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  • 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
    Tags: , , , , , Standard Model   

    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

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  • richardmitnick 12:48 pm on September 16, 2014 Permalink | Reply
    Tags: , , , , Standard Model   

    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
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    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.

    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 10:34 am on February 15, 2013 Permalink | Reply
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    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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