Session H7: Electroweak Interactions

Update on the Los Alamos UCN Source

The ultracold neutron (UCN) source at Los Alamos National Lab has been running since 2005. During this time the source production has steadily increased due to upgrades. The source feeds two experimental beam lines. The primary beam line feeds the UCNA spectrometer and the other feeds the UCN lifetime experiment and various small scale experiments. The source produces UCN from spallation neutrons by first moderating them to cold temperatures with cold polyethylene and five Kelvin deuterium; these cold neutrons then knock off a phonon in the cold deuterium and become UCN (this final step is not an equilibrium process). In preparation for upgrading the beam delivery system to the spallation target several studies have been done to determine the best beam pattern to derive the maximum UCN density in experiments. The results of these studies and the predicted increase in ucn density will be presented. In addition to these studies a new ucn source design will be presented.   

UCN Transport for the UCNA Experiment

The UCNA Experiment at Los Alamos National Laboratory utilizes polarized ultracold neutrons (UCN) from a spallation-driven solid deuterium UCN converter. The polarized UCN are bottled in a 1 Tesla $2\times2\pi$ magnetic spectrometer to measure the $\beta$ asymmetry parameter $A$. In order to store the UCN, the materials used for transport and storage of UCN is critical. Diamond-like carbon (DLC) coatings are used in order to minimize depolarization and loss. We discuss the fabrication, characterization, and modeling of DLC-coated guides used in the experiment.   

UCNB Experimental Overview: Recent Progress and Future Goals

The UCNB experiment is an effort to measure the neutrino-asymmetry $B$, between the neutrino momentum and the neutron spin in polarized neutron beta-decay. Bottled ultracold neutrons are held in a magnetic field until they decay, and a 30 kV accelerating potential allows both the electrons and protons to be detected by thin dead layer pixellated silicon detectors. Proton-electron coincidences have been directly observed, and a second detector has been implemented. Continued improvements are planned, including better data acquisition, improved electrostatic configuration, and improvements to the decay trap to prevent neutron loss and escape.   

The Data Acquisition System for the Nab Experiment

The Nab experiment will measure the unpolarized electron-neutrino correlation coefficient 'a' in neutron decay with an absolute uncertainty of $10^{-4}$. This requires high energy and timing resolution, and a multipixel low threshold trigger to efficiently detect 30 keV protons. Digital waveforms must be read out for offline pulse-shape analysis from all neighboring channels of hits in the two 128-pixel ion implanted silicon detectors. We are testing three DAQ candidates based on flash ADC digitizers and FPGA digital pulse processing on a prototype Nab detector mounted in the UCNA apparatus at Los Alamos National Laboratory. We have tested the systems to determine the energy and time resolution, as well as to characterize the noise in each digitizer. We will present the noise level, time and energy resolution, and wave form quality of three systems.   

Resonant Frequency Spin Flipper for the nHe3 Experiment

The n$^3$He experiment, currently being installed on beamline-13 at ORNL's Spallation Neutron Source (SNS), is designed to measure the proton asymmetry associated with the interaction of neutrons with a gas of $^3$He via \begin{equation} n + _2^3\!\textrm{He} = _1^3\! \textrm{H} + _1^1\!\textrm{H} + 765\, \textrm{KeV} \end{equation} The experiment uses a Resonant Frequency Spin Flipper (RFSF) to flip the neutron spins. The spin flipper is similar to the one described by P.N. Seo et al (PR ST Accel. Beams 11 084701, 2008) with significant improvements. Most important is the inclusion of a ``double cosine-theta'' winding pattern that provides a highly uniform interior field with no fringing. A critical feature of the coil is complex flux returns whose construction was made possible through the utilization of 3D print technology.   

Development of an Electrostatic Ion Beam Trap for the Study of Beta Decay Correlations

Precision measurements of beta decay correlation parameters, to the level of 0.1\% or better, can be used to test the Standard Model and to search for possible evidence of new physics such as Supersymmetry. We are developing an Electrostatic Ion Beam Trap (EIBT) to measure the beta-neutrino correlation parameter of short lived radioactive isotopes produced by the 88-inch Cyclotron at LBNL. The EIBT uses two opposing sets of electrodes to create a parallel pair of electrostatic mirrors to confine ions. Position sensitive beta telescopes and micro-channel plates will be used to detect the beta and recoil nucleus, thus allowing the reconstruction of the momentum vectors of both beta and recoil nucleus on an event-by-event basis. I will describe the measurement technique and update on the status and progress of this program.