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 DJ: Mini-Symposium on Fundamental Neutron Physics II |
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Chair: Adam Holley, Tennessee Technological University Room: Hilton Kona 5 |
Thursday, October 25, 2018 9:00AM - 9:15AM |
DJ.00001: Understanding the UCNτ Neutron Lifetime Experiment Through Simulations of Trapped Neutrons Francisco Gonzalez The UCNτ experiment at Los Alamos National Lab measures the neutron β-decay lifetime by storing ultracold neutrons (UCNs) in a magneto-gravitational trap for holding times longer than the neutron's lifetime. Systematic effects can stem from changes in the UCN phase space distribution between different holding times, and potential exposure of neutrons to additional loss mechanisms. We have utilized a Monte Carlo simulation of UCN trajectories to understand this evolution, and constrain possible sources of loss. Additionally, this simulation allows us to model the UCN capture efficiency of the in-situ dagger detector. The simulation uses Indiana University's Big Red II supercomputer to symplectically integrate neutrons in a magnetic potential, derived from an analytic expression for the trap's field. By adjusting simulated trap characteristics such as heating amount or cleaning height, we can look for shifts in the measured lifetime. We will present results of these simulations, as part of an effort to reduce UCNτ's total uncertainty to about 0.2 seconds. |
Thursday, October 25, 2018 9:15AM - 9:30AM |
DJ.00002: Precision Measurement of Cold Neutron Flux Evan R Adamek, Maynard Dewey, Nadia Fomin, David Gilliam, Geoffrey L Greene, Shannon M Fogwell Hoogerheide, Hans P Mumm, Jeffrey Scott Nico, William Michael Snow The use of cold neutron beams in experiments such as the neutron beam lifetime experiment BL-2 necessitates a means of accurately measuring their flux to high precision. The Alpha-Gamma device at the National Institute of Standards and Technology (NIST) provides a sub-0.1% measurement of the flux of a monochromatic cold neutron beam. This is accomplished through measurement of the alpha and gamma production rate following neutron absorption on a totally absorbing 10B target. The Alpha-Gamma device has most notably been used to recalibrate the flux monitor used in the neutron beam lifetime experiment leading to a re-evaluation of its result in 2012; we will discuss recent efforts in the current beam lifetime experiment at NIST. We will also cover other current projects including high precision measurements of the 235U(n,f) and 6Li(n,t)4He cross sections and a novel calibration technique for the NIST manganese bath neutron source calibration facility. |
Thursday, October 25, 2018 9:30AM - 9:45AM |
DJ.00003: Upgrade of Neutron Lifetime Measurement at J-PARC Hideaki Uehara, J-PARC Neutron lifetime collaboration Neutron lifetime is an important parameter, and it has been precisely measured with two methods. However, there is 8.4 sec difference between these two methods. In Japan, we are measuring the neutron lifetime using new method. This experiment is using a polarized neutron beam branch of BL05, MLF, J-PARC. A Time Projection Chamber (TPC) is used for counting both the beta-decay product and neutron flux, and it is operated using a mixture of He and CO_2 gas with 100 kPa total pressure. We are planning 2 updates in order to reduce the uncertainty. One is spin flip chopper update, and the other is taking data with a low gas pressure condition. The most significant background is gas scattering event, and it can be reduced by lowering the TPC gas pressure. We have carried out the first physics run of the low gas pressure measurement in 2017. We also have developed a new amplifier for further lower pressure operation. Details of the data analysis and new amplifier will be presented in this talk. |
Thursday, October 25, 2018 9:45AM - 10:00AM |
DJ.00004: Upgrade scheme of upstream optics for neutron lifetime measurement at J-PARC Hiroki Okabe, J-PARC Neutron lifetime collaboration Neutron lifetime is an important parameter in CKM matrix and Big Bang Nucleosynthesis. There is 4.0 sigma difference between two typical method: storage the UCN and detecting the beam of neutron. Therefore, we try to measure the neutron lifetime by using the different method with 1 sec accuracy. Our measurement is carried out at a polarized beam branch on BL05 NOP beam line in the MLF at the J-PARC. We use a time projection chamber (TPC) as a beta-decay detector with little environmental background. We use the device called a spin flip chopper (SFC) to form neutron beam into bunches. The bunches have about half of the TPC length. These devices enable us to detect beta-decay electrons with a 4π solid angle acceptance and achieve good signal-to-noise ratio. |
Thursday, October 25, 2018 10:00AM - 10:15AM |
DJ.00005: BL3: A next-generation free neutron lifetime experiment using the beam method Fred E Wietfeldt Recent measurements of the free neutron beta decay lifetime using the cold neutron beam method and the ultracold neutron storage method differ by four standard deviations. While new physics models have been proposed to explain the discrepancy, a more probable culprit is misunderstood systematic effects in one or both methods. BL3 is a next generation beam neutron lifetime experiment based on the Sussex-ILL-NIST technique. A cold neutron beam passes through a quasi-Penning trap. Recoil protons from neutron decay are trapped and periodically counted by a silicon detector and the neutron beam density is measured using a thin foil target. BL3 will employ a larger superconducting magnet, a larger high-flux beam, and a large diameter segmented silicon detector, giving a 100 times increase in proton trapping rate compared to previous experiments. A number of new features to test and explore systematic effects will be included. The goal of BL3 is twofold: 1) to search for an explanation of the neutron lifetime discrepancy and validate systematics in the beam method; and 2) reduce the ultimate precision in the beam method to <0.3 s. Plans for the design and operation of the experiment will be discussed. |
Thursday, October 25, 2018 10:15AM - 10:30AM |
DJ.00006: A next generation neutron lifetime experiment based on UCNτ Alexander Saunders The UCNτ experiment measures the free neutron lifetime by in situ counting of surviving ultracold neutrons after different storage times in an asymmetric magneto-gravitational storage volume. This experiment has acquired sufficient data for a measurement of the neutron lifetime with a statistical uncertainty of about 0.35 s and has demonstrated a systematic uncertainty of 0.28 s [1]; it is expected to ultimately reach a total uncertainty of about 0.2 s. To achieve even better precision in follow-on experiments, at the 0.1 s level and beyond, the leading sources of uncertainty, including counting statistics, vibrational heating of the stored neutrons, evolution of the stored neutron population in phase space, rate-dependent counting efficiency effects, and depolarization of stored neutrons, must be addressed. In this talk, we will discuss strategies for how to reduce these sources of uncertainty to achieve a total uncertainty on the neutron lifetime well below 0.1 s in future experiments based on the UCNτ concept, including increasing the storage volume, the strength of the confining magnetic field, or both. [1] R. W. Pattie Jr. et al., Science 10.1126/science.aan8895 (2018). |
Thursday, October 25, 2018 10:30AM - 10:45AM |
DJ.00007: Search for the Neutron Decay n$\rightarrow$γ+X where X is a dark matter particle. Christopher Lee Morris, Zhaowen Tang, Leah J Broussard, Marie Blatnik, Jin Ha Choi, Steven Clayton, Chris Cude-Woods, Deion Fellers, Eric M Fries, Peter Geltenbort, Frank Gonzalez, Kevin P Hickerson, Takeyasu M Ito, Chen-Yu Liu, Mark Makela, Robert W Pattie, Christopher O'Shaughnessy, Bradley Plaster, Jared Lambert, Albert R. Young, Adam Tarte Holley Fornal and Grinstein(1) propose that the discrepancy between the beam and bottle methods of neutron lifetime measurements can be explained by a previously unobserved dark matter decay mode n$\rightarrow$γ+X. We have performed a search for this decay mode over the allowed range of energies of the monoenergetic gamma ray (2). In this recent work, a Compton-suppressed high-purity germanium detector was used to identify γ-rays from the decay of ultra-cold neutrons (UCNs) stored in a nickel-phosphorous coated stainless-steel bottle. The possibility of a sufficiently strong branch to explain the lifetime discrepancy was excluded with 97% confidence. Setup for a new experiment with a factor of 5 improved gamma ray resolution, and about two times higher UCN density. Results with approximately 5 times higher sensitivity will be presented. 1. Fornal B, Grinstein B. "Dark Matter Interpretation of the Neutron Decay Anomaly". Phys. Rev. Lett. 120, 191801 (2018). 2. Tang Z, Blatnik M, Broussard L, Choi J, Clayton S, Cude-Woods C, et al. Search for the Neutron Decay n $\rightarrow $ X+ $\gamma $ where X is a dark matter particle. arXiv preprint arXiv:180201595. 2018.
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Thursday, October 25, 2018 10:45AM - 11:00AM |
DJ.00008: UCNb&[chi]: a proposal for a high-precision neutron decay branching ratio experiment using ultracold neutrons. Kevin Peter Hickerson Neutron lifetime results confirm a discrepancy between counting protons, and bottled ultracold neutrons (UCN). One explanation is n-decay into a dark matter fermion, χ, via an intermediate leptoquark scalar, Φ = (3, 1)−1/3. Such a scalar may also interfere with Standard Model (SM) β-decay, in the form of a spectral shape parameter b, the Fierz interference term. First constraints on b for the free neutron were set with the UCNA experiment, limited by systematic energy response uncertainty. To overcome this, a UCNbχ (“ultracold neutron branch”) experiment is proposed as a successor to the UCNb prototype, developed at Los Alamos National Laboratory. Data and modeling from UCNb will be presented to motivate UCNbχ’s design. An upgrade will include a larger 4π PTFE Ulbricht sphere and a DPS/Eu:CaF2 scintillator storage volume. Calibration of UCNbχ can be greatly improved using in situ activated xenon isotopes and volatile stannic compounds. To suppress neutron generated background, dominant in UCNb, a 4π, half-ton, active gamma veto surrounding the decay chamber, will measure radiative branches, both from SM and aprotonic dark-matter model decays. |
Thursday, October 25, 2018 11:00AM - 11:15AM |
DJ.00009: Ultra-Cold Neutron measurement of Proton branching in neutron Beta decay (UCNProBe) Jared Campbell Lambert, Zhaowen Tang, Christopher Lee Morris, Christopher O'Shaughnessy, Alexander Saunders, Steven Clayton, Takeyasu M Ito, Deion Fellers, Chris Cude-Woods, Mark Makela, Albert Raymond Young, Chen-Yu Liu, Robert W Pattie, Kevin P Hickerson, Bryan A Zeck The lifetime of the free neutron has been measured many times, each experiment using one of two methods: measuring the decay products of neutrons in a well calibrated neutron beam (beam experiment), or counting the number of surviving neutrons stored in a UCN trap over time (bottle experiment). The lifetime results from the two different methods of experiments differ by 10 seconds or five standard deviations. Our goal is to resolve the difference between the two measurements by measuring the proton branching ratio of neutron decay using UCNs. Detecting a proton branching ratio of less than one will indicate new physics beyond the Standard Model of particle physics. The experiment is realized by storing the neutrons in a scintillating material trap. To measure the proton branching ratio, we will attempt to measure the absolute number of UCNs inside the trap and the absolute number of electrons from beta decay to 0.1% precision. In this talk, we will describe the concept of the experiment and its systematic error. |
Thursday, October 25, 2018 11:15AM - 11:30AM |
DJ.00010: Search for deviations from the inverse square law of gravity at nm range using a pulsed neutron beam Christopher Haddock
Recently published results and ongoing experimental efforts to search for deviations from the inverse square law of gravity at the nanometer length scale using slow neutron scattering from the noble gases will be discussed. Using the pulsed slow neutron beamline BL05 at the Materials and Life Sciences Facility at J-PARC, we measure the neutron momentum transfer (q) dependence of the neutron differential scattering cross section for the noble gases He, Ne, Ar, Kr, and Xe. By comparison to theory we place an upper bound on the strength of a new interaction as a function of interaction length λ which improves upon existing results in the region λ<0.1nm, and remains competitive in the larger λ region. Ongoing efforts to improve the sensitivity of our method, as well as apply our technique on an apparatus with a larger accessible q range (e.g. BL21 at J-PARC), which would allow for measurement of the so called “neutron-electron scattering length,” will also be discussed. |
Thursday, October 25, 2018 11:30AM - 11:45AM |
DJ.00011: A Search for Possible Long Range Spin Dependent Interactions of the Neutron From Exotic Vector Boson Exchange Kirill Korsak We sought for a possible new axial vector interaction with a range in the millimeter to micron range using spin dependent interactions of neutrons with matter though exchange of spin 1 bosons as predicted in some extensions of the Standard Model. This experiment was performed on FP12 at the LANSCE facility at Los Alamos by sending transversely polarized slow neutrons through gaps near slabs of copper and float glass arranged so that the possible exotic interaction would tilt the plane of polarization along the neutron momentum [3]. The resulting rotation angle φ′ =[2.8±4.6(stat.)±4.0(sys.)]×10−5rad/m was consistent with zero [1]. The upper bound on an exotic axial vector neutron-matter coupling g2A was improved by about three orders of magnitude for force ranges in the mm-μm [2]. We discuss this result along with our plan to further improve the sensitivity of our search by at least 2 orders of magnitude at the NIST NG-C beam using tungsten slabs as the source. [1] C. Haddock et al., arXiv:1802.05907, (2018), accepted for publication in Physics Letters (2018). |
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