Fri·Feb 22, 2019Friday·February 22, 2019

1. 01*

   Prompt Fission Neutrons in the ${}^{239}$Pu($n,f$) Reaction

   P. Marini🇫🇷 · J. Taieb🇫🇷 · B. Laurent🇫🇷 · G. Belier🇫🇷 · A. Chatillon🇫🇷 · D. Etasse🇫🇷 · P. Morfouace🇫🇷 · M. Devlin🇺🇸 · J. A. Gomez🇺🇸 · R. C. Haight🇺🇸 · K. J. Kelly🇺🇸 · J. M. O'Donnel🇺🇸 · K. T. Schmitt🇺🇸

   Prompt fission neutron spectra from ${}^{239}$Pu($n,f$) were measured for incident neutron energies from $0.7$ to $700$MeV at the Weapons Neutron Research facility (WNR) of the Los Alamos Neutron Science Center. A newly designed high-efficiency fission chamber was coupled to the highly segmented Chi-Nu array to detect neutrons emitted in fission events. The double time-of-flight technique was used to deduce the incident-neutron energies from the spallation target and the outgoing-neutron energies from the fission chamber. Prompt fission neutron spectra (PFNS) were measured with respect to ${}^{252}$Cf spontaneous fission down to $200$keV and up to about $12$MeV for all the incident neutron energies with typical uncertainties well below $2\%$ up to about $10$MeV outgoing-neutron energy. The general trend of PFNS is well reproduced by JEFF3.3 and ENDF-B\VIII.0 evaluations. Discrepancies were however observed for the low-energy part of the spectra, where evaluations overestimate the number of emitted neutrons. Neutron multiplicities and average kinetic energies as a function of incident-neutron energy are obtained experimentally with reported uncertainties below $0.4\%$. Neutron multiplicities disagree with some older datasets above $6$ MeV, indicating the need of using a high-efficiency fission detector, which does not bias the data. The measured mean kinetic energies agree with the most recent data. Evaluations fairly reproduce the trend, but fail to reproduce the experimental values within their uncertainties.

   nucl-exPRC(2020)·23 citations
2. 02*

   Experimental Upper Bound and Theoretical Expectations for Parity-Violating Neutron Spin Rotation in 4He

   H. E. Swanson🇺🇸 · C. D. Bass · T. D. Bass · B. E. Crawford🇺🇸 · J. M. Dawkins🇺🇸 · K. Gan🇺🇸 · B. R. Heckel🇺🇸 · J. C. Horton🇺🇸 · C. Huffer🇺🇸 · D. Luo🇺🇸 · D. M. Markoff🇺🇸 · A. M. Micherdzinska🇺🇸 and 7 other authors

   Neutron spin rotation is expected from quark-quark weak interactions in the Standard Model, which induce weak interactions among nucleons that violate parity. We present the results from an experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid ${}^4$He medium. The value for the neutron spin rotation angle per unit length in ${}^4$He, $d\varphi /dz=(+2.1\pm 8.3(stat.)\pm 2.9(sys.))\times 10^{-7}$ rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in the $\vec{n}{+}^4$He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.

   nucl-exPRC(2019)·13 citations
3. 03*

   Transverse single spin asymmetry for very forward ${\pi }^0$ production in polarized proton-proton collisions at $\sqrt{s}$ = 510 GeV

   M. H. Kim🇰🇷 · B. Hong🇰🇷 · Y. Goto🇯🇵 · I. Nakagawa🇯🇵 · R. Seidl🇯🇵 · J. S. Park🇯🇵 · K. Tanida🇯🇵 · Y. Itow🇯🇵 · H. Menjo🇯🇵 · K. Sato🇯🇵 · M. Ueno🇯🇵 · Q. D. Zhou🇯🇵 and 10 other authors

   Transverse single spin asymmetry, $A_N$, of very forward ${\pi }^0$ production from polarized $p+p$ collisions provides new information toward an understanding of its production mechanism. $A_N$ of forward ${\pi }^0$ in the pseudorapidity region of $3<\eta <4$ has been described by the partonic structure of the proton in the perturbative QCD framework. However, recent data indicates a potential contribution from not only partonic but also diffractive interactions. In order to provide a new insight on the origin of the $A_N$, we measured the very forward ${\pi }^0$ production in the pseudorapidity region of $6<\eta$ from $\sqrt{s}$ = 510 GeV polarized $p+p$ collisions at RHIC in 2017. We report our measurement of the very forward ${\pi }^0$ over the transverse momentum range of $0<p_T<1$ GeV/$c$ and the preliminary result.

   ↳ hep-exnucl-exEPJ Web Conf.(2019)·0 citations
4. 04*

   How Analytic Choices Can Affect the Extraction of Electromagnetic Form Factors from Elastic Electron Scattering Cross Section Data

   Scott K. Barcus · Douglas W. Higinbotham🇺🇸 · Randall E. McClellan🇺🇸

   Scientists often try to incorporate prior knowledge into their regression algorithms, such as a particular analytic behavior or a known value at a kinematic endpoint. Unfortunately, there is often no unique way to make use of this prior knowledge, and thus, different analytic choices can lead to very different regression results from the same set of data. To illustrate this point in the context of the proton electromagnetic form factors, we use the Mainz elastic data with its 1422 cross section points and 31 normalization parameters. Starting with a complex unbound non-linear regression, we will show how the addition of a single theory-motivated constraint removes an oscillation from the magnetic form factor and shifts the extracted proton charge radius. We then repeat both regressions using the same algorithm, but with a rebinned version of the Mainz dataset. These examples illustrate how analytic choices, such as the function that is being used or even the binning of the data, can dramatically affect the results of a complex regression. These results also demonstrate why it is critical when using regression algorithms to have either a physical model in mind or a firm mathematical basis

   ↳ physics.data-annucl-exPRC(2020)·28 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.