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  • richardmitnick 5:34 pm on March 22, 2018 Permalink | Reply
    Tags: , , , , , , , , Rutgers Physics, , The Standard Model   

    From Rutgers: “Physicists at Crossroads in Trying to Understand Universe” 

    Rutgers smaller
    Our once and future Great Seal.

    Rutgers University

    March 21, 2018
    Todd Bates

    This image shows the evolution of the universe from its Big Bang birth (on the left) to the present (on the right), a timespan of nearly 14 billion years. By producing the world’s highest energy collisions, CERN’s Large Hadron Collider in Switzerland acts as a time machine that takes Rutgers physics professors Scott Thomas and Sunil Somalwar all the way back to the first trillionth of a second after the Big Bang.
    Image: NASA/WMAP Science Team

    Scientists at Rutgers University–New Brunswick and elsewhere are at a crossroads in their 50-year quest to go beyond the Standard Model in physics.

    Rutgers Today asked professors Sunil Somalwar and Scott Thomas in the Department of Physics and Astronomy at the School of Arts and Sciences to discuss mysteries of the universe. Somalwar’s research focuses on experimental elementary particle physics, or high energy physics, which involves smashing particles together at large particle accelerators such as the one at CERN in Switzerland. Thomas’s research focuses on theoretical particle physics.

    The duo, who collaborate on experiments, and other Rutgers physicists – including Yuri Gershtein – contributed to the historic 2012 discovery of the Higgs boson, a subatomic particle responsible for the structure of all matter and a key component of the Standard Model.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Standard Model of Particle Physics from Symmetry Magazine

    Rutgers Today: What is the Standard Model?

    Thomas: It is a theory started about 50 years ago. It should be called “the most fantastically successful theory of everything ever” because it’s a triumph of human intellect. It explains, in a theoretical structure and in great quantitative detail, every single experiment ever done in the laboratory. And no experiment so far conflicts with this theory. The capstone to the Standard Model experimentally was the discovery of the Higgs boson. It predicted the existence and interactions of lots of different particles, all of which were found. The problem is that as theorists, we are victims of our own success. The Standard Model is so successful that the theory does not point to answers to some of the questions we still have. The Higgs boson answered many questions, but we don’t get clues directly from this theoretical structure how the remaining questions might be answered, so we’re at a crossroads in this 50-year quest. We need some hints from experiments and then, hopefully, the hints will be enough to tell us the next theoretical structure that underlies the Standard Model.

    Rutgers Today: What questions remain?

    Somalwar: The Standard Model says that matter and antimatter should be nearly equal. But after the Big Bang about 13.8 billion years ago, matter amounted to one part in 10 billion and antimatter dropped to virtually zero. A big mystery is what happened to all the antimatter. And why are neutrinos (also subatomic particles) so light? Is the Higgs boson particle by itself or is there a Higgs zoo? There are good reasons that the Higgs boson could not possibly be alone. There’s got to be more to the picture.

    Rutgers Today: What are you focusing on?

    Somalwar: I am looking for evidence of heavy particles that might have existed a picosecond after the Big Bang. These particles don’t exist anymore because they degenerate. They’re very unstable. They could explain why neutrinos are so light and why virtually all antimatter disappeared but not all matter disappeared. What we do is called frontier science – it’s at the forefront of physics: the smallest distances and highest energies. Once you get to the frontier, you occupy much of the area and start prospecting. But at some point, things are mined out and you need a new frontier. We’ve just begun prospecting here. We don’t have enough mined areas and we may have some gems lying there and more will come in the next year or two. So, it’s a very exciting time right now because it’s like we’ve gotten to the gold rush.

    Thomas: I am trying to understand the physics underlying the Higgs sector of the Standard Model theory, which must include at least one particle – the Higgs boson. This sector is very important because it determines the size of atoms and the mass of elementary particles. The physics underlying the Higgs sector is a roadblock to understanding physics at a more fundamental scale. Are there other species of Higgs particles? What are their interactions and what properties do they have? That would start to give us clues and then maybe we could reconstruct a theory of what underlies the Standard Model. The real motivation is to understand the way the universe works at its most fundamental level. That’s what drives us all.

    See the full article here.

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    Rutgers, The State University of New Jersey, is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.

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  • richardmitnick 2:48 pm on April 17, 2017 Permalink | Reply
    Tags: , The Five Forces, The Great Courses Daily, The Standard Model   

    From Don Lincoln of FNAL via The Great Courses Daily 


    The Great Courses Daily

    A Search For the Theory of Everything

    FNAL Don Lincoln

    From a lecture series by Professor Don Lincoln, Ph.D. & Head Scientist at FermiLab

    The unifying theories of physics are among the greatest and most complex in all of science; their progression toward ever-grander insights will transform our understanding of the universe, and is nothing less than a search for the theory of everything.

    No image caption. No image credit.

    “Dream no small dreams for they have no power to move the hearts of men.”

    This quote by Johann Wolfgang von Goethe is still powerful today, two centuries after he first wrote it down. It doesn’t matter whether you’re trying to broker an international peace treaty or cure a disease or change a society, it’s not the incremental improvements that stir the blood; it’s the big ideas.

    There is a class of scientists who who live by these words. They keep thinking big and asking “why,” with each answer resulting in yet another question. They do that over and over and over again, and the hope is that, one day, there will be no more questions, because we understand the reasons for everything. That is dreaming big!

    Our mastery of the atom made chemistry possible and also allowed us to build electronics and computers that can calculate faster than human imagination. No image credit.

    In science, humanity has had great success over the centuries. Isaac Newton’s amazing ideas about gravity were the first major scientific steps toward a theory of everything, ideas that we still use to guide our space probes to distant targets, like when the New Horizons spacecraft buzzed by Pluto.

    NASA/New Horizons spacecraft

    Our mastery of the atom made chemistry possible and also allowed us to build electronics and computers that can calculate faster than human imagination.

    Each of these achievements is big in its own way, but they aren’t the biggest possible. While there’s no denying that these ideas originated from a grand dream, each represents merely a single facet of human knowledge. The ultimate goal of science is much bigger. The ultimate goal of science is nothing less than an understanding of the fundamental rules of the universe itself. That’s a pretty ambitious goal and it depends crucially on the idea, which seems to be a fact, that all of the phenomena we see around us are interconnected and arise from even deeper causes.

    The Standard Model

    While nobody claims that science is done in their search, you can regard the standard model as the current best guess of a grand unified theory.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    That’s why it’s so important to understand it and what it signifies. For one thing, whatever the final theory of everything looks like, the standard model will be part of it.

    The key components of the standard model consist of:

    Quarks – found inside protons and neutrons in the center of atom;
    Leptons – the lightest of the subatomic particles, the most familiar one is the electron is found in the outskirts of every atom;
    Force-carrying particles, sometimes called gauge bosons – responsible for transmitting three of the four known forces;
    Higgs Boson – a particle whose existence was confirmed in 2012, the final missing piece to the standard model.

    Over the last few decades, science has unified forces that historically have seemed distinct. That’s incredibly exciting, but it also leads to a bit of confusion, so let’s clear that up a bit, by talking about the five forces — the third item in the components of the standard model.

    Earth gravity. ThinkstockPhotos

    The Five Forces

    The five forces are as follows:

    Gravity, which keeps us firmly planted on the ground and guides the planets through their trajectories
    Electromagnetism, which includes electricity, magnetism, light and chemistry
    The strong nuclear force, which binds protons and neutrons together in the nucleus of atoms
    The weak force, which is responsible for forms of radioactivity
    The Higgs field, which gives mass to subatomic particles

    But why then, in some cases, does science refer to only three or four forces? Well, in the late 1960s, physicists showed that the weak force and electromagnetism were really two facets of a single thing, much in the same way that electricity and magnetism turned out to be two facets of something that we now call electromagnetism.

    Therefore, scientists often talk about an electroweak theory, so they might say that the forces are gravity, the electroweak force, the strong force, and the Higgs field. On the other hand, the Higgs field is inextricably tied with the electroweak force, so maybe it can get tucked under the electroweak umbrella. Under that way of thinking, there are but three: gravity, the strong force, and the electroweak complex.

    And how about the term forces? A better word for these would be interaction, because the word interaction means that some change is caused, like changing a particle’s identity without actually moving it. However, the word force is ingrained in the literature, so let’s stick with that word most of the time.

    The Strong force is used to explain why the sun burns at such high temperatures. No image credit.

    The strong force is the strongest of the known forces. For example, it’s the force that explains why the sun burns so very hot. But it also has a weird behavior. It’s incredibly strong over very short ranges—say, the size of a proton. Once two particles are separated by a distance much larger than that, the strong force goes to zero. It’s a little like Velcro. If two pieces of Velcro are touching, they’re strongly bound together, but once they’re separated, they feel no attractive force at all. That particular facet plays a big role in understanding the large range observed in the mass of atoms. That’s the strong force.

    The next strongest force is electromagnetism, which unifies electricity and magnetism into a single force. It’s much weaker than the strong force, but it has a different behavior as far as distance is concerned. Two particles experiencing the electromagnetic force will, in principle, feel a force between one another even if they are located on opposite sides of the universe. Granted, that force will be very small, but it won’t be mathematically zero, because electromagnetism has an infinite range.

    Because of the difference in how the two forces change with distance, you have to be very careful to specify distances when you compare electromagnetism to the strong force, so you traditionally pick a separation distance of about the size of a proton, which is a femtometer, or 10−15 meters. At that separation distance, the strong force is about 100 times stronger than electromagnetism. Of course, given the short range of the strong force and the infinite range of electromagnetism, if two particles are separated by just a meter, or even a millimeter, electromagnetism is actually much stronger.

    The next weakest force is the weak force. The natural range of the weak force is about 1/1000 the size of a proton. However, if we ask how strong it is at the separation of a femtometer, it’s about 100,000 times weaker than the strong force. When we look at the weak force at its natural scale, we see that it’s actually similar to electromagnetism, and that was the beautiful insight that allowed for electroweak unification.

    Then there’s gravity. It has an infinite range like electromagnetism, but at the femtometer distance scale, gravity is approximately like 1040 times weaker than the strong force. That’s a one over a one followed by 40 zeros. “Approximately” because you get a different answer if you’re talking about the gravitational force between two protons, two electrons, or a proton and an electron, but the 1040 number gives you the right message: gravity is crazy weak. And, indeed, gravity is so weak that we’ve never figured out a way to study it on these super-small scales. If we tried, the measurements would just get swamped by the effects of the other forces. So gravity is not covered by the standard model.

    The Higgs field is a bit different — it actually gives mass to particles, so it’s not a force in the way that the others are. Therefore, it isn’t discussed in quite the same way because we don’t know how its strength compares to the others. This is one of the times where the word interaction is more apt. Because of its interaction, the Higgs field turns massless particles into massive particles.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    The standard model is amazing, and we’ve only bareley discussed one of it’s four components. With this standard model, science can explain basically everything we see, from why cells divide, to how stars burn, to why objects move in a particular manner, and on and on. The hope is that one day, we will be able to unify the electroweak and strong forces into a single force called a grand unified theory, which I’m certain we will discuss in a later article.

    See the full article here .

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  • richardmitnick 3:11 pm on July 28, 2016 Permalink | Reply
    Tags: , , , The Standard Model   

    From Symmetry: “The deconstructed Standard Model equation” 

    Symmetry Mag


    Rashmi Shivni

    Yvonne Tang, SLAC National Accelerator Laboratory

    The Standard Model is far more than elementary particles arranged in a table.

    The Standard Model of particle physics is often visualized as a table, similar to the periodic table of elements, and used to describe particle properties, such as mass, charge and spin.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The table is also organized to represent how these teeny, tiny bits of matter interact with the fundamental forces of nature.

    But it didn’t begin as a table. The grand theory of almost everything actually represents a collection of several mathematical models that proved to be timeless interpretations of the laws of physics.

    Here is a brief tour of the topics covered in this gargantuan equation.

    The whole thing

    This version of the Standard Model is written in the Lagrangian form. The Lagrangian is a fancy way of writing an equation to determine the state of a changing system and explain the maximum possible energy the system can maintain.

    Technically, the Standard Model can be written in several different formulations, but, despite appearances, the Lagrangian is one of the easiest and most compact ways of presenting the theory.


    Section 1

    These three lines in the Standard Model are ultraspecific to the gluon, the boson that carries the strong force. Gluons come in eight types, interact among themselves and have what’s called a color charge.


    Section 2

    Almost half of this equation is dedicated to explaining interactions between bosons, particularly W and Z bosons.

    Bosons are force-carrying particles, and there are four species of bosons that interact with other particles using three fundamental forces. Photons carry electromagnetism, gluons carry the strong force and W and Z bosons carry the weak force. The most recently discovered boson, the Higgs boson, is a bit different; its interactions appear in the next part of the equation.


    Section 3

    This part of the equation describes how elementary matter particles interact with the weak force. According to this formulation, matter particles come in three generations, each with different masses. The weak force helps massive matter particles decay into less massive matter particles.

    This section also includes basic interactions with the Higgs field, from which some elementary particles receive their mass.

    Intriguingly, this part of the equation makes an assumption that contradicts discoveries made by physicists in recent years. It incorrectly assumes that particles called neutrinos have no mass.


    Section 4

    In quantum mechanics, there is no single path or trajectory a particle can take, which means that sometimes redundancies appear in this type of mathematical formulation. To clean up these redundancies, theorists use virtual particles they call ghosts.

    This part of the equation describes how matter particles interact with Higgs ghosts, virtual artifacts from the Higgs field.


    Section 5

    This last part of the equation includes more ghosts. These ones are called Faddeev-Popov ghosts, and they cancel out redundancies that occur in interactions through the weak force.


    Note: Thomas Gutierrez, an assistant professor of Physics at California Polytechnic State University, transcribed the Standard Model Lagrangian for the web. He derived it from Diagrammatica, a theoretical physics reference written by Nobel Laureate Martinus Veltman. In Gutierrez’s dissemination of the transcript, he noted a sign error he made somewhere in the equation. Good luck finding it!

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

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