• New clues to why there's so little antim

    From ScienceDaily@1:317/3 to All on Wed Jul 7 21:30:36 2021
    New clues to why there's so little antimatter in the universe

    Date:
    July 7, 2021
    Source:
    Massachusetts Institute of Technology
    Summary:
    New research shows radioactive molecules are sensitive to subtle
    nuclear phenomena. The molecules might help physicists probe
    violation of the most fundamental symmetries of nature, including
    why the universe contains relatively little antimatter.



    FULL STORY ========================================================================== [Model atom rendering | Credit: (c) koya979 / stock.adobe.com] Model
    atom rendering (stock image).

    Credit: (c) koya979 / stock.adobe.com [Model atom rendering | Credit:
    (c) koya979 / stock.adobe.com] Model atom rendering (stock image).

    Credit: (c) koya979 / stock.adobe.com Close Imagine a dust particle in
    a storm cloud, and you can get an idea of a neutron's insignificance
    compared to the magnitude of the molecule it inhabits.


    ==========================================================================
    But just as a dust mote might affect a cloud's track, a neutron can
    influence the energy of its molecule despite being less than one-millionth
    its size. And now physicists at MIT and elsewhere have successfully
    measured a neutron's tiny effect in a radioactive molecule.

    The team has developed a new technique to produce and study short-lived radioactive molecules with neutron numbers they can precisely
    control. They hand-picked several isotopes of the same molecule, each
    with one more neutron than the next. When they measured each molecule's
    energy, they were able to detect small, nearly imperceptible changes of
    the nuclear size, due to the effect of a single neutron.

    The fact that they were able to see such small nuclear effects suggests
    that scientists now have a chance to search such radioactive molecules
    for even subtler effects, caused by dark matter, for example, or by the
    effects of new sources of symmetry violations related to some of the
    current mysteries of the universe.

    "If the laws of physics are symmetrical as we think they are, then the Big
    Bang should have created matter and antimatter in the same amount. The
    fact that most of what we see is matter, and there is only about one
    part per billon of antimatter, means there is a violation of the most fundamental symmetries of physics, in a way that we can't explain with
    all that we know," says Ronald Fernando Garcia Ruiz, assistant professor
    of physics at MIT.

    "Now we have a chance to measure these symmetry violations, using
    these heavy radioactive molecules, which have extreme sensitivity to
    nuclear phenomena that we cannot see in other molecules in nature,"
    he says. "That could provide answers to one of the main mysteries of
    how the universe was created." Ruiz and his colleagues have published
    their results today in Physical Review Letters.



    ==========================================================================
    A special asymmetry Most atoms in nature host a symmetrical, spherical
    nucleus, with neutrons and protons evenly distributed throughout. But
    in certain radioactive elements like radium, atomic nuclei are weirdly pear-shaped, with an uneven distribution of neutrons and protons
    within. Physicists hypothesize that this shape distortion can enhance the violation of symmetries that gave origin to the matter in the universe.

    "Radioactive nuclei could allow us to easily see these symmetry-violating effects," says study lead author Silviu-Marian Udrescu, a graduate
    student in MIT's Department of Physics. "The disadvantage is, they're very unstable and live for a very short amount of time, so we need sensitive
    methods to produce and detect them, fast." Rather than attempt to pin
    down radioactive nuclei on their own, the team placed them in a molecule
    that futher amplifies the sensitivity to symmetry violations. Radioactive molecules consist of at least one radioactive atom, bound to one or
    more other atoms. Each atom is surrounded by a cloud of electrons that
    together generate an extremely high electric field in the molecule that physicists believe could amplify subtle nuclear effects, such as effects
    of symmetry violation.

    However, aside from certain astrophysical processes, such as merging
    neutron stars, and stellar explosions, the radioactive molecules
    of interest do not exist in nature and therefore must be created
    artificially. Garcia Ruiz and his colleagues have been refining techniques
    to create radioactive molecules in the lab and precisely study their properties. Last year, they reported on a method to produce molecules
    of radium monofluoride, or RaF, a radioactive molecule that contains
    one unstable radium atom and a fluoride atom.



    ==========================================================================
    In their new study, the team used similar techniques to produce RaF
    isotopes, or versions of the radioactive molecule with varying numbers
    of neutrons. As they did in their previous experiment, the researchers
    utilized the Isotope mass Separator On-Line, or ISOLDE, facility at CERN,
    in Geneva, Switzerland, to produce small quantities of RaF isotopes.

    The facility houses a low-energy proton beam, which the team directed
    toward a target -- a half-dollar-sized disc of uranium-carbide, onto which
    they also injected a carbon fluoride gas. The ensuing chemical reactions produced a zoo of molecules, including RaF, which the team separated
    using a precise system of lasers, electromagnetic fields, and ion traps.

    The researchers measured each molecule's mass to estimate of the number
    of neutrons in a molecule's radium nucleus. They then sorted the molecules
    by isotopes, according to their neutron numbers.

    In the end, they sorted out bunches of five different isotopes of RaF,
    each bearing more neutrons than the next. With a separate system of
    lasers, the team measured the quantum levels of each molecule.

    "Imagine a molecule vibrating like two balls on a spring, with a certain
    amount of energy," explains Udrescu, who is a graduate student of MIT's Laboratory for Nuclear Science. "If you change the number of neutrons in
    one of these balls, the amount of energy could change. But one neutron
    is 10 million times smaller than a molecule, and with our current
    precision we didn't expect that changing one would create an energy
    difference, but it did. And we were able to clearly see this effect."
    Udrescu compares the sensitivity of the measurements to being able to
    see how Mount Everest, placed on the surface of the sun, could, however minutely, change the sun's radius. By comparison, seeing certain effects
    of symmetry violation would be like seeing how the width of a single
    human hair would alter the sun's radius.

    The results demonstrate that radioactive molecules such as RaF are ultrasensitive to nuclear effects and that their sensitivity may
    likely reveal more subtle, never-before-seen effects, such as tiny symmetry-violating nuclear properties, that could help to explain the universe's matter-antimmater asymmetry.

    "These very heavy radioactive molecules are special and have
    sensitivity to nuclear phenomena that we cannot see in other molecules
    in nature," Udrescu says. "This shows that, when we start to search
    for symmetry-violating effects, we have a high chance of seeing them in
    these molecules." This research was supported, in part, by the Office
    of Nuclear Physics, U.S.

    Department of Energy; the MISTI Global Seed Funds; the European Research Council; the Belgian FWO Vlaanderen and BriX IAP Research Program; the
    German Research Foundation; the UK Science and Technology Facilities
    Council, and the Ernest Rutherford Fellowship Grant.

    ========================================================================== Story Source: Materials provided by
    Massachusetts_Institute_of_Technology. Original written by Jennifer
    Chu. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. S.M. Udrescu, A.J. Brinson, R.F. Garcia Ruiz, K. Gaul, R. Berger, J.

    Billowes, C.L. Binnersley, M.L. Bissell, A.A. Breier,
    K. Chrysalidis, T.E. Cocolios, B.S. Cooper, K.T. Flanagan,
    T.F. Giesen, R.P. de Groote, S. Franchoo, F.P. Gustafsson,
    T.A. Isaev, A. Koszorus, G. Neyens, H.A.

    Perrett, C.M. Ricketts, S. Rothe, A.R. Vernon, K.D.A. Wendt, F.

    Wienholtz, S.G. Wilkins, X.F. Yang. Isotope Shifts of Radium
    Monofluoride Molecules. arXiv.org, May 21, 2021; [abstract] ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/07/210707112356.htm

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