Thu·Sep 1, 2011Thursday·September 1, 2011

1. 01*

   Neutral Pion Production in the Threshold Region

   D. Hornidge (Mount Allison University) A. M. Bernstein (Massachusetts Institute of Technology)

   We give an overview of the physics motivation and evolution of the neutral pion photoproduction measurements in the threshold region conducted in the A2 collaboration at MAMI. The latest two experiments have been performed with the almost 4-pi Crystal Ball detector. The first was with a linearly polarized photon beam and unpolarized liquid-hydrogen target. The data analysis is now complete and the linearly polarized beam asymmetry along with differential cross sections provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of convergence. More recently a measurement was performed using both circularly polarized photons and a transversely polarized butanol frozen-spin target, with the goal of extracting both the target and beam-target asymmetries. From these we intend to extract pi-N scattering sensitive information for the first time in photo-pion reactions. This will be used to test isospin conservation and further test dynamics of chiral symmetry breaking in QCD as calculated at low energies by Chiral Perturbation Theory.

   nucl-exhep-exhep-phnucl-thEur.Phys.J.ST(2011)·5 citations
2. 02*

   Recent PHENIX Results on Open Heavy Flavor

   J. Matthew Durham (for the PHENIX Collaboration)🇺🇸

   Throughout the history of the RHIC physics program, questions concerning the dynamics of heavy quarks have generated much experimental and theoretical investigation. A major focus of the PHENIX experiment is the measurement of these quarks through their semi-leptonic decay channels at mid and forward rapidity. Heavy quark measurements in $p+p$ collisions give information on the production of heavy flavor, without complications from medium effects. New measurements in $d+$Au and Cu+Cu indicate surprising cold nuclear matter effects on these quarks at midrapidity, and provide a new baseline for interpretation of the observed suppression in Au+Au collisions. When considered all together, these measurements present a detailed study of nuclear matter across a wide range of system size and temperature. Here we present preliminary PHENIX measurements of non-photonic electron spectra and their centrality dependence in $d$+Au and Cu+Cu, and discuss their implications on the current understanding of parton energy loss in the nuclear medium.

   nucl-exJ.Phys.G(2011)·0 citations
3. 03*

   High-spin {\mu}s isomeric states in 96Ag

   A. D. Becerril🇺🇸 · G. Lorusso🇺🇸 · A. M. Amthor🇺🇸 · T. Baumann🇺🇸 · D. Bazin🇺🇸 · J. S. Berryman🇺🇸 · B. A. Brown🇺🇸 · H. L. Crawford🇺🇸 · A. Estrade🇺🇸 · A. Gade🇺🇸 · T. Ginter🇺🇸 · C. J. Guess🇺🇸 and 15 other authors

   The isomeric and {\beta} decays of the N = Z +2 nucleus 96Ag were investigated at NSCL. A cascade of {\gamma}-ray transitions originating from the de-excitation of a {\mu}s isomer was observed for the first time and was found in coincidence with two previously-known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) {\mu}s, more precise than previously reported. The existence of a second, longer-lived {\mu}s isomer, associated with a 743-keV transition, is also proposed here. Shell model results within the (p_{3/2}p_{1/2}f_{5/2}g_{9/2}) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.

   nucl-exPRC(2011)·12 citations
4. 04*

   Single and Double Pion Photoproduction off the Deuteron

   Manuel Dieterle🇨🇭

   There is evidence that the photoproduction of single and double pions off bound nucleons inside a nucleus are not only affected by Fermi motion but also by other nuclear effects, such as final state interactions or meson rescattering. We will present preliminary results of a high statistics measurement of single and double pion photoproduction of quasi-free protons and neutrons off the deuteron carried out at the Mainzer Microtron.

   nucl-ex0 citations
5. 05*

   Photoproduction of eta-Mesons off 3He

   Lilian Witthauer🇨🇭

   Photoproduction of eta-mesons off 3He has been studied at the MAMI accelerator using the Crystal Ball/TAPS detector setup. The total cross section for the coherent eta-photoproduction was measured with improved statistical quality. Both, the total and differential cross sections show evidence for dominant final state interaction. Additionally, the photoproduction of eta- mesons off quasi-free protons and neutrons was studied. The preliminary cross section on the neutron confirms the narrow bump-like structure at W \simeq 1.7 GeV, which was already seen in different experiments on the deuterium target

   nucl-ex0 citations
6. 06*

   The Search for Exotic Mesons in gamma p -> pi+pi+pi-n with CLAS at Jefferson Lab

   Craig Bookwalter🇺🇸

   The ${\pi }_1(1600)$, a $J^{PC}=1^{-+}$ exotic meson has been observed by experiments using pion beams. Theorists predict that photon beams could produce gluonic hybrid mesons, of which the ${\pi }_1(1600)$ is a candidate, at enhanced levels relative to pion beams. The g12 rungroup at Jefferson Lab's CEBAF Large Acceptance Spectrometer (CLAS) has recently acquired a large photoproduction dataset, using a liquid hydrogen target and tagged photons from a 5.71 GeV electron beam. A partial-wave analysis of 502K $\gamma p\to {\pi }^{+}{\pi }^{+}{\pi }^{-}n$ events selected from the g12 dataset has been performed, and preliminary fit results show strong evidence for well-known states such as the $a_1(1260)$, $a_2(1320)$, and ${\pi }_2(1670)$. However, we observe no evidence for the production of the ${\pi }_1(1600)$ in either the partial-wave intensities or the relative complex phase between the $1^{-+}$ and the $2^{-+}$ (corresponding to the ${\pi }_2$) partial waves.

   ↳ hep-exnucl-ex7 citations
7. 07*

   Rare dileptonic decays of \Lambda_b in a quark model

   Lonnie Mott🇺🇸 · Winston Roberts🇺🇸

   Hadronic form factors for the rare weak transitions ${\Lambda }_b\to {\Lambda }^{(\ast )}$ are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Although there are differences between the two sets of form factors, both sets satisfy the relationships expected from the heavy quark effective theory (HQET). Differential decay rates, branching ratios and forward-backward asymmetries (FBAs) are calculated for the dileptonic decays ${\Lambda }_b\to {\Lambda }^{(\ast )}{\ell }^{+}{\ell }^{-}$, for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. In the MCN model the $\Lambda (1600)$ mode is the dominant mode in the $\mu$ channel when charmonium resonances are considered; the $\Lambda (1520)$ mode is also found to have a comparable branching ratio to that of the ground state in the $\mu$ channel.

   ↳ nucl-thhep-exhep-phnucl-exInt.J.Mod.Phys.A(2012)·76 citations
8. 08*

   Jet momentum balance independent of shear viscosity

   R.B. Neufeld🇺🇸

   Jet momentum balance measurements, such as those recently performed by the CMS collaboration, provide an opportunity to quantify the energy transferred from a parton shower to the underlying medium in heavy-ion collisions. Specifically, I argue that the Cooper-Frye freezeout distribution associated with the energy and momentum deposited by the parton shower is controlled to a significant extent by the distribution of the underlying bulk matter and independent of the details of how deposited energy is redistributed in the medium, which is largely determined by transport coefficients such as shear viscosity. Thus by matching the distribution of momentum associated with the secondary jet in such measurements to the thermal distribution of the underlying medium, one can obtain a model independent estimate on the amount of parton shower energy deposited.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2012)·1 citation

* 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.