Thu·Jul 18, 2019Thursday·July 18, 2019

1. 01*

   How much two-photon exchange is needed to resolve the proton form factor discrepancy?

   Axel Schmidt🇺🇸

   One possible explanation for the proton form factor discrepancy is a contribution to the elastic electron-proton cross section from hard two-photon exchange (TPE), a typically neglected radiative correction. Hard TPE cannot be calculated in a model-independent way, but it can be determined experimentally by looking for deviations from unity in the ratio of positron-proton to electron-proton cross sections. Three recent experiments have measured this cross section ratio to quantify hard TPE. To interpret the results of these experiments, it is germane to ask: 'How large of a deviation from unity is necessary to fully resolve the form factor discrepancy?' With a minimal set of assumptions and using global fits to unpolarized and polarized elastic scattering data, I estimate the necessary size of the TPE correction in the kinematics of the three recent experiments and compare to their measurements. I find wide variation when using different global fits, implying that the magnitude of the form factor discrepancy is not well-constrained. The recent hard TPE measurements can easily accommodate the hypothesis that TPE underlies the proton form factor discrepancy.

   nucl-exJ.Phys.G(2020)·18 citations
2. 02*

   The Hoyle state in relativistic dissociation of light nuclei

   A.A. Zaitsev🇷🇺 · P.I. Zarubin🇷🇺

   In the context of the search for triples of relativistic $\alpha$-particles in the Hoyle state, the analysis of available data on the dissociation of the nuclei ${}^{12}$C, ${}^{16}$O and ${}^{22}$Ne in the nuclear emulsion was carried out. The Hoyle state is identified by the invariant mass calculated from pair angles of expansion in $\alpha$-triples in the approximation of the conservation of the momentum per nucleon of the parent nucleus. The contribution of the Hoyle state to the dissociation of ${}^{12}$C $\to$ 3$\alpha$ is 11\%. In the case of the coherent dissociation of ${}^{16}$O $\to$ 4$\alpha$ it reaches 22\% when the portion of the channel ${}^{16}$O $\to$ 2${}^8$Be is equal to 5\%.

   nucl-exhep-exPhys.Atom.Nucl.(2020)·3 citations
3. 03*

   Resonance strengths in the 14N(p,gamma)15O astrophysical key reaction measured with activation

   Gy. Gyürky🇭🇺 · Z. Halász🇭🇺 · G.G. Kiss🇭🇺 · T. Szücs🇩🇪 · A. Csík · Zs. Török · R. Huszánk🇭🇺 · M.G. Kohan · L. Wagner🇩🇪 · Zs. Fülöp🇭🇺

   The 14N(p,gamma)15O reaction plays a vital role in various astrophysical scenarios. Its reaction rate must be accurately known in the present era of high precision astrophysics. The cross section of the reaction is often measured relative to a low energy resonance, the strength of which must therefore be determined precisely. The activation method, based on the measurement of 15O decay, has not been used in modern measurements of the 14N(p,gamma)15O reaction. The aim of the present work is to provide strength data for two resonances in the 14N(p,gamma)15O reaction using the activation method. The obtained values are largely independent from previous data measured by in-beam gamma-spectroscopy and are free from some of their systematic uncertainties. Solid state TiN targets were irradiated with a proton beam provided by the Tandetron accelerator of Atomki using a cyclic activation. The decay of the produced 15O isotopes was measured by detecting the 511 keV positron annihilation gamma-rays. The strength of the Ep = 278 keV resonance was measured to be 13.4 +- 0.8 meV while for the Ep = 1058 keV resonance the strength is 442 +- 27 meV. The obtained Ep = 278 keV resonance strength is in fair agreement with the values recommended by two recent works. On the other hand, the Ep = 1058 keV resonance strength is about 20% higher than the previous value. The discrepancy may be caused in part by a previously neglected finite target thickness correction. As only the low energy resonance is used as a normalization point for cross section measurements, the calculated astrophysical reaction rate of the 14N(p,gamma)15O reaction and therefore the astrophysical consequences are not changed by the present results.

   nucl-exastro-ph.SRPRC(2019)·17 citations
4. 04*

   Simulation of charge readout with segmented tiles in nEXO

   Z. Li · W.R. Cen🇨🇳 · A. Robinson🇨🇦 · D.C. Moore🇺🇸 · L.J. Wen🇨🇳 · A. Odian🇺🇸 · S. Al Kharusi🇨🇦 · G. Anton🇩🇪 · I.J. Arnquist🇺🇸 · I. Badhrees🇨🇦 · P.S. Barbeau🇺🇸 · D. Beck🇺🇸 and 141 other authors

   nEXO is a proposed experiment to search for the neutrino-less double beta decay ($0\nu \beta \beta$) of ${}^{136}$Xe in a tonne-scale liquid xenon time projection chamber (TPC). The nEXO TPC will be equipped with charge collection tiles to form the anode. In this work, the charge reconstruction performance of this anode design is studied with a dedicated simulation package. A multi-variate method and a deep neural network are developed to distinguish simulated $0\nu \beta \beta$ signals from backgrounds arising from trace levels of natural radioactivity in the detector materials. These simulations indicate that the nEXO TPC with charge-collection tiles shows promising capability to discriminate the $0\nu \beta \beta$ signal from backgrounds. The estimated half-life sensitivity for $0\nu \beta \beta$ decay is improved by $\sim$20$(32)\%$ with the multi-variate~(deep neural network) methods considered here, relative to the sensitivity estimated in the nEXO pre-conceptual design report.

   ↳ physics.ins-detnucl-exJINST(2019)·22 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.