Search results for " Polarization"
showing 10 items of 668 documents
The polarized double cell target of the SMC
1999
The polarized target of the Spin Muon Collaboration at CERN was used for deep inelastic muon scattering experiments during 1993-1996 with a polarized muon beam to investigate the spin structure of the nucleon. Most of the experiments were carried out with longitudinal target polarization and 190 GeV muons, and some were done with transverse polarization and 100 GeV muons. Protons as well as deuterons were polarized by dynamic nuclear polarization (DNP) in three kinds of solid materials - butanol, ammonia, and deuterated butanol - with maximum degrees of polarization of 94%, 91% and 60%, respectively. Considerable attention was paid to the accuracies of the NMR polarization measurements and …
On the observability of parity and time reversal violating interactions by trapped ion spectroscopy
1982
The feasibility to measure neutral weak current interactions by spectroscopy on trapped ions is investigated. The sensitivity of the proposed experiment is compared to the sensitivity of similar experiments using atomic gases or beams. It is shown that there is no advantage as far as that part of the interaction is concerned which is a vector in the nucleon current and an axial vector in the electron current. This is mainly due to the relatively low ion density. The circular polarization however depending upon the nuclear spin orientation appears to be proportional to the coherence time, which is three orders of magnitude longer than in ordinary atomic beam resonance experiments. It is poin…
The selection and performance of diamond radiators used in coherent bremsstrahlung experiments
2005
The bremsstrahlung emitted as a result of scattering electrons in thin diamond crystals provides a useful source of high energy photons for use in photonuclear experiments, since the coherent bremsstrahlung produced is linearly polarized. Techniques for selecting the most favorable diamonds have been investigated. These are optical polaroid analysis, X-ray topography and rocking curve measurements. The diamonds are characterized with a view to determining their performance as radiators, and bremsstrahlung spectra from a diamond radiator used at the Mainz MAMI-B facility are presented. The changes caused by high energy electrons to the crystal properties of the diamond and to the resulting c…
Ab initio calculation of nuclear structure corrections in muonic atoms
2018
The measurement of the Lamb shift in muonic hydrogen and the subsequent emergence of the proton-radius puzzle have motivated an experimental campaign devoted to measuring the Lamb shift in other light muonic atoms, such as muonic deuterium and helium. For these systems it has been shown that two-photon exchange nuclear structure corrections are the largest source of uncertainty and consequently the bottleneck for exploiting the experimental precision to extract the nuclear charge radius. Utilizing techniques and methods developed to study electromagnetic reactions in light nuclei, recent calculations of nuclear structure corrections to the muonic Lamb shift have reached unprecedented precis…
Isospin-symmetry restoration within the nuclear density functional theory: formalism and applications
2009
Isospin symmetry of atomic nuclei is explicitly broken by the charge-dependent interactions, primarily the Coulomb force. Within the nuclear density functional theory, isospin is also broken spontaneously. We propose a projection scheme rooted in a mean field theory, that allows the consistent treatment of isospin breaking in both ground and exited nuclear states. We demonstrate that this scheme is essentially free from spurious divergences plaguing particle-number and angular-momentum restoration approaches. Applications of the new technique include excited high-spin states in medium-mass N=Z nuclei, such as superdeformed bands and many-particle-many-hole terminating states.
Measurements of the Hadronic Cross Section and of Meson Transition Form Factors at BESIII for an improved Standard Model Prediction of (g−2)μ
2015
Abstract The BESIII experiment at the Beijing tau-charm factory BEPCII recently has embarked on a series of form factor measurements with the goal to improve the hadronic vacuum polarization as well as the hadronic light-by-light contributions to ( g − 2 ) μ . The status of the flagship measurements and preliminary results are presented.
Next-to-next-to-leading order τ+τ- production cross section close to threshold
2001
13 páginas, 5 figuras.-- PACS number(s): 12.20.Ds, 14.60.Fg
Electroweak Effective Charges and their relation to Physical Cross Sections
1997
In quantum electrodynamics with fermions f = e,\mu..., knowledge of the vacuum polarization spectral function determined from the tree level e^+e^- -> f^+f^- cross sections, together with a single low energy measurement of the fine structure constant \alpha, enables the construction of the one-loop effective charge \alpha_eff(q^2) for all q^2. It is shown how an identical procedure can be followed in the electroweak sector of the Standard Model to construct three gauge-, scale- and scheme-independent one-loop electroweak effective charges and an effective weak mixing angle from the tree level e^+e^- -> W^+W^-, ZH and e^+\nu_e -> W^+Z, W^+\gamma, W^+H differential cross sections, together wi…
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
2002
We study spin-dependent sum rules for forward virtual Compton scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at order $O(p^4)$. We show how these sum rules can be evaluated from low energy expansions (in the virtual photon energy) of the forward VVCS amplitudes. We study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher terms in the low energy expansion, which can be related to the generalized forward spin polarizabilities of the nucleon. The dependence of these observables on the photon virtuality $Q^2$ can be accessed, at small and intermediate $Q^2$ values, from existing and forthcoming data at Jefferson Lab.
Initial State Radiation Measurements at BESIII
2019
Precision measurements of the hadronic cross sections e+ e−→ π+ π− , π+π−π0, π+π−2π0, ωπ0 and π+π−3π0 are performed at the BESIII experiment located in Beijing, China. These cross section measurements are needed as input for the Standard Model prediction of the anomalous magnetic moment of the muon, (g − 2)µ.The initial state radiation method is used to access the energy regions of interest for (g − 2)µ. Our results will improve the precision of the Standard Model prediction of (g − 2)µ .