Peer deeper into the heart of the atom than any microscope allows and scientists hypothesize that you will find a rich world of particles popping in and out of the vacuum, decaying into other particles, and adding to the weirdness of the visible world. These subatomic particles are governed by the quantum nature of the Universe and find tangible, physical form in experimental results.
Some subatomic particles were first discovered over a century ago with relatively simple experiments. More recently, however, the endeavor to understand these particles has spawned the largest, most ambitious and complex experiments in the world, including those at particle physics laboratories such as the European Organization for Nuclear Research (CERN) in Europe, Fermilab in Illinois, and the High Energy Accelerator Research Organization (KEK) in Japan.
These experiments have a mission to expand our understanding of the Universe, characterized most harmoniously in the Standard Model of particle physics; and to look beyond the Standard Model for as-yet-unknown physics.
“The Standard Model explains so much of what we observe in elementary particle and nuclear physics, but it leaves many questions unanswered,” said Steven Gottlieb, distinguished professor of Physics at Indiana University. “We are trying to unravel the mystery of what lies beyond the Standard Model.”
Ever since the beginning of the study of particle physics, experimental and theoretical approaches have complemented each other in the attempt to understand nature. In the past four to five decades, advanced computing has become an important part of both approaches. Great progress has been made in understanding the behavior of the zoo of subatomic particles, including bosons (especially the long sought and recently discovered Higgs boson), various flavors of quarks, gluons, muons, neutrinos and many states made from combinations of quarks or anti-quarks bound together.
Quantum field theory is the theoretical framework from which the Standard Model of particle physics is constructed. It combines classical field theory, special relativity and quantum mechanics, developed with contributions from Einstein, Dirac, Fermi, Feynman, and others. Within the Standard Model, quantum chromodynamics, or QCD, is the theory of the strong interaction between quarks and gluons, the fundamental particles that make up some of the larger composite particles such as the proton, neutron and pion.
Peering Through The Lattice
Carleton DeTar and Steven Gottlieb are two of the leading contemporary scholars of QCD research and practitioners of an approach known as lattice QCD. Lattice QCD represents continuous space as a discrete set of spacetime points (called the lattice). It uses supercomputers to study the interactions of quarks, and importantly, to determine more precisely several parameters of the Standard Model, thereby reducing the uncertainties in its predictions. It’s a slow and resource-intensive approach, but it has proven to have wide applicability, giving insight into parts of the theory inaccessible by other means, in particular the explicit forces acting between quarks and antiquarks.
DeTar and Gottlieb are part of the MIMD Lattice Computation (MILC) Collaboration and work very closely with the Fermilab Lattice Collaboration on the vast majority of their work. They also work with the High Precision QCD (HPQCD) Collaboration for the study of the muon anomalous magnetic moment. As part of these efforts, they use the fastest supercomputers in the world.
Since 2019, they have used Frontera at the Texas Advanced Computing Center (TACC)—the fastest academic supercomputer in the world and the 9th fastest overall—to propel their work. They are among the largest users of that resource, which is funded by the National Science Foundation. The team also uses Summit at the Oak Ridge National Laboratory (the #2 fastest supercomputer in the world); Cori at the National Energy Research Scientific Computing Center (#20), and Stampede2 (#25) at TACC, for the lattice calculations.
The efforts of the lattice QCD community over decades have brought greater accuracy to particle predictions through a combination of faster computers and improved algorithms and methodologies.
“We can do calculations and make predictions with high precision for how strong interactions work,” said DeTar, professor of Physics and Astronomy at the University of Utah. “When I started as a graduate student in the late 1960s, some of our best estimates were within 20 percent of experimental results. Now we can get answers with sub-percent accuracy.”
In particle physics, physical experiment and theory travel in tandem, informing each other, but sometimes producing different results. These differences suggest areas of further exploration or improvement.
“There are some tensions in these tests,” said Gottlieb, distinguished professor of Physics at Indiana University. “The tensions are not large enough to say that there is a problem here—the usual requirement is at least five standard deviations. But it means either you make the theory and experiment more precise and find that the agreement is better; or you do it and you find out, ‘Wait a minute, what was the three sigma tension is now a five standard deviation tension, and maybe we really have evidence for new physics.'”
DeTar calls these small discrepancies between theory and experiment ‘tantalizing.’ “They might be telling us something.”
Over the last several years, DeTar, Gottlieb and their collaborators have followed the paths of quarks and antiquarks with ever-greater resolution as they move through a background cloud of gluons and virtual quark-antiquark pairs, as prescribed precisely by QCD. The results of the calculation are used to determine physically meaningful quantities such as particle masses and decays.
One of the current state-of-the-art approaches that is applied by the researchers uses the so-called highly improved staggered quark (HISQ) formalism to simulate interactions of quarks with gluons. On Frontera, DeTar and Gottlieb are currently simulating at a lattice spacing of 0.06 femtometers (10-15 meters), but they are quickly approaching their ultimate goal of 0.03 femtometers, a distance where the lattice spacing is smaller than the wavelength of the heaviest quark, consequently removing a significant source of uncertainty from these calculations.
Each doubling of resolution, however, requires about two orders of magnitude more computing power, putting a 0.03 femtometers lattice spacing firmly in the quickly-approaching ‘exascale’ regime.
“The costs of calculations keeps rising as you make the lattice spacing smaller,” DeTar said. “For smaller lattice spacing, we’re thinking of future Department of Energy machines and the Leadership Class Computing Facility [TACC’s future system in planning]. But we can make do with extrapolations now.”
The Anomalous Magnetic Moment Of The Muon And Other Outstanding Mysteries
Among the phenomena that DeTar and Gottlieb are tackling is the anomalous magnetic moment of the muon (essentially a heavy electron) – which, in quantum field theory, arises from a weak cloud of elementary particles that surrounds the muon. The same sort of cloud affects particle decays. Theorists believe yet-undiscovered elementary particles could potentially be in that cloud.
A large international collaboration called the Muon g-2 Theory Initiative recently reviewed the present status of the Standard Model calculation of the muon’s anomalous magnetic moment. Their review appeared in Physics Reports in December 2020. DeTar, Gottlieb and several of their Fermilab Lattice, HPQCD and MILC collaborators are among the coauthors. They find a 3.7 standard deviation difference between experiment and theory.
“… the processes that were important in the earliest instance of the Universe involve the same interactions that we’re working with here. So, the mysteries we’re trying to solve in the microcosm may very well provide answers to the mysteries on the cosmological scale as well.”
Carleton DeTar, Professor of Physics, University of UtahWhile some parts of the theoretical contributions can be calculated with extreme accuracy, the hadronic contributions (the class of subatomic particles that are composed of two or three quarks and participate in strong interactions) are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. Lattice QCD is one of two ways to calculate these contributions.
“The experimental uncertainty will soon be reduced by up to a factor of four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment,” they wrote. “This and the prospects to further reduce the theoretical uncertainty in the near future… make this quantity one of the most promising places to look for evidence of new physics.”
Gottlieb, DeTar and collaborators have calculated the hadronic contribution to the anomalous magnetic moment with a precision of 2.2 percent. “This give us confidence that our short-term goal of achieving a precision of 1 percent on the hadronic contribution to the muon anomalous magnetic moment is now a realistic one,” Gottlieb said. They hope to achieve a precision of 0.5 percent a few years later.
Other ‘tantalizing’ hints of new physics involve measurements of the decay of B mesons. There, various experimental methods arrive at different results. “The decay properties and mixings of the D and B mesons are critical to a more accurate determination of several of the least well-known parameters of the Standard Model,” Gottlieb said. “Our work is improving the determinations of the masses of the up, down, strange, charm and bottom quarks and how they mix under weak decays.” The mixing is described by the so-called CKM mixing matrix for which Kobayashi and Maskawa won the 2008 Nobel Prize in Physics.
The answers DeTar and Gottlieb seek are the most fundamental in science: What is matter made of? And where did it come from?
“The Universe is very connected in many ways,” said DeTar. “We want to understand how the Universe began. The current understanding is that it began with the Big Bang. And the processes that were important in the earliest instance of the Universe involve the same interactions that we’re working with here. So, the mysteries we’re trying to solve in the microcosm may very well provide answers to the mysteries on the cosmological scale as well.”
T. Aoyama et al, The anomalous magnetic moment of the muon in the Standard Model, Physics Reports (2020). DOI: 10.1016/j.physrep.2020.07.006
University of Texas at Austin
Searching for hints of new physics in the subatomic world (2021, March 24)
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SpaceX lands NASA launch contract for mission to Jupiter's moon Europa – Euronews
By Steve Gorman
LOSANGELES – Elon Musk’s private rocket company SpaceX was awarded a $178 million launch services contract for NASA‘s first mission focusing on Jupiter’s icy moon Europa and whether it may host conditions suitable for life, the space agency said on Friday.
The Europa Clipper mission is due for blastoff in October 2024 on a Falcon Heavy rocket owned by Musk’s company, Space Exploration Technologies Corp, from NASA‘s Kennedy Space Center in Florida, NASA said in a statement posted online.
The contract marked NASA‘s latest vote of confidence in the Hawthorne, California-based company, which has carried several cargo payloads and astronauts to the International Space Station for NASA in recent years.
In April, SpaceX was awarded a $2.9 billion contract to build the lunar lander spacecraft for the planned Artemis program that would carry NASA astronauts back to the moon for the first time since 1972.
But that contract was suspended after two rival space companies, Jeff Bezos’s Blue Origin and defense contractor Dynetics Inc, protested against the SpaceX selection.
The company’s partly reusable 23-story Falcon Heavy, currently the most powerful operational space launch vehicle in the world, flew its first commercial payload into orbit in 2019.
NASA did not say what other companies may have bid on the Europa Clipper launch contract.
The probe is to conduct a detailed survey of the ice-covered Jovian satellite, which is a bit smaller than Earth’s moon and is a leading candidate in the search for life elsewhere in the solar system.
A bend in Europa’s magnetic field observed by NASA‘s Galileo spacecraft in 1997 appeared to have been caused by a geyser gushing through the moon’s frozen crust from a vast subsurface ocean, researchers concluded in 2018. Those findings supported other evidence of Europa plumes.
Among the Clipper mission’s objectives are to produce high-resolution images of Europa’s surface, determine its composition, look for signs of geologic activity, measure the thickness of its icy shell and determine the depth and salinity of its ocean, NASA said.
NASA’s Europa Clipper will fly on SpaceX’s Falcon Heavy – The Verge
The Europa Clipper got the green light from NASA in 2015. It will fly by the moon 45 times, providing researchers with a tantalizing look at the icy world, believed to have an ocean lurking under its icy crust. The Clipper is equipped with instruments that will help scientists figure out if the moon could support life.
For years, the Clipper was legally obligated to launch on NASA’s long-delayed Space Launch System (SLS). But with the SLS perpetually delayed and over budget, NASA has urged Congress to consider allowing the Europa Clipper to fly commercial. Switching to another vehicle could save up to $1 billion, NASA’s inspector general said in 2019.
NASA got permission to consider commercial alternatives to the SLS in the 2021 budget, and started officially looking for a commercial alternative soon after.
The SLS has powerful allies in Congress, who have kept the costly program alive for years, even as it blew past budgets and deadlines. The first flight of the SLS was originally supposed to happen in 2017. That mission — launching an uncrewed trip around the Moon — has since been pushed to November 2021, and keeping to that new schedule remains “highly unlikely” according to NASA’s Office of Inspector General, a watchdog agency.
SpaceX first launched its Falcon Heavy rocket in 2018, and started flying satellites in 2019. Earlier this year, NASA selected the rocket as the ride to space for two parts of a planned space station orbiting the Moon.
Researchers Develop Genome Techniques to Analyze Adaptation of Cattle – AZoCleantech
Jared Decker, a fourth-generation cattle farmer, has been aware of cattle suffering from health and productivity problems when they are moved from one location to another. The shift is from a region where they had spent generations to another place with a different climate, grass, or elevation.
Decker, as a researcher at the University of Missouri, looks at the chances of using science to resolve this issue, thereby serving a dual purpose to enhance the cattle’s welfare and sealing the leak in an almost $50 billion industry in the United States.
When I joined MU in 2013, I moved cattle from a family farm in New Mexico to my farm here in Missouri. New Mexico is hot and dry, and Missouri is also hot but has much more humidity. The cattle certainly didn’t do as well as they did in New Mexico, and that spurred me to think about how we could give farmers more information about what their animals need to thrive.
Jared Decker, Associate Professor and Wurdack Chair, Animal Genetics, College of Agriculture, Food and Natural Resources
The study was published in the journal PLOS Genetics on July 23rd, 2021.
Decker and his research team have revealed the proof exposing the fact that cattle are losing their key environmental adaptations. The researchers regard this as a loss due to the lack of genetic information available to farmers.
After assessing the genetic materials dating back to the 1960s, the team determined particular DNA variations linked with adaptations that could someday be used to develop DNA tests for cattle. These tests could help educate the farmers regarding the adaptability of cattle from one environment or another.
We can see that, for example, historically cows in Colorado are likely to have adaptations that ease the stress on their hearts at high altitudes. But if you bring in bulls or semen from a different environment, the frequency of those beneficial adaptations is going to decrease. Over generations, that cow herd will lose advantages that would have been very useful to a farmer in Colorado.
Jared Decker, Associate Professor and Wurdack Chair, Animal Genetics, College of Agriculture, Food and Natural Resources, University of Missouri
The research team included then-doctoral student Troy Rowan who had examined 60 years’ worth of bovine DNA data from tests of cryo-preserved semen produced by cattle breed associations. They observed that, as time runs, the genes related to higher fertility and productivity increased as a result of careful selection by farmers. Also, many genes relating to environmental adaptations have decreased.
According to Decker, the farmers are not to be blamed as there are no affordable methods available at present to identify the suitability of cattle for a specific environment. The study also proposes easy-to-use cattle DNA tests that focus on the particular adaptations identified in the study.
Such adaptations include resistance to vasoconstriction, which is a process of blood vessel narrowing that takes place at high elevation and puts excessive stress on the heart. Also creating resistance to the toxin in the grass can result in vasoconstriction and tolerance for increased temperature or humidity. All these factors tend to decline over generations when the cattle are shifted from the associated surroundings.
Sometimes, natural and artificial selection are moving in the same direction, and other times there is a tug of war between them. Efficiency and productivity have vastly improved in the last 60 years, but environmental stressors are never going to go away. Farmers need to know more about the genetic makeup of their herd, not only for the short-term success of their farm, but for the success of future generations.
Jared Decker, Associate Professor and Wurdack Chair, Animal Genetics, College of Agriculture, Food and Natural Resources
The first widely adopted genetic test for cattle was developed at the University of Missouri in 2007. Decker and Rowan are looking forward to giving further details of the development. Both the researchers grew up on farms with a desire to use research to help farmers to balance farm traditions of America with the requirement for eco-friendly business practices.
“As a society, we must produce food more sustainably and be good environmental stewards. Making sure a cow’s genetics match their environment makes life better for cattle and helps farmers run efficient and productive operations. It’s a win-win,” concluded Decker.
Rowan, T. N., et al. (2021) Powerful detection of polygenic selection and evidence of environmental adaptation in US beef cattle. PLOS Genetics. doi.org/10.1371/journal.pgen.1009652.
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