What is the CERN Particle Accelerator?

Particle Collider

What if it were possible to observe the fundamental building blocks upon which the Universe is based? Not a problem! All you would need is a massive particle accelerator, an underground facility large enough to cross a border between two countries, and the ability to accelerate particles to the point where they annihilate each other – releasing energy and mass which you could then observe with a series of special monitors.

Well, as luck would have it, such a facility already exists, and is known as the CERN Large Hardron Collider (LHC), also known as the CERN Particle Accelerator. Measuring roughly 27 kilometers in circumference and located deep beneath the surface near Geneva, Switzerland, it is the largest particle accelerator in the world. And since CERN flipped the switch, the LHC has shed some serious light on some deeper mysteries of the Universe.

Purpose:

Colliders, by definition, are a type of a particle accelerator that rely on two directed beams of particles. Particles are accelerated in these instruments to very high kinetic energies and then made to collide with each other. The byproducts of these collisions are then analyzed by scientists in order ascertain the structure of the subatomic world and the laws which govern it.

The Large Hadron Collider is the most powerful particle accelerator in the world. Image: CERN
The Large Hadron Collider is the most powerful particle accelerator in the world. Credit: CERN

The purpose of colliders is to simulate the kind of high-energy collisions to produce particle byproducts that would otherwise not exist in nature. What’s more, these sorts of particle byproducts decay after very short period of time, and are are therefor difficult or near-impossible to study under normal conditions.

The term hadron refers to composite particles composed of quarks that are held together by the strong nuclear force, one of the four forces governing particle interaction (the others being weak nuclear force, electromagnetism and gravity). The best-known hadrons are baryons – protons and neutrons – but also include mesons and unstable particles composed of one quark and one antiquark.

Design:

The LHC operates by accelerating two beams of “hadrons” – either protons or lead ions – in opposite directions around its circular apparatus. The hadrons then collide after they’ve achieved very high levels of energy, and the resulting particles are analyzed and studied. It is the largest high-energy accelerator in the world, measuring 27 km (17 mi) in circumference and at a depth of 50 to 175 m (164 to 574 ft).

The tunnel which houses the collider is 3.8-meters (12 ft) wide, and was previously used to house the Large Electron-Positron Collider (which operated between 1989 and 2000). This tunnel contains two adjacent parallel beamlines that intersect at four points, each containing a beam that travels in opposite directions around the ring. The beam is controlled by 1,232 dipole magnets while 392 quadrupole magnets are used to keep the beams focused.

Superconducting quadrupole electromagnets are used to direct the beams to four intersection points, where interactions between accelerated protons will take place. Credit: Wikipedia Commons/gamsiz
Superconducting quadrupole electromagnets are used to direct the beams to four intersection points, where interactions between accelerated protons will take place.Credit: Wikipedia Commons/gamsiz

About 10,000 superconducting magnets are used in total, which are kept at an operational temperature of -271.25 °C (-456.25 °F) – which is just shy of absolute zero – by approximately 96 tonnes of liquid helium-4. This also makes the LHC the largest cryogenic facility in the world.

When conducting proton collisions, the process begins with the linear particle accelerator (LINAC 2). After the LINAC 2 increases the energy of the protons, these particles are then injected into the Proton Synchrotron Booster (PSB), which accelerates them to high speeds.

They are then injected into the Proton Synchrotron (PS), and then onto the Super Proton Synchrtron (SPS), where they are sped up even further before being injected into the main accelerator. Once there, the proton bunches are accumulated and accelerated to their peak energy over a period of 20 minutes. Last, they are circulated for a period of 5 to 24 hours, during which time collisions occur at the four intersection points.

During shorter running periods, heavy-ion collisions (typically lead ions) are included the program. The lead ions are first accelerated by the linear accelerator LINAC 3, and the Low Energy Ion Ring (LEIR) is used as an ion storage and cooler unit. The ions are then further accelerated by the PS and SPS before being injected into LHC ring.

While protons and lead ions are being collided, seven detectors are used to scan for their byproducts. These include the A Toroidal LHC ApparatuS (ATLAS) experiment and the Compact Muon Solenoid (CMS), which are both general purpose detectors designed to see many different types of subatomic particles.

Then there are the more specific A Large Ion Collider Experiment (ALICE) and Large Hadron Collider beauty (LHCb) detectors. Whereas ALICE is a heavy-ion detector that studies strongly-interacting matter at extreme energy densities, the LHCb records the decay of particles and attempts to filter b and anti-b quarks from the products of their decay.

Then there are the three small and highly-specialized detectors – the TOTal Elastic and diffractive cross section Measurement (TOTEM) experiment, which measures total cross section, elastic scattering, and diffractive processes; the Monopole & Exotics Detector (MoEDAL), which searches magnetic monopoles or massive (pseudo-)stable charged particles; and the Large Hadron Collider forward (LHCf) that monitor for astroparticles (aka. cosmic rays).

History of Operation:

CERN, which stands for Conseil Européen pour la Recherche Nucléaire (or European Council for Nuclear Research in English) was established on Sept 29th, 1954, by twelve western European signatory nations. The council’s main purpose was to oversee the creation of a particle physics laboratory in Geneva where nuclear studies would be conducted.

Illustration showing the byproducts of lead ion collisions, as monitored by the ATLAS detector. Credit: CERN
Illustration showing the byproducts of lead ion collisions, as monitored by the ATLAS detector. Credit: CERN

Soon after its creation, the laboratory went beyond this and began conducting high-energy physics research as well. It has also grown to include twenty European member states: France, Switzerland, Germany, Belgium, the Netherlands, Denmark, Norway, Sweden, Finland, Spain, Portugal, Greece, Italy, the UK, Poland, Hungary, the Czech Republic, Slovakia, Bulgaria and Israel.

Construction of the LHC was approved in 1995 and was initially intended to be completed by 2005. However, cost overruns, budget cuts, and various engineering difficulties pushed the completion date to April of 2007. The LHC first went online on September 10th, 2008, but initial testing was delayed for 14 months following an accident that caused extensive damage to many of the collider’s key components (such as the superconducting magnets).

On November 20th, 2009, the LHC was brought back online and its First Run ran from 2010 to 2013. During this run, it collided two opposing particle beams of protons and lead nuclei at energies of 4 teraelectronvolts (4 TeV) and 2.76 TeV per nucleon, respectively. The main purpose of the LHC is to recreate conditions just after the Big Bang when collisions between high-energy particles was taking place.

Major Discoveries:

During its First Run, the LHCs discoveries included a particle thought to be the long sought-after Higgs Boson, which was announced on July 4th, 2012. This particle, which gives other particles mass, is a key part of the Standard Model of physics. Due to its high mass and elusive nature, the existence of this particle was based solely in theory and had never been previously observed.

The discovery of the Higgs Boson and the ongoing operation of the LHC has also allowed researchers to investigate physics beyond the Standard Model. This has included tests concerning supersymmetry theory. The results show that certain types of particle decay are less common than some forms of supersymmetry predict, but could still match the predictions of other versions of supersymmetry theory.

In May of 2011, it was reported that quark–gluon plasma (theoretically, the densest matter besides black holes) had been created in the LHC. On November 19th, 2014, the LHCb experiment announced the discovery of two new heavy subatomic particles, both of which were baryons composed of one bottom, one down, and one strange quark. The LHCb collaboration also observed multiple exotic hadrons during the first run, possibly pentaquarks or tetraquarks.

Since 2015, the LHC has been conducting its Second Run. In that time, it has been dedicated to confirming the detection of the Higgs Boson, and making further investigations into supersymmetry theory and the existence of exotic particles at higher-energy levels.

The ATLAS detector, one of two general-purpose detectors at the Large Hadron Collider (LHC). Credit: CERN
The ATLAS detector, one of two general-purpose detectors at the Large Hadron Collider (LHC). Credit: CERN

In the coming years, the LHC is scheduled for a series of upgrades to ensure that it does not suffer from diminished returns. In 2017-18, the LHC is scheduled to undergo an upgrade that will increase its collision energy to 14 TeV. In addition, after 2022, the ATLAS detector is to receive an upgrade designed to increase the likelihood of it detecting rare processes, known as the High Luminosity LHC.

The collaborative research effort known as the LHC Accelerator Research Program (LARP) is currently conducting research into how to upgrade the LHC further. Foremost among these are increases in the beam current and the modification of the two high-luminosity interaction regions, and the ATLAS and CMS detectors.

Who knows what the LHC will discover between now and the day when they finally turn the power off? With luck, it will shed more light on the deeper mysteries of the Universe, which could include the deep structure of space and time, the intersection of quantum mechanics and general relativity, the relationship between matter and antimatter, and the existence of “Dark Matter”.

We have written many articles about CERN and the LHC for Universe Today. Here’s What is the Higgs Boson?, The Hype Machine Deflates After CERN Data Shows No New Particle, BICEP2 All Over Again? Researchers Place Higgs Boson Discovery in Doubt, Two New Subatomic Particles Found, Is a New Particle about to be Announced?, Physicists Maybe, Just Maybe, Confirm the Possible Discovery of 5th Force of Nature.

If you’d like more info on the Large Hadron Collider, check out the LHC Homepage, and here’s a link to the CERN website.

Astronomy Cast also has some episodes on the subject. Listen here, Episode 69: The Large Hadron Collider and The Search for the Higgs Boson and Episode 392: The Standard Model – Intro.

Sources:

Could You Put a Black Hole in Your Pocket?

How small do black holes get? Could you carry one around in your pocket? Does that even like a sane thing to do?

I’m pleased to announce that the Large Hadron Collider, the enormous particle accelerator in Europe has begun operations again with twice the colliding power. Smashing atoms with 15 Tera-electron volts.

The LHC double-down has a laundry list of science to get done, like determining the nature of dark matter, searching for particles to confirm the theory of supersymmetry, and probing the Universe for extra dimensions. One of its tasks will be to search for Hawking Radiation, the stream of particles that come out of black holes as they evaporate.

So, in order to watch them evaporate, the LHC is going to try and create little tiny black holes. We only know one natural process for creating black holes: the death of massive stars as supernova. Oh, and whatever it took to make supermassive black holes – that’s still pretty much a mystery.

As a side note, we are going to be supermassively embarrassed if it turns out they’re created by species messing with forces far beyond their comprehension by doubling the power at their biggest particle accelerator, and turning their region of the Universe into a giant mess. Clean up, aisle Milky Way.

Apparently, you could get a black hole of any size, even microscopic. If you took the mass of the Earth, compressed it down to the size of a marble, it would become a black hole. A black hole with the mass of the Earth.

The only place this might have been possible was at the very beginning of the Universe, shortly after the Big Bang. When the Universe was unimaginably hot and dense, there were tiny fluctuations of density, nooks in spacetime where tiny black holes might have formed. Maybe they don’t exist at all, the conditions of the early Universe didn’t bring them about. It’s just a theory. A theory that the Large Hadron Collider will try to confirm or deny.

Artist illustration of a black hole. Image credit: NASA
Artist illustration of a black hole. Image credit: NASA

The important question is, will it kill us all? Could a black hole fall out of the experiment, and roll down into the sewer drain. Chewing its way down into the center of the Earth, gobbling away the core of the planet, eventually creating an Earth-massed black hole?

Here’s the good news. The less massive, the hotter it is, and the faster it evaporates. Microscopic black holes would evaporate in a faction of a second. Any that the LHC could create, would disintegrate in a faction of a second. In fact, they should be gone in 10^-27 seconds.

So it turns out, you could put a black hole in your pocket. An Earth-mass black hole would fit nicely in your pocket. An Earth’s worth of gravity, however, could prove problematic.

Fortunately, there’s no natural process that can create these objects, and any black holes that we could create would be gone before you could get them anywhere near a pocket. So, you should probably stop thinking of it in terms of one of Lord Nibbler’s doodies.

What would you do with a pocket-sized black hole? Tell us in the comments below.

What’s Next for the Large Hadron Collider?

The world’s most powerful particle collider is waking up from a well-earned rest. After roughly two years of heavy maintenance, scientists have nearly doubled the power of the Large Hadron Collider (LHC) in preparation for its next run. Now, it’s being cooled to just 1.9 degrees above absolute zero.

“We have unfinished business with understanding the universe,” said Tara Shears from the University of Liverpool in a news release. Shears and other LHC physicists will work to better understand the Higgs Boson and hopefully unravel some of the secrets of supersymmetry and dark matter.

On February 11, 2013 the LHC shut down for roughly two years. The break, known as LS1 for “long stop one,” was needed to correct several flaws in the original design of the collider.

The LHC’s first run got off to a rough start in 2008. Shortly after it was fired up, a single electrical connection triggered an explosion, damaging an entire sector (one-eighth) of the accelerator. To protect the accelerator from further disaster, scientists decided to run it at half power until all 10,000 copper connections could be repaired.

So over the last two years, scientists have worked around the clock to rework every single connection in the accelerator.

Now that the step (along with many others) is complete, the collider will operate at almost double its previous power. This was tested early last week, when scientists powered up the magnets of one sector to the level needed to reach the high energy expected in its second run.

“The machine that’s now being started up is almost a new LHC,” said John Womersley, the Chief Executive Officer of the Science and Technology Facilities Council.

With such a powerful new tool, scientists will look for deviations from their initial detection of the Higgs boson, potentially revealing a deeper level of physics that goes well beyond the Standard Model of particle physics.

Many theorists have turned to supersymmetry — the idea that for every known fundamental particle there exists a “supersymmetric” partner particle. If true, the enhanced LHC could be powerful enough to create supersymmetric particles themselves or prove their existence in subtler ways.

“The higher energy and more frequent proton collisions in Run 2 will allow us to investigate the Higgs particle in much more detail,” said Victoria Martin from Edinburgh University. “Higher energy may also allow the mysterious “dark matter” observed in galaxies to be made and studied in the lab for the first time.”

It’s possible that the Higgs could interact with — or even decay into — dark matter particles. If the latter occurs, then the dark matter particles would fly out of the LHC without ever being detected. But their absence would be evident.

So stay turned because these issues might be resolved in the spring of 2015 when the particle accelerator roars back to life.

Macro View Makes Dark Matter Look Even Stranger

We know dark matter exists. We know this because without it and dark energy, our Universe would be missing 95.4% of its mass. What’s more, scientists would be hard pressed to explain what accounts for the gravitational effects they routinely see at work in the cosmos.

For decades, scientists have sought to prove its existence by smashing protons together in the Large Hadron Collider. Unfortunately, these efforts have not provided any concrete evidence.

Hence, it might be time to rethink dark matter. And physicists David M. Jacobs, Glenn D. Starkman, and Bryan Lynn of Case Western Reserve University have a theory that does just that, even if it does sound a bit strange.

In their new study, they argue that instead of dark matter consisting of elementary particles that are invisible and do not emit or absorb light and electromagnetic radiation, it takes the form of chunks of matter that vary widely in terms of mass and size.

As it stands, there are many leading candidates for what dark matter could be, which range from Weakly-Interacting Massive Particles (aka WIMPs) to axions. These candidates are attractive, particularly WIMPs, because the existence of such particles might help confirm supersymmetry theory – which in turn could help lead to a working Theory of Everything (ToE).

According to supersymmetry, dark-matter particles known as neutralinos (which are often called WIMPs) annihilate each other, creating a cascade of particles and radiation that includes medium-energy gamma rays. If neutralinos exist, the LAT might see the gamma rays associated with their demise. Credit: Sky & Telescope / Gregg Dinderman.
According to supersymmetry, dark-matter particles known as neutralinos (aka WIMPs) annihilate each other, creating a cascade of particles and radiation. Credit: Sky & Telescope / Gregg Dinderman.

But so far, no evidence has been obtained that definitively proves the existence of either. Beyond being necessary in order for General Relativity to work, this invisible mass seems content to remain invisible to detection.

According to Jacobs, Starkman, and Lynn, this could indicate that dark matter exists within the realm of normal matter. In particular, they consider the possibility that dark matter consists of macroscopic objects – which they dub “Macros” – that can be characterized in units of grams and square centimeters respectively.

Macros are not only significantly larger than WIMPS and axions, but could potentially be assembled out of particles in the Standard Model of particle physics – such as quarks and leptons from the early universe – instead of requiring new physics to explain their existence. WIMPS and axions remain possible candidates for dark matter, but Jacobs and Starkman argue that there’s a reason to search elsewhere.

“The possibility that dark matter could be macroscopic and even emerge from the Standard Model is an old but exciting one,” Starkman told Universe Today, via email. “It is the most economical possibility, and in the face of our failure so far to find dark matter candidates in our dark matter detectors, or to make them in our accelerators, it is one that deserves our renewed attention.”

After eliminating most ordinary matter – including failed Jupiters, white dwarfs, neutron stars, stellar black holes, the black holes in centers of galaxies, and neutrinos with a lot of mass – as possible candidates, physicists turned their focus on the exotics.

Particle Collider
Ongoing experiments at the Large Hadron Collider have so far failed to produce evidence of WIMPs. Credit: CERN/LHC/GridPP

Nevertheless, matter that was somewhere in between ordinary and exotic – relatives of neutron stars or large nuclei – was left on the table, Starkman said. “We say relatives because they probably have a considerable admixture of strange quarks, which are made in accelerators and ordinarily have extremely short lives,” he said.

Although strange quarks are highly unstable, Starkman points out that neutrons are also highly unstable. But in helium, bound with stable protons, neutrons remain stable.

“That opens the possibility that stable strange nuclear matter was made in the early Universe and dark matter is nothing more than chunks of strange nuclear matter or other bound states of quarks, or of baryons, which are themselves made of quarks,” said Starkman.

Such dark matter would fit the Standard Model.

This is perhaps the most appealing aspect of the Macros theory: the notion that dark matter, which our cosmological model of the Universe depends upon, can be proven without the need for additional particles.

Still, the idea that the universe is filled with a chunky, invisible mass rather than countless invisible particles does make the universe seem a bit stranger, doesn’t it?

Further Reading: Case Western

Q&A with Brian Cox, part 1: Recent Hints of the Higgs

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At two separate conferences in July, particle physicists announced some provoking news about the Higgs boson, and while the Higgs has not yet been found, physicists are continuing to zero in on the elusive particle. Universe Today had the chance to talk with Professor Brian Cox about these latest findings, and he says that within six to twelve months, physicists should be able to make a definite statement about the existence of the Higgs particle. Cox is the Chair in Particle Physics at the University of Manchester, and works on the ATLAS experiment (A Toroidal LHC ApparatuS) at the Large Hadron Collider at CERN. But he’s also active in the popularization of science, specifically with his new television series and companion book, Wonders of the Universe, a follow up to the 2010 Peabody Award-winning series, Wonders of the Solar System.

Universe Today readers will have a chance to win a copy of the book, so stay tuned for more information on that. But today, enjoy the first of a three-part interview with Cox:


Universe Today: Can you tell us about your work with ATLAS and its potential for finding things like extra dimensions, the unification of forces or dark matter?

Brian Cox, during the filming of one of his television series. Image courtesy Brian Cox.

Brian Cox: The big question is the origin and mass of the universe. It is very, very important because it is not an end in itself. It is a fundamental part of Quantum Field Theory, which is our theory of three of the four forces of nature. So if you ask the question on the most basic level of how does the universe work, there are only two pillars of our understanding at the moment. There is Einstein’s Theory of General Relatively, which deals with gravity — the weakest force in the Universe that deals with the shape of space and time and all those things. But everything else – electromagnetism, the way the atomic nuclei works, the way molecules work, chemistry, all that – everything else is what’s called a Quantum Field Theory. Embedded in that is called the Standard Model of particle physics. And embedded in that is this mechanism for generating mass, and it’s just so fundamental. It’s not just kind of an interesting add-on, it’s right in the heart of the way the theory works.

So, understanding whether our current picture of the Universe is right — and if there is this thing called the Higgs mechanism or whether there is something else going on — is critical to our progress because it is built into that picture. There are hints in the data recently that maybe that mechanism is right. We have to be careful. It’s not a very scientific thing to say that we have hints. We have these thresholds for scientific discovery, and we have them for a reason, because you get these statistical flukes that appear in the data and when you get more data they go away again.

The statement from CERN now is that if they turn out to be more than just fluctuations, really, within six months we should be able to make some definite statement about the existence of the Higgs particle.

I think it is very important to emphasize that this is not just a lot of particle physicists looking for particles because that’s their job. It is the fundamental part of our understanding of three of the four forces of nature.

Brian Cox at Fermilab. Photo by Paul Olding.

UT : So these very interesting results from CERN and the Tevatron at Fermilab giving us hints about the Higgs, could you can talk little bit more about that and your take on the latest findings?

COX: The latest results were published in a set of conferences a few weeks ago and they are just under what is called the Three Sigma level. That is the way of assessing how significant the results are. The thing about all quantum theory and particle physics in general, is it is all statistical. If you do this a thousand times, then three times this should happen, and eight times that should happen. So it’s all statistics. As you know if you toss a coin, it can come up heads ten times, there is a probability for that to happen. It doesn’t mean the coin is weighted or there’s something wrong with it. That’s just how statistics is.

So there are intriguing hints that they have found something interesting. Both experiments at the Large Hadron Collider, the ATLAS and the Compact Muon Solenoid (CMS) recently reported “excess events” where there were more events than would be expected if the Higgs does not exist. It is about the right mass: we think the Higgs particle should be somewhere between about 120 and 150 gigaelectron volts [GeV—a unit of energy that is also a unit of mass, via E = mc2, where the speed of light, c, is set to a value of one] which is the expected mass range of the Higgs. These hints are around 140, so that’s good, it’s where it should be, and it is behaving in the way that it is predicted to by the theory. The theory also predicts how it should decay away, and what the probability should be, so all the data is that this is consistent with the so-called standard model Higgs.

But so far, these events are not consistently significant enough to make the call. It is important that the Tevatron has glimpsed it as well, but that has even a lower significance because that was low energy and not as many collisions there. So you’ve got to be scientific about things. There is a reason we have these barriers. These thresholds are to be cleared to claim discoveries. And we haven’t cleared it yet.

But it is fascinating. It’s the first time one of these rumors have been, you know, not just nonsense. It really is a genuine piece of exciting physics. But you have to be scientific about these things. It’s not that we know it is there and we’re just not going to announce it yet. It’s the statistics aren’t here yet to claim the discovery.

Brian Cox, while filming a BBC series in the Sahara. Image courtesy Brian Cox

UT : Well, my next question was going to be, what happens next? But maybe you can’t really answer that because all you can do is keep doing the research!

COX: The thing about the Higgs, it is so fundamentally embedded in quantum theory. You’ve got to explore it because it is one thing to see a hint of a new particle, but it’s another thing to understand how that particle behaves. There are lots of different ways the Higgs particles can behave and there are lots of different mechanisms.

There is a very popular theory called supersymmetry which also would explain dark matter, one of the great mysteries in astrophysics. There seems to be a lot of extra stuff in the Universe that is not behaving the way that particles of matter that we know of behave, and with five times more “stuff” as what makes up everything we can see in the Universe. We can’t see dark matter, but we see its gravitational influence. There are theories where we have a very strong candidate for that — a new kind of particle called a supersymmetry particles. There are five Higgs particles in them rather than one. So the next question is, if that is a Higgs-like particle that we’ve discovered, then what is it? How does it behave? How does it talk to the other particles?

And then there are a huge amount of questions. The Higgs theory as it is now doesn’t explain why the particles have the masses they do. It doesn’t explain why the top quark, which is the heaviest of the fundamental particles, is something like 180 times heavier than the proton. It’s a tiny point-like thing with no size but it’s 180 times the mass of a proton! That is heavier than some of the heaviest atomic nuclei!

Why? We don’t know.

I think it is correct to say there is a door that needs to be opened that has been closed in our understanding of the Universe for decades. It is so fundamental that we’ve got to open it before we can start answering these further questions, which are equally intriguing but we need this answered first.

UT: When we do get some of these questions answered, how is that going to change our outlook and the way that we do things, or perhaps the way YOU do things, anyway! Maybe not us regular folks…

COX: Well, I think it will – because this is part of THE fundamental theory of the forces of nature. So quantum theory in the past has given us an understanding, for example, of the way semiconductors work, and it underpins our understanding of modern technology, and the way chemistry works, the way that biological systems work – it’s all there. This is the theory that describes it all. I think having a radical shift and deepening in understanding of the basic laws of nature will change the way that physics proceeds in 21st century, without a doubt. It is that fundamental. So, who knows? At every paradigm shift in science, you never really could predict what it was going to do; but the history of science tells you that it did something quite remarkable.

There is a famous quote by Alexander Fleming, who discovered penicillin, who said that when he woke up on a certain September morning of 1928, he certainly didn’t expect to revolutionize modern medicine by discovering the world’s first antibiotic. He said that in hindsight, but he just discovered some mold, basically, but there it was.

But it was fundamental and that is the thing to emphasize.

Some of our theories, you look at them and wonder how we worked them! The answer is mathematically, the same way that Einstein came up with General Relativity, with mathematical predictions. It is remarkable we’ve been able to predict something so fundamental about the way that empty space behaves. We might turn out to be right.

Tomorrow: Part 2: The space exploration and hopes for the future

Find out more about Brian Cox at his website, Apollo’s Children

Hunt for Dark Matter Closes in at the LHC

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From an Imperial College London press release:

Physicists say they are closer than ever to finding the source of the Universe’s mysterious dark matter, following a better than expected year of research at the Compact Muon Solenoid (CMS) particle detector, part of the Large Hadron Collider (LHC) at CERN in Geneva.

The scientists have now carried out the first full run of experiments that smash protons together at almost the speed of light. When these sub-atomic particles collide at the heart of the CMS detector, the resultant energies and densities are similar to those that were present in the first instants of the Universe, immediately after the Big Bang some 13.7 billion years ago. The unique conditions created by these collisions can lead to the production of new particles that would have existed in those early instants and have since disappeared.

The researchers say they are well on their way to being able to either confirm or rule out one of the primary theories that could solve many of the outstanding questions of particle physics, known as Supersymmetry (SUSY). Many hope it could be a valid extension for the Standard Model of particle physics, which describes the interactions of known subatomic particles with astonishing precision but fails to incorporate general relativity, dark matter and dark energy.

In particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known assuperpartners. In a theory with unbroken supersymmetry, for every type of boson there exists a corresponding type of fermion with the same mass and internal quantum numbers, and vice-versa.

Dark matter is an invisible substance that we cannot detect directly but whose presence is inferred from the rotation of galaxies. Physicists believe that it makes up about a quarter of the mass of the Universe whilst the ordinary and visible matter only makes up about 5% of the mass of the Universe. Its composition is a mystery, leading to intriguing possibilities of hitherto undiscovered physics.

Professor Geoff Hall from the Department of Physics at Imperial College London, who works on the CMS experiment, said, “We have made an important step forward in the hunt for dark matter, although no discovery has yet been made. These results have come faster than we expected because the LHC and CMS ran better last year than we dared hope and we are now very optimistic about the prospects of pinning down Supersymmetry in the next few years.”

The energy released in proton-proton collisions in CMS manifests itself as particles that fly away in all directions. Most collisions produce known particles but, on rare occasions, new ones may be produced, including those predicted by SUSY – known as supersymmetric particles, or ‘sparticles’. The lightest sparticle is a natural candidate for dark matter as it is stable and CMS would only ‘see’ these objects through an absence of their signal in the detector, leading to an imbalance of energy and momentum.

In order to search for sparticles, CMS looks for collisions that produce two or more high-energy ‘jets’ (bunches of particles traveling in approximately the same direction) and significant missing energy.

Dr. Oliver Buchmueller, also from the Department of Physics at Imperial College London, but who is based at CERN, said, “We need a good understanding of the ordinary collisions so that we can recognise the unusual ones when they happen. Such collisions are rare but can be produced by known physics. We examined some 3 trillion proton-proton collisions and found 13 ‘SUSY-like’ ones, around the number that we expected. Although no evidence for sparticles was found, this measurement narrows down the area for the search for dark matter significantly.”

The physicists are now looking forward to the 2011 run of the LHC and CMS, which is expected to bring in data that could confirm Supersymmetry as an explanation for dark matter.

The CMS experiment is one of two general purpose experiments designed to collect data from the LHC, along with ATLAS (A Toroidal LHC ApparatuS). Imperial’s High Energy Physics Group has played a major role in the design and construction of CMS and now many of the members are working on the mission to find new particles, including the elusive Higgs boson particle (if it exists), and solve some of the mysteries of nature, such as where mass comes from, why there is no anti-matter in our Universe and whether there are more than three spatial dimensions.