptions about the evolution of the universe.

Measuring motions of various particles

Now, a team including Mark Raizen at the University of Texas at Austin and Joshua Klein at the University of Pennsylvania has proposed a new way of making extremely precise measurements of the motions of the various particles involved in the beta decay of tritium.

To ensure that the system is initially as close to absolute standstill as possible, this proposal involves cooling a gas of tritium atoms to within a few millionths of a degree of absolute zero. Raizen’s group is currently working out how to cool tritium and other hydrogen isotopes by slowing down beams of these atoms using magnets and then gradually transferring their remaining momentum to individual photons. They then propose two alternative ways of measuring the neutrino mass (arXiv:0901.3111).

The first of these involves studying what is known as the “boundstate” beta decay of tritium. In this process, which has not yet been observed, the emitted electron becomes bound into the helium atom rather than escaping. This makes the decay a straightforward two-body process, in which the energy of the emitted neutrino is equal to the energy difference between the initial tritium atom and the daughter helium atom. The neutrino mass can be calculated simply by measuring the velocity of the nuclear recoil, which can in principle be done by detecting the time it takes for the helium atom to arrive at a detector placed some known distance from the tritium source.

The second method studies the three-body beta decay of tritium and involves using various detectors to work out the momenta of the daughter helium ion and the emitted electron. The neutrino mass is then calculated directly from these quantities.

Maximizing the number of decays

Both of these techniques rely on maximizing the number of decays in order to achieve as high a sensitivity as possible. Raizen and co-workers have worked out that by trapping some 10¹³ tritium atoms — the maximum that can feasibly be attained over the course of about a year — they would reach a somewhat disappointing upper limit on the neutrino mass of around 9 eV with the first approach, but could get down to roughly the limit possible with KATRIN — 0.2 eV — with the second.

These figures, however, were generated using a computer simulation. Whether the 0.2 eV limit could be reproduced in an actual experiment — which the researchers hope to carry out within the next decade — depends on overcoming several significant engineering challenges, not least of which is finding out how many atoms can in fact be trapped.

KATRIN project leader Guido Drexlin says that the approach of Raizen’s team is, in principle, very interesting. But he emphasizes that much work must be done to put the idea into practice. “Nature does not easily reveal the secrets of the neutrino mass,” he adds. “The name of the game in direct neutrino mass sensitivity is always the same: statistics, statistics, statistics, and carefully control all your systematics.”

Happy Chinese New Year

Lanterns in Kota Kinabalu, East Malaysia

by James Dacey

Last Monday was dubbed Blue Monday after “official” calculations deemed it to be the most depressing day of the year. Thankfully, this Monday, things are a lot more celebratory; the colour red takes centre stage as more than a billion people across the globe celebrate Chinese New Year.

Physics World would like to extend you all a warm welcome to the year of the Ox!

It struck me today that this year’s celebrations have fallen especially close to the Gregorian New Year. In my ignorance I’ve only just realised that the date changes each year – but how and why?

Well, if you were as in the dark as I was, check out this short video by Xinhua, a Chinese Government news agency. It gives a nice overview of key dates in the Chinese New Year Calendar.

And this year’s festivities seem to be in full flow already. According to Xinhua, Beijing last night was covered in 68 tonnes of firework debris.

UN Secretary-General Ban Ki-moon on Friday sent a message in Chinese, which read: “Happy New Year to the Chinese people and all the ethnic Chinese all over the world.”

One more slightly interesting fact for you: 2009 is the year of the Ox — the “brave leader” — and famous “oxen” include Barack Obama…

… but I’ll leave it there because this is rapidly slipping away from physics!