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.
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.
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.
122999945
Pfeiffer et al. Reply
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.
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.
13937306
A possible resolution of the proton spin problem
A number of lines of investigation into the structure of the nucleon have converged to the point where we believe that one has a consistent explanation of the well known proton spin crisis.
120054350
Invariant Spin in the Proton
We discuss recent theoretical progress in understanding the distribution of spin and orbital angular momentum in the proton. Particular attention is devoted to the effect of QCD evolution and to the distinction between “chiral” and “invariant” spin. This is particularly significant with respect to the possible presence of polarized strange quarks.
55053473
Charge symmetry breaking from a chiral extrapolation of moments of quark distribution functions
[...] We present a determination, from lattice QCD, of charge symmetry violation in the spin-independent and spin-dependent parton distribution functions of the nucleon. This is done by chirally extrapolating recent QCDSF/UKQCD Collaboration lattice simulations of the first several Mellin moments of the parton distribution functions of octet baryons to the physical point. We find small chiral corrections for the polarized moments, while the corrections are quantitatively significant in the unpolarized case.
119535354
A microscopic approach to sigma-hypernuclei
Abstract A separable potential model is constructed to describe the coupled Σ N- Λ N systems. From this the Σ single-particle potential is developed including Pauli effects. The momentum-space Schrodinger equation is then solved self-consistently for the complex eigenvalues of 1s and 1p state light ( A ⩽ 16) Σ ° hypernuclei. Because of two distinct mechanisms these states are all found to be long-lived, with widths as small as 1.8 MeV in the Σ 0 5 He s-state, and 0.5 MeV in the Σ 0 9 Be p-state.
119033960
Decoupling heavy particles simultaneously
The renormalization group is extended to cases where several heavy particles are decoupled at the same time. This involves large logarithms which are scale-invariant and so cannot be eliminated by a change of renormalization scheme. A set of scale-invariant running couplings, one for each heavy particle, is constructed without reference to intermediate thresholds. The entire heavy-quark correction to the axial charge of the weak neutral current is derived to next-to-leading order, and checked in leading order by evaluating diagrams explicitly. The mechanism for cancelling contributions from the top and bottom quarks in the equal-mass limit is surprisingly non-trivial.