A team of theoretical high-energy physicists in the Fermilab Lattice and MILC Collaborations has published a new high-precision calculation that could significantly advance the indirect search for physics beyond the Standard Model (SM). The calculation applies to a particularly rare decay of the B meson (a subatomic particle), which is sometimes also called a "penguin decay" process.
After being produced in a collision, subatomic particles spontaneously decay into other particles, following one of many possible decay paths. Out of one billion B mesons detected in a collider, only about twenty decay through this particular process.
With the discovery of the Higgs boson, the last missing piece, the SM of particle physics now accounts for all known subatomic particles and correctly describes their interactions. It's a highly successful theory, in that its predictions have been verified consistently by experimental measurements. But scientists know that the SM doesn't tell the whole story, and researchers around the globe are eagerly searching for evidence of physics beyond the SM.
"We have reason to believe that there are yet undiscovered subatomic particles that are not part of the SM," explains Fermilab scientist Ruth Van De Water. "Generally, we expect them to be heavier than any subatomic particles we have found so far. The new particles would be part of a new theory that would look like the SM at low energies. Additionally, the new theory should account for the astrophysical observations of dark matter and dark energy. The particle nature of dark matter is a complete mystery."
University of Illinois physicist Aida El-Khadra adds, "Scientists are attacking this problem from several directions. Indirect searches focus on virtual effects that the conjectured new heavy particles may have on low-energy processes. Direct searches look for the production of new heavy particles in high-energy collisions. The interplay of both indirect and direct searches may ultimately provide us with enough pieces of the puzzle to make out the new underlying theory that would explain all of these phenomena."
Syracuse University physicist John "Jack" Laiho describes why "penguin decays" provide powerful probes of new physics: "In the observation of a rare decay, because contributions from the SM are relatively small, there is a good possibility that contributions from new virtual heavy particles may be significant. These would be observed as deviations from SM predictions. However, in order to know that such a deviation (if observed) is not just a statistical fluctuation, the difference must be conclusive--it must be at least five times larger than the experimental and theoretical uncertainties. So rare decays require high precision in both the experimental measurements and the theoretical calculations."
B mesons belong to class of subatomic particles that are bound states of quarks and they feel the so-called strong interactions, also known by the colorful name Quantum Chromodynamics (QCD). Quarks are found inside protons and neutrons--which make up the atomic nucleus--as well as within other sub-atomic particles, such as pions and the aforementioned B mesons.
The new high-precision calculation employs lattice QCD to calculate the effects of the strong interaction on the process in question.
"Decay processes that involve bound states of quarks receive contributions from the strong interactions, which are very difficult to quantify, especially at low energies," explains Fermilab scientist Andreas Kronfeld. The only first-principles method for calculating with controlled errors the properties of subatomic particles containing quarks is lattice QCD, where the unwieldy integrals of QCD are cast into a form that makes it possible to calculate them numerically."
The project was started when Syracuse University researcher Daping Du was a postdoctoral fellow at Illinois with El-Khadra.
"Our calculation is clean," asserts Du. "We focused on a process for which lattice QCD methods yield small and completely quantified uncertainties."
"We have witnessed amazing progress in lattice QCD calculations in recent years," observes Enrico Lunghi, a non-lattice theorist at Indiana University, who joined the team for his expertise in rare decay phenomenology. "Lattice calculations have advanced to the point where they provide ab initio predictions of strong interaction effects with small and reliable uncertainties. This is how we are able to obtain a SM prediction of this process with better precision than previously possible."
The team's high precision lattice QCD calculation required large-scale computational resources.
"Fortunately, we were able to leverage supercomputing resources across the U.S. for this project," comments Indiana University physicist Steven Gottlieb. "In fact, this project is part of a larger effort by the Fermilab Lattice and MILC Collaborations to produce precise theoretical calculations of the strong interaction effects for a range of important processes relevant to precision frontier experiments. We used allocations at Fermilab (provided by the USQCD Collaboration), at the Argonne Leadership Computing Facility, the National Energy Research Scientific Computing Center, the Los Alamos National Laboratory, the National Institute for Computational Science, the Pittsburgh Supercomputer Center, the San Diego Supercomputer Center, and the Texas Advanced Computing Center. "
After completing the new calculation and prior to its publication in Physical Review Letters [115, 152002 (2015)] in the article entitled, " B?π?? Form Factors for New Physics Searches from Lattice QCD", the LHCb experiment at CERN in Switzerland announced a new experimental measurement of the differential decay rate for this decay process.
Fermilab scientist Ran Zhou concludes, "The recent measurements are compatible with our SM predictions, with commensurate uncertainties from theory and experiment. This puts interesting constraints on possible new physics contributions which are very useful for building models of beyond the SM physics."
The team also recently completed another paper, "Phenomenology of semileptonic B meson decays with form factors from lattice QCD", in which they make additional predictions for related rare decays that have not yet been experimentally observed. Once observed, these decay processes likewise may play an important role in the quest to find the new fundamental theory that lies beyond the SM.
Members of the Fermilab Lattice and MILC Collaborations who contributed to this work in addition to those named above include Alexei Bazavov and Yannick Meurice of University of Iowa; Claude Bernard of Washington University, Chris Bouchard of College of William and Mary; Carleton DeTar, Ludmila Levkova, and Si-Wei Qiu of the University of Utah; Elizabeth D. Freeland of the School of the Art Institute of Chicago; Maria Elvira Gámiz of Universidad de Granada; Urs M. Heller of American Physical Society; Paul B. Mackenzie, James N. Simone of Fermi National Accelerator Laboratory; Yuzhi Liu and Ethan Neil of University of Colorado, Boulder; Robert Sugar of University of California, Santa Barbara; Doug Toussaint of University of Arizona, Tucson; and Jon A. Bailey of Seoul National University.
Aida El-Khadra | EurekAlert!
NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center
Researchers create artificial materials atom-by-atom
28.03.2017 | Aalto University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
28.03.2017 | Life Sciences
28.03.2017 | Information Technology
28.03.2017 | Physics and Astronomy