Wed·Jan 15, 2020Wednesday·January 15, 2020

1. 01*

   Measured velocity spectra and neutron densities of the PF2 ultracold-neutron beam ports at the Institut Laue--Langevin

   Stefan Döge🇫🇷 · Jürgen Hingerl🇫🇷 · Christoph Morkel🇩🇪

   Ultracold neutrons (UCNs) are a useful tool for fundamental physics experiments. They can be used to probe the lifetime of free neutrons, search for new CP violating processes and exotic interactions beyond the Standard Model, perform Ramsey spectroscopy, and carry out neutron-optical interference experiments. All of these experiments require high neutron count rates for good statistics. For optimal exploitation of experimental beam time, these experiments need to be prepared and, at times, even simulated in advance. To this end, it is crucial to know the velocity-dependent UCN flux at each beam position. Knowing the absolute neutron flux also allows for an absolute calibration of previously gathered data. Using the same time-of-fight experimental setup, we have measured the differential neutron flux of three out of the four UCN beam ports at the PF2 instrument at Institut Laue--Langevin, Grenoble. These beam ports are commonly used for UCN flux experiments and proof-of-principle tests.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2020)·3 citations
2. 02*

   Open string QED meson description of the X17 particle and dark matter

   Cheuk-Yin Wong🇺🇸

   As a quark and an antiquark cannot be isolated, the intrinsic motion of a composite $q\bar{q}$ system in its lowest-energy states lies predominantly in 1+1 dimensions, as in an open string with the quark and the antiquark at its two ends. Accordingly, we study the lowest-energy states of an open string $q\bar{q}$ system in QCD and QED in 1+1 dimensions. We show that ${\pi }^0,\eta$, and ${\eta }^{\prime }$ can be adequately described as open string $q\bar{q}$ QCD mesons. By extrapolating into the $q\bar{q}$ QED sector in which a quark and an antiquark interact with the QED interaction, we find an open string isoscalar $I(J^{\pi })$=$0(0^{-})$ QED meson state at 17.9$\pm$1.5 MeV and an isovector $(I(J^{\pi })$=$1(0^{-}),I_3$=0) QED meson state at 36.4$\pm$3.8 MeV. The predicted masses of the isoscalar and isovector QED mesons are close to the masses of the hypothetical X17 and E38 particles observed recently, making them good candidates for these particles. The decay products of QED mesons may show up as excess $e^{+}{e}^{-}$ and $\gamma \gamma$ pairs in the anomalous soft photon phenomenon associated with hadron productions in high-energy hadron-proton collisions and $e^{+}$-$e^{-}$ annihilations. Measurements of the invariant masses of excess $e^{+}{e}^{-}$ and $\gamma \gamma$ pairs will provide tests for the existence of the open string $q\bar{q}$ QED mesons. An assembly of gravitating QED mesons are expected to emit electron-positron pairs and/or gamma rays and their decay energies and lifetimes will be modified by their gravitational binding energies. Consequently, a self-gravitating isoscalar QED meson assembly whose mass $M$ and radius $R$ satisfy $(M/M_{\odot })/(R/R_{\odot })\gtrsim 4.71\times 10^5$ will not produce electron-positron pairs nor gamma rays and may be a good candidate for the primordial dark matter.

   ↳ nucl-thastro-ph.HEhep-phnucl-exJHEP(2020)·32 citations
3. 03*

   Pion valence quark distribution from current-current correlation in lattice QCD

   Raza Sabbir Sufian🇺🇸 · Colin Egerer🇺🇸 · Joseph Karpie🇺🇸 · Robert G. Edwards🇺🇸 · Bálint Joó🇺🇸 · Yan-Qing Ma🇨🇳 · Kostas Orginos🇺🇸 · Jian-Wei Qiu🇺🇸 · David G. Richards🇺🇸

   We extract the pion valence quark distribution $q_{\mathrm{v}}^{\pi }(x)$ from lattice QCD (LQCD) calculated matrix elements of spacelike correlations of one vector and one axial vector current analyzed in terms of QCD collinear factorization, using a new short-distance matching coefficient calculated to one-loop accuracy. We derive the Ioffe time distribution of the two-current correlations in the physical limit by investigating the finite lattice spacing, volume, quark mass, and higher-twist dependencies in a simultaneous fit of matrix elements computed on four gauge ensembles. We find remarkable consistency between our extracted $q_{\mathrm{v}}^{\pi }(x)$ and that obtained from experimental data across the entire $x$-range. Further, we demonstrate that the one-loop matching coefficient relating the LQCD matrix computed in position space to the $q_{\mathrm{v}}^{\pi }(x)$ in momentum space has well-controlled behavior with Ioffe time. This justifies that LQCD calculated current-current correlations are good observables for extracting partonic structures by using QCD factorization, which complements to the global effort to extract partonic structure from experimental data.

   ↳ hep-lathep-exhep-phnucl-ex+1PRD(2020)·124 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.