Post by Andrei Tchentchik on Aug 25, 2020 15:37:34 GMT 2
(.#498).- Antimatter's enigma: CERN on its track.
Antimatter enigma: CERN on its track with the Lamb shift in antihydrogen.
Laurent Sacco, Journalist
Published on 02/21/2020
The Alpha experiment at Cern tracks possible differences between the atoms of hydrogen and antihydrogen, in search of new physics and a solution to the enigma of antimatter in cosmology. With antihydrogen atoms, physicists have managed to observe the equivalent of the famous Lamb shift in quantum electrodynamics, the source of several Nobel Prize winners in physics.
Almost 90 years after its theoretical discovery by Paul Dirac from his relativistic version of the Schrödinger equation describing the quantum behavior of electrons in atoms as the simplest of them, the hydrogen atom, antimatter has not yet revealed all of its secrets.
Helped by experimenters since the 1930s, after the discovery in 1932 in the cosmic rays of the antiparticle of the electron, the positron, by the American physicist Carl Anderson (he will receive the Nobel Prize for this in 1936) then by that of the antiproton by Emilio Segré and his colleagues in 1955, theorists understood that there must be worlds formed of antiatoms and why not galaxies of antimatter not very far from the Milky Way. Research on this subject remained in vain and the problems worsened with the rise of the theory of Big Bang, today particularly well confirmed, because with known physics, as much matter as antimatter should have been produced during the Big Bang before these particles annihilate each other at its end.
Now we are indeed there, which means that what we conventionally call matter seems to have been produced in larger quantities than antimatter and this requires new physics, perhaps key to other puzzles like those dark matter and dark energy. This new physics would force certain properties of antiparticles to be different from those of particles. This could be seen by studying the spectral lines of antihydrogen atoms for example.
VIDEO :
ALPHA: A new era of precision for antimatter research.
A few years ago, the members of the Alpha CERN experiment managed to make fine measurements of the energy levels of antihydrogen atoms to compare them with measurements already made for decades with the atoms of hydrogen. To get a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © 2018 CERN
CERN, a factory with antihydrogen atoms
Futura regularly reports on the progress made on the track of the missing cosmological antimatter by Cern researchers who, for years, have been precisely making antihydrogen atoms to study their properties and trying to discover phenomena which are not not the symmetrics of those of hydrogen atoms by reversing the signs of electric charges in the equations of quantum electrodynamics describing these atoms. As Futura explained in the numerous articles below, already devoted to this research with antihydrogen, it is a means of testing a theorem and a fundamental symmetry of the quantum theory of relativistic fields behind the standard model of the elementary particle physics, the CPT theorem. But new effects which do not fall under a violation of this theorem are possible, for example the influence of new particles more easily detectable with antihydrogen.
Again, the Alpha (Antihydrogen Laser Physics Apparatus) experience is in the spotlight. Its members have just published an article in Nature where they announce that they have taken even further the precise measurement of the transitions between energy levels for positrons in antihydrogen atoms, exploring what is called the fine structure of these levels and in particular by highlighting a mythical effect, that of the displacement of Lamb discovered by the Nobel Prize winner in physics Willis Lamb.
Born July 12, 1913 in Los Angeles, and although destined to become famous for his experimental work, Willis Lamb began by being a researcher in theoretical physics. He was indeed one of the first PhD students at Berkeley of Robert Oppenheimer, the founder of the American theoretical physics school and the prime contractor for the Manhattan project (the development of the atomic bomb in the United States) ). After exploring the electromagnetic properties of nuclei for his thesis, he joined Columbia University where he began his work in the field of microwave atomic spectroscopy. © DP
In 1947, he discovered that the fine structure of certain energy levels of the hydrogen atom was not explained by the relativistic theory of electrons established by Paul Dirac from his famous wave equation. At the time, we already knew that by observing more precisely the energy levels of a hydrogen atom, we showed that some were in fact multiple and very close together due to various effects, notably relativistic. because of the speed of the electrons in these atoms but also because of the existence of the spin of an electron and its magnetic moment.
The spectrum of hydrogen atoms and quantum field theory
Lamb then highlights the existence of levels separated by an inexplicable energy difference in the context of quantum electrodynamics of the time. The same year, the Nobel Prize winner in physics Hans Bethe gave a first explanation, but without involving the theory of special relativity. This was the key that enabled Tomonaga, Schwinger and Feynman to verify that their relativistic quantum theories of electromagnetism were correct by using Bethe's calculations as part of the new formulations of relativistic quantum electrodynamics that they had discovered and which solved problems encountered in theory during the 1930s.
Previously, relativistic quantum electrodynamics was indeed blocked by the appearance of infinite divergences, making all the somewhat precise calculations of the interaction processes between matter and light absurd. Lamb's result, by showing a modification of certain energy levels, was decisive proof of the existence of the appearance and disappearance of virtual electron and positron pairs from quantum vacuum and good- founded processes of renormalization of the mass and the charge of the electrons introduced by Feynman and Schwinger in order to find the finite values measured by the experimenters.
Today, we are therefore starting to explore the physics of Lamb's displacement, the Lamb shift as the Anglo-Saxons say, with the Alpha experience. The effects of the quantum vacuum which could manifest there can betray the existence of new particles beyond that of the electroweak Model which includes relativistic quantum electrodynamics. But we are only at preliminary results and for the moment the new physics is not showing up.
VIDEO :
Quantum electrodynamics: theory, with Dr. Don Lincoln
Some explanations on Feynman's work in quantum electrodynamics with his famous diagrams at the origin of his Nobel Prize. To obtain a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © Fermilab
WHAT YOU MUST REMEMBER
A fundamental theorem of physics, based on the theory of relativity and quantum theory, implies that there should be no difference between matter and antimatter and therefore, that protons, neutrons and electrons should have been made same number at the time of the Big Bang.
This is not the case, and physicists therefore suspect the differences between matter and antimatter that they seek to highlight, by measuring the spectrum of antihydrogen atoms in the framework of the Alpha experiment at CERN.
After 30 years of effort, the precision reached is close to the measurements of the spectrum of the hydrogen atom with the 1S-2S and 1S-2P transitions (Lyman-α line) and we now measure the Lamb effect caused by the quantum fluctuations of the vacuum ... but still no trace of new physics.
TO KNOW MORE
Will the spectrum of antihydrogen reveal the enigma of antimatter?
Article by Laurent Sacco
Published on 08/29/2018
Archives
The Alpha experiment at Cern tracks possible differences between the atoms of hydrogen and antihydrogen, in search of new physics and a solution to the enigma of antimatter in cosmology. Physicists have managed to observe the equivalent of the Lyman-α line of hydrogen ... but still no revolution in sight.
In 1928, seeking a relativistic version of the Schrödinger equation describing an electron (not to be confused with a relativistic version of the Schrödinger equation which is a much more general problem), the physicist Paul Dirac discovered his famous equation. As he himself will say, it was "smarter" than him because its mathematical formulation provided automatically, and completely unexpectedly, not only the intrinsic angular momentum of the electrons, their spin, but also their magnetic moment.
The most spectacular, but also the most disturbing, for Dirac and his colleagues in the late 1930s was the existence of solutions of these equations with negative energies, due to the appearance of a square root for energy. . We could not really dismiss these solutions on the basis that they must not be physical, which ultimately led Dirac to postulate the existence of what we now call antimatter. These cascading discoveries are one of the best proofs that at least, up to a certain point, the world is built on mathematical bases which we discover, do not invent, and which allow us to anticipate the existence of laws and objects, almost completely a priori (a multimillennial thesis vigorously defended today by Max Tegmark).
VIDEO :
The anti-electron
Dirac's equation gives two solutions: the electron ... and the positron. Is this antielectron a mathematical artefact or a new particle? © Synchrotron SOLEIL
Dirac's antimatter, antigravity and cosmology
Dirac's equation would, however, lead to an enigma in cosmology. One of the basics of quantum particle field theory. It implies that to every charged particle must correspond another particle having, as far as we know, in flat space-time the same properties of mass, spin and electric charge, except that it must be opposite sign. We do know that there are anti-electrons, positrons and even antinucleons (a little complicated by the fact that antiprotons and antineutrons are not really elementary particles), etc. However, at the time of the Big Bang, as many particles of matter as antimatter were formed, theoretically, while we observe a very clear asymmetry in the observable universe.
There are several ways to solve this conundrum. Perhaps there are subtle differences between particles of matter and antimatter which lead a little more particles of matter than antimatter to be synthesized under conditions similar to those of the Big Bang.
We can also imagine that antimatter does not behave like matter in a gravitational field. Perhaps matter and antimatter repel each other due to antigravity, which might have led, for example, to a separation in the form of the equivalent of an emulsion of matter and antimatter, with regions filled only with matter and others with antimatter. These regions would therefore have little contact due to repulsive forces, which would explain why we do not see gigantic sources of gamma rays at the borders of these regions, due to the annihilation of particles of matter and antimatter.
CERN researchers have been tracking possible differences between matter and antimatter for years in multiple experiments. They are based on the production and storage of antiprotons as well as on the manufacture of antihydrogen atoms formed by the capture of positrons by antiprotons. The discovery of these differences would automatically open a door on new physics and could even fail, for the first time, the theory of special relativity via a violation of what is called CPT symmetry.
Futura has devoted several articles to these experiments, one of which is quite often in the spotlight, which is currently the case with a new publication in the journal Nature by the members of the Alpha collaboration (Antihydrogen Laser PHysics Apparatus). This experiment consists, first of all, of provoking and measuring transitions between the energy levels occupied by positrons in antihydrogen atoms with a laser beam. These measurements must constantly gain in precision, as much as possible, hoping to see differences with the hydrogen atoms.
VIDEO YOUTUBE:
The electron in all its forms
Specters are like butterflies, thinks Danish physicist Niels Bohr at the beginning of 1913. The colors are very beautiful, but we have gone around the problem: thanks to the prism spectroscope developed 50 years earlier by German physicists Kirchhoff and Bunsen, all the chemical elements have provided their identity in the form of characteristic lines. However, it is these luminous lines which will offer Bohr the key to the secret of atoms. © Synchrotron SOLEIL
Anti-hydrogen and the Lyman-α line
The researchers had succeeded in first exploring so-called hyperfine transitions, technically the one called 1S-2S, similar to that giving the famous line at 21 cm. But today, it is another transition called 1S-2P, between the energy levels of the Bohr atom which is called a Lyman-α line and which was discovered by Theodore Lyman in 1906, in the extreme ultraviolet region of the atomic hydrogen spectrum, which has been observed with antihydrogen. In the case of hydrogen, the transition occurs when an electron goes from its lowest energy level (1S) to a higher energy level (2P), before falling back to its initial level by emitting a photon at a wavelength of 121.6 nanometers. It showed that we could extend the famous Balmer formula for the lines in the visible of this atom. This line is also very well known in astronomy where it leads to the famous phenomenon of the “Lyman-α forest”.
The Alpha experiment therefore made it possible to detect the Lyman-α transition in an antihydrogen atom with positrons by measuring its frequency, with an accuracy of the order of a few parts per hundred million, obtaining good agreement with the equivalent transition. in hydrogen.
This success led Jeffrey Hangst, spokesperson for the Alpha experiment, to declare “We are really happy with this result. The Lyman-alpha transition is, as we know, difficult to analyze - even in "normal" hydrogen. It was by taking advantage of our ability to trap and keep a large number of antihydrogen atoms for several hours, and by using a pulsed source of Lyman-alpha laser light, that we were able to observe it. The next step will be laser cooling, which will be a game-changer for precision spectroscopic and gravitational measurements. "
In fact, access to the Lyman-alpha line makes it possible to envisage transposing the techniques of atom cooling by laser that we know. By slowing down the movements in a gas of atoms, we can then perform even more precise line measurements and therefore set even more severe limits on new physics.
VIDEO :
CERN VIDEO STORY: CERN’s Unique Antimatter factory
A presentation in English of experiences tracking down the mysteries of antiprotons and antihydrogen atoms. © Cern
Alpha, antimatter and a hyperfine line of antihydrogen
Article by Laurent Sacco,
Published on 06/04/2018
Archives
The Alpha experiment at Cern tracks possible differences between the atoms of hydrogen and antihydrogen in search of new physics and a solution to the enigma of antimatter in cosmology. A new precision record was reached but still no revolution in sight.
The LHC came out recently, on March 30, 2018 to be precise, from its winter sleep with the great return of the proton beams in its rings of 27 kilometers in circumference. The hunt for new physics will actually only start in May, as there are still adjustments to be made before colliding with the giant detectors at the LHC. Physicists will then be able to start a seventh year of data acquisition, and the fourth year at 13 TeV collision energy. It will however be the last year of the LHC's second run, which will then stop for two years to be upgraded, more precisely to prepare the HL-LHC, the high-brightness LHC.
Fundamental physics is not going to stop there, because there are other lower energy experiments at CERN, like the one called Alpha (Antihydrogen Laser Physics Apparatus) to which Futura has devoted numerous articles for several years. Cern has not only made a name for itself with the discovery of the Z, W bosons and of course Brout-Englert-Higgs, but also by becoming a master in the storage of antiprotons and finally, in the production and trapping of atoms. antihydrogen.
VIDEO :
Antihydrogen formation and 1S-2S excitation in ALPHA
A video explaining how the Alpha experiment works at CERN. To get a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © Cern, Niels Madsen
The antihydrogen atom, a laboratory for new physics
The Alpha experiment proposes to study more and more finely the spectrum of these atoms in the hope of discovering differences with that, very well known and very well measured, of hydrogen atoms. In this case, it is a question of causing atomic transitions in the atoms of antihydrogen using laser beams. The observation of these potential differences would automatically shake the foundations of physics by calling into question the theory of special relativity, even also the quantum theory. It could also provide the key to the riddle of antimatter in cosmology, because the laws of the standard model in particle physics are silent when it comes to explaining why we do not find as much antimatter as matter on the scale of the observable cosmos, while these same laws predict that they should have been produced in equal quantities during the Big Bang.
The members of the Alpha collaboration have just announced via an article published in Nature that they had succeeded in pushing several notches further, a fine measure of the spectrum resulting from the atomic transition 1S-2S in antihydrogen. The precision obtained is of the order of a few parts per thousand billion, a result 100 times more precise than the last measurement carried out in 2016 (see the article below).
Jeffrey Hangst, spokesperson for the Alpha experiment, does not hide his enthusiasm as we can see by a statement reported on the CERN site: “The precision obtained with this new measurement is a final success for us. We've been trying to get it for 30 years, and we finally got it. ”
However, progress remains to be made before matching the accuracy of the same measurement with the hydrogen atom. The margin of progress is 3 orders of magnitude, that is to say a factor of 1,000.
The spectrum of antihydrogen continues to reveal its secrets
Article by Laurent Sacco,
Published on 21/12/2016
Archives
In search of new physics and a better understanding of the Big Bang, CERN physicists track down the differences between matter and antimatter. Their latest results concern the way in which antihydrogen atoms absorb and emit light.
The members of the Alpha (Antihydrogen Laser Physics Apparatus) collaboration at CERN have announced via an article published in Nature that they had taken a step further the study of the spectrum of an antihydrogen atom, that is that is, the characteristics of the electromagnetic radiation that this atom can absorb and emit.
As we saw in a previous article, these are so-called hyperfine transitions between the energy levels of a positron in such an anti-atom that had been produced and then measured a few years ago. Physicists, as they announced at that time, managed to observe transitions in the field of ultraviolet light, that is to say in their terminology, the equivalent of transitions between levels 1S and 2S of a Bohr atom where a positron has been substituted for an electron, and an antiproton for a proton.
Recall that CERN researchers have a long tradition in the production and storage of antiprotons thanks in particular to the work of the Nobel Prize in physics Simon van der Meer. This allowed them to manufacture in 1995, the first antihydrogen atom and then to produce large quantities with the Athena experiment in 2002. Thanks to that baptized Alpha, which started in 2010, the physicists of Cern finally arrived to trap these antiatoms to study them as they please.
In 2016, to study antihydrogen, the researchers began by mixing approximately 90,000 antiprotons, from a machine called Antiproton decelerator, with positrons from the radioactive decay of sodium nuclei 22, which allowed synthesis about 25,000 atoms of antihydrogen. The gas obtained was cooled below 1 degree Kelvin and some of these antihydrogen atoms were then magnetically trapped. This then made it possible to study atomic transitions finely by exciting these atoms using laser beams.
VIDEO :
The ALPHA experiment observes light spectrum of antimatter for the ...
A presentation of the latest results of the members of the Alpha collaboration by their spokesperson, Jeffrey Hangst. To get a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © Cern
A violation of special relativity with antihydrogen?
For the moment, with the accuracy of the measurements reached (they should improve in the near future), there is no observable difference between the way in which a hydrogen atom absorbs and emits light at well frequencies. precise and how does it, at these same frequencies, an antihydrogen atom. If however such a difference were to be observed, it would mean that we are in the presence of a violation of the CPT theorem, a very deep theorem, resulting from the laws of symmetry, which applies to all relativistic quantum theories of fields , so to the standard model.
This theorem was first proven by the Nobel Prize in physics Julian Schwinger in 1951, then more rigorously and completely in 1954 by Gerhart Lüders and Wolfgang Pauli. According to this theorem, the behavior of an antihydrogen atom should be the same as that of a hydrogen atom. It should fall into the Earth's gravitational field in the same way and it should not be possible to discover differences in the emission and absorption spectra of the two objects. If this were not the case, we could perhaps understand why the universe does not seem to contain antimatter, apart from that present in cosmic rays and which results, as on Earth, from collisions or disintegrations with matter particles.
A violation of this theorem in the Alpha experiment would anyway indicate that the theory of special relativity does not apply in certain situations, which would be a revolution opening a window on new physics.
First studies of the antihydrogen spectrum
Article by Laurent Sacco,
Published on 19/03/2012
Archives
Is antigravity possible? Can we detect antigalaxies in the universe? A good way to answer these questions is to study the spectrum of antihydrogen atoms. This is what researchers from the Alpha experiment at CERN are starting to do.
Humanity created its first antihydrogen atom in 1995 at Cern. If we know how to produce antiprotons since the 1950s and antielectrons for even longer, the synthesis of an antiatome is not easy because the antimatter particles theoretically predicted by Paul Dirac in 1928 have the defect of annihilate with their associated matter particles when they meet. Preventing a positron from disappearing by colliding with an electron, or preventing an antiproton from doing the same with the protons of a nucleus is not easy in our world where, strangely, matter predominates overwhelmingly over antimatter .
However, at the beginning of the birth of the observable universe, there should have been created as much matter as antimatter. At least that's what the standard model equations tell us. One way to explain this asymmetry, this enigma of the absence of antimatter in cosmology, is to involve physics beyond the standard model. It could for example be that at high energies, our universe is effectively described by GUT type theories as Julien Baglio has just explained to us. The discovery of a supersymmetric Higgs boson could be a good indication that the architecture of the cosmos really rests on these foundations.
Others offer even crazier hypotheses. Are we sure that antimatter falls into the gravitational field of an object made of normal matter? What if a weak antigravity existed between matter and antimatter, having led the primitive universe to separate into two or multiple distinct regions? If this is the case, perhaps even galaxies and antigalaxies form clusters that repel each other. They would thus stand at a good distance, avoiding destructive contacts which would generate waves of gamma rays ... which are not observed.
Left Wolfgang Pauli and right Paul Dirac. Both are Nobel Prize winners in physics and are among the founding fathers of quantum mechanics. Our theoretical knowledge of antimatter is heavily based on their work in the years 1930-1940. If Dirac was the first to predict the existence of antimatter, it was Pauli who first understood, in 1924, that the hyperfine spectral structure of hydrogen discovered in the 19th century by Michelson could be explained well if electrons and nuclei had their own magnetic moment. © Cern
To hopefully answer all of these questions, one of the surest ways is probably to create a large number of antihydrogen atoms to study their properties in the laboratory to find out if antiatoms are really the equivalent of atoms of matter. Do they have the same emission spectra? In other words, is the light of an anti-galaxy indistinguishable from that of a galaxy composed of "normal" matter? Do they fall in the same way in the Earth's gravitational field?
To track down the mysteries of antimatter, Cern researchers had to manage to create a large number of these antiatoms, and, above all, that they exist long enough to be the subject of measurements. These two conditions have been achieved for a few years with the Alpha experiment (Antihydrogen Laser Physics Apparatus).
In a publication in the journal Nature, members of the Alpha collaboration announce today that they are starting to be able to study the spectrum of antihydrogen atoms.
The hyperfine spectral structure of antihydrogen
For the moment, researchers have not observed the main atomic transitions equivalent to those of an electron jumping into different orbits of a Bohr atom. They were content to cause transitions at the level of what is called the hyperfine spectral structure of the atom of neutral antihydrogen. For this, microwaves caused the tilting of the intrinsic magnetic moment of the positron, which occurs at a very specific frequency. The choice of this type of transition is probably not trivial.
We know that the hydrogen atom has fine energy levels resulting from the magnetic interaction of the spin of its electron with that of its proton. Depending on whether these two spins are parallel or antiparallel, the energy level of the electron is not the same and a transition with emission of a photon with a wavelength of 21 cm is possible. This transition is very useful in astrophysics to map atomic hydrogen in a galaxy. It is the famous line at 21 cm from hydrogen.
In the case of the Alpha experiment, the fact that a transition of this type does indeed occur with some of the antiatoms captured in a Penning trap is signaled by the escape of these antiatoms from the trap. Colliding with atoms, they annihilate themselves leaving characteristic measurable traces.
Researchers are now preparing to go further by performing atomic transitions with lasers. It is only when fine and precise measurements of the spectrum of antihydrogen atoms have been made that differences between matter and antimatter, coming from physics beyond the standard model, may perhaps appear in the open.
Interview: what is the quantum vacuum? The vacuum in physics is a difficult concept to define. One might think that it designates the absence of everything, but it seems that this is not really the case in quantum mechanics ... Futura-Sciences interviewed Claude Aslangul so that he could tell us a little more about the subject.
Sorry !
Please update your browser or try a different one.
(reportld: 1e24hj1s055vbec00p9)
F I N .
Antimatter enigma: CERN on its track with the Lamb shift in antihydrogen.
Laurent Sacco, Journalist
Published on 02/21/2020
The Alpha experiment at Cern tracks possible differences between the atoms of hydrogen and antihydrogen, in search of new physics and a solution to the enigma of antimatter in cosmology. With antihydrogen atoms, physicists have managed to observe the equivalent of the famous Lamb shift in quantum electrodynamics, the source of several Nobel Prize winners in physics.
Almost 90 years after its theoretical discovery by Paul Dirac from his relativistic version of the Schrödinger equation describing the quantum behavior of electrons in atoms as the simplest of them, the hydrogen atom, antimatter has not yet revealed all of its secrets.
Helped by experimenters since the 1930s, after the discovery in 1932 in the cosmic rays of the antiparticle of the electron, the positron, by the American physicist Carl Anderson (he will receive the Nobel Prize for this in 1936) then by that of the antiproton by Emilio Segré and his colleagues in 1955, theorists understood that there must be worlds formed of antiatoms and why not galaxies of antimatter not very far from the Milky Way. Research on this subject remained in vain and the problems worsened with the rise of the theory of Big Bang, today particularly well confirmed, because with known physics, as much matter as antimatter should have been produced during the Big Bang before these particles annihilate each other at its end.
Now we are indeed there, which means that what we conventionally call matter seems to have been produced in larger quantities than antimatter and this requires new physics, perhaps key to other puzzles like those dark matter and dark energy. This new physics would force certain properties of antiparticles to be different from those of particles. This could be seen by studying the spectral lines of antihydrogen atoms for example.
VIDEO :
ALPHA: A new era of precision for antimatter research.
A few years ago, the members of the Alpha CERN experiment managed to make fine measurements of the energy levels of antihydrogen atoms to compare them with measurements already made for decades with the atoms of hydrogen. To get a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © 2018 CERN
CERN, a factory with antihydrogen atoms
Futura regularly reports on the progress made on the track of the missing cosmological antimatter by Cern researchers who, for years, have been precisely making antihydrogen atoms to study their properties and trying to discover phenomena which are not not the symmetrics of those of hydrogen atoms by reversing the signs of electric charges in the equations of quantum electrodynamics describing these atoms. As Futura explained in the numerous articles below, already devoted to this research with antihydrogen, it is a means of testing a theorem and a fundamental symmetry of the quantum theory of relativistic fields behind the standard model of the elementary particle physics, the CPT theorem. But new effects which do not fall under a violation of this theorem are possible, for example the influence of new particles more easily detectable with antihydrogen.
Again, the Alpha (Antihydrogen Laser Physics Apparatus) experience is in the spotlight. Its members have just published an article in Nature where they announce that they have taken even further the precise measurement of the transitions between energy levels for positrons in antihydrogen atoms, exploring what is called the fine structure of these levels and in particular by highlighting a mythical effect, that of the displacement of Lamb discovered by the Nobel Prize winner in physics Willis Lamb.
Born July 12, 1913 in Los Angeles, and although destined to become famous for his experimental work, Willis Lamb began by being a researcher in theoretical physics. He was indeed one of the first PhD students at Berkeley of Robert Oppenheimer, the founder of the American theoretical physics school and the prime contractor for the Manhattan project (the development of the atomic bomb in the United States) ). After exploring the electromagnetic properties of nuclei for his thesis, he joined Columbia University where he began his work in the field of microwave atomic spectroscopy. © DP
In 1947, he discovered that the fine structure of certain energy levels of the hydrogen atom was not explained by the relativistic theory of electrons established by Paul Dirac from his famous wave equation. At the time, we already knew that by observing more precisely the energy levels of a hydrogen atom, we showed that some were in fact multiple and very close together due to various effects, notably relativistic. because of the speed of the electrons in these atoms but also because of the existence of the spin of an electron and its magnetic moment.
The spectrum of hydrogen atoms and quantum field theory
Lamb then highlights the existence of levels separated by an inexplicable energy difference in the context of quantum electrodynamics of the time. The same year, the Nobel Prize winner in physics Hans Bethe gave a first explanation, but without involving the theory of special relativity. This was the key that enabled Tomonaga, Schwinger and Feynman to verify that their relativistic quantum theories of electromagnetism were correct by using Bethe's calculations as part of the new formulations of relativistic quantum electrodynamics that they had discovered and which solved problems encountered in theory during the 1930s.
Previously, relativistic quantum electrodynamics was indeed blocked by the appearance of infinite divergences, making all the somewhat precise calculations of the interaction processes between matter and light absurd. Lamb's result, by showing a modification of certain energy levels, was decisive proof of the existence of the appearance and disappearance of virtual electron and positron pairs from quantum vacuum and good- founded processes of renormalization of the mass and the charge of the electrons introduced by Feynman and Schwinger in order to find the finite values measured by the experimenters.
Today, we are therefore starting to explore the physics of Lamb's displacement, the Lamb shift as the Anglo-Saxons say, with the Alpha experience. The effects of the quantum vacuum which could manifest there can betray the existence of new particles beyond that of the electroweak Model which includes relativistic quantum electrodynamics. But we are only at preliminary results and for the moment the new physics is not showing up.
VIDEO :
Quantum electrodynamics: theory, with Dr. Don Lincoln
Some explanations on Feynman's work in quantum electrodynamics with his famous diagrams at the origin of his Nobel Prize. To obtain a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © Fermilab
WHAT YOU MUST REMEMBER
A fundamental theorem of physics, based on the theory of relativity and quantum theory, implies that there should be no difference between matter and antimatter and therefore, that protons, neutrons and electrons should have been made same number at the time of the Big Bang.
This is not the case, and physicists therefore suspect the differences between matter and antimatter that they seek to highlight, by measuring the spectrum of antihydrogen atoms in the framework of the Alpha experiment at CERN.
After 30 years of effort, the precision reached is close to the measurements of the spectrum of the hydrogen atom with the 1S-2S and 1S-2P transitions (Lyman-α line) and we now measure the Lamb effect caused by the quantum fluctuations of the vacuum ... but still no trace of new physics.
TO KNOW MORE
Will the spectrum of antihydrogen reveal the enigma of antimatter?
Article by Laurent Sacco
Published on 08/29/2018
Archives
The Alpha experiment at Cern tracks possible differences between the atoms of hydrogen and antihydrogen, in search of new physics and a solution to the enigma of antimatter in cosmology. Physicists have managed to observe the equivalent of the Lyman-α line of hydrogen ... but still no revolution in sight.
In 1928, seeking a relativistic version of the Schrödinger equation describing an electron (not to be confused with a relativistic version of the Schrödinger equation which is a much more general problem), the physicist Paul Dirac discovered his famous equation. As he himself will say, it was "smarter" than him because its mathematical formulation provided automatically, and completely unexpectedly, not only the intrinsic angular momentum of the electrons, their spin, but also their magnetic moment.
The most spectacular, but also the most disturbing, for Dirac and his colleagues in the late 1930s was the existence of solutions of these equations with negative energies, due to the appearance of a square root for energy. . We could not really dismiss these solutions on the basis that they must not be physical, which ultimately led Dirac to postulate the existence of what we now call antimatter. These cascading discoveries are one of the best proofs that at least, up to a certain point, the world is built on mathematical bases which we discover, do not invent, and which allow us to anticipate the existence of laws and objects, almost completely a priori (a multimillennial thesis vigorously defended today by Max Tegmark).
VIDEO :
The anti-electron
Dirac's equation gives two solutions: the electron ... and the positron. Is this antielectron a mathematical artefact or a new particle? © Synchrotron SOLEIL
Dirac's antimatter, antigravity and cosmology
Dirac's equation would, however, lead to an enigma in cosmology. One of the basics of quantum particle field theory. It implies that to every charged particle must correspond another particle having, as far as we know, in flat space-time the same properties of mass, spin and electric charge, except that it must be opposite sign. We do know that there are anti-electrons, positrons and even antinucleons (a little complicated by the fact that antiprotons and antineutrons are not really elementary particles), etc. However, at the time of the Big Bang, as many particles of matter as antimatter were formed, theoretically, while we observe a very clear asymmetry in the observable universe.
There are several ways to solve this conundrum. Perhaps there are subtle differences between particles of matter and antimatter which lead a little more particles of matter than antimatter to be synthesized under conditions similar to those of the Big Bang.
We can also imagine that antimatter does not behave like matter in a gravitational field. Perhaps matter and antimatter repel each other due to antigravity, which might have led, for example, to a separation in the form of the equivalent of an emulsion of matter and antimatter, with regions filled only with matter and others with antimatter. These regions would therefore have little contact due to repulsive forces, which would explain why we do not see gigantic sources of gamma rays at the borders of these regions, due to the annihilation of particles of matter and antimatter.
CERN researchers have been tracking possible differences between matter and antimatter for years in multiple experiments. They are based on the production and storage of antiprotons as well as on the manufacture of antihydrogen atoms formed by the capture of positrons by antiprotons. The discovery of these differences would automatically open a door on new physics and could even fail, for the first time, the theory of special relativity via a violation of what is called CPT symmetry.
Futura has devoted several articles to these experiments, one of which is quite often in the spotlight, which is currently the case with a new publication in the journal Nature by the members of the Alpha collaboration (Antihydrogen Laser PHysics Apparatus). This experiment consists, first of all, of provoking and measuring transitions between the energy levels occupied by positrons in antihydrogen atoms with a laser beam. These measurements must constantly gain in precision, as much as possible, hoping to see differences with the hydrogen atoms.
VIDEO YOUTUBE:
The electron in all its forms
Specters are like butterflies, thinks Danish physicist Niels Bohr at the beginning of 1913. The colors are very beautiful, but we have gone around the problem: thanks to the prism spectroscope developed 50 years earlier by German physicists Kirchhoff and Bunsen, all the chemical elements have provided their identity in the form of characteristic lines. However, it is these luminous lines which will offer Bohr the key to the secret of atoms. © Synchrotron SOLEIL
Anti-hydrogen and the Lyman-α line
The researchers had succeeded in first exploring so-called hyperfine transitions, technically the one called 1S-2S, similar to that giving the famous line at 21 cm. But today, it is another transition called 1S-2P, between the energy levels of the Bohr atom which is called a Lyman-α line and which was discovered by Theodore Lyman in 1906, in the extreme ultraviolet region of the atomic hydrogen spectrum, which has been observed with antihydrogen. In the case of hydrogen, the transition occurs when an electron goes from its lowest energy level (1S) to a higher energy level (2P), before falling back to its initial level by emitting a photon at a wavelength of 121.6 nanometers. It showed that we could extend the famous Balmer formula for the lines in the visible of this atom. This line is also very well known in astronomy where it leads to the famous phenomenon of the “Lyman-α forest”.
The Alpha experiment therefore made it possible to detect the Lyman-α transition in an antihydrogen atom with positrons by measuring its frequency, with an accuracy of the order of a few parts per hundred million, obtaining good agreement with the equivalent transition. in hydrogen.
This success led Jeffrey Hangst, spokesperson for the Alpha experiment, to declare “We are really happy with this result. The Lyman-alpha transition is, as we know, difficult to analyze - even in "normal" hydrogen. It was by taking advantage of our ability to trap and keep a large number of antihydrogen atoms for several hours, and by using a pulsed source of Lyman-alpha laser light, that we were able to observe it. The next step will be laser cooling, which will be a game-changer for precision spectroscopic and gravitational measurements. "
In fact, access to the Lyman-alpha line makes it possible to envisage transposing the techniques of atom cooling by laser that we know. By slowing down the movements in a gas of atoms, we can then perform even more precise line measurements and therefore set even more severe limits on new physics.
VIDEO :
CERN VIDEO STORY: CERN’s Unique Antimatter factory
A presentation in English of experiences tracking down the mysteries of antiprotons and antihydrogen atoms. © Cern
Alpha, antimatter and a hyperfine line of antihydrogen
Article by Laurent Sacco,
Published on 06/04/2018
Archives
The Alpha experiment at Cern tracks possible differences between the atoms of hydrogen and antihydrogen in search of new physics and a solution to the enigma of antimatter in cosmology. A new precision record was reached but still no revolution in sight.
The LHC came out recently, on March 30, 2018 to be precise, from its winter sleep with the great return of the proton beams in its rings of 27 kilometers in circumference. The hunt for new physics will actually only start in May, as there are still adjustments to be made before colliding with the giant detectors at the LHC. Physicists will then be able to start a seventh year of data acquisition, and the fourth year at 13 TeV collision energy. It will however be the last year of the LHC's second run, which will then stop for two years to be upgraded, more precisely to prepare the HL-LHC, the high-brightness LHC.
Fundamental physics is not going to stop there, because there are other lower energy experiments at CERN, like the one called Alpha (Antihydrogen Laser Physics Apparatus) to which Futura has devoted numerous articles for several years. Cern has not only made a name for itself with the discovery of the Z, W bosons and of course Brout-Englert-Higgs, but also by becoming a master in the storage of antiprotons and finally, in the production and trapping of atoms. antihydrogen.
VIDEO :
Antihydrogen formation and 1S-2S excitation in ALPHA
A video explaining how the Alpha experiment works at CERN. To get a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © Cern, Niels Madsen
The antihydrogen atom, a laboratory for new physics
The Alpha experiment proposes to study more and more finely the spectrum of these atoms in the hope of discovering differences with that, very well known and very well measured, of hydrogen atoms. In this case, it is a question of causing atomic transitions in the atoms of antihydrogen using laser beams. The observation of these potential differences would automatically shake the foundations of physics by calling into question the theory of special relativity, even also the quantum theory. It could also provide the key to the riddle of antimatter in cosmology, because the laws of the standard model in particle physics are silent when it comes to explaining why we do not find as much antimatter as matter on the scale of the observable cosmos, while these same laws predict that they should have been produced in equal quantities during the Big Bang.
The members of the Alpha collaboration have just announced via an article published in Nature that they had succeeded in pushing several notches further, a fine measure of the spectrum resulting from the atomic transition 1S-2S in antihydrogen. The precision obtained is of the order of a few parts per thousand billion, a result 100 times more precise than the last measurement carried out in 2016 (see the article below).
Jeffrey Hangst, spokesperson for the Alpha experiment, does not hide his enthusiasm as we can see by a statement reported on the CERN site: “The precision obtained with this new measurement is a final success for us. We've been trying to get it for 30 years, and we finally got it. ”
However, progress remains to be made before matching the accuracy of the same measurement with the hydrogen atom. The margin of progress is 3 orders of magnitude, that is to say a factor of 1,000.
The spectrum of antihydrogen continues to reveal its secrets
Article by Laurent Sacco,
Published on 21/12/2016
Archives
In search of new physics and a better understanding of the Big Bang, CERN physicists track down the differences between matter and antimatter. Their latest results concern the way in which antihydrogen atoms absorb and emit light.
The members of the Alpha (Antihydrogen Laser Physics Apparatus) collaboration at CERN have announced via an article published in Nature that they had taken a step further the study of the spectrum of an antihydrogen atom, that is that is, the characteristics of the electromagnetic radiation that this atom can absorb and emit.
As we saw in a previous article, these are so-called hyperfine transitions between the energy levels of a positron in such an anti-atom that had been produced and then measured a few years ago. Physicists, as they announced at that time, managed to observe transitions in the field of ultraviolet light, that is to say in their terminology, the equivalent of transitions between levels 1S and 2S of a Bohr atom where a positron has been substituted for an electron, and an antiproton for a proton.
Recall that CERN researchers have a long tradition in the production and storage of antiprotons thanks in particular to the work of the Nobel Prize in physics Simon van der Meer. This allowed them to manufacture in 1995, the first antihydrogen atom and then to produce large quantities with the Athena experiment in 2002. Thanks to that baptized Alpha, which started in 2010, the physicists of Cern finally arrived to trap these antiatoms to study them as they please.
In 2016, to study antihydrogen, the researchers began by mixing approximately 90,000 antiprotons, from a machine called Antiproton decelerator, with positrons from the radioactive decay of sodium nuclei 22, which allowed synthesis about 25,000 atoms of antihydrogen. The gas obtained was cooled below 1 degree Kelvin and some of these antihydrogen atoms were then magnetically trapped. This then made it possible to study atomic transitions finely by exciting these atoms using laser beams.
VIDEO :
The ALPHA experiment observes light spectrum of antimatter for the ...
A presentation of the latest results of the members of the Alpha collaboration by their spokesperson, Jeffrey Hangst. To get a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on "Subtitles" and finally on "Translate automatically". Choose "French". © Cern
A violation of special relativity with antihydrogen?
For the moment, with the accuracy of the measurements reached (they should improve in the near future), there is no observable difference between the way in which a hydrogen atom absorbs and emits light at well frequencies. precise and how does it, at these same frequencies, an antihydrogen atom. If however such a difference were to be observed, it would mean that we are in the presence of a violation of the CPT theorem, a very deep theorem, resulting from the laws of symmetry, which applies to all relativistic quantum theories of fields , so to the standard model.
This theorem was first proven by the Nobel Prize in physics Julian Schwinger in 1951, then more rigorously and completely in 1954 by Gerhart Lüders and Wolfgang Pauli. According to this theorem, the behavior of an antihydrogen atom should be the same as that of a hydrogen atom. It should fall into the Earth's gravitational field in the same way and it should not be possible to discover differences in the emission and absorption spectra of the two objects. If this were not the case, we could perhaps understand why the universe does not seem to contain antimatter, apart from that present in cosmic rays and which results, as on Earth, from collisions or disintegrations with matter particles.
A violation of this theorem in the Alpha experiment would anyway indicate that the theory of special relativity does not apply in certain situations, which would be a revolution opening a window on new physics.
First studies of the antihydrogen spectrum
Article by Laurent Sacco,
Published on 19/03/2012
Archives
Is antigravity possible? Can we detect antigalaxies in the universe? A good way to answer these questions is to study the spectrum of antihydrogen atoms. This is what researchers from the Alpha experiment at CERN are starting to do.
Humanity created its first antihydrogen atom in 1995 at Cern. If we know how to produce antiprotons since the 1950s and antielectrons for even longer, the synthesis of an antiatome is not easy because the antimatter particles theoretically predicted by Paul Dirac in 1928 have the defect of annihilate with their associated matter particles when they meet. Preventing a positron from disappearing by colliding with an electron, or preventing an antiproton from doing the same with the protons of a nucleus is not easy in our world where, strangely, matter predominates overwhelmingly over antimatter .
However, at the beginning of the birth of the observable universe, there should have been created as much matter as antimatter. At least that's what the standard model equations tell us. One way to explain this asymmetry, this enigma of the absence of antimatter in cosmology, is to involve physics beyond the standard model. It could for example be that at high energies, our universe is effectively described by GUT type theories as Julien Baglio has just explained to us. The discovery of a supersymmetric Higgs boson could be a good indication that the architecture of the cosmos really rests on these foundations.
Others offer even crazier hypotheses. Are we sure that antimatter falls into the gravitational field of an object made of normal matter? What if a weak antigravity existed between matter and antimatter, having led the primitive universe to separate into two or multiple distinct regions? If this is the case, perhaps even galaxies and antigalaxies form clusters that repel each other. They would thus stand at a good distance, avoiding destructive contacts which would generate waves of gamma rays ... which are not observed.
Left Wolfgang Pauli and right Paul Dirac. Both are Nobel Prize winners in physics and are among the founding fathers of quantum mechanics. Our theoretical knowledge of antimatter is heavily based on their work in the years 1930-1940. If Dirac was the first to predict the existence of antimatter, it was Pauli who first understood, in 1924, that the hyperfine spectral structure of hydrogen discovered in the 19th century by Michelson could be explained well if electrons and nuclei had their own magnetic moment. © Cern
To hopefully answer all of these questions, one of the surest ways is probably to create a large number of antihydrogen atoms to study their properties in the laboratory to find out if antiatoms are really the equivalent of atoms of matter. Do they have the same emission spectra? In other words, is the light of an anti-galaxy indistinguishable from that of a galaxy composed of "normal" matter? Do they fall in the same way in the Earth's gravitational field?
To track down the mysteries of antimatter, Cern researchers had to manage to create a large number of these antiatoms, and, above all, that they exist long enough to be the subject of measurements. These two conditions have been achieved for a few years with the Alpha experiment (Antihydrogen Laser Physics Apparatus).
In a publication in the journal Nature, members of the Alpha collaboration announce today that they are starting to be able to study the spectrum of antihydrogen atoms.
The hyperfine spectral structure of antihydrogen
For the moment, researchers have not observed the main atomic transitions equivalent to those of an electron jumping into different orbits of a Bohr atom. They were content to cause transitions at the level of what is called the hyperfine spectral structure of the atom of neutral antihydrogen. For this, microwaves caused the tilting of the intrinsic magnetic moment of the positron, which occurs at a very specific frequency. The choice of this type of transition is probably not trivial.
We know that the hydrogen atom has fine energy levels resulting from the magnetic interaction of the spin of its electron with that of its proton. Depending on whether these two spins are parallel or antiparallel, the energy level of the electron is not the same and a transition with emission of a photon with a wavelength of 21 cm is possible. This transition is very useful in astrophysics to map atomic hydrogen in a galaxy. It is the famous line at 21 cm from hydrogen.
In the case of the Alpha experiment, the fact that a transition of this type does indeed occur with some of the antiatoms captured in a Penning trap is signaled by the escape of these antiatoms from the trap. Colliding with atoms, they annihilate themselves leaving characteristic measurable traces.
Researchers are now preparing to go further by performing atomic transitions with lasers. It is only when fine and precise measurements of the spectrum of antihydrogen atoms have been made that differences between matter and antimatter, coming from physics beyond the standard model, may perhaps appear in the open.
Interview: what is the quantum vacuum? The vacuum in physics is a difficult concept to define. One might think that it designates the absence of everything, but it seems that this is not really the case in quantum mechanics ... Futura-Sciences interviewed Claude Aslangul so that he could tell us a little more about the subject.
Sorry !
Please update your browser or try a different one.
(reportld: 1e24hj1s055vbec00p9)
F I N .
