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  • richardmitnick 4:47 pm on May 9, 2016 Permalink | Reply
    Tags: , , , Standard Model   

    From COSMOS: “Particle physics: a primer to the theory of (almost) everything” 

    Cosmos Magazine bloc

    COSMOS

    9 May 2016
    Cathal O’Connell

    Are you a boson bozo? Do quarks leave you quizzical? Do gluons get you unstuck? Cathal O’Connell has a guide to the zoo of particles, known as the Standard Model of particle physics.

    1
    Graphic of a transverse section through a detector showing one of the numerous particle collision events recorded during the search for the Higgs boson.Credit: ATLAS COLLABORATION/CERN

    CERN ATLAS Higgs Event
    CERN/ATLAS
    ATLAS

    Around the turn of the 4th century BC, the Greek philosopher Democritus caught the smell of baking and thought that little bits of bread must be floating through the air and into his nose. He called the little bits “atoms” (meaning “uncuttable”) and imagined them as tiny spherical balls.

    But atoms are not little solid spheres. They are made of even smaller bits, called particles.

    Scientists’ best description of those particles and the forces that govern their behaviour is called the Standard Model of particle physics, or just “The Standard Model”.

    The Standard Model categorises all of the particles of nature, in the same way that the periodic table categorises the elements. The theory is called the Standard Model because it is so successful it has become “standard”.

    And no, there is no Economy Model, nor a Deluxe one.

    There are, however, still a few kinks to be ironed out (as well as a couple of whopping omissions). That’s why it is sometimes called the “Theory of Almost Everything”.

    How did it all kick off?

    Back in the early 20th century, scientists thought there were only three fundamental particles in nature: protons and neutrons, which make up the nucleus of an atom, and electrons that whizz round it.

    But in the 1950s and 1960s physicists started smashing these particles together and some of them broke. It turned out the protons and neutrons had even smaller particles inside them.

    Many dozens of new particles were discovered – and for a while, nobody could explain them. Physicists called it the “particle zoo”.

    In the 1970s, physicists such as Murray Gell-Mann found an order amongst the chaos. The step they took was similar to the one Russian chemist Dmitri Mendeleev took to find an order to the chemical elements in his periodic table.

    The new ordering of the particles explained many of the properties of the newly discovered particles, as well as correctly predicting some new ones.

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

    Meet the family

    The particles of the Standard Model make up one big family. Your first introduction can be daunting, a bit like attending a gathering with a lot of distant cousins you’ve never heard of. No matter how strange these cousins are, it is important to remember that they are all related.
    The basics

    Gell-Mann and others placed the particles in two main categories: fermions and bosons.

    Fermions, such as the electron, make up the stuff we call matter. Bosons, such as the photon, transmit forces.

    Fermions are subdivided again into two kinds of particles, depending on the forces they feel. These are the quarks and the leptons (see below).
    Forces of nature

    Particles communicate with one another via four forces: electromagnetism, the strong force, the weak force and gravity.

    The Standard Model describes the first three (gravity does not feature in the Standard Model, as explained below).

    Different particles communicate through different forces, similar to the way people can communicate in different languages. For example, only the quarks speak “gluon”. While electrons can speak “photon” as well as “W boson” and “Z boson”.

    Electromagnetism is the force that holds electrons in an atom. It is communicated by photons.

    The strong force keeps the nuclei of atoms together. Without it, every atom in the universe would spontaneously explode. It is communicated by gluons.

    The weak force causes radioactive decay. It’s transmitted by W and Z bosons.

    The fundamental particles

    All matter is made of two types of particles known as quarks and leptons.

    Quarks: (the purple particles in the figure) come in six “flavours”, all with weird names. It’s useful to see them as coming in pairs to make three generations. These are “up” and “down” (first generation), “charmed” and “strange” (second generation) and “top” and “bottom” (third generation).

    Only the up and down quarks are important in day-to-day life because they make protons and neutrons.

    The others make only “exotic” matter, which is too unstable to form atoms. Physicists can create exotic matter in particle accelerators, but it usually only lasts a fraction of a second before decaying.

    Leptons: there are six leptons, the best known of which is the electron, a tiny fundamental particle with a negative charge.

    The muon (second generation) and tau (third generation) particles are like fatter versions of the electron. They also have negative electric charge, but they are too unstable to feature in ordinary matter.

    And each of these particles has a corresponding neutrino, with no charge.

    Neutrinos deserve a special mention because they are perhaps the least understood of all the particles in the Standard Model.

    They are fast but interact only through the weak force, which means they can easily zip straight through a planet. They are created in nuclear reactions, such as those powering the Sun’s core.

    Hadrons: the composite particles

    Now that we know the fundamental particles of nature, we can begin to stack them together in different ways to make bigger particles.

    The most important composite particles are the baryons, made of three quarks. Protons and neutrons are both kinds of baryon.

    The European Organisation for Nuclear Research’s (CERN) biggest particle collider smashes protons together. Because protons are a kind of hadron, it’s called the Large Hadron Collider, or LHC.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Antimatter: double or nothing?

    As far as we know, all quarks and leptons have twin particles of antimatter. Antimatter is like matter except it has the opposite charge. For example, the electron has a counterpart that’s exactly the same mass, except with positive charge instead of negative. When a particle of matter meets its antimatter twin, they both annihilate in a burst of pure energy.

    Antimatter is incredibly rare in the Universe, although it does have some important roles in technology. Positron emission tomography (PET) scanners, for instance, use the annihilation of positrons to see inside the body.

    One of the great mysteries of physics is why the Universe is made almost entirely of matter. Many particle physicists are striving to answer it.

    Atoms: composites of composites

    The bread that Democritus sniffed is made of only the first generation of fundamental particles.

    Up and down quarks bind together through the strong force to make protons and neutrons, and the strong force also sticks them together to form the nucleus of an atom.

    Electrons orbit the nucleus in arrangements determined by quantum mechanics (see our primer Quantum physics for the terminally confused).
    The Higgs: the god particle

    You probably noticed the loner off to the right side of particle table – the Higgs boson. The Higgs is a special kind of particle that gives the other fundamental particles their mass.

    The idea is that there is a field existing everywhere in space. And when particles move through space, they tend to bump into this field, and this interaction slows them down (similar to how it’s more difficult to move through water than air). This interaction is what gives fundamental particles their mass.

    Some particles such as photons and gluons don’t interact with the Higgs field, so are massless.

    Just as photons communicate the electromagnetic force, the Higgs Boson communicates the Higgs Field.

    The Higgs Boson was a theoretical particle until 2013 when CERN announced it had been discovered at last, although scientists are still uncovering its properties.
    What’s missing?

    Gravity

    The biggest hole in the Standard Model is the lack of gravity. The fourth force of nature just does not fit into the current picture.

    Gravity is also incredibly weak compared to the other forces (the strong force is 100,000,000,000,000,000,000,000,000,000,000,000,000 times stronger than gravity, for example).

    Some physicists think gravity is also transmitted by a kind of particle, called a graviton, but so far there is no evidence that this particle exists.

    Neutrino mass

    The neutrino is so tiny compared to all the other particles that it really begs an explanation. It’s possible that the neutrino doesn’t get its mass from the Higgs in the same way other particles do.

    Dark matter: For observing the Universe, it looks like a huge portion of it is made of Dark Matter – a new kind of stuff that doesn’t interact with regular matter and so is probably missing from the Standard Model entirely.

    Supersymmetry

    Some physicists are looking for extensions to the Standard Model to explain these mysteries. Supersymmetry is one extension where every particle has another twin with higher mass.

    Some of these particles would interact very weakly with ordinary stuff and so could be good candidates for Dark Matter.

    See the full article here .

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  • richardmitnick 10:57 am on August 5, 2015 Permalink | Reply
    Tags: , , Standard Model,   

    From Symmetry: “The mystery of particle generations” 

    Symmetry

    August 05, 2015
    Matthew R. Francis

    Why are there three almost identical copies of each particle of matter?

    1
    Artwork by Sandbox Studio, Chicago

    The Standard Model of particles and interactions is remarkably successful for a theory everyone knows is missing big pieces.

    1
    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.

    It accounts for the everyday stuff we know like protons, neutrons, electrons and photons, and even exotic stuff like Higgs bosons and top quarks. But it isn’t complete; it doesn’t explain phenomena such as dark matter and dark energy.

    The Standard Model is successful because it is a useful guide to the particles of matter we see. One convenient pattern that has proven valuable is generations. Each particle of matter seems to come in three different versions, differentiated only by mass.

    Scientists wonder whether that pattern has a deeper explanation or if it’s just convenient for now, to be superseded by a deeper truth.
    The next generations

    The Standard Model is a menu listing all of the known fundamental particles: particles that cannot be broken down into constituent parts. It distinguishes between the fermions, which are particles of matter, and the bosons, which carry forces.

    The matter particles include six quarks and six leptons. The six quarks are called the up, down, charm, strange, top and bottom quark. Quarks typically don’t exist as single particles but lump together to form heavier particles such as protons and neutrons. Leptons include electrons and their cousins the muons and tau particles, along with the three types of neutrinos.

    All of these matter particles fall into three “generations.”

    “The three generations are literally copy-paste of the first generation,” says Carleton University physicist Heather Logan. The up, charm and top quarks have the same electric charge, along with the same weak and strong interactions—they primarily differ in the mass, which comes from the Higgs field. The same thing holds for the down, strange and bottom quarks, along with the electron, muon and tau leptons.

    “The fact that the three generations couple differently to the Higgs sector is maybe telling us something, but we don’t really know what yet,” Logan says. Most of the generations differ in mass by a lot. For example, the tau lepton is roughly 3600 times more massive than the electron, and the top quark is nearly 100,000 times heavier than the up quark. That difference manifests itself in stability: The heavier generations decay into the lighter generations, until they reach the lightest, which are (as far as we can tell) stable forever.

    The generations play a big role in experiments. The Higgs boson, for instance, is an unstable particle that decays into a variety of other particles, including tau leptons. “Since the tau is the heaviest, the Higgs [boson] prefers to change into taus more than electrons or muons,” says Clara Nellist, an experimental particle physicist at the Laboratoire de l’Accélérateur Linéaire (LAL) in Orsay, France. “The best way to study how the Higgs interacts with leptons is by looking at a Higgs changing into two taus.”

    That sort of observation is the heart of Standard Model physics: Crash two or more particles together, watch what new particles are born, look for patterns in the detritus, and—if we’re really lucky—see what doesn’t fit into the map we have.
    Roads outward

    While some stuff like dark matter obviously lies outside the charts, the Standard Model itself has a few problems. For example, neutrinos should be massless according to the Standard Model, but real-world experiments show they have very tiny masses. And unlike quarks and electrically charged leptons, the mass differences between the generations of neutrinos are very small, which is why we see them oscillating from one type to another.

    Without mass, neutrinos are exactly identical; with the mass, they’re different. And that generational difference is puzzling to theorist Richard Ruiz of the University of Pittsburgh. “There is a pattern here staring at us but we cannot quite figure out how to make sense of it.”

    Even if there is only the one Standard Model Higgs, we can learn a lot by how it interacts and decays. For instance, Nellist says, “by studying how often the Higgs boson changes into taus compared to other particles, we can test the validity of the Standard Model and see if there are hints of other generations.”

    It’s unlikely, since any fourth generation quark would need to be far more massive even than the top quark. But any anomaly in Higgs decay could tell us a lot.

    “Nobody knows why there are three generations,” Logan says. However, the structure of the Standard Model is a clue to what might be beyond, including the theory known as Supersymmetry: “If there are supersymmetric partners of the fermions, they should also fall into the three generations. How their masses are set might give us clues to understanding how the masses of the Standard Model fermions are set and why we have those patterns.”

    No matter how many there are, nobody knows why there are generations to begin with. “‘Generations’ is just a conventional organization of the Standard Model’s matter content,” Ruiz says. That organization might survive in a deeper theory (for instance, theories in which quarks are made up of smaller particles called “preons”, which are unlikely based on present data), but new ideas would have to explain why the quarks and leptons seem to fall into the patterns they do.

    Ultimately, even though the Standard Model is not the final description of the cosmos, it’s been a good guide so far. As we look for the edges of the map it provides, we get closer to a true and accurate chart of all the particles and their interactions.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:24 am on July 16, 2015 Permalink | Reply
    Tags: , , Helmholtz Association, , Standard Model,   

    From Helmholtz via DESY: “What is supersymmetry?” 

    DESY
    DESY

    1

    28.04.2015
    Kristine August

    Using huge particle accelerators, physicists are searching for supersymmetry.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Their existence could help us to understand the composition of dark matter. But is it possible for something to be more symmetrical than symmetrical? Wilfried Buchmüller from the Deutsches Elektronen-Synchrotron facility (DESY) explains:

    “We usually associate symmetry with spatial symmetry – in connection with an image or a form, for example. But in the standard model of physics, when we think about symmetries we are thinking about something else – the forces between particles. When, for example, the force between two matter particles remains the same after reversal of the electrical charges, we are referring to “a symmetry”.

    The various forces in the standard model possess a number of such symmetries. According to the standard model, it is valid that the smaller the gaps between the matter particles, the greater the similarity becomes between the mathematical formulas that describe the forces there. We would say here that the theory becomes more symmetrical.

    2
    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.

    Expanding on this concept, the last remaining differences are likely to cancel each other out at some point. It is our goal to describe all forces – gravity as well – and all particles on the basis of one unified principle of symmetry – supersymmetry (“SUSY”).

    But the fundamental difference still exists between matter particles and the particles that transfer forces. Although there are different types of particles, the supersymmetry theory is nevertheless able to interconnect them mathematically. We suspect that every particle has an attendant partner, a hidden supersymmetrical partner, i.e. a “superpartner”; in other words, one half of all matter is completed by its mirror image. Such a superpartner, in supersymmetrical theories, comprises the cornerstone of dark matter. Whenever the different types of particles then appear together, all of the forces become more similar to one another due to the superpartners. It is our ambition that we can also finally prove the existence of “SUSY” in reality. Namely, by finding the superpartners. They would play a key role in helping us to understand the origins of our universe.”

    See the full article here.

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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 2:00 pm on November 20, 2014 Permalink | Reply
    Tags: , , , , Standard Model   

    From phys.org: “Gravity may have saved the universe after the Big Bang, say researchers” 

    physdotorg
    phys.org

    Nov 18, 2014
    No Writer Credit

    New research by a team of European physicists could explain why the universe did not collapse immediately after the Big Bang.

    Studies of the Higgs particle – discovered at CERN in 2012 and responsible for giving mass to all particles – have suggested that the production of Higgs particles during the accelerating expansion of the very early universe (inflation) should have led to instability and collapse.

    in
    Time Line of the Universe. Credit: NASA/WMAP Science Team

    Scientists have been trying to find out why this didn’t happen, leading to theories that there must be some new physics that will help explain the origins of the universe that has not yet been discovered. Physicists from Imperial College London, and the Universities of Copenhagen and Helsinki, however, believe there is a simpler explanation.

    In a new study in Physical Review Letters, the team describe how the spacetime curvature – in effect, gravity – provided the stability needed for the universe to survive expansion in that early period. The team investigated the interaction between the Higgs particles and gravity, taking into account how it would vary with energy.

    They show that even a small interaction would have been enough to stabilise the universe against decay.

    “The Standard Model of particle physics, which scientists use to explain elementary particles and their interactions, has so far not provided an answer to why the universe did not collapse following the Big Bang,” explains Professor Arttu Rajantie, from the Department of Physics at Imperial College London.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    “Our research investigates the last unknown parameter in the Standard Model – the interaction between the Higgs particle and gravity. This parameter cannot be measured in particle accelerator experiments, but it has a big effect on the Higgs instability during inflation. Even a relatively small value is enough to explain the survival of the universe without any new physics!”

    The team plan to continue their research using cosmological observations to look at this interaction in more detail and explain what effect it would have had on the development of the early universe. In particular, they will use data from current and future European Space Agency missions measuring cosmic microwave background radiation and gravitational waves.

    “Our aim is to measure the interaction between gravity and the Higgs field using cosmological data,” says Professor Rajantie. “If we are able to do that, we will have supplied the last unknown number in the Standard Model of particle physics and be closer to answering fundamental questions about how we are all here.”

    See the full article here.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

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  • richardmitnick 3:17 pm on November 11, 2014 Permalink | Reply
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    From Symmetry: “The November Revolution” 

    Symmetry

    November 11, 2014
    Amanda Solliday

    Forty years ago today, two different research groups announced the discovery of the same new particle and redefined how physicists view the universe.

    On November 11, 1974, members of the Cornell high-energy physics group could have spent the lulls during their lunch meeting chatting about the aftermath of Nixon’s resignation or the upcoming Big Red hockey season.

    But on that particular Monday, the most sensational topic was physics-related. One of the researchers in the audience stood up to report that two labs on opposite sides of the country were about to announce the same thing: the discovery of a new particle that heralded the birth of the Standard Model of particle physics.

    tr
    Ting and Richter

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    “Nobody at the meeting knew what the hell it was,” says physicist Kenneth Lane of Boston University, a former postdoctoral researcher at Cornell. Lane, among others, would spend the next few years describing the theory and consequences of this new particle.

    It isn’t often that a discovery comes along that forces everyone to reevaluate the way the world works. It’s even rarer for two groups to make such a discovery at the same time, using different methods.

    One announcement would come from a research group led by MIT physicist Sam Ting at Brookhaven National Laboratory in New York. The other was to come from a team headed by physicist Burton Richter at SLAC National Accelerator Laboratory, then called the Stanford Linear Accelerator Center, in California. Word traveled fast.

    “We started getting all sorts of inquiries and congratulations before we even finished writing the paper,” Richter says. “Somebody told a friend, and then a friend told another friend.”

    Ting called the new particle the J particle. Richter called it psi. It became known as J/psi, the discovery that sparked the November Revolution.

    Independently, the researchers at Brookhaven and SLAC had designed two complementary experiments.

    Ting and his team had made the discovery using a proton machine, shooting an intense beam of particles at a fixed target. Ting was interested in how photons, particles of light, turn into heavy photons, particles with mass, and he wanted to know how many of these types of heavy photons existed in nature. So his team—consisting of 13 scientists from MIT with help from researchers at Brookhaven—designed and built a detector that would accept a wide range of heavy photon masses.

    “The experiment was quite difficult,” Ting says. “I guess when you’re younger, you’re more courageous.”

    In early summer 1974, they started the experiment at a high mass, around 4 to 5 billion electronvolts. They saw nothing. Later, they lowered the mass and soon saw a peak near 3 billion electronvolts that indicated a high production rate of a previously unknown particle.

    At SLAC, Richter had created a new type of collider, the Stanford Positron Electron Asymmetric Rings (SPEAR). His research group used a beam of electrons produced by a linear accelerator and stored the particles in a ring of magnets. Then, they would generate positrons in a linear accelerator and inject them in the other direction. The detector was able to look at everything produced in electron-positron collisions.

    The goal was to determine the masses of known elementary particles, but the researchers saw strange effects in the summer of 1974. They looked at that particular region with finer resolution, and over the weekend of November 9-10, discovered a tall, thin energy peak around 3 billion electronvolts.

    At the time, Ting visited SLAC as part of an advisory committee. The laboratory’s director, Pief Panofsky, asked Richter to meet with him.

    “He called and said, ‘It sounds like you guys have found the same thing,’” Richter says.

    Both researchers sent their findings to the journal Physical Review Letters. Their papers were published in the same issue. Other labs quickly replicated and confirmed the results.

    At the time, the basic pieces of today’s Standard Model of particle physics were still falling into place. Just a decade before, it had resembled the periodic table of the elements, including a wide, unruly collection of different types of particles called hadrons.

    Theorists Murray Gell-Mann and George Zweig were the first to propose that all of those different types of hadrons were actually made up of the same building blocks, called quarks. This model included three types of quark: up, down and strange. Other theorists—Sheldon Lee Glashow, James Bjorken, and then also John Iliopoulos and Luciano Maiani—proposed the existence of a fourth quark.

    On the day of the J/psi announcement, the Cornell researchers talked about the findings well into the afternoon. One of the professors in the department, Ken Wilson, made a connection between the discovery and a seminar given earlier that fall by Tom Appelquist, a physicist at Harvard University. Appelquist had been working with his colleague David Politzer to describe something they called “charmonium,” a bound state of a new type of quark and antiquark.

    “Only a few of us were thinking about the idea of a fourth quark,” says Appelquist, now a professor at Yale. “Ken called me right after the discovery and urged me to get our paper out ASAP.”

    The J/psi news inspired many other theorists to pick up their chalk as well.

    “It was clear from day one that J/psi was a major discovery,” Appelquist says. “It almost completely reoriented the theoretical community. Everyone wanted to think about it.”

    Less than two weeks after the initial discovery, Richter’s group also found psi-prime, a relative of J/psi that showed even more cracks in the three-quark model.

    “There was a whole collection of possibilities of what could exist outside the current model, and people were speculating about what that may be,” Richter says. “Our experiment pruned the weeds.”

    The findings of the J/psi teams triggered additional searches for unknown elementary particles, exploration that would reveal the final shape of the Standard Model. In 1976, the two experiment leaders were awarded the Nobel Prize for their achievement.

    In 1977, scientists at Fermilab discovered the fifth quark, the bottom quark. In 1995, they discovered the sixth one, the top.

    Today, theorists and experimentalists are still driven to answer questions not explained by the current prevailing model. Does supersymmetry exist? What are dark matter and dark energy? What particles have we yet to discover?

    Supersymmetry standard model
    Standard Model of Supersymmetry

    “If the answers are found, it will take us even deeper into what we are supposed to be doing as high-energy physicists,” Lane says. “But it probably isn’t going to be this lightning flash that happens on one Monday afternoon.”

    t&R
    Ting and Richter
    Courtesy of: SLAC National Accelerator Laboratory

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 2:33 pm on October 13, 2014 Permalink | Reply
    Tags: , Standard Model   

    From CERN via FNAL: “CERN and the rise of the Standard Model” 

    CERN New Masthead

    Curiosity is as old as humankind, and it is CERN’s raison d’être. When the Laboratory was founded, the structure of matter was a mystery. Today, we know that all visible matter in the Universe is composed of a remarkably small number of particles, whose behaviour is governed by four distinct forces. CERN has played a vital role in reaching this understanding.

    Watch, enjoy, learn.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries

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  • richardmitnick 12:48 pm on September 16, 2014 Permalink | Reply
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    From phys.org: “Neutrino trident production may offer powerful probe of new physics” 

    physdotorg
    phys.org

    September 15, 2014
    Lisa Zyga

    The standard model (SM) of particle physics has four types of force carrier particles: photons, W and Z bosons, and gluons. But recently there has been renewed interest in the question of whether there might exist a new force, which, if confirmed, would result in an extension of the SM. Theoretically, the new force would be carried by a new gauge boson called Z’ or the “dark photon” because this “dark force” would be difficult to detect, as it would affect only neutrinos and unstable leptons.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    “Much of the complexity and beauty of our physical world depends on only four forces,” Wolfgang Altmannshofer, a researcher at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, told Phys.org. “It stands to reason that any additional new force discovered will bring with it interesting and unexpected phenomena, although it might take some time to fully appreciate and understand its implications.”

    Now in a new study published in Physical Review Letters, Altmannshofer and his coauthors from the Perimeter Institute have shown that the parameter space where a new dark force would exist is significantly restricted by a rare process called neutrino trident production, which has only been experimentally observed twice.

    graph
    Parameter space for the Z’ gauge boson. The light gray area is excluded at 95% C.L. by the CCFR measurement of the neutrino trident cross section. The dark gray region with the dotted contour is excluded by measurements of the SM Z boson decay to four leptons at the LHC. The purple region is the area favored by the muon g-2 discrepancy that has not yet been ruled out, but future high-energy neutrino experiments are expected to be highly sensitive to this low-mass region. Credit: Altmannshofer, et al. ©2014 American Physical Society

    In neutrino trident production, a pair of muons is produced from the scattering of a muon neutrino off a heavy atomic nucleus. If the new Z’ boson exists, it would increase the rate of neutrino trident production by inducing additional particle interactions that would constructively interfere with the expected SM contribution.

    The new force could also solve a long-standing discrepancy in the [Fermilab] muon g-2 experiment compared to the SM prediction. By coupling to muons, the new force might solve this problem.

    However, the two existing experimental results of neutrino trident production (performed by the CHARM-II collaboration and the CCFR collaboration) are both in good agreement with SM predictions, which places strong constraints on any possible contributions from a new force.

    In the new paper, the physicists have analyzed the two experimental results and extended the support for ruling out a dark force, at least over a large portion of the parameter space relevant to solving the muon g-2 discrepancy (when the mass of the Z’ boson is greater than about 400 MeV). The results not only constrain the dark force, but more generally any new force that couples to both muons and muon neutrinos.

    “We showed that neutrino trident production is the most sensitive probe of a certain type of new force,” Altmannshofer said. “Particle physics is driven by the desire to discover new building blocks of nature, and ultimately the principles that organize these building blocks. Our findings establish a new direction where new forces can be searched for, and highlight the planned neutrino facility at Fermilab (the Long-Baseline Neutrino Experiment [LBNE]) as a potentially powerful experiment where such forces can be searched for in the future.”

    Overall, the current results suggest that LBNE would have very favorable prospects for searching for the Z’ boson in the relevant, though restricted, regions of parameter space.

    See the full article here.

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

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  • richardmitnick 11:37 am on October 8, 2013 Permalink | Reply
    Tags: , , Standard Model   

    From CERN: “CERN congratulates Englert and Higgs on Nobel in physics” 

    CERN New Masthead

    8 Oct 2013
    Cian O’Luanaigh

    CERN congratulates François Englert and Peter W. Higgs on the award of the Nobel prize in physics “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.” The announcement by the ATLAS and CMS experiments took place on 4 July last year.

    englert higgs
    François Englert (left) and Peter Higgs at CERN on 4 July 2012, on the occasion of the announcement of the discovery of a Higgs boson by the ATLAS and CMS experiments (Image: Maximilien Brice/CERN)

    “I’m thrilled that this year’s Nobel prize has gone to particle physics,” says CERN Director-General Rolf Heuer. “The discovery of the Higgs boson at CERN last year, which validates the Brout-Englert-Higgs mechanism, marks the culmination of decades of intellectual effort by many people around the world.”

    The Brout-Englert-Higgs (BEH) mechanism was first proposed in 1964 in two papers published independently, the first by Belgian physicists Robert Brout and François Englert, and the second by British physicist Peter Higgs. It explains how the force responsible for beta decay is much weaker than electromagnetism, but is better known as the mechanism that endows fundamental particles with mass. A third paper, published by Americans Gerald Guralnik and Carl Hagen with their British colleague Tom Kibble further contributed to the development of the new idea, which now forms an essential part of the Standard Model of particle physics. As was pointed out by Higgs, a key prediction of the idea is the existence of a massive boson of a new type, which was discovered by the ATLAS and CMS experiments at CERN in 2012.

    sm
    Standard Model

    The Standard Model describes the fundamental particles from which we, and all the visible matter in the universe, are made, along with the interactions that govern their behaviour. It is a remarkably successful theory that has been thoroughly tested by experiment over many years. Until last year, the BEH mechanism was the last remaining piece of the model to be experimentally verified. Now that it has been found, experiments at CERN are eagerly looking for physics beyond the Standard Model.

    See the full article here.

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    CERN ATLAS New
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    CERN ALICE New

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    CERN CMS New

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    CERN LHCb New

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    CERN LHC New

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    Quantum Diaries


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  • richardmitnick 10:34 am on February 15, 2013 Permalink | Reply
    Tags: , , , , Standard Model   

    From Don Lincoln at Fermilab: “Physics in a Nutshell – What’s the point?” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Fermilab Don Lincoln
    Dr. Don Lincoln

    The field of particle physics is full of what can be confusing dichotomies: fermion vs. boson, hadron vs. lepton, paper vs. plastic (okay, not that last one). You can add yet another to the list: extended particles vs. point-like particles.

    The quarks, leptons and bosons of the Standard Model are point-like particles. Every other subatomic particle you’ve heard of is an extended particle. The most familiar are the protons and neutrons that make up the nucleus of an atom, but there are many others—pions, kaons, Lambda particles, omegas and lots more. The defining feature of these kinds of particles is that they have a reasonably measurable size (which happens to be about the size of a proton).”

    Standard Model
    Standard Model with proposed Higgs boson

    points
    If you magnify an extended particle, it will look bigger. A point-like particle will not change in size, but the more closely you look at it, the stronger the field surrounding it becomes. No image credit.

    pointa
    A point particle has no size, but it does have a field around it. The field gets stronger the closer you get to the particle. This field interacts with the particles in the quantum foam of empty space and orients them. In this manner, the point particle has influence in an extended way. No image credit.

    Don is a physicist, and a very articulate communicator and teacher. So, I am going no farther. Read Don’s full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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  • richardmitnick 11:40 am on November 30, 2012 Permalink | Reply
    Tags: , , , , , , , Standard Model   

    From Fermilab Today – Don Lincoln: “CMS Result – Subatomic excitement” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Fermilab Don Lincoln
    Don Lincoln

    Friday, Nov. 30, 201

    “The Standard Model of particle physics is truly a triumph of scientific achievement. By combining 12 fundamental (i.e. structureless) particles and four forces, we can explain essentially every measurement that has investigated the nature and structure of matter. And, for most descriptions of nature, only four particles are needed. All of humanity can rightfully be proud of this accomplishment.

    sm
    The Standard Model of elementary particles, with gauge bosons in the rightmost column. (Wikipedia)

    Nevertheless, the Standard Model is an incomplete model. There are unanswered questions and lots of them. While they are all interesting and should be solved, there’s usually one that bugs some scientist a bit more than the others. The one that bugs me the most personally is why—if all ordinary matter can be constructed of up and down quarks, electrons and electron neutrinos (the first column of the quarks and leptons in the figure)—why there are two additional columns of seemingly redundant particles. As Nobel laureate I.I. Rabi is reported to have exclaimed when he heard of the muon, the first-discovered of these seemingly redundant particles, “Who ordered that?!”

    Well!! Read on in the article for the excitement. The full article is here.

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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