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nuclear seminar

High-precision measurement of the W boson mass with the CDF II detector

Joint with theory seminar

The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. The Higgs boson was the last missing component of the model. After observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model. We measure the W boson mass, MW, using data corresponding to 8.8 inverse femtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 tera–electron volt center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately 4 million W boson candidates is used to obtainMW=80,433.5±6.4stat±6.9syst=80,433.5±9.4 MeV/c2 the precision of which exceeds that of all previous measurements combined (stat, statistical uncertainty; syst, systematic uncertainty; MeV, mega–electron volts; c, speed of light in a vacuum). This measurement is in significant tension with the standard model expectation.

 

=80,433.5±6.4stat±6.9syst=80,433.5±9.4 MeV/𝑐2

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Zoom/Online
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Electron-Nucleus Scattering Constraints For Neutrino Interactions And Oscillations

The ability of current and next generation accelerator-based neutrino-oscillation measurements to
reach their desired sensitivity requires a detailed understanding of neutrino-nucleus interactions.
These include precise knowledge of the relevant cross sections and of our ability to reconstruct
the incident neutrino energy from the measured final state particles. Incomplete understanding of
these interactions can skew the reconstructed neutrino spectrum and therefore bias the extraction
of fundamental oscillation parameters. In this talk, I will present new wide phase-space electron-
nucleus scattering data, collected using the decommissioned CLAS6 spectrometer at the Thomas
Jefferson National Accelerator Facility (JLab), where we studied how well we can reconstruct the
incident lepton energy from the measured final state particles. Disagreements with the commonly
used GENIE event generator are observed, indicating a potential bias for future oscillation analyses

and pointing the way for improving these event generators.

 

Meeting Recording:
 
Date:
Location:
Online
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Heterodyne Detection of Axion Dark Matter

Detecting ultralight axion dark matter has recently become one of the benchmark goals of future direct detection experiments. I will discuss a new idea to detect such particles whose mass is well below the micro-eV scale, corresponding to Compton wavelengths much greater than the typical size of tabletop experiments. The approach involves detecting axion-induced transitions between two quasi-degenerate resonant modes of a superconducting accelerator cavity. Compared to more traditional setups, the sensitivity is parametrically enhanced for ultralight axions, allowing for the exploration of vast new areas of parameter space relevant to the QCD axion and astrophysically long-ranged fuzzy dark matter.
 

 

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Smoothing things over: Building better magnetic fields

Next generation searches for beyond standard model physics such as nEDM and neutron spin rotation rely on exquisitely uniform magnetic fields. Recent advances in theory and computation have yielded a streamlined pipeline to design coils satisfying increasingly stringent design requirements. nEDM@LANL is a natural progression of nEDM measurements, and we expect it will ultimately be limited by the well-known systematic of magnetic gradients, which ultimately induce a false EDM. In spite of our best efforts to design and build a perfect magnetically shielded room (MSR) and B0 coils, we will need a coil package capable of shimming away specific unwanted gradients. We are designing our gradient correction coils in two generations. The focus of this talk will be on the second-generation coils. We are pursuing coils designed with modern CAD tooling: I'll discuss stream-function generated coils as well as a family of continuously wound coils designed with a nod to the weakly perturbed scalar potential method before introducing the fabrication and validation of these coils and their implementation as a full gradient correction package.

 
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Speed of Gravitational Waves as a New Probe of Ultra-light Dark Matter

There exists a class of ultralight Dark Matter (DM) models which could form a Bose-Einstein condensate (BEC) in the early universe and behave as a single coherent wave instead of individual particles in galaxies. We show that a generic BEC DM halo intervening along the line of sight of a gravitational wave (GW) signal could induce an observable change in the speed of GW, with the effective refractive index depending only on the mass and self-interaction of the constituent DM particles and the GW frequency. Hence, we propose to use the deviation in the speed of GW as a new probe of the BEC DM parameter space. With a multi-messenger approach to GW astronomy and/or with extended sensitivity to lower GW frequencies, the entire BEC DM parameter space can be effectively probed by our new method in the near future.

Date:
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Location:
CP 179
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Baryogenesis, Dark Matter, Neutron-Antineutron Oscillation and Collider Signals

We will discuss a simple model of low-energy baryon number violation in order to simultaneously explain the observed matter-antimatter asymmetry and dark matter relic density in the universe. The stability of dark matter is related to the stability of the proton. The model predicts a sizeable rate for the neutron-antineutron oscillation at low energy and a new type of monojet signal at the LHC. There exists an interesting complementarity between the observed baryon asymmetry, ratio of dark matter and baryon abundances, neutron-antineutron oscillation lifetime and the LHC monojet signal. 

Date:
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Location:
CP 179
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The measurement of neutron beta decay observables with the Nab spectrometer

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.

Date:
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Location:
CP 179
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Nuclear Seminar: Taming the nuclear beta decay Hydra: One theoretical head at a time

The study of nuclear beta decay has been at the forefront of our current understanding of the physical landscape, 
and continues to play an essential role in the search for beyond Standard Model physics. In order to separate the 
wheat from the chaff of the myriad possible theoretical extensions, a reliable estimate of the Standard Model 
contribution is indispensable. Recently, the description of the allowed beta spectrum shape was revisited and 
extended in order to tackle these challenges. Besides the study of the fundamental nature of the weak interaction, 
the beta spectrum shape is an essential ingredient in several outstanding problems in particle physics, such as 
the reactor antineutrino anomaly. We will provide an overview of the current state-of-the-art and its challenges, 
and discuss its implications on the reactor anomaly.
Date:
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Location:
CP 179
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