Mon·Aug 29, 2011Monday·August 29, 2011

1. 01*

   Measurement of Jets and Jet Suppression in sqrt(s_NN)=2.76 TeV Lead-Lead Collisions with the ATLAS detector at the LHC

   Aaron Angerami · ATLAS Collaboration

   The first results of single jet observables in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented. Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4, using an event-by-event subtraction procedure to correct for the effects of the underlying event including elliptic flow. The geometrically-scaled ratio of jet yields in central and peripheral events,Rcp, indicates a clear suppression of jets with ET >100 GeV. The transverse and longitudinal distributions of jet fragments is also presented. We find little no substantial change to the fragmentation properties and no significant change in the level of suppression when moving to the larger jet definition.

   nucl-exhep-exJ.Phys.G(2011)·13 citations
2. 02*

   Light Baryon Spectroscopy using the CLAS Spectrometer at Jefferson Laboratory

   Volker Crede (for the CLAS Collaboration)🇺🇸

   Baryons are complex systems of confined quarks and gluons and exhibit the characteristic spectra of excited states. The systematics of the baryon excitation spectrum is important to our understanding of the effective degrees of freedom underlying nucleon matter. High-energy electrons and photons are a remarkably clean probe of hadronic matter, providing a microscope for examining the nucleon and the strong nuclear force. Current experimental efforts with the CLAS spectrometer at Jefferson Laboratory utilize highly-polarized frozen-spin targets in combination with polarized photon beams. The status of the recent double-polarization experiments and some preliminary results are discussed in this contribution.

   nucl-ex1 citation
3. 03*

   Measurement of the polarization observables I^s and I^c in the reaction \gamma p -> p \pi^0 \pi^0 with the CBELSA/TAPS experiment

   Vahe Sokhoyan🇩🇪

   To unambiguously identify baryon resonances the measurement of polarization observables is of great importance. With the CBELSA/TAPS experiment, located at the ELSA accelerator facility in Bonn, polarization observables have been determined. Using a linearly polarized photon beam impinging on a liquid hydrogen target, the polarization observables I^s and I^c for the reaction \gamma p -> p \pi^0 \pi^0 have been determined for the first time.

   nucl-exAIP Conf.Proc.(2012)·5 citations
4. 04*

   Experimental Validation of the Largest Calculated Isospin-Symmetry-Breaking Effect in a Superallowed Fermi Decay

   D. Melconian🇺🇸 · S. Triambak🇺🇸 · C. Bordeanu🇺🇸 · A. García🇺🇸 · J. C. Hardy🇺🇸 · V. E. Iacob🇺🇸 · N. Nica🇺🇸 · H. I. Park🇺🇸 · G. Tabacaru🇺🇸 · L. Trache🇺🇸 · I. S. Towner🇺🇸 · R. E. Tribble🇺🇸 · Y. Zhai🇺🇸

   A precision measurement of the gamma yields following the beta decay of 32Cl has determined its isobaric analogue branch to be (22.47^{+0.21}_{-0.19})%. Since it is an almost pure Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, delta_C=5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly-calculated, yet smaller, corrections that are currently applied to 0+ -> 0+ transitions for tests of the Standard Model.

   nucl-exnucl-thPRL(2011)·32 citations
5. 05*

   Do radioactive half-lives vary with the Earth-to-Sun distance?

   J.C. Hardy🇺🇸 · J.R. Goodwin🇺🇸 · V.E. Iacob🇺🇸

   Recently, Jenkins, Fischbach and collaborators have claimed evidence that radioactive half-lives vary systematically over a +/- 0.1% range as a function of the oscillating distance between the Earth and the Sun, based on multi-year activity measurements. We have avoided the time-dependent instabilities to which such measurements are susceptible by directly measuring the half-life of 198Au (t1/2 = 2.695 d) on seven occasions spread out in time to cover the complete range of Earth-Sun distances. We observe no systematic oscillations in half-life and can set an upper limit on their amplitude of +/- 0.02%.

   nucl-exastro-ph.EPastro-ph.SRAppl.Radiat.Isot.(2012)·17 citations
6. 06*

   The viscosity of quark-gluon plasma at RHIC and the LHC

   Ulrich W. Heinz (Ohio State)🇺🇸 · Chun Shen (Ohio State)🇺🇸 · Huichao Song (LBNL)🇺🇸

   The specific shear viscosity (eta/s)_QGP of quark-gluon plasma (QGP) can be extracted from elliptic flow data in heavy-ion collisions by comparing them with the dynamical model VISHNU which couples a viscous fluid dynamic description of the QGP with a microscopic kinetic description of the late hadronic rescattering and freeze-out stage. A robust method for fixing (eta/s)_QGP from the collision centrality dependence of the eccentricity-scaled charged hadron elliptic flow is presented. The systematic uncertainties associated with this extraction method are discussed, with specific attention to our presently restricted knowledge of initial conditions. With the (eta/s)_QGP extracted in this way, VISHNU yields an excellent description of all soft-hadron data from Au+Au collisions at top RHIC energy. Extrapolations to Pb+Pb collisions at the LHC, using both a purely hydrodynamic approach and VISHNU, are presented and compared with recent experimental results from the ALICE Collaboration. The LHC data are again well described by VISHNU, with the same (eta/s)_QGP value as at RHIC energies.

   ↳ nucl-thhep-phnucl-exAIP Conf.Proc.(2012)·140 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.