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  • richardmitnick 12:06 pm on August 10, 2022 Permalink | Reply
    Tags: "Charming particle has a record-breaking lifetime", , , , , , , , Physics Today,   

    From “Physics Today” : “Charming particle has a record-breaking lifetime” 

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    From “Physics Today”

    8.9.22
    Heather M. Hill

    Four quarks form a particle that outlives other exotic matter.

    [For display only as the tetraquark pictured in the article would not copy and paste.]

    When quarks come together to form composite particles known as hadrons, they’re typically trios or quark–antiquark pairs. Although the possibility of more complex structures was hypothesized in the 1970s, it took about 30 years to find the first confirmed particle with four quarks. In the intervening years, researchers have observed nearly two dozen so-called tetraquarks and even several pentaquarks (see the Quick Study by Steve Olsen, Physics Today, September 2014, page 56). Those exotic particles offer a window to a particular regime of quantum chromodynamics, which describes the strong force (see the article by Frank Wilczek, Physics Today, August 2000, page 22).

    Quantum chromodynamics readily predicts the behaviors of high-energy particles, but at the lower energies found for quarks in hadrons, it struggles. At those energies, experiments, in particular on exotic particles, are a better guide. Now the Large Hadron Collider beauty (LHCb) collaboration has identified a new tetraquark with an impressively long lifetime.

    The tetraquark—composed of two charm quarks, an up antiquark, and a down antiquark—is promising for future research and hints at the existence of a similar particle of even greater interest.

    For the data set of proton–proton collisions at the LHC between 2011 and 2018, the LHCb collaboration found a sharp peak in the mass spectrum of events with two DØ mesons and a π+ meson, the decay products of the proposed tetraquark. The peak corresponds to a particle mass of about 3875 MeV and falls just below the value for the summed masses of a DØ meson, which comprises a charm quark and an up antiquark, and a D*+ meson, which comprises a charm quark and a down antiquark.

    The signal isn’t noise or chance—the statistical significance is more than 22σ. And the lifetime, as determined from the inverse of the peak’s width, is the longest of the tetraquarks found thus far. Most decay in just 10^−23 seconds, a lifetime the new tetraquark outlasts by two orders of magnitude. A longer lifetime and corresponding narrower signal peak make detecting the particle’s properties easier and more accurate.

    The four quarks could take two different structures: together in a single compact cluster or in two separated lobes, akin to a diatomic molecule but made of a DØ and a D*+ meson. So far, the LHCb results aren’t conclusive but suggest a molecule-type structure.

    Values for the tetraquark’s quantum numbers are among the next tasks for the collaboration. The researchers also hope, inspired by their result, that they might find a tetraquark in which the charm quarks are replaced with two beauty quarks. The beauty version of the tetraquark is predicted to be stable with respect to the strong interaction, so its decay would happen even more slowly through the weak interaction. (R. Aaij et al., LHCb collaboration, Nat. Phys. 18, 751, 2022 [below]; R. Aaij et al., LHCb collaboration, Nat. Commun. 13, 3351, 2022 [below].)

    Nature Physics
    Nature Communications

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Our mission

    The mission of ”Physics Today” is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

    It does that in three ways:

    • by providing authoritative, engaging coverage of physical science research and its applications without regard to disciplinary boundaries;
    • by providing authoritative, engaging coverage of the often complex interactions of the physical sciences with each other and with other spheres of human endeavor; and
    • by providing a forum for the exchange of ideas within the scientific community.”

     
  • richardmitnick 11:27 am on July 3, 2022 Permalink | Reply
    Tags: "CERN’s Higgs boson discovery:: The pinnacle of international scientific collaboration?", , , , , , , , Physics Today,   

    From “Physics Today” : “CERN’s Higgs boson discovery:: The pinnacle of international scientific collaboration?” 

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    From “Physics Today”

    30 Jun 2022
    Michael Riordan

    Decades of effort to establish a global, scientist-managed high-energy-physics laboratory culminated in the discovery of the final missing piece of the discipline’s standard model.


    Credit: Abigail Malate for Physics Today

    Ten years ago, two of the largest scientific collaborations ever—spanning six continents and encompassing more than 60 nations—announced their discovery at CERN of the long-sought Higgs boson, the capstone of the standard model.

    Physicists from all the countries involved could take well-earned credit for what will surely stand as one of the 21st century’s greatest scientific breakthroughs. It was a remarkable diplomatic achievement, too, at a moment of relative world peace, perhaps the pinnacle of international scientific cooperation. And it would not have been possible without a series of farsighted decisions and actions.

    _______________________________________________
    Higgs


    _______________________________________________
    Part of CERN’s success as a citadel of modern physics is due to the early-1950s decision to establish it in Geneva, Switzerland, a city and nation widely recognized for cosmopolitanism and political neutrality. Many thousands of scientists of diverse nationalities, not just Europeans, have eagerly pursued high-energy-physics research in this highly appealing environment, given its many cultural amenities—plus world-class hiking, mountain climbing, and skiing in the nearby Alps.

    CERN grew steadily during more than five decades of increasingly important high-energy-physics research, reusing existing accelerators and colliders wherever possible in the construction of new facilities. It gradually developed a talented, cohesive staff that could effectively manage the difficult construction of the multibillion-euro Large Hadron Collider (LHC) and its four gigantic detectors: ALICE, ATLAS, CMS, and LHCb.

    ___________________________________________________________________
    LHC

    LHC

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    ALICE

    CMS

    LHCb


    ___________________________________________________________________

    After the 1993 demise of the Superconducting Super Collider (SSC), CERN leaders decided to pursue construction of the LHC, but they realized they needed to attract significant funds for the project from beyond Europe. That transformation—effectively to make it a “world laboratory”—required extending its organizational framework and lab culture to embrace those contributions and the large contingents of non-European physicists that would accompany them.

    Given that accomplishment, CERN will likely remain the focus of world high-energy physics as the discipline begins building the next generation of particle colliders.

    Especially after the savage Russian invasion of Ukraine and the looming bifurcation of the world order, the lab now offers an island of stability in a global sea of uncertainty. National governments require strong assurances that the money and equipment they send abroad for scientific megaprojects are being well managed on behalf of their scientists and citizenry. In that regard, CERN has a remarkably robust, decades-long track record.

    Funding international collaborations

    Establishing a vigorous, productive laboratory culture does not happen overnight. It requires years, if not decades. In the late 1980s, SSC proponents failed to appreciate that essential process. Rather than electing to build their gargantuan new collider in Illinois adjacent to Fermilab and adapt the lab’s existing Tevatron to serve as a proton injector, they selected a new, “green field” site just south of Dallas, Texas.

    __________________________________________________________
    [Earlier than the LHC at CERN, The DOE’s Fermi National Accelerator Laboratory had sought the Higgs with the Tevatron Accelerator.

    But the Tevatron could barely muster 2 TeV [Terraelecton volts], not enough energy to find the Higgs. CERN’s LHC is capable of 13 TeV.

    Another possible attempt in the U.S. would have been the Super Conducting Supercollider.

    Fermilab has gone on to become a world powerhouse in neutrino research with the LBNF/DUNE project which will send neutrinos 800 miles to SURF-The Sanford Underground Research Facility in in Lead, South Dakota.]
    __________________________________________________________

    Other factors were involved in the project’s collapse, too, among them the internecine politics of Washington, DC (see my article, Physics Today, October 2016, page 48). But mismanagement of the project (whether real or perceived) by a contentious, untested organization of accelerator physicists and military managers contributed heavily to the SSC’s October 1993 termination by the US Congress.

    When the US quest to build the SSC finally ended, CERN was ready to push ahead with plans for its fledgling LHC project—and to make it a global endeavor. Whereas the SSC project had severe difficulty in securing foreign contributions for building the collider, CERN reached beyond its 19 European member states for contributions to the LHC. By the time the CERN Council gave conditional approval to proceed with the project in December 1994, the lab could anticipate sufficient funding from Europe for an initial construction phase based on a proposed “missing magnet” scheme: Just two-thirds of the proton collider’s superconducting dipole magnets would at first be installed in the existing 27 km tunnel of the Large Electron–Positron (LEP) Collider after its physics research ended. Some doubted whether the scheme was feasible, but it permitted the project to begin hardly a year after the SSC termination. And CERN then opened the door to additional contributions from nonmember states that would allow LHC construction to occur in a single phase.

    In May 1995 Japan became the first non-European nation to offer a major contribution to LHC construction, committing a total of 5 billion yen (then worth about 65 million Swiss francs or $50 million). Russia made a similar commitment the following year, mainly for the construction of the LHC detectors. Canada, China, India, and Israel soon followed suit (although with smaller contributions). The US—still smarting from the SSC debacle—took longer. After lengthy negotiations with the Department of Energy and Congress, CERN director general Christopher Llewellyn Smith finally succeeded in securing a major US commitment worth $531 million in December 1997, including $200 million for collider construction. The US, Japan, and Russia were granted special “observer” status on the CERN Council, giving them a say in LHC management.

    Russia provides an excellent case history of the negotiations and agreements involved in extending CERN participation to include nonmember states. Soviet and Russian physicists had been involved in research there since the mid 1970s, when they began working on fixed-target experiments on the Super Proton Synchrotron.

    In the early 1990s, Russian physicists made major contributions to the design of the CMS detector for the LHC, for which the RDMS (Russia and Dubna member states) collaboration, led by the Joint Institute of Nuclear Research (JINR) in Dubna, Russia, played a formative role.

    4
    Cutaway view of the original Compact Muon Solenoid, or CMS, detector. Credit: CERN.

    The total cost of materials and equipment produced in Russia for the CMS has been estimated at $15 million, with part of the amount provided by CERN and its member states. Russian institutes contributed a similar value of equipment and materials to the ATLAS experiment—again funded partly by CERN and its member states. Hundreds of Russian physicists have since been involved in both experiments.

    And those globe-spanning experimental collaborations benefited extensively from the creation and development of the World Wide Web at CERN by Tim Berners-Lee.

    By the time CERN shut down the LEP in November 2000 and began full-fledged LHC construction, the lab had effectively been transformed from a European center for high-energy physics into a world laboratory for the discipline. The “globalization” of high-energy physics was off to a good start.

    A crucial aspect of that global scientific laboratory is the Worldwide LHC Computing Grid, a multitier system of more than 150 computers linked by high-speed internet and private fiber-optic cables designed to cope with the torrent of information being generated by the LHC detectors—typically many terabytes of data daily. Initial event processing occurs on CERN mainframe computers, which send the results to 13 regional academic institutions (Fermilab and JINR, for example) for further processing and distribution. The grid enables experimenters to do much of the data analysis at their home institutions, supplemented by occasional in-person visits to CERN to interact directly with collaborators and detector hardware. In addition, thousands of these physicists make extensive use of the World Wide Web to share designs, R&D efforts, and initial results as well as to draft scientific articles for publication.

    CERN has been able to establish a successful laboratory culture, conducive to the best possible work by thousands of high-energy physicists, because the lab has essentially complete control of its budget, which exceeded a billion Swiss francs annually as the new century began. Accommodations have been made for specific national needs (for example, the costs of German reunification), but the resulting budget remains under CERN auspices. Important decisions are made by physicists—not bureaucrats or politicians—who better appreciate the ramifications of those decisions for the quality of the scientific research to be done. Contrary to the case of the SSC, meddlesome military managers were not involved.

    Discovering the Higgs boson

    Scientists’ control of their own workplace, which begins with laboratory design and construction and continues into its management and operations, is an important factor in doing successful research. When a meltdown of dozens of superconducting dipole magnets occurred shortly after LHC commissioning began in September 2008, for example, it was a crack team of CERN accelerator physicists who dealt with and solved the utterly challenging problem, taking more than a year to bring the machine back to life. Protons finally began colliding in November 2009, albeit at a reduced collision energy of 7 TeV and at very low luminosity (collision rate).

    Serious data taking began in 2011, as LHC operators nudged the luminosity steadily higher and proton collisions began to surge in. By year’s end, both the ATLAS and CMS experiments were experiencing small excesses of two-photon and four-lepton events—the decay channels expected to give the clearest indication of Higgs boson production—in the vicinity of 125 GeV. But both collaborations stopped short of claiming its discovery.

    When similar excesses appeared in the experiments during the spring 2012 run, their confidence swelled—especially after combinations of the two-photon and four-lepton events exceeded the rigorous five-sigma statistical significance required in high-energy physics. I was fortunate to be present at CERN (if a little groggy from jet lag) when that crucial threshold was crossed in late June by a group of ATLAS experimenters, many hailing from China and the US, who began noisily celebrating in an adjacent office. (See the accompanying essay by Sau Lan Wu.)

    The 4 July 2012 CERN press conference announcing the Higgs discovery—timed to coincide with the opening day of the 36th International Conference on High Energy Physics in Melbourne, Australia—was televised around the globe to rapt physicist audiences on at least six continents. Americans had to awaken in the early morning hours of their nation’s 236th birthday to watch the proceedings. In the packed auditorium, along with former CERN directors (including Llewellyn Smith) and current managers sitting prominently and proudly in the front row, sat theorists François Englert and Peter Higgs, who would soon share the Nobel Prize in physics for anticipating this epochal discovery (see Physics Today, December 2013, page 10). “I think we have it,” stated CERN director general Rolf-Dieter Heuer after the ATLAS and CMS presentations, perhaps a bit guardedly. “We have observed a new particle consistent with a Higgs boson.”

    5
    At the Higgs discovery announcement, CERN Director General Rolf Heuer congratulates François Englert and Peter Higgs, who would later receive the 2013 Nobel Prize in Physics for their theoretical description of the origin of mass—which was confirmed by the Higgs boson detection.

    It was certainly a European triumph, a vindication of the continent’s patient and enduring support of science—but also a triumph for the global physics community. Both the ATLAS and CMS collaborations then involved about 3000 physicists. ATLAS physicists hailed from 177 institutions in 38 nations; CMS included 182 institutions in 40 nations. Physicists from Brazil, Canada, China, India, Japan, Russia, Ukraine, and the US, among many other nations, could rejoice in the superb achievement, along with those from Belgium, France, Germany, Italy, the Netherlands, Poland, Spain, Sweden, the UK, and other CERN member states.

    If the Higgs boson discovery does not represent the pinnacle of international scientific cooperation, it surely sets a high standard. It will be a difficult one to match in the coming decades, given the conflicts and cleavages that have been erupting since Russia’s brutal Ukraine invasion. Russian scientific institutes have been at least temporarily excluded from future CERN projects—and the ban may well become permanent. And the costs of European rearmament could easily impact the CERN budget in the coming years. The first two decades of the 21st century will certainly represent a special moment in history when so many nations could work together peacefully in a common scientific pursuit of the greatest significance.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Our mission

    The mission of ”Physics Today” is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

    It does that in three ways:

    • by providing authoritative, engaging coverage of physical science research and its applications without regard to disciplinary boundaries;
    • by providing authoritative, engaging coverage of the often complex interactions of the physical sciences with each other and with other spheres of human endeavor; and
    • by providing a forum for the exchange of ideas within the scientific community.”

     
  • richardmitnick 3:39 pm on June 23, 2022 Permalink | Reply
    Tags: "A star’s demise is connected to a neutrino outburst", , Ground based Neutrino Observation, , , , On 1 October 2019 the IceCube Neutrino Observatory in Antarctica detected a 0.2 PeV neutrino., , , Physics Today, Recently the Zwicky Transient Facility observed another TDE that was coincident with a high-energy neutrino detected by IceCube., Seven hours later the Zwicky Transient Facility observed optical an emission in the direction of the incoming neutrino., , The optical emission was caused by a bright transient phenomenon known as a tidal disruption event (TDE)., The prospect of high-energy neutrinos being formed by tidal forces ripping apart a star near a supermassive black hole has garnered new support.   

    From “Physics Today” : “A star’s demise is connected to a neutrino outburst” 

    Physics Today bloc

    From “Physics Today”

    23 Jun 2022
    Alex Lopatka

    The prospect of high-energy neutrinos being formed by tidal forces ripping apart a star near a supermassive black hole has garnered new support.

    (S. Reusch et al., Phys. Rev. Lett. 128, 221101, 2022.)

    1
    Technicians install a camera at the Zwicky Transient Facility. Credit: Caltech/Palomar.

    On 1 October 2019 the IceCube Neutrino Observatory in Antarctica detected a 0.2 PeV neutrino.

    Seven hours later the Zwicky Transient Facility in California followed up with a wide-field survey of the sky at optical and IR wavelengths. The facility observed optical emission in the direction of the incoming neutrino.

    Researchers concluded [Nature Astronomy] that the two observations could be connected after studying the exceptional energy flux of the emission, its location within the reported uncertainty region of the high-energy neutrino, and some modeling results. The optical emission was caused by a bright transient phenomenon known as a tidal disruption event (TDE), and that particular one had first been observed one year before the neutrino. Such events occur when stars get close enough to supermassive black holes to experience spaghettification—the stretching and compression of an object into a long, thin shape due to the black hole’s extreme tidal forces. (See the article by Suvi Gezari, Physics Today, May 2014, page 37.)

    A theory paper [Nature Astronomy] proposed that neutrinos with energies above 100 TeV, like the 2019 sighting, could be produced in relativistic jets of plasma, which are composed of stellar debris that’s flung outward after such an event. TDEs and many other sources for high-energy neutrinos have been debated in the literature. But with only one reported TDE–neutrino association researchers haven’t been able to conclusively establish TDEs as high-energy neutrino sources.

    3
    Credit: S. Reusch et al., Phys. Rev. Lett. 128, 221101 (2022)

    Recently the Zwicky Transient Facility observed another TDE that was coincident with a high-energy neutrino detected by IceCube. Simeon Reusch, Marek Kowalski, and their colleagues estimated that the probability of a second such pairing happening by chance is 0.034%, lending more credence to TDEs as a source for high-energy neutrinos.

    The second TDE caused a long-duration optical flare which reached its peak luminosity in August 2019. The neutrino was detected by IceCube in May 2020, by which point the flare’s flux had decreased by about 30% from its peak. Such flares often last several months, though this one was still detectable as of June 2022.

    To better understand how the unusually long-lasting TDE may have produced high-energy neutrinos, the research team simulated three mechanisms. The figure shows the predicted neutrino flux as a function of energy, and the vertical dotted line indicates the energy of the neutrino observed by IceCube. Any of the three mechanisms could reasonably explain the neutrino. Besides relativistic jets, a TDE could also generate an accretion disk, and emission from its corona or a subrelativistic wind of ejected material may generate neutrinos too.

    Other uncertainties remain. The radio-emission measurements of the flare, for example, mean that it could have originated from an active galactic nucleus instead of a TDE. In addition, IceCube’s statistical analysis cannot rule out that the neutrino may have formed from atmospheric processes on Earth.

    Although it’ll take more observations to lower those uncertainties, the latest detection of a TDE–neutrino pairing reinforces the significance of TDEs as neutrino sources. And if the association is true, TDEs would have to be surprisingly efficient particle accelerators, a possibility that could only be further studied with more comprehensive multimessenger data.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Our mission

    The mission of ”Physics Today” is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

    It does that in three ways:

    • by providing authoritative, engaging coverage of physical science research and its applications without regard to disciplinary boundaries;
    • by providing authoritative, engaging coverage of the often complex interactions of the physical sciences with each other and with other spheres of human endeavor; and
    • by providing a forum for the exchange of ideas within the scientific community.”

     
  • richardmitnick 9:35 am on June 11, 2022 Permalink | Reply
    Tags: "Collider data yield insights into neutron star structure", , Measurements of heavy-ion collisions predict properties of neutron stars that are consistent with those informed by astrophysical observations., Neutron stars—the culmination of the gravitational collapse of certain massive stars—pack about one to two solar masses into spheres 20–30 km across., , Physics Today,   

    From “Physics Today”: “Collider data yield insights into neutron star structure” 

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    From “Physics Today”

    10 Jun 2022
    Andrew Grant

    Measurements of heavy-ion collisions predict properties of neutron stars that are consistent with those informed by astrophysical observations.

    1
    A high-frequency accelerator cavity at the GSI Helmholtz Centre for Heavy Ion Research in Germany. Data from heavy-ion collision experiments at GSI helped constrain the properties of dense matter in neutron stars. Credit: J. Hosan/GSI Helmholtzzentrum für Schwerionenforschung GmbH.

    Through a combination of quantum chromodynamics theory and astronomical observations, researchers have established that neutron stars—the culmination of the gravitational collapse of certain massive stars—pack about one to two solar masses into spheres 20–30 km across. Pinning down the properties of such small objects located so far away is an impressive achievement, but astrophysicists and nuclear physicists want to do even better.

    The compression in a neutron star is so high that it may force the nuclear matter into exotic phases (see the Quick Study by Nanda Rea, Physics Today, October 2015, page 62). For a 1.4-solar-mass neutron star, a few-kilometer difference in radius could determine whether the nucleons exist as hyperons, free quarks, or something else. To help pinpoint the parameters of the densest matter in the universe, Sabrina Huth of Technical University of Darmstadt in Germany, Peter T. H. Pang of Nikhef in Amsterdam, and their colleagues have incorporated data from the densest matter on Earth: heavy ions that collide in particle accelerators.

    The researchers strove to home in on the nuclear equation of state, which encompasses the relationship between neutron stars’ masses and radii and quantifies the stiffness of nuclear matter. The stiffer the matter, the greater its resistance to gravitational collapse and the larger the neutron star radius. Similarly, the nuclear stiffness dictates the dynamics of the compression and subsequent expansion when heavy nuclei such as those of gold slam into each other at relativistic energies inside particle colliders. The expansion of the post-collision nucleons is sensitive to the nuclear symmetry energy, a measure of how the nuclear binding energy changes with the neutron-to-proton ratio of the nucleus. That energy, in turn, is related to symmetry pressure, an important factor in the determination of the equation of state (see the article by Jorge Piekarewicz and Farrukh Fattoyev, Physics Today, July 2019, page 30).

    Huth, Pang, and colleagues analyzed data from accelerators at the GSI Helmholtz Centre for Heavy Ion Research in Germany and at the US’s Lawrence Berkeley and Brookhaven National Laboratories. After combining the heavy-ion data with nuclear-theory calculations, the researchers set constraints on the radii of and the typical pressures within 1.4-solar-mass neutron stars that are consistent with those based on astrophysical measurements. They then merged the astrophysical and heavy-ion data to tighten the constraints for both properties. The data suggest a slight increase over the prior predicted value for the radius, which is supported by recent observations from NASA’s x-ray-observing Neutron Star Interior Composition Explorer mission.

    The study highlights the value of looking beyond astrophysics and theory to understand the dense matter in neutron stars. Accelerators at GSI and elsewhere should soon be able to achieve particle densities comparable to those in neutron star cores, providing even more useful data for pinning down the equation of state. (S. Huth et al., Nature 606, 276, 2022.)

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Our mission

    The mission of ”Physics Today” is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

    It does that in three ways:

    • by providing authoritative, engaging coverage of physical science research and its applications without regard to disciplinary boundaries;
    • by providing authoritative, engaging coverage of the often complex interactions of the physical sciences with each other and with other spheres of human endeavor; and
    • by providing a forum for the exchange of ideas within the scientific community.”

     
  • richardmitnick 10:21 am on February 28, 2022 Permalink | Reply
    Tags: "Laser experiments re-create iron dynamics in planetary interiors", and that’s expected to be true for other terrestrial planets too., , Astronomers have discovered a lot of exoplanets—nearly 5000 according to NASA., Earth’s core is mostly iron, , New measurements of pressurized iron offer clues as to the kinds of exoplanets that can sustain liquid-iron cores and magnetospheres., Physics Today, Researchers are studying how those planets may have formed and whether they could harbor life.   

    From Physics Today: “Laser experiments re-create iron dynamics in planetary interiors” 

    Physics Today bloc

    From Physics Today

    24 Feb 2022

    New measurements of pressurized iron offer clues as to the kinds of exoplanets that can sustain liquid-iron cores and magnetospheres.

    1
    The world’s highest-energy laser enters the target chamber (blue) of the National Ignition Facility. Credit: Damien Jemison/NIF.

    Astronomers have discovered a lot of exoplanets—nearly 5000 according to NASA. Now that so many distant worlds have been identified, researchers are studying how those planets may have formed and whether they could harbor life. (For more on the search for life on exoplanets, see the article by Mario Livio and Joe Silk, Physics Today, March 2017, page 50.) A critical step toward those research goals is determining the exoplanets’ interior structure (see Physics Today, March 2019, page 24).

    Earth’s core is mostly iron, and that’s expected to be true for other terrestrial planets too. The swirling liquid-iron outer core of Earth generates the planet’s magnetosphere, which protects us and every other organism from genetic damage due to cosmic radiation. A better understanding of the melting curve of iron at the temperatures and pressures of planetary interiors may help identify the kinds of planets that have magnetospheres.

    Of course, finding that an exoplanet has a life-preserving magnetosphere doesn’t necessarily mean there’s life there. And potential life beyond Earth may not even need a planetary magnetosphere to survive. Still, understanding whether certain planets have magnetospheres would be an important data point for evaluating those worlds’ evolution and potential habitability.

    The search for planetary magnetospheres, however, has been hampered by a lack of experimental data on the pressure–temperature melting curve of iron. Until recently the record-high-pressure measurement [Earth and Planetary Science Letters], accomplished by using diamond anvil cells heated with a laser, was taken at 290 GPa, lower than the 330 GPa found at the boundary between Earth’s solid inner core and the liquid-iron outer core. That mismatch means that to study the melt curve and phase space of iron, researchers have had to extrapolate by about an order of magnitude to the pressures expected in some terrestrial planet interiors.

    That pressure limit has now been overcome. Using the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California, Richard Kraus and his colleagues have determined the melting curve for iron at up to 1000 GPa [Science]. From their results, the researchers predict that planets with masses four to six times that of Earth can sustain magnetospheres for the longest time, approximately eight billion years.

    Sébastien Merkel, a geophysicist at the University of Lille [Université de Lille](FR), is enthusiastic about the experimental advance. “The melting curve of iron has been debated for decades,” he says. “This paper and the data it contains anchor the melting curve of iron at pressures well above previous work.”

    Competing models

    With only low-pressure iron data to work with, conclusions of researchers studying the interiors of exoplanets “have varied dramatically,” says Kraus. One model [Icarus] predicts that the outer core of a planet smaller than or similar to Earth in size would be composed of liquid iron. Larger planets would have a completely solid core. But another model [Icarus] predicts the exact opposite. And yet another model [The Astrophysical Journal],—which focuses on super-Earths whose masses are several times that of Earth—finds that iron crystallization begins at the outer core and precipitates toward the center as iron snow.

    To break the impasse among the various competing models, Kraus and some of his collaborators emulated the pressure conditions at the center of a super-Earth core using light sources at NIF, the largest laser facility in the world. They combined 16 laser beams to create a coherent shock wave that passed through a 2 mm2 iron sample. The ensuing compression and decompression of the sample melted it to a liquid phase. Then the laser intensity was dialed up in precise increments to increase the pressure applied to the sample, up to 1000 GPa in about 10 ns.

    Kraus and colleagues compressed the sample incrementally so that the thermodynamic path on which the sample traveled was nearly isentropic—that is, the increase in pressure added negligible entropy to the sample. That detail matters because no appreciable heat flow or work done by viscous forces modified the pressure–entropy phase measurements of the experiment.

    During the experiments, an additional 24 laser beams energized a germanium or zirconium foil, which produced a hot plasma. The plasma emitted x rays that were then directed to the iron sample. The resulting x-ray diffraction pattern was used to determine whether the iron solidified at various pressure states and, if so, to identify its atomic structure.

    Bottom-up solidification

    The P–S (pressure–entropy) experimental results indicated that the solidification of iron is pressure driven, which implies that exoplanet cores will solidify from the bottom up. “I was surprised we actually saw solidification,” Kraus says. “Before this experiment, many experts thought you could not dynamically solidify any material on a nanosecond time scale.” He argues that the small amount of impurities in their high-purity iron sample and the 10 000 °C temperature maximum helped to accelerate the kinetics of solidification.

    To better compare the measurements with other results, the researchers transformed their P–S data into a P–T (pressure–temperature) phase diagram. They found that the melting temperature of iron at Earth’s inner-core boundary is 6230 K, which is about the same, within the uncertainties, as temperature estimates obtained from extrapolations of previous lower-pressure experiments.

    The results, plotted in the figure below with previous lower-pressure research, support the idea that large exoplanets with a compositional structure similar to Earth’s may have bottom-up core solidification. That mechanism would allow those planets to have liquid-iron outer cores and potentially magnetospheres.

    From the new data, the researchers infer that core solidification in super-Earths would take 30% longer than for Earth because of the additional heat that must dissipate. (The model estimates that Earth’s core would take 6 billion years to cool.) That means that the liquid core would stick around longer and thus provide a prolonged period of protection from cosmic radiation. To reach that inference, the researchers used their measurement of the entropy change along the melt curve and assumed that the heat flow out of the core scales as a function of planet size.

    Most of the work on core solidification has focused on iron. But Earth’s core also has nickel. Other planetary cores may have nickel, too, and perhaps other metals. “We’re starting with pure iron to provide a baseline of fundamental information,” says Kraus. “People can take this information and say, based on the composition of a super-Earth, how do melting curves change with alloying effects?”

    See the full article here .

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    The mission of Physics Today is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

    It does that in three ways:

    • by providing authoritative, engaging coverage of physical science research and its applications without regard to disciplinary boundaries;
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  • richardmitnick 11:41 am on December 1, 2021 Permalink | Reply
    Tags: "An x-ray observatory spots a possible planet in another galaxy", , , , Even if the discovery is never confirmed its method may spawn a new generation of exoplanet searches., Physics Today, Recommendation: Astronomers should turn their telescopes toward x-ray binary systems to efficiently hunt for planets in certain extreme environments., Spacxe based X-ray Astronomy, The newly found exoplanet is comparable in size to Saturn and moves around the binary’s center of mass at 17 km/s.   

    From Physics Today : “An x-ray observatory spots a possible planet in another galaxy” 

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    From Physics Today

    30 Nov 2021
    R. Mark Wilson

    Even if the discovery is never confirmed its method may spawn a new generation of exoplanet searches.

    In the 30 years since astronomers discovered the first exoplanets, two methods of searching for them have been most common—looking for periodic redshifts and blueshifts in a star’s wobble that are caused by an exoplanet’s gravitational tugs, and looking for the dip in a star’s brightness when an exoplanet passes in front of it.

    Doppler method – The European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte](EU)(CL).

    Planet transit. NASA/Ames

    Those methods account for more than 4800 exoplanets spotted in the Milky Way, all of them less than 3000 light-years from Earth.

    Three years ago, Rosanne Di Stefano and Nia Imara, both at The Harvard–Smithsonian Center for Astrophysics (US), made a bold recommendation: Astronomers should turn their telescopes toward x-ray binary systems to efficiently hunt for planets in certain extreme environments. Each binary consists of a collapsed star—a black hole, neutron star, or white dwarf—that is gravitationally bound to a normal star. The collapsed star accretes plasma from its much larger companion. Spiraling inward through an accretion disk, the plasma reaches temperatures high enough to emit x rays. So long as the distance between the bound stars is less than the so-called Roche lobe, in which tidal forces stream the gas from one star to the other, the x-ray-emitting region is exceedingly compact, on the order of a few Jupiter-sized planets. The dip in the x-ray light curve from a transiting planet against so small a region can be huge, large enough to produce a total eclipse. Planets orbiting ordinary stars typically cast a far smaller shadow from the host star, which makes them more difficult to spot.

    Di Stefano, Imara (now at The University of California-Santa Cruz (US)), and their collaborators now report finding what may be a planet orbiting one of the brightest x-ray binaries in Messier 51, known as the Whirlpool galaxy. The binary, whose x-ray spectrum is shown (boxed) in figure 1, its visible spectrum enlarged, resides 23 million light-years from Earth. To find it, the astronomers mined the vast archives of the Chandra X-Ray Observatory.

    National Aeronautics and Space Administration Chandra X-ray telescope(US)

    From their analysis, the accreting object is thought to be either a black hole or a neutron star gravitationally bound to a blue supergiant companion with the luminosity and spectrum of a 20- to 30-solar-mass star. The newly found exoplanet is comparable in size to Saturn and moves around the binary’s center of mass at 17 km/s. According to Kepler’s laws, the exoplanet orbits the center at a distance of about 45 AU with a period of roughly 70 years.

    That period would be the longest ever found for an exoplanet. And it may put the exoplanet’s confirmation—either from a repeat transit observation, Doppler spectroscopy, or both—out of reach. Even so, much of the researchers’ analysis is devoted to analyzing the transiting object’s identity. Fortunately, there is much more Chandra data to mine. To move the field ahead, more exoplanet candidates need to be found.

    Science paper:
    Nature Astronomy

    See the full article here .

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  • richardmitnick 9:51 pm on July 9, 2021 Permalink | Reply
    Tags: "ATLAS measurement supports lepton universality", , , , , , , Physics Today   

    From Physics Today : “ATLAS measurement supports lepton universality” 

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    From Physics Today

    9 Jul 2021
    Christine Middleton

    The collaboration’s result is consistent with the standard-model prediction that W bosons are equally likely to decay into muons and tauons.

    Particle-physics collaborations are always on the lookout for discrepancies between their measurements and the standard model’s predictions.

    Deviations can help point the researchers in the right direction (see, for example, Physics Today, June 2021, page 14). Researchers were therefore excited when a working group combed through data from four earlier experiments performed at European Organization for Nuclear Research [Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) [CERN]’s now-dismantled Large Electron–Positron Collider (LEP) and found that the results were inconsistent with the standard model’s assertion of lepton universality, albeit with a probability of less than 1%.

    All three leptonic generations—electronic, muonic, and tauonic—supposedly have the same coupling to weak force–mediating W bosons. So when a W boson decays, it should be equally likely to produce any one of the leptons, along with its associated antineutrino. Several experiments at DOE’s Fermi National Accelerator Laboratory (US) and CERN have confirmed that W bosons generate electrons and muons at the same rate. But the LEP data showed that tauons were produced slightly more often than muons; the ratio of their production rates was R(τ/μ) = 1.070 ± 0.026. Other experiments studying particles that contain bottom quarks have seen hints of the same problem.

    Now the ATLAS collaboration has collected and analyzed data at the Large Hadron Collider (LHC) that resolves the apparent disagreement. The precision of the collaboration’s measurement is twice that of the LEP result, and the value, R(τ/μ) = 0.992 ± 0.013, agrees with the standard-model prediction of unity.

    The experiment exploited the fact that the LHC’s proton–proton collisions produce a large number of top–antitop quark pairs. A top quark nearly always decays into a W boson and a bottom quark, so the researchers had easy access to many W bosons whose decays they could observe. Some of the W bosons directly produced muons, whereas others produced intermediate tauons that later decayed into muons. Because of their different origins, the muons formed two populations whose signals in the detector could be differentiated by the particles’ impact parameters and transverse momenta. The ATLAS researchers analyzed tens of thousands of W-boson decays for each type of lepton, compared with only a couple thousand each in the LEP data, and counted how many took each path.

    On the whole, data now support the standard model’s prediction of lepton universality in W-boson decays. But the search continues: Hints of lepton universality violations have also been seen in beauty-meson decays at significance levels that are starting to draw attention from high-energy physicists.

    See the full article here .

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  • richardmitnick 3:13 pm on February 25, 2021 Permalink | Reply
    Tags: "A tabletop waveguide delivers focused x rays", , Bright X-ray beams that are emitted in a single direction onto the target of interest are difficult to come by in a laboratory setting., Physics Today, , University of Göttingen [Georg-August-Universität Göttingen](DE) has now developed and demonstrated an approach for generating the radiation directly within a waveguide structure.,   

    From Physics Today: “A tabletop waveguide delivers focused x rays” 

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    From Physics Today(US)

    25 Feb 2021
    Rachel Berkowitz

    By simultaneously generating and guiding beams, the layered anode emits x rays in one direction without the need for mirrors or large-scale accelerators.

    1
    Credit: University of Göttingen [Georg-August-Universität Göttingen](DE)/Julius Hilbig.

    Despite the widespread use of x rays as a fundamental tool for visualizing interior features of solid objects, bright X-ray beams that are emitted in a single direction onto the target of interest are difficult to come by in a laboratory setting. Unlike large-scale accelerators, which emit highly collimated beams, conventional small-scale sources generate x-ray radiation in all directions. Once they’re emitted, x rays cannot easily be manipulated with mirrors or lenses.

    To obtain bright x rays in a clearly defined path, Malte Vassholz and Tim Salditt of the University of Göttingen [Georg-August-Universität Göttingen](DE) have now developed and demonstrated an approach for generating the radiation directly within a waveguide structure. The layered material that makes up the waveguide emits x rays within a nanometers-wide channel, and the resulting beam’s brilliance exceeds that of a conventional µ-focus x-ray tube by two orders of magnitude. The method could lead to a tool for soft-matter imaging and coherent scattering experiments in laboratories.

    Laboratory-scale sources produce x rays by hitting a metal anode with electrons accelerated by a high voltage. Radiation is emitted at all angles when the atoms in the metal deflect and slow those electrons as well as when the electrons excite the metal atoms. To better control the angles at which a metal emits x rays, Vassholz and Salditt built a sandwich-like structure, illustrated in the figure, that was made up of a fluorescent metal layer embedded between guiding and cladding layers. Using a high-energy electron beam that was generated by an instrument adapted from an x-ray tube, the researchers excited the central metal layer, which caused it to emit x rays that were funneled into the guiding layers. Those beams traveled through the guiding layers and were emitted through the waveguide exit. A detector placed across from the exit showed sharp emission peaks corresponding to the waveguide modes, indicating that the device had effectively channeled x rays of up to 35 keV onto a target.

    Additional experiments and calculations suggested that the brightness of the emitted x rays could be further enhanced by using different metals or by varying the thickness of the layers. The researchers propose that the design could enable benchtop measurements of microscale structures that until now have only been accessible using synchrotron radiation. (M. Vassholz, T. Salditt, Sci. Adv. 7, eabd5677, 2021.)

    Science paper:
    Observation of electron-induced characteristic x-ray and bremsstrahlung radiation from a waveguide cavity
    Science Advances

    See the full article here .

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    • by providing authoritative, engaging coverage of the often complex interactions of the physical sciences with each other and with other spheres of human endeavor; and
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  • richardmitnick 10:37 am on February 21, 2021 Permalink | Reply
    Tags: , , Einsteinium [Es] chemistry captured, LBNLheavy element chemistry program, , Physics Today, To date researchers have created more than two dozen synthetic chemical elements that don’t exist naturally on Earth.   

    From Physics Today: “Einsteinium chemistry captured” 

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    From Physics Today

    18 Feb 2021
    Johanna L. Miller

    The creation of a rare molecule offers a glimpse of how atoms behave at the Periodic Table’s outer reaches.

    To date, researchers have created more than two dozen synthetic chemical elements that don’t exist naturally on Earth. Neptunium (atomic number Z = 93) and plutonium (Z = 94), the first two artificial elements after naturally occurring uranium, are produced in nuclear reactors by the thousands of kilograms. But the accessibility of transuranic elements drops quickly with Z: Einsteinium (Z = 99) can be made only in microgram quantities in specialized laboratories, fermium (Z = 100) is produced by the picogram and has never been purified, and all elements after that are made just one atom at a time.

    There are ways to probe the atomic properties of elements produced atom by atom (see, for example, Physics Today, June 2015, page 14). But when it comes to the traditional way of investigating how atoms behave—mixing them with other substances in solution to form chemical compounds—Es is effectively the end of the periodic table.

    Now Rebecca Abergel (head of Lawrence Berkeley National Laboratory’s heavy element chemistry program) and her colleagues have performed the most complicated and informative Es chemistry experiment to date. They chose to react Einsteinium [Es] with a so-called octadentate ligand—a single organic molecule, held together by the backbone shown in blue, that wraps around a central metal atom and binds to it from all sides—to create the molecular structure shown in the figure. In their previous work, Abergel and colleagues used the same ligand to study transition metals, lanthanides, and lighter actinides. When they were fortunate enough to acquire a few hundred nanograms of Es from Oak Ridge National Laboratory, they used it on that as well.

    1
    Credit: Adapted from K. P. Carter et al., Nature 590, 85 (2021)

    Among other useful properties, the ligand acts as an antenna: It absorbs light in the UV and efficiently channels the energy to the central metal atom, which emits light at a range of longer wavelengths. That luminescence spectrum, which can be measured with just a tiny quantity of material, carries information about the central atom’s electronic energy levels.

    Between the luminescence spectroscopy and complementary x-ray absorption measurements, the researchers discovered that Es differs significantly in its behavior from both its upstairs neighbor holmium and the lighter actinides. The difference is almost certainly due to relativistic effects. The more highly charged an atomic nucleus, the faster the electrons whiz around it. When the electron speed is a significant fraction of the speed of light, it affects the atom’s quantum states in a way that’s extraordinarily difficult to model.

    All actinides exhibit relativistic effects, but the heavier ones especially so. Although Es is so scarce that its chemistry is unlikely to be of any technological importance, it could provide a benchmark for better theoretical understanding of the more abundant lighter actinides’ chemical behavior. Abergel and colleagues are especially interested in how those radioactive elements behave inside the human body—with an eye toward both harnessing their radiation as a cancer treatment and designing new drugs to treat radiation poisoning. (K. P. Carter et al., Nature 590, 85, 2021 [above]).

    See the full article here .

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  • richardmitnick 2:36 pm on February 12, 2021 Permalink | Reply
    Tags: , , , , Physics Today, The red supergiant Betelgeuse, The researchers determined that VY CMa underwent significant localized mass-loss events about 250; 200; 120; and 70 years ago., VY Canis Majoris   

    From Physics Today: “Outbursts from a Milky Way hypergiant” 

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    From Physics Today

    12 Feb 2021
    Andrew Grant

    The star VY Canis Majoris’s recent episodes of mass loss may provide clues about what’s behind the fading of fellow giant Betelgeuse.

    A luminous, sprawling red star in the Milky Way, surrounded by gas and dust and prone to violent mass ejections, abruptly fades in brightness when viewed from Earth. That could well describe Betelgeuse, the famous red supergiant whose fluctuations in apparent magnitude since 2019 have captured the attention of sky watchers and stellar astronomers.

    But that description also fits the profile of VY Canis Majoris, a red hypergiant—and one of the largest known stars in the galaxy by radius—that has fluctuated in brightness and shed mass frequently for at least a century and a half. After obtaining the highest precision measurements of VY CMa and its surroundings to date, Roberta Humphreys of the University of Minnesota Twin Cities and her colleagues now report a correlation in the timing of major episodes of mass loss with that of reported dimming of the star. The findings could help astronomers understand the interplay between surface activity, magnetic fields, and mass loss in the extreme red stars, including Betelgeuse, that sit atop the Hertzsprung–Russell diagram.

    1
    This Hubble image of VY Canis Majoris reveals the asymmetric distribution of material surrounding the star. Credit: R. Humphreys/ NASA/ESA.

    Betelgeuse in the infrared from the Herschel Space Observatory is a superluminous red giant star 650 light-years away. Stars much more massive- like Betelgeuse- end their lives as supernova. Credit: ESA/Herschel/PACS/L. Decin et al).

    When Humphreys, who specializes in very massive stars in the Milky Way and its neighbors, started studying VY CMa, it was thought to be shrouded in a relatively uniform shell of previously expelled gas and dust. In 1999 Humphreys and her team found evidence that the red hypergiant is surrounded instead by knots, filaments, and other discrete clumps of material—presumably the remnants of multiple recent outbursts. The clumps’ movements in different directions suggest that localized instabilities on the stellar surface are responsible.

    In their new study [The Astronomical Journal], Humphreys and colleagues examined several of the clumps nearest to the star by using observations taken in 2018 by the Hubble Space Telescope. An order-of-magnitude improvement in spatial resolution over previous measurements, combined with the strong potassium emission lines from the ejecta, allowed the researchers to pinpoint the positions and velocities of the clumps. Extrapolating from those measurements, the researchers determined that VY CMa underwent significant, localized mass-loss events about 250, 200, 120, and 70 years ago. A small knot of material closer to the star may have been expelled as recently as 1995, which indicates that the star remains highly active.

    In a final step, Humphreys and colleagues compared the timing of VY CMa’s outbursts with measurements of the star’s apparent magnitude dating back to the early 19th century, when the star clocked in at about +6.5 magnitude. The events matched up with periods of variable and fading brightness, which have culminated in the star’s apparent magnitude dipping to around +8.5 today. The researchers attribute the star’s prolonged dimming to a dust-filled expulsion whose direction toward Earth has led to sustained obscuration. Other outbursts in different directions obscured our line of sight only temporarily.

    Does VY CMa yield lessons for those examining Betelgeuse’s mysterious and precipitous drop in brightness? Humphreys and colleagues highlight evidence that Betelgeuse has recently ejected material of its own. Studying the outbursts and brightness changes of a remarkable star like VY CMa, the researchers say, may expose the slightly smaller-scale processes that are influencing the merely extraordinary Betelgeuse.

    See the full article here .

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    The mission of Physics Today is to be a unifying influence for the diverse areas of physics and the physics-related sciences.

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