Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session FE: Mini-Symposium on Fundamental Symmetries (Neutrons and Gravity I) |
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Chair: Pieter Mumm, National Institute of Standards and Technology Room: King's 1 |
Friday, October 10, 2014 9:00AM - 9:30AM |
FE.00001: Fundamental Physics with Cold and Ultracold Neutrons Invited Speaker: Brad Plaster Advances in techniques for neutron production, neutron transport, and particle detection over the past several decades have culminated in a now burgeoning era of precision work in fundamental neutron physics experiments. These advances have enabled a broad spectrum of fundamental physics tests to be carried out in experiments utilizing cold neutron beams and ultracold neutrons, with physics implications ranging from the hadronic weak interaction to searches for beyond Standard Model physics to Big Bang Nucleosynthesis. This talk will review the physics case for this diverse program of measurements, highlight recent progress in the field, and point to prospects for studies of fundamental physics in ongoing and future experiments. [Preview Abstract] |
Friday, October 10, 2014 9:30AM - 9:45AM |
FE.00002: Status of Analysis for the UCNA Experiment's 2011-2012 and 2012-2013 Data Sets Michael A. Brown The UCNA Experiment at the Los Alamos Neutron Science Center (LANSCE) is the first measurement of the $\beta$-decay asymmetry parameter $A_0$ using polarized ultracold neutrons (UCN). $A_0$, which represents the parity-violating angular correlation between the direction of the initial neutron spin and the emitted decay electron's momentum, determines $\lambda=g_{A}/g_{V}$, the ratio of the weak axial-vector and vector coupling constants. A high-precision determination of $\lambda$ is important for weak interaction physics, and when combined with the neutron lifetime it permits an extraction of the CKM matrix element $V_{ud}$ solely from neutron decay. At LANSCE, UCN are produced in a pulsed, spallation driven solid deuterium source and then polarized via transport through a 7 T magnetic field. The UCN then travel to a decay storage volume situated within a 1 T solenoidal spectrometer with electron detectors at each end for measurement of decay electrons. Data collected during run periods in 2011-2012 and 2012-2013 are currently under analysis, for which the projected uncertainty on $A_0$ is $<0.6$\%. The status of this analysis will be presented in this talk. [Preview Abstract] |
Friday, October 10, 2014 9:45AM - 10:00AM |
FE.00003: Improving the Precision of the UCNA Neutron Beta Asymmetry Experiment Alexander Saunders The UCNA experiment has published a measurement of the neutron beta decay asymmetry coefficient, A, with a total uncertainty of less than 1\%, and is preparing the publication of a more recent data set with a total uncertainty expected to be about 0.5\%. The experiment measures the correlation between decay beta particle emission direction and ultracold neutron spin as a function of the electron's energy. The leading sources of uncertainty in the most recent results are statistics, depolarization of the neutrons, missed backscatter of the electrons from insensitive layers of their detectors and the neutron storage trap, and energy loss of the electrons as they penetrate those same insensitive layers. We will present our progress on four efforts to reduce these sources of uncertainty in order to achieve a total uncertainty of about 0.35\% in future UCNA results: a higher neutron decay rate in the experiment, improved depolarization monitoring techniques, and methods to better understand and control the electron backscatter and energy loss. [Preview Abstract] |
Friday, October 10, 2014 10:00AM - 10:15AM |
FE.00004: The UCN$\tau$ experiment at LANL Daniel Salvat A precision measurement of the neutron lifetime, when combined with other neutron beta decay observables, is a sensitive test of the $V-A$ law of the weak interaction, a probe of certain types of beyond standard model interactions, and an input for models of nucleosynthesis in the early universe. There is a difference of $4\sigma$ between the two prevalent techniques for measuring the neutron lifetime: the beam measurement technique -- an absolute measurement of the decay rate of neutrons in a cold neutron beam, and the bottle technique -- a measurement of the disappearance rate of ultracold neutrons (UCN) confined in material traps. Magnetic trapping of polarized UCN has the potential to resolve the discrepancy between these techniques and eliminate certain systematic corrections due to the loss of UCN on the walls of material traps. The UCN$\tau$ experiment at the Los Alamos Neutron Science Center uses a $\sim$600 liter volume lined with a NdFeB Halbach array to magnetically and gravitationally confine neutrons. The trap exhibits a long storage time for UCN, and we have commissioned a new UCN detection scheme which counts $\beta$-decays of a vanadium foil activated by the trapped neutrons. In this talk, I will provide an overview of the experiment. [Preview Abstract] |
Friday, October 10, 2014 10:15AM - 10:30AM |
FE.00005: Ultracold Neutron Transport and Density Monitoring in the UCN$\tau$ Experiment A.T. Holley The UCN$\tau$ experiment is designed to help resolve the current tension between in-beam and bottle measurements of the free neutron lifetime $\tau_{\mathrm{n}}$. This is an important goal since a high-precision value of $\tau_{\mathrm{n}}$ will shed light on the implications of other free neutron decay measurements for beyond the Standard Model physics and because of the critical role that $\tau_{\mathrm{n}}$ plays in Big Bang Nucleosynthesis. Our focus is on providing a bottle measurement of $\tau_{\mathrm{n}}$ to better than one second ($<0.1\%$) by reducing the systematic effects generally associated with storage techniques. Our strategy uses ultracold neutrons (UCN) confined in a magneto-gravitational trap and detected both traditionally and using a novel \textit{in situ} approach. The full potential of our technique is best realized when we are able to maximize the density of polarized, trappable UCN in our $\sim$670~L storage volume while simultaneously monitoring that density during filling with $<0.1\%$ precision. We will report on measurements conducted during the 2013 run cycle at the Los Alamos Neutron Science Center designed to optimize the transport of polarized UCN into our trap and to investigate strategies for monitoring the resulting density with high precision. [Preview Abstract] |
Friday, October 10, 2014 10:30AM - 10:45AM |
FE.00006: Neutron lifetime measurement with pulsed beam at JPARC: Overview Kenji Mishima, Takashi Ino, Kaoru Taketani, Takahito Yamada, Ryo Katayama, Nao Higashi, Harumichi Yokoyama, Hirochika Sumino, Satoru Yamashita, Risa Sakakibara, Tomoaki Sugino, Masaaki Kitaguchi, Katsuya Hirota, Hirohiko M. Shimizu, Genki Tanaka, Naoyuki Sumi, Hidetoshi Otono, Tamaki Yoshioka, Ryunosuke Kitahara, Yoshihisa Iwashita, Hideyuki Oide, Tatsushi Shima, Yoshichika Seki The neutron lifetime is an important parameter for a test of the Standard Model of elementary particles, as well for the production of light mass nuclei in big bang nucleosynthesis. There are two principally different approaches to measure the neutron lifetime: In-beam methods and storage of ultracold neutron. At present, there is a discrepancy of 8.4 sec (3.8 sigma) between the two methods. We are performing a new In-beam experiment with an intense pulsed neutron source at J-PARC, which has different systematic uncertainties from the previous experiments. We introduce the overview of the experiment and report present status. [Preview Abstract] |
Friday, October 10, 2014 10:45AM - 11:00AM |
FE.00007: Neutron Lifetime Measurement Initiated at J-PARC/MLF/BL05 Genki Tanaka, Tamaki Yoshioka, Hidetoshi Otono, Naoyuki Sumi, Satoru Yamashita, Ryo Katayama, Takahito Yamada, Nao Higashi, Harumichi Yokoyama, Hirochika Sumino, Hirohiko Shimizu, Masaaki Kitaguchi, Katsuya Hirota, Risa Sakakibara, Tomoaki Sugino, Yoshihisa Iwashita, Ryunosuke Kitahara, Hideyuki Oide, Tatsushi Shima, Takashi Ino, Kenji Mishima, Kaoru Taketani, Yoshichika Seki The neutron lifetime $\tau_{n}$ is one of the important parameters for the Big Bang Nucleosynthesis (BBN) which predicts an abundance of the light elements in the early universe. However, the He/(H+He) ratio recently measured by Izotov et al. has been deviated from that of the BBN prediction. Thus a precise $\tau_{n}$ measurement is desired. Historically, there are two methods for $\tau_{n}$ measurement, and there exists 3.8$\sigma$ deviation between their results. We are therefore conducting the $\tau_{n}$ measurement at the J-PARC/MLF/BL05 by using a third method. In this experiment we count the number of decay electrons by using Time Projection Chamber (TPC). We expect 1\% accuracy with the collected data in JFY 2014. In this presentation, we will report some analysis results and future plan. [Preview Abstract] |
Friday, October 10, 2014 11:00AM - 11:15AM |
FE.00008: Plans for a measurement of the neutron lifetime to better than 0.3s using a Penning trap and absolute measurement of neutron fluence Jonathan Mulholland The decay of the free neutron is the prototypical charged current semi-leptonic weak process. A precise value for the neutron lifetime is required for consistency tests of the Standard Model and is needed to predict the primordial He4 abundance from the theory of Big Bang Nucleosynthesis. Plans are being made for an in-beam measurement of the neutron lifetime with an anticipated 0.3s of uncertainty or better. This effort is part of a phased campaign of neutron lifetime measurements based at the NIST Center for Neutron Research, using the Sussex-ILL-NIST technique [1]. Advances in neutron fluence measurement, used in [2] to provide the best existing in-beam determination of the neutron lifetime, as well as new silicon detector technology, in use now at LANSCE [3], address the two largest contributors to the uncertainty of in-beam measurements--the statistical uncertainty associated with proton counting and the systematic uncertainty in the neutron fluence measurement. The experimental design and projected uncertainties for the 0.3s measurement will be discussed.\\[4pt] [1] J. S. Nico et al., Phys. Rev. C 71, 055502 (2005).\\[0pt] [2] A. Yue et al. Phys. Rev. Lett. 111, 222501.\\[0pt] [3] Salas-Bacci et al. Nucl. Instrum. Methods A 735 (2014) 408-414 [Preview Abstract] |
Friday, October 10, 2014 11:15AM - 11:30AM |
FE.00009: UCNB and Nab Detector Development Bryan Zeck The UCNB and Nab experiments are designed to measure angular correlations in neutron beta decay via the detection of the decay beta and recoil protons in coincidence. UCNB uses polarized ultracold neutrons (UCN) stored in a material trap to measure angular correlations between the neutron spin and the electron and proton momenta, characterized by the parameter $B$, as well as other angular correlations in polarized neutron decay. Nab is designed to measure the correlation of electron momentum to neutrino momentum, characterized by the parameter $a$, and the Fierz interference term, characterized by the parameter $b$, using a beam of unpolarized cold neutrons. These experiments require a very thin dead layer and a strong electrical field to detect protons, and a thick detector with fast timing to determine the electron energy. Both experiments will employ a large area pixelated thick silicon detector developed at the UCN facility at the Los Alamos Neutron Science Center (LANSCE) as part of a combined effort to completely characterize the detector and develop the electronic amplification system. We will present preliminary results from the 2013-2014 UCNB data run, as well as the results of development of pogo-pin style connectors to be used in the Nab apparatus. [Preview Abstract] |
Friday, October 10, 2014 11:30AM - 11:45AM |
FE.00010: Tensor coupling limits from $\beta$ decay Kevin Hickerson The recent discovery of B-modes in the cosmic microwave background by BICEP2 strongly implies that the Standard Model needs to be extended to include tensor currents, at least near the Planck scale. In addition, collisionless cold dark matter models may need to be modified to include beyond the Standard Model (BSM) collisions mediated by scalar or tensor couplings. So far, superallowed $0+ \to 0+$ nuclear $\beta$ decay experiments have provided the tightest limits on scalar couplings near the TeV scale by analyzing the so-called, Fermi Fierz interference term, $b_{\mathrm{F}}$. The tensor coupling constant, $C_T$, however, can be recovered from free neutron decay parameters extracted from recent experiments, improved in part, by using ultracold neutrons (UCN). In this talk, we present our new result for limits on BSM tensors couplings using a combined fit from neutron parameters, which include mixtures from Gamow--Teller Fierz interference, $b_{\mathrm{GT}}$, and existing scalar limits. We show $-0.0026 < C_T / C_A < 0.0024$ (95\% C.L.). We further discus limits on neutron Fierz interference from Big Bang Nucleosynthesis as well as current efforts to measure it directly. [Preview Abstract] |
Friday, October 10, 2014 11:45AM - 12:00PM |
FE.00011: Neutron lifetime measurement with pulsed beam at J- PARC: TPC and DAQ Takahito Yamada, Ryo Katayama, Nao Higashi, Harumichi Yokoyama, Hirochika Sumino, Satoru Yamashita, Risa Sakakibara, Tomoaki Sugino, Masaaki Kitaguchi, Katsuya Hirota, Hirohiko M. Shimizu, Genki Tanaka, Naoyukio Sumi, Hidetoshi Otono, Tamaki Yoshioka, Ryunosuke Kitahara, Yoshihisa Iwashita, Hideyuki Oide, Tatsushi Shima, Yoshichika Seki, Kenji Mishima, Kaoru Taketani, Takashi Ino The neutron lifetime is an important parameter for Big Bang nucleosynthesis (BBN). The best neutron lifetime measurements have uncertainties at the 0.1\% level; however, they differ by 3.8 sigma. In order to resolve this discrepancy, we plan to measure the neutron lifetime using a method originally developed by Kossakowski et al. which is different from the other 0.1\% accuracy experiments. In our method, which uses a pulsed cold neutron beam at J-PARC, the electrons from the beta decay of the neutron are detected with a time projection chamber (TPC). A small amount of $^{3}$He is added to the gas mixture in order to simultaneously measure the neutron flux. We report on the recent upgrade of the TPC and the Data Acquisition System which were used to take data during the period of February-June 2014. [Preview Abstract] |
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