Wed·Oct 15, 2014Wednesday·October 15, 2014

1. 01*

   Di-Hadron Correlations with Identified Leading Hadrons in 200 GeV Au+Au and d+Au Collisions at STAR

   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 321 other authors

   The STAR collaboration presents for the first time two-dimensional di-hadron correlations with identified leading hadrons in 200 GeV central Au+Au and minimum-bias d+Au collisions to explore hadronization mechanisms in the quark gluon plasma. The enhancement of the jet-like yield for leading pions in Au+Au data with respect to the d+Au reference and the absence of such an enhancement for leading non-pions (protons and kaons) are discussed within the context of a quark recombination scenario. The correlated yield at large angles, specifically in the \emph{ridge region}, is found to be significantly higher for leading non-pions than pions. The consistencies of the constituent quark scaling, azimuthal harmonic model and a mini-jet modification model description of the data are tested, providing further constraints on hadronization.

   nucl-exPLB(2015)·21 citations
2. 02*

   Upsilon Production at the STAR Experiment with a Focus on New U+U Results

   Robert Vertesi (for the STAR Collaboration)🇨🇿

   We report recent Upsilon measurements in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV, and detail the analysis in U+U collisions at $\sqrt{s_{NN}}$=193 GeV. Results on Upsilon production versus rapidity are consistent with pQCD predictions in p+p collisions. However, Upsilon production in mid-rapidity (|y|<0.5) d+Au collisions is suppressed with respect to p+p collisions beyond model predictions that take into account modification of parton distribution functions and initial parton energy loss inside nuclei. The nuclear modification factor R_AA shows a significant suppression in central Au+Au and U+U collisions, consistent with model calculations including color screening effects in a deconfined medium.

   nucl-ex0 citations
3. 03*

   Nuclear breathing mode in neutron-rich Nickel isotopes: sensitivity to the symmetry energy and the role of the continuum

   J. Piekarewicz🇺🇸

   In this new era of radioactive beam facilities, the discovery of novel modes of excitation in nuclei far away from stability represents an area of intense research activity. In addition, these modes of excitation appear to be sensitive to the uncertain density dependence of the symmetry energy. We study the emergence, evolution, and nature of both the soft and giant isoscalar monopole modes as a function of neutron excess in three unstable Nickel isotopes: 56Ni, 68Ni, and 78Ni. The distribution of isoscalar monopole strength is computed in a relativistic random-phase approximation using several accurately calibrated effective interactions. In particular, a non-spectral Green's function approach is adopted that allows for an exact treatment of the continuum without any reliance on discretization. The discretization of the continuum is neither required nor admitted. In the case of 56Ni, the lack of low-energy strength results in a direct correlation between the centroid energy of the giant monopole resonance and the incompressibility coefficient of symmetric nuclear matter. In contrast, the large neutron excess in both 68Ni and 78Ni generates a significant, yet relatively featureless, amount of low-energy strength that is driven by transitions into the continuum. Moreover, the evolution of monopole strength with neutron excess displays sensitivity to the density dependence of the symmetry energy. Our results suggest that future measurements of the distribution of isoscalar monopole strength at radioactive beam facilities using a very long chain of both stable and unstable isotopes could place important constraints on the equation of state of neutron-rich matter and ultimately on the properties of neutron stars. However, given the nature of the low-energy monopole excitations, a proper treatment of the continuum is essential.

   ↳ nucl-thnucl-exPRC(2015)·7 citations
4. 04*

   Spin Density Matrix of the $\omega$ in the Reaction $\bar{p}p\to \omega {\pi }^0$

   Crystal Barrel Collaboration: C. Amsler🇨🇭 · F.H. Heinsius🇩🇪 · H. Koch🇩🇪 · B. Kopf🇩🇪 · U. Kurilla🇩🇪 · C.A. Meyer🇺🇸 · K. Peters🇩🇪 · J. Pychy🇩🇪 · M. Steinke🇩🇪 · U. Wiedner🇩🇪

   The spin density matrix of the $\omega$ has been determined for the reaction $\bar{p}p\to \omega {\pi }^0$ with unpolarized in-flight data measured by the Crystal Barrel LEAR experiment at CERN. The two main decay modes of the $\omega$ into ${\pi }^0\gamma$ and ${\pi }^{+}{\pi }^{-}{\pi }^0$ have been separately analyzed for various $\bar{p}$ momenta between 600 and 1940 MeV/c. The results obtained with the usual method by extracting the matrix elements via the $\omega$ decay angular distributions and with the more sophisticated method via a full partial wave analysis are in good agreement. A strong spin alignment of the $\omega$ is clearly visible in this energy regime and all individual spin density matrix elements exhibit an oscillatory dependence on the production angle. In addition, the largest contributing orbital angular momentum of the $\bar{p}p$ system has been identified for the different beam momenta. It increases from $L_{\bar{p}p}^{max}$ = 2 at 600 MeV/c to $L_{\bar{p}p}^{max}$ = 5 at 1940 MeV/c.

   ↳ hep-exnucl-exEPJC(2015)·8 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.