Monday, November 17, 2008

Hadron Collider repairs cost £14m

Repairing the Large Hadron Collider (LHC) near Geneva will cost almost £14m ($21m) and "realistically" take until at least next summer to start back up.
An electrical failure shut the £3.6bn ($6.6bn) machine down in September.
The European Organization for Nuclear Research (Cern) thought it would only be out of action until November but the damage was worse than expected.
It is hoped repairs will be completed by May or early June with the machine restarted at the end of June or later.
Cern spokesman James Gillies said: "If we can do it sooner, all well and good. But I think we can do it realistically (in) early summer."

The fault occurred just nine days after it was turned on with Cern blaming the shutdown on the failure of a single, badly soldered electrical connection in one of its super-cooled magnet sections.
The collider operates at temperatures colder than outer space for maximum efficiency and experts needed to gradually warm the damaged section to assess it.
"Now the sector is warm so they are able to go in and physically look at each of the interconnections," Mr Gillies told Associated Press.

Monday, November 3, 2008

The LHC: broken, but officially inaugurated with rhymes

lhc.jpgKate McAlpine (aka LHC rapper AlpineKat) writes:

CERN released a technical report last week, detailing the causes of the most recent Large Hadron Collider delays  but that didn't stop the 21 October start-up celebration - "LHC Fest" - from staying on schedule.

Following the unexpected success of the Large Hadron Rap - 3.6 million views and counting - I seem to have become something of a regular at CERN functions, alongside Les Horribles Cernettes - the subject of the first ever photograph on the web - and the Cannettes Blues Band. But sadly, most of my original backup crew has left CERN, so we've had different personnel each time.

During the hi-fives all around at the end of the performance, Lizzie Gibney, a dancer in the original video and on backing vocals last night, put it best with: "Give me some skin, Lyn!"

Sunday, September 21, 2008

Hadron Collider halted for months

The Large Hadron Collider near Geneva will be out of action for at least two months, the European Organization for Nuclear Research (Cern) says.

Part of the giant physics experiment was turned off for the weekend while engineers probed a magnet failure.

But a Cern spokesman said damage to the £3.6bn ($6.6bn) particle accelerator was worse than anticipated.

Section damaged

On Friday, a failure, known as a quench, caused around 100 of the LHC's super-cooled magnets to heat up by as much as 100C.

The fire brigade were called out after a tonne of liquid helium leaked into the tunnel at Cern, near Geneva.

Cern spokesman James Gillies said on Saturday that the sector that was damaged would have to be warmed up to above its operating temperature - of near absolute zero - so that repairs could be made, and then cooled down again.

While he said there was never any danger to the public, Mr Gillies admitted that the breakdown would be costly.

He said: "A full investigation is still under way but the most likely cause seems to be a faulty electrical connection between two of the magnets which probably melted, leading to a mechanical failure.

"We're investigating and we can't really say more than that now.

"But we do know that we will have to warm the machine up, make the repair, cool it down, and that's what brings you to two months of downtime for the LHC."

Setback

The first beams were fired successfully around the accelerator's 27km (16.7 miles) underground ring over a week ago.

The crucial next step is to collide those beams head on. However, the fault appears to have ruled out any chance of these experiments taking place for the next two months at least.

Hadron Collider forced to halt

Plans to begin smashing particles at the Large Hadron Collider (LHC) may be delayed after a magnet failure forced engineers to halt work.

The failure, known as a quench, caused around 100 of the LHC's super-cooled magnets to heat up by as much as 100C.
viz from -271 deg. C to -171 deg. C

The fire brigade were called out after a tonne of liquid helium leaked into the tunnel at Cern, near Geneva.

The LHC beam will remain turned off over the weekend while engineers investigate the severity of the fault.

A spokesman for Cern told the BBC it was not yet clear how soon progress could resume at the £3.6bn ($6.6bn) particle accelerator.

While the failure was "not good news", he said glitches of this kind were not unexpected during testing.

Delays

The first beams were fired successfully around the accelerator's 27km (16.7 miles) underground ring over a week ago.

Superconducting magnet (Cern/M. Brice)
Superconducting magnets are cooled down using liquid helium

The crucial next step is to collide those beams head on. However, the fault appears to have ruled out any chance of these experiments taking place for the next week at least.

The quench occurred during final testing of the last of the LHC's electrical circuits to be commissioned.

At 1127 (0927 GMT) on Friday, the LHC's online logbook recorded a quench in sector 3-4 of the accelerator, which lies between the Alice and CMS detectors.

The entry stated that helium had been lost to the tunnel and that vacuum conditions had also been lost.

It added that the Cern fire brigade had been called to the scene.

CMS (Cern/M. Hoch)
The LHC has been in construction for some 13 years

The superconducting magnets in the LHC must be supercooled to 1.9 kelvin above absolute zero, to allow them to steer particle beams around the circuit.

As a result of the quench, the temperature of about 100 of the magnets in the machine's final sector rose by around 100C.

A spokesman for Cern confirmed that it would now be difficult, if not impossible, to stage the first trial collisions next week.

Further delays could follow once the damage has been fully assessed over the weekend.

The setback comes just a day after the LHC's beam was restored after engineers replaced a faulty transformer that had hindered progress for much of the past week.

Thursday, September 11, 2008

Big Bang Day: The Genuine Particle

Listen to Steve Punts very funny play

Broadcast on:
BBC Radio 4, 11:30pm Wednesday 10th September
Duration:
30 minutes
Available until:
12:02am Thursday 18th September



The Standard Model of Particle Physics


The Standard Model of particle physics is a theory that describes three ( electromagnetism, the weak interaction, and the strong interaction) of the four (gravitation) known fundamental interactions among the elementary particles that make up all matter.

The Standard Model falls short of being a complete theory of fundamental interactions, primarily because of its lack of inclusion of gravity, the fourth known fundamental interaction.

The particles of the standard model are organized into three classes according to their spin:

I dont understand what is meant by spin!


fermions (spin is ½ particles of matter), gauge bosons (spin is 1 force-mediating particles), and the (spin is 0) Higgs boson.

Particles of matter

Apart from their antiparticle partners, a total of twelve different fermions are known and accounted for. They are classified according to how they interact (or equivalently, what charges they carry): six of them are classified as quarks (up, down, charm, strange, top, bottom), and the other six as leptons (electron, muon, tau, and their corresponding neutrinos).

The defining property of the quarks is that they carry color charge, and hence, interact via the strong force. The infrared confining behavior of the strong force results in the quarks being perpetually bound to one another forming color-neutral composite particles (hadrons) of either two quarks (mesons) or three quarks (baryons). The familiar proton and the neutron are examples of the two lightest baryons.

The remaining six fermions that do not carry color charge are defined to be the leptons. The three neutrinos do not carry electric charge either, so their motion is directly influenced only by means of the weak nuclear force. For this reason neutrinos are notoriously difficult to detect in laboratories. However, the electron, muon and the tau lepton carry an electric charge so they interact electromagnetically, too.

Force mediating particles

Forces in physics are the ways that particles interact and influence each other. At a macro level, the electromagnetic force allows particles to interact with one another via electric and magnetic fields, and the force of gravitation allows two particles with mass to attract one another in accordance with Newton's Law of Gravitation. The standard model explains such forces as resulting from matter particles exchanging other particles, known as force mediating particles. When a force mediating particle is exchanged, at a macro level the effect is equivalent to a force influencing both of them, and the particle is therefore said to have mediated (i.e., been the agent of) that force. Force mediating particles are believed to be the reason why the forces and interactions between particles observed in the laboratory and in the universe exist.

The known force mediating particles described by the Standard Model also all have spin (as do matter particles), but in their case, the value of the spin is 1, meaning that all force mediating particles are bosons. As a result, they do not follow the Pauli Exclusion Principle. The different types of force mediating particles are described below.

  • Photons mediate the electromagnetic force between electrically charged particles. The photon is massless and is well-described by the theory of quantum electrodynamics.
  • The W+, W, and Z gauge bosons mediate the weak interactions between particles of different flavors (all quarks and leptons). They are massive, with the Z being more massive than the W±. The weak interactions involving the W± act on exclusively left-handed particles and right-handed antiparticles. Furthermore, the W± carry an electric charge of +1 and −1 and couple to the electromagnetic interactions. The electrically neutral Z boson interacts with both left-handed particles and antiparticles. These three gauge bosons along with the photons are grouped together which collectively mediate the electroweak interactions.
  • The eight gluons mediate the strong interactions between color charged particles (the quarks). Gluons are massless. The eightfold multiplicity of gluons is labeled by a combination of color and an anticolor charge (e.g., red–antigreen).[9] Because the gluon has an effective color charge, they can interact among themselves. The gluons and their interactions are described by the theory of quantum chromodynamics.

The interactions between all the particles described by the Standard Model are summarized below.

The Higgs boson

Main article: Higgs boson

The Higgs particle is a hypothetical massive scalar elementary particle predicted by the Standard Model,

and the only fundamental particle predicted by that model which has not been directly observed as yet.
This is because it requires an exceptionally large amount of energy to create and observe at high energy colliders. It has no intrinsic spin, and thus, (like the force mediating particles, which also have integral spin) is also classified as a boson.

The Higgs boson plays a unique role in the Standard Model, and a key role in explaining the origins of the mass of other elementary particles, in particular the difference between the massless photon and the very heavy W and Z bosons. Elementary particle masses, and the differences between electromagnetism (caused by the photon) and the weak force (caused by the W and Z bosons), are critical to many aspects of the structure of microscopic (and hence macroscopic) matter. In electroweak theory it generates the masses of the massive leptons (electron, muon and tau); and also of the quarks.

As of September 2008, no experiment has directly detected the existence of the Higgs boson, but there is some indirect evidence for it. It is hoped that upon the completion of the Large Hadron Collider, experiments conducted at CERN would bring experimental evidence confirming the existence of the particle.

The Standard Model predicted the existence of W and Z bosons, the gluon, the top quark and the charm quark before these particles had been observed. Their predicted properties were experimentally confirmed with good precision.

The Large Electron-Positron Collider at CERN tested various predictions about the decay of Z bosons, and found them confirmed.

To get an idea of the success of the Standard Model a comparison between the measured and the predicted values of some quantities are shown in the following table:

Quantity Measured (GeV) SM prediction (GeV)
Mass of W boson 80.398±0.025 80.3900±0.0180
Mass of Z boson 91.1876±0.0021 91.1874±0.0021

Antiparticles

Main article: antimatter

There are also 12 fundamental fermionic antiparticles which correspond to these 12 particles. The positron e+ corresponds to the electron and has an electric charge of +1 and so on:

Antiparticles
First generation
  • positron: e+
  • electron-antineutrino:  \bar{\nu}_e
  • up antiquark:  \bar{u}
  • down antiquark:  \bar{d}
Second generation
  • positive muon: μ+
  • muon-antineutrino:  \bar{\nu}_\mu
  • charm antiquark:  \bar{c}
  • strange antiquark:  \bar{s}
Third generation
  • positive tau: τ+
  • tau-antineutrino:  \bar{\nu}_\tau
  • top antiquark:  \bar{t}
  • bottom antiquark:  \bar{b}

It should be noted that the table below lists properties of a conceptual model that is still subject to research in modern physics.

Interaction Current Theory Mediators Relative Strength Long-Distance Behavior Range(m)
Strong Quantum chromodynamics
(QCD)
gluons 1038 1
(see discussion below)
10-15
Electromagnetic Quantum electrodynamics
(QED)
photons 1036 \frac{1}{r^2} infinite
Weak Electroweak Theory W and Z bosons 1025 \frac{e^{-m_{W,Z}r}}{r} 10-18
Gravitation General Relativity
(GR)
gravitons (not yet discovered) 1 \frac{1}{r^2} infinite

The modern quantum mechanical view of the three fundamental forces (all except gravity) is that particles of matter (fermions) do not directly interact with each other, but rather carry a charge, and exchange virtual particles (gauge bosons), which are the interaction carriers or force mediators. For example, photons are the mediators of the interaction of electric charges; and gluons are the mediators of the interaction of color charges.

The interactions

Gravitation

Main article: Gravitation

Gravitation is by far the weakest interaction, but at long distances gravity's strength relative to other forces becomes important. There are three reasons for this. First, gravity has an infinite range, like that of electromagnetism. Secondly, all masses are positive and therefore gravity's interaction cannot be screened like in electromagnetism. Finally, gravitational force cannot be absorbed or transformed, and so is permanent. Thus large celestial bodies such as planets, stars and galaxies dominantly feel gravitational forces. In comparison, the total electric charge of these bodies is zero because half of all charges are negative. In addition, unlike the other interactions, gravity acts universally on all matter. There are no objects that lack a gravitational "charge".

Because of its long range, gravity is responsible for such large-scale phenomena as the structure of galaxies, black holes and the expansion of the universe, as well as more elementary astronomical phenomena like the orbits of planets, and everyday experience: objects fall; heavy objects act as if they were glued to the ground; people are limited in how high they can jump.

Gravitation was the first kind of interaction which was described by a mathematical theory. In ancient times, Aristotle theorized that objects of different masses fall at different rates. During the Scientific Revolution, Galileo Galilei experimentally determined that this was not the case — if friction due to air resistance is neglected, all objects accelerate toward the ground at the same rate. Isaac Newton's law of Universal Gravitation (1687) was a good approximation of the general behaviour of gravity. In 1915, Albert Einstein completed the General Theory of Relativity, a more accurate description of gravity in terms of the geometry of space-time.

An area of active research today involves merging the theories of general relativity and quantum mechanics into a more general theory of quantum gravity. It is widely believed that in a theory of quantum gravity, gravity would be mediated by a massless spin 2 particle which is known as the graviton. Gravitons are hypothetical particles not yet observed.

Electromagnetism

Main article: Electromagnetism

Electromagnetism is the force that acts between electrically charged particles. This phenomenon includes the electrostatic force, acting between charges at rest, and the combined effect of electric and magnetic forces acting between charges moving relative to each other.

Electromagnetism is also an infinite-ranged force, but it is much stronger than gravity, and therefore describes almost all phenomena of our everyday experience, ranging from the impenetrability of macroscopic bodies, to lasers and radios, to the structure of atoms and metals, to phenomena such as friction and rainbows.

Electrical and magnetic phenomena have been observed since ancient times, but it was only in the 1800s that scientists discovered that electricity and magnetism are two aspects of the same fundamental interaction. By 1864, Maxwell's equations had rigorously quantified the unified phenomenon. In 1905, Einstein's theory of special relativity resolved the issue of the constancy of the speed of light, and Einstein also explained the photoelectric effect by theorizing that light was transmitted in quanta, which we now call photons. Starting around 1927, Paul Dirac unified quantum mechanics with the relativistic theory of electromagnetism; the theory of quantum electrodynamics was completed in the 1940s by Richard Feynman, Freeman Dyson, Julian Schwinger, and Sin-Itiro Tomonaga.

Weak interaction

Main article: Weak interaction

The weak interaction or weak nuclear force is responsible for some phenomena at the scales of the atomic nucleus, such as beta decay. Electromagnetism and the weak force are theoretically understood to be two aspects of a unified electroweak interaction — this realization was the first step toward the unified theory known as the Standard Model. In electroweak theory, the carriers of the weak force are massive gauge bosons called the W and Z bosons.

Strong interaction

Main article: Strong interaction

The strong interaction, or strong nuclear force, is the most complicated force because it behaves differently at different distances. At distances larger than 10 femtometers, the strong force is practically unobservable, which is why it wasn't noticed until the beginning of the 20th century.

After the nucleus was discovered, it was clear that a new force was needed to keep the positive protons in the nucleus from flying out. The force had to be much stronger than electromagnetism, so that the nucleus could be stable even though the protons were so close together, squeezed down to a volume which is 10-15 of the volume of an atom. From the short range of the force, Hideki Yukawa predicted that it was associated with a massive particle, whose mass is approximately 100 MeV. The pion was discovered in 1947 and this discovery marks the beginning of the modern era of particle physics.

QCD is a theory of fractionally charged quarks interacting with 8 photon-like particles called gluons. The gluons interact with each other, not just with the quarks, and at long distances the lines of force collimate into strings.

Challenges to the standard model

The Standard Model of particle physics has been empirically determined through experiments over the past fifty years. Currently the Standard Model predicts that there is one more particle to be discovered, the Higgs boson. One of the reasons for building the Large Hadron Collider is that the increase in energy is expected to make the Higgs observable. However, as of August 2008, there are only indirect experimental indications for the existence of the Higgs boson and it can not be claimed to be found.

There has been a great deal of both theoretical and experimental research exploring whether the Standard Model could be extended into a complete theory of everything. This area of research is often described by the term 'Beyond the Standard Model'. There are several motivations for this research. First, the Standard Model does not attempt to explain gravity, and it is unknown how to combine quantum field theory which is used for the Standard Model with general relativity which is the best physical model of gravity. This means that there is not a good theoretical model for phenomena such as the early universe.

Unsolved problems in physics: Parameters in the Standard Model: What gives rise to the Standard Model of particle physics? Why do its particle masses and coupling constants possess the values we have measured? Does the Higgs boson predicted by the model really exist? Why are there three generations of particles in the Standard Model?


The Quark

Listen on iPlayer (to 25/9/08)

By 1930s it was accepted that everything was made of protons, neutrons and electrons. In the 1960s a plethera of particles were discovered. Some particles decayed quicker than others. Particles were named lambda, p11, k, sigma, x,y, strange - the particle zoo. Murray-Gelman came up with an organising structure - a periodic table of particles. He hypothesised that all particles were a combination of 3 quarks eg Up/Down/Strange quarks eg 2 up quarks + 1 down quark was a proton, 2 down quarks + 1 up quark was a neutron. Experimental evidence for quarks was derived in the 1960s - from Stanford in California - electrons were used to bounce of protons. Protons were shown to made of 3 different particles eg football with 3 ball bearings inside it. If fire a bullet at the football some of the bullets will bounce of some of the ball bearings occassioanly.

Up down strange discovered first then charm, top, bottom. Always held together by the strong force eg 2 and 3 quarks never one quark. Look inside a prison or proton can see the quarks. Marcos Chown (book: Afterglow of creation) cf Tomatoes all quark gluon plasma. Gluon (wikipedia) glue together the quarks in a proton!

Timeline of Particle discovery (wikipedia).

Search BBC iPlayer for 'big bang'

Search BBC iPlayer for 'big bang'

Wednesday, September 10, 2008

On the hunt for the Higgs boson - Stephen Hawking

On the hunt for the Higgs boson

Stephen Hawking in his study
Hawking’s books have made him a world-renowned theoretical physicist
The sum of human knowledge could be massively increased on Wednesday - but Professor Stephen Hawking could find himself $100 poorer.

As Cern prepares to switch on the Large Hadron Collider (LHC) below the French-Swiss border, the physicist has a bet that it will not find the Higgs boson - the most highly sought-after particle in physics.

Dubbed the "God particle" because it is so crucial to our understanding of the Universe, it is thought to give everything its mass.

The most powerful physics experiment ever built, the LHC will re-create the conditions present in the Universe just after the Big Bang.

When subatomic particles like protons are smashed together in the LHC, the energies released will create an array of new particles - some of which have not been seen since the big bang itself. It will give scientists a glimpse into how these building blocks of matter are made.

Both the LHC, and the space programme, are vital if the human race is not to stultify, and eventually die out

"The LHC will increase the energy at which we can study particle interactions, by a factor of four. According to present thinking, this should be enough to discover the Higgs particle, the particle that gives mass to all the other particles," Professor Hawking told the Today programme.

Previous particle accelerators have failed to find it, but because the LHC is so much more powerful, there is hope that it will succeed. Even a failure, Professor Hawking says, would be exciting, because that would pose new questions about the laws of nature.

"I think it will be much more exciting if we don't find the Higgs. That will show something is wrong, and we need to think again. I have a bet of $100 that we won't find the Higgs."

He believes another important discovery that the experiment could make is superpartners, or particles that should theoretically exist. They are "supersymmetric partners" to those particles we already know of at present.

"Their existence would be a key confirmation of string theory, and they could make up the mysterious dark matter that holds galaxies together. Whatever the LHC finds, or fails to find, the results will tell us a lot about the structure of the Universe," he says.

The magnet core of the world's largest superconducting solenoid magnet at Cern
The CMS detector will search for the Higgs boson

Some fear the experiment may create a black hole that will tear the Earth apart - there have even been two last-minute legal attempts to stop it - but Professor Hawking dismisses the idea that the LHC is in any way dangerous.

"If the collisions in the LHC produced a micro black hole, and this is unlikely, it would just evaporate away again, producing a characteristic pattern of particles. Collisions at these and greater energies occur millions of times a day in the Earth's atmosphere, and nothing terrible happens."

Parallel universe?

The human race is characterised by an insatiable quest to understand things, and the LHC is an example of our willingness to invest in that quest.

It is however difficult to predict whether it will bring any practical advances in the scale of our lifetime. But the LHC might reveal something completely unexpected about the workings of our Universe, and that, says Professor Hawking, is what makes physics so satisfying.

"Throughout history, people have studied pure science from a desire to understand the Universe, rather than for practical applications, or commercial gain. But their discoveries have later turned out to have great practical benefits.

"It is difficult to see an economic return from research at the LHC, but that doesn't mean there won't be any."

Asked if he would be able to choose whether the LHC or the space programme is more important in advancing our knowledge of the Universe, Professor Hawking says that would be like "asking which of my children I would choose to sacrifice".

"Both the LHC, and the space programme, are vital if the human race is not to stultify, and eventually die out. Together they cost less than one tenth of a percent of world GDP. If the human race cannot afford that, it doesn't deserve the epithet, human," he added.

Scientists have spoken, if cautiously, of the experiments at Cern venturing into realms long regarded as those of speculative science fiction - multiple universes, parallel worlds, black holes in space linking different levels of existence.

Simulated production of a black hole in Atlas (Cern)
If a black hole is produced, it might look like this in LHC data

Professor Hawking says that a parallel universe may be a universe very different to the one we recognise.

"According to the sum over histories idea of Richard Feynman, the Universe doesn't just have a single history, as one might think, but it has every possible history, each with its own weight. A few of the histories will contain creatures like me, doing different things, but the vast majority of histories will be very different."

In 1974 Professor Hawking argued that due to quantum effects, primordial black holes created during the Big Bang could "evaporate" by a theoretical process now referred to as Hawking Radiation in which particles of matter would be emitted.

Under this theory, the smaller the size of the micro black hole, the faster the evaporation rate, resulting in a sudden burst of particles as the micro black hole suddenly explodes.

In the past Professor Hawking has joked that if the LHC does creates micro black holes - even if they are rather short-lived ones - it could win him the Nobel prize. However, he now says he does not believe this is something that is imminent.

"If the LHC were to produce little black holes, I don't think there's any doubt I would get a Nobel prize, if they showed the properties I predict. However, I think the probability that the LHC has enough energy to create black holes, is less than 1%, so I'm not holding my breath."

Science of LHC

The Large Hadron Collider (LHC) will smash two beams of particles head-on at super-fast speeds, recreating the conditions in the Universe moments after the Big Bang, writes BBC science reporter Paul Rincon.

Scientists hope to see new particles in the debris of these collisions, revealing fundamental new insights into the nature of the cosmos.

They will be looking for new physics beyond the Standard Model – the framework devised in the 1970s to explain how sub-atomic particles interact.

The Standard Model comprises 16 particles – 12 matter particles and four force-carrier particles. The Standard Model has worked remarkably well so far.

But it cannot explain the best known of the so-called four fundamental forces: gravity; and it describes only ordinary matter, which makes up but a small part of the total Universe.

Also, one of the most important particles in the Standard Model – the Higgs boson – has yet to be found in an experiment.

Today, the Standard Model is regarded as incomplete, a mere stepping stone to something else. So the LHC should help reinvigorate physics' biggest endeavour: a grand theory to explain all physical phenomena in Nature.

However, some physicists point out that Nature has a habit of throwing curve balls. And some of the most exciting discoveries at the LHC could be those that no-one expects.

THE HUNT FOR THE HIGGS

There is an essential ingredient missing from the Standard Model. Without it, none of the 16 particles in the scheme would have any mass.

An extra particle is required to provide all the others with mass – the Higgs boson. This idea was proposed in 1964 by physicists Peter Higgs, Francois Englert and Robert Brout.

According to their theory, particles acquire mass through their interactions with an all-pervading field, called the Higgs field, which is carried by the Higgs boson. It is the only Standard Model particle that has yet to be observed experimentally.

CMS (M. Brice/Cern)
The CMS is one of two LHC experiments looking for the Higgs

As such, the search for the Higgs has become something of a cause celebre in particle physics. Finding the Higgs is one of the main science objectives for the LHC.

The Atlas and CMS experiments are both designed to see it, if it is there. This means that scientists working on these respective experiments will be competing to see it first, once the LHC begins its "science run" sometime in 2009.

The US Tevatron particle accelerator, though less powerful than the LHC, is also engaged in the hunt for the Higgs.

IN THE DARK

All the matter that we can see in the Universe – planets, stars and galaxies – makes up a minuscule 4% of what is actually out there. The rest is dark energy (which accounts for 73% of the cosmos) and dark matter (23%).

Dark energy cannot be observed directly, but it is responsible for speeding up the expansion of the Universe – a phenomenon that can be detected in astronomical observations.

Artist's impression of dark matter distribution (Nasa/Esa/Richard Massey-Caltech)
Astronomers have mapped dark matter's distribution, but have no idea what it is

Like dark energy, dark matter can only be detected indirectly, as it does not emit or reflect enough light to be seen. But its presence can be inferred through its effects on galaxies and galaxy clusters.

Physicists know virtually nothing about the nature of either dark energy or dark matter. But they can speculate.

According to one idea, dark matter could be made up of "supersymmetric particles" - massive particles that are partners to those already known in the Standard Model.

A leading dark matter candidate is the neutralino, the lightest of these "super-partners". And some theoretical physicists have proposed a link between the Higgs mechanism and dark energy.

MIRROR, MIRROR

Each basic particle of "ordinary" matter has its own anti-particle. Matter and antimatter have the same mass, but opposite electric charge.

For example, a proton has an anti-particle called an anti-proton (a proton with a negative charge). An electron has an anti-particle called a positron (an electron with a positive charge).

In the same way that an ordinary proton and electron can come together to form a hydrogen atom, an anti-proton and a positron can form an atom of anti-hydrogen.

When a particle of ordinary matter meets its anti-particle, the two disappear in a flash, as their mass is transformed into energy.

They are said to "annihilate" one another. But equal amounts of matter and anti-matter must have been produced in the Big Bang.

So why did matter and anti-matter not completely annihilate each another after the birth of the Universe?

Today, we live in a Universe almost entirely composed of ordinary matter. Scientists will use the LHC to investigate why this is, and what happened to all the anti-matter.

DOUBLE TROUBLE

Attempts to unify gravity with the other fundamental forces have come to a startling prediction: that every known particle has a massive "shadow" partner particle.

Atlas wheel (Cern)
Atlas is one of the experiments that could find evidence for supersymmetry

All particles are classified as either fermions or bosons. A particle in one class has superpartner in the other class, "balancing the books" and doubling the number of particles in the Standard Model.

For example, the superpartner of an electron (a fermion) is called a selectron (a boson). Evidence for supersymmetry would enable the "unification" of three fundamental forces - the strong, weak, and electromagnetic – helping to explain why particles have the masses they have.

It would also give a boost to string theory – one stab at a grand "theory of everything". But string theory is not dependent on discovering evidence for supersymmetry.

OTHER DIMENSIONS
In addition to the four dimensions we already know about, string theory predicts the existence of six more.

Some physicists even think the existence of these extra dimensions could explain why gravity is so much weaker than the other fundamental forces. Perhaps, they argue, we are not feeling its full effects.

This might be explained if its force was being shared with other dimensions. If these extra dimensions do exist, the LHC could be the first accelerator to detect them experimentally.

At high energies, physicists could see evidence of particles moving between our world and these unseen realms. For example, they could see particles suddenly disappear into one of these dimensions.

Alternatively, particles originating from an extra dimension could suddenly appear in our world.

THE HOLE TRUTH

According to some physicists, the LHC can operate at high enough energies to generate mini-black holes.

However, the vast majority of particle physicists say there is no need for alarm. If any should be created, they should evaporate quickly.

How a black hole might look if it is generated in the collider (Atlas)
How a black hole might look if it is generated in the collider
A recent report dealing with the collider's safety acknowledged the possibility that the LHC could create these primordial black holes.

The report says: "If microscopic black holes were to be singly produced by colliding the quarks and gluons inside protons, they would also be able to decay into the same types of particles that produced them.”

The suggestion that black holes could be made in the LHC has stoked fears that one of these micro-black holes could swell in size, swallowing up the Earth.

In March, plaintiffs requested an injunction in a US court stopping the LHC from switching on.

However, physicists stress that any such phenomena would be short-lived and thus would pose no threat to our planet.

'Big Bang' experiment starts well

My daughter and I sat in the car today spellbound listening to Andrew Marr on the Today programme on Radio 4. At 8.30am today the LHC experiments started in earnest with the first protons being fired around the LHC.

More from Today programme

By Paul Rincon
Science reporter, BBC News

CMS (Cern/M. Hoch)
The LHC has been in construction for some 13 years

Scientists have hailed a successful switch-on for an enormous experiment which will recreate the conditions a few moments after the Big Bang.

They have now fired two beams of particles called protons around the 27km-long tunnel which houses the Large Hadron Collider (LHC).

The £5bn machine on the Swiss-French border is designed to smash protons together with cataclysmic force.

Scientists hope it will shed light on fundamental questions in physics.

The first - clockwise - beam completed its first circuit of the underground tunnel at just before 0930 BST. The second - anti-clockwise - beam successfully circled the ring after 1400 BST.

We will be looking at what the Universe was made of billionths of a second after the Big Bang
Dr Tara Shears, University of Liverpool

The beams have not yet been run continuously. So far, they have been stopped, or "dumped", after just a few circuits.

By Wednesday evening, engineers hope to inject clockwise and anti-clockwise protons again, but this time they will "close the orbit", letting the beams run continuously for a few seconds each.

Cern has not yet announced when it plans to carry out the first collisions, but the BBC understands that low-energy collisions could happen in the next few days. This will allow engineers to calibrate instruments, but will not produce data of scientific interest.

"There it is," project leader Lyn Evans said when the beam completed its lap. There were cheers in the control room when engineers heard of the successful test.

Montage of key moments from switch-on

He added later: "We had a very good start-up."

The LHC is arguably the most complicated and ambitious experiment ever built; the project has been hit by cost overruns, equipment trouble and construction problems. The switch-on itself is two years late.

The collider is operated by the European Organization for Nuclear Research - better known by its French acronym Cern.

The vast circular tunnel - the "ring" - which runs under the French-Swiss border contains more than 1,000 cylindrical magnets arranged end-to-end.

The magnets are there to steer the beam - made up of particles called protons - around this 27km-long ring.

Infographic

Eventually, two proton beams will be steered in opposite directions around the LHC at close to the speed of light, completing about 11,000 laps each second.

At allotted points around the tunnel, the beams will cross paths, smashing together near four massive "detectors" that monitor the collisions for interesting events.

Scientists are hoping that new sub-atomic particles will emerge, revealing fundamental insights into the nature of the cosmos.

Major effort

"We will be able to see deeper into matter than ever before," said Dr Tara Shears, a particle physicist at the University of Liverpool.

"We will be looking at what the Universe was made of billionths of a second after the Big Bang. That is amazing, that really is fantastic."

The LHC should answer one very simple question: What is mass?

LHC DETECTORS

ATLAS - one of two so-called general purpose detectors. Atlas will be used to look for signs of new physics, including the origins of mass and extra dimensions

CMS - the second general purpose detector will, like ATLAS, hunt for the Higgs boson and look for clues to the nature of dark matter

ALICE - will study a "liquid" form of matter called quark-gluon plasma that existed shortly after the Big Bang

LHCb - Equal amounts of matter and anti-matter were created in the Big Bang. LHCb will try to investigate what happened to the "missing" anti-matter

"We know the answer will be found at the LHC," said Jim Virdee, a particle physicist at Imperial College London.

The currently favoured model involves a particle called the Higgs boson - dubbed the "God Particle". According to the theory, particles acquire their mass through interactions with an all-pervading field carried by the Higgs.

The latest astronomical observations suggest ordinary matter - such as the galaxies, gas, stars and planets - makes up just 4% of the Universe.

The rest is dark matter (23%) and dark energy (73%). Physicists think the LHC could provide clues about the nature of this mysterious "stuff".

But Professor Virdee told BBC News: "Nature can surprise us... we have to be ready to detect anything it throws at us."

Full beam ahead

Engineers injected the first low-intensity proton beams into the LHC in August. But they did not go all the way around the ring.

Technicians had to be on the lookout for potential problems.

Steve Myers, head of the accelerator and beam department, said: "There are on the order of 2,000 magnetic circuits in the machine. This means there are 2,000 power supplies which generate the current which flows in the coils of the magnets."

If there was a fault with any of these, he said, it would have stopped the beams. They were also wary of obstacles in the beam pipe which could prevent the protons from completing their first circuit.

Superconducting magnet (Cern/M. Brice)
Superconducting magnets are cooled down using liquid helium

Mr Myers has experience of the latter problem. While working on the LHC's predecessor, a machine called the Large-Electron Positron Collider, engineers found two beer bottles wedged into the beam pipe - a deliberate, one-off act of sabotage.

The culprits - who were drinking a particular brand that advertising once claimed would "refresh the parts other beers cannot reach" - were never found.

In order to get both beams to circulate continuously around the LHC, engineers have to "close the orbit". The beams themselves are made up of several "packets" - each about a metre long - containing billions of protons.

HAVE YOUR SAY
I think it is disgraceful that huge sums of cash have been spent on this project
Robert, Spain

The protons would disperse if left to their own devices, so engineers use electrical forces to "grab" them, keeping the particles tightly huddled in packets.

Once the beams are captured, the same system of electrical forces is used to give the particles an energetic kick, accelerating them to greater and greater speeds.

Long haul

The idea of the Large Hadron Collider emerged in the early 1980s. The project was eventually approved in 1996 at a cost of 2.6bn Swiss Francs, which amounts to about £1.3bn at present exchange rates.

However, Cern underestimated equipment and engineering costs when it set out its original budget, plunging the lab into a cash crisis.

FROM THE TODAY PROGRAMME

Cern had to borrow hundreds of millions of euros in bank loans to get the LHC completed. The current price is nearly four times that originally envisaged.

During winter, the LHC will be shut down, allowing equipment to be fine-tuned for collisions at full energy.

"What's so exciting is that we haven't had a large new facility starting up for years," explained Dr Shears.

"Our experiments are so huge, so complex and so expensive that they don't come along very often. When they do, we get all the physics out of them that we can."

Engineers celebrated the success with champagne, but a certain brand of beer was not on the menu.

Paul.Rincon-INTERNET@bbc.co.uk

Tuesday, September 9, 2008

The LHC's dress rehearsal goes with a hitch.

  • Tom Feilden
  • Tue 9 Sep 08, 03:09 PM
  • Source: BBC
The LHC's dress rehearsal goes with a hitch.

Things are hotting up in the main control room here at Cern. We've just been through a full dress rehearsal for the big "switch on" of the Large Hadron Collider - due to take place at 8.30 tomorrow morning.
I watched on a giant computer screen alongside dozens of scientists and technicians as a beam of protons was fired down a linear accelerator, slung round two synchotrons to pick up energy, and finally dumped at the gates of the LHC.
Tomorrow those gates will be open, and - if all goes well - the first proton beam will shoot clockwise round all 27 kilometres of the LHC at very nearly the speed of light.
But it could have been very different. Last night a component on one of the cryogenics units - which cool the core of the machine to minus 271 degrees - snapped, and two sections of the LHC began to warm up again.
"It's just a little piece of wire about six inches long," operations group leader Paul Collier told me.
"But it just goes to show what can go wrong with a machine of this size and complexity."
The problem has now been fixed, and the temperature in both sections is falling back towards absolute zero. "Fingers crossed," Paul Collier says. "We're still on course for tomorrow. But if it happens again now we'll be in a lot of trouble".
But after all, something should go wrong in a dress rehearsal if it's going to be all right on the night...

Monday, September 8, 2008

The Big Bang Machine

Professor Brian Cox visits Geneva to take a look around Cern's Large Hadron Collider before this vast, 27km long machine is sealed-off and the experiment to create the simulation of a black hole begins. 

When it's up and running, it will be capable of creating the conditions that existed just a billionth of a second after the Big Bang. Brian joins the scientists who hope that the LHC will change our understanding of the early universe and solve some of its mysteries.
Broadcast on:
BBC Four, 9:00pm Thursday 4th September
Duration:
60 minutes
Available until:
9:59pm Thursday 11th September

Big Bang Day: Five Particles: The Electron

Simon Singh examines the significance of subatomic particles.

British physicist JJ Thompson's experiments with electric currents showed that atoms are divisible into elementary particles. But how has the power of electrons been harnessed for everyday use?
Broadcast on:
BBC Radio 4, 3:45pm Monday 8th September
Duration:
15 minutes
Available until:
4:02pm Monday 15th September

Sunday, September 7, 2008

Saturday, September 6, 2008

Mysteries of the Universe will be solved, starting next Wednesday

Source: The Times.

Beneath the foothills of the Jura mountains, in a network of tunnels that bring to mind the lair of a crazed Bond villain, scientists will fire a first beam of particles around a ring as long as the Circle Line on the London Underground. This colossal circuit, 17 miles (27km) in circumference,

In the years ahead it will recreate the high-energy conditions that existed one trillionth of a second after the big bang. In doing so, it should solve many of the most enduring mysteries of the Universe.

This extraordinary feat of engineering will accelerate two streams of protons to within 99.9999991 per cent of the speed of light, so that they complete 11,245 17-mile laps in a single second. The two streams will collide, at four points, with the energy of two aircraft carriers sailing into each other at 11 knots, inside detectors so vast that one is housed in a cavern that could enclose the nave of Westminster Abbey.

The mountains of data produced will shed light on some of the toughest questions in physics. The origin of mass, the workings of gravity, the existence of extra dimensions and the nature of the 95 per cent of the Universe that cannot be seen will all be examined. Perhaps the biggest prize of all is the “God particle” – the Higgs boson.

“What we find honestly depends on what’s there,” said Brian Cox, of the University of Manchester, an investigator on one of the four detectors, named Atlas. “I don’t believe there’s ever been a machine like this, that’s guaranteed to deliver. We know it will discover exciting things. We just don’t know what they are yet.”

“The beam is 2mm in diameter and has to be threaded into a vacuum pipe the size of a 50p piece around a 27km loop,” said Lyn Evans, the LHC’s project manager, who will oversee the insertion. “It is not going to be trivial.”