120805738
The Bonn polarized target NMR-system
Abstract The Bonn frozen spin target is used for meson photoproduction experiments in combination with the facility PHOENICS at ELSA. The maximum polarization field of 7 T is provided by a superconducting solenoid. For electron scattering experiments a target apparatus which uses a superconducting 4 T magnet in a Helmholtz configuration is employed. For dynamic nuclear polarization of protons or deuterons various microwaves sources with frequencies of 70 GHz, 98 GHz or 140 GHz are available. Ammonia, butanol and lithium hydrids are used as target materials. The main part of the polarization detection system is the so-called Liverpool nuclear magnetic resonance module, which ensures a high flexibility for the polarization measurements of different nuclear species, e.g. 15 N at 2.5 T ( f L =10.8 MHz) and protons at 50 T ( f L =213 MHz).
122005636
New Spin-Physics Experiments with Frozen-Spin Target at MAMI
In the physics program for the MAMI C accelerator the investigation of the spin dependent excitation spectrum of the nucleon and fundamental properties, such as the spin polarizabilities of the nucleon are an important goal. This will be tackled in the framework of the A2‐collaboration by doing double polarization experiments, using the linearly or circularly polarized energy marked photon beam in combination with a new solid state polarized target. The horizontal dilution refrigerator of the Frozen Spin Target was constructed by and is operated in close cooperation with, the Joint Institute for Nuclear Research in Dubna, Russia. The system offers both longitudinally and transversely polarized protons and deuterons. The target material, butanol and deuterated butanol, was developed and produced by the Ruhr‐University of Bochum and provides the highest degree of polarization, measured with a new NMR apparatus. The status of the experiment and preliminary results will be presented.
120449636
The new Bonn frozen spin target for experiments with real photons
At the new Bonn Electron Stretcher Accelerator ELSA scattering experiments with real photons in the single pion photoproduction γ N → π N and in the photodisintegration of the deuteron γ N pn are prepared. To determine these processes completely, it is nessesary to measure single and double polarisation observables. For these experiments a new’bonn frozen spin target’ BOFROST was developed. The target with a maximum volume of 30 cm3 is cooled in a vertical 3He/4He — dilution refrigerator. In the’frozen spin mode’ a lowest temperature of 64 mK was reached.
120916993
Photoproduction of positive pions from polarized protons
Abstract Target asymmetry data for single positive pion photoproduction from polarized protons have been obtained at the Bonn Electron Stretcher Accelerator ELSA. Data were taken in a wide kinematical range of E γ = 215–800 MeV and Θ CMS π = 35°–135° with the PHOENICS-detector. This detector permits a considerable kinematical overdetermination so that the nominal process could be clearly separated from the background. For the first time a combination of a frozen spin target with a tagged photon beam has been used. Butanol (C 4 H 9 OH) was used as target material with a maximum proton polarization of more than ±90%. Due to the simultaneous energy and angle coverage the systematical error in the order of ΔT sys = ±2.5% is common for all data points. The results at low photon energies show significant deviations from existing multipole analyses.
122999945
Pfeiffer et al. Reply
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.
11540608
The Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter
Abstract The quark-meson coupling model which we have developed previously is extended to incorporate the δ meson. It is then used to study the Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter. We find that, in combination with the u - d mass difference, the difference between quark scalar densities in protons and neutrons generates an effective neutron-proton mass difference of the right magnitude. Finally we find that isospin symmetry breaking in the quark condensates can be directly related to the δ meson field.
10421165
Power counting regime of chiral extrapolation and beyond
Finite-range regularized chiral effective field theory is presented in the context of approximation schemes ubiquitous in modern lattice QCD calculations. Using FRR techniques, the power-counting regime (PCR) of chiral perturbation theory can be estimated. To fourth-order in the expansion at the 1% tolerance level, we find 0 {le} m{sub {pi}} {le} 180 MeV for the PCR, extending only a small distance beyond the physical pion mass.
119501192
Heavy-quark axial charges to nonleading order
We combine Witten's renormalization group with the matching conditions of Bernreuther and Wetzel to calculate at next-to-leading order the complete heavy-quark contribution to the neutral-current axial-charge measurable in neutrino-proton elastic scattering. Our results are manifestly renormalization group invariant.
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.
120955970
Hadron structure in medium
Abstract The quark meson coupling model may be viewed as a natural generalization of QHD which takes into account the internal structure of the nucleon. In such an approach it is natural for the properties of the nucleon to change in medium. We discuss the change in the proton electric and magnetic form factors when it is bound in a specific shell model orbit. Modern quasi-elastic electron scattering experiments should be able to detect effects of the size predicted. We also examine the mean field potential felt by an ω in a finite nucleus, concluding that the ω should be bound by between 50 and 100 MeV.