Nab, an experiment that allows studying unpolarized neutron beta decay at the Spallation Neutron Source at Oak Ridge National Lab, aims to determine a, the neutrino-electron correlation coefficient, and b, the Fierz interference term, with high precision. Such measurements provide opportunities to search for evidence of extensions to the Standard Model. Nab is presently being constructed. The spectrometer magnet is supposed to arrive in the week I am giving this seminar. Beam readiness planned for end of summer 2018. I will discuss the experiment’s motivation and design, the planned modes of operation, and the performance of its components.

Title: Constraining dense matter properties from thermal and spin evolution of neutron stars

Abstract:  Neutron star interiors are the only laboratory to harbor cold (temperatures less than tens of MeV) and dense (densities higher than normal nuclear density but lower than those where perturbative QCD is applicable) matter in the universe. In this talk, I will report on our recent endeavors to answer the intriguing question: are exotic degrees of freedom realized in the densest cores of the most compact stars?

We analyze the thermal states of accreting neutron stars in quiescence, confining the studies within nucleons-only framework, and find the stringent limitation imposed by observation of the hottest and coldest sources disfavors the assumption without exotic matter. In addition, combining temperature and spin frequency data I will describe an interesting feature of hybrid stars with a sharp interface between nuclear matter mantle and quark matter core: capability of damping density oscillations e.g. r-modes in neutron stars that otherwise cannot be explained in the standard scenario of purely hadronic matter. These results we obtained could therefore provide theoretical predictions of the presence of exotic matter for future observations to confirm or rule out.

Over the past several years, “hidden sectors” have attracted a surge of interest in the particle physics community. I’ll summarize the underlying physics motivation and give an update on various search strategies. Most of the talk will focus on new bounds on dark sector models, emphasizing where Standard Model uncertainties still play a big part. In particular, we’ll examine bounds on "dark photons" from Supernova 1987A, where we have incorporated finite-temperature effects on the production and trapping for the first time, utilized a realistic model of the high-mixing parameter space, and shown the effect of systematic uncertainties from stellar progenitor models. Other hidden sector scenarios will be addressed as time permits.

The existence of dark matter is one of the few solid hints for physics beyond the standard model. If dark matter has indeed particle nature, then direct detection via scattering on atomic nuclei is one of the most promising discovery channels. In order to connect this nonrelativistic process with astrophysical and collider searches, as well as UV model building, a consistent setup of effective field theories for the different energy scales is necessary.

After an introduction to the physics of dark matter, I will present our work on the explicit connection between these energy scales, from the UV down to the nuclear scale, including a systematic error estimate. I will, in particular, discuss the effects of higher-order chiral and electroweak corrections.

I will discuss our ongoing efforts aimed at constraining the systematic errors in long-baseline neutrino experiments through ab initio computations of neutrino-nucleus quasielastic scattering cross sections using a powerful quantum many-body method---the coupled-cluster theory---with nuclear forces and electroweak currents derived in chiral effective field theory ($\chi$EFT). After showing  precision results for the electroweak properties of the deuteron, which we use to benchmark our harmonic oscillator-basis representation of the $\chi$EFT electroweak currents, I will present recent results for some electron-scattering observables of $^4$He and $^{40}$Ca. 

Many of the Air Force Research Laboratory’s experimental efforts are focused on precision navigation and timing. The establishment and testing of an optical frequency standard is useful for numerous terrestrial and space based applications. Therefore, an optical atomic clock based upon a 778 nm two-photon transition in rubidium, is an excellent candidate to meet GPS-III frequency stability requirements, as commercial off-the-shelf components allow for a simple set-up that supports 7 x 10^-13 at 1 second.

The Nab collaboration proposes to measure the electron-neutrino correlation parameter a with a precision of δa/a = 10^−3 and the Fierz interference term b to δb = 3 × 10^−3 in unpolarized free neutron β decay. These results are expected to lead to a new, precise, independent determination of the ratio λ = GA/GV that will sensitively test CKM unitarity. A long asymmetric spectrometer guides the decay products to two large area silicon detectors in order to precisely determine the electron energy and proton momentum. The Nab apparatus is under installation on the Fundamental Neutron Physics Beamline at the SNS at ORNL and commissioning will begin in the near future. An overview of the Nab experiment, systematics effects associated with spectrometer magnetic fields, and the first tests of the spectrometer will be presented.

Neutron-induced failures in semiconductor devices are an increasing concern in the semiconductor industry. Neutrons are produced in the upper atmosphere by cosmic-ray bombardment of nuclei in the air. Because the neutrons are uncharged, they have long mean-free paths and can reach aircraft altitudes and below. Neutron interactions in semiconductor devices produce ionized recoils or reaction products that deposit charge in the vicinity of nodes and cause the devices to fail. These types of failures include bit flips, latchups, burnout etc. Many semiconductor companies have measured the system response at an accelerated rate by using the high-energy Los Alamos Neutron Science Center (LANSCE) spallation neutron source. The LANSCE source produces a neutron spectrum that is very similar in shape to the neutron spectrum produced by cosmic rays in the earth’s atmosphere but is approximately 108 times more intense than the sea-level neutron flux. This acceleration factor allows testing of semiconductor devices to measure their response, and to develop and test failure models and mitigation approaches.