Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session CJ: Mini-Symposium on Fundamental Neutron Physics I |
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Chair: Geoffrey Greene, University of Tennessee Room: Hilton Kona 5 |
Wednesday, October 24, 2018 7:00PM - 7:30PM |
CJ.00001: Fundamental Neutron Physics: Current Experimental Landscape and Future Directions Invited Speaker: Adam Tarte Holley The neutron is an unstable but long-lived neutral baryon, characteristics that conspire to make it a versatile laboratory for testing the Standard Model at the precision frontier. The familiar neutron plays a central role in attempts to discover new symmetries that underlie fundamental particle interactions, it is a powerful tool for understanding the baryon asymmetry of the universe and the nature of dark matter, it can be used to search for new exotic interactions, to probe the non-perturbative nature of the strong interaction, and to test foundational issues in quantum mechanics and general relativity. Its ability to facilitate such investigations means that the neutron also plays a significant role in cosmology. The experimental techniques that harness the unique properties of the neutron for such a diverse array of investigations are similarly varied. Collectively, they deal with neutrons that have energies ranging from "ultracold" (neV) to eV, but probe physics at the TeV scale. They encompass techniques from high energy particle physics, nuclear physics, optics, and condensed matter physics to achieve the extraordinary precision that determines their potential for discovering new physics. This overview will summarize aspects of the current neutron fundamental physics experimental program, highlighting the significant activity in the field by focusing on recent accomplishments and anticipated advances, and their potential impact on our understanding of the Standard Model. |
Wednesday, October 24, 2018 7:30PM - 7:45PM |
CJ.00002: The BL2 Experiment: An In-Beam Measurement of the Neutron Lifetime Jimmy Caylor Neutron beta decay is the simplest example of semi-leptonic decay. A precise measurement of the neutron lifetime and λ, the ratio of axial vector and vector coupling constants of the weak interaction, allow for a determination of the CKM matrix element Vud that is free from nuclear structure effects. The neutron lifetime provides an important test of unitarity and consistency of the Standard Model. The neutron lifetime is also the largest uncertainty in Big Bang Nucleosynthesis calculations of light element abundance. A new measurement of the neutron lifetime using the in-beam method is ongoing at the NIST Center for Neutron Research. This method requires the absolute counting of the decay protons in a neutron beam of precisely known flux. Improvements in the neutron and proton detection systems as well as the use of a new analysis technique should permit an overall uncertainty of 1s. The experimental status, technical improvements, analysis techniques and early data will be presented. |
Wednesday, October 24, 2018 7:45PM - 8:00PM |
CJ.00003: The UCN$\tau$ measurement of the free neutron lifetime: status report Chris Cude-Woods The UCN$\tau$ experiment measures the $\Beta$ decay lifetime of the free neutron. Ultracold neutrons (UCN) are loaded into a trap wherein they are confined by gravity and an array of permanent magnets, and, after varying storage times, the surviving UCN are counted in-situ. The experiment completed its first production science run during the 2017 beam cycle at the Los Alamos Neutron Science Center, roughly quadrupling data taken during previous commissioning and engineering runs and leading to a statistical uncertainty well below 0.5 s. We will present the status of the analysis and the ongoing production run. |
Wednesday, October 24, 2018 8:00PM - 8:15PM |
CJ.00004: Precise Neutron Lifetime Measurement Using Pulsed Neutron Beams at J-PARC Naoki Nagakura, J-PARC Neutron lifetime collaboration
The neutron decay lifetime (~ 880 sec) is an important parameter in the weak interaction. For example, it can be used to determine the Vud parameter of the CKM quark mixing matrix. However, experimental measurements of the neutron lifetime today are significantly different (4.0 sigma or 8.4 sec) depending on the method used. We are therefore performing an experiment using a different method with a goal precision of 1 sec on the neutron lifetime. The experiment is carried out at the polarized beam branch of BL05, MLF, J-PARC. A Time Projection Chamber (TPC) operated with He and CO2 gas is used as a beta-decay detector. Neutrons are formed into bunches, the length of which is half of the TPC length, by Spin Flip Chopper. The neutron flux can be evaluated by the number of 3He(n, p)3H events in the TPC and its cross section. The data acquisition started at J-PARC in 2014, and by 2018 we already took the data giving a statistical error of a few seconds on the neutron lifetime. We will present the analysis result of the neutron lifetime. We also present some future upgrade plans to achieve our goal precision of 1 sec. |
Wednesday, October 24, 2018 8:15PM - 8:30PM |
CJ.00005: Precise Neutron Lifetime Measurement with a Gaseous Detector and a Solenoidal Magnet Naoyuki Sumi, Hideaki Uehara, Tomoya Nagano, So Makise, Tamaki Yoshioka, Hidetoshi Otono, Kenji Mishima, Yasuhiro Makida The neutron lifetime, τ = 880.2 ± 1.0 sec, is an important parameter for particle/nuclear physics and cosmology. There is, however, an 8.4 sec (4.0 σ) deviation between the measured value of the neutron lifetime using two methods. A new method is being implemented at J-PARC / MLF / BL05 using a pulsed cold neutron beam. A Time Projection Chamber records both the electrons from neutron beta decay and protons from the neutron-3He capture reactions in order to estimate the neutron flux. However, electron background signals require the largest correction and are source of uncertainty for this type experiment. It is confirmed by Monte Carlo simulation that an uniform magnetic field along the neutron beam can greatly reduce this background. Hence, we proposed another experiment (LiNA experiment) using a solenoidal magnet. The detector was constructed and operation with neutron beam is carried out soon. We will present the status and future plan of this experiment. |
Wednesday, October 24, 2018 8:30PM - 8:45PM |
CJ.00006: UCNA Results and Prospects for Improvement: Update on High Precision Polarimetry and the Beta Asymmetry Eric B Dees The UCNA experiment determines the axial coupling constant in neutron decay, critical input for a high precision characterization of the charged weak current from neutron decay, through a measurement of the beta asymmetry in polarized ultracold neutron(UCN) decay. We present an update on the analysis of the 2011-2013 UCNA runs, primarily through an expanded Monte Carlo analysis of polarization and polarimetry. We summarize the current status of UCNA and update our assessment of the systematic error budget, and compare to previous geometries associated with 2008-2010 datasets. Our new analysis provides insight into the management of systematic errors for the UCNA geometry in the 2011-2013 run cycle and for future upgrades of the experiment, made possible by recent progress at the LANL Area B UCN source increasing the available UCN density by a factor of 4 to 5 (depending on experimental details). |
Wednesday, October 24, 2018 8:45PM - 9:00PM |
CJ.00007: Update on the Status of the UCNB Experiment Aaron Jezghani, Christopher B Crawford Precision neutron beta decay experiments serve well as a test of the Standard Model, and act as a sensitive probe for Beyond the Standard Model (BSM) physics. The UCNB experiment at the Los Alamos Neutron Science Center (LANSCE) uses a direct measurement of the proton and coincident electron from free neutron beta decay to determine the neutrino asymmetry, B, to a target precision of 1 × 10-3. Recent efforts have led to an improved analysis of digitized detector traces and a more detailed understanding of detector systematics. An updated analysis of a first attempt to measure B using ultracold neutrons and a discussion of implications for future experimental efforts such as Nab will be presented. |
Wednesday, October 24, 2018 9:00PM - 9:15PM |
CJ.00008: Research and Development Goals for Angular Correlations Experiments with Ultracold Neutrons Albert Young Neutron decay correlation measurements provide a direct determination of the axial coupling constant of the nucleon, and play a central role in the high precision characterization of the charged weak interaction. The upgraded ultracold neutron (UCN) source at the Los Alamos Neutron Science Center has created an opportunity for significant improvements in the sensitivity of decay correlation measurements with UCNs. Although UCNs offer significant advantages with key sources of systematic error, the UCNA experiment is the only high precision angular correlation experiment which utilizes UCN, and determines the angular correlation between the neutron spin and the emitted beta particle. Experience with the UCNA experiment has set the stage for upgrades to the experiment which can push the precision to between 0.2% and 0.1%. The motivation and R&D goals identified to achieve a sensitivity below 0.2% for an upgrade of UCNA are presented, together with recent progress at Los Alamos. |
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