摘要:

We review recent progress in the understanding of the spin structure of the nucleon. For the free nucleon the issues addressed include the status of the Bjorken and Ellis‐Jaffe sum‐rules and the role of the axial anomaly. We outline recent work connecting the quark models familiar from hadron spectroscopy to the spin and flavor dependence of the parton distributions. Finally we review the current understanding of nuclear spin structure functions and particularly the extraction of the neutron spin structure function from deuteron data.

ISSN:0094-243X    

DOI:10.1063/1.48682

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The determination of the neutron electric formfactor from quasielastic reactions3H&drarr;e(e&drarr;,e′n) andD(e&drarr;,e′,n&drarr;) respectively is one of the present goals of experiments with polarized electrons at the Mainz race track microtron MAMI. A GaAsP‐photoelectron source is used at MAMI to get an 855 MeV electron beam spinpolarized to a degree of 35% at a current of 10 &mgr;A. Polarized3He‐nuclei are produced by optical pumping metastable3He. Scattered electrons are detected in coincidence with the recoil neutrons, the transverse spinpolarization of the neutrons may be analyzed by neutron‐proton scattering in a double wall plastic scintillator detector. A subset of the final detector set‐up has been tested successfully now by investigating the polarization transfer to the proton in reactionsH(e&drarr;,e′p&drarr;) andD(e&drarr;,e′p&drarr;) and to the neutron inD(e&drarr;,e′n&drarr;) at a 4‐momentum transfer with −Q2=8fm−2. First data from the exclusive quasielastic collision3H&drarr;e(e&drarr;,e′n) indicate a value of the neutron electric formfactor ofGnE=0.035±0.015 at −Q2=8fm−2.

ISSN:0094-243X    

DOI:10.1063/1.48651

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Recent experimental and theoretical work indicates that strange quark pairs play a non‐negligible role in determining nucleon properties. Their effects contribute to the electroweak nucleon form factors and thus can be isolated through measurements of neutral weak neutrino‐nucleon scattering. In particular, thess¯contribution to the nucleon spin can be determined by measuring the ratio of proton‐to‐neutron neutrino‐induced quasielastic yield. Preliminary results from the LSND experiment are presented, experiment which, at the end of the scheduled 94–95 run period, should obtain a measurement of the strange axial form factor,Gs1(0), with an absolute accuracy of approximately ±0.04.

ISSN:0094-243X    

DOI:10.1063/1.48667

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In a continuing effort to improve the quality of measurements for extracting the neutron electronic form factor (GnE) from the2H(e&drarr;,e′n&drarr;)1Hreaction, one of us (RM) proposed a new configuration for a neutron polarimeter (NPOL) to measureGnEfrom the2H(e&drarr;,e′n&drarr;)1Hreaction in Bates E89‐04 and CEBAF E93‐038. Substantially higher count rates with this new neutron polarimeter reduce the uncertainties inGnE. A description of the new NPOL is given here followed by an outline of the experiment with projections of uncertainties inGnE.

ISSN:0094-243X    

DOI:10.1063/1.48684

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report a measurement of the transverse‐longitudinal asymmetryATL, in3He&drarr;(e&drarr;,e′) quasielastic scattering atQ3=0.14 (GeV/c)2. A straightforward extraction of the neutron electric form factor,GnE, is made using a PWIA model. No meaningful result forGnEis obtained due to large uncertainties and possible final‐state interaction effects. At higherQ2, the determination ofGnEin3He&drarr;(e&drarr;,e′) appears feasible.

ISSN:0094-243X    

DOI:10.1063/1.48633

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Recent experimental evidence on nucleon structure has provided indications that some strange quark matrix elements can be comparable to those involving up and down quarks. The SAMPLE experiment will determine the strange magnetic form factorGsMatQ2=0.1 (GeV/c)2from a measurement of the asymmetry in the scattering of polarized electrons from the proton. The error on the extraction ofGsMis ultimately limited by a theoretical uncertainty—the uncertain electroweak hadronic radiative correction to the axial form factor,RT=1A. To address this issue, the collaboration is also approved to measure the asymmetry in parity‐violating quasielastic electron scattering from the deuteron. The combination of the proton and deuteron measurements will yield a value ofGsMthat is almost completely free of the uncertainty inRT=1A.

ISSN:0094-243X    

DOI:10.1063/1.48594

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new experiment, designed to measure spin‐dependent lepton‐nucleon deep inelastic scattering, is being built on the HERA electron storage ring at DESY, Hamburg. The HERMES experiment will use a windowless internal gas cell of polarized H, D, or3He nuclei as a target for the stored 27 GeV electron (or positron) beam. The pure target, coupled with a high luminosity, will enable greater statistical precision and much smaller systematic errors that has been possible thus far in previous measurements at CERN and SLAC. The construction of the experiment is underway. At the same time, a test experiment is being conducted on the HERA ring, using an unpolarized gas cell and prototypes of the detectors. This report briefly summarizes the results of the test run and the status of the construction of the full experiment.

ISSN:0094-243X    

DOI:10.1063/1.48607

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The nuclear effects in the spin‐dependent structure functionsgD1andbD2are calculated in the relativistic approach based on the Bethe‐Salpeter equation with a realistic meson‐exchange potential. The results of calculations are compared with the non‐relativistic calculations. The problem of extraction of the neutron spin structure function,gn1, from the deuteron data is discussed.

ISSN:0094-243X    

DOI:10.1063/1.48679

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The semi‐inclusive deep inelastic scattering, ep→e′h+X, allows to study new transverse spin distributions and spin dependent fragmentation functions which have never been measured. A polarized target in conjunction with an unpolarized lepton beam is required for this type of experiment. A possible experimental apparatus is described.

ISSN:0094-243X    

DOI:10.1063/1.48609

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

For many years electron scattering has been used as a probe of the structure of hadrons. Polarization observables add the possibility of determining small quantities which are difficult to isolate in other ways. The two parallel sessions summarized here focussed on the use of polarization observables to study electromagnetic properties of the neutron, neutral weak form factors, and transverse polarization in deep‐inelastic scattering. Each tolpic is related to the contributions of sea quarks to the structure of hadrons.

ISSN:0094-243X    

DOI:10.1063/1.48610

出版商:AIP    

年代:1995

数据来源: AIP