If there was any doubt in your mind that physicists working on the Large Hadron Collider (LHC) have found a particle best described as a Standard Model Higgs boson, two preprints uploaded yesterday by the CMS and ATLAS collaborations should put you at ease.
The preprints provide the latest analysis of the data gathered by the two experiments. While much of this information was presented at a special seminar at CERN on 4 July, the preprints do include some new information.
In particular, the statistical significance of the ATLAS result seems to have gone from 5.0σ to 5.9σ. In particle physics, anything greater than 5.0σ is considered a “discovery”. The significance of the CMS result seems to remain the same as it was on 4 July at 5.0σ.
Both experiments continue to suggest that the particle they have discovered bears a striking resemblance to a Higgs boson as described by the Standard Model of particle physics.
You can read the ATLAS preprint here and the CMS preprint is here.
Italian physicists have reacted with anger to proposed cuts to the country’s research funding. Particularly hard hit would be the National Institute of Nuclear Physics (INFN), which has been slated to absorb nearly half of the €120m reduction in the research ministry’s budget as outlined in a decree earlier this month.
The cuts to research are part of a broader “spending review” carried out by the government of Mario Monti to try to contain Italy’s enormous public debt, which will see spending slashed by €26bn over the next three years. The INFN stands to lose just over €9m this year – some 3.8% of its budget – and more than €24m (10%) in both 2013 and 2014. This compares with the 1.2% and 3.3% cuts that the country’s largest research organization, the National Research Council, has to contend with in 2013 and 2014, respectively, and the 0.2% and 0.6% reduction for the Italian Space Agency. These cuts come in addition to a 10% reduction in research agencies’ technical and administrative staff, in line with other civil-service bodies. The timing of the cuts came just two days after the announcement that a Higgs-boson like particle had been observed at the CERN laboratory in Geneva.
Letter to the president
INFN president Fernando Ferroni expressed his outrage at the cuts in a letter to Italian president Giorgio Napolitano, who a few days earlier had himself written to CERN’s research director Sergio Bertolucci to offer his congratulations on the Higgs discovery. Ferroni wrote that the INFN is ready to make economic “sacrifices” but that the spending review “penalizes quality and excellence”, arguing that “if Italy wants to exit the crisis with a long-term vision, science cannot be seen exclusively as an accounting problem”.
Ferroni was separately quoted by the newspaper La Repubblica as saying that the INFN had been hit hardest because it spends only 55% of its budget on wages and other non-negotiable expenses, whereas that percentage can be as high as 90% at other institutes. He estimated that the INFN’s spending on experiments – at CERN, the Gran Sasso underground laboratory and elsewhere – would therefore have to be reduced by around 30%.
Strategic consequences
Along with Fabiola Gianotti, spokesperson for CERN’s ATLAS experiment, and Guido Tonelli, former spokesperson of the neighbouring CMS detector, Bertolucci wrote an open letter to the media saying that if the cuts are confirmed, “the INFN would find it impossible to continue its activities effectively and to honour its national and international commitments”. They also complained that the government had not consulted the INFN in drawing up its spending review, which, they said, showed a “worrying imprudence in evaluating the strategic consequences of the cuts”.
Because the decree is still being discussed in parliament, researchers are hopeful that the government might scale back the cuts to nuclear and particle physics. Unfortunately, the Italian senate has approved the decree and it will now go back to the lower house for approval, but the specific details will not be known until the final decision is made over the next few days.
According to a source inside the research ministry, it is likely that while the total reduction in research funding will be cut as planned, research minister Francesco Profumo will decide how that total is divided up, in which case the cut to the INFN budget would “certainly be lower” than planned.
A team of South Korean researchers has produced a simple, highly sensitive and flexible sensor based on the intermolecular forces between “nanohairs”. The device was fabricated as a synthetic equivalent to human skin. It is capable of distinguishing and measuring pressure, as well as shear stress and torsional forces, and can be easily and economically manufactured.
Reproducing the qualities of skin in a suitable synthetic sensor has proved a challenge because there are severe design constraints on such sensors that make them highly complex to fabricate. Most significantly, the devices need to be thin and flexible enough to wrap around areas of high curvature such as fingers and toes without being damaged. This is problematic because most of the materials used in electronics, such as silicon and germanium, are, in their bulk state, hard and brittle.
Epidermal electronics
Various research groups have made progress in “epidermal electronics” using a variety of methods. John Rogers’ group at the University of Illinois at Urbana-Champaign, for example, has used a transfer-printing method to cut individual silicon chiplets to micrometre size and attach them to a flexible substrate, allowing the researchers to create wireless heart-rate monitors that stick to the skin like temporary tattoos using just Van der Waals forces. Other groups have created flexible electric circuits using carbon nanotubes or graphene. But doubts remain about whether such approaches can realistically be used to produce an affordable sensor able to measure and distinguish between different types of forces on a large area of “skin”, as the circuitry would become increasingly complex and the engineering demands ever greater.
Instead, researchers at Seoul National University (SNU), together with a colleague from Rogers’ group in Illinois, have created a simpler sensor based on piezoresistance – where changes in the electrical conductivity of a semiconductor are caused by applied mechanical stress. Their design uses two slightly separated thin layers of a flexible polymer – polymethylsiloxane (PDMS) – each covered with a very thin layer of platinum to make them conduct electricity. The team then covered the inner surface of both layers of polymer with a dense carpet of platinum-covered “nanohairs”. Van der Waals forces between the intertwined hairs cause the two layers of polymer to be drawn together like a kind of molecular Velcro. However, the hairs’ resistance to bending simultaneously acts to push them apart. The two forces balance at an equilibrium distance.
As the hairs are covered with platinum, they provide an electrical connection between the otherwise separate layers of polymer. Any pressure on the sensor at a particular point brings the two layers closer together, thus increasing the amount of contact between the hairs and reducing the electrical resistance. When the pressure is removed, the two layers return to their equilibrium separation and the resistance returns to normal. Shear and torsion forces also affect the membrane double layer, albeit in more complex ways. Using established engineering technology, the researchers were able to collect resistance measurements from a closely spaced 2D array of points on the sensor and use them to distinguish and measure pressure, shear and torsion.
The researchers have shown their device’s sensitivity via several demonstrations. They measured a small water droplet bouncing on a hydrophobic surface and also measured the change in the speed and intensity of a volunteer’s heartbeat after vigorous exercise using a sensor attached to the artery at their wrist. They also demonstrated the sensor’s ability to measure the spatial distribution of pressure by using an interconnected sensor network of 64 pixels and placing two ladybird beetles at separate locations on its surface, mapping their pressure displacement as the insects walked over the sensor.
Principal investigator Kahp-Yang Suh explains that the techniques used in the manufacture of the sensor are easily reproducible and are economical. “It’s very easy to replicate this hairy structure using a standard soft-lithography process,” he says, “You can easily replicate from a single silicon master by a process called replica moulding, which is well established in our field.”
John Rogers is impressed by the researchers’ design. “It represents a clever way to combine materials, mechanics and structure layouts for a class of tactile sensor technology that has exceptional performance and the ability to integrate naturally with the surface of the skin,” he says. He is sceptical, however, about the researchers’ claim to have removed the need for complex electronic circuitry. “If one is interested in real, multifunctional artificial skin, then you need a lot more and different stuff, such as different sensors, electronic amplifiers and multiplexers. The need for and benefits of active electronics do not go away,” he adds.
How will the discovery of the Higgs boson at the LHC affect the design of a future linear collider?
Now that it looks like we have got the Higgs at a low mass, we know the minimum energy – around 250 GeV – at which a linear collider could start to do interesting physics. However, we still need the LHC to operate at its full energy of 14 TeV to guide us towards what else we may need.
How do CLIC and the ILC stack up against each other?
CLIC and the ILC are two separate concepts. Both are designed to accelerate and smash together electrons and positrons. Although there are similarities between the two projects – especially in the detectors – there are big differences in the accelerating structures. The ILC is based on a superconducting technology, involving a series of accelerating cavities that are powered by klystrons. The technology is mature and most of the development effort on the ILC is currently focused on industrializing the technology. In terms of energy, the technology is a bit limited but if we wanted a total collision energy of 500 GeV, the ILC would be perfect. We might eventually be able to push that energy up to around 1 TeV.
So what about CLIC?
CLIC is based on completely new technology, and is still very much in the R&D stage. It has a much higher accelerating gradient and therefore could operate at higher collision energies. CLIC relies on a two-beam concept in which a “drive” beam runs in parallel with the accelerated beam – and energy is transferred from one beam to the other.
CLIC would operate at 11 GHz, whereas the ILC would run at about 1 GHz. This would give CLIC a higher accelerating gradient of 100 MV/m compared with the 31 MV/m of the ILC. This means that, for a given accelerating energy, CLIC would be considerably shorter than the ILC – or to put it another way, CLIC can go to a higher energy, up to 3 TeV, for a given length.
What needs to be done before the winning design is chosen?
An early decision to build a linear collider would imply using ILC technology since it is already mature. In the meantime, without the guarantee of an early decision, we will continue to develop CLIC technology to a level of maturity where we could compare the two options in terms of scientific capability and cost.
The plan is to bring the CLIC and ILC development teams together and give them a common direction. Both technologies will be developed in parallel for three or four years until a final decision is made about what is actually going to be built. The decision will be made in terms of physics and not politics or personal prejudices. My job is to encourage much more dialogue between the CLIC and ILC communities. I also need to ensure that we are in the position to take a collective decision, based on scientific needs about which collider design to choose – without too much emotion.
What are the main differences between a linear collider and the LHC?
A linear collider smashes leptons such as electrons and positrons, which are fundamental particles. As a result the collisions produce a relatively small number of particles. The LHC collides hadrons, which themselves are made of quarks and gluons. In the LHC we want to study the hard collisions between the fundamental components, but there are lots of other ways that protons can collide. It’s a bit like smashing two oranges together just to watch the pips collide – it is very messy. The LHC is a beautiful machine for discovery but is less good at precision measurement than a linear collider. There are also fundamental processes that only a lepton collider can address.
What do you make of suggestions that a linear collider might be built in stages?
A staged approach looks attractive in terms of keeping the initial cost down. We could start at a low energy and boost the energy by simply making the collider longer over the years – something that cannot be done with a circular collider. Somewhere around 250 GeV would be a good place to start and that would bring the cost down a lot.
Will the linear collider be built in Japan?
Japan is taking the matter very seriously. It made a big contribution to the construction of the LHC and may now be prepared to host a new international facility. There are two sites in Japan that have been financed for geological surveys and it would not surprise me if the Japanese make a proposal to build a linear collider in the next few years.
But where will the collider development effort be based?
Like the LHC it is very much an international effort. I will be based at CERN and the CLIC team is also here in Geneva with collaborating institutes mainly in Europe, but also in the US, Australia and Japan. The ILC project is dispersed all over the world. There is work going on at KEK in Japan, DESY in Germany and at several labs in the US including Fermilab and Brookhaven. There is a station at Fermilab where ILC modules are tested. The first module is there and the second one is being built. However, the funding situation in the US is very uncertain at the moment. At DESY they are building a free-electron laser using technology that is very similar to the ILC and this will be an important testbed. There is also ILC development work going on in Japan.
As for the machine you masterminded, can we expect an upgrade to the LHC beyond its 14 TeV design energy?
An upgrade to the LHC is a no-brainer – it is a beautiful machine and can do much better than its original design. An upgrade programme has to be the main effort of CERN over the next 15 years. We will definitely be increasing the energy from 8 TeV to 14 TeV after the 2013–2014 technical stop and there is also a plan to boost the LHC’s luminosity over five years, but doubling the energy to around 30 TeV would require 16 T magnets. When we started planning the LHC we couldn’t make its current 8 T magnets so it is possible that R&D could deliver the technology. However, it is important to realize that a higher-energy LHC would essentially be a new collider, whereas luminosity can be increased incrementally. Everyone agrees that the top priority for CERN is to exploit the LHC to its full potential while contributing to the worldwide effort towards the next linear collider.
An international team of researchers has developed a new way to pattern complex 3D arrays of wires and interconnects on a microchip with the help of self-assembling block co-polymers. The technique could be used to pack more electronic components onto a memory chip – an important advance as device feature sizes continue to shrink.
The team, led by Caroline Ross and Karl Berggren of the Massachusetts Institute of Technology (MIT) in the US, has shown that a block co-polymer – polystyrene-polydimethylsiloxane – can be “forced” to form a complex set of 3D patterns on a substrate surface. Block co-polymers are made of blocks of different polymerized monomers. The technique, detailed in the journal Advanced Materials, involves using a simple template comprising an array of small pillars made of silica, explains team member Amir Tavakkoli. “We have found that we can create a rich variety of microdomain morphologies on a single substrate by modifying the layout of the pillars,” he says. “One such morphology is a high-resolution square lattice of dots, but cylinders, spheres, ellipsoids and double cylinders can easily be produced too.”
Smaller the better
The spaces between features in the final patterns can be smaller than the original periodicity in the block co-polymer, Tavakkoli says. This means that the number of components that can be packed onto the sample substrate is increased. Indeed, the feature sizes that can be made in this way are very small, at about 10–20 nm. In contrast, those produced by conventional photolithography are at least 10 nm bigger. “Being able to fabricate such small structures will be important in the future because feature sizes are continuing to shrink, in accordance with Moore’s law,” he adds.
Shapes in a box
Another big advantage of the new technique is that it can produce square and rectangular structures. These shapes are the basis of most microchip layouts but are quite difficult to produce through conventional self-assembly processes. “When molecules self-assemble, they have a natural tendency to create hexagonal shapes – as in a honeycomb or an array of soap bubbles between sheets of glass. They do not naturally form squares or rectangles,” says Ross.
The MIT researchers’ fabrication technique starts with the construction of a precisely controlled pattern of nanopillars on a silicon substrate surface using high-resolution electron-beam lithography. Next, the pillars are chemically coated with a thin polystyrene “brush” layer that subsequently interacts with the block co-polymer when it is applied to the substrate surface. The co-polymer then self-assembles into a pattern that is guided by the pillars.
Repellent shapes
The process works because the template coating is arranged in such a way as to repel one of the components in the polymer. This produces a significant amount of strain in the polymer, forcing it to twist and turn. “In doing so, the polymer rearranges itself on the substrate surface into more interesting patterns,” explains Berggren.
The team says that it now plans to investigate how to remove the physical post template from the final pattern, and then transfer the pattern to the substrate. “We would then like to make some functional devices and we also want to understand and model the self-assembly process so that we can generalize this work to other block co-polymers and feature geometries,” Tavakkoli told physicsworld.com.
While the vibrant image above might, at first glance, look like a painter’s colour chart, it actually shows how different categories of polyhedral particles in a fluid would pack together as a solid. The method used to obtain the findings has been developed by Pablo Damasceno and colleagues at the University of Michigan, US, and is based on only two parameters: the shape of the particles and the number of neighbours they have in the fluid phase. What Damasceno and his team have done is run computer simulations to study how 145 different types of polyhedra pack into various structures, based on interactions driven solely by the particle shape, to come up with simple predictive criteria for the final shape that is formed. As a material’s physical properties are intrinsically dependent on its structure, understanding exactly how materials assemble and evolve is essential to designing them. The team’s calculations show that, depending on their initial shape, hard polyhedra will assemble in one of four ways: crystals, plastic crystals, liquid crystals or fully disordered structures. And these all depend only on a ratio based on the particle’s volume and surface area and on the number of neighbouring particles. In the image, the four colours depict the four assembly categories, while the shades indicate subcategories of formation. (Image courtesy of Michael Engel.) The researchers also found some abnormalities and unexpected results, with some polyhedra never assembling into any kind of structure. Take a look at the Science paper here .
The world’s biggest computer-chip maker, Intel Corporation, has signed a major agreement with Dutch lithography firm ASML Holding to collaborate on developing the next generation of technology for manufacturing semiconductor chips. Under the terms of the deal, US firm Intel will take a 15% stake in ASML for around €2.5bn and will contribute €829m towards ASML’s research and development in new lithography-based chip-manufacturing systems.
Wafer etching
Chip manufacturers currently use production systems based on deep-ultraviolet lithography, which focuses light through lenses to etch circuit patterns onto silicon wafers. While this technology is limited to wavelengths of 193 nm, ASML is developing extreme ultraviolet (EUV) production systems that use light with wavelengths of just 20 nm. ASML says the new technology will enable chip makers “to deliver smaller, faster, cheaper and lower-power devices through smaller geometries on advanced manufacturing nodes”.
Chip makers currently produce chips on 300 mm silicon wafers but ASML is developing a system that can make chips on 450 mm-diameter wafers, which the firm says would basically double the capacity of chip-making factories at only a fraction of the cost. Brian Krzanich, Intel’s chief operating officer, says the firm’s investment could result in 450 mm prototypes as early as 2015, noting that in the past transitions to bigger wafers have helped to cut costs by 30–40%.
Next-generation chips
Jörg Stephan, project manager and research co-ordinator for the Berlin-based Fraunhofer Group for Microelectronics, says that Intel’s decision to invest in ASML is a boost for near-term development of EUV technology, which some experts previously thought would not be ready for the next generation of chip-making technology. “Intel is saying it believes in this technology,” he adds. “It is really new but also really expensive. It is not something that a research institute could buy and use in the laboratory.”
ASML says it is also in discussions with Samsung and the Taiwan Semiconductor Manufacturing Company about a stake in the firm. If those two companies agree to participate, their stakes combined with Intel’s could total a 25% share of ASML.
Earlier this week we learned the sad news that Sally Ride, the first American woman in space, died of cancer at the age of 61. Ride made history as a crew member on the _Challenger _mission that blasted off from the Kennedy Space Center in Florida on 18 June 1983. She was also aboard the 13th shuttle flight, STS 41-G, which launched on 5 October 1984.
Before embarking on her space travel Ride had a strong and diverse academic background, holding degrees in physics and English from Stanford University. Then in 1989 she returned to academia by joining the University of California, San Diego as a professor of physics and director of the California Space Institute.
Alongside her academic activities, Ride of course underwent intense physical training in preparing for her space missions. And the biography on Ride’s website reveals that her passion for athletic activities began at an early age. She apparently competed in national junior tennis tournaments and was good enough to win a tennis scholarship to Westlake School for Girls in Los Angeles.
Clearly, Ride is an extreme example of somebody with drive who achieved incredible things during her lifetime by devoting countless hours to both academic study and physical training. Both of these passions brought a focus to her life that helped her to achieve her goals. But I wonder whether we mere mortals could also benefit to a more modest extent from this combination of physical and mental exercise.
We all know of people who excel in academia and sport. And we’re forever being told that regular exercise can help contribute to a balanced lifestyle – improving our concentration, sense of wellbeing, yada yada yada. But then equally I’m sure you know plenty of clever, successful, happy people who despise physical activity, can’t think of anything worse in fact. We’re interested to know where you fall in this debate, so please take part in this week’s poll
Do you find that regular exercise helps you to focus when studying?
Yes No
Have your say by visiting our Facebook page, and please feel free to explain your response – or suggest something in-between – by posting a comment below the poll.
In last week’s poll we looked at the impact of science and technology on society. We asked you to select which physics-based technology to emerge from the Second World War has had the most significant impact on society. The most popular choice with 65% of the vote was modern computing, followed by nuclear power/weapons with 19%, then radar and microwave technology with 8%. In 5th and 6th place were the jet engine with 5% and rocket systems with just 3%.
Thank you to everyone who took part and we look forward to hearing from you again in this week’s poll.
Researchers in Japan have unveiled a prototype of a “Mott transistor”. If implemented commercially, such a transistor could offer significant advantages over current designs in energy efficiency and switching speed.
As transistors are the basis of modern electronics, scientists are continually seeking ways to improve and enhance them. Transistors used for switching in modern computers are based on the field effect. In such transistors, a voltage applied between the gate and drain electrodes increases the conductivity of a semiconductor, allowing electricity to flow between the source and drain electrodes. A transistor should ideally carry as little current as possible when there is no voltage between the gate and drain (the off state) and as much as possible when gate voltage is present (the on state). A low off current is important for energy efficiency, while a large on current is important because it allows circuits to run faster.
Ideal transistor
An ideal transistor would be a total insulator in the off state and a perfect conductor in the on state. Therefore, an important measure of the quality of a transistor is the ratio of the on current to the off current. However, with a standard field-effect transistor (FET), this change in conductivity is influenced by only a thin layer close to where the current flows between gate and drain. This limits the ratio of on current to off current that can be achieved.
Scientists have suggested that it might be possible to improve this ratio by exploiting Mott insulators in transistors. Mott insulators are materials that should behave as metals according to conventional band theories but that act as insulators under certain conditions owing to quantum-mechanical correlations between neighbouring electrons. For reasons that are complex and not entirely understood, however, sudden phase transitions can be induced between the insulating state and the metallic state. Among other things, this metal–insulator transition can be induced by an electric field. While the gate voltage in an ordinary transistor simply modulates the resistance of a semiconductor, the gate voltage in a Mott transistor could turn an insulator into a metal.
Bulk transitions
Various research groups have tried to produce Mott transistors in the past, but they have failed to generate the electric fields needed to induce the metal–insulator transition at the surface of the Mott insulator. Now, scientists from the RIKEN Advance Science Institute in Wako, Japan, have covered the surface of the vanadium-dioxide Mott insulator with a drop of ionic liquid. When a small gate voltage was applied to the ionic liquid, this generated a huge electric field at the surface of the Mott insulator, inducing it to change to the metallic state. Best of all, unlike in a standard transistor, the phase transition – and so the change in conductivity – occurred not just at the surface, but also throughout the entire bulk of the material. The researchers are not entirely clear why this is the case, but they suspect that the electric field at the surface of the Mott insulator induces a phase transition in a thin layer near the surface, and that this introduces energy to the lattice of the material, thereby triggering a kind of cascade effect with the phase boundary propagating into the material like a wave.
The researchers achieved an on current to off current ratio of 100:1. This might seem disappointing alongside the figures for modern FETs, which can achieve ratios as high as a million to one, but Jochen Mannhart, a condensed-matter physicist at the Max Planck Institute for Solid State Research in Stuttgart, Germany, insists that is not the case. “The most significant feature of this research”, he says, “is that the researchers showed that in some material – in this case vanadium dioxide – by applying a gate voltage one can switch the whole volume of the material from being insulating to being conducting and thereby switch a very large volume of electrons from being immobile to being mobile.” He explains that, while the modern FET is the result of 30 years of optimization, the Mott transistor is a proof of principle and has not been optimized at all. Mannhart says the only real problem for the device is the presence of the ionic liquid, which would be impractical in a real circuit component and will need to be replaced by a solid insulator.
Masaki Nakano, who led the research, agrees that will be important, but he says that, for the moment, the group is not focusing on developing its device further. “Currently, we still have to spend a lot of time understanding our device,” he explains, “and there are many things still unclear.”
When I heard that Fermilab’s Tevatron particle accelerator was going to be shut down, my first thought wasn’t about the race to discover the Higgs boson, or the shutdown’s implications for CERN and the rival Large Hadron Collider (LHC). Instead, it was “What will happen to the scientists?”.
One of the great things about being a science journalist is that, once in a while, you get the chance to find answers to questions like this. So when Physics World sent me to Fermilab last autumn to learn more about the lab’s scientific plans for a post-Tevatron future, I added a few personal questions to my interviews, such as “What are you going to do now?” and “What was the day of the shutdown like?”.
You can hear a few of the answers in this podcast, which is drawn from more than nine hours of interviews with 25 different physicists. Most of the interviews were conducted at Fermilab, but I also did a few at CERN, because I wanted to hear from people who had followed the “energy frontier” as it moved from the Tevatron to the LHC. As one of these emigrants explained to me, being a particle physicist is sometimes a little like being a surf bum: “you go where the waves are good, where the beam is good”.
You can listen to the podcast here, or download it via this link.
