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The first paper on LHC collisions?

Figure 1 of the first of many papers

By Hamish Johnston

What surely must be the first paper reporting proton-proton collisions in the Large Hadron Collider (LHC) has appeared on the arXiv preprint server.

It’s by the ALICE collaboration — over two pages of authors from 113 institutes — and describes collisions in the ALICE detector that occured last week.

Aamodt et al describes 284 collisions that occured when both beams were at 450 GeV.

The events were used to determine something called the ‘pseudorapidity density’ of charged particles in the detector.

And what exactly is pseudorapidity? As far as I can tell, it’s a rather complicated way of expressing the angle between the momentum of a particle in the detector and the momentum of the beam.

The paper says this about these early results:

“They demonstrate that the LHC and its experiments have finally entered the phase of physics exploitation, within days of starting up the accelerator complex in November 2009.”

Quark-like confinement seen in the lab

Particle-like entities in a magnetic crystal are confined to form composite particles just as quarks are bound together within protons and neutrons – according to experiments done by physicists in Germany and the UK. The ability to observe spinon confinement within a controllable condensed-matter system could improve our current qualitative understanding of quark confinement in particle physics.

According to the theory of quantum chromodynamics (QCD), quarks are held together by the strong force. This force gets stronger with increasing distance, meaning that quarks cannot be pulled apart but are “confined” within composite particles such as protons and neutrons – which consist of three quarks – and mesons, which consist of two quarks.

Confinement means that quarks can never be observed individually and their properties can therefore only be studied indirectly. However, in 1996 Alexei Tsvelik, Alexander Nersesyan and David Shelton predicted confinement in certain easier-to-study condensed matter systems known as spin ladders consisting of two chains of copper oxide chemically bonded together. In each chain electrons should behave collectively so that the aggregate charge and spin separate out to form entities not tied to particular electrons. Tsvelik and colleagues argued that the spin entities – called spinons – would be analogous to quarks and would be confined when two chains are brought together to form a ladder.

Inelastic scattering

That idea has now been demonstrated experimentally by Bella Lake of the Helmholtz-Zentrum in Berlin and colleagues. Lake’s team used the ISIS neutron source at Rutherford Appleton Laboratory in the UK to scatter neutrons with a known energy off magnetic crystals of the copper-oxide compound calcium cuprate. By measuring the energies and scattering angles of the emerging neutrons the researchers were able to calculate the energy and momentum taken up by the sample. This in turn revealed information about the magnetic state of the crystals. They found that at high neutron energies the crystals behaved like individual chains with free spinons, whereas at low energies the interchain coupling within the ladders binds the spinons together (this is not the only condensed-matter system that, according to theory, should display confinement but it is the only one so far to have been realized experimentally).

The researchers say that ladders lead to confinement because within a single chain the spins between two spinons point in the opposite direction to that in which they would point were there no spinons. When this chain is coupled antiferromagnetically to another chain these reversed spins take up energy because they line up in parallel with the spins on the neighbouring chain (i.e. they go against the antiferromagnetic grain).

As the distance between spinons increases the number of spins aligned parallel to one another increases, rendering the arrangement ever less energetically favourable and so confining the spinons. Each spinon carries the quantum number spin-1/2, meaning that a pair of spinons has integer spin, just as quarks, which each carry a fractional charge, combine to form particles with integer charge.

Shedding light on QCD

This research could also shed some light on QCD. The mathematics underpinning QCD make it impossible to precisely calculate analytically the values of the various fundamental properties of both quarks and the particles that they make up. For example, physicists have struggled to calculate the mass of the proton – a value that is known to great precision experimentally – using numerical techniques. Tsvelik, now at the Brookhaven National Laboratory in the US, says that being able to calculate the properties of spinons analytically and then compare these calculations with experiment should tell us more about confinement in general and could therefore provide some hints about the nature of quark confinement. But he cautions that the comparison cannot be taken too far.

Frank Wilczek of the Massachusetts Institute of Technology in the US, who shared the Nobel prize for his work on the strong force, welcomes this experimental demonstration of confinement pointing out that condensed-matter systems are “interesting in their own right, and much easier to work with” than systems of fundamental particles. However, like Tsvelik he believes that the approach has its limitations. “The mechanisms of confinement in particle physics are significantly different from those in one-dimensional systems,” he says. “So I don’t think those simpler systems can in any real sense provide analogue computers for the harder problems; rather, they can be a source of inspiration and a testbed for ideas.”

The research is published online in the journal Nature Physics.

LHC beams hit 1.18 TeV

Nearly there…

By Hamish Johnston

Early this morning the Large Hadron Collider passed yet another milestone as both beams reached 1.18 TeV — smashing the previous record of 980 GeV held by the Tevatron at Fermilab.

“We are still coming to terms with just how smoothly the LHC commissioning is going,” said CERN Director General Rolf Heuer.

So far, the accelerator has been run with a low intensity pilot beam — but now LHC beam jockeys will try to boost the intensity so the collider’s experiments can be further calibrated by gathering collision data before Christmas.

This intensity ramp-up is expected to take a week, and then it’s time for collisions.

The first physics experiments are scheduled for the first quarter of 2010, at a collision energy of 7 TeV (3.5 TeV per beam).

It’s going to be another exciting week at CERN!

Physical forces at work in biocomposites

An electron microscopy study by researchers in the US could provide important insights into the structure of shells, spines and other biological materials that are crystalline in nature. The team looked at how certain polymer strands are incorporated into a single crystal of calcite and found that the process involves physical interactions between the materials, rather than chemical reactions.

Single crystal structures are surprisingly common in living organisms. Each spine of a sea urchin, for example, is a single crystal of calcite. However, such spines have a very different shape than calcite crystals grown in the lab – and are often much tougher and more flexible. Understanding how these biomaterials are formed could lead to new types of manmade materials.

While scientists know that the properties of calcite are modified by the presence of organic molecules within the crystal lattice, it had proved difficult to obtain electron microscopic images of the interfaces between the calcite and organic molecules. Such images are crucial to understanding the nature of the composite materials. The problem is that electrons can only probe regions near to the surface of a sample, where the interfaces could be different than those in the bulk of a crystal.

Agarose hydrogel

Now Lara Estroff and colleagues at Cornell University have developed a new technique to study these interfaces. They began by growing a calcite crystal in a hydrogel containing agarose – a polymer that is found in seaweed and is known to incorporate into calcite.

The team use an ion beam to carefully carve an extremely thin wedge-shaped pillar from the crystal – exposing the bulk of the crystal. The pillar is then placed in a transmission electron microscope (TEM) and a series of images is taken of a section of the pillar that is about 300 nm thick. The images are acquired at 2° intervals as the pillar is rotated through about 140°. Using computer tomography, the team is able to build up a 3D image of the crystal that shows exact locations of the agarose strands.

Electron diffraction data from the pillar confirmed that it was a single crystal – and allowed the team to determine the orientation of crystalline planes to individual agarose strands.

High-energy facets

The team found that the polymer strands sit next to “high-energy” crystal facets that would never be seen at the surface of a pure crystal.

Estroff told physicsworld.com that agarose is known to react very weakly with calcite, so it is unlikely that a chemical interaction is involved with this “stabilization” of high-energy facets. Instead she believes the stabilization is related to how a strand trapped in a growing crystal flexes and pushes back against its surroundings.

The team is now applying the technique to the study of biomaterials.

The research is described in Science.

Hawking portrait unveiled at the Royal Society

Stephen Hawking by Tai-Shan Schierenberg (Courtesy: Royal Society)

By Hamish Johnston

Stephen Hawking was in London yesterday to unveil this portrait of himself at the Royal Society.

The painting is by the English artist Tai-Shan Schierenberg, who also has four works just down the road in the National Portrait Gallery.

If you happen to visit the Royal Society, make sure you make time for organization’s fantastic collection of portraits. You can admire likenesses of John Flamsteed, who founded the Royal Observatory at Greenwich, the great Victorian scientist Michael Faraday — and even the mathematician Gottfried Leibniz, who was famously vilified by Isaac Newton and the Royal Society.

And apparently, there is a portrait of Newton but I haven’t managed to come across it.

Snail shell spiral switched

Researchers in Japan have altered the destiny of a rout of snails by changing the chirality of their shells before birth. By delicately manipulating a batch of developing embryos, the scientists successfully reversed the spiral shells of over 100 Lymnaea stagnalis. The results illustrate the importance of developing embryo structure in determining the physical appearance of snail newborns, say the researchers.

Chirality or “handedness” is a property of those physical systems that cannot be superposed on their mirror images. This property crops up time and again throughout nature from the human hand to DNA to the spin of sub-atomic particles.

The spiral shells of snails are often used as a textbook example of biological structures that possess chirality. Shell-coiling is important because a snail’s sexual organs are usually twisted and it is difficult for snails of opposite handedness to reproduce. In addition, the way a snail catches prey depends on the handedness of the micro-organism or plant. The handededness of a snail’s shell is inherited from its mother but the gene that gives snail shells their chirality in the first place is yet to be identified.

In this latest research, Reiko Kurodo of the University of Tokyo and her colleagues investigated chirality in Lymnaea stagnalis – a large, air-breathing freshwater snail. They isolated a series of developing embryos that had already acquired a particular handedness – either “dextralized” (right-handed) or “sinistralized” (left-handed). By adding two glass nanorods to an 8-cell bundle they were able to alter its cleavage — the plains along which it sub-divides — to reverse its handedness. Nearly 78% (71 out of 91) of sinistral embryos were reversed to dextral, and 78% (67 out of 86) of dextral embryos were reversed to sinistral.

Reiko told physicsworld.com that she hopes this research will help his team to isolate the gene responsible for giving this snail its handedness. She hopes this knowledge could help researchers to shed light on some of the mystery that still surrounds chirality in nature. “In everyday life, the effects of medicinal drugs, agricultural chemicals and food sweeteners are all dependent on the handedness of their molecules,” she said. “Even the origin of life can be explained from the point of chirality.”

Henri Brunner, an inorganic chemist at the University of Regensburg, is impressed with the new research describing it as an “extremely interesting result”. “Chirality is not only a basic concept for biology and chemistry but also for physics,” he said.

This research is published in the latest edition of Nature.

Plasmas have healing powers

Two related studies have demonstrated the effectiveness of low-temperature plasma for killing drug-resistant bacteria on human skin – one of the biggest challenges facing modern medicine. In one study, researchers in Germany describe a device that can disinfect hands in seconds, while in the other they reveal how low-temperature plasmas can safely disinfect open wounds.

Bacterial infection is a serious problem in hospitals. Studies show that the infamous superbug methicillin-resistant Straphylococcus Aureus (MRSA) alone infects 100,000 people every year in the US and results in about 18,000 deaths.

The best way to tackle the problem is disinfectant, but this can be laborious. Every day hospital staff must disinfect their hands on dozens of occasions, each taking up to several minutes. Keeping open wounds free from bacteria can be even harder.

Cool plasmas

In recent years, scientists have begun to investigate how plasmas – gases of ions and free electrons – can help. A fully ionized plasma can have a temperature in the region of 100,000°, which is far too hot for human tissue, but the temperature can be reduced if the degree of ionization is much lower, at say one part in a billion.

Gregor Morfill and colleagues at the Max-Planck Institute for Extraterrestrial Physics in Garching have shown how low-temperature plasmas can be used to clean hands conveniently in seconds. Their device contains a slab of dielectric material sandwiched between a solid electrode and a sheet of wire mesh. When they put a large voltage of 18 kV across the solid electrode and mesh, the resultant strong electric field generates numerous nano- and microsecond discharges that partially ionize the air. This ionization leaves ultraviolet radiation and a cocktail of chemical products – including ozone, nitrogen oxide, hydrogen peroxide and free radicals – which together kill bacteria.

“It will even sterilize your socks, although you should probably wash them too” Gregor Morfill, Max-Planck Institute for Extraterrestrial Physics

Morfill told physicsworld.com that hospital staff could use the device routinely to clean hands and, if so desired, feet. “It will even sterilize your socks, although you should probably wash them too,” he adds.

With other colleagues at the Max-Planck Institute, Morfill has examined the best way to use low-temperature plasma for cleaning open wounds. In some ways this is more difficult because ideally the plasma would not only kill bacteria but also prevent further growth of bacteria without having any negative side-effects on the living human cells.

Chemicals and plasma

The researchers performed a series of tests in which they subjected E. coli bacteria to both the chemical and UV products of plasma and, by shielding the bacteria with a quartz disc, just the UV products. They found that the UV radiation tended to kill bacteria in the short term, whereas the chemical products cause a lasting “after irradiation” inhibition of bacterial growth. With this knowledge, the researchers could determine the right composition and dosage of plasmas for future devices.

One of the group members, Tetyana Nosenko, said that the next step is to optimize the plasma composition for different types of wound, such as diabetic ulcers or those containing blood.

The research is described in two papers in the New Journal of Physics.

Physics of the Turkey Bowl

By Hamish Johnston

If you are in the US you are probably looking forward to two things this Thanksgiving Day: turkey and football.

And from the safety of your couch, you might just wonder about the forces involved in a big hit out on the field.

In the video above, you can watch physicist Dan Dahlberg calculating that a particularly hard tackle can accelerate a player at 10 G.

To put that into perspective, heavy braking of a top range sports car will deliver about 1 G and if you drive that car into a brick wall at 30 MPH you would experience 40–50 G.

The player in question is the University of Minnesota’s Eric Decker who was launched into the end zone by an opposing player, but managed to hold on to the ball to score a touchdown.

Although slightly shaken, Decker was back in the game, which was played earlier this year.

Dahlberg – who is normally found in his spintronics lab at the University of Minnesota – is not the first to work out that football players are subject to massive accelerations.

Last month the New Yorker ran an article by Malcolm Gladwell about the potential harm that such hits can cause to the brains of players.

Spins spotted in room-temperature silicon

Physicists in the Netherlands are the first to show that spin-polarized electrons can be injected into silicon at room temperature. The team injected the electrons into both p-type and n-type silicon and measured how long the polarization lasted. Although the lifetime was shorter than expected the physicists believe it is long enough to support the development of spintronics devices.

The team are also the first to detect spin-polarized electrons in p-type silicon at any temperature.

The intrinsic spin of the electron can either be “up” or “down”, and this property could be used to store and process information in spintronic devices. Such circuits could be smaller and more energy efficient than conventional electronic circuits because they would rely on flipping spins rather than switching charge.

Silicon is the material of choice for conventional electronic circuits and physicists already know that it can support and transport spin-polarized electrons at temperatures lower than about 150 K. The challenge is to boost this to room temperature so that practical devices can be made from silicon.

Room temperature injection

Now Ron Jansen and colleagues at the University of Twente are the first to show that spin-polarized electrons can be injected into silicon at room temperature. The team began by depositing three insulating oxide contacts onto a piece of silicon, and then topped each contact with a magnetic metal electrode.

The metal is magnetized parallel to the surface of the silicon and a constant current of electrons is made to flow out of one electrode, through the silicon and into a second electrode. The resistance of the silicon is determined by measuring the voltage between the first (source) electrode and the third electrode.

The electrons in the magnetic electrode are polarized, with most spins pointing along a specific direction. Some of this polarization is preserved as the electrons tunnel across the oxide and into the silicon leading to an accumulation of spin in the region under the source electrode (see diagram above).

Change in resistance

Electrons are fermions and tend to avoid each other if their spins point in the same direction. This means that the resistance of the contact interface increases as more polarized electrons accumulate in the silicon. However, if a magnetic field is applied perpendicular to the polarization, the spins precess about the field. This reduces the spin accumulation and the resistance of the contact interface.

Jansen and colleagues observed this effect by measuring the voltage (and therefore resistance) across the two electrodes while changing the strength of the applied field. The overall change in resistance allowed them to calculate the spin accumulation in the silicon – about 5% at room temperature. They were also able to determine the mean lifetime of a spin in silicon by studying the shape of the voltage versus applied field curve.

In n-type silicon this lifetime was about 140 ps in n-type silicon and 270 ps in p-type. This is shorter than electron spin resonance (ESR) measurements, which suggest lifetimes of about 1 ns at room temperature for the n-type silicon.

Long enough?

However, a lifetime of about 200 ps should allow a spin to travel a few hundred nanometres through a spintronic device before decaying – and Jansen says that in principle this is more than enough to make spintronics circuits that are tens of nanometres in size and operate at frequencies of 10–100 GHz.

Ian Appelbaum of the University of Maryland described the short lifetimes as “disappointing [but] not entirely surprising: this may be caused by high doping and the presence of interfaces”. Appelbaum told physicsworld.com that, while the injection of spins into room temperature silicon is important, the researchers have not shown that spins are transported through the material – the latter being crucial for any practical spintronic device.

Jansen and his team are now planning to study the transport of spins between electrodes as well as studying how the spin lifetime is affected by doping, temperature and the interface between the silicon and the magnetic metal.

David Awschalom of the University of California Santa Barbara said that the Twente structure could “serve as a ‘spin laboratory’ within which one may begin to optimize electron spin transport and control in this material”.

The work is reported in Nature.

All spaced out

By Michael Banks

With raps about the Large Hadron Collider at CERN near Geneva and Fermilab in the US, I should have suspected it would only be a matter of time before hearing a song about the International Year of Astronomy (IYA), which is taking place this year.

So here it is. Taking over a year to make, astronomy enthusiast Michael Davis has created a music video about astronomy entitled “Spaced Out”.

Lasting four and half minutes, the video shows astronomers at a park in Patoka Lake, Southern Indiana, US, along with their various telescopes (some quite impressive) getting ready for a night of star-gazing.

The film also features more bizarre, and less well put together, clips such as a woman ice-skating on Saturn’s rings or someone riding a comet. “Put a saddle on a comet, joy-ride ‘til you pull on the reins,” Davis sings.

The main fun of science songs is, of course, the lyrics. The song does have a few catchy lines such as “refraction, reflection, telescopic connection,” and “the universe is yours, to discover, go observe, go uncover”.

However, the chorus is perhaps a bit cheesy (and maybe a little on the unimaginative side): “International Year of Astronomy two thousand nine, International Year of Astronomy two thousand nine” — the repeat and fade out on the ‘nine’ adding an extra layer of cheese. (But if you really like it then you can just speed to the end of the song where it is repeated quite often.)

“The IYA2009 team loved it,” Davis told physicsworld.com. “They then wanted a link to the video on the main IYA2009 website.

The International Year of Astronomy medley is not Davis’s first song about science. He made a music video about the insect world, entitled “I’m Not a Bug Squasher”. So perhaps he could use that video to promote the International Year of Biodiveristy, which is taking place next year.

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The first paper on LHC collisions?