Defining Higgs-Boson: The Celestial Mechanics of The God Particle...

"There are children playing in the streets who could solve some of my top problems in physics, because they have modes of sensory perception that I lost long ago."

-J. Robert Oppenheimer

The Higgs Mechanism:

"Imagine a cocktail party of political party workers who are uniformly distributed across the floor, all talking to their nearest neighbours. The ex-Prime Minister enters and crosses the room. All of the workers in her neighbourhood are strongly attracted to her and cluster round her. As she moves she attracts the people she comes close to, while the ones she has left return to their even spacing. Because of the knot of people always clustered around her she acquires a greater mass than normal, that is she has more momentum for the same speed of movement across the room. Once moving she is hard to stop, and once stopped she is harder to get moving again because the clustering process has to be restarted.

In three dimensions, and with the complications of relativity, this is the Higgs mechanism. In order to give particles mass, a background field is invented which becomes locally distorted whenever a particle moves through it. The distortion - the clustering of the field around the particle - generates the particle's mass. The idea comes directly from the physics of solids. Instead of a field spread throughout all space a solid contains a lattice of positively charged crystal atoms. When an electron moves through the lattice the atoms are attracted to it, causing the electron's effective mass to be as much as 40 times bigger than the mass of a free electron.

The postulated Higgs field in the vacuum is a sort of hypothetical lattice which fills our Universe. We need it because otherwise we cannot explain why the Z and W particles which carry the weak interactions are so heavy while the photon which carries electromagnetic forces is massless.

The Higgs Boson aka The God Particle:

Now consider a rumour passing through our room full of uniformly spread political workers. Those near the door hear of it first and cluster together to get the details, then they turn and move closer to their next neighbours who want to know about it too. A wave of clustering passes through the room. It may spread to all the corners or it may form a compact bunch which carries the news along a line of workers from the door to some dignitary at the other side of the room. Since the information is carried by clusters of people, and since it was clustering that gave extra mass to the ex-Prime Minister, then the rumour-carrying clusters also have mass.

The Higgs boson is predicted to be just such a clustering in the Higgs field. We will find it much easier to believe that the field exists, and that the mechanism for giving other particles is true, if we actually see the Higgs particle itself. Again, there are analogies in the physics of solids. A crystal lattice can carry waves of clustering without needing an electron to move and attract the atoms. These waves can behave as if they are particles. They are called phonons and they too are bosons. There could be a Higgs mechanism, and a Higgs field throughout our Universe, without there being a Higgs boson."

"I maintain that the cosmic religious feeling is the strongest and noblest motive for scientific research. Only those who realize the immense efforts and, above all, the devotion without which pioneer work in theoretical science cannot be achieved are able to grasp the strength of the emotion out of which alone such work, remote as it is from the immediate realities of life, can issue. What a deep conviction of the rationality of the universe and what a yearning to understand, were it but a feeble reflection of the mind revealed in this world, Kepler and Newton must have had to enable them to spend years of solitary labor in disentangling the principles of celestial mechanics." -Albert Einstein (New York Times Magazine, 11.9.1930).

- David Miller ( Article: "Politics, Solid State and the Higgs," Dept of Physics and Astronomy, University College, UK, 2000s. Image: -Woman as Higgs Mechanism, 1930s).

The Dark Matters: Colliding & Annihilating In Space...

"Is this the dark side speaking?

A concatenation of puzzling results from an alphabet soup of satellites and experiments has led a growing number of astronomers and physicists to suspect that they are getting signals from a shadow universe of dark matter that makes up a quarter of creation but has eluded direct detection until now. Maybe...

“Nobody really knows what’s going on,” said Gordon Kane, a theorist at the University of Michigan. Physicists caution that there could still be a relatively simple astronomical explanation for the recent observations. But the nature of this dark matter is one of the burning issues of science. Identifying it would point the way to a deeper understanding of the laws of nature and the Einsteinian dream of a unified theory of physics.

The last few weeks have seen a blizzard of papers trying to explain the observations in terms of things like “minimal dark matter” or “exciting dark matter,” or “hidden valley” theory, and to suggest how to look for them in particle accelerators like the Large Hadron Collider, set to begin operation again outside Geneva next summer. “It could be deliriously exciting, an incredibly cool story,” said Nima Arkani-Hamed of the Institute for Advanced Study in Princeton, N.J., who has been churning out papers with his colleagues. “Anomalies in the sky tell you what to look for in the collider.”

On Thursday, a team of astrophysicists working on one of the experiments reported in the journal Nature that a cosmic ray detector onboard a balloon flying around the South Pole had recorded an excess number of high-energy electrons and their antimatter opposites, positrons, sailing through local space. The particles, they conceded, could have been created by a previously undiscovered pulsar, the magnetized spinning remnant of a supernova explosion, blasting nearby space with electric and magnetic fields. But, they say, a better and more enticing explanation for the excess is that the particles are being spit out of the fireballs created by dark matter particles colliding and annihilating one another in space.

“We cannot disprove that the signal could come from an astrophysical object. We also cannot eliminate a dark matter annihilation explanation based upon current data,” said John P. Wefel of Louisiana State University, the leader of the team, adding, “Whichever way it goes, for us it is exciting.”

The results came on the heels of a report earlier this fall from Pamela, a satellite built by Italian, German, Russian and Swedish scientists to study cosmic rays. Pamela scientists reported in talks and a paper posted on the Internet that the satellite had recorded an excess of high-energy positrons. This, they said, “may constitute the first indirect evidence of dark matter particle annihilations,” or a nearby pulsar.

Antimatter is rare in the universe, and so looking for it is a good way of hunting for exotic phenomena like dark matter. Another indication that something funny is happening on the dark side of the universe is evident in maps of the cosmic background radiation left over from the Big Bang. Those maps, produced most recently this year by the Wilkinson Microwave Anisotropy Probe satellite, show a haze of what seem to be charged particles hovering around the Milky Way galaxy, according to an analysis by Douglas Finkbeiner of the Harvard-Smithsonian Center for Astrophysics.

Adding to the mix and mystery, the European Space Agency’s Integral satellite detected gamma rays emanating from the center of the Milky Way, suggesting the presence of positrons there, but with much lower energies than Pamela and Dr. Wefel’s experiments have seen. What all this adds up to, or indeed whether it all adds up to anything at all, depends on which observations you trust and your theoretical presumptions about particle physics and the nature of dark matter. Moreover, efforts to calculate the background level of high-energy particles in the galaxy are beset with messy uncertainties. “The dark matter signal is easy to calculate,” Dr. Kane said. “The background is much harder.”

Dark matter has teased and obsessed astronomers since the 1930s, when the Caltech astronomer Fritz Zwicky deduced that some invisible “missing mass” was required to supply the gravitational glue to hold clusters of galaxies together. The idea became respectable in the 1970s when Vera C. Rubin of the Carnegie Institution of Washington and her collaborators found from studying the motions of stars that most galaxies seemed to be surrounded by halos of dark matter.

The stakes for dark matter go beyond cosmology. The most favored candidates for its identity come from a theory called supersymmetry, which unifies three of the four known forces of nature mathematically and posits the existence of a realm of as-yet-undiscovered particles. They would be so-called wimps — weakly interacting massive particles — which feel gravity and little else, and could drift through the Earth like wind through a screen door. Such particles left over from the Big Bang could form a shadow universe clumping together into dark clouds that then attract ordinary matter.

The discovery of a supersymmetric particle would also be a boost for string theory, the controversial “theory of everything,” and would explicate the nature of a quarter of the universe. But until now, the dark matter particles have mostly eluded direct detection in the laboratory, the exception being a controversial underground experiment called Dama/Libra, for Dark Matter/Large Sodium Iodide Bulk for Rare Processes, under the Italian Alps, where scientists claimed in April to have seen a seasonal effect of a “dark matter wind” as the Earth goes around its orbit.

The sky could be a different story. Dark matter particles floating in the halos around galaxies would occasionally collide and annihilate one another in tiny fireballs of radiation and lighter particles.

Dr. Wefel and his colleagues have been chasing sparks in the sky since 2000, when they flew an instrument known as ATIC, for Advanced Thin Ionization Calorimeter, around Antarctica on a balloon at an altitude of 23 miles, looking for high-energy particles known as cosmic rays raining from space.

The Nature paper includes data from the first two balloon flights. It shows a bump, over theoretical calculations of cosmic ray intensities, at energies of 500 billion to 800 billion electron volts, a measure of both energy and mass in physics. One way to explain that energy bump would be by the disintegration or annihilation of a very massive dark particle. A proton by comparison is about one billion electron volts. Dr. Wefel noted, however, that according to most models, a pulsar could generate particles with even more energy, up to trillions of volts, whereas the bump in the ATIC data seems to fall off at around 800 billion electron volts. The ATIC results, he said, dovetail nicely with those from Pamela, which recorded a rising number of positrons relative to electrons, but only up to energies of about 200 billion electron volts.

Reached in China, where he was attending a workshop, Neal Weiner of New York University, who is working with Dr. Arkani-Hamed on dark matter models, said he was plotting ATIC data gleaned from the Web and Pamela data on the same graph to see how they fit, which was apparently very well. But Piergiorgio Picozza, a professor at the University of Rome and the Pamela spokesman, said in an e-mail message that it was too soon to say the experiments agreed. That will depend on more data now being analyzed to learn whether Pamela continues to see more positrons as the energy rises.

Moreover, as Dr. Kane pointed out, Pamela carries a magnet that allows it to distinguish electrons from positrons — being oppositely charged, they bend in opposite directions going through the magnetic field. But the ATIC instrument did not include a magnet and so cannot be sure that it was seeing any positrons at all: no antimatter, no exotic dark matter, at least at those high energies. But if he is right, Dr. Wefel said that the ATIC data favored something even more exotic than supersymmetry, namely a particle that is lost in the fifth dimension. String theory predicts that there are at least six dimensions beyond our simple grasp, wrapped up so tightly we cannot see them or park in them. A particle in one of these dimensions would not appear to us directly. You could think of it as a hamster running around on a wheel in its cage. We cannot see the hamster or the cage, but we can sort of feel the impact of the hamster running; according to Einsteinian relativity, its momentum in the extra dimension would register as mass in our own space-time. Such particles are called Kaluza-Klein particles, after Theodor Kaluza and Oscar Klein, theorists who suggested such an extra-dimensional framework in the 1920s to unify Einstein’s general theory of relativity and electromagnetism.

Dr. Wefel’s particle would have a mass of around 620 billion electron volts. “That’s the one that seems to fit the best,” he said in an interview. The emergence of a sharp edge in the data, he said, “would be a smoking gun” for such a strange particle. But Dr. Arkani-Hamed said that Kaluza-Klein particles would not annihilate one another at a fast enough rate to explain the strength of the ATIC signal, nor other anomalies like the microwave haze. He and his colleagues, including Dr. Weiner, Dr. Finkbeiner and Tracy Slatyer, also of Harvard, drawing on work by Matthew Strassler of Rutgers, have tried to connect all the dots with a new brand of dark matter, in which there are not only dark particles but also a “dark force” between them.

That theory was called “a delightful castle in the sky” by Dr. Kane, who said he was glad it kept Dr. Arkani-Hamed and his colleagues busy and diverted them from competing with him. Dr. Kane and his colleagues favor a 200 billion-electron-volt supersymmetric particle known as a wino as the dark matter culprit, in which case the Pamela bump would not extend to higher energies. Dr. Wefel said he had not kept up with all the theorizing. “I’m just waiting for one of these modelers to say here is the data, here is the model,” he said. “Fit it out. I’m not sure I’ve seen it yet.” Dr. Picozza said that it was the job of theorists to come up with models and that they were proliferating. “At the end of the story only one will be accepted from the scientific community, but now it is too early."

Sorting all this out will take time, but not forever. “With so many experiments, we will soon know so much more about all of this,” Dr. Weiner said. “In a year or two, we’ll either not be talking about this idea at all, or it will be all we’re talking about.”

- Dennis Overbye (A Whisper, Perhaps, From the Universe’s Dark Side, NY Times, 11.25.08. Image: -Loomis Dean, "Shadows Of The Junior Astronomy Club Peering Through A Telescope, Greeley,CO, Life Magazine, 1955 ).