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The STAR endcap electromagnetic calorimeter will provide full azimuthal coverage for high-pT photons, electrons and electromagnetically decaying mesons over the pseudorapidity range 1.086⩽η⩽2.00. It includes a scintillating-strip shower-maximum detector to provide π0/γ discrimination and preshower and postshower layers to aid in distinguishing between electrons and charged hadrons. The triggering capabilities and coverage it offers are crucial for much of the spin physics program to be carried out in polarized proton–proton collisions.

Details concerning the design, fabrication and performance of the STAR Barrel Electromagnetic Calorimeter are presented.

The HERMES experiment is investigating the spin structure of the proton and neutron via deep-inelastic scattering of polarized positrons from polarized nuclear targets. The polarized positrons are provided by the HERA positron storage ring at DESY, Hamburg, Germany. The targets are pure internal gas targets. Data acquisition began in 1995, utilizing a polarized 3 He internal gas target to study the spin structure of the neutron. The target gas was polarized using the metastability-exchange optical-pumping technique and then injected into a cryogenically cooled target cell. The target was designed to operate with either longitudinal or transverse directions of polarization. Operating conditions included polarizations of up to 54% and target thicknesses of 1×10 15 nucleons/cm 2 . In this paper the HERMES polarized 3 He internal gas target is described in detail.

An experiment utilizing a polarized 3He target and other 3-nucleon experiments at the Indiana University Cyclotron Facility are discussed. The 3He(p, pN) reaction has been used to investigate the spin dependent momentum distributions of protons and neutrons in 3He. It was found that with large momentum transfer the PWIA is valid, thus allowing extraction of the distributions directly from the data. A similar experiment is currently under preparation to investigate the spin structure of the deuteron via the 2H(p, pN) reaction. Other experiments will study n-d and p-d breakup spin observables in final state interaction kinematics where intermediate energy Faddeev calculations predict large 3-body force effects.

A cryogenic polarized proton target has been developed for use in nuclear physics experiments. This target makes use of the “spin refrigerator” mechanism to produce the polarization, instead of the microwave pumping used in conventional polarized targets. The design, operating procedures and experience are discussed. While the polarization is low, typically 40% during actual experiments, other advantages make the target useful for certain applications. These include low development and operating costs, magnetic fields as low as 590 G during data acquisition, open geometry, the possibility of large-area targets, and the ability to change the polarization direction on a 10 min time scale.

We describe the first experiment to use a polarized internal gas target and polarized beam in a storage ring. A laser optically pumped polarized He internal gas target has been used with circulating beams of 197-414 MeV polarized protons to carry out an extensive set of measurements of spin dependent scattering. A large acceptance non-magnetic detector system consisting of wie-chambers, scintillators and microstrip detectors was used to detect protons, neutrons, deuterons, and He-3 nuclei from the beam-target interaction. It is demonstrated that these techniques result in low backgrounds (< 1%) due to scattering from species other than the polarized target gas and allow detection of low energy recoiling nuclei. Specific issues such as interfacing the experiment to the storage ring and monitoring the luminosity and polarizations are discussed in detail.

Stored ion beams offer the possibility to use polarized internal targets that consist of a source of polarized atoms in conjunction with a long, narrow, windowless target cell to enhance the target thickness. In this paper, we discuss the effect of such a cell on the performance of the storage ring, based on measurements carried out with the Indiana Cooler. A prototype target cell was constructed and was operated with a controlled flow of H2 target gas in a beam of stored protons. Detection of protons scattered at angles from 4° to 15° in coincidence with the associated recoil particles was used to identify elastic scattering. The results show that the presence of a 25 cm long target cell with a rectangular opening of 6.4 mm by 7.9 mm is compatible with operation of the Cooler ring. This demonstrates the feasibility of an important component of experiments with stored, polarized beams and carrier-free polarized, internal targets.