Fri·Feb 10, 2017Friday·February 10, 2017

1. 01*

   Flow dominance and factorization of transverse momentum correlations in Pb-Pb collisions at the LHC

   ALICE Collaboration

   We present the first measurement of the two-particle transverse momentum differential correlation function, $P_2\equiv ⟨\Delta p_{\mathrm{T}}\Delta p_{\mathrm{T}}⟩/⟨p_{\mathrm{T}}{⟩}^2$, in Pb-Pb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=$ 2.76 TeV. Results for $P_2$ are reported as a function of relative pseudorapidity ($\Delta \eta$) and azimuthal angle ($\Delta \phi$) between two particles for different collision centralities. The $\Delta \varphi$ dependence is found to be largely independent of $\Delta \eta$ for $|\Delta \eta |\ge$ 0.9. In 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around $\Delta \phi =\pi$ (i.e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of $P_2$, studied as a function of collision centrality, show that correlations at $|\Delta \eta |\ge$ 0.9 can be well reproduced by a flow ansatz based on the notion that measured momentum correlations are strictly determined by the collective motion of the system.

   nucl-exhep-exPRL(2017)·31 citations
2. 02*

   Measurement of $W^{\pm }$ single spin asymmetries and $W$ cross section ratio in polarized $p+p$ collisions at $\sqrt{s}=510$ GeV at STAR

   Devika Gunarathne (for the STAR colloboration)🇺🇸

   We present the preliminary results of measurements of single spin asymmetries, $A_L$ for $W^{\pm }$ boson production in longitudinally polarized p+p collisions at $\sqrt{s}=510$ GeV and measurements of cross section ratios, ${\sigma }_{W^{+}}/{\sigma }_{W^{-}}$, for $W^{+},W^{-}$ boson production in $p+p$ collisions at $\sqrt{s}$ = 500 and 510 GeV. The asymmetry measurements are based on 246.2 pb${}^{-1}$ of data taken in the RHIC 2013 run and the cross section ratio measurements are based on 102 pb${}^{-1}$ of data taken during RHIC 2011 and 2012 runs by the STAR experiment. While the asymmetry results are shown as a function of the decay lepton pseudorapidity, ${\eta }_e$, the cross section results are shown as a function of both ${\eta }_e$ and W boson rapidity, $y_W$ in the mid-rapidity region ($|{\eta }_e|<1$). At this kinematics, $W^{\pm }$ single spin asymmetries provide a theoretically clean probe of the proton's polarized quark and antiquark distributions and the W cross section ratio provides sensitivity to unpolarized sea quark distributions at the scale of the W mass. The asymmetry results are consistent with recently published STAR $A_L^{W^{\pm }}$ results based on the data collected during RHIC 2011 and 2012 runs which showed a preference for a sizable, positive up antiquark polarization in the range $0.05<x<0.2$. The new preliminary results can be considered as the most precise results of $A_L^{W^{\pm }}$ in the world to date, with uncertainties reduced by 40\% in comparison to the published results.

   nucl-ex4 citations
3. 03*

   Double-$\beta$ Decay Matrix Elements from Lattice Quantum Chromodynamics

   Brian C. Tiburzi🇺🇸 · Michael L. Wagman🇺🇸 · Frank Winter🇺🇸 · Emmanuel Chang🇺🇸 · Zohreh Davoudi🇺🇸 · William Detmold🇺🇸 · Kostas Orginos🇺🇸 · Martin J. Savage🇺🇸 · Phiala E. Shanahan🇺🇸

   A lattice quantum chromodynamics (LQCD) calculation of the nuclear matrix element relevant to the $nn\to ppee{\overline{\nu }}_e{\overline{\nu }}_e$ transition is described in detail, expanding on the results presented in Ref. [1]. This matrix element, which involves two insertions of the weak axial current, is an important input for phenomenological determinations of double-$\beta$ decay rates of nuclei. From this exploratory study, performed using unphysical values of the quark masses, the long-distance deuteron-pole contribution to the matrix element is separated from shorter-distance hadronic contributions. This polarizability, which is only accessible in double-weak processes, cannot be constrained from single-$\beta$ decay of nuclei, and is found to be smaller than the long-distance contributions in this calculation, but non-negligible. In this work, technical aspects of the LQCD calculations, and of the relevant formalism in the pionless effective field theory, are described. Further calculations of the isotensor axial polarizability, in particular near and at the physical values of the light-quark masses, are required for precise determinations of both two-neutrino and neutrinoless double-$\beta$ decay rates in heavy nuclei.

   ↳ hep-lathep-phnucl-exnucl-thPRD(2017)·84 citations
4. 04*

   Investigating the temperature dependence of the specific shear viscosity of QCD matter with dilepton radiation

   Gojko Vujanovic🇺🇸 · Gabriel S. Denicol🇧🇷 · Matthew Luzum🇧🇷 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

   This work reports on investigations of the effects on the evolution of viscous hydrodynamics and on the flow coefficients of thermal dileptons, originating from a temperature-dependent specific shear viscosity $\eta /s(T)$ at temperatures beyond 180 MeV formed at the Relativistic Heavy-Ion Collider (RHIC). We show that the elliptic flow of thermal dileptons can resolve the magnitude of $\eta /s$ at the high temperatures, where partonic degrees of freedom become relevant, whereas discriminating between different specific functional forms will likely not be possible at RHIC using this observable.

   ↳ nucl-thhep-phnucl-exPRC(2018)·25 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.