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  • richardmitnick 2:49 pm on October 26, 2018 Permalink | Reply
    Tags: Antimatter and Matter, , , , J-PARC accelerator, , , Super Kamiokande experiment, T2K (Tokai to Kamiokande) experiment   

    From Live Science: “Could Misbehaving Neutrinos Explain Why the Universe Exists?” 

    From Live Science

    October 24, 2018

    FNAL’s Don Lincoln

    Credit: Shutterstock

    Scientists revel in exploring mysteries, and the bigger the mystery, the greater the enthusiasm. There are many huge unanswered questions in science, but when you’re going big, it’s hard to beat “Why is there something, instead of nothing?”

    That might seem like a philosophical question, but it’s one that is very amenable to scientific inquiry. Stated a little more concretely, “Why is the universe made of the kinds of matter that makes human life possible so that we can even ask this question?” Scientists conducting research in Japan have announced a measurement last month that directly addresses that most fascinating of inquiries. It appears that their measurement disagrees with the simplest expectations of current theory and could well point toward an answer of this timeless question.

    Their measurement seems to say that for a particular set of subatomic particles, matter and antimatter act differently.

    Matter v. Antimatter

    Using the J-PARC accelerator, located in Tokai, Japan, scientists fired a beam of ghostly subatomic particles called neutrinos and their antimatter counterparts (antineutrinos) through the Earth to the Super Kamiokande experiment, located in Kamioka, also in Japan.

    J-PARC Facility Japan Proton Accelerator Research Complex , located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    This experiment, called T2K (Tokai to Kamiokande), is designed to determine why our universe is made of matter. A peculiar behavior exhibited by neutrinos, called neutrino oscillation, might shed some light on this very vexing problem.

    T2K map, T2K Experiment, Tokai to Kamioka, Japan

    Asking why the universe is made of matter might sound like a peculiar question, but there is a very good reason that scientists are surprised by this. It’s because, in addition to knowing of the existence of matter, scientists also know of antimatter.

    In 1928, British physicist Paul Dirac proposed the existence of antimatter — an antagonistic sibling of matter. Combine equal amounts of matter and antimatter and the two annihilate each other, resulting in the release of an enormous amount of energy. And, because physics principles usually work equally well in reverse, if you have a prodigious quantity of energy, it can convert into exactly equal amounts of matter and antimatter. Antimatter was discovered in 1932 by American Carl Anderson and researchers have had nearly a century to study its properties.

    However, that “into exactly equal amounts” phrase is the crux of the conundrum. In the brief moments immediately after the Big Bang, the universe was full of energy. As it expanded and cooled, that energy should have converted into equal parts matter and antimatter subatomic particles, which should be observable today. And yet our universe consists essentially entirely of matter. How can that be?

    By counting the number of atoms in the universe and comparing that with the amount of energy we see, scientists determined that “exactly equal” isn’t quite right. Somehow, when the universe was about a tenth of a trillionth of a second old, the laws of nature skewed ever-so-slightly in the direction of matter. For every 3,000,000,000 antimatter particles, there were 3,000,000,001 matter particles. The 3 billion matter particles and 3 billion antimatter particles combined — and annihilated back into energy, leaving the slight matter excess to make up the universe we see today.

    Since this puzzle was understood nearly a century ago, researchers have been studying matter and antimatter to see if they could find behavior in subatomic particles that would explain the excess of matter. They are confident that matter and antimatter are made in equal quantities, but they have also observed that a class of subatomic particles called quarks exhibit behaviors that slightly favor matter over antimatter. That particular measurement was subtle, involving a class of particles called K mesons which can convert from matter to antimatter and back again. But there is a slight difference in matter converting to antimatter as compared to the reverse. This phenomenon was unexpected and its discovery led to the 1980 Nobel prize, but the magnitude of the effect was not enough to explain why matter dominates in our universe.

    Ghostly beams

    Thus, scientists have turned their attention to neutrinos, to see if their behavior can explain the excess matter. Neutrinos are the ghosts of the subatomic world. Interacting via only the weak nuclear force, they can pass through matter without interacting nearly at all. To give a sense of scale, neutrinos are most commonly created in nuclear reactions and the biggest nuclear reactor around is the Sun. To shield one’s self from half of the solar neutrinos would take a mass of solid lead about 5 light-years in depth. Neutrinos really don’t interact very much.

    Between 1998 and 2001, a series of experiments — one using the Super Kamiokande detector, and another using the SNO detector in Sudbury, Ontario ­­— proved definitively that neutrinos also exhibit another surprising behavior. They change their identity.

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    SNOLAB, Sudbury, Ontario, Canada.

    Physicists know of three distinct kinds of neutrinos, each associated with a unique subatomic sibling, called electrons, muons and taus. Electrons are what causes electricity and the muon and tau particle are very much like electrons, but heavier and unstable.

    The three kinds of neutrinos, called the electron neutrino, muon neutrino and tau neutrino, can “morph” into other types of neutrinos and back again. This behavior is called neutrino oscillation.

    Neutrino oscillation is a uniquely quantum phenomenon, but it is roughly analogous to starting out with a bowl of vanilla ice cream and, after you go and find a spoon, you come back to find that the bowl is half vanilla and half chocolate. Neutrinos change their identity from being entirely one type, to a mix of types, to an entirely different type, and then back to the original type.

    Antineutrino oscillations

    Neutrinos are matter particles, but antimatter neutrinos, called antineutrinos, also exist. And that leads to a very important question. Neutrinos oscillate, but do antineutrinos also oscillate and do they oscillate in exactly the same way as neutrinos? The answer to the first question is yes, while the answer to the second is not known.

    Let’s consider this a little more fully, but in a simplified way: Suppose that there were only two neutrino types — muon and electron. Suppose further that you had a beam of purely muon type neutrinos. Neutrinos oscillate at a specific speed and, since they move near the speed of light, they oscillate as a function of distance from where they were created. Thus, a beam of pure muon neutrinos will look like a mix of muon and electron types at some distance, then purely electron types at another distance and then back to muon-only. Antimatter neutrinos do the same thing.

    However, if matter and antimatter neutrinos oscillate at slightly different rates, you’d expect that if you were a fixed distance from the point at which a beam of pure muon neutrinos or muon antineutrinos were created, then in the neutrino case you’d see one blend of muon and electron neutrinos, but in the antimatter neutrino case, you’d see a different blend of antimatter muon and electron neutrinos. The actual situation is complicated by the fact that there are three kinds of neutrinos and the oscillation depends on beam energy, but these are the big ideas.

    The observation of different oscillation frequencies by neutrinos and antineutrinos would be an important step towards understanding the fact that the universe is made of matter. It’s not the entire story, because additional new phenomena must also hold, but the difference between matter and antimatter neutrinos is necessary to explain why there is more matter in the universe.

    In the current prevailing theory describing neutrino interactions, there is a variable that is sensitive to the possibility that neutrinos and antineutrinos oscillate differently. If that variable is zero, the two types of particles oscillate at identical rates; if that variable differs from zero, the two particle types oscillate differently.

    When T2K measured this variable, they found it was inconsistent with the hypothesis that neutrinos and antineutrinos oscillate identically. A little more technically, they determined a range of possible values for this variable. There is a 95 percent chance that the true value for that variable is within that range and only a 5 percent chance that the true variable is outside that range. The “no difference” hypothesis is outside the 95 percent range.

    In simpler terms, the current measurement suggests that neutrinos and antimatter neutrinos oscillate differently, although the certainty does not rise to the level to make a definitive claim. In fact, critics point out that measurements with this level of statistical significance should be viewed very, very skeptically. But it is certainly an enormously provocative initial result, and the world’s scientific community is extremely interested in seeing improved and more precise studies.

    The T2K experiment will continue to record additional data in hopes of making a definitive measurement, but it’s not the only game in town. At Fermilab, located outside Chicago, a similar experiment called NOvA is shooting both neutrinos and antimatter neutrinos to northern Minnesota, hoping to beat T2K to the punch.

    FNAL NOvA Near Detector

    FNAL/NOvA experiment map

    FNAL NOvA far detector in northern Minnesota

    NOvA Far Detector Block

    And, looking more to the future, Fermilab is working hard on what will be its flagship experiment, called DUNE (Deep Underground Neutrino Experiment), which will have far superior capabilities to study this important phenomenon.

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    SURF DUNE LBNF Caverns at Sanford Lab

    While the T2K result is not definitive and caution is warranted, it is certainly tantalizing. Given the enormity of the question of why our universe seems to have no appreciable antimatter, the world’s scientific community will avidly await further updates.

    See the full article here .


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  • richardmitnick 2:18 pm on February 3, 2018 Permalink | Reply
    Tags: Antimatter and Matter, , , ,   

    From Ethan Siegel: “What’s So ‘Anti’ About Antimatter?” 

    From Ethan Siegel
    Feb 3. 2018

    High-energy collisions of particles can create matter-antimatter pairs or photons, while matter-antimatter pairs annihilate to produce photons as well, as these bubble chamber tracks show. But what determines whether a particle is matter or antimatter? Image credit: Fermilab.

    There are lots of properties inherent to particles, and while everyone has an antiparticle, not everyone is matter or antimatter.

    For every particle of matter that’s known to exist in the Universe, there’s an antimatter counterpart. Antimatter has many of the same properties as normal matter, including the types of interaction it undergoes, its mass, the magnitude of its electric charge, and so on. But there are a few fundamental differences as well. Yet two things are certain about matter-antimatter interactions: if you collide a matter particle with an antimatter counterpart, they both immediately annihilate away to pure energy, and if you undergo any interaction in the Universe that creates a matter particle, you must also create its antimatter counterpart. So what makes antimatter so “anti,” anyway? That’s what Robert Nagle wants to know, as he asks:

    On a fundamental level, what is the difference between matter and its counterpart antimatter? Is there some sort of intrinsic property that causes a particle to be matter or antimatter? Is there some intrinsic property (like spin) that distinguishes quarks and antiquarks? What what puts the ‘anti’ in anti matter?

    To understand the answer, we need to take a look at all the particles (and antiparticles) that exist.

    The particles and antiparticles of the Standard Model obey all sorts of conservation laws, but there are fundamental differences between fermionic particles and antiparticles and bosonic ones. Image credit: E. Siegel / Beyond The Galaxy.

    This is the Standard Model of elementary particles: the full suite of discovered particles in the known Universe. There are generally two classes of these particles, the bosons, which have integer spins (…, -2, -1, 0, +1, +2, …) and are neither matter nor antimatter, and the fermions, which have half-integer spins (…, -3/2, -1/2, +1/2, +3/2, …) and must either be “matter-type” or “antimatter-type” particles. For any particle you can think about creating, there are going to be a slew of inherent properties to it, defined by what we call quantum numbers. For an individual particle in isolation, this includes a number of traits you’re likely familiar with, as well as some that you may not be familiar with.

    These possible configurations for an electron in a hydrogen atom are extraordinarily different from one another, yet all represent the same exact particle in a slightly different quantum state. Particles (and antiparticles) also have intrinsic quantum numbers that cannot be changed, and those numbers are key in defining whether a particle is matter, antimatter, or neither. Image credit: PoorLeno / Wikimedia Commons.

    The easy ones are things like mass and electric charge. An electron, for example, has a rest mass of 9.11 × 10^–31 kg, and an electric charge of -1.6 × 10^–19 C. Electrons can also bind together with protons to produce a hydrogen atom, with a series of spectral lines and emission/absorption features based on the electromagnetic force between them. Electrons have a spin of either +1/2 or -1/2, a lepton number of +1, and a lepton family number of +1 for the first (electron) of the three (electron, mu, tau) lepton families. (We’re going to ignore numbers like weak isospin and weak hypercharge, for simplicity.)

    Given these properties of an electron, we can ask ourselves what the antimatter counterpart of the electron would need to look like, based on the rules governing elementary particles.

    In a simple hydrogen atom a single electron orbits a single proton. In an antihydrogen atom a single positron (anti-electron) orbits a single antiproton. Positrons and antiprotons are the antimatter counterparts of electrons and protons, respectively. Image credit: Lawrence Berkeley Labs.

    The magnitudes of all the quantum numbers must remain the same. But for antiparticles, the signs of these quantum numbers must be reversed. For an anti-electron, that means it should have the following quantum numbers:

    a rest mass of 9.11 × 10^–31 kg,
    an electric charge of +1.6 × 10^–19 C,
    a spin of (respectively) either -1/2 or +1/2,
    a lepton number of -1,
    and a lepton family number of -1 for the first (electron) lepton family.

    And when you bind it together with an antiproton, it should produce exactly the same series of spectral lines and emission/absorption features that the electron/proton system produced.

    Electron transitions in the hydrogen atom, along with the wavelengths of the resultant photons, showcase the effect of binding energy and the relationship between the electron and the proton in quantum physics. The spectral lines between positrons and antiprotons have been verified to be exactly the same. Image credit: Wikimedia Commons users Szdori and OrangeDog.

    All of these facts have been verified experimentally. The particle matching this exact description of the anti-electron is the particle known as a positron! The reason why this is necessary comes when you consider how you make matter and antimatter: you typically make them from nothing. Which is to say, if you collide two particles together at a high enough energy, you can often create an extra “particle-antiparticle” pair out of the excess energy (from Einstein’s E = mc2), which conserves energy.

    Whenever you collide a particle with its antiparticle, it can annihilate away into pure energy. This means if you collide any two particles at all with enough energy, you can create a matter-antimatter pair. Image credit: Andrew Deniszczyc, 2017.

    But you don’t just need to conserve energy; there are a slew of quantum numbers you also have to conserve! And these include all of the following:

    electric charge,
    angular momentum (which combines “spin” and “orbital” angular momentum; for individual, unbound particles, that’s only “spin”),
    lepton number,
    baryon number,
    lepton family number,
    and color charge.

    Of these intrinsic properties, there are two that define you as either “matter” or “antimatter,” and those are “baryon number” and “lepton number.”

    In the early Universe, the full suite of particles and their antimatter particles were extraordinarily abundant, but as they Universe cooled, the majority annihilated away. All the conventional matter we have left over today is from the quarks and leptons, with positive baryon and lepton numbers, that outnumbered their antiquark and antilepton counterparts. (Only quarks and antiquarks are shown here.) Image credit: E. Siegel / Beyond The Galaxy.

    If either of those numbers are positive, you’re matter. That’s why quarks (which each have baryon number of +1/3), electrons, muons, taus, and neutrinos (which each have lepton number of +1) are all matter, while antiquarks, positrons, anti-muons, anti-taus, and anti-neutrinos are all antimatter. These are all the fermions and antifermions, and every fermion is a matter particle while every antifermion is an antimatter particle.

    The particles of the standard model, with masses (in MeV) in the upper right. The Fermions make up the left three columns; the bosons populate the right two columns. While all particles have a corresponding antiparticle, only the fermions can be matter or antimatter. Image credit: Wikimedia Commons user MissMJ, PBS NOVA, Fermilab, Office of Science, United States Department of Energy, Particle Data Group.

    But there are also the bosons. There are gluons which have for their antiparticles the gluons of the opposite color combinations; there is the W+ which is the antiparticle of the W- (with opposite electric charge), and there are the Z0, the Higgs boson, and the photon, which are their own antiparticles. However, bosons are neither matter nor antimatter. Without a lepton number or baryon number, these particles may have electric charges, color charges, spins, etc., but no one can rightfully call themselves either “matter” or “antimatter” and their antiparticle counterpart the other one. In this case, bosons are simply bosons, and if they have no charges, then they’re simply their own antiparticles.

    On all scales in the Universe, from our local neighborhood to the interstellar medium to individual galaxies to clusters to filaments and the great cosmic web, everything we observe appears to be made out of normal matter and not antimatter. This is an unexplained mystery. Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

    So what puts the “anti” in antimatter? If you’re an individual particle, then your antiparticle is the same mass as you with all the opposite conserved quantum numbers: it’s the particle that’s capable of annihilating with you back to pure energy if ever the two of you meet. But if you want to be matter, you need to have either positive baryon or positive lepton number; if you want to be antimatter, you must have either negative baryon or negative lepton number. Beyond that, there’s no known fundamental reason for our Universe to have favored matter over antimatter; we still don’t know how that symmetry was broken. (Although we have ideas.) If things had turned out differently, we’d probably call whatever we were made of “matter” and its opposite “antimatter,” but who gets which name is completely arbitrary. As in all things, the Universe is biased towards the survivors.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

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