RECENT RESULTS FROM HERMES ON gp 1 AND POLARISEDQUARK

Preliminary results are reported from the HERMES experiment at HERA/DESY for the spin asymmetry g 1 =F 1 and the polarised structure function g p 1 of the proton and for an extraction of polarised quark-distributions from a combination of Helium-3 and Hydrogen data The HERMES experiment at DESY uses the HERA 27.5 GeV polarised positron beam in combination with a polarised internal gas target to study the spin structure of the nucleon via inclusive and semi-inclusive deep inelastic lepton-nucleon scattering. Polarised atomic gas targets have the advantage of high nuclear polarisation (p T 0:9 for hydrogen and deuterium) with no dilution by unpolarisable nucleons. The HERMES polarised gas target is generated by injecting a nuclear polarised atomic beam of hydrogen (H), deuterium (D) or helium-3 (3 He) from a polarised source into a tubular 40-cm-long open ended storage cell which connnes the atoms in the region of the circulating positron beam. In 1995, the commissioning year of the experiment, 3 He was used as a polarised target, with a target areal density of 1:0 10 15 nucleons/cm 2. From the data (2.7 million deep inelastic events after geometrical and kinematical cuts) the spin asymmetry A n 1 and the polarised structure function g n 1 of the neutron have been determined 1. In 1996 and 1997 data were taken with a polarised H target with an areal target density of 7 10 13 nucleons/cm 2 , limited by the atomic beam ux delivered by the HERMES atomic beam source (ABS). The ABS 2 , the storage cell technique 5 , the target polarimetry 3 and the HERMES spectrometer 8 are discussed in detail elsewhere. In this contribution preliminary results are reported for g p 1 =F p 1 and g p 1 from the '97 H data and for the polarised quark distributions from a combination of the '95 3 He data and the '96 H data. Detailed studies of the target polarisation and the fraction of molecules, generated by recombination on the storage cell walls, have been performed as a function of several parameters like cell temperature and static holding eld and compared to extensive Monte Carlo simulations and rate equation calculations. All these studies resulted in a rather good understanding of the target polar