Session D07: Novel Approaches

6He-CRES: Apparatus Upgrades

The ⁶He-CRES experiment aims to precisely measure the beta spectra of ${}^{19} extrm{Ne}$ and ${}^6 extrm{He}$ using Cyclotron Radiation Emission Spectroscopy (CRES). The technique is based on determining the beta energy from measurements of the cyclotron frequency. In order to minimize sensitivity to frequency-dependent RF response, the experiment uses the ratio of these spectra. The ratio exhibits enhanced sensitivity to chirality-flipping currents because the latter have opposite signs for positron versus electron emission. First results of broadband CRES have been reportedfootnote{https://doi.org/10.48550/arXiv.2209.02870}. 

Since that data was collected, improvements to the apparatus were made. These include changes to the RF systems to improve the frequency dependence of noise and signal. Various other improvements to the source, vacuum system, and data collection were also made. These refinements and their impacts for planned CRES measurements will be presented.   

Techniques for Improving Event Reconstruction in He6-CRES

The $^6$He-CRES experiment at the University of Washington CENPA aims to precisely measure the Fierz coefficient $b_{fierz}$ which parameterizes exotic currents in the Weak Interaction representing a violation of SM physics. A measurement of $b_{fierz}$ with a $10^{-3}$ uncertainty would be competitive with current LHC searches for tensor currents.  The first results of broadband CRES were recently reported by our collaboration footnote{https://doi.org/10.48550/arXiv.2209.02870}. 

This talk will discuss those results, and the CRES event reconstruction techniques developed to perform this broadband CRES measurement. Recent improvements in event recognition and reconstruction fidelity will be presented, as well as a new method of keeping track of the times of events which allows vetoing artifacts that can cause spectral distortions.   

He6-CRES: Cyclotron Radiation of Relativistic Particles in a Waveguide

Cyclotron Radiation Emission Spectroscopy (CRES) is a modern technique for high-precision beta spectroscopy, in which the energy of an $e^pm$ in an external magnetic field is measured via the frequency of the emitted cyclotron radiation ($f_ extrm{c}$). The He6-CRES experiment aims to use CRES for discovery-level sensitivity to Fierz interference by high-resolution $e^pm$-decay measurements of ${}^{19} extrm{Ne}$ and ${}^6 extrm{He}$. 

In addition to its primary physics objective, the experiment provides a novel experimental window into the radiation of relativistic charged particles in a waveguide via the chirp-rate ($ extrm{d} f_ extrm{c}/ extrm{d}t$) of cyclotron radiation signals. Characterizing this phenomenon is critical for accurate energy measurements across high-endpoint beta spectra. We show numerical and experimental evidence that CRES chirp-rates for highly-relativistic betas are consistent with the free-space Larmor formula, scaling with the Lorentz factor of the underlying beta as $gamma^4$. We also briefly discuss the potential implications regarding detection efficiency and energy resolution given this more comprehensive model for CRES signals in a waveguide.   

Progress towards measuring the parity-violating nuclear anapole moment of 137Ba in BaF molecules

This talk will describe progress towards measuring the nuclear anapole moment of ¹³⁷Ba in barium monofluoride (BaF) molecules. First, an outline of our quantum-enabled measurement scheme will be described. A proof of principle for our measurement technique was demonstrated recently using the ¹⁹F nucleus in ¹³⁸Ba¹⁹F; there a sensitivity sufficient to measure the predicted effect in ¹³⁷BaF, at the 10% level, was achieved. Since then several major improvements have been incorporated into the system, such as a cryogenic buffer gas beam source (for lower molecule velocity and higher flux), a home-built, highly stable reference laser locked to a cesium atom line (for improved laser frequency stabilization). We have recently measured details of the hyperfine structure in the A²Π_1/2 state of ¹³⁷BaF, and are performing measurements of hyperfine structure in the D²Σ⁺ state as well. This structure must be known to employ our method for quantum state preparation and detection needed to measure the anapole moment in ¹³⁷Ba.   

Demonstration of Novel Neutron Interferometer for Fundamental Physics

Neutron interferometers can measure interactions acquired by neutron waves with high sensitivity. In previous research, it has been widely used for fundamental physics experiments such as the measurement of neutron-nuclear scattering length, verification of earth gravity, verification of spinor 4π rotation symmetry, and the search for exotic interactions. However, its measurement sensitivity has not evolved significantly over the past 50 years, and the development of high-sensitivity interferometers is necessary for the precise measurement of physical quantities.

​​​The measurement sensitivity of the interferometer is proportional to the neutron wavelength and the interaction length. We have developed a novel neutron interferometer using multilayer neutron mirrors, which can use longer wavelengths and longer interaction lengths compared to the conventional interferometer. The use of pulsed neutron beams and time-of-flight methods can significantly increase the number of neutrons used and suppress systematic uncertainties based on the wavelength-dependent information of the interference fringes. Thanks to the fully two-path separation, the measurement of neutron-nuclear scattering lengths obtained by insertion of solid samples has been realized. The measured neutron-nuclear scattering lengths for several nuclei were consistent with the literature values. In this talk, we report the result of the demonstration of the novel neutron interferometer.   

Simulations of Neutron Spin Rotation Measurements by the NSR Collaboration

The Neutron Spin Rotation (NSR) Collaboration seeks to constrain the hadronic weak interaction as well as place limits on the possibility of long-range spin-dependent forces [1,2,3]. The NSR polarimeter is capable of measuring rotations on the order of 10^-7 radians per meter of target material. As transversely polarized neutrons pass through a pair of 0.5-m liquid Helium targets, the weak interaction causes minute rotations of the neutron spin about the longitudinal axis. Similarly, transversely polarized neutrons can tip forward due to a spin-dependent long-range force as they pass between different-mass plates. For the latter experiment, our target consists of a series of 0.5-m long glass and tungsten plates and can accept a 10 by 10-cm beam. The primary challenge of these high-precision measurements is the suppression of and cancellation of rotations due to the interaction of the neutron spin with ambient magnetic fields. Computer simulations of these experiments have proved a valuable tool in investigating the size of these affects and how to mitigate them. Discussion of recent simulation work will be presented.   

Search for CP-Violation in ortho-Positronium Decay

The combined charge and parity (CP) transformation is an exact symmetry in QED. Within the Standard Model only small amounts of CP-violation are generated in processes involving quark mixing and possibly neutrino mixing. Positronium is an electromagnetically bound state of an electron and a positron, and as such is insensitive to any Standard Model CP-violation. We are carrying out an experiment to search for a CP-violating angular correlation in the decay photons of positronium, that could only be induced by beyond Standard Model physics [1]. Our goal is a tenfold increase in sensitivity over previous searches [2-3].

 

We will present the design, construction, and testing of a dedicated gamma detector array that fits within a superconducting solenoid magnet at the Facility for Rare Isotope Beams. We also report on progress on a positronium formation cell and fast scintillators for positron tagging. With our setup we expect to reach the target sensitivity with one month of continuous runtime.

 

[1] W. Bernreuther, U. Löw, J.P. Ma, et al. Z. Phys. C - Particles and Fields 41, 143–158 (1988).

[2] M. Skalsey and J. Van House, Phys. Rev. Lett. 67 (1993)

[3] T. Yamazaki, T. Namba, S. Asai, T. Kobayashi, Phys. Rev. Lett. 104 (2010)       

Development of a Superconducting Switch to Improve Temporal Stability of Magnetic Coils for nEDM@SNS

Discovery of the neutron electric dipole moment (nEDM) would provide direct evidence of CP-violation and could be used to benchmark beyond the Standard Model physics. However, the nEDM has not yet be found; today, the upper limit is set at 1*10^-26 e*cm. At the Spallation Neutron Source (SNS), the nEDM@SNS collaboration aims to perform a measurement with a sensitivity  of 3*10^-28 e*cm. In order to reach the desired precision, the magnetic field of the experiment must be extremely stable over time. Power supplies cannot achieve the required stability; therefore, a superconducting switch will be used to close the superconducting coil that creates the field. In this talk, I present progress on the design, fabrication, and testing of a low current superconducting switch. The initial prototype switch will be used in SOS@PULSTAR - a test system for nEDM@SNS - and may be used for the larger-scale nEDM@SNS experiment. The switch will operate at a current of <500 mA, is made of nonmagnetic materials, and will be joined to the coil using superconducting solder (Ostalloy 203) joints. Initial tests have confirmed the creation of a superconducting joint with a resistance ~3.1*10^-16 Ω, which meets the temporal stability requirements of the experiment.   

Search for new gravity-like short range interactions in the submicron range by means of neutron-nanoparticle scatteringⅠ

The large-extra-dimension models are the candidate of the theoretical solution for so-called hierarchy problem in the energy scale of elementary particles. Some of those models suggest deviation of the gravitational force from the inverse-square law in the range shorter than a few mm due to the effect of a new interaction induced by the graviton traveling through the extra dimensions. We previously performed an experimental search for new gravity-like interactions in the submicron range by measuring small-angle neutron scattering with noble gas atoms at the Japan Proton Accelerator Research Complex (J-PARC) [1], and we are now improving the sensitivity of the measurement by using a target made of nanoparticles which are about six orders of magnitude heavier than noble gas atoms. In this new method the sensitivity to new interactions is expected to increase thanks to the coherent neutron scattering. In principle, the background from the nuclear scattering is also enhanced by the coherent scattering. To suppress the coherent nuclear scattering, we will employ nanoparticles made of the elements with positive coherent scattering length and the one with negative one such as vanadium and titanium [2]. Currently, we are developing the production method of nanoparticles of vanadium-nickel alloy and pure vanadium using the RF thermal plasma method. In this presentation, the current status of nanoparticle development and the results of SANS measurements will be presented.   

Search for New Gravity-like Short Range Interactions in the Submicron Range by means of Neutron-nanoparticle Scattering Ⅱ

 The small-angle neutron scattering (SANS) measures the scattering intensity as a function of the momentum transfer which is the Fourier transform of the shape of the scattering potential which is used to distinguish new gravitylike interaction from the nuclear potential.

 The SANS experiments using noble gas targets have been performed to search for new gravitylike interaction in the nanometer range[1][2]. But the sensitivity of those measurements is many orders of magnitude worse than the range of the coupling constant predicted by the Large-Extra-Dimension (LED) models [3].

 Therefore, we proposed using coherent scattering for nanoparticle targets to improve sensitivity significantly [4].

 Since the angular distribution also depends on the target size, it is necessary to subtract this effect measure the particle size distribution accurately.by using X-ray small-angle scattering to obtain the particle size distribution. For that purpose, X-ray small-angle scattering measurement is performedmeasured at the Aichi Synchrotron Radiation Center in Japan.

 We are also planning experiments using hydrogen-absorbing vanadium nanoparticle targets.

 In this presentation, I will describe the analysis results of the SANS experiment in June 2023 and the plan for future experiments on hydrogen-absorbing vanadium nanoparticles.   

Electron Accelerator for Detector Characterization with Incident Particle Energies Between 0.1 to 1 MeV Construction, Design, and Experimental Result Updates

Neutron decay provides a mechanism for studying the fundamental properties of the weak nuclear force. Modern neutron decay experiments require accurate energy reconstruction which must be corrected for energy loss due to bremsstrahlung radiation during the detection process. A linear, pulsed electron accelerator was designed using Autodesk Inventor and Kassiopeia and is currently under construction at the Triangle Universities Nuclear Laboratory (TUNL) in Durham, North Carolina. The completed accelerator will be mounted inside a pressure vessel filled with insulating gas to allow the accelerator to reach a peak energy of 1MeV. The accelerator will be used to study bremsstrahlung production and to characterize semiconductor detectors that are used to study Nab experiment at the Spallation Neutron Source. Construction, design, and experimental result updates and developments will be presented and discussed.