According to organic chemistry 101, carbon can form up to four bonds because it only has four shareable electrons. In certain conditions, however, this limit can be broken as German chemists from the Free University of Berlin recently showed.

In the 1970s, another group of researchers from Germany made some intriguing observations about a molecule called hexamethylbenzene which can exist in a stable configuration of six carbon atoms arranged in a flat hexagonal ring. Off each vertex of the ring, an extra carbon atom sticks out where it’s bonded to three hydrogen atom. Finally, leftover electrons which hadn’t been shared zip around the middle of the ring.

More than 40 years ago, the researchers proposed that if you removed two electrons from hexamethylbenzene it would drastically change its shape. According to their calculations, the exotic molecule would rearrange itself into a configuration where one carbon atom was bonded to six other carbons. The implications were staggering but, at the time, no one confirmed the structure experimentally.

ADVERTISEMENT

Moritz Malischewski and colleagues from the Free University of Berlin decided to sweep the dust off this old paper and try it out. It was a bit difficult at first because the original paper was poor on details but the researchers eventually managed to make the charged hexamethylbenzene molecule.

After the molecule was crystallized, a 3-D map of the crystal’s structure was made using X-rays. Strikingly, the experiment proved that when hexamethylbenzene lost two electrons, it reordered itself in the six carbon bond configuration. Specifically, one carbon atom jumped out of the flat hexagon eventually turning the structure into a five-sided carbon pyramid. The carbon right atop the pyramid was bonded to six other carbon atoms: five in the ring and one above.

Previously, other molecules with a carbon atom associated with more than four bonds have been demonstrated, like Si 2 (CH 3 ) 7 +. This is, however, the first molecule associated with six bonds, as reported in the journal Angewandte Chemie.

It’s important to note that the carbon at the top of the hexamethylbenzene reconfigured pyramid still only has four electrons to share. “The carbon isn’t making six bonds in the sense that we usually think of a carbon-carbon bond as a two-electron bond,” Dean Tantillo, a chemist at the University of California, Davis who wasn’t part of the study, told Science News. Instead, the carbon shares electrons among the six bonds. Case in point, when the researchers measured the molecule’s chemical bonds, these were longer than the typical carbon-carbon bond, which means they’re weaker. </s> BONDING TIME When hexamethylbenzene loses two electrons, it rearranges from a flat hexagonal ring into the five-sided pyramid shown here. The carbon atom on top of the pyramid bonds to six other carbon atoms as opposed to the usual four. </s> Image copyright HARVARD UNIVERSIT/R.DIAS/I.SILVERA Image caption Smaller than the cross-section of a hair on your head: The tiny sample went from transparent, to black, to highly reflective as the pressure was increased. Becoming shiny and reflective is a sign the material has become a solid metal, the Harvard team claims

Scientists in the US say they have at last managed to turn hydrogen into a state where it behaves like a metal.

If that is true - and it is a controversial claim - it fulfils a more than 80-year quest to produce what many have said would be a wonder material.

Theory suggests metallic hydrogen could be used to make zero-resistance electrical wiring and super-powerful rocket fuel, among many applications.

Ranga Dias and Isaac Silvera are the Harvard researchers behind the work.

They report their experiments in this week’s Science Magazine.

"It's the first time solid metallic hydrogen has ever existed on Earth," Prof Silvera told the BBC.

The pair say the quantity of metallic hydrogen created so far is tiny - a speck that is less than the cross section of a human hair. But in time, they believe, ways could be found to boost its production.

Image copyright Harvard University Image caption Ranga Dias stands in front of the experimental set-up

Their laboratory approach - as is common in this field of study - was to squeeze a cell containing a small sample of molecular hydrogen between two synthetic diamonds.

In the Science paper, Dias and Silvera say this diamond anvil cell (DAC) achieved pressures up to 495 gigapascals.

That is the equivalent of sitting under almost five million Earth atmospheres. The DAC was also chilled down to close to minus 270 Celsius.

The scepticism here is probably a good thing, in that it will drive many groups towards attempting to reproduce this experiment Marcus Knudson, Sandia National Laboratories

The intention was to pack the atoms of hydrogen so close together that they formed a crystal lattice and started to share their electrons - behaviour that is exactly that of a metal.

Dias and Silvera report that this state became obvious to them when the material in the diamond anvil cell developed the kind of lustrous surface so ubiquitous of metals.

"As we turned the pressure up, it went to a transparent molecular solid. And then as the pressure kept going up, it went black, and we think it goes black because it becomes like a semi-conductor and it can absorb light," Prof Silvera recalled on the BBC’s Science In Action programme.

"And then we turned the pressure up higher and it started shining. It was very exciting. It's got extremely high reflectance. The reflectance we measured is about 90%. It's about the reflectivity of an aluminium mirror."

Image copyright SCIENCE PHOTO LIBRARY Image caption Artwork: In a metal, the atoms pack closely together in a lattice arrangement, which enables them to share their electrons. This is why metals make such good electrical conductors

It has to be said, however, that news of the Harvard experiment has already attracted a good degree of scepticism.

Other scientists working in the same and related fields have told the BBC that the team's paper is short on the kind of data needed to make a proper assessment of its achievements.

"Complete garbage," is how Eugene Gregoryanz from Edinburgh University described the research. "Like everybody else who works with hydrogen at high pressures, I am appalled by what is being published in Science."

That there is so much scepticism is natural. If what is being claimed pans out, it would represent one of the major physics breakthroughs of recent decades.

Metallic hydrogen was first predicted more than 80 years ago, and there has been a race to create it ever since. That is because of the stunning properties that are promised.

It has been suggested for example that metallic hydrogen might be metastable; that is - once made under extreme conditions it would maintain its state even when brought back up to ambient pressures and temperatures.

And if, as some think, it is also a zero-resistance superconductor, that could lead to a revolution in the transmission and storage of electricity. For example, cables made from metallic hydrogen could feed energy across a country without the sort of electrical losses experienced in standard power grids.

The US space agency is also fascinated by the material. Already super-cold liquid hydrogen makes for a very powerful rocket propellant, but the dense metallic form of hydrogen promises to deliver really colossal levels of thrust that would enable huge payloads to be lifted off Earth.

But all this is in the realms of speculation for now. First, it must be shown that the Harvard work can be reproduced. If that's possible - and some are saying that is a very big "if" - then more sizeable quantities of metallic hydrogen need to be created.

Image copyright NASA Image caption Metallic hydrogen would give a rocket prodigious capability

"I understand that others in the DAC community have been rather sceptical (arguing that the apparent reflectivity might be coming from contaminants in the sample, the aluminium oxide coating on the diamonds, etc.). However, if they really have achieved nearly 500 gigapascals in the DAC it is not unreasonable to have observed a transition to metallic hydrogen,” commented Marcus Knudson from Sandia National Laboratories.

"The scepticism here is probably a good thing, in that it will drive many groups towards attempting to reproduce this experiment. This publication will certainly incite the field. Again, if it holds up, this is an exciting result. I think in this case time will tell," he told BBC News.

And Jeffrey McMahon from Washington State University concurred: "With respect to the tiny sample amount: Such experiments are performed in small diamond anvil cells. One challenge would be to make a larger quantity (at once); another, perhaps bigger challenge is to recover even the small sample (ie, remove it from the extreme pressures that it is under in the diamond anvil cell).

"Whether the latter is possible is an important open question."

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos </s> As the element that makes up 75 percent of all the mass in the Universe, and more than 90 percent of all the atoms, we’re all pretty well acquainted with hydrogen.

But the simplest and most abundant element in the Universe still has some tricks up its sleeve, because physicists have just created a never-before-seen form of hydrogen - negatively charged hydrogen clusters.

To understand what negatively charged hydrogen clusters are, you first have to wrap your head around their far more common counterparts - positively charged hydrogen clusters.

Positively charged hydrogen clusters are pretty much exactly what they sound like - positively charged clusters of a few or many hydrogen molecules.

Known simply as hydrogen ion clusters, they form at very low temperatures, and can contain as many as 100 individual atoms.

Physicists confirmed the existence of hydrogen ion clusters some 40 years ago, and while a negative counterpart to these clusters boasting large numbers of atoms were theorised, no one could figure out how to create one.

But that didn't stop a team of physicists led by Michael Renzler from the University of Innsbruck in Austria from giving it a shot.

First, they injected cold liquid helium droplets with hydrogen (H2) molecules. This caused the mixture to form clusters with a neutral charge.

Next, they exposed these H2-infused droplets to an electron beam, and that caused some of the hydrogen molecules to ionise, and be flung out into the surrounding vacuum as negatively charged hydrogen ions.

Soon, nearby hydrogen molecules started clustering around the negatively charged ions, and the researchers discovered that these newly formed groups could boast a few, or many molecules each.

As is often the case with the most elusive structures in particle physics, these negatively charged hydrogen clusters existed only for an incredibly fleeting moment - several microseconds (1 microsecond = 0.000001 seconds).

But that was enough time for the team to determine their geometric structures.

As Michael Schirber reports for the American Physical Society, the researchers found that the clusters only had odd atom numbers, ranging from n= 5 to n = 129.

The most stable clusters had a central, negatively charged H− ion core sounded by shells that were completely filled up by hydrogen molecules.

"The odd values implied that the clusters were a combination of several H2 molecules and a single H− ion core, held together through an induced dipole attraction," Schirber explains.

The most commonly recorded clusters had the atomic numbers n = 25, n = 65, and n = 89.

These 'magic numbers', as the team calls them, correspond to symmetrical, almost solid arrangements of H2 molecules, such as a 20-sided icosahedron. (You can see one of these formations in the image at the top of the page.)

So why does all this matter? For years now, researchers have suspected that these large hydrogen clusters could form naturally in outer space, either in cold, dense clouds, or the atmospheres of gas planets.

Now that we know that negatively charged hydrogen clusters aren't impossible, and what their most common and stable form could be, it could make it easier to identify them in nature for the time.

And at a time when researchers are questioning if dark matter - the stuff that hypothetically makes up 27 percent of the observable Universe - even exists, we need all the help we can get when it comes to deciphering the smallest constituents of the space around us.

The research has been published in Physical Review Letters. </s> State of hydrogen predicted to be a room temperature superconductor reportedly seen – but the methods used are being questioned

It has been over 80 years in the making but the metallic form of hydrogen has finally been created in the lab at extreme pressures. Isaac Silvera and Ranga Dias from Harvard University in the US estimate that they subjected hydrogen to 495 gigapascals (GPa), 4.95 million times the standard pressure exerted by Earth’s atmosphere. ‘It’s the first time that metallic hydrogen has existed on Earth,’ Silvera tells Chemistry World.

Yet, with this achievement long prized in the high pressure science community, Silvera’s rival experimentalists have responded with extreme scepticism. Eugene Gregoryanz, whose University of Edinburgh team took hydrogen to 380GPa in 2016, expects the study to be debunked within a year. Doubts centre on approximations used by the Harvard researchers in measuring the pressures involved.

It’s the first time that metallic hydrogen has existed on Earth Isaac Silvera, Harvard University

Modern calculations suggest metallic hydrogen could be a valuable room temperature superconductor and stable on returning to atmospheric pressure, and in its dense form also potentially useful as a rocket propellant. University of Cambridge materials scientist Chris Pickard is one of those trying to predict metallic hydrogen’s properties, and the pressure at which it might form. ‘Interestingly, it’s been settling down around the pressure that [Silvera and Dias] have found,’ Pickard says.

Crushing hydrogen so comprehensively means squeezing it between micrometre-scale points in diamond anvil cells (DACs). At such extreme conditions, however, diamonds regularly break, especially because they become brittle when hydrogen works its way among their carbon atoms. Consequently, Silvera and Dias were extremely cautious, starting by making anvils from synthetic diamonds that are less likely to have defects than natural ones.

‘We remove five or six microns of the surface and the possible defects that might be there,’ Silvera explains. ‘Then we coat the diamonds with alumina as a diffusion barrier against hydrogen. We never let the diamonds get above 80K, because at low temperature you supress diffusion. We put a lot of attention into getting good alignment. And we don’t shine intense laser beams at the sample until the end, because it’s known that lasers break diamonds.’ However, the final measure casts a shadow over what researchers can learn from the experiment, because they rely on lasers to gather information.

More illumination needed?

Silvera and Dias assert that their hydrogen sample is metallic because it became reflective, which they can see with laser beams that don’t damage the diamond. They also use lasers to measure the pressure the hydrogen and diamond experience, largely by monitoring variations in the light wavelengths the materials absorb, which indicate structural changes. However, above 335GPa that does require damaging beams, and so past that point they only risked one pressure measurement, when they had observed reflection.

The changes in reflectivity are too big to believe it’s actually hydrogen Eugene Gregoryanz, University of Edinburgh

The resulting pressure estimations in the paper are ‘strange, if not incorrect’, according to Mikhail Eremets from the Max Planck Institute for Chemistry in Mainz, Germany. Dias and Silvera find that pressure changes in direct proportion to the force applied by turning the screws that crush the anvils together. That’s not what Eremets has observed in his own high pressure hydrogen research. The Harvard scientists extrapolate this relationship to get the 495GPa measurement, he explains, whereas if they’d used the more conventional pressure–force relationship they would get 590GPa. That stretches plausibility, he underlines.

‘They might be lucky,’ Eremets says. ‘They used good diamonds, maybe it helped. But we’ve done the same for three years at least. In our experience it’s impossible to reach such high pressures.’ He’s therefore ‘very surprised’ the paper was published.

Gregoryanz’s many objections include – but go beyond – pressure measurements. He also questions whether the Harvard team even saw metallic hydrogen, and suggests they might instead be measuring a rhenium gasket used in the DAC. ‘The changes in reflectivity are too big to believe it’s actually hydrogen,’ Gregoryanz says.

Peer pressure

Paul McMillan from University College London notes Silvera’s team is ‘known internationally for careful and pioneering work’. ‘Although the researchers record the existence of a metallic state, they could not conclude on the crystalline nature of the sample,’ he adds. ‘Now the worldwide community, including extreme conditions researchers, planetary physicists and energy scientists, will look forward to discussing and debating these new data.’ Pickard echoes this. ‘As a landmark scientific result, this will have to stand up to the scrutiny of the experimental groups, but it’s very exciting,’ he says.

Silvera stands by his results but accepts that the pressure measurement may be revised. ‘In high pressure research things aren’t always well calibrated,’ Silvera says. ‘If people disagree, they should go to measure it and try to show that it’s different than what was claimed.’ Among the next steps for his own team will be measuring the high pressure hydrogen sample’s conductivity directly.

In the meantime, many have already visited Silvera’s lab to see the DAC containing a 10µm diameter hydrogen particle that they believe is unique in the planet’s history. ‘After we made it we told the staff here at Harvard,’ Silvera says. ‘We got 200 or 300 people come to see it, it went on all day.’ </s> Scientists in the US say they have at last managed to turn hydrogen into a state where it behaves like a metal.

If that is true - and it is a controversial claim - it fulfils a more than 80-year quest to produce what many have said would be a wonder material.

Theory suggests metallic hydrogen could be used to make zero-resistance electrical wiring and super-powerful rocket fuel, among many applications.

Ranga Dias and Isaac Silvera are the Harvard researchers behind the work.

They report their experiments in this week’s Science Magazine.

"It's the first time solid metallic hydrogen has ever existed on Earth," Prof Silvera told the BBC.

The pair say the quantity of metallic hydrogen created so far is tiny - an amount less than the cross section of a human hair. But in time, they believe, ways could be found to boost its production.

Their laboratory approach - as is common in this field of study - was to squeeze a cell containing a small sample of molecular hydrogen between two synthetic diamonds.

In the Science paper, Dias and Silvera say this diamond anvil cell (DAC) achieved pressures up to 495 gigapascals.

That is the equivalent of sitting under almost five million Earth atmospheres. The DAC was also chilled down to close to minus 270 Celsius.

The intention was to pack the atoms of hydrogen so close together that they formed a crystal lattice and started to share their electrons - behaviour that is exactly that of a metal.

Dias and Silvera report that this state became obvious to them when the material in the diamond anvil cell developed a lustrous surface.

"As we turned the pressure up, it went to a transparent molecular solid. And then as the pressure kept going up, it went black, and we think it goes black because it becomes like a semi-conductor and it can absorb light," he recalled on the BBC’s Science In Action programme.

"And then we turned the pressure up higher and it started shining. It was very exciting. It's got extremely high reflectance. The reflectance we measured is about 90%. It's about the reflectivity of an aluminium mirror."

It has to be said, however, that news of the Harvard experiment has already attracted a good degree of scepticism.

Other scientists working in the same and related fields have told the BBC that the team's paper is short on the kind of data needed to make a proper assessment of its achievements.

"Complete garbage," is how Eugene Gregoryanz from Edinburgh University described the research. "Like everybody else who works with hydrogen at high pressures, I am appalled by what is being published in Science."

Such resistance is natural. If what is being claimed pans out, it would represent one of the major physics breakthroughs of recent decades.

Metallic hydrogen was first predicted more than 80 years ago, and there has been a race to create it ever since. That is because of the stunning properties that are promised.

It has been suggested for example that metallic hydrogen might be metastable; that is - once made under extreme conditions it would maintain its state even when brought back up to ambient pressures and temperatures.

And if, as some think, it is also a zero-resistance superconductor, that could lead to a revolution in the transmission and storage of electricity.

The US space agency is also fascinated by the material. Already super-cold liquid hydrogen makes for a very powerful rocket propellant, but the dense metallic form of hydrogen promises to deliver really colossal levels of thrust that would enable huge payloads to be lifted off Earth.

But all this is in the realms of speculation for now. First, it must be shown that the Harvard work can be reproduced. If that's possible - and some are saying that is a very big "if" - then more sizeable quantities of metallic hydrogen need to be created.

"I understand that others in the DAC community have been rather sceptical (arguing that the apparent reflectivity might be coming from contaminants in the sample, the aluminium oxide coating on the diamonds, etc.). However, if they really have achieved nearly 500 gigapascals in the DAC it is not unreasonable to have observed a transition to metallic hydrogen,” commented Marcus Knudson from Sandia National Laboratories.

"The scepticism here is probably a good thing, in that it will drive many groups towards attempting to reproduce this experiment. This publication will certainly incite the field. Again, if it holds up, this is an exciting result. I think in this case time will tell," he told BBC News.

And Jeffrey McMahon from Washington State University concurred: "With respect to the tiny sample amount: Such experiments are performed in small diamond anvil cells. One challenge would be to make a larger quantity (at once); another, perhaps bigger challenge is to recover even the small sample (ie, remove it from the extreme pressures that it is under in the diamond anvil cell).

"Whether the latter is possible is an important open question."

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos </s> Scientists may not have turned hydrogen into metal, a move that was hailed as an astonishing scientific breakthrough.

Two physicists at Harvard University claimed that they had finally managed to do what scientists have been trying to do for almost a century.

That is, crushing hydrogen and turning into metal through an ‘alchemical’ process.

But the scientific community has questioned the claims of Ranga Dias and Isaac Silvera, claiming they have made a mistake when identifying the tiny amount of shiny substance they saw as hydrogen metal.

Dias and Silvera first published their work on arXiv in October, where it attracted a lot of criticism from other scientists who claimed it was based on a mistake. However, it was still published this week in the journal Science.

Five different experts have since spoken to Nature magazine, saying that they don’t believe the claim and they need more evidence.

‘I don’t think the paper is convincing at all,’ Paul Loubeyre, a physicist at the Atomic Energy Commission in Bruyeres-le-Chatel, France.

Dias and Silvera had crushed tiny amounts of hydrogen underneath diamond anvils, putting more pressure on it than is found at the Earth’s core.

What they found was a small amount of shiny material that can be viewed through a microscope. After seeing it, the two said that ‘you can only believe [it] is a metal’.

However, this ‘metal’ that they apparently produced is still stuck between the jaws of the anvil – and the two researchers say that removing it could cause it to completely disappear.

‘It is far from clear that the shiny material the researchers see is actually hydrogen,’ Alexander Goncharov, a geophysicist from the Carnegie Institution for Science in Washington DC, told Nature.

Goncharov suggested that the reflective substance may be alumina (aluminium oxide), which coats the tips of the diamonds in the anvil.

Loubeyre added that they need to redo the measurement, using a much more precise method of measuring the amount of pressure they’re placing.

Silvera, however, said he just wanted to get the information out there before he carried out confirmation tests – which, he said, could break the specimen.

Despite the doubt cast on the study’s results, press releases issued by Science and Harvard University confidently claimed that metallic hydrogen had been made.

‘This is the holy grail of high-pressure physics,’ Silvera says in the Harvard press release. ‘It’s the first ever sample of metallic hydrogen on Earth.’ </s> In a breakthrough for optical computing, researchers have used graphene to confine light to the smallest possible space, just one atom wide.

Confining light to small spaces is a fundamental challenge for computing using light rather than electric current. The smaller the space into which a pulse of light can be confined, the more compact a device using this technology, such as sensors or nanoscale lasers can be. Up to now, light has been confined to a space smaller than its own wavelength using the atomic lattices of metals to trap and guide photons. Now, researchers from the European Graphene Flagship, led by a team from ICFO (the Institute of Photonic Sciences in Barcelona), have found that this is yet another property that can be accessed using the single atom thick form of elemental carbon

“Graphene keeps surprising us: nobody thought that confining light to the one atom limit would be possible,” said research leader Prof Frank Koppens. In a paper published in Science, Koppens and colleagues at the University of Minho, Portugal, and MIT describe how they fabricated a composite nano-optical device starting with a layer of graphene, topped with an insulating hexagonal boron nitride layer, which was in turn topped with an array of metallic rods. Graphene is already known to have the ability to guide light in the form of plasmons, which are oscillations of electrons within the material structure that interact strongly with light.

“At first, we were looking for a new way to excite graphene plasmons,” said David Alcaraz Iranzo, lead author of the Science paper. “On the way, we found that the confinement was stronger than before and the additional losses minimal.” This is a step forward, because confinement using metal lattices has always led to a sharp drop in the energy of the light pulse. “So we decided to go to the one atom limit,” he continued, “with surprising results.”

The team sent infrared light through the device stack and observed that plasmon is propagated between the metal and the graphene. Reducing the thickness of hexagonal boron nitride layer to a single atom thick, they found to their surprise that the plasmons were still in an excited state – that is, the electrons were vibrating – and that this vibration could propagate freely along the single atom thick channel. This plasmon propagation could be switched on and off by applying an electric voltage, which demonstrates the ability of the channel less than 1nm thick to control the light.

“The impressive results reported in this paper are testimony to the relevance for cutting-edge science of the Flagship work,” said Prof Andrea Ferrari, chair of the Graphene Flagship management panel. “Having read the ultimate limit of light confinement could lead to new devices with unprecedented small dimensions.”

CLICK HERE FOR MORE ENGINEERING NEWS </s> Scientists at the Large Hadron Collider in Switzerland have discovered an exciting new particle—or rather, an exciting combination of particles. It doesn’t have quite the same impact that the Higgs Boson (the one people called the God Particle) did five years ago. But it does have people talking, and many folks are thinking about a controversial set of results from an older experiment.

The particle in question is an arrangement of three quarks called the Ξ ++ or the “doubly charged, doubly charmed xi particle” in English, discovered by the LHC’s LHCb detector. You may remember that the nucleus of an atom consists of protons and neutrons. Protons have two up quarks and a down quark, and one unit of positive electric charge. Neutrons have an up quark and two down quarks, and their charge is zero. The new xi particle consists of two of a very heavy flavor of quark, called the charm quark, and its charge equals two.

“We produce charm quarks in pairs, but having two charm quarks in the same particle is very rare,” physicist Patrick Koppenburg from Nikhef, the Dutch National Institute for Subatomic Physics, told Gizmodo. The charm quark makes up one of six possible quarks, including the up, down, charm, strange, top and bottom. The heaviest are the charm, bottom [also called beauty] and top [also called truth], but the top is probably too heavy to arrange with other quarks, he said. The other quarks should theoretically be able to arrange into groups of two, three, four or five, or even into a sort of quark liquid if things get hot enough.

But “most of these particles” with three or more quarks “containing two heavy quarks, charm or beauty, have not yet been found,” said Koppenburg. “This is the first in a sense.”

In a sense, said Koppenburg, because there’s a contested result from as early as 2002, when the SELEX collaboration at Fermilab in Illinois announced that they’d found a related particle called the Ξ +, the singly-charged, doubly charmed xi particle (that’s one plus sign instead of two). That particle also has two charm quarks, but has a down quark instead of an up quark like the new xi from LHCb. The one plus sign-xi also has an elemental charge of one, like a proton.

Koppenburg said that several other experiments have failed to reproduce SELEX’s particle. And this new particle casts further doubt on the SELEX discovery. “This one,” the LHCb’s new particle, “had a mass so different than the mass from the SELEX collaboration that it makes their mass unlikely,” said Koppenburg. The new xi particle weighs around 3600 MeV, or four times the mass of the proton. SELEX’s similar-but-different xi particle weighs about 100 MeV less, despite differing in composition only by the very light up or down quarks.

But the new CERN paper, which will be published in an upcoming edition of Physical Review Letters, points out that past attempts to recreate SELEX’s xi particle were different kinds of experiments than SELEX, so those “null results do not exclude the original observations.”

I reached out to James Russ, Professor of Physics at Carnegie Mellon and one of SELEX’s spokespeople, who was only just sitting down to read the new paper when I called. He reminded me that the two particles in question are different and that SELEX’s results were very clean. He stands by his experiment’s observed particle but remarked that LHCb’s results are certainly important. “Having a new observation will push theory in a certain direction,” he said, “so this is definitely an important observation.”

When Russ finished looking over the LHCb paper, he told Gizmodo: “The LHCb observation is very solid.” As far as the third, lighter quarks causing such a large mass difference, he’s said it’s unlikely to be related to differences arising from the quarks’ properties. “Both experiments seem to have done their analysis correctly,” he said. “If both particles are really there, there is a theoretical question about how two charm-charm-quark systems can behave so differently.”

None of this stuff is easy. Scientists are looking for incredibly elusive particles that exist for less than a picosecond, or a trillionth of a second. But since they’re moving at nearly the speed of light, they still travel a few millimeters before decaying into particles detected by the trails they leave in the LHCb experiment. Specific particles can set off a trigger letting the experiment know to keep the data on the event to analyse later. Reconstructing the specific tracks the particles left allows researchers to determine whether they spotted their xi.

And that particle must emerge as a signal over all of the background noise caused by other physics and other particles flying through the detector. In this case, the scientists saw a “12-sigma” significance, meaning it’s incredibly unlikely that their observations were random noise that just so happened to look like the new xi particle.

Regardless of past results, the LHCb scientists I spoke with pointed out that this new particle will allow them to better understand particle physics in general, and continue refining their theories about what quarks do when they stick together.

“We’re understanding that there are more complicated structures in nature than we thought there were before,” Sheldon Stone, Syracuse University physicist, told Gizmodo. This new xi particle can’t really exist on Earth except for in experiments, but probably existed right after the Big Bang when things were a lot hotter and closer together. Understanding the ways quarks could arrange themselves might offer further insights into the physics of that primordial era.

And while disproving a theory is exciting, this new xi quark seems to have the mass theorists expected, said Stone.
Free University of Berlin chemists confirm that carbon can bond with more than four atoms, previously seen as its limit because carbon has only four shareable electrons. The researchers used X-rays to, for the first time, map the molecule — a carbon atom bonded to six other carbon atoms.