Tue·Apr 7, 2015Tuesday·April 7, 2015

1. 01*

   Electric Dipole Polarizability in ${}^{208}$Pb as a Probe of the Symmetry Energy and Neutron Matter around ${\rho }_0/3$

   Zhen Zhang🇨🇳 · Lie-Wen Chen🇨🇳

   It is currently a big challenge to accurately determine the symmetry energy $E_{\text{sym}}(\rho )$ and the pure neutron matter equation of state $E_{\text{PNM}}(\rho )$, even their values around saturation density ${\rho }_0$. We find that the electric dipole polarizability ${\alpha }_{\text{D}}$ in ${}^{208}$Pb can be determined uniquely by the magnitude of the $E_{\text{sym}}(\rho )$ or almost equivalently the $E_{\text{PNM}}(\rho )$ at subsaturation densities around ${\rho }_0/3$, shedding a light upon the genuine correlation between the ${\alpha }_{\text{D}}$ and the $E_{\text{sym}}(\rho )$. By analyzing the experimental data of the ${\alpha }_{\text{D}}$ in ${}^{208}$Pb from RCNP using a number of non-relativistic and relativistic mean-field models, we obtain very stringent constraints on $E_{\text{sym}}(\rho )$ and $E_{\text{PNM}}(\rho )$ around ${\rho }_0/3$. The obtained constraints are found to be in good agreement with the results extracted in other analyses. In particular, our results provide for the first time the experimental constraints on $E_{\text{PNM}}(\rho )$ around ${\rho }_0/3$, which are in harmony with the recent determination of $E_{\text{PNM}}(\rho )$ from microscopic theoretical studies and potentially useful in constraining the largely uncertain many-nucleon interactions in microscopic calculations of neutron matter.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2015)·107 citations
2. 02*

   Measurement of the correlation between flow harmonics of different order in lead-lead collisions at $\sqrt{s_{NN}}$=2.76 TeV with the ATLAS detector

   ATLAS Collaboration

   Correlations between the elliptic or triangular flow coefficients $v_m$ ($m$=2 or 3) and other flow harmonics $v_n$ ($n$=2 to 5) are measured using $\sqrt{s_{NN}}=2.76$ TeV Pb+Pb collision data collected in 2010 by the ATLAS experiment at the LHC, corresponding to an integrated lumonisity of 7 $\mu$b${}^{-1}$. The $v_m$-$v_n$ correlations are measured in midrapidity as a function of centrality, and, for events within the same centrality interval, as a function of event ellipticity or triangularity defined in a forward rapidity region. For events within the same centrality interval, $v_3$ is found to be anticorrelated with $v_2$ and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities ${ϵ}_2$ and ${ϵ}_3$. On the other hand, it is observed that $v_4$ increases strongly with $v_2$, and $v_5$ increases strongly with both $v_2$ and $v_3$. The trend and strength of the $v_m$-$v_n$ correlations for $n$=4 and 5 are found to disagree with ${ϵ}_m$-${ϵ}_n$ correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to $v_n$ and a nonlinear term that is a function of $v_2^2$ or of $v_2{v}_3$, as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to $v_4$ and $v_5$ are found to be consistent with previously measured event-plane correlations.

   ↳ hep-exnucl-exPRC(2015)·171 citations
3. 03*

   Axion Induced Oscillating Electric Dipole Moments

   Christopher T. Hill🇺🇸

   The axion electromagnetic anomaly induces an oscillating electric dipole for {\em any} static magnetic dipole. Static electric dipoles do not produce oscillating magnetic moments. This is a low energy theorem which is a consequence of the space-time dependent cosmic background field of the axion in the limit that it is only locally time dependent $(\overrightarrow{\beta }=0)$. The electron will acquire an oscillating electric dipole of frequency $m_a$ and strength $\sim 10^{-32}$ e-cm, three orders of magnitude above the nucleon, and within four orders of magnitude of the present standard model DC limit. This may suggest sensitive new experimental venues for the axion dark matter search.

   ↳ hep-phastro-ph.COhep-exhep-th+1PRD(2015)·35 citations
4. 04*

   Measurements of Dielectron Production in Au$+$Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV from the STAR Experiment

   STAR Collaboration: L. Adamczyk🇵🇱 · J. K. Adkins🇺🇸 · G. Agakishiev🇷🇺 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · I. Alekseev🇷🇺 · J. Alford🇺🇸 · A. Aparin🇷🇺 · D. Arkhipkin🇺🇸 · E. C. Aschenauer🇺🇸 · G. S. Averichev🇷🇺 · A. Banerjee🇮🇳 and 320 other authors

   We report on measurements of dielectron ($e^{+}{e}^{-}$) production in Au$+$Au collisions at a center-of-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at RHIC. Systematic measurements of the dielectron yield as a function of transverse momentum ($p_{\mathrm{T}}$) and collision centrality show an enhancement compared to a cocktail simulation of hadronic sources in the low invariant-mass region ($M_{ee}<$ 1 GeV/$c^2$). This enhancement cannot be reproduced by the $\rho$-meson vacuum spectral function. In minimum-bias collisions, in the invariant-mass range of 0.30 $-$ 0.76 GeV/$c^2$, integrated over the full $p_{\mathrm{T}}$ acceptance, the enhancement factor is 1.76 $\pm$ 0.06 (stat.) $\pm$ 0.26 (sys.) $\pm$ 0.29 (cocktail). The enhancement factor exhibits weak centrality and $p_{\mathrm{T}}$ dependence in STAR's accessible kinematic regions, while the excess yield in this invariant-mass region as a function of the number of participating nucleons follows a power-law shape with a power of 1.44 $\pm$ 0.10. Models that assume an in-medium broadening of the $\rho$ meson spectral function consistently describe the observed excess in these measurements. Additionally, we report on measurements of $\omega$ and $\varphi$-meson production through their $e^{+}{e}^{-}$ decay channel. These measurements show good agreement with Tsallis Blast-Wave model predictions as well as, in the case of the $\varphi$-meson, results through its $K^{+}{K}^{-}$ decay channel. In the intermediate invariant-mass region (1.1$<M_{ee}<$ 3 GeV/$c^2$), we investigate the spectral shapes from different collision centralities. Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed.

   ↳ hep-exnucl-exPRC(2015)·144 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.