Thu·Mar 5, 2020Thursday·March 5, 2020

1. 01*

   Linear and non-linear flow modes of charged and identified particles in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=5.02 TeV with ALICE

   Jasper Parkkila (for the ALICE Collaboration)🇨🇭

   The higher order harmonic flow observables $v_n$ ($n>3$) and their non-linear responses to the initial state anisotropy have the strong potential to constrain shear and bulk viscosity to entropy ratios because of different sensitivities for various stages of heavy-ion collisions. The measurements of the flow coefficients and the non-linear coefficients up to the ninth and fifth harmonic, respectively, are presented in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ for charged hadrons. In addition, the results of $p_{\mathrm{T}}$-differential non-linear flow modes for ${\pi }^{\pm }$, ${\mathrm{K}}^{\pm }$, $\mathrm{p}+\bar{\mathrm{p}}$, ${\mathrm{K}}_s^0$, $\Lambda +{\bar{\Lambda }}_s^0$ and $\varphi$ are presented. The results are compared to the same measurements at 2.76 TeV and calculations from state of the art hydrodynamic models.

   nucl-exhep-exNPA(2021)·1 citation
2. 02*

   The possible explanation of neutron lifetime beam anomaly

   A. P. Serebrov🇷🇺 · M. E. Chaikovskii🇷🇺 · G. N. Klushnikov · O. M. Zherebtsov🇷🇺 · A. V. Chechkin🇷🇺

   The results of measurements performed using UCN storing method are in good agreement. The latest most accurate measurements of the neutron decay asymmetry and neutron lifetime measurements by storage method are in agreement within the Standard Model. However, there is a significant discrepancy at $3.6\sigma$ (1% of decay probability) level with beam method experiment. This article discusses the possible causes of discrepancy in the measurements of the neutron lifetime with beam method experiment. The most probable cause, apparently, is the loss of protons in beam method experiment during storage in a magnetic trap due to charge exchange collisions of protons with the residual gas. The proton becomes neutral and leaves the trap, which leads to a decrease in the number of registered protons, i.e. to a decrease in the probability of neutron decay or to an increase in the measured neutron lifetime.

   nucl-exphysics.ins-det3 citations
3. 03*

   Parametrisations of relativistic energy density functionals with tensor couplings

   Stefan Typel🇩🇪 · Diana Alvear Terrero🇨🇺

   The relativistic density functional with minimal density dependent nucleon-meson couplings for nuclei and nuclear matter is extended to include tensor couplings of the nucleons to the vector mesons. The dependence of the minimal couplings on either vector or scalar densities is explored. New parametrisations are obtained by a fit to nuclear observables with uncertainties that are determined self-consistently. The corresponding nuclear matter parameters at saturation are determined including their uncertainties. An improvement in the description of nuclear observables, in particular for binding energies and diffraction radii, is found when tensor couplings are considered, accompanied by an increase of the Dirac effective mass. The equations of state for symmetric nuclear matter and pure neutron matter are studied for all models. The density dependence of the nuclear symmetry energy, the Dirac effective masses and scalar densities is explored. Problems at high densities for parametrisations using a scalar density dependence of the couplings are identified due to the rearrangement contributions in the scalar self-energies that lead to vanishing Dirac effective masses.

   ↳ nucl-thnucl-exEPJA(2020)·35 citations
4. 04*

   Magnetic dipole excitations based on the relativistic nuclear energy density functional

   G. Kruzic · T. Oishi🇭🇷 · D. Vale · N. Paar🇭🇷

   Magnetic dipole (M1) excitations build not only a fundamental mode of nucleonic transitions, but they are also relevant for nuclear astrophysics applications. We have established a theory framework for description of M1 transitions based on the relativistic nuclear energy density functional. For this purpose the relativistic quasiparticle random phase approximation (RQRPA) is established using density dependent point coupling interaction DD-PC1, supplemented with the isovector-pseudovector interaction channel in order to study unnatural parity transitions. The introduced framework has been validated using the M1 sum rule for core-plus-two-nucleon systems, and employed in studies of the spin, orbital, isoscalar and isovector M1 transition strengths, that relate to the electromagnetic probe, in magic nuclei ${}^{48}$Ca and ${}^{208}$Pb, and open shell nuclei ${}^{42}$Ca and ${}^{50}$Ti. In these systems, the isovector spin-flip M1 transition is dominant, mainly between one or two spin-orbit partner states. It is shown that pairing correlations have a significant impact on the centroid energy and major peak position of the M1 mode. The M1 excitations could provide an additional constraint to improve nuclear energy density functionals in the future studies.

   ↳ nucl-thnucl-exPRC(2020)·28 citations
5. 05*

   How long does the hydrogen atom live?

   David McKeen🇨🇦 · Maxim Pospelov🇺🇸

   It is possible that the proton is stable while atomic hydrogen is not. This is the case in models with new particles carrying baryon number which are light enough to be stable themselves but heavy enough so that proton decay is kinematically blocked. Models of new physics that explain the neutron lifetime anomaly generically have this feature, allowing for atomic hydrogen to decay through electron capture on a proton. We calculate the radiative hydrogen decay rate involving the emission of a few hundred keV photon, which makes this process detectable in experiment. In particular, we show that the low energy part of the Borexino spectrum is sensitive to radiative hydrogen decay, and turn this into a limit on the hydrogen lifetime of order $10^{30}\mathrm{s}$ or stronger. For models where the neutron mixes with a dark baryon, $\chi$, this limits the mixing angle to roughly $10^{-11}$, restricting the $n\to \chi \gamma$ branching to $10^{-4}$, over a wide range of parameter space.

   ↳ hep-phhep-exnucl-exnucl-thUniverse(2023)·31 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.