6463902
Dynamical pion collapse and the coherence of conventional neutrino beams
In this paper we consider the coherence properties of neutrinos produced by the decays of pions in conventional neutrino beams. Using a multiparticle density matrix formalism we derive the oscillation probability for neutrinos emitted by a decaying pion in an arbitrary quantum state. Then, using methods from decoherence theory, we calculate the pion state which evolves through interaction with decay-pipe gases in a typical accelerator neutrino experiment. These two ingredients are used to obtain the distance scales for neutrino beam coherence loss. We find that for the known neutrino mass splittings, no nonstandard oscillation effects are expected on terrestrial baselines. Heavy sterile neutrinos may experience terrestrial loss of coherence, and we calculate both the distance over which this occurs and the energy resolution required to observe the effect. By treating the pion-muon-neutrino-environment system quantum mechanically, neutrino beam coherence properties are obtained without assuming arbitrary spatial or temporal scales at the neutrino production vertex.
121612933
Results from the Bo Liquid Argon Scintillation Test Stand at Fermilab
In these proceedings I discuss results from the Bo test stand at the Proton Assembly Building, Fermilab. This test stand has been used to characterize elements of the MicroBooNE optical system as well as to perform studies of processes affecting argon scintillation light such as scintillation quenching and optical absorption by impurities. I review in detail a recent measurement of the absorption of liquid argon scintillation light by dissolved nitrogen at the part-per-million level.
118404822
A simulation of the optical attenuation of TPB coated light-guide detectors
This note is provided as a supplementary section to accompany the paper [1] which has been included in these proceedings. It describes some simple simulations which were performed in order to understand the attenuation behaviors of acrylic light-guides operated in air and argon, which were characterized in [2]. Whilst these simulations are only at the level of sophistication of a toy model, they illustrate interesting non-exponential light attenuation effects and the differences between operating light-guide based detectors in argon and air environments. We investigate the effects of surface absorption, surface roughness and wavelength dependence, and use a model tuned on the light-guide attenuation curve measured in air to make a prediction of the light-guide attenuation curve in argon. This curve is compared with data from a liquid argon test stand, and an improvement over a simple exponential model is observed.
118983427
Similarity flow of a neutral scalar coupled to a fixed source
A neutral scalar meson interacting with a fixed isoscalar nucleon is evolved according to the similarity renormalization group. The fixed source ends up being too singular and an appropriately dressed static source arises from the similarity flow. The fixed source is dressed by a virtual cloud of mesons extending out past the inverse meson mass according to the Yukawa potential. For low energies the source produces a Yukawa mean field which decouples from the remaining meson field fluctuations. The renormalization group procedure for effective particles is also illustrated for this fixed-source model.
14842371
Singlet-Triplet Splitting of Positronium in Light-Front QED
We study the QED bound-state problem in a light-front hamiltonian approach. It is important to establish the equivalence (or not) of equal-time and light-front approaches in the well-understood arena of Quantum Electrodynamics. Along these lines, the singlet-triplet ground state spin splitting in positronium is calculated. The well-known result, \(\frac{7}{6}{\alpha ^2}\) Ryd, is obtained analytically, which establishes the equivalence between the equal-time and light-front approaches (at least to this order). The true equivalence of the two approaches can only be established after higher-order calculations. It was previously shown that this light-front result could be obtained analytically [1], but a simpler method is presented in this paper.
17088589
Analytic treatment of positronium spin splittings in light-front QED
We study the QED bound-state problem in a light-front Hamiltonian approach. Starting with a bare cutoff QED Hamiltonian H{sub B} with matrix elements between free states of drastically different energies removed, we perform a similarity transformation that removes the matrix elements between free states with energy differences between the bare cutoff {Lambda} and effective cutoff {lambda} ({lambda}{lt}{Lambda}). This generates effective interactions in the renormalized Hamiltonian H{sub R}. These effective interactions are derived to order {alpha} in this work, with {alpha}{lt}1. H{sub R} is renormalized by requiring it to satisfy coupling coherence. A nonrelativistic limit of the theory is taken, and the resulting Hamiltonian is studied using bound-state perturbation theory. The effective cutoff {lambda}{sup 2} is fixed, and the limit 0{l_arrow}m{sup 2}{alpha}{sup 2}{lt}{lambda}{sup 2}{lt}m{sup 2}{alpha}{r_arrow}{infinity} is taken. This upper bound on {lambda}{sup 2} places the effects of low-energy (energy transfer below {lambda}) emission in the effective interactions in the {vert_bar}e{bar e}{r_angle} sector. This lower bound on {lambda}{sup 2} ensures that the nonperturbative scale of interest is not removed by the similarity transformation. As an explicit example of the general formalism introduced, we show that the Hamiltonian renormalized to O({alpha}) reproduces the exact spectrum of spin splittings, with degeneracies dictated by rotationalmore » symmetry, for the ground state through O({alpha}{sup 4}). The entire calculation is performed analytically, and gives the well-known singlet-triplet ground-state spin splitting of positronium, (7)/(6){alpha}{sup 2}Ryd. We discuss the remaining corrections other than the spin splittings and how they can be treated in calculating the spectrum with higher precision. {copyright} {ital 1997} {ital The American Physical Society}« less