A peek inside the earliest moments of the universe August 1, 2016 by Kathy Kincade Please Register or Log in to view the hidden image! The MuSun experiment at the Paul Scherrer Institute is measuring the rate for muon capture on the deuteron to better than 1.5% precision. This process is the simplest weak interaction on a nucleus that can be measured to a high degree of precision. Credit: Lawrence Berkeley National Laboratory The Big Bang. That spontaneous explosion some 14 billion years ago that created our universe and, in the process, all matter as we know it today. In the first few minutes following "the bang," the universe quickly began expanding and cooling, allowing the formation of subatomic particles that joined forces to become protons and neutrons. These particles then began interacting with one another to create the first simple atoms. A little more time, a little more expansion, a lot more cooling—along with ever-present gravitational pull—and clouds of these elements began to morph into stars and galaxies. For William Detmold, an assistant professor of physics at MIT who uses lattice quantum chromodynamics (LQCD) to study subatomic particles, one of the most interesting aspects of the formation of the early universe is what happened in those first few minutes—a period known as the "big bang nucleosynthesis." Read more at: http://phys.org/news/2016-08-peek-earliest-moments-universe.html#jCp
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.132001 PHYSICAL REVIEW LETTERS ABSTRACT Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process np→dγ, and the photo-disintegration processes γ(*)d→np. In nuclear potential models, such contributions are described by phenomenological meson-exchange currents, while in the present work, they are determined directly from the quark and gluon interactions of QCD. Calculations of neutron-proton energy levels in multiple background magnetic fields are performed at two values of the quark masses, corresponding to pion masses of mπ∼450 and 806 MeV, and are combined with pionless nuclear effective field theory to determine the amplitudes for these low-energy inelastic processes. At mπ∼806MeV, using only lattice QCD inputs, a cross section σ806MeV∼17mb is found at an incident neutron speed of v=2,200m/s. Extrapolating the short-distance contribution to the physical pion mass and combining the result with phenomenological scattering information and one-body couplings, a cross section of σlqcd(np→dγ)=334.9(+5.2−5.4)mb is obtained at the same incident neutron speed, consistent with the experimental value of σexpt(np→dγ)=334.2(0.5)mb. Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image!
