Mon·Jan 4, 2016Monday·January 4, 2016

1. 01*

   Measurements of $D_S^{\pm }$-meson production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR

   Md. Nasim (for the STAR collaboration)🇺🇸

   We present the first measurement of the nuclear modification factor $R_{AA}$ and elliptic flow $v_2$ of $D_s$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector. These results have been compared with those of other open charm mesons and strange mesons to determine how the (possibly) strangeness equilibrated partonic matter affects the $D_s$ meson production. We find that the nuclear modification factor of $D_S$ are systematically higher than unity and $D^0$ $R_{\mathrm{AA}}$. The ratio $D_s/D^0$ is shown as a function of transverse momentum for the 10-40$\%$ most central Au+Au collisions and compared with that in $p+p$ collisions obtained from PYTHIA. It is also compared with that in Pb-Pb collisions at 2.76 TeV by the ALICE experiment. Our measurement indicates a hint of enhancement of $D_S$ production in Au+Au collisions with respect to $p+p$ collisions as compared to non-strange $D$ mesons.

   nucl-exhep-exnucl-thNPA(2016)·4 citations
2. 02*

   Allowed rare pion and muon decays as tests of the Standard Model

   Dinko Pocanic (PEN Collaboration)🇺🇸

   Simple dynamics, few available decay channels, and extremely well controlled radiative and loop corrections, make pion and muon decays a sensitive means for testing the underlying symmetries, the universality of weak fermion couplings, as well as for study of pion structure and chiral dynamics. We review the current state of experimental study of the allowed rare decays of charged pions: (a) electronic, ${\pi }^{+}\to e^{+}{\nu }_e$, or ${\pi }_{e2}$, (b) radiative, ${\pi }^{+}\to e^{+}{\nu }_e\gamma$, or ${\pi }_{e2\gamma }$, and (c) semileptonic, ${\pi }^{+}\to {\pi }^0{e}^{+}\nu$, or ${\pi }_{e3}$, as well as muon radiative decay, ${\mu }^{+}\to e^{+}{\nu }_{\text{e}}{\bar{\nu }}_{\mu }\gamma$. Taken together, these data present an internally consistent picture that also agrees well with Standard Model (SM) predictions. However, even following the great strides of the recent decades, experimental accuracy is lagging far behind that of the theoretical description for all above processes. We review the implications of the present state of knowledge and prospects for further improvement in the near term.

   nucl-exhep-exhep-ph3 citations
3. 03*

   Correlations between jets and charged particles in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV

   CMS Collaboration

   The quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at sqrt(s[NN]) = 2.76 TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity (Delta eta) and relative azimuthal angle (Delta phi) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pt) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pt, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle pt. A centrality-dependent excess of low-pt particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pt particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of Delta eta approximately 1 and Delta phi approximately 1.

   nucl-exhep-exJHEP(2016)·95 citations
4. 04*

   High-Sensitivity Measurement of 3He-4He Isotopic Ratios for Ultracold Neutron Experiments

   H. P. Mumm · M. G. Huber · W. Bauder · N. Abrams · C. M. Deibel🇺🇸 · C. R. Huffer · P. R. Huffman🇺🇸 · K. W. Schelhammer · C. M. Swank🇺🇸 · R. Janssens · C. L. Jiang · R. H. Scott and 6 other authors

   Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of 3He to 4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10e-14 level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of 3He/4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

   ↳ physics.ins-detnucl-exPRC(2016)·3 citations
5. 05*

   Thermalization of mini-jets in a quark-gluon plasma

   Edmond Iancu🇫🇷 · Bin Wu🇺🇸

   We present the complete physical picture for the evolution of a high-energy jet propagating through a weakly-coupled quark-gluon plasma (QGP) by analytical and numerical investigation of thermalization of the soft components of the jet. Our results support the following physical picture: the leading particle emits a significant number of mini-jets which promptly evolve via multiple branching and thus degrade into a myriad of soft gluons, with energies of the order of the medium temperature $T$. Via elastic collisions with the medium constituents, these soft gluons relax to local thermal equilibrium with the plasma over a time scale which is considerably shorter than the typical lifetime of the mini-jet. The thermalized gluons form a tail which lags behind the hard components of the jet. Together with the background QGP, they behave hydrodynamically.

   ↳ hep-phhep-exnucl-exnucl-thNPA(2016)·0 citations
6. 06*

   Nonlinear hydrodynamic response confronts LHC data

   Li Yan🇫🇷 · Subrata Pal🇮🇳 · Jean-Yves Ollitrault🇫🇷

   Higher order harmonic flow $v_n$ (with $n\ge 4$) in heavy-ion collisions can be measured either with respect to their own plane, or with respect to a plane constructed using lower-order harmonics. By assuming that higher flow harmonics are the superposition of medium nonlinear and linear responses to initial anisotropies, we propose a set of nonlinear response coefficients ${\chi }_n$'s, which are independent of initial state by construction. In experiments, ${\chi }_n$'s can be extracted as the ratio between higher order harmonic flow measured in the plane constructed by $v_2$ and $v_3$, and moments of lower order harmonic flow. Simulations with single-shot hydrodynamics and AMPT model lead to results of these nonlinear response coefficients in good agreement with the experimental data at the LHC energy. Predictions for $v_7$ and $v_8$ measured with respect to plane of lower order harmonics are given accordingly.

   ↳ nucl-thnucl-exNPA(2016)·8 citations
7. 07*

   An Evidence of Mass Dependent Differential Kinetic Freeze-out Scenario Observed in Pb-Pb Collisions at 2.76 TeV

   Hai-Ling Lao🇨🇳 · Hua-Rong Wei🇨🇳 · Fu-Hu Liu🇨🇳 · Roy A. Lacey🇺🇸

   Transverse momentum spectra of different particles produced in mid-rapidity interval in lead-lead (Pb-Pb) collisions with different centrality intervals, measured by the ALICE Collaboration at center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=2.76$ TeV, are conformably and approximately described by the Tsallis distribution. The dependences of parameters (effective temperature, entropy index, and normalization factor) on event centrality and particle rest mass are obtained. The source temperature at the kinetic freeze-out is obtained to be the intercept in the linear relation between effective temperature and particle rest mass, while the particle transverse flow velocity is approximately extracted to be the slope in the linear relation between mean transverse momentum and particle rest mass. It is shown that the source temperature increases with increase of particle rest mass, which exhibits an evidence of mass dependent differential kinetic freeze-out scenario or multiple kinetic freeze-out scenario.

   ↳ nucl-thhep-exhep-phnucl-exEPJA(2016)·46 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.