Wed·Feb 25, 2015Wednesday·February 25, 2015

1. 01*

   Ultra-peripheral Collisions at RHIC: An Experimental Overview

   Spencer R. Klein🇺🇸

   Ultra-peripheral collisions (UPCs) of ions allow us to study photonuclear and two-photon interactions at energies above those available at fixed target accelerators. For heavy ions, the couplings are large enough so that multi-photon interactions are possible, and higher order corrections are expected to be significant. In this writeup, I present some recent UPC results from the Relativistic Heavy Ion Collider (RHIC), and discuss some future prospects. I also draw parallels between UPC data and that expected at an electron-ion collider (EIC), and show how UPCs are a useful lead-in to EIC physics. This writeup is based on a talk at "Initial State 2014," (IS2014), with a focus on the newest results. One important result is that comparison of the RHIC (and LHC) results on coherent ${\rho }^0$ photoproduction show evidence for nuclear suppression, compared to a calculating based on $\gamma p$ cross-sections.

   nucl-exhep-ph7 citations
2. 02*

   Upper bound on neutrino mass based on T2K neutrino timing measurements

   T2K Collaboration

   The Tokai to Kamioka (T2K) long-baseline neutrino experiment consists of a muon neutrino beam, produced at the J-PARC accelerator, a near detector complex and a large 295km distant far detector. The present work utilizes the T2K event timing measurements at the near and far detectors to study neutrino time of flight as function of derived neutrino energy. Under the assumption of a relativistic relation between energy and time of flight, constraints on the neutrino rest mass can be derived. The sub-GeV neutrino beam in conjunction with timing precision of order tens of ns provide sensitivity to neutrino mass in the few MeV/$c^2$ range. We study the distribution of relative arrival times of muon and electron neutrino candidate events at the T2K far detector as a function of neutrino energy. The 90% C.L. upper limit on the mixture of neutrino mass eigenstates represented in the data sample is found to be m${}_{\nu }^2<5.6\mathrm{M}e{V}^2/c^4$.

   ↳ hep-exhep-phnucl-exphysics.ins-detPRD(2016)·16 citations
3. 03*

   Emergence of a secondary rainbow and the dynamical polarization potential for 16O on 12C at 330 MeV

   R.S. Mackintosh🇬🇧 · Y. Hirabayashi🇯🇵 · S. Ohkubo🇯🇵

   Background: An anomaly in the elastic scattering of O-16 on C-12 around 300 MeV was resolved by including collective excitations of both nuclei, leading to a secondary rainbow. There is little systematic knowledge of the contribution of collective excitations to the interaction between nuclei, particularly in the overlap region of heavy nuclei. Purpose: To study the dynamic polarization potential (DPP) generated by channel coupling that had been validated for a case where scattering is sensitive to the nuclear potential over a wide radial range; to exhibit evidence of the non-locality due to collective coupling; to validate, or otherwise, the representation of DPPs by uniform renormalization of potentials. Methods: S-matrix to potential inversion yields local potentials reproducing the elastic channel S-matrix of coupled channel calculations. Subtracting the elastic channel uncoupled potential yields a local L-independent representation of the DPP. The dependence of the DPP on the nature of the coupled states and other parameters can be studied. Results: Local DPPs were found due to the excitation of C-12 and the combined excitation of O-16 and C-12. The radial forms found were very different from uniform renormalization of the potential. Full coupling led to a 10 percent increase in the volume integral of the real potential. Evidence for the non-locality of the underlying formal DPP and the effect of direct coupling between the collective states is found. Conclusions: The local DPP generating the secondary rainbow is found. DPPs have forms depending on the specific excitations and cannot be represented by a uniform renormalization of the potential. The method is useful for study of the contribution of collective excitations to internuclear potentials, concerning which remarkably little is known in general.

   ↳ nucl-thnucl-exPRC(2015)·14 citations
4. 04*

   A device for simultaneous spin analysis of ultracold neutrons

   S. Afach🇨🇭 · G. Ban🇫🇷 · G. Bison🇨🇭 · K. Bodek🇵🇱 · Z. Chowdhuri🇨🇭 · M. Daum🇨🇭 · M. Fertl🇨🇭 · B. Franke🇨🇭 · P. Geltenbort🇫🇷 · Z.D. Grujić🇨🇭 · L. Hayen🇧🇪 · V. Hélaine🇨🇭 and 28 other authors

   We report on the design and first tests of a device allowing for measurement of ultracold neutrons polarisation by means of the simultaneous analysis of the two spin components. The device was developed in the framework of the neutron electric dipole moment experiment at the Paul Scherrer Institute. Individual parts and the entire newly built system have been characterised with ultracold neutrons. The gain in statistical sensitivity obtained with the simultaneous spin analyser is $(18.2\pm 6.1)\%$ relative to the former sequential analyser under nominal running conditions.

   ↳ physics.ins-detnucl-exEPJA(2015)·36 citations
5. 05*

   A longitudinal study of field emission in CEBAF's SRF cavities 1995-2015

   Jay Benesch🇺🇸

   Field emission is one of the key issues in superconducting RF. When present, it limits operating gradient directly or via induced heat load at 2K. In order to minimize particulate contamination of and thus field emission in the CEBAF SRF cavities during assembly, a ceramic RF window was placed very close to the accelerating cavity proper. As an unintended consequence of this, it has been possible to monitor and model field emission in the CEBAF cavities since in-tunnel operation began. The ceramic is charged by field emission to a stable voltage and then discharges. This phenomenon had to be studied statistically to minimize the number of interruptions to accelerator operation for nuclear physics. We report here the results of our twenty year study of this and related phenomena.

   ↳ physics.acc-phcond-mat.supr-conhep-exnucl-ex9 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.