W.D. Ramsay

Search for double-Λ hypernuclei and the H-dibaryon in the (K−,K+) reaction on 12C

Abstract A search for double- Λ hypernuclei ( 12 ΛΛ Be) and H -dibaryons using the 12 C( K − , K + ) reaction was performed at the BNL-AGS using a high-intensity 1.8 GeV/ c K − beam. A missing-mass analysis below the end point of the quasi-free Ξ − production was used to investigate these S =−2 systems. The upper limit obtained for the forward-angle cross section of 12 ΛΛ Be production is 6 to 10 nb/sr. This is the first search for the direct production of double- Λ hypernuclei to reach the sensitivity required to observe the signal predicted by theoretical calculations. For the H -production cross section, we have obtained an upper limit in the range of a few nb/sr to 10 nb/sr for the H mass below 2100 MeV/ c 2 . This upper limit is the most sensitive H search result to date for a tightly bound H .

Transverse beam spin asymmetries in forward-angle elastic electron-proton scattering

We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A(n) provides a direct probe of the imaginary component of the 2gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.

A current mode detector array for γ-ray asymmetry measurements

Abstract We have built a CsI(Tl) γ -ray detector array for the NPDGamma experiment to search for a small parity-violating directional asymmetry in the angular distribution of 2.2xa0MeV γ -rays from the capture of polarized cold neutrons by protons with a sensitivity of several ppb. The weak pion–nucleon coupling constant can be determined from this asymmetry. The small size of the asymmetry requires a high cold neutron flux, control of systematic errors at the ppb level, and the use of current mode γ -ray detection with vacuum photodiodes and low-noise solid-state preamplifiers. The average detector photoelectron yield was determined to be 1300 photoelectrons per MeV. The RMS width seen in the measurement is therefore dominated by the fluctuations in the number of γ -rays absorbed in the detector (counting statistics) rather than the intrinsic detector noise. The detectors were tested for noise performance, sensitivity to magnetic fields, pedestal stability and cosmic background. False asymmetries due to gain changes and electronic pickup in the detector system were measured to be consistent with zero to an accuracy of 10 - 9 in a few hours. We report on the design, operating criteria, and the results of measurements performed to test the detector array.

A time-of-flight array for 1 to 2 GeV/c particles

A time-of-flight detector array has been developed for an experiment searching for the strangeness −2 H-particle. The array consists of 40 logs of plastic scintillator with dimensions 2.00 × 0.085 × 0.050 m3. The photomultiplier tubes are coupled to the scintillators without the use of light guides, and the mounting of the bars is designed for easy adjustment and servicing. The average intrinsic time resolution was found to be 110 ps σ.

Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasielastic Electron-Deuteron Scattering

We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasielastic scattering on the deuteron, at backward angles (lab scattering angle of 108°) for Q² = 0.22 GeV²/c² and 0.63 GeV²/c² at beam energies of 362 and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single-photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (πN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasistatic deuterium approximation, and is also in agreement with theory.

A beam intensity profile monitor based on secondary electron emission

Two dual function intensity profile monitors have been designed for a measurement of parity violation in p-p scattering at about 230 MeV using longitudinally polarized protons. Each device contains a set of split secondary electron emission (SEM) foils to determine the median of the beam current distribution (in x and y). The split foils, coupled through servoamplifiers and operational amplifiers to upstream aircore steering magnets, have demonstrated the ability to hold the beam position stable to ±5 μm for beam position fluctuations up to 1000 Hz. These monitors also contain a set of foil strip planes giving information on the intensity distribution projected onto the two orthogonal axes, x and y. Data were acquired using 0.008 mm thick, 0.90 mm wide aluminum foil strips at 1.00 mm centers. The foil strip planes were able to determine the beam centroid to within ±3 μm after one hour of data taking with a 100 nA, 15 mm FWHM Gaussian beam.

Proton target polarization measured with a polarized neutron beam at 477 MeV

Abstract The polarization of a proton target is determined with elastic neutron-proton scattering at 477 MeV. The results agree well with the nuclear magnetic resonance measurements at the error level of 4%.

Parity violation in P‐P scattering at TRIUMF

The TRIUMPF experiment 497 which will measure the (weak) parity violating component of the nucleon‐nucleon interaction with proton‐proton quasi‐elastic scattering at 223 MeV is described. The longitudinal analyzing power Az=(σ+−σ−)/(σ++σ−) where σ+ and σ− are the scattering cross sections for positive and negative beam helicity, respectively, with an expected precision of ±2×10−8. (AIP)

Parity violation in p-p scattering

Abstract An outline is given of an experiment to measure parity violation in p-p scattering at 230 MeV at TRIUMF. The parity-violating longitudinal analysing power A z will be measured to a precision of 2×10 −8 and will isolate the parity-violating 3 P 2 − 1 D 2 partial wave amplitude.

Measurement of the Parity-Violating Asymmetry in Inclusive Electroproduction of π- near the Δ0 Resonance

The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2u2009u2009ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03u2009u2009ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.