Dietrich von Harrach

Large gluon polarization from correlated high-pT hadron pairs in polarized electro-production

Abstract We propose to measure the polarized gluon distribution function ΔG ( η ) at η ≲0.2 via pseudo jet production in polarized fixed target lepton nucleon scattering at typical lepton beam energies of 200 GeV. The measurement of the spin-asymmetry for the production of correlated charge conjugated hadrons of opposite transverse momentum can be directly related to ΔG ( η ) through the photon-gluon fusion process. We also present a numerical analysis of the accuracy which can be obtained for different flavors and kinematics of the observed hadron pair.

Pulse response of thin III/V semiconductor photocathodes

The response time and spin relaxation time of thin unstrained and strained III/V-semiconductor photocathodes installed in sources of polarized electrons have been investigated. Cathodes of various active layer thicknesses have been studied. An upper limit for the response time of a 150 nm thick strained layer photocathode has been found to be 2.5 ps. As a consequence, the average depolarization during transport in the conduction band to the surface is estimated to be lower than 3% and does not contribute substantially to the upper limit of about 80% for the spin polarization of the emitted electrons. The results indicate a high surface recombination velocity of S>1.2×107u2009cm/s at the surface band bending region.

The COMPASS experiment at CERN

Abstract The recently approved COMPASS experiment attempts a measurement of the gluon polarization around η ⋍ 0.1 with a precision of δ(Δ g / g ) ⋍ 0.1. The experiment uses open charm muo-production and large PT hadron pairs to tag the photon-gluon fusion process. COMPASS will also cover a rich spin-physics program in polarized DIS.

The electron-nucleus collider project

Abstract In the context of the discussion about the future physics program of the GSI laboratory the physics potential of an electron-nucleus collider at about s = 1000GeV2 is being explored.

Nucleon structure functions from deep inelastic muon scattering

Abstract Recent experimental results from the CERN NA37 (NMC) experiment on deep inelastic muon scattering on hydrogen and deuterium are presented. Absolute structure functions have been measured at 90 and 280 GeV incident energy covering the kinematical range 0.006 2 2 . The new results help to resolve the severe discrepancies between the data of the previous experiments. In addition data on the structure function ratio F 2 n /F 2 p are reviewed. Evidence for a non-leading twist at × ⪆ 0.20 is extracted from the Q 2 dependence of the structure function ratio. Its effect on the determination of the Gottfried sum rule is discussed.

Spin-polarized electron kinetics under high-intensity picosecond excitation

Spin-polarized electron kinetics is studied by time-resolved polarized photoemission with picosecond resolution. The response time of strained layer photocathodes is found to be in a range of a few picosecond offering an ultrafast response and high spin-polarization of emitted electrons. The studies of the sub-picosecond spin dynamics are facilitated in high-intensity excitation regime when the length of the emission pulse is enlarged due to the dispersion of acceleration time and Coulomb repulsion of the electrons in their flight in the vacuum.

Picosecond time scale spin-polarized electron kinetics in thin semiconductor layers

Time resolved photoemission of highly spin-polarized electrons from thin strained and unstrained GaAsxP1-x films of various thicknesses has been investigated. An upper limit for the response time of a photocathode has been found to be 1 ps for layer thicknesses less than 150 nm. We show that the electron depolarization during the electron extraction to the surface band bending region can be as low as 2% while the losses in the band bending region can contribute to 4% spin relaxation.

ΔGfrom correlated high-pThadron pairs in polarized l−Nscattering

We propose to access the gluon polarization ΔG by measuring the cross section spin-asymmetry in semi-inclusive polarized lepton—nucleon scattering. The photon-gluon fusion sub-process will be tagged by detecting high- p T correlated hadron pairs in the forward hemisphere. Selecting oppositely charged kaon pairs will allow to suppress the background coming from gluon radiation.

ΔG from correlated high-pT hadron pairs in polarized l−N scattering

We propose to access the gluon polarization ΔG by measuring the cross section spin-asymmetry in semi-inclusive polarized lepton—nucleon scattering. The photon-gluon fusion sub-process will be tagged by detecting high- p T correlated hadron pairs in the forward hemisphere. Selecting oppositely charged kaon pairs will allow to suppress the background coming from gluon radiation.