摘要:

Spin is a beautiful concept that plays an ever important role in modern physics. In this talk, I start with a discussion of the origin of spin, and then turn to three themes in which spin has been crucial in subatomic physics: a lab to explore physics beyond the standard model, a tool to measure physical observables that are hard to obtain otherwise, a probe to unravel nonperturbative QCD. I conclude with some remarks on a world without spin. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607111

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The Muong‐ 2 collaboration has measured the anomalous magneticgvalue,a= (g‐ 2)/2, of the positive muon with an unprecedented uncertainty of 0.7 parts per million. The resulta&mgr;+(expt) = 11659204(7)(5) × 10−10, based on data collected in the year 2000 at Brookhaven National Laboratory, is in good agreement with the preceeding data ona&mgr;+anda&mgr;−. The measurement tests standard model theory, which at the level of the current experimental uncertainty involves quantum electrodynamics, quantum chromodynamics, and electroweak interaction in a significant way. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607112

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Some prominent new semi‐inclusive DIS results fromJLabandHermesthat have appeared since SPIN 2000 are presented. Polarized quark distributions have been extracted from the completeHermesdata set on H and D from 1996–2000, based on Monte Carlo “purities”. The data quality permits for the first time the separation of theu¯,d¯ands + s¯sea quark polarizations. Also, both laboratories have produced new single‐spin asymmetries in the azimuthal distributions of semi‐inclusive hadrons. New SSAs from longitudinally polarized proton and deuteron targets are presented, as well as beam‐helicity SSAs from unpolarized protons. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607113

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Sum rules involving the spin structure of the nucleon like those due to Bjorken, Ellis and Jaffe and the one due to Gerasimov, Drell and Hearn offer the opportunity to study the structure of strong interactions. At long distance scales in the confinement regime the Gerasimov‐Drell‐Hearn (GDH) Sum Rule connects static properties of the nucleon like the anomalous magnetic moment &kgr; and the nucleon massm, with the spin dependent absorption of real photons with total cross sections &sgr;3/2and &sgr;1/2:0∞ dvv &sgr;3/2(v) − &sgr;1/2(v) = 2&pgr;2&agr;m2 ⋅ &kgr;2(1) Hence the full spin‐dependent excitation spectrum of the nucleon is related to its static properties. The sum rule has not been investigated experimentally until recently. For the first time this fundamental sum rule is verified by the GDH‐Collaboration with circularly polarized real photons and longitudinally polarized nucleons at the two acceleratorsElsaandMami. The investigation of the response of the proton as well as of the neutron allows to perform an isospin decomposition. Data from the resonance region up to the onset of the Regge regime are shown. The “sum” on the left hand side of the GDH Sum Rule can be generalized to the case of virtual photons. This allows to establish aQ2dependency and to study the transition to the perturbative regime of QCD. This is the subject of several experiments e.g. atJLabfor the resonance region and of theHermesexperiment atDesyfor higherQ2. Moreover, this paper covers the status of theory concerning the GDH Sum Rule, the different experimental approaches and the results for the absorption of real and virtual photons will be reviewed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607114

出版商:AIP    

年代:1903

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.1607115

出版商:AIP    

年代:1903

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.1607116

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In this talk I would like to present a retrospective view of the work done by Vladimir L. Solovianov. He began his work in sixties in Dubna. And it happened to be that he participated in many experiments, which were in the main stream of the experimental program over the decades. In the last years he initiated several projects, which were again at the edge of the investigation of the spin puzzle in the High Energy Physics domain. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607117

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Experiment E950 at AGS, BNL has provided data with high statistics for the left‐right asymmetry of proton‐carbon elastic scattering in the Coulomb‐nuclear interference region of momentum transfer. It allows to access information about spin properties of the Pomeron and has practical implications for polarimetry at high energies. Relying on Regge factorization the results for the parameterr5, ratio of spin‐flip to non‐flip amplitudes, is compared with the same parameter measured earlier in pion‐proton elastic and charge exchange scattering. While data for Imr5agree (within large systematic errors), there might be a problem for Rer5. The &pgr;Ndata indicate at a rather small contribution of the f‐Reggeon to the spin‐flip part of the iso‐scalar amplitude which is dominated by the Pomeron. This conclusion is supported by direct analysis of data for elastic and charge exchangeppandpnscattering which also indicate at a vanishing real part of the hadronic spin‐flip amplitude at energies 20 GeV and higher. This is a good news for polarimetry, since the E950 results enhanced by forthcoming new measurements at AGS can be safely used for polarimetry at RHIC at higher energies. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607118

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Theoretical descriptions of three‐nucleon systems, which are based on a summation over pairwise NN interactions, fail to describe existing data. For instance, the binding energy of the triton is underpredicted as well as the unpolarized cross section in pd elastic scattering around &thgr;cm= 100°. It has been demonstrated that the inclusion of a three‐nucleon‐force, which has been adjusted to reproduce the measured binding energy of the triton, also reduces the discrepancy of the calculation with the measured cross section. In the case of many spin observables — the most notorious being the analyzing power in nd scattering below 10 MeV (“Aypuzzle”) — inclusion of any one of the modelled three‐nucleon‐forces does not explain the data. Several precise data sets of spin observables exist between 100 MeV and the pion production threshold. A theoretical description of the three‐nucleon system must be able to reproduce all spin observables simultaneously. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607119

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We review data for nucleon electromagnetic form factors, emphasizing recent measurements ofGE/GMthat use recoil or target polarization to minimize systematic errors and model dependence. The data are parametrized in terms of densities that are consistent with the Lorentz contraction of the Breit frame and with pQCD. The dramatic linear decrease inGEp/GMpfor 1 ⩽Q2⩽ 6 (GeV/c)2demonstrates that the charge is broader than the magnetization of the proton. High‐precision recoil polarization measurements ofGEnshow clearly the positive core and negative surface charge of the neutron. Combining these measurements, we display spatial densities foruanddquarks in nucleons. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1607120

出版商:AIP    

年代:1903

数据来源: AIP