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Con-CERNs About the Large Hadron Collider

06/08/2008 06:58PM

Con-CERNs About the Large Hadron Collider
The European Center for Nuclear Research (CERN) is just weeks away from firing up the Large Hadron Collider (LHC). LHC is the latest and most powerful in a series of particle accelerators that, over the last 70 years, have allowed researchers to penetrate deeper and deeper into the heart of matter and further and further back in time. The next steps in the journey will bring new knowledge about the beginning of our Universe and how it works, as the LHC recreates, on a micro-scale, conditions that existed billionths of a second after the birth of our Universe.

This is the most powerful particle collider ever created and it will accelerate trillions of heavy lead particles to almost the speed of light and then smash them together head on. These head-on collisions will create an enormous concentrated energy of 1,150 TeV, (Trillion electronVolts), or 1.15 Quadrillion electronVolts of energy. This is expected to create conditions that haven’t existed since the big bang. Many scientists and researchers are excited about the possible new discoveries that will result from this experiment. Others are concerned that this is a very dangerous experiment because at this energy almost all we know is based on theories and some of these theories predict that when hadrons smash together at such a high energy, the conversion of energy to mass could create miniature black holes or a theorized exotic form of matter called Strangelets.

The LHC is, as the name suggests, a large collider of hadrons. Hadrons are atomic particles made of quarks. One example of a hadron is the proton, a particle found in every atomic nucleus. Protons contain 3 quarks of two different types (2 ‘up’ quarks and 1 ‘down’ quark). The neutron is the other particle commonly found in atomic nuclei, these are also hadrons and are made up of 1 ‘up’ and 2 ‘down’ quarks.

LHC refers to the collider -- a machine that deserves to be labelled ‘large’ not only because it weighs more than 38,000 tons, but because it runs for 27km (16.5m) in a circular tunnel 100 meters beneath the Swiss/French border near Geneva. The LHC will allow scientists to probe deeper into the heart of matter and further back in time than has been possible using previous colliders.

The LHC was built to help scientists to answer key unresolved questions in particle physics. The unprecedented energy it achieves may even reveal some unexpected results that no one has ever thought of.

For the past few decades, physicists have been able to describe with increasing detail the fundamental particles that make up the Universe and the interactions between them. This understanding is encapsulated in the Standard Model of particle physics, but it contains gaps and cannot tell us the whole story. To fill in the missing knowledge requires experimental data, and the next big step to achieving this is with LHC.

Researchers think that the Universe originated in the Big Bang (an unimaginably violent explosion) and since then the Universe has been cooling down and becoming less energetic. Very early in the cooling process, the matter and forces that make up our world ‘condensed’ out of this ball of energy.

The LHC will produce tiny patches of very high energy by colliding together atomic particles that are travelling at very high speed. The more energy produced in the collisions the further back we can look towards the very high energies that existed early in the evolution of the Universe. Collisions in the LHC will have up to 7x the energy of those produced in previous machines; recreating energies and conditions that existed billionths of a second after the start of the Big Bang.

The results from the LHC are not completely predictable as the experiments are testing ideas that are at the frontiers of our knowledge and understanding. Researchers expect to confirm predictions made on the basis of what we know from previous experiments and theories. However, part of the excitement of the LHC project is that it may uncover new facts about matter and the origins of the Universe.

One of the most interesting theories the LHC will test was put forward by the UK physicist Peter Higgs, among others. The different types of fundamental particles that make up matter have very different masses, while the particles that make up light (photons) have no mass at all.

Higgs’ theory is one explanation of why this is so and the LHC will allow us to test the theory.
The LHC accelerates two beams of atomic particles in opposite directions around the 27km collider. When the particle beams reach their maximum speed, the LHC allows them to ‘collide’ at 4 points on their circular journey.

Thousands of new particles are produced when particles collide and detectors, placed around the collision points, allow scientists to identify these new particles by tracking their behavior.

The detectors are able to follow the millions of collisions and the new particles produced every second and identify the distinctive behavior of interesting new particles from among the many thousands that are of little interest.

As the energy produced in the collisions increases, researchers are able to peer deeper into the fundamental structure of the Universe and further back in its history. In these extreme conditions unknown atomic particles may appear.

What is mass?

What is the origin of mass? Why do tiny particles weigh the amount they do? Why do some particles have no mass at all? At present, there are no established answers to these questions. The most likely explanation may be found in the Higgs boson, a key undiscovered particle that is essential for the Standard Model to work. First hypothesized in 1964, it has yet to be observed.

What is 96% of the universe made of?

Everything we see in the Universe is made up of ordinary particles. These are collectively referred to as matter, forming 4% of the Universe. Dark matter and dark energy are believed to make up the remaining proportion, but they are incredibly difficult to detect and study, other than through the gravitational forces they exert. Investigating the nature of dark matter and dark energy is one of the biggest challenges today in the fields of particle physics and cosmology.

Why is there no more antimatter?

We live in a world of matter – everything in the Universe, including ourselves, is made of matter. Antimatter is like a twin version of matter, but with opposite electric charge. At the birth of the Universe, equal amounts of matter and antimatter should have been produced in the Big Bang. But when matter and antimatter particles meet, they annihilate each other, transforming into energy. Somehow, a tiny fraction of matter must have survived to form the Universe we live in today, with hardly any antimatter left. Why does Nature appear to have this bias for matter over antimatter?

What was matter like within the first second of the Universe’s life?

Matter, from which everything in the Universe is made, is believed to have originated from a dense and hot cocktail of fundamental particles. Today, the ordinary matter of the Universe is made of atoms, which contain a nucleus composed of protons and neutrons, which in turn are made quarks bound together by other particles called gluons. The bond is very strong, but in the very early Universe conditions would have been too hot and energetic for the gluons to hold the quarks together. Instead, it seems likely that during the first microseconds after the Big Bang the Universe would have contained a very hot and dense mixture of quarks and gluons called quark–gluon plasma.

Do extra dimensions of space really exist?

Einstein showed that the three dimensions of space are related to time. Subsequent theories propose that further hidden dimensions of space may exist; for example, string theory implies that there are additional spatial dimensions yet to be observed. These may become detectable at very high energies, so data from all the detectors will be carefully analyzed to look for signs of extra dimensions.

The Large Hadron Collider (LHC) can achieve energies that no other particle accelerators have reached before. The energy of its particle collisions has previously only been found in Nature. And it is only by using such a powerful machine that physicists can probe deeper into the key mysteries of the Universe. Some people have expressed concerns about the safety of whatever may be created in high-energy particle collisions. However CERN believes that there are no reasons for concern.

Accelerators recreate the natural phenomena of cosmic rays under controlled laboratory conditions. Cosmic rays are particles produced in outer space in events such as supernovae or the formation of black holes, during which they can be accelerated to energies far exceeding those of the LHC. Cosmic rays travel throughout the Universe, and have been bombarding the Earth's atmosphere continually since its formation 4.5 billion years ago. Despite the impressive power of the LHC in comparison with other accelerators, the energies produced in its collisions are greatly exceeded by those found in some cosmic rays. Since the much higher-energy collisions provided by Nature for billions of years have not harmed the Earth, CERN believes that there is no reason to think that any phenomenon produced by the LHC will do so.

The total energy in each beam of protons in the LHC is equivalent to a 400 ton train travelling at 150 km/h. However, only an infinitesimal part of this energy is released in each particle collision – according to CERN, roughly equivalent to the energy of a dozen flying mosquitoes. In fact, whenever you try to swat a mosquito by clapping your hands together, you create a energy much higher than the protons inside the LHC. The LHC's specialty is its impressive ability to concentrate this collision energy into a minuscule area on a subatomic scale. But even this capability is just a pale shadow of what Nature achieves routinely in cosmic-ray collisions.

During part of its operation, the LHC will collide beams of lead nuclei, which have greater collision energy, equivalent to just over a thousand mosquitoes. However, this will be much more spread out than the energy produced in the proton collisions, and according to CERN also presents no risk.

Is there Danger from the Creation of Microscopic Black Holes on Earth?

Massive black holes are created in the Universe by the collapse of massive stars, which contain enormous amounts of gravitational energy that pulls in surrounding matter. The gravitational pull of a black hole is related to the amount of matter or energy it contains – the less there is, the weaker the pull. Some physicists suggest that microscopic black holes could be produced in the collisions at the LHC. However, these would only be created with the energies of the colliding particles, so CEREN believes that no microscopic black holes produced inside the LHC could generate a strong enough gravitational force to pull in surrounding matter.

If the LHC can produce microscopic black holes, CERN believes that cosmic rays of much higher energies would already have produced many more. Since the Earth is still here, CERN states that there is no reason to believe that collisions inside the LHC are harmful.

Black holes lose matter through the emission of energy via a process originally theorized by Stephen Hawking. CERN believes that any black hole that cannot attract matter, such as those that might be produced at the LHC, will shrink, evaporate, and disappear. The smaller the black hole, the faster it will vanish. If microscopic black holes were to be found at the LHC, CERN believes that they would exist only for a fleeting moment. They would be so short-lived that the only way they could be detected would be by detecting the products of their decay.

Is there Danger from the Creation of Strangelets on Earth?

Strangelets are hypothetical small pieces of matter whose existence has never been proven. They would be made of 'strange quarks' – heavier and unstable relatives of the basic quarks that make up stable matter. Even if strangelets do exist, CERN believes that they would be unstable. Furthermore, their electromagnetic charge should repel normal matter, and instead of combining with stable substances, CERN believes that they would simply decay. If strangelets were produced at the LHC, CERN believes that they would not wreak havoc. If they exist, CERN believes they would already have been created by high-energy cosmic rays, with no harmful consequences.

Other scientists are not so sure. Any amount of matter, if crushed in upon itself, can theoretically form a black-hole -- a very small one if only a small amount of matter is crushed. Some theories suggested that miniature black holes might have been formed in the earliest history of the Universe. Other theories suggest that particle colliders, by crushing two atoms together at tremendous speed, might create a miniature black hole of very tiny dimension.

Stephen Hawking in the early 1970s theorized that such miniature black holes were once in great abundance, but later “evaporated” by a quantum tunneling process, so that such miniature black holes no longer exist in our Universe. This process, according to Stephen Hawking, would possibly cause a black hole to evaporate.

If virtual particles are produced in the vicinity of a black hole, it might be possible for one member of the matter-antimatter pair to be pulled into the black hole while the other escapes into space. The particle that would fall into the black hole would negate some of its mass and so the black hole would shrink a little. This would make it look as if the particle that escaped into space had come from the black hole.

Hawking radiation would be particularly important in the case of miniature black holes, which might explode in this way. Black holes of very low mass, such as would be created in particle colliders, would have masses of about 10,000,000 atomic mass units (the mass of one proton), and lifetimes of about 1x10 ^-23 seconds, if Hawking Radiation works as predicted. However, Hawking Radiation has never been experimentally detected, and exists only in theory and that is what concerns some physicists.

In theory, a miniature black hole created at rest relative to Earth is considerably different that one created by high-energy cosmic rays striking the Earth. If such high energy cosmic rays were to on occasion create a miniature black hole, as some theories have suggested, it would be traveling at very high speed (99.99% the speed of light) relative to Earth, and much like a neutrino, simply zip right through Earth in 1/4 second without interacting, or if it did interact, it would pull in a few quarks and barely slow.

Conversely, any miniature black hole created at rest in a collider would essentially be trapped in Earth’s gravitational field, and over seconds to hours, slowly interact and acquire more mass if Hawking radiation does not work as predicted. In that case, the miniature black hole would not “evaporate,” but remain trapped on or in the Earth. That is a concern to some physicists.

Another concern involves an exotic form of matter referred to as Strangelets, a theoretical form of matter that might exist in nature. Under some theories, Strangelets are a more stable form of nuclear matter, when compared to our normal form of nuclear matter that is formed of up and down quarks combined into protons and neutrons.

Under these theories, an equal number of up, down, and strange quarks would form a slightly more stable form (with slightly less mass) and more stable than the Iron nucleus, the most stable form of normal nuclear matter. This is more stable form of matter is referred to as strange matter, or Strange Quark Matter (SQM). Unlike normal matter, in which increasing the number of protons and neutrons beyond the 56 present in Iron increases the coulombic repulsion and de-stabilizes the nucleus, no such repulsion would exist in Strange Quark Matter, and the larger the nucleus, the more stable the SQM nucleus becomes. A very small chunk of SQM is called a Strangelet. This SQM could be either slightly positive, or slightly negative, or neutral, under various theories.

Strangelets are also theorized to be creatable in colliders if two large atoms, such as two lead atoms, are collided. In nature, such large atoms do not collide at LHC energies. Instead, high-energy incoming cosmic rays are believed to be single protons, which would likely plow right through a large nucleus. Also, as is true for miniature black holes, if natural Strangelets are neutral they would simply pass through Earth like a neutrino at high speed if created by cosmic rays. If created instead at rest relative to the Earth in a collider however, they could be trapped by Earth’s gravitational field, and potentially be able to interact with normal matter, acquire quarks, and grow larger.

Cosmologists have theorized that so-called “Neutron Stars” form from collapsed stars in which the electrons and protons of a massive collapsed star, not quite large enough to form a black hole, combine together to from neutrons, so the entire star becomes a massive single nucleus of nothing but neutrons. Most theories about such neutron stars now show that they would more likely form into SQM. These stars are now starting to be referred to as “Strange Stars” instead of “Neutron Stars.”

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