Wed·Mar 28, 2018Wednesday·March 28, 2018

1. 01*

   Direct photon production at low transverse momentum in proton-proton collisions at $\sqrt{s}$ = 2.76 and 8 TeV

   ALICE Collaboration

   Measurements of inclusive and direct photon production at mid-rapidity in pp collisions at $\sqrt{s}=2.76$ and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of $0.4<p_T<10$ GeV/$c$ and $0.3<p_T<16$ GeV/$c$, respectively. Photons are detected with the electromagnetic calorimeter~(EMCal) and via reconstruction of e${}^{+}$e${}^{-}$ pairs from conversions in the ALICE detector material using the central tracking system. For the final measurement of the inclusive photon spectra the results are combined in the overlapping $p_T$ interval of both methods. Direct photon spectra, or their upper limits at 90% C.L. are extracted using the direct photon excess ratio $R_{\gamma }$, which quantifies the ratio of inclusive photons over decay photons generated with a decay-photon simulation. An additional hybrid method, combining photons reconstructed from conversions with those identified in the EMCal, is used for the combination of the direct photon excess ratio $R_{\gamma }$, as well as the extraction of direct photon spectra or their upper limits. While no significant signal of direct photons is seen over the full $p_T$ range, $R_{\gamma }$ for $p_T>7$ GeV/$c$ is at least one $\sigma$ above unity and consistent with expectations from next-to-leading order pQCD calculations.

   nucl-exhep-exPRC(2019)·68 citations
2. 02*

   Neutron background measurements with a hybrid neutron detector at the Kuo-Sheng Reactor Neutrino Laboratory

   A. Sonay · M. Deniz · H. T. Wong · M. Agartioglu · G. Asryan · J. H. Chen · S. Kerman · H. B. Li · J. Li · F. K. Lin · S. T. Lin · B. Sevda and 10 other authors

   We report in situ neutron background measurements at the Kuo-Sheng Reactor Neutrino Laboratory (KSNL) by a hybrid neutron detector (HND) with a data size of 33.8 days under identical shielding configurations as during the neutrino physics data taking. The HND consists of BC-501A liquid and BC-702 phosphor powder scintillation neutron detectors, which is sensitive to both fast and thermal neutrons, respectively. Neutron-induced events for the two channels are identified and differentiated by pulse shape analysis, such that background of both are simultaneously measured. The fast neutron fluxes are derived by an iterative unfolding algorithm. Neutron induced background in the germanium detector under the same fluxes, both due to cosmic-rays and ambient radioactivity, are derived and compared with the measurements. The results are valuable to background understanding of the neutrino data at the KSNL. In particular, neutron-induced background events due to ambient radioactivity as well as from reactor operation are negligible compared to intrinsic cosmogenic activity and ambient $\gamma$-activity. The detector concept and analysis procedures are applicable to neutron background characterization in similar rare-event experiments.

   nucl-exPRC(2018)·17 citations
3. 03*

   Measurement of the absolute neutron beam polarization from a supermirror polarizer and the absolute efficiency of a neutron spin rotator for the NPDGamma experiment using a polarized ${}^3$He neutron spin-filter

   M. M. Musgrave🇺🇸 · S. Baessler🇺🇸 · S. Balascuta🇺🇸 · L. Barron-Palos🇲🇽 · D. Blyth🇺🇸 · J. D. Bowman🇺🇸 · T. E. Chupp🇺🇸 · V. Cianciolo🇺🇸 · C. Crawford🇺🇸 · K. Craycraft🇺🇸 · N. Fomin🇺🇸 · J. Fry🇺🇸 and 17 other authors

   Accurately measuring the neutron beam polarization of a high flux, large area neutron beam is necessary for many neutron physics experiments. The Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS) is a pulsed neutron beam that was polarized with a supermirror polarizer for the NPDGamma experiment. The polarized neutron beam had a flux of $\sim 10^9$ neutrons per second per cm${}^2$ and a cross sectional area of 10$\times$12~cm${}^2$. The polarization of this neutron beam and the efficiency of a RF neutron spin rotator installed downstream on this beam were measured by neutron transmission through a polarized ${}^3$He neutron spin-filter. The pulsed nature of the SNS enabled us to employ an absolute measurement technique for both quantities which does not depend on accurate knowledge of the phase space of the neutron beam or the ${}^3$He polarization in the spin filter and is therefore of interest for any experiments on slow neutron beams from pulsed neutron sources which require knowledge of the absolute value of the neutron polarization. The polarization and spin-reversal efficiency measured in this work were done for the NPDGamma experiment, which measures the parity violating $\gamma$-ray angular distribution asymmetry with respect to the neutron spin direction in the capture of polarized neutrons on protons. The experimental technique, results, systematic effects, and applications to neutron capture targets are discussed.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2018)·12 citations
4. 04*

   A hydrogen leak-tight, transparent cryogenic sample container for ultracold-neutron transmission measurements

   Stefan Döge🇫🇷 · Jürgen Hingerl🇫🇷

   The improvement of the number of extractable ultracold neutrons (UCNs) from converters based on solid deuterium (sD${}_2$) crystals requires a good understanding of UCN transport and how the crystal's morphology influences its transparency to UCNs. Measurements of the UCN transmission through cryogenic liquids and solids of interest, such as hydrogen (H${}_2$) and deuterium (D${}_2$), require sample containers with thin, highly polished and optically transparent windows and a well defined sample thickness. One of the most difficult sealing problems is that of light gases like hydrogen and helium at low temperatures against a high vacuum. Here we report on the design of a sample container with two 1 mm thin amorphous silica windows cold-welded to aluminum clamps using indium wire gaskets, in order to form a simple, reusable and hydrogen-tight cryogenic seal. The container meets the above-mentioned requirements and withstands up to 2 bar hydrogen gas pressure against isolation vacuum in the range of $10^{-5}$ to $10^{-7}$ mbar at temperatures down to 4.5 K. Additionally, photographs of the crystallization process are shown and discussed.

   ↳ physics.ins-detcond-mat.mtrl-scinucl-exRev.Sci.Instrum.(2018)·4 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.