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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” 


    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.

    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.

    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.

    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



    CERN CMS New

    CERN LHCb New


    CERN LHC New

    LHC particles

    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

    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.

    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.

    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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