Mon·Jan 11, 2016Monday·January 11, 2016

1. 01*

   Measurement of hadron suppression and study of its connection with vanishing $v_3$ at low $\sqrt{s_{\mathrm{NN}}}$ in Au+Au collisions with STAR

   Stephen Horvat (STAR Collaboration)🇺🇸

   At top RHIC and LHC energies the suppression of high transverse momentum ($p_{\mathrm{T}}$) hadrons provides evidence for partonic energy loss in QGP. We study partonic energy loss in the RHIC Beam Energy Scan (BES) by investigating the centrality dependence of the binary-collision-scaled high-$p_{\mathrm{T}}$ yields. Observing a decrease of the scaled yield in more central collisions is proposed as a possible signature for jet quenching. Even at energies and centralities where this signature is lost a QGP may still be formed since competing phenomena responsible for enhancements may overwhelm the suppression from energy loss. Measurements in several ranges of $p_{\mathrm{T}}$ from $\sqrt{s_{{}_{\mathrm{NN}}}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV data show that relative hadron suppression persists at least down to 14.5 GeV. To further investigate both the possible formation of a QGP at these lower energies and whether the observed hadron suppression coincides with the onset of other QGP signatures, we examine the energy and centrality dependence of $v_3$. Models have shown that the development of $v_3$ requires the presence of a low viscosity phase early in the collision. We find that for collisions with $N_{\mathrm{part}}$<50, $v_3$ disappears for energies below 14.5 GeV, suggestive of a turn-off of the QGP. But for $N_{\mathrm{part}}$>50, $v_3$ persists down to the lowest energies. Together, these signatures provide possible evidence for the formation of a QGP in the lowest energy collisions at RHIC.

   nucl-exNPA(2016)·13 citations
2. 02*

   Magnetic dipole excitations of ${}^{50}$Cr

   H. Pai · T. Beck · J. Beller · R. Beyer · M. Bhike · V. Derya · U. Gayer · J. Isaak · J. Kvasil · B. Loher · V. O. Nesterenko · N. Pietralla and 14 other authors

   The low-lying $M1$-strength of the open-shell nucleus ${}^{50}$Cr has been studied with the method of nuclear resonance fluorescence up to 9.7 MeV, using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC and Compton backscattered photons at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility between 6 and 9.7 MeV of the initial photon energy. Fifteen $1^{+}$ states have been observed between 3.6 and 9.7 MeV. Following our analysis, the lowest $1^{+}$ state at 3.6 MeV can be considered as an isovector orbital mode with some spin admixture. The obtained results generally match the estimations and trends typical for the scissors-like mode. Detailed calculations within the Skyrme Quasiparticle Random-Phase-Approximation method and the Large-Scale Shell Model justify our conclusions. The calculated distributions of the orbital current for the lowest $1^{+}$-state suggest the schematic view of Lipparini and Stringari (isovector rotation-like oscillations inside the rigid surface) rather than the scissors-like picture of Lo Iudice and Palumbo. The spin M1 resonance is shown to be mainly generated by spin-flip transitions between the orbitals of the $fp$-shell.

   nucl-exnucl-thPRC(2016)·28 citations
3. 03*

   Studies of relative gain and timing response of fine-mesh photomultiplier tubes in high magnetic fields

   V. Sulkosky🇺🇸 · L. Allison🇺🇸 · C. Barber · T. Cao🇺🇸 · Y. Ilieva🇺🇸 · K. Jin · G. Kalicy🇺🇸 · K. Park🇺🇸 · N. Ton🇺🇸 · X. Zheng🇺🇸

   We investigated the use of Hamamatsu fine-mesh photomultiplier tube assemblies H6152-70 and H6614-70 with regards to their gain and timing resolution in magnetic fields up to 1.9 T. Our results show that the H6614-70 assembly can operate reliably in magnetic fields exceeding 1.5 T, while preserving a reasonable timing resolution even with a gain reduction of a factor of approximately 100. The reduction of the relative gain of the H6152-70 is similar to the H6614-70's near 1.5 T, but its timing resolution worsens considerably at this high field.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2016)·2 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.