Mon·Dec 4, 2017Monday·December 4, 2017

1. 01*

   Spectroscopy of ${}^{54}$Ti and the systematic behavior of low energy octupole states in Ca and Ti isotopes

   L. A. Riley🇺🇸 · M. L. Agiorgousis🇺🇸 · T.R. Baugher🇺🇸 · D. Bazin🇺🇸 · R.L. Blanchard🇺🇸 · M. Bowry🇺🇸 · P. D. Cottle🇺🇸 · F. G. DeVone🇺🇸 · A. Gade🇺🇸 · M. T. Glowacki🇺🇸 · K. W. Kemper🇺🇸 · J.S. Kustina🇺🇸 and 9 other authors

   Excited states of the $N=32$ nucleus ${}^{54}$Ti have been studied, via both inverse-kinematics proton scattering and one-neutron knockout from ${}^{55}$Ti by a liquid hydrogen target, using the GRETINA $\gamma$-ray tracking array. Inelastic proton-scattering cross sections and deformation lengths have been determined. A low-lying octupole state has been tentatively identified in ${}^{54}$Ti for the first time. A comparison of $(p,p^{\prime })$ results on low-energy octupole states in the neutron-rich Ca and Ti isotopes with the results of Random Phase Approximation calculations demonstrates that the observed systematic behavior of these states is unexpected.

   nucl-exPRC(2017)·3 citations
2. 02*

   A Method to Determine the Maximum Radius of Defocused Protons after Self-Modulation in AWAKE

   Turner Marlene🇨🇭 · Edda Gschwendtner🇨🇭 · Patric Muggli🇨🇭

   The AWAKE experiment at CERN aims to drive GV/m plasma wakefields with a self-modulated proton drive bunch, and to use them for electron acceleration. During the self-modulation process, protons are defocused by the transverse plasma wakefields and form a halo around the focused bunch core. The two-screen setup integrated in AWAKE measures the transverse, time-integrated proton bunch distribution downstream the \unit[10]{m} long plasma to detect defocused protons. By measuring the maximum radius of the defocused protons we attempt calculate properties of the self-modulation. In this article, we develop a routine to identify the maximum radius of the defocused protons, based on a standard contour method. We compare the maximum radius obtained from the contour to the logarithmic lineouts of the image to show that the determined radius identifies the edge of the distribution.

   ↳ physics.acc-phnucl-exNucl.Instrum.Meth.A(2018)·4 citations
3. 03*

   Chiral magnetic effect search in p+Au, d+Au and Au+Au collisions at RHIC

   Jie Zhao (for the STAR collaboration)🇺🇸

   Metastable domains of fluctuating topological charges can change the chirality of quarks and induce local parity violation in quantum chromodynamics. This can lead to observable charge separation along the direction of the strong magnetic field produced by spectator protons in relativistic heavy-ion collisions, a phenomenon called the chiral magnetic effect (CME). A major background source for CME measurements using the charge-dependent azimuthal correlator ($\Delta \gamma$) is the intrinsic particle correlations (such as resonance decays) coupled with the azimuthal elliptical anisotropy ($v_2$). In heavy-ion collisions, the magnetic field direction and event plane angle are correlated, thus the CME and the $v_2$-induced background are entangled. In this report, we present two studies from STAR to shed further lights on the background issue. (1) The $\Delta \gamma$ should be all background in small system p+Au and d+Au collisions, because the event plane angles are dominated by geometry fluctuations uncorrelated to the magnetic field direction. However, significant $\Delta \gamma$ is observed, comparable to the peripheral Au+Au data, suggesting a background dominance in the latter, and likely also in the mid-central Au+Au collisions where the multiplicity and $v_2$ scaled correlator is similar. (2) A new approach is devised to study $\Delta \gamma$ as a function of the particle pair invariant mass ($m_{inv}$) to identify the resonance backgrounds and hence to extract the possible CME signal. Signal is consistent with zero within uncertainties at high $m_{inv}$. Signal at low $m_{inv}$, extracted from a two-component model assuming smooth mass dependence, is consistent with zero within uncertainties.

   ↳ hep-exnucl-exnucl-thEPJ Web Conf.(2018)·9 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.