T. Iwata

A new frozen-spin target for 4π particle detection

Abstract A new frozen-spin target has been developed, that allows the detection of emitted particles in an angular acceptance of almost 4π in the laboratory frame. The central part of this new target represents a 3He/4He dilution refrigerator that is installed horizontally along the beam axis. The refrigerator includes an internal superconducting holding coil to maintain the nucleon polarization in the frozen-spin mode longitudinally to the beam. The design of the dilution refrigerator and the use of an internal holding coil enabled for the first time the measurement of a spin-dependent total cross section in combination with a polarized solid state target. This new frozen-spin target was used successfully to measure the helicity asymmetry of the total photoabsorption cross-section at the Mainz accelerator facility MAMI. This experiment has been performed in order to verify for the first time the GDH sum rule.

First results of the large COMPASS 6LiD polarized target

The COMPASS (NA58) experiment at CERN operates with a large solid polarized target (PT) to study the spin structure of the nucleon. The COMPASS PT system started its operation with the target material 6 LiD in 2001. Deuteron polarizations of þ54:2% and � 47:1% were achieved in a 3 He= 4 He dilution refrigerator at a magnetic field of 2: 5T : The equal spin temperature (EST) concept was found to hold among the deuteron, the 6 Li and the 7 Li nuclei during the dynamic nuclear polarization (DNP) process. The agreement with the EST concept allows the permanent monitoring of only one nuclear species by the nuclear magnetic resonance (NMR) method. r 2003 Elsevier Science B.V. All rights reserved.

Study of the ηπ− system in the π−p reaction at 6.3 GeV/c

Abstract Data of the ηπ− system were obtained in the reaction π−p → ηπ−p at 6.3 GeV/c beam momentum. About 17 k events of ηπ− were collected in the mass range 0.8 ⩽ Mηπ- ⩽ 1.8 GeV/c2 and in the range of the momentum transfer squared 0.075 ⩽ |t′| ⩽ 0.60 (GeV/c)2. A large forward-backward asymmetry was observed around 1.3 GeV/c2 in the Gottfried-Jackson frame of the ηπ− system. A partial wave analysis of the data was performed. A peak of the D+ wave attributed to a2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/c2 in the P+ wave.

Measurement of the tensor analyzing power Ayy in inclusive breakup of 9 GeV/c deuterons on carbon at large transverse momenta of protons

Abstract The tensor analyzing power A yy in inclusive breakup of 9 GeV/c deuterons on carbon has been measured at the detected proton angle of 85 mr. The analyzing power remains positive at the highest measured momentum of the proton in definite contradiction with the predictions of the existing models. The vector analyzing power A y has been obtained simultaneously with A yy .

Vector resonances around 1.6 GeV of the ηπ+π− system in the π−p charge exchange reaction at 8.95 GeVc

Abstract High statistics data of the ηππ system in π − p → ηπ + π − n were obtained. A partial wave analysis was performed in the mass region between 1.37 and 1.85 GeV. Resonant structures were observed in the IJ PC = 11 −− wave around 1.6 GeV and in 13 −− around 1.7 GeV. The structure in 11 −− was fitted with a single Breit-Wigner and also fitted with two Breit-Wigners. The result suggests the possible existence of two vector resonances around 1.6 GeV. The structure in 13 −− is considered to be the π 3 (1690).

Study on the ηπ+π− system in the π−p charge exchange reaction at 8.95 GeV/c

Abstract A further study on the ηππ system in the charge exchange reaction π−p→ηπ+π−n at 8.95 GeV/c has been performed at KEK. A partial wave analysis was done for three t′ regions, 0–0.05, 0.05–0.20 and 0.20–0.60 (GeV/c)2 in the mass range between 1.155 and 1.555 GeV. The IJpc=00−+ wave via a0(980)π intermediate state shows clear peaks of η(1295) and η(1400) in the third t′ region. The state η(1400) shows a mass value of 1388±4 MeV. The 01++ wave via a0π shows also a clear peak of f1 (1285) in the third t′ region. The higher mass region between 1.51 and 1.83 GeV was also studied for the same three t′ regions. No I=0 pseudoscalar state is seen in the analysis.

Helicity dependence of the reaction in the second resonance region

The helicity dependence of the total cross section for the reaction has been measured for the first time at incident photon energies from 400 to 800xa0MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D13 resonance.The helicity dependence of the total cross section for the (γ) over right arrow(p) over right arrownpi(+) pi(0) reaction has been measured for the first time at incident photon energies from 400 to 800 MeV The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D-13 resonance

Test of phototube bases for high counting rates

Abstract We report on test measurements of the counting efficiency using a newly developed miniature photomultiplier R1635. Two methods of the voltage stabilization have been used: (1) the emitter follower type by NPN transistors and (2) the booster type in which the constant dynode voltage is supplied from a separate power supply. The test was performed by using a light emitting diode and 10 MeV protons from a tandem accelerator. Both methods of voltage stabilization have shown good results. A counting efficiency of about 100% could be obtained up to a flux of 2×10 6 particles/s (pps) and 85% at 10 7 pps.

Fragmentation of tensor polarized deuterons into cumulative pions

Abstract The tensor analyzing power T20 of the reaction d +A→π − (0°)+X has been measured in the fragmentation of 9 GeV tensor polarized deuterons into pions with momenta from 3.5 to 5.3 GeV/c on hydrogen, beryllium and carbon targets. This kinematic range corresponds to the region of cumulative hadron production with the cumulative variable xc from 1.08 to 1.76. The values of T20 have been found to be small and consistent with positive values. This contradicts the predictions based on a direct mechanism assuming NN collision between a high momentum nucleon in the deuteron and a target nucleon (NN→NNπ).

Tensor analyzing power T20 for cumulative pion production from deuterons in the GeV energy region

Abstract The tensor analyzing power T 20 for the reaction d ↑ + 12 C → π ± (0°) + X has been measured with a polarized deuteron beam from 6.2 to 9.0 GeV/ c at a pion momentum3.0 GeV/ c . This experiment is focused on “cumulatively produced pions”, which are produced beyond the kinematically allowed limit for free nucleon-nucleon collisions. The measured values of T 20 turn out to be close to zero. They are in disagreement with the results of our impulse approximation calculation which is based on a single NN → πNN interaction and takes into account the internal motion of nucleons in the deuteron. Possible explanations of the result are discussed.