The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns. K: Beam-line instrumentation (beam position and profile monitors, beam-intensity monitors, bunch length monitors); Spectrometers; Gas systems and purification; Neutrino detectors A X P : 2103.04755Neutrino-mass mode. This is the standard mode of operation to continually adjust the retarding voltage of the MS in the range of [ 0 − 40 eV; 0 + 50 eV] while tritium is in the system. This scanning range can be adjusted if required. The voltage and the time spent at each setting are defined by the Measurement Time Distribution (MTD) (figure 3). A typical run at a given voltage lasts between 20 s and 600 s; a full scan of the energy range given above takes about 2 h. Of these standard neutrino-mass runs, a small portion will be dedicated to sterile neutrino searches. These searches involve scanning much farther (order of keV) below the endpoint 0 .Calibration mode. To check the long-term system stability, calibration measurements are done regularly. The neutrino-mass mode is suspended for the duration of these measurement:• An energy calibration of the FPD (section 6) is performed weekly, which requires closing off the detector system from the main beamline for about 4 h.• The offset and the gain correction factor of the low-voltage readout in the high-voltage measurement chain needs to be calibrated based on standard reference sources (section 5.3.4). This requires stopping the precision monitoring of the MS retarding potential twice per week for about 0.5 h each.

At the tagged photon facility PHOENICS at the Bonn accelerator ELSA a measurement of the target asymmetry of the reaction gp ! ph from threshold to 1150 MeV has been performed. Simultaneously the reaction gp ! pp 0 has been measured in the first resonance region. Results are presented for both reactions. The target asymmetry data are suited to put considerable constraints on the model parameters used for the theoretical description of meson photoproduction. [S0031-9007(98)06654-X] PACS numbers: 25.20.Lj, 13.60.Le, 14.20.Gk, 24.70. + s Meson production from nucleons is a major tool for the investigation of nucleon resonances. The technical development of tagged photon beams at high duty cycle accelerators has initiated a series of high precision experiments dedicated to the study of meson photoproduction. A lot of data have been obtained for the production of pions, and theoretical models have been developed which describe the data by resonance excitation and Born terms. The application of these models to another meson provides a good test of the assumptions and the predictive power. Moreover, a model which covers different meson production channels leads to a consistent picture of meson nucleon dynamics.In the case of h photoproduction some special aspects occur. The eta has isospin I 0 and, accordingly, only I 1͞2 nucleon resonances N ‫ء‬ can be excited. Further, a resonance state has several decay channels with different decay probabilities. This offers the possibility that a resonance state is almost hidden in pion production while it is rather prominent in eta photoproduction, as is the case for the S 11 ͑1535͒ [1]. The dominance of the S 11 ͑1535͒ in the reaction gN ! hN has been seen in the total and in the differential cross section in the threshold region [2]. Consequently, the eta channel is well suited for the precise determination of the S 11 ͑1535͒ resonance parameters. The contribution of weakly excited resonances to the cross section is only small and is hard to disentangle [3]. One example is the resonance D 13 ͑1520͒ which might be the source of an observed small anisotropy of the gp ! hp cross section [1]. Here, polarization observables offer an enhanced sensitivity because they contain bilinear products of partial waves, respectively, of multipoles. For the D 13 ͑1520͒, an observable such as the target asymmetry, which contains an interference of the strong S 11 ͑1535͒ with the weak D 13 ͑1520͒, is very advantageous.The experiment presented here is part of the extended program of h photoproduction that has been carried out at the PHOENICS facility at the Bonn accelerator ELSA. It included measurements of differential and total cross sections on the proton, neutron, deuteron, and nitrogen over a wide kinematic range [4,5]. In this framework the reaction gp ! ph has been investigated using a polarized proton target.The electron beam extracted from ELSA was used to produce a photon beam by bremsstrahlung at a thin radiator. The tagging system in the PHOENICS area [6] determined the energy and fl...

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The 1996 data taking of the SMC experiment used polarized protons to measure the spin dependent structure function g 1 of the proton. Three liters of solid granular ammonia were irradiated at the Bonn electron linac in order to create the paramagnetic radicals which are needed for polarizing the protons. Proton polarizations of (90 2:5) % were routinely reached. An analysis based on a theoretical line-shape for spin-1 systems with large quadrupolar broadening was developed which allowed the nitrogen polarization in the ammonia to be determined with a 10 % relative error. The measured quadrupolar coupling constant of 14 N agrees well with earlier extrapolated values. The polarization of the nitrogen nuclei was measured as a function of the proton polarization in order to provide a test of the equal spin temperature (EST) hypothesis. It was found to be closely valid under the dynamic nuclear polarization conditions with which the protons are polarized. Large deviations from EST could be induced by cross relaxing the proton and nitrogen spin systems at low elds. Nitrogen polarizations up to 40% were reached by these means.