Session MM: Postdeadline Session II

Dispersive approach to the muon's anomalous magnetic moment

In view of the new muon (g-2) experiments at Fermilab and at J-PARC, we present a new dispersive formalism for evaluating the hadronic light-by-light (HLbL) scattering contribution to the muon's anomalous magnetic moment $a_\mu$. It is suggested to represent this contribution as a dispersive integral of the vertex function discontinuity in the virtuality of the external photon. By unitarity this discontinuity is related to the amplitudes of decay and production of hadrons. As a test of the dispersive formalism, we firstly apply it to the case of a scalar two-loop vertex diagram of similar topology as entering the HLbL contribution to $a_\mu$ [1]. We provide a first realistic application of the proposed formalism to the case of pseudoscalar meson pole exchanges. A crucial distinctive feature of the dispersion approach is that it allows extension to implement the form factors beyond the simplest monopole or dipole approximations and to include multi-meson channels. Moreover, it allows for a more straightforward implementation of the experimental data. The ongoing measurements by the BES-III Collaboration will be a crucial input into the presented dispersive formalism. \\[4pt] [1] V. Pauk and M. Vanderhaeghen, arXiv:1403.7503 [hep-ph].   

Proton structure in muonic hydrogen Lamb shift

Calculations of proton structure effects in muonic hydrogen Lamb shift, based on dispersion theory [1,2] and chiral perturbation theory [3,4], will be presented within the context of the ``proton charge radius puzzle.'' \\[4pt] [1] C.E.~Carlson \& M.~Vanderhaeghen: Phys.Rev.\ A84 (2011) 020102\\[0pt] [2] C.E.~Carlson, M.~Gorchtein \& M.~Vanderhaeghen: Phys.Rev.\ A89 (2014) 022504\\[0pt] [3] J.M.~Alarcon, V.~Lensky \& V.~Pascalutsa: Eur.Phys.J.\ C74 (2014) 2852\\[0pt] [4] V.~Lensky, J.M.~Alarcon \& V.~Pascalutsa: arXiv:1407.2574   

Neutron-induced reactions relevant for Inertial-Cofinement Fusion Experiments

The typical ignition experiment at the National Ignition Facility ablatively implodes a plastic capsule filled with DT fuel, generating a high flux of 14-MeV neutrons from the d(t,n)$\alpha$ reaction. There is some spread in the energy of these primary 14-MeV neutrons, which is mainly attributable to Doppler shifting from the relative thermal motion of the burning DT fuel. Neutrons created during this reaction have 5-10\% chance of scattering before escaping the fuel assembly, losing some fraction of their energy in the scattering process. Neutrons emerging with an energy greater than the reaction energy are generated by a two-step process where neutrons first transfer momentum to a deuteron or tritium ion, these enhanced energy ions then fuse in flight to produce higher energy neutrons; some of these neutrons have energies in excess of 30 MeV. Measuring the fluencies of both the low- and high-energy neutrons is a powerful mechanism for studying the properties of the fuel assembly, and the various parameters important to inertial confinement fusion. We have developed a number of tools to measure the spectral characteristics of the NIF neutron spectrum. Most of these methods rely on exploiting the energy dependence of (n,$\gamma$), (n,2n), (n,3n) and (n,p) reactions on a variety o   

Systematic Uncertainties in the Analysis of the Reactor Neutrino Anomaly

We examine uncertainties in the analysis of the reactor neutrino anomaly, wherein it is suggested that only about $94\%$ of the emitted antineutrino flux was detected in short baseline experiments. We find that the form of the corrections that lead to the anomaly are very uncertain for the $30\%$ of the flux that arises from forbidden decays. This uncertainty was estimated in four ways, is as large as the size of the anomaly, and is unlikely to be reduced without accurate direct measurements of the antineutrino flux. Given the present lack of detailed knowledge of the structure of the forbidden transitions, it is not possible to convert the measured aggregate fission beta spectra to antineutrino spectra to the accuracy needed to infer an anomaly. Neutrino physics conclusions based on the original anomaly need to be revisited, as do oscillation analyses that assumed that the antineutrino flux is known to better than approximately $4\%$.   

Calculated scission-neutron properties in agreement with experimental data on prompt neutrons

The main properties of the neutrons released during the neck rupture and emitted immediately thereafter are calculated for 236U in the frame of the dynamical scission model [1, 2]. These properties are: the angular distribution with respect to the fission axis (calculated on spheres of radii R=30 fm and 40 fm at time T=4 $\times$ 10$^{21}$ sec), the distribution of the average energies of neutrons emitted from each state (calculated for durations of the neck rupture T = 1 and 2 $\times$ 10$^{22}$ sec) and the total neutron multiplicity (calculated for two values of the minimum neck-radius, 1.6 fm and 1.9 fm). They are compared with measurements of prompt fission neutrons during 235U(nth, f). The experimental trends are well reproduced, i.e., the focussing of the neutrons along the fission axis, the preference of emission from the light fragment, the range, slope and average value of the neutron energyspectrum and the average total neutron multiplicity. One can therefore not exclude that prompt fission neutrons and scission neutrons are one and the same.\\[4pt] [1] N. Carjan, M. Rizea, Int. J. Mod. Phys. E 21 (2012) 1250031.\\[0pt] [2] M. Rizea, N. Carjan, Nucl. Phys. A 909 (2013) 50-68   

Theory and Detection of Highly Multiplying Fission Chains

LLNL has been making significant advances to the field of neutron multiplicity theory and experiments for several decades. Recently the statistical theory of fission chains with respect to neutron count distributions was brought into analytical form after three decades. We use this analytical form in our analysis of multiplying systems. I will discuss recent work designed to test our ability to deal with highly multiplying fissioning systems (M \textgreater 5). I will further discuss the current detector we have developed, and analysis tools used, to passively analyze these systems with both fast and thermal neutron detector arrays.   

$^{3}$He Co-magnetometer Readout for the SNS nEDM Experiment

A search for a permanent electric dipole moment (EDM) of the neutron would provide one of the most important low energy tests of the discrete symmetries beyond the Standard Model of particle physics. A new experimental search of neutron EDM, to be conducted at the Spallation Neutron Source (SNS) at ORNL, has been proposed with a goal of 100-fold improvement in the present experimental limit of 10$^{-26}$e$\cdot$cm The experiment is based on the magnetic-resonance technique in which polarized neutrons precess at the Larmor frequency when placed in a static magnetic field; a non-zero EDM would be evident as a difference in precession frequency when a strong electric field is applied parallel vs. anti-parallel to the magnetic field. In addition to its role as neutron spin-analyzer via the spin-dependent n$+^{3}$He nuclear capture process, polarized helium-3 (which has negligible EDM) will serve as co-magnetometer to correct for drifts in the magnetic field. The helium-3 co-magnetometer will be directly read out by superconducting gradiometers coupled to SQUIDs. We describe a proposed SQUID system suitable for the complex neutron EDM apparatus, and demonstrate that the field noise in the SQUID system, tested in an environment similar to the EDM apparatus, meets the nEDM requirement. We also present a test of the compatibility of low-noise SQUID operation with other devices, potential sources of electromagnetic interference, which are necessarily operating during the EDM measurement period and effective ambient magnetic field noise cancellation with an implementation of reference channels.   

Heterogonous Nanofluids for Nuclear Power Plants

Nuclear reactions can be associated with high heat energy release. Extracting such energy efficiently requires the use of high-rate heat exchangers. Conventional heat transfer fluids, such as water and oils are limited in their thermal conductivity, and hence nanofluids have been introduced lately to overcome such limitation. By suspending metal nanoparticles with high thermal conductivity in conventional heat transfer fluids, thermal conductivity of the resulting homogeneous nanofluid is increased. Heterogeneous nanofluids offer yet more potential for heat transfer enhancement. By stratifying nanoparticles within the boundary layer, thermal conductivity is increased where temperature gradients are highest, thereby increasing overall heat transfer of a flowing fluid. In order to test the merit of this novel technique, a numerical study of a laminar pipe flow of a heterogeneous nanofluid was conducted. Effect of Iron-Oxide distribution on flow and heat transfer characteristics was investigated. With Iron-Oxide volume concentration of 0.009 in water, up to 50{\%} local heat transfer enhancement was predicted for the heterogeneous compared to homogeneous nanofluids. Increasing the Reynolds number is shown to increase enhancement while having negligible effect on pressure drop. Using permanent magnets attached externally to the pipe, an experimental investigation conducted at MIT nuclear reactor laboratory for similar flow characteristics of a heterogeneous nanofluid have shown upto 160{\%} enhancement in heat transfer. Such results show that heterogeneous nanofluids are promising for augmenting heat transfer rates in nuclear power heat exchanger systems.