Mon·Jun 6, 2016Monday·June 6, 2016

1. 01*

   Neutron lifetime measurements and effective spectral cleaning with an ultracold neutron trap using a vertical Halbach octupole permanent magnet array

   K. K. H. Leung🇫🇷 · P. Geltenbort🇫🇷 · S. Ivanov🇫🇷 · F. Rosenau🇫🇷 · O. Zimmer🇫🇷

   Ultracold neutron (UCN) storage measurements were made in a trap constructed from a 1.3 T Halbach Octupole PErmanent (HOPE) magnet array aligned vertically, using the TES-port of the PF2 source at the Institut Laue-Langevin. A mechanical UCN valve at the bottom of the trap was used for filling and emptying. This valve was covered with Fomblin grease to induce non-specular reflections and was used in combination with a movable polyethylene UCN remover inserted from the top for cleaning of above-threshold UCNs. Loss due to UCN depolarization was suppressed with a minimum 2 mT bias field. Without using the UCN remover, a total storage time constant of $(712\pm 19)$ s was observed; with the remover inserted for 80 s and used at either 80 cm or 65 cm from the bottom of the trap, time constants of $(824\pm 32)$ s and $(835\pm 36)$ s were observed. Combining the latter two values, a neutron lifetime of ${\tau }_{\mathrm{n}}=(887\pm 39)$ s is extracted after primarily correcting for losses at the UCN valve. The time constants of the UCN population during cleaning were observed and compared to calculations based on UCN kinetic theory as well as Monte-Carlo studies. These calculations are used to predict above-threshold populations of $\sim 5\%$, $\sim 0.5\%$ and $\sim 10^{-12}\%$ remaining after cleaning in the no remover, 80~cm remover and 65~cm remover measurements. Thus, by using a non-specular reflector covering the entire bottom of the trap and a remover at the top of the trap, we have established an effective cleaning procedure for removing a major systematic effect in high-precision ${\tau }_{\mathrm{n}}$ experiments with magnetically stored UCNs.

   nucl-exphysics.ins-detPRC(2016)·23 citations
2. 02*

   Measurement of the $p(e,e^{\prime }{\pi }^{+})n$ reaction close to threshold and at low $Q^2$

   A1 Collaboration: I. Friščić🇭🇷 · P. Achenbach🇩🇪 · C. Ayerbe Gayoso🇩🇪 · D. Baumann🇩🇪 · R. Böhm🇩🇪 · D. Bosnar🇭🇷 · L. Debenjak🇸🇮 · A. Denig🇩🇪 · M. Ding🇩🇪 · M. O. Distler🇩🇪 · A. Esser🇩🇪 · H. Merkel🇩🇪 and 11 other authors

   The cross section of the $p(e,e^{\prime }{\pi }^{+})n$ reaction has been measured for five kinematic settings at an invariant mass of $W=1094$ MeV and for a four-momentum transfer of $Q^2=0.078$ (GeV/$c$)${}^2$. The measurement has been performed at MAMI using a new short-orbit spectrometer (SOS) of the A1 collaboration, intended for detection of low-energy pions. The transverse and longitudinal cross section terms were separated using the Rosenbluth method and the transverse-longitudinal interference term has been determined from the left-right asymmetry. The experimental cross section terms are compared with the calculations of three models: DMT2001, MAID2007 and $\chi$MAID. The results show that we do not yet understand the dynamics of the fundamental pion.

   nucl-exPLB(2017)·7 citations
3. 03*

   Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR

   PANDA Collaboration: B. Singh · W. Erni · B. Krusche · M. Steinacher · N. Walford · B. Liu · H. Liu · Z. Liu · X. Shen · C. Wang · J. Zhao · M. Albrecht and 494 other authors

   Simulation results for future measurements of electromagnetic proton form factors at \PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel $\bar{p}p\to e^{+}{e}^{-}$ is studied on the basis of two different but consistent procedures. The suppression of the main background channel, $\text{i.e.}$ $\bar{p}p\to {\pi }^{+}{\pi }^{-}$, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.

   ↳ hep-exnucl-exEPJA(2016)·64 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.