Thu·Jan 28, 2016Thursday·January 28, 2016

1. 01*

   Measuring the Weak Charge of the Proton via Elastic Electron-Proton Scattering

   Donald Jones🇺🇸

   The Qweak experiment which ran at Jefferson Lab in Newport News, VA, measured the weak charge of the proton $Q_W^p$ via elastic electron-proton scattering. Longitudinally polarized electrons were scattered from an unpolarized liquid hydrogen target. The Standard Model predicts a small parity-violating asymmetry of scattering rates between electron right and left helicity states due to the weak interaction. An initial result using 4% of the data was published in October 2013 with a measured parity-violating asymmetry of $-279\pm 35(\text{stat})\pm 31$ (syst) parts per billion (ppb). This asymmetry, along with other data from parity-violating electron scattering experiments, provided the world's first determination of the weak charge of the proton. The weak charge of the proton was found to be $Q_W^p=0.064\pm 0.012$, in agreement with the Standard Model prediction of $Q_W^p(SM)=0.0708\pm 0.0003$. The results of the full dataset are expected to decrease the statistical error from the initial publication by a factor of 4-5. The level of precision of the final result makes it a useful test of Standard Model predictions and particularly of the "running" of ${\sin }^2{\theta }_W$ from the Z-mass to low energies. This thesis focuses on reduction of systematic error in two key systematics for the Qweak experiment. First, techniques for measuring and removing false asymmetries arising from helicity-correlated electron beam properties at the few ppb level are discussed. Second, as a parity-violating experiment, Qweak relies on accurate knowledge of electron beam polarimetry. To help address the requirement of accurate polarimetry, a Compton polarimeter built specifically for Qweak. Compton polarimetry requires accurate knowledge of laser polarization inside a Fabry-Perot cavity enclosed in the electron beam pipe. A new technique was developed for Qweak that nearly eliminates this systematic error.

   nucl-exphysics.ins-det3 citations
2. 02*

   First Search for Lorentz and CPT Violation in Double Beta Decay with EXO-200

   EXO-200 Collaboration: J. B. Albert · P. S. Barbeau · D. Beck · V. Belov · M. Breidenbach · T. Brunner · A. Burenkov · G. F. Cao · C. Chambers · B. Cleveland · M. Coon · A. Craycraft and 76 other authors

   A search for Lorentz- and CPT-violating signals in the double beta decay spectrum of ${}^{136}$Xe has been performed using an exposure of 100 kg$\cdot$yr with the EXO-200 detector. No significant evidence of the spectral modification due to isotropic Lorentz-violation was found, and a two-sided limit of $-2.65\times 10^{-5}\text{GeV}<{\mathring{a}}_{\text{of}}^{(3)}<7.60\times 10^{-6}\text{GeV}$ (90% C.L.) is placed on the relevant coefficient within the Standard-Model Extension (SME). This is the first experimental study of the effect of the SME-defined oscillation-free and momentum-independent neutrino coupling operator on the double beta decay process.

   nucl-exhep-phPRD(2016)·57 citations
3. 03*

   Nuclear Physics Programs for the Future Rare Isotope Beams Accelerator Facility in Korea

   Chang-Bum Moon

   We present nuclear physics programs based on the planned experiments using rare isotope beams (RIBs) for the future Korean Rare Isotope Beams Accelerator facility; RAON. This ambitious facility has both an Isotope Separation On Line (ISOL) and fragmentation capability for producing RIBs and accelerating beams of wide range mass of nuclides with energies of a few to hundreds MeV per nucleon. Low energy RIBs at Elab = 5 to 20 MeV per nucleon are for the study of nuclear structure and nuclear astrophysics toward and beyond the drip lines while higher energy RIBs produced by in-flight fragmentation with the re-accelerated ions from the ISOL enable to explore the neutron drip lines in intermediate mass regions. The planned programs have goals for investigating nuclear structures of the exotic nuclei toward and beyond the nucleon drip lines by addressing the following issues: how the shell structure evolves in areas of extreme proton to neutron imbalance; whether the isospin symmetry maintains in isobaric mirror nuclei at and beyond the drip lines, how two-proton radioactivity affects abundances of the elements, what the role of the continuum states including resonant states above the neutron- and proton-decay threshold in exotic nuclei is in astrophysical nuclear reaction processes, and how the nuclear reaction rates triggered by unbound proton-rich nuclei make an effect on rapid proton capture processes in a very hot stellar plasma.

   nucl-exNucl.Phys.Rev.(2016)·1 citation
4. 04*

   Atomic ionization by sterile-to-active neutrino conversion and constraints on dark matter sterile neutrinos with germanium detectors

   Jiunn-Wei Chen🇹🇼 · Hsin-Chang Chi🇹🇼 · Shin-Ted Lin🇨🇳 · C.-P. Liu🇹🇼 · Lakhwinder Singh🇹🇼 · Henry T. Wong🇹🇼 · Chih-Liang Wu🇹🇼 · Chih-Pan Wu🇹🇼

   The transition magnetic moment of a sterile-to-active neutrino conversion gives rise to not only radiative decay of a sterile neutrino, but also its non-standard interaction (NSI) with matter. For sterile neutrinos of keV-mass as dark matter candidates, their decay signals are actively searched for in cosmic X-ray spectra. In this work, we consider the NSI that leads to atomic ionization, which can be detected by direct dark matter experiments. It is found that this inelastic scattering process for a nonrelativistic sterile neutrino has a pronounced enhancement in the differential cross section at energy transfer about half of its mass, manifesting experimentally as peaks in the measurable energy spectra. The enhancement effects gradually smear out as the sterile neutrino becomes relativistic. Using data taken with germanium detectors that have fine energy resolution in keV and sub-keV regimes, constraints on sterile neutrino mass and its transition magnetic moment are derived and compared with those from astrophysical observations.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2016)·15 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.