Nuclear Theory·nucl-th

Wednesday·January 15, 2020

6 papers—4 primary·2 cross-listed

01
Nuclear structure uncertainties in coherent elastic neutrino-nucleus scattering
G. Co'🇮🇹 · M. Anguiano🇪🇸 · A.M. Lallena🇪🇸
The effects of the nuclear structure uncertainties on the description of processes induced by coherent scattering of neutrinos on nuclei are investigated. A reference calculation based on a specific nuclear model is defined and the cross sections and also the expected number of events produced by neutrinos generated by the explosion of a supernova in our galaxy, and by a spallation neutron source are evaluated. By changing the input parameters of the reference calculation their relevance on cross sections and on the number of the detected events is estimated. Seven spherical nuclei with different proton to neutron ratios are considered as possible targets of the neutrinos in the detector, the lightest being $^{12}$ C and the heaviest $^{208}$ Pb. The effects generated by the uncertainties of the nuclear model are much smaller than those due to the supernova neutrino flux models. This makes the coherent elastic neutrino-nucleus scattering a reliable tool to investigate the details of the neutrino sources, the neutrino-nucleus interaction, and, eventually, also to extract information about neutron distributions in nuclei.
nucl-thJCAP(2020)·21 citations
02
Lorentz violation effects in two neutrino double-beta decay
Ovidiu Nitescu🇷🇴 · Stefan Ghinescu🇷🇴 · Sabin Stoica🇷🇴
Observable effects for the Lorentz invariance violation (LIV) at a low energy scale can also be investigated in double beta decay (DBD). For example, by comparing the theoretical predictions with a precise analysis of the summed energy spectra of electrons in $2 ν β β$ decay, one can constrain the $a ˚_{o f}^{(3)}$ coefficient that governs the time-like component of the Lorentz invariance violating operator that appears in the Standard Model extension theory. In this work, we perform calculations of the phase space factors and summed energy spectra of electrons as well as of their deviations due to LIV necessary in such experimental investigations. The Fermi functions needed in the calculation are built up with exact electron wave functions obtained by numerically solving the Dirac equation in a realistic Coulomb-type potential with the inclusion of the finite nuclear size and screening effects. We compared our results with those used in previous LIV investigations that were obtained with approximate (analytical) Fermi functions and found differences of up to $30%$ for heavier nuclei. Our work includes eight experimentally interesting nuclei. Next, we estimate and discuss the uncertainties of our calculations associated with uncertainties in Q-values measurements and the differences raised from the inclusion of the kinematic terms in the formalism. Finally, we provide the ratio between the standard phase space factors and their LIV deviations and the energies where the LIV effects are expected to be maximal. We expect our study to be useful in the current LIV investigations in $2 ν β β$ decay and to lead to improved constraints on the $a ˚_{o f}^{(3)}$ coefficient.
nucl-thJ.Phys.G(2020)·22 citations
03
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 $q q ˉ$ 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 $q q ˉ$ system in QCD and QED in 1+1 dimensions. We show that $π^{0}, η$ , and $η^{'}$ can be adequately described as open string $q q ˉ$ QCD mesons. By extrapolating into the $q q ˉ$ QED sector in which a quark and an antiquark interact with the QED interaction, we find an open string isoscalar $I (J^{π})$ = $0 (0^{-})$ QED meson state at 17.9 $\pm$ 1.5 MeV and an isovector $(I (J^{π})$ = $1 (0^{-}), I_{3}$ =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 $γ γ$ 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 $γ γ$ pairs will provide tests for the existence of the open string $q q ˉ$ 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 $(M / M_{⊙}) / (R / R_{⊙}) ≳ 4.71 \times 1 0^{5}$ 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)·31 citations
04
Shadow poles in Brune parametrization of R-matrix theory
Pablo Ducru · Vladimir Sobes · Benoit Forget · Mark Paris · Gerald Hale
Our collective knowledge of nuclear cross sections is recorded as resonance parameters in nuclear data libraries. To evaluate these parameters, campaigns of measurements are fitted with a parametric model of nuclear cross sections called R-matrix theory. In order to remove the arbitrary boundary parameters in the Wigner-Eisenbud R-matrix parametrization, the community is considering converting all nuclear data libraries to Brune parameters. In this article, we show there are more Brune parameters than previously thought. Below the channel threshold, we prove there exists two types of additional 'shadow poles' - branch shadow poles and analytic shadow poles - depending on how we continue R-matrix operators to complex wavenumbers (to do so we establish Mittag-Leffler expansions of R-matrix operators). This entails there are more Brune resonance energies than levels. Yet, we also prove that choosing any subset of Brune poles will yield the same cross sections than using the entire set of Brune poles, as long as it has at least the number of levels. In practice, this means that shadow Brune poles can be discarded from the new nuclear data libraries. Many isotopes are evaluated with the Reich-Moore approximation, introducing complex resonance energies to eliminate certain channels. We generalize Brune's parameterization to encompass the Reich-Moore approximation and the additional shadow poles, and show that all Brune parameters depend on what convention we choose to continue the R-matrix operators to complex wavenumbers. To convert nuclear data libraries to Brune parameters, the nuclear scientists community must thus first decide on such a convention. The authors argue in favor of analytic continuation. The first evidence of shadow poles in Brune's alternative parametrization of R-matrix theory is observed in isotope xenon-134, spin-parity group 1/2(-).
nucl-th0 citations
05
Sub-femtometer scale color charge correlations in the proton
Adrian Dumitru🇺🇸 · Vladimir Skokov🇺🇸 · Tomasz Stebel🇵🇱
Color charge correlations in the proton at moderately small $x \sim 0.1$ are extracted from its light-cone wave function. The charge fluctuations are far from Gaussian and they exhibit interesting dependence on impact parameter and on the relative transverse momentum (or distance) of the gluon probes. We provide initial conditions for small- $x$ Balitsky-Kovchegov evolution of the dipole scattering amplitude with impact parameter and $r^\cdot b^$ dependence, and with non-zero $C$ -odd component due to three-gluon exchange. Lastly, we compute the (forward) Weizsaecker-Williams gluon distributions, including the distribution of linearly polarized gluons, up to fourth order in $A^{+}$ . The correction due to the quartic correlator provides a transverse momentum scale, $q > 0.5$ GeV, for nearly maximal polarization.
↳ hep-phnucl-thPRD(2020)·23 citations
06
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 $q_{v}^{π} (x)$ 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 $q_{v}^{π} (x)$ 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 $q_{v}^{π} (x)$ 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)·125 citations

Affiliations

first authorsco-authorsvia INSPIRE

Nuclear structure uncertainties in coherent elastic neutrino-nucleus scattering

Lorentz violation effects in two neutrino double-beta decay

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

Shadow poles in Brune parametrization of R-matrix theory

Sub-femtometer scale color charge correlations in the proton

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

Affiliations