Mon·Feb 22, 2021Monday·February 22, 2021

1. 01*

   Germanium response to sub-keV nuclear recoils: a multipronged experimental characterization

   J.I. Collar🇺🇸 · A.R.L. Kavner🇺🇸 · C.M. Lewis🇺🇸

   Germanium is the detector material of choice in many rare-event searches looking for low-energy nuclear recoils induced by dark matter particles or neutrinos. We perform a systematic exploration of its quenching factor for sub-keV nuclear recoils, using multiple techniques: photo-neutron sources, recoils from gamma-emission following thermal neutron capture, and a monochromatic filtered neutron beam. Our results point to a marked deviation from the predictions of the Lindhard model in this mostly unexplored energy range. We comment on the compatibility of our data with low-energy processes such as the Migdal effect, and on the impact of our measurements on upcoming searches.

   nucl-exastro-ph.COhep-exhep-phPRD(2021)·87 citations
2. 02*

   Precise Neutron Lifetime Measurement Using Pulsed Neutron Beams at J-PARC

   N. Sumi🇯🇵 · K. Hirota🇯🇵 · G. Ichikawa🇯🇵 · T. Ino🇯🇵 · Y. Iwashita🇯🇵 · S. Kajiwara🇯🇵 · Y. Kato🇯🇵 · M. Kitaguchi🇯🇵 · K. Mishima🇯🇵 · K. Morikawa🇯🇵 · T. Mogi🇯🇵 · H. Oide🇯🇵 and 9 other authors

   A neutron decays into a proton, an electron, and an anti-neutrino through the beta-decay process. The decay lifetime ($\sim$880 s) is an important parameter in the weak interaction. For example, the neutron lifetime is a parameter used to determine the |$V_{\mathrm{ud}}$| parameter of the CKM quark mixing matrix. The lifetime is also one of the input parameters for the Big Bang Nucleosynthesis, which predicts light element synthesis in the early universe. However, experimental measurements of the neutron lifetime today are significantly different (8.4 s or 4.0$\sigma$) depending on the methods. One is a bottle method measuring surviving neutron in the neutron storage bottle. The other is a beam method measuring neutron beam flux and neutron decay rate in the detector. There is a discussion that the discrepancy comes from unconsidered systematic error or undetectable decay mode, such as dark decay. A new type of beam experiment is performed at the BL05 MLF J-PARC. This experiment measured neutron flux and decay rate simultaneously with a time projection chamber using a pulsed neutron beam. We will present the world situation of neutron lifetime and the latest results at J-PARC.

   ↳ hep-exnucl-exJPS Conf.Proc.(2021)·9 citations
3. 03*

   Astrophysical Constraints on the Symmetry Energy and the Neutron Skin of ${}^{208}$Pb with Minimal Modeling Assumptions

   Reed Essick🇺🇸 · Ingo Tews🇺🇸 · Philippe Landry🇨🇦 · Achim Schwenk🇩🇪

   The symmetry energy and its density dependence are crucial inputs for many nuclear physics and astrophysics applications, as they determine properties ranging from the neutron-skin thickness of nuclei to the crust thickness and the radius of neutron stars. Recently, PREX-II reported a value of $0.283\pm 0.071$ fm for the neutron-skin thickness of ${}^{208}$Pb, implying a slope parameter $L=106\pm 37$ MeV, larger than most ranges obtained from microscopic calculations and other nuclear experiments. We use a nonparametric equation of state representation based on Gaussian processes to constrain the symmetry energy $S_0$, $L$, and $R_{\mathrm{skin}}^{{}^{208}\mathrm{Pb}}$ directly from observations of neutron stars with minimal modeling assumptions. The resulting astrophysical constraints from heavy pulsar masses, LIGO/Virgo, and NICER clearly favor smaller values of the neutron skin and $L$, as well as negative symmetry incompressibilities. Combining astrophysical data with PREX-II and chiral effective field theory constraints yields $S_0=33.0_{-1.8}^{+2.0}$ MeV, $L=53_{-15}^{+14}$ MeV, and $R_{\mathrm{skin}}^{{}^{208}\mathrm{Pb}}=0.17_{-0.04}^{+0.04}$ fm.

   ↳ nucl-thastro-ph.HEnucl-exPRL(2021)·225 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.