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April 27th11 notes
Damn, this has been a decent week for the sciences:
Members of the CMS collaboration announced the experiment’s first discovery of a new particle today.
In a paper submitted to Physical Review Letters, the CMS collaboration described the first observation of an excited, neutral Xi_b baryon, a particle made up of three quarks, including one beauty quark.
The new baryon is one of many particles made up of quarks predicted by the theory of quantum chromodynamics. -
A simple atomic nucleus could reveal properties associated with the mysterious phenomenon known as time reversal and lead to an explanation for one of the greatest mysteries of physics: the imbalance of matter and antimatter in the universe.
The physics world was rocked recently by the news that a class of subatomic particles known as neutrinos may have broken the speed of light.
Adding to the rash of new ideas, University of Arizona theoretical physicist Bira van Kolck recently proposed that experiments with another small particle called a deuteron could lead to an explanation for one of the most daunting puzzles physicists face: the imbalance of matter and antimatter in the universe.
A deuteron is a simple atomic nucleus, or the core of an atom. Its simplicity makes it one of the best objects for experiments in nuclear physics.
A property of the deuteron known as a magnetic quadrupole moment could reveal sources of a phenomenon known as time reversal violation, Van Kolck and his collaborators, including recently graduated UA doctoral student Emanuele Mereghetti, show in a recent paper published in Physical Review Letters.
Most of what physicists know about the universe can be described by what is called the standard model of particle physics. Developed by Van Kolck’s former doctoral advisor, Nobel Laureate Steven Weinberg, the standard model describes everything from Newton’s laws of motion to the behavior of subatomic particles with what is known as quantum mechanics.
“This theory explains almost everything we know about the universe up to this point,” said Van Kolck. “However,” he added, “there is one problem that the standard model does not explain.”
“Like the protons and neutrons – the particles making up the nucleus of an atom – every particle has what’s called an antiparticle, things like antiprotons or antineutrons. The universe seems to have many more particles than antiparticles,” said Van Kolck. “So there is a question of why the universe seems to have such an asymmetry between particles and antiparticles.” (via Time reversal: A simple particle could reveal new physics)
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'Light-speed' neutrinos point to new physical reality
[This New Scientist article is only available to subscribers so it has been presented in its entirety.]
SUBATOMIC particles have broken the universe’s fundamental speed limit, or so it was reported last week. The speed of light is the ultimate limit on travel in the universe, and the basis for Einstein’s special theory of relativity, so if the finding stands up to scrutiny, does it spell the end for physics as we know it? The reality is less simplistic and far more interesting.
“People were saying this means Einstein is wrong,” says physicist Heinrich Päs of the Technical University of Dortmund in Germany. “But that’s not really correct.”
Instead, the result could be the first evidence for a reality built out of extra dimensions. Future historians of science may regard it not as the moment we abandoned Einstein and broke physics, but rather as the point at which our view of space vastly expanded, from three dimensions to four, or more.
“This may be a physics revolution,” says Thomas Weiler at Vanderbilt University in Nashville, Tennessee, who has devised theories built on extra dimensions. “The famous words ‘paradigm shift’ are used too often and tritely, but they might be relevant.”
The subatomic particles - neutrinos - seem to have zipped faster than light from CERN, near Geneva, Switzerland, to the OPERA detector at the Gran Sasso lab near L’Aquila, Italy. It’s a conceptually simple result: neutrinos making the 730-kilometre journey arrived 60 nanoseconds earlier than they would have if they were travelling at light speed. And it relies on three seemingly simple measurements, says Dario Autiero of the Institute of Nuclear Physics in Lyon, France, a member of the OPERA collaboration: the distance between the labs, the time the neutrinos left CERN, and the time they arrived at Gran Sasso.
But actually measuring those times and distances to the accuracy needed to detect nanosecond differences is no easy task. The OPERA collaboration spent three years chasing down every source of error they could imagine (see illustration) before Autiero made the result public in a seminar at CERN on 23 September.
Physicists grilled Autiero for an hour after his talk to ensure the team had considered details like the curvature of the Earth, the tidal effects of the moon and the general relativistic effects of having two clocks at different heights (gravity slows time so a clock closer to Earth’s surface runs a tiny bit slower).
They were impressed. “I want to congratulate you on this extremely beautiful experiment,” said Nobel laureate Samuel Ting of the Massachusetts Institute of Technology after Autiero’s talk. “The experiment is very carefully done, and the systematic error carefully checked.”
Most physicists still expect some sort of experimental error to crop up and explain the anomaly, mainly because it contravenes the incredibly successful law of special relativity which holds that the speed of light is a constant that no object can exceed. The theory also leads to the famous equation E = mc2.
Hotly anticipated are results from other neutrino detectors, including T2K in Japan and MINOS at Fermilab in Illinois, which will run similar experiments and confirm the results or rule them out (see “Fermilab stops hunting Higgs, starts neutrino quest”).
In 2007, the MINOS experiment searched for faster-than-light neutrinos but didn’t see anything statistically significant. The team plans to reanalyse its data and upgrade the detector’s stopwatch. “These are the kind of things that we have to follow through, and make sure that our prejudices don’t get in the way of discovering something truly fantastic,” says Stephen Parke of Fermilab.
In the meantime, suggests Sandip Pakvasa of the University of Hawaii, let’s suppose the OPERA result is real. If the experiment is tested and replicated and the only explanation is faster-than-light neutrinos, is E = mc2 done for?
Not necessarily. In 2006, Pakvasa, Päs and Weiler came up with a model that allows certain particles to break the cosmic speed limit while leaving special relativity intact. “One can, if not rescue Einstein, at least leave him valid,” Weiler says.
The trick is to send neutrinos on a shortcut through a fourth, thus-far-unobserved dimension of space, reducing the distance they have to travel. Then the neutrinos wouldn’t have to outstrip light to reach their destination in the observed time.
In such a universe, the particles and forces we are familiar with are anchored to a four-dimensional membrane, or “brane”, with three dimensions of space and one of time. Crucially, the brane floats in a higher dimensional space-time called the bulk, which we are normally completely oblivious to.
The fantastic success of special relativity up to now, plus other cosmological observations, have led physicists to think that the brane might be flat, like a sheet of paper. Quantum fluctuations could make it ripple and roll like the surface of the ocean, Weiler says. Then, if neutrinos can break free of the brane, they might get from one point on it to another by dashing through the bulk, like a flying fish taking a shortcut between the waves (see illustration).
This model is attractive because it offers a way out of one of the biggest theoretical problems posed by the OPERA result: busting the apparent speed limit set by neutrinos detected pouring from a supernova in 1987.
As stars explode in a supernova, most of their energy streams out as neutrinos. These particles hardly ever interact with matter. That means they should escape the star almost immediately, while photons of light will take about 3 hours. In 1987, trillions of neutrinos arrived at Earth 3 hours before the dying star’s light caught up. If the neutrinos were travelling as fast as those going from CERN to OPERA, they should have arrived in 1982.
OPERA’s neutrinos were about 1000 times as energetic as the supernova’s neutrinos, though. And Pakvasa and colleagues’ model calls for neutrinos with a specific energy that makes them prefer tunnelling through the bulk to travelling along the brane. If that energy is around 20 gigaelectronvolts - and the team don’t yet know that it is - “then you expect large effects in the OPERA region, and small effects at the supernova energies,” Pakvasa says. He and Päs are meeting next week to work out the details.
The flying fish shortcut isn’t available to all particles. In the language of string theory, a mathematical model some physicists hope will lead to a comprehensive “theory of everything”, most particles are represented by tiny vibrating strings whose ends are permanently stuck to the brane. One of the only exceptions is the theoretical “sterile neutrino”, represented by a closed loop of string. These are also the only type of neutrino thought capable of escaping the brane.
Neutrinos are known to switch back and forth between their three observed types (electron, muon and tau neutrinos), and OPERA was originally designed to detect these shifts. In Pakvasa’s model, the muon neutrinos produced at CERN could have transformed to sterile neutrinos mid-flight, made a short hop through the bulk, and then switched back to muon before reappearing on the brane.
So if OPERA’s results hold up, they could provide support for the existence of sterile neutrinos, extra dimensions and perhaps string theory. Such theories could also explain why gravity is so weak compared with the other fundamental forces. The theoretical particles that mediate gravity, known as gravitons, may also be closed loops of string that leak off into the bulk. “If, in the end, nobody sees anything wrong and other people reproduce OPERA’s results, then I think it’s evidence for string theory, in that string theory is what makes extra dimensions credible in the first place,” Weiler says.
Meanwhile, alternative theories are likely to abound. Weiler expects papers to appear in a matter of days or weeks.
Even if relativity is pushed aside, Einstein has worked so well for so long that he will never really go away. At worst, relativity will turn out to work for most of the universe but not all, just as Newton’s mechanics work until things get extremely large or small. “The fact that Einstein has worked for 106 years means he’ll always be there, either as the right answer or a low-energy effective theory,” Weiler says.
(via New Scientist)
Related reading » Neutrinos: Everything you need to know
(via section5)
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Tevatron produces neutron-like particle with strange, bottom quarks
Most of the matter we can see (as opposed to all the dark stuff out there) is comprised of baryons, particles that are a combination of three quarks. The two most familiar baryons, protons and neutrons, are made up of the lightest quarks, the up and down (either two up and one down or vice versa, respectively). But it’s also possible to construct similar baryons with the heavier, unstable quarks; many of these have been observed, and some of them have been incorporated into atomic nuclei within the brief time that they survive.
Baryons with strange and charm quarks have been spotted in various particle accelerators over the years, but those containing a heavy, bottom quark have been harder to come by. This is both because the weight of a bottom quark means that high energy collisions are needed to produce it (it’s over 4GeV, compared to the up quark’s 3MeV), and because these particles only live for a very short time before decaying. Nevertheless, a few baryons that contain a bottom quark had been spotted over the years: an up/down/bottom combination called the Λb (spotted at CERN); a strange/strange/bottom called Ωb-; and a down/strange/bottom Ξb- (the latter two from Fermi). The last was the first particle spotted to have quarks from all three generations.
Yesterday, the CDF detector team at Fermilab released a paper in which they describe the neutral version of the Ξb, which contains an up, a strange, and a bottom quark.
(via Ars Technica)
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Proton Somersault Study Could Explain Why Matter Still Exists
For the first time, physicists have watched a single proton flip over on its axis. Aside from being a technical triumph, the measurement may eventually help determine why the universe contains more matter than antimatter.
Cosmologists think the Big Bang should have produced the same amount of ordinary matter — the particles that make up stars, planets and people — and antimatter, which is just like matter, only with an opposite charge. But when matter and antimatter meet, they annihilate each other. That there’s enough matter left for us to exist is one of modern physics’ biggest puzzles.
One possibility is that, opposite charge aside, antimatter isn’t always truly identical to matter, and so it doesn’t meet the requirements for triggering annihilation. To determine if this is true, physicists need a way to compare matter and antimatter. In a June 24 Physical Review Letters study, physicists take an important step toward comparing protons and antiprotons by measuring a property called the magnetic moment.
“For the proton and the antiproton, magnetic moments have never been compared before,” said quantum physicist Stefan Ulmer of the Helmholtz Institute Mainz in Germany, co-author of the new paper. “Our new methods make this comparison possible.”
The magnetic moment is a description of how a magnetic field pulls on a particle. It has an intrinsic direction, similar to how a compass needle always points north, but can point up or down depending on what other magnetic forces act on it.
(via Wired.com)
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Sketch for ‘Symmetry Break’, 2009
Steel chain and mixed media
17” x 20” x 8” (43 cm x 51 cm x 20 cm)
The spontaneous breaking of symmetry is a phenomenon that is ubiquitous in nature. In physics those situations are described by an energy landscape, called a potential that goes from having only one minimum (the lowest energy configuration to which the system is driven towards) to having more than one minimum. The appearance of a second minimum forces the system to ‘make a decision’ which minimum it will occupy. Seen from the outside, the system suddenly flips into a new state. In this sculptural sketch, I used pieces of chain that go from a physically possible hanging configuration to configurations that seem to violate the laws of physics more and more. The initial hanging curve gets penetrated from below with a narrower curve such that the chain successively develops two minima. This evolution suggests something miraculous, similar to the surprising and counter-intuitive phenomenon of symmetry breaking.
This is awesome!!
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Check out the awesome audio clip on the first page of the article.
(via Ars photo essay: standing in the beam line of a neutrino detector)
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Electron Positron Physics for the Layman by Dr Claus Grupen (Siegen University, Department of Physics)
(IMHO something is doing wrong the interpreter)
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Antihydrogen trapped at long last - physics-math - 17 November 2010 - New Scientist
“ATOMS made of antimatter have been trapped for the first time, a feat that will allow us to test whether antimatter responds to the fundamental forces in the same way as regular matter.
Antiparticles are the oppositely charged twins of normal particles. Since matter and antimatter annihilate on contact, antimatter experiments have been limited to using charged antiparticles, which can be corralled within electromagnetic traps.
Several teams have made antihydrogen atoms in the past, but no one had managed to trap them for detailed experiments as they have no net charge. Now an experiment called the Antihydrogen Laser Physics Apparatus(ALPHA) at the CERN particle physics laboratory near Geneva, Switzerland, has finally managed to ensnare atoms of antihydrogen.
ALPHA produced anti-atoms by combining antiprotons from CERN’s Antiproton Decelerator ring with positrons emitted by a radioactive isotope of sodium. Where it went one better than previous experiments was in being able to manipulate the anti-atoms magnetically.”
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Image: Simulated Lead-Lead Collisions in ALICE
‘Start of the Universe’: mini Big Bang recreated
Scientists at the Large Hadron Collider have come the closest ever to re-enacting the beginning of the Universe – reproducing conditions a millionth of a second after the Big Bang.
“Colliding particles of lead at each other at close to the speed of light, they produced heat a million times hotter than the centre of the Sun - temperatures close to those generated at the beginning of time.
The series of “mini-Big Bangs” were so powerful, scientists were hopeful they would cause sub-atomic particles to “melt” into their most basic ingredients and bring researchers closer to finding the fundamental building blocks of the Universe.
It was hoped the resulting hot dense “soup” would also prove the existence of a whole new state of matter known as the Quark Gluon Plasma.
Quarks are thought to be tiny particle s which make up protons and neutrons. They are held together by gluons, another kind of sub-atomic particle.
This discovery in turn could lead to the uncovering of one of the fundamental forces that bind everything together.
Dr David Evans, a member of the UK team from the University of Birmingham, said there was a lot of cheering “out of joy and relief”.
“We are thrilled with the achievement,” he said.
“The collisions generated mini Big Bangs and the highest temperatures and densities ever achieved in an experiment.
“At these temperatures even protons and neutrons, which make up the nuclei of atoms, melt resulting in a hot dense soup of quarks and gluons known as a quark-gluon plasma.”
Scientists, including the Birmingham team led by Dr Evans, will now study the particles in the hope of discovering what holds atoms together and gives them their mass they have a created
The collisions, officially started at 10.20am today, were produced by firing lead ions – atoms stripped of their electrons – at 0.9999 the speed of light - 670 million miles per hour - in opposite directions around the LHC’s underground tunnel at CERN, the European Organization for Nuclear Research, near Geneva.
Flying in opposite directions, the particles were focused into a narrow beam and forced to collide inside the massive ALICE (A Large Ion Collider Experiment) detector.
The impacts threw off thousands of particles and generated temperatures of 10 trillion degrees centigrade, as close as we have ever been to reproducing conditions not seen since the Big Bang 13.75 billion years ago.
They were 13 times more powerful than the previous record for ion collisions.
Scientists hope the quark-gluon plasma will allow them to learn more about the Strong Force, one of the four fundamental forces of nature.”
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The strange behavior of positronium could unlock the secrets of the universe
“Positronium is a particle created when you bind together an electron and its antimatter counterpart, the positron. It doesn’t interact with other atoms in the way we would expect, and this discovery could help us solve the universe’s biggest mysteries.
Positronium is sort of like a hydrogen atom, except if you took away the lone proton in the nucleus and replace it with a positron. Because electrons - and, by extension, positrons - are only 1/1836 the mass of a proton, that means positronium particles are much less massive than their hydrogen counterparts. The particle is a common byproduct of the interaction between regular matter and positrons. It’s an unstable particle, only remaining together for an average of 142 nanoseconds before decaying into two gamma ray particles.
During their very short lifetimes, however, it’s possible to probe some of their properties and characteristics, and that’s what researchers at University College London recently attempted. They tried a scattering experiment, in which they sent streams of positronium particles at different atoms and molecules and measured how they interacted. Because positronium is a hybrid of an electron and positron, they expected the particle to act in a way that was some sort of average of these two.
But that isn’t what they found. Instead, positronium acted precisely the same as an electron would. That doesn’t make much sense - electrons are negatively charged, while positronium is neutral, and it’s obviously twice the mass of a lone electron. In some weird way, the effects of the positron’s presence seems to be cloaked so that only the electron half of the positronium interacts with other matter. Of course, “in some weird way” is a nice way of saying we currently have no idea why the hell this is happening, and there’s a lot of theoretical work that will be needed to explain this effect.”
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Physicists discover “violation of a fundamental symmetry of the universe”
‘Today physicists announced that they may have found the key to explaining dark matter in the universe. It all has to do with the potential discovery of a “sterile neutrino.”
According to a release about the new study:
Neutrinos are neutral elementary particles born in the radioactive decay of other particles. The known “flavors” of neutrinos are the neutral counterparts of electrons and their heavier cousins, muons and taus. Regardless of a neutrino’s original flavor, the particles constantly flip from one type to another in a phenomenon called “neutrino flavor oscillation.”
An electron neutrino might become a muon neutrino, and then later an electron neutrino again. Scientists previously believed three flavors of neutrino exist. In this Mini Booster Neutrino Experiment, dubbed MiniBooNE, researchers detected more oscillations than would be possible if there were only three flavors.
“These results imply that there are either new particles or forces we had not previously imagined,” said Byron Roe, professor emeritus in the Department of Physics, and an author of a paper on the results newly published online in Physical Review Letters.’
Paper referenced in this article is available here.
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If you want to calculate the position of a particle, in other words its mechanics, the equation you use is the Schrödinger Wave Equation. Say you have an electron, and it is oscillating back and forth a certain distance from a nucleus. This is an example of the harmonic oscillator, mentioned previously. Now, if it were a baseball on a spring oscillating (same idea), you could use some relatively simple equations on it—maybe ones you would see in an advanced high school physics class. Instead, the Schrödinger Equation is required. Let’s explain some aspects of it:
What is H?: H is an operator, called the Hamiltonian, which describes the physics of the particle. Hamiltonians are a very fancy way to do physics, not peculiar to quantum mechanics. Basically, H will contain derivatives with respect to location.
What is E?: E describes the energy eigenvalues of the system. Long story short: there is not just one solution to this equation, but an infinite number of solutions. But they are regularly placed, and can be numbered “solution #1,” “#2,” etc. So we write E in such a way that we can enter in which solution we want (e.g. n = 0 for solution #1, etc).
Why is it a “wave equation”?: The quantity you have to solve for is Ψ (psi), and that is called the wave function. It gives not the location of the particle, but the probability the particle is at a particular place. The reason it’s a “wave equation” requires a little calculus or differential equations to understand, but here goes: H contains derivatives and E doesn’t. So when you have derivatives of something (Ψ) equalling that something (Ψ), the solution is often in the form sin, as in a sine wave. So, an equation that looks like that makes waves.
(via fuckyeahphysics)
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Technology Review: Blogs: arXiv blog: Particle Accelerators Could Work As Power Generators
Particle accelerators are not the most obvious machines to use for generating energy. And yet the idea that they could produce more power than they consume is not entirely far-fetched, as pointed out today by Robert Wilson, an accelerator physicist who was the driving force behind the creation of Fermilab near Chicago.
Wilson died in 2000 but a paper he wrote on this topic in 1976 has now found its way onto the arXiv and it highlights some thought-provoking ideas.
At the time, Wilson was director of Fermilab where he was building an accelerator called the Energy Doubler/Saver, which employed superconducting magnets to steer a beam of high energy protons in a giant circle. These protons were to have energies of up to 1000 GeV.
The Energy Doubler was special because it was the first time superconductivity had been used on a large scale, something that had significant implications for the amount of juice required to make the thing work. “One consequence of the application of superconductivity to accelerator construction is that the power consumption of accelerators will become much smaller,” said Wilson. And that raised an interesting prospect.
Imagine the protons in this accelerator are sent into a block of uranium. Each proton might then be expected to generate a shower of some 60,000 neutrons in the material and most of these would go on to be absorbed by the nuclei to form 60,000 plutonium atoms. When burned in a nuclear reactor, each plutonium atom produces 0.2 GeV of fission energy. So 60,000 of them would produce 12,000 GeV.
Using this back-of-an-envelope calculation, Wilson worked out that a single 1000 GeV proton could lead to the release of 12,000 GeV of fission energy. Of course, this neglects all the messy fine details in which large amounts of energy can be lost. For example, it takes some 20MW of power to produce an 0.2MW beam in the Energy Doubler.
But even with those kinds of losses, it certainly seems worthwhile to study the process in more detail to see if overall energy production is possible.
Wilson’s conclusion is this: “There are probably better ways of producing plutonium, but it does appear that it would be feasible to construct an intense proton accelerator that would produce more energy than it consumes.”
30 years later, accelerator technology has moved on but in a way that surely makes Wilson’s ideas even more pertinent—accelerators today are even more energy efficient than they were in 1976. And given the blue skies thinking associated with power generation today, these ideas may well be worth revisiting.
They may also solve another problem. Interplanetary spacecraft such as Galileo and Cassini rely on plutonium batteries for power. But NASA’s stocks of plutonium are running low so nobody is quite sure how future generations of these vehicles will get their juice. Wilson’s approach could help.
However, it also raises the ugly spectre of proliferation. The possibility of making plutonium on this scale using 30-year old accelerator technology must surely be of more than passing concern for anybody worried about the spread of technology that could lead to nuclear proliferation.
That’s a potential fly in the ointment that may need greater attention..
Ref: arxiv.org/abs/1007.5338: Very Big Accelerators as Energy Producers
