Physics Articles - 2

Scientists Hold Light Particles Captive

January 19, 2001 - Reuters

It may be impossible to grasp a sunbeam, but physicists said on Thursday they had managed to capture light, play with it a while, and then let it go.

They said their achievement could speed the development of quantum computers, which would calculate millions of times faster than present-day computers, and inventions that no one has yet dreamed of.

The secret was slowing down atoms of rubidium so they would not absorb the photons, as atoms usually do, the team at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts said.

Instead, they report in the Jan. 29 issue of Physical Review Letters, the atoms change their magnetic spin just slightly -- a change that allows them to store information from the photons. Hitting the cloud of hot rubidium gas with another laser pulse releases the first pulse, they said.

Usually, when a photon hits an atom -- even an atom in a highly reflective mirror -- it gets absorbed and heats up the atom, putting it into what physicists call a higher energy state.

``Here, the light pulse does get dimmer and dimmer and slower and slower,'' Ben Stein, a spokesman for the American Institute of Physics, said in a telephone interview.

``The light does disappear but instead of getting absorbed in the usual way as it heats up atoms, it goes to storing its information in the atoms in the form of something called spin.''

This little change could work just like the switches in computers. ``You could store zeros and ones just like they are stored in computers,'' Stein said. But it would happen much faster and, using the sometimes weird laws of quantum mechanics, one photon could have more than one ``on-off'' position at the same time.

Ultra-Fast Quantum Computers

This property could be used to make ultra-fast quantum computers.

Even better, the physicists were able to get the light back out of the rubidium.

``Later on, you can shine another light pulse which coaxes the atoms into spitting out the original light wave,'' Stein said. ``The beam of light will come out again.''

Stein said the applications, beyond the use of light in a quantum computer, are not clear. But the same was true of lasers when they were first invented.

``No one foresaw their use in supermarket scanners and so on,'' he said.

In a second paper, to be published in next week's issue of the journal Nature, Lene Hau and colleagues at the Harvard/Rowland Institute of Science said they had done a similar experiment using ultra-cold gas.

They used sodium atoms for their experiment, and were also able to store the light and get it back out again.

``We believe that this system could be used for quantum information transfer,'' they wrote in their report.

Light travels in packages called photons, which have properties resembling both waves and particles. In nature it moves at 186,000 miles (300,000 km) per second, the fastest speed possible according to Einstein's theories.

BBC Story

Higgs Boson

Scientists Think They've Glimpsed the 'God Particle'

November 5, 2000 - CERN - Geneva

Matter: If a Higgs boson has left tracks in an accelerator, it opens a 'whole new world' for physicists.

For more than 20 years, scientists around the world have been searching for an invisible particle that determines the basic properties of matter.

The particle, called a Higgs boson, is thought to be a vibrating chunk of the unseen vacuum that underlies everything in the universe.

Today, physicists at the European laboratory CERN are set to announce what they believe is the first glimpse of the Higgs boson.

The evidence is by no means conclusive. However, the discovery is considered critical to physics--not only concluding one chapter but also opening the door to another completely undiscovered realm.

"The Higgs is not just a particle,' said CERN theorist John March-Russell. "It means there's this whole new world out there."

Once physicists understand this pervasive, unseen influence, they will be able to answer a question so fundamental that ancient thinkers probably never even dared to ask it: "Why does matter have mass?"

Said Princeton experimentalist Chris Tully: "I think it will eventually be hailed as one of the greatest achievements you can make in science."

The vacuum of physics gives structure to everything else. Like the strings of an unseen puppeteer, it holds all matter under its influence.

The Higgs field is a fundamental part of this nothingness. It's like water to a fish, an essential ingredient of the universe. And the Higgs boson has enormous consequences: Without this hidden field, all particles would travel at the speed of light. Atoms could not exist.

Possible traces of the long-sought particle were detected during experiments in the 17-mile-around Large Electron Positron collider, or LEP, by crashing atomic particles together at high speeds.

Tracks suggesting the possible presence of the so-far-unseen Higgs have teased CERN physicists with a frustrating succession of appearances and disappearances over the last month.

However, evidence accumulated last week finally convinced the experimenters to request an emergency resuscitation of the aging accelerator.

CERN officials had previously decided to tear down LEP and start construction of a replacement.

"It's a very pleasant emergency," CERN director general Luciano Maiani, who has been a confirmed skeptic, told The Times on Thursday. "Last week changed everything."

The final decision on the fate of the collider will have to await a vote by CERN's 20 member states, probably next week.

However, for the time being, it looks as if the hordes of workers waiting with "blowtorches and axes," as one physicist put it, to dismantle the machine will have to go home.

Skeptics Had a Good Case

Skeptics have been saying for weeks that the hints that surfaced at CERN last month were only wishful thinking--a desperate attempt to claim a prize that almost surely would have gone to the rival Fermilab outside Chicago if CERN's accelerator had shut down.

The skeptics had a good case: Of the four cathedral-sized electronic "eyes" that watch for the Higgs, only one initially saw telltale tracks of the particle. A few weeks later, another detector saw something, only to have the evidence evaporate under later scrutiny.

"Maybe they persuaded themselves that, in spite of the warts, these [tracks] are OK," Chris Quigg of Fermilab said at the time. "But my judgment is, they're going to have a pretty hard time." In a dizzying series of events since mid-October, however, two other detectors at LEP have spied what scientists believe are definite Higgs tracks.

"Among physicists, we believe we have them. But we don't believe we have enough of them" to claim a discovery, said Jason Nielsen, a graduate student from the University of Wisconsin. So, after a week of sleepless nights and tense hallway conversations, Maiani has decided to ask for a reprieve for the collider.

It won't come cheaply. In addition to the $70 million it will cost to pay contractors who were standing by to destroy LEP and build the next machine, the change of plans will take a big toll in careers disrupted and personal plans.

Normally, the physicists would not have gone public with their findings until physics conferences next spring, said a spokesman for the experiment, physicist Tiziano Camporesi. "But by next spring, the detector would be gone." Why all the fuss? If the Higgs had different properties, our universe would be an entirely different kind of place.

Bosons are one type among the almost unimaginably small subatomic particles that, according to theoretical physics, are the ultimate building blocks of the universe.

The Higgs boson, often described as a kind of cosmic molasses, changes the properties of particles that travel through it. It imparts a kind of sluggishness--or mass. Until recently, mass was considered so basic a property of matter that scientists didn't even think to ask where it came from. "It was God-given," Maiani said.

"The fact that human beings can frame the question--much less find the answer--is amazing," Tully said.

How can the physicists see the vacuum? The same way a brick "sees" the Earth when it falls to the floor, or a magnet "sees" metal.

The unseen influence affects the way things move. In fact, the very observation that things have mass confirms that the Higgs exists, physicists say.

To prove their theories, however, they need to set the vacuum vibrating with enough energy to send a chunk of it, in effect, "free." Only that way can they study its properties.

The CERN machine accomplishes that by making two beams of particles collide head-on at enormous energies. Electrons circling in one direction meet their anti-matter counterparts, called positrons, circling in the opposite direction at four intersections along an accelerator ring.

Continuously accelerated as they fly through the ring, the particles cannot exceed the speed of light. Instead, their energy translates directly into mass (according to Einstein's E=mc2 formula). By the time they collide, they have been fattened to 200,000 times their normal "weight."

All that energy goes into mutual annihilation--a burst of pure energy. And out of that ball of energy come new particles. If the physicists at CERN are right, their collisions have produced a so-called Z particle, massive enough to set the vacuum twanging for a tiny fraction of a second and produce the Higgs boson. The exact "pitch" of that twang is the natural frequency of the vacuum. Frequency, in the world of particles, translates directly into energy, which in turn translates into mass.

Things would be simple if either the Z or the Higgs could be seen directly. Alas, both dissolve into other particles before traveling even a few inches at nearly the speed of light

Therefore, the details of the collision must be inferred from the tracks left in the four detectors placed at the intersections of the particle beams. As pieces fly out from the site of the collision, every stray bit is identified, tracked and counted.

Buried in pits hundreds of yards beneath the rolling French and Swiss countryside, the enormous, tinkertoy-like detectors operate in ways surprisingly similar to human eyes: After collecting detailed information on properties of particles that pass through--speed, electric charge, mass and so forth--they make what amount to intelligent "guesses" on what they "see."

At the end, what they have is a carefully measured probability of being right. The process is very much like staring at a strange flickering light in the distance, explained CERN physicist John Ellis. The longer you look, the more certain you can be that you're looking at a planet instead of an airplane.

Tully, who is one of three independent physicists in charge of calculating those probabilities, says the current odds that the CERN Higgs is not real stand at about 3 in 1,000. That may sound good, he said, but to claim a "discovery," CERN would need the probability that the signals were the result of random chance to fall to 5 in 10 million.

That will require staring at the flickering signals for another year. And that, in turn, means running the 11-year-old accelerator well beyond its current capacity. The operations people say they can do that, but it will take its toll: As the accelerator ages, insulation becomes brittle, cooling coils crack, sensitive electronics get destroyed.

And with the Higgs so nearly in sight, it seems a shame to give up--especially with Fermilab potentially so close behind, CERN officials say.

Looking for 'the God Particle'

LEP has been looking for the Higgs since the collider was commissioned in 1989, but the search goes back way before that. The Higgs is considered so important that Nobel laureate Leon Lederman has called it "the god particle." It is the last piece in the so-called "standard model" of particle physics, but paradoxically, "it proves that the standard model is wrong," said Ellis.

For one thing, if the Higgs is where the CERN results suggest it is, it means at the very least that there must be at least one other Higgs, and that they mix together somewhat like oil and water, said CERN's March-Russell. Ellis even made the admittedly "crazy" suggestion in a talk Wednesday at CERN that a lighter Higgs particle may have already been missed by LEP.

But for theorists, the real question is: What lies beyond?

The point, March-Russell said, is to study the structure of this unseen stage on which the universe lives. And that will probably have to await the new accelerator that replaces LEP. Called the Large Hadron Collider, or LHC, it has already been delayed many times for other reasons.

Even if the Higgs really has been discovered, March-Russell--echoing many of his colleagues--stressed that LEP "can only see the shadows. It's only when you go further that you see the structure underneath. I think we're going to start seeing incredible things."

Tracking a Particle

A particle detector at the European accelerator laboratory CERN has seen the best evidence yet for the so-called Higgs boson, a profoundly important particle. The detector is layered like an onion. Each layer measures different properties of the particles. Possible traces of the Higgs particle were detected in the experiment shown below:

* Higgs and Z particles are created during the collision of an electron and a positron. The collision occurs in the center of the small cylinder, which is the innermost tracking chamber of the detector. Both kinds of particles transform into other particles before reaching the boundaries of the small cylinder.

* The force of the collision sends the particles flying out through the small cylinder into the large cylinder, which is another tracking chamber. In the large cylinder, the paths of the particles are bent by strong magnetic fields. The paths of the lightweight particles curl around under the influence of the magnetic field.

* The heaviest particles pass through the small and large chambers without bending their paths, dumping all their energy into another layer of the "onion." The fragments outside the large cylinder represent the areas where the heaviest particles deposit their energy and come to a stop.

Beam smashes light barrier

July 20, 2000 - BBC

Scientists have seen a pulse of light emerge from a cloud of gas before it even entered.

This astonishing and baffling observation was made by researchers from the NEC Research Institute in Princeton, US.

They conducted an experiment that involved lasers, a chamber containing cold caesium atoms and a super-fast stopwatch.

The end result was a beam of light that moved at 300 times the theoretical limit for the speed of light.

It was Einstein who said nothing physical could break this barrier because, among other things, to do so would also mean travelling back in time.

Dramatic demonstration

But the NEC scientists believe their work does not violate Einstein's theory.

Writing in the journal Nature, Dr Lijun Wang and colleagues say their light beam raced through the atom trap so quickly that the leading edge of the pulse's peak actually exited before it had entered.

If this sounds confusing, then do not worry. Many physicists are uncomfortable with it too despite their explanations that it is a natural consequence of the wave nature of light.

Although the work of Dr Wang's team is remarkable, it is not the first time that this sort of "trick" has been performed - but it is certainly the most dramatic demonstration.

Earlier this year, a team of physicists made a microwave beam travel at 7% faster than light speed. Last year, they announced that they had even slowed light down to almost a crawl.

Anomalous refractive index

To achieve their peculiar effect, Dr Wang's group fired laser beams through a trap of caesium atoms.

By adjusting the frequency of the laser beams to match those of the energy levels in the atoms, the researchers were able to achieve an effect called "anomalous refractive index." This boosts the pulses' so-called "group velocity" to a speed faster than what we understand to be the speed of light - just short of 300 million metres per second.

The group velocity of a light pulse depends upon the mixture of frequencies within the pulse and the medium through which it travels. It need not be the speed of the pulse itself.

The important thing, however, is that whilst the group velocity can be manipulated to be faster than the speed of light, it is not possible to use this effect to send information faster than the speed of light.

Because of the fast group velocity, the leading edge of the pulse appears to leave the caesium-filled chamber 62 billionths of a second before it arrives.

Causality principle

And according to Dr Wang, this strange result does not threaten Einstein's theories or violate the causality principle, which states that a cause must precede its effect.

Or so almost all physicists think - for now. Privately, some admit that experiments such as Dr Wang's may force them to reassess some of their most cherished ideas.

Scientists create new state of matter

Such matter has not existed for 15bn years (Cern impression)

February 10, 2000 - BBC

Scientists have created what they describe as a "Little Bang" inside which are the conditions that existed a thousandth of a second after the birth of the Universe in the so-called Big Bang.

In doing so, they have made a form of matter that has not existed for 15 billion years.

It is called a "quark-gluon" soup or plasma. By studying its properties, and the laws it obeys, scientists will gain a fresh insight into the evolution of the Universe during one of its formative phases.

In short, the reason why there are stars, galaxies and indeed planets and people is because of the properties of the quark-gluon plasma.

The breakthrough is the result of several experiments by researchers from 20 countries working on the Heavy Ion programme at the Cern nuclear research centre in Geneva, Switzerland.

The scientists say they have produced compelling evidence for the new state of matter in which quarks, instead of being bound up by gluons into more complex particles such as protons and neutrons, are liberated to roam freely.

Building blocks

It is believed that quarks are one of the fundamental building blocks of matter. In the Universe we know today, the particles come in pairs or threes. But when the Universe was more energetic, in its earliest moments, things were probably different.

Theory predicts that the new state of matter that the scientists have created, in which quarks were single and free to move about, must have existed before the formation of matter as we see it now.

But until Cern's success, such a state of matter has not been confirmed experimentally.

Professor Luciano Maiani, Cern's Director General, said: "The combined data coming from the seven experiments on Cern's Heavy Ion programme have given a clear picture of a new state of matter.

"This result verifies an important prediction of the present theory of fundamental forces between quarks." He added: "It is also an important step forward in the understanding of the early evolution of the Universe. We now have evidence of a new state of matter where quarks and gluons are not confined. There is still an entirely new territory to be explored."

Staggering properties

The crucial data was obtained by colliding ionised lead atoms to create microscopic explosions that although very small have very high concentrations of energy. Such "Little Bangs" have staggering properties, being at a temperature of two million million degrees and 20 times denser than the nucleus of an atom.

These high energies, it was hoped, would break down the forces which confined quarks inside more complex particles.

The tracks produced by particles after a collision

This is what the scientists appear to have witnessed. The high-energy lead ions were crashed into targets inside seven different detectors. The collisions created conditions that have never before been reached in laboratory experiments.

The data from the collisions provides compelling evidence that a new state of matter has been created. It has many of the characteristics of the theoretically-predicted quark-gluon plasma.

The researchers point out that the data from any one of the seven lead ion experiments were not enough to give them the full picture, but the combined results from all experiments do provide the evidence required.

Creating the new state of matter is only a beginning for the Cern researchers. The next step is to study how it behaves at different temperatures and densities. This will allow the scientists to probe key moments in the evolution of the Universe of stars and galaxies from the Universe of quarks and gluons.

Russian scientists add new element to periodic table

July 15, 1999 - AP

Physicists in Russia have created a new, super-heavy element that lasted a surprisingly long 30 seconds before disintegrating, according to a report in Thursday's issue of the journal Nature. Using an atom smasher to bombard plutonium with calcium ions, the physicists created an element with an atomic weight of 114.

The newest addition to the periodic table has yet to be named.

Ninety-four elements exist in nature. Scientists have spent 60 years creating elements in the lab, registering 21 so far. But some of the more recent elements were so unstable that they disintegrated in milliseconds.

For decades, physicists have theorized the existence of super-heavy manmade elements with a much longer life. These elements would make up an "island of stability."

In the study, researchers at the Joint Institute for Nuclear Research in Dubna, Russia, reported creating two atoms of element 114 that lasted for as long as 30 seconds before flickering out. This, they say, is proof the island exists.

The discovery, and more recent creations of even heavier elements, have no practical applications as far as today's scientists know.

But for academics, it's thrilling. The study of super-heavies could shed light on supernovas and origins of the universe. And chemists are interested in how they bond with compounds.

The new manmade elements are numbered according to how many protons are in their nuclei, not by their order of discovery. Numbers 95 through 112 were created between 1944 and 1996. In the past year, scientists have created not just 114, but also 116 and 118. The ones in between have not yet been created.

For decades, scientists thought one isotope, or version, of element 114 - with 114 protons and 184 neutrons - would be very stable because its nucleus would have a full complement of neutrons and protons. No more could be squeezed inside.

Late last year, the Dubna scientists made an isotope of element 114 with 175 neutrons. In March, the lab created another 114 isotope, but it had only 173 neutrons and was therefore less stable than the first one they created.

This year, another major lab trying to create elements, Lawrence Berkeley National Laboratory in California, forged the heaviest element yet, 118, and when it decayed, it morphed into element 116, then an isotope of 114 with even fewer neutrons than Dubna's. It lasted for milliseconds.

These three types of 114 are just off the "island of stability," scientists say, because they are all short of the 184 neutrons needed. But physicists say they are in "shallow water," and that's proof enough.

If they can create a 114 isotope with 184 neutrons, they would reach real stability: perhaps a life measured in years.

One physicist, Albert Ghiorso of Lawrence Berkeley, said he is skeptical the Russians really did create such an element. He said that with their setup, it is too difficult to pinpoint a single atom among all the collision byproducts.

But Neil Rowley, of the Institute for Subatomic Research in France, is convinced the Dubna observations are real. "Everything behaves the way it ought to," he said.

Physicists Succeed In Creating New Ultra-Heavy Element

February 1, 1999 - Discovery

Russian and American nuclear physicists say they've created a new ultra-heavy element that may open the door to a host of new elements once considered impossible.

If confirmed, it would mark a major goal of nuclear physics: to create an element far heavier than any in nature that would survive for long enough to permit scientific study, the New York Times reports in Friday's edition.

The journal Science published a brief account of the work Friday.

The as-yet-unnamed element was created at the Joint Institute for Nuclear Research at Dubna, Russia, under Yuri Oganessian, a nuclear physicist.

The American participants in the experiment, from Lawrence Livermore National Laboratory in California, say that even though the news is slightly premature -- the results haven't yet been formally published -- the evidence for the creation of the element was very strong.

It appears, they say, that scientists bombarded a rare isotope, or form, of plutonium with atoms of a rare isotope of calcium to create a single atom of the new element.

The nucleus of a calcium projectile atom fused with the nucleus of a target plutonium atom to form an element with 114 protons and about 184 neutrons in its nucleus. The resulting atom of Element 114 survived for about 30 seconds, they say, a long time co mpared with the decay rates of most other heavy man-made elements.

Of the 92 elements in the basic periodic table, all but two, technetium and promethium, are found in nature. Hydrogen is the lightest on the table, with only one proton in its nucleus, and uranium, with 92 protons, is the heaviest.

With the exception of a tiny amount of natural plutonium, all elements with proton numbers greater than 92 must be created. With Element 114, 21 artificial elements were made.

Albert Ghiorso of Lawrence Berkeley National Laboratory in Calif., co-creator of 12 artificial elements beyond uranium, says, "It's one of the greatest achievements in physics."

Energy Secretary Bill Richardson, who is in charge of national physics labs, says, "If confirmed, the synthesis of Element 114 will create an important new opportunity to study the physics of extremely heavy elements."