Mon·Feb 27, 2017Monday·February 27, 2017

1. 01*

   Precise measurement of alpha_K for the 88.2-keV M4 transition in 127Te: Test of internal-conversion theory

   N. Nica🇺🇸 · J.C. Hardy🇺🇸 · V.E. Iacob🇺🇸 · H.I. Park🇺🇸 · K. Brandenburg · M.B. Trzhaskovskaya

   We have measured the K-shell internal conversion coefficient, alpha_K, for the 88.2-keV M4 transition from the 106-day isomer to the ground state in 127Te to be 484(6). When compared with Dirac-Fock calculations of alpha_K, this result agrees well with the version of the theory that incorporates the effect of the K-shell atomic vacancy and disagrees with the one that does not. As a byproduct of this measurement, we have determined the beta branching from the isomer to be 2.14(3)%.

   nucl-exPRC(2017)·6 citations
2. 02*

   Coherent diffractive photoproduction of ${\rho }^0$ mesons on gold nuclei at RHIC

   STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer and 338 other authors

   The STAR Collaboration reports on the photoproduction of ${\pi }^{+}{\pi }^{-}$ pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly-real photon emitted by one ion scatters from the other ion. We fit the ${\pi }^{+}{\pi }^{-}$ invariant mass spectrum with a combination of $\rho$ and $\omega$ resonances and a direct ${\pi }^{+}{\pi }^{-}$ continuum. This is the first observation of the $\omega$ in ultra-peripheral collisions, and the first measurement of $\rho -\omega$ interference at energies where photoproduction is dominated by Pomeron exchange. The $\omega$ amplitude is consistent with the measured $\gamma p\to \omega p$ cross section, a classical Glauber calculation and the $\omega \to {\pi }^{+}{\pi }^{-}$ branching ratio. The $\omega$ phase angle is similar to that observed at much lower energies, showing that the $\rho -\omega$ phase difference does not depend significantly on photon energy. The ${\rho }^0$ differential cross section $d\sigma /dt$ exhibits a clear diffraction pattern, compatible with scattering from a gold nucleus, with 2 minima visible. The positions of the diffractive minima agree better with the predictions of a quantum Glauber calculation that does not include nuclear shadowing than with a calculation that does include shadowing.

   nucl-exhep-exPRC(2017)·102 citations
3. 03*

   New approach to initializing hydrodynamic fields and mini-jet propagation in quark-gluon fluids

   Michito Okai🇯🇵 · Koji Kawaguchi🇯🇵 · Yasuki Tachibana🇨🇳 · Tetsufumi Hirano🇯🇵

   We propose a new approach to initialize the hydrodynamic fields such as energy density distributions and four flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting the initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of the initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. The resultant initial profile of the quark-gluon fluid looks highly bumpy as seen in the conventional event-by-event initial conditions. In addition, initial random flow velocity fields also are generated as a consequence of momentum deposition from the initial partons. We regard the partons that survive after the dynamical initialization process as the mini-jets and find sizable effects of both mini-jet propagation in the quark-gluon fluids and initial random transverse flow on the final momentum spectra and anisotropic flow observables. We perform event-by-event $(3+1)$-dimensional ideal hydrodynamic simulations with this new framework that enables us to describe the hydrodynamic bulk collectivity, parton energy loss, and interplay among them in a unified manner.

   ↳ nucl-thhep-phnucl-exPRC(2017)·60 citations
4. 04*

   Tensor-polarized structure function $b_1$ by convolution picture for deuteron

   W. Cosyn🇧🇪 · Yu-Bing Dong🇨🇳 · S. Kumano🇯🇵 · M. Sargsian🇺🇸

   There are polarized structure functions $b_{1-4}$ for the spin-1 deuteron. We calculated the leading-twist tensor structure function $b_1$ by using convolution description for the deuteron. We found large differences between our theoretical functions and HERMES experimental data on $b_1$. Although higher-twist effects should be considered in obtaining experimental $b_1$, it suggests a possible existence of new hadron physics mechanism for spin-1 hadrons. Furthermore, we found that there are significant distributions at large Bjorken $x$. In future, an experimental measurement is planned at JLab for $b_1$ and there is a possibility of a proton-deuteron Drell-Yan experiment at Fermilab with the tensor-polarized deuteron, so that further theoretical studies are needed for clarifying the physics origin of tensor structure in terms of quark and gluon degrees of freedom.

   ↳ hep-phhep-exhep-latnucl-ex+11 citation
5. 05*

   Probing QCD critical fluctuations from light nuclei production in relativistic heavy-ion collisions

   Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳 · Che Ming Ko🇺🇸 · Zhangbu Xu🇺🇸

   Based on the coalescence model for light nuclei production, we show that the yield ratio ${\mathcal{O}}_{\text{p-d-t}}=N_{{}^3\text{H}}{N}_p/N_{\text{d}}^2$ of $p$, d, and ${}^3$H in heavy-ion collisions is sensitive to the neutron relative density fluctuation $\Delta n=⟨(\delta n{)}^2⟩/⟨n{⟩}^2$ at kinetic freeze-out. From recent experimental data in central Pb+Pb collisions at $\sqrt{s_{NN}}=6.3$~GeV, $7.6$~GeV, $8.8$~GeV, $12.3$~GeV and $17.3$~GeV measured by the NA49 Collaboration at the CERN Super Proton Synchrotron (SPS), we find a possible non-monotonic behavior of $\Delta n$ as a function of the collision energy with a peak at $\sqrt{s_{NN}}=8.8$~GeV, indicating that the density fluctuations become the largest in collisions at this energy. With the known chemical freeze-out conditions determined from the statistical model fit to experimental data, we obtain a chemical freeze-out temperature of $\sim 144$MeV and baryon chemical potential of $\sim 385$MeV at this collision energy, which are close to the critical endpoint in the QCD phase diagram predicted by various theoretical studies. Our results thus suggest the potential usefulness of the yield ratio of light nuclei in relativistic heavy-ion collisions as a direct probe of the large density fluctuations associated with the QCD critical phenomena.

   ↳ nucl-thhep-phnucl-exPLB(2017)·136 citations
6. 06*

   Measurement of charged jet cross sections and jet shapes in proton-proton collisions at sqrt(s) = 2.76 TeV with the ALICE detector at LHC

   Rathijit Biswas (for the ALICE Collaboration)🇮🇳

   We present measurements of charged jet cross sections and jet shape observables in leading jet in proton-proton (pp) collisions at sqrt(s) = 2.76 TeV with the ALICE detector at LHC. Jets are reconstructed at the midrapidity from charged particle using sequential recombination anti-kT jet finding algorithm for various R values. The results are compared to measurements from HERWIG, PHOJET and different tunes of PYTHIA6 and earlier measurements at 7 TeV.

   ↳ hep-exnucl-exSpringer Proc.Phys.(2018)·0 citations
7. 07*

   Nuclear effects in leading neutron production

   B. Z. Kopeliovich🇨🇱 · I. K. Potashnikova🇨🇱 · Ivan Schmidt🇨🇱

   Absorptive corrections, known to suppress proton-neutron transitions with large fractional momentum $z\to 1$ in pp collisions, become dramatically strong on a nuclear target, and push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of $\pi$-$a_1$ interference, which successfully explains the observed single-spin asymmetry in polarized $pp\to nX$, is extended to collisions of polarized protons with nuclei. Corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons, produced in inelastic events, where the nucleus violently breaks up. The single-spin asymmetry is found to be negative and nearly $A$-independent.

   ↳ hep-phhep-exnucl-ex5 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.