Narrow Results

We present preliminary data for the T and F asymmetries in η photoproduction from the proton, along with comparisons to theoretical predictions. The data used in the present analysis were taken using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab, a cryogenic target which utilized transversely polarized protons in a butanol target, and incident tagged photons with energy between 0.62 and 2.93 GeV.

Polarization observables are vital for disentangling overlapping resonances in the baryon spectrum. Extensive data have been collected at Jefferson Lab in Hall B with circularly and linearly polarized tagged photon beam incident on longitudinally polarized protons provided by the Frozen Spin Target (FROST). The focus of the described work is on η photoproduction, which acts as an "isospin filter", isolating the N*(I = 1/2) resonances. Preliminary results for the double-polarization observables E and G are presented. There are currently no data on these in the world database for η photoproduction.

One of the continuing puzzles in QCD is the origin of the nucleon spin. All of the existing experimental data suggest that the contributions from the quark and gluon spins account only for about 50% of the nucleon spin. In order to account for the remaining 50%, one has to include the orbital angular momentum of the quarks and gluons. One way to establish if quarks carry significant angular momentum, is to perform a measurement of the Sivers function, which describes the correlation of the spin direction of the nucleon with the transverse momentum of the quark. We will describe the E1039 experiment at Fermilab, which will measure the Sivers asymmetry of the sea quarks via the Drell-Yan process, using a 120 GeV unpolarized proton beam on a transversely polarized NH₃ target.

The method of experiments with internal targets in the storage ring was proposed at the moment of creation of the first storage ring of charged particles. This method has demonstrated dramatic advances during the last 50 years. The most clearly visible progress can be seen in experiments with polarized gas targets. In this report we shall review: (a) the experiments on nuclear physics in the storage rings on the measure of polarization observables in different reactions with electron/positron and proton/deuteron beams, (b) the use of polarized gas targets in the storage ring for polarimetry of the circulated beams. The present status of the activity in this field of experimental physics is given.

Roles of spin-dependent interactions in unstable nuclei have been investigated via the direct reaction of radioactive ions with a solid spin-polarized proton target. The target has a unique advantage of a high polarization of 20–30% under low magnetic field of 0.1 T and at a high temperature of 100 K, which allow us to detect recoil protons with good angular resolution. Present status of on-going experimental studies at intermediate energies, such as proton elastic scattering and ($p,2p$) knockout reaction, and new physics opportunities expected with low-energy RI beams are overviewed.

We plan to have hadron photoproduction experiments by using polarized photon beams at the laser-electron photon facility (LEPS) at SPring-8. We develope a HD (Hydrogen-Deuteride) target as a polarized target for future experiments using both the polarized photon beams and the polarized target since 2005.¹ The HD polarized target will be prodeced at RCNP (Osaka University) and installed in the LEPS facility. Such a double polarization experiment is expected to give important information to investigate the nucleon hidden structure and hadron photoproduction dynamics. We report on the present status of the developement of the polarzed HD target at RCNP.

Polarized targets, both solid and gas, are in ever-increasing demand for nuclear scattering experiments. On top of this, the technology for producing these targets is now being applied in other fields, such as materials science and medical research. In this article the author will review recent advances that have been made in the arena of solid polarized targets.

Proton polarization will find new applications if it is achieved in a low magnetic field and at high temperature. Use as a polarized proton target in studies of neutron-rich unstable nuclei is one of the fascinating examples. A polarized solid proton target based on electron polarization in photo-excited triplet states of aromatic molecule has been constructed at the Center for Nuclear Study (CNS), at the University of Tokyo. The target works in a low magnetic field of 0.1 T and at high temperature of 100 K and has been applied to radioactive isotope beam experiments at RIPS at RIKEN.

The proton polarization is obtained at high temperature and in low magnetic field by means of photo-excited triplet state of aromatic molecules. For this method, we use a continuous wave Ar-ion laser which is pulsed by an optical chopper. In this system, the photon number is the bottleneck in achieving higher polarization. The proton polarization rate was measured by changing a duty from 5 % to 50 % and a reputation frequency from 0.75 kHz to 10.6 kHz. For a duty factor of 50 % and a repetition frequency of 10.6 kHz, the polarization rate can be a factor five larger than that for the old setting.

A Polarized Internal gas Target (PIT) has been developed for the ANKE spectrometer at COSY. After its first installation at the ANKE target position in summer 2005, commissioning studies were carried out. In March 2006, the first single polarization measurements with the polarized hydrogen beam from an Atomic Beam Source (ABS) were performed. The beam was injected into a storage cell made from aluminum foil. The data analysis showed that the events from the extended gas target can be clearly identified in the ANKE forward detection system. Using unpolarized nitrogen, the background from the cell walls could be determined as well. The thickness of the gas in the storage cell with the hydrogen atoms in hyperfinestate |1〉 was measured as 2 × 10¹³ atoms/cm². The ABS jet target thickness was (1.5 ± 0.1) × 10¹¹ atoms/cm². In November 2006, the commissioning of a Silicon Tracking Telescope (STT) was successfully finished. In the following beam time in January 2007, a new storage cell made from aluminum coated with teflon was used together with the STT. The Lamb-shift polarimeter (LSP) was mounted below the target chamber to allow online tuning of the transition units and monitoring of the ABS jet polarization. A first double-polarized experiment was performed in January 2007. The results will be presented.

Polarized ³He from metastability exchange optical pumping is used for various double polarized experiments at the MAinz MIcrotron (MAMI). More than 70 % initial target polarization has been obtained at the experimental area. Besides the description and the performance of the target for the electron beam, details of the newly developed target for the photon beam inside the Crystal Ball (CB) detector will be given.

Transverse spin and transverse momentum distribution functions of the constituents of the nucleon are a crucial input for a complete description of the nucleon. COMPASS measured such for longitudinally and transversely polarized deuterons and protons. In the following we will focus on recent results from the 2007 transverse proton data and on the results for unpolarized deuterons.