119454330
HiX2000: Theory Summary
We summarize the theoretical consensus of the HiX workshop concerning those measurements which seem most appropriate for inclusion in the ``white paper'' being prepared to justify the proposed 12 GeV upgrade at Jefferson Lab. The criteria for inclusion are that such measurements should be decisive, not possible elsewhere and should answer crucial physics questions with broad implications.
16608552
Kaon-nucleus Drell-Yan processes and kaon structure functions.
Abstract We investigate the information which could be obtained from Drell-Yan processes with sufficiently intense beams of charged kaons on isoscalar targets. It is found that combinations of K + and K − Drell-Yan measurements on isoscalar nuclear targets would allow one to extract the kaon sea quark distributions. These cross sections are also sensitive to the strange valence quark distribution in the kaon, although one would need a significant increase over the presently available kaon fluxes in order to extract this quantity with sufficient accuracy.
120073991
Role of the U(1) ghost beyond leading order in a large-Nc expansion
The 1/Nc expansion is one of the very few methods we have for generating a systematic expansion of QCD at the energy scale relevant to hadron structure. The present formulation of this theory relies on the double-line notation for calculating the leading order of a diagram in the 1/Nc expansion, where the local SU(Nc) gauge symmetry is substituted by a U(Nc) symmetry and the associated U(1) ghost field is ignored. In the current work we demonstrate the insufficiency of this formulation for describing certain non-planar diagrams of interest in current attempts to model QCD. We derive a more complete set of Feynman rules that include the U(1) ghost field and provide a useful tool for calculating both color factors and 1/Nc orders of all color-singlet diagrams.
18714425
Near-threshold Isospin Violation in the Pion Form Factor from Chiral Perturbation Theory
We examine the isospin violation in the timelike pion form factor near threshold at next-to-leading order in the chiral expansion using the techniques of Chiral Perturbation Theory. This next-to-leading order contribution contains the first nonvanishing isospin violation. This isospin violation is found to be very small near threshold. In particular, the isospin violation at threshold is found to be of order 10 4 , which should be compared with the few percent level seen in the vector
122078954
Proton pole contribution in proton decay
We show that nucleon pole terms contribute significantly to proton decay, increasing the branching ratio for e+π0 and νRπ+ modes. The total lifetime is decreased to the point where keeping the SU(5) value of the lifetime below the experimental upper bound forces us to the choice of QCD scale parameter and proton radius parameter which are near the edge of the allowed region.
54190998
Scale setting, sigma terms and the Feynman-Hellman theorem
The authors recently presented new values for the octet baryon sigma terms. These were extracted using the Feynman-Hellman theorem from a chiral perturbation theory fit to octet baryon mass data from the PACS-CS collaboration. Of particular interest is the precise determination of the strangeness sigma term $\sigma_s = 21 \pm 6$ MeV. In this work, we elaborate on the critical effect which the choice of scale setting has on this value. We discuss the prospect that the comparison of direct and 'spectrum' determinations of the sigma terms from the lattice can provide insight not only into scale setting on the lattice, but into QCD itself.
121573165
Polarization reversal of proton spins in a solid-state target by superradiance
The new Bonn frozen spin target developed for spin physics experiments with tagged photons from the Bonn electron stretcher accelerator ELSA has successfully been used in pion photoproduction experiments. Proton polarization values of −99% and +94% in ammonia, −96% and +90% in butanol have been achieved in a dilution refrigerator at a magnetic field of 3.53 T. At a temperature below 100 mK and a magnetic field of 0.35 T a very fast spontaneous polarization reversal within a time interval of 800 μs has been observed. This effect occurred only at negative polarization and has been identified as a collective spontaneous emission — i.e. superradiance — in the two level proton spin system. Detailed investigations have been made in order to study whether this effect is useful for a fast polarization reversal of the entire sample. Up to now the highest polarization reversal from −90% to +60% has been obtained in a target volume of 6.5 cm3.
15366431
Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
The Glasgow photon tagging spectrometer at Mainz has been upgraded so that it can be used with the 1500MeV electron beam now available from the Mainz microtron MAMI-C. The changes made and the resulting properties of the spectrometer are discussed.
94396828
Butanol in the Frozen Spin Mode
Measurements of the polarization build-up in butanol at 3.5 T are presented. Measurements of the proton relaxation times in the frozen spin mode were performed at magnetic fields of 0.5 and 0.35 Tesla, leading to the conclusion that butanol is a suitable material for the Bonn Frozen Spin Target.
59806645
After Leibniz...: discussions on philosophy and artificial intelligence.
This is an edited transcript of informal conversations which we have had over recent months, in which we looked at some of the issues which seem to arise when artificial intelligence and philosophy meet. Our aim was to see what might be some of the fundamental principles of attempts to build intelligent machines. The major topics covered are the relationship of AI and philosophy and what help they might be to each other: the mechanisms of natural inference and deduction; the question of what kind of theory of meaning would be involved in a successful natural language understanding program, and the nature of models in AI research.
122902871
An internal superconducting “holding-coil” for frozen spin targets
Abstract A new concept of a small superconducting holding magnet, placed inside a polarizing refrigerator, has been developed for frozen spin targets. The superconducting wire has been wound on the inner cooling shield of the vertical dilution refrigerator of the Bonn frozen spin target. The maximum field of the magnet is 0.35 T. The total thickness of the superconducting coil consisting of the wire and the copper carrier is of the order of 500 μm. Based on this concept, a frozen spin target is under construction for the measurement of the Gerasimov-Drell-Hearn sum rule with polarized real photons at the Mainz microtron MAMI and the Bonn electron stretcher accelerator ELSA.