Search

We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries $B_n$ on $^{12}$C and $^{27}$Al, obtained with an electron beam polarized transverse to its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of $B_n$ on $^{12}$C and provide a first measurement on $^{27}$Al. The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average lab scattering angle for both targets was 7.7 degrees, and the average $Q^2$ for both targets was 0.02437 GeV$^2$ (Q=0.1561 GeV). The asymmetries are $B_n$ = -10.68 $\pm$ 0.90 stat) $\pm$ 0.57 (syst) ppm for $^{12}$C and $B_n$ = -12.16 $\pm$ 0.58 (stat) $\pm$ 0.62 (syst) ppm for $^{27}$Al. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by Z/A, the Q-dependence of all the far-forward angle (theta < 10 degrees) data from $^{1}$H to $^{27}$Al can be described by the same slope out to $Q \approx 0.35$ GeV. Larger-angle data from other experiments in the same Q range are consistent with a slope about twice as steep.

In May 2012, the $Q^{p}_{\rm Weak}$ collaboration completed a two year measurement program to determine the weak charge of the proton ${Q^{p}_W} = ( 1 - 4\sin^2{\theta_{W}})$ at the Thomas Jefferson National Accelerator Facility (TJNAF). The experiment was designed to produce a 4.0 % measurement of the weak charge, via a 2.5 % measurement of the parity violating asymmetry in the number of elastically scattered 1.165 GeV electrons from protons, at forward angles. At the proposed precision, the experiment would produce a 0.3 % measurement of the weak mixing angle at a momentum transfer of Q 2 = 0.026 GeV2, making it the most precise stand alone measurement of the weak mixing angle at low momentum transfer. In combination with other parity measurements, $Q^{p}_{\rm Weak}$ will also provide a high precision determination of the weak charges of the up and down quarks. At the proposed precision, a significant deviation from the Standard Model prediction could be a signal of new physics at mass scales up to ≃ 6 TeV, whereas agreement would place new and significant constraints on possible Standard Model extensions at mass scales up to ≃ 2 TeV. This paper provides an overview of the physics and the experiment, as well as a brief look at some preliminary diagnostic and analysis data.

The Q-weak experiment at Jefferson Laboratory measured the parity violating asymmetry (A P V ) in elastic electron-proton scattering at small momentum transfer squared (Q 2=0.025 (G e V/c)2), with the aim of extracting the proton’s weak charge ( ${Q^p_W}$ ) to an accuracy of 5 %. As one of the major uncertainty contribution sources to ${Q^p_W}$ , Q 2 needs to be determined to ∼1 % so as to reach the proposed experimental precision. For this purpose, two sets of high resolution tracking chambers were employed in the experiment, to measure tracks before and after the magnetic spectrometer. Data collected by the tracking system were then reconstructed with dedicated software into individual electron trajectories for experimental kinematics determination. The Q-weak kinematics and the analysis scheme for tracking data are briefly described here. The sources that contribute to the uncertainty of Q 2 are discussed, and the current analysis status is reported.

The Jefferson Lab Q weak experiment determined the weak charge of the proton by measuring the parity-violating elastic scattering asymmetry of longitudinally polarized electrons from an unpolarized liquid hydrogen target at small momentum transfer. A custom apparatus was designed for this experiment to meet the technical challenges presented by the smallest and most precise e → p asymmetry ever measured. Technical milestones were achieved at Jefferson Lab in target power, beam current, beam helicity reversal rate, polarimetry, detected rates, and control of helicity-correlated beam properties. The experiment employed 180 μA of 89% longitudinally polarized electrons whose helicity was reversed 960 times per second. The electrons were accelerated to 1.16 GeV and directed to a beamline with extensive instrumentation to measure helicity-correlated beam properties that can induce false asymmetries. Moller and Compton polarimetry were used to measure the electron beam polarization to better than 1%. The electron beam was incident on a 34.4 cm liquid hydrogen target. After passing through a triple collimator system, scattered electrons between 5.8° and 11.6° were bent in the toroidal magnetic field of a resistive copper-coil magnet. The electrons inside this acceptance were focused onto eight fused silica Cherenkov detectors arrayed symmetrically around the beam axis. A total scattered electron rate of about 7 GHz was incident on the detector array. The detectors were read out in integrating mode by custom-built low-noise pre-amplifiers and 18-bit sampling ADC modules. The momentum transfer Q 2 =0.025 GeV 2 was determined using dedicated low-current ( ~ 100 pA ) measurements with a set of drift chambers before (and a set of drift chambers and trigger scintillation counters after) the toroidal magnet.

The Q weak experiment, which took data at Jefferson Lab in the period 2010 - 2012, will precisely determine the weak charge of the proton by measuring the parity-violating asymmetry in elastic e-p scattering at 1.1 GeV using a longitudinally polarized electron beam and a liquid hydrogen target at a low momentum transfer of Q 2 = 0.025 (GeV/c)2 . The weak charge of the proton is predicted by the Standard Model and any significant deviation would indicate physics beyond the Standard Model. The technical challenges and experimental apparatus for measuring the weak charge of the proton will be discussed, as well as the method of extracting the weak charge of the proton. The results from a small subset of the data, that has been published, will also be presented. Furthermore an update will be given of the current status of the data analysis.

A subset of results from the recently completed Jefferson Lab Qweak experiment are reported. This experiment, sensitive to physics beyond the Standard Model, exploits the small parity-violating asymmetry in elastic ep scattering to provide the first determination of the protons weak charge Qweak(p). The experiment employed a 180 uA longitudinally polarized 1.16 GeV electron beam on a 35 cm long liquid hydrogen target. Scattered electrons corresponding to Q2 of 0.025 GeV2 were detected in eight Cerenkov detectors arrayed symmetrically around the beam axis. The goals of the experiment were to provide a measure of Qweak(p) to 4.2 percent (combined statistical and systematic error), which implies a measure of sin2(thetaw) at the level of 0.3 percent, and to help constrain the vector weak quark charges C1u and C1d. The experimental method is described, with particular focus on the challenges associated with the worlds highest power LH2 target. The new constraints on C1u and C1d provided by the subset of the experiments data analyzed to date will also be shown, together with the extracted weak charge of the neutron., Comment: 8 pages, 4 figures, INPC2013

Properties of the TRIUMF neutron beam (4A2) are presented and compared with a Monte Carlo prediction. The beam intensity profile, energy spectrum and polarization are predicted taking into account the beamline geometry, energy losses in the LD2 production target, the properties of the pd → npp reaction, and the scattering of neutrons from the collimator walls. The results allow for improved corrections to systematic errors in a number of TRIUMF neutron experiments.

We have measured the relative differential cross section and spin observables for the reaction {ital np}{r_arrow}{ital pp}{pi}{sup {minus}} at 443 MeV. Our measurements have been compared with predictions of the model of Kloet and Lomon. Some of the variables show marked disagreement with predictions; for other variables there is surprisingly good agreement.

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 Δ^0 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 +5.2 ppm. The measurement performed in this work leads to A_γ^-=-0.36±1.06±0.37±0.03 ppm (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.

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 quasi-elastic scattering on the deuteron, at backward angles (lab scattering angle of 108 degrees) for Q2 = 0.22 GeV^2/c^2 and 0.63 GeV^2/c^2 at beam energies of 362 MeV 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 (piN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasi-static deuterium approximation, and is also in agreement with theory.

In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed., Comment: Submitted to Nuclear Instruments and Methods

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.

We have measured parity violating asymmetries in elastic electron-proton and quasi-elastic electrondeuteron scattering at backward electron angle. These measurements have been done at two momentum transfers : Q2 = 0.22 and 0.63 (GeV/c)2 . Together with our previous forward angle measurement [1], we can extract strange quark contributions to the electromagnetic form factors of the nucleon, as well as nucleon axial form factor coming from the neutral weak interaction. The results indicate a strange quark magnetic contribution close to zero at these Q2 , and a possible non zero strange quark electric contribution for the high Q2 . The first Q2 behavior measurement of the nucleon axial form factor in elastic electron scattering shows a good agreement with radiative corrections calculated at Q2 = 0 and with a dipole form using the axial mass determined in neutrino scattering.

We have measured parity-violating asymmetries in elastic electron-proton and quasi-elastic electron-deuteron scattering at Q^2 = 0.22 and 0.63 GeV^2. They are sensitive to strange quark contributions to currents in the nucleon, and to the nucleon axial current. The results indicate strange quark contributions of < 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. We also present the first measurement of anapole moment effects in the axial current at these four-momentum transfers., 5 pages, 2 figures, changed references, typo, and content

A recent experiment, measuring the spin correlation parameter Ann in neutron-proton elastic scattering to a precision of ±0.03 at several energies in the range 200 to 500 MeV, required the polarization of the proton frozen-spin target used in the experiment to be known to an accuracy of ±2%. The calibration of the polarization of the frozen-spin target was accomplished through an experiment interleaved with the Ann experiment. An unpolarized proton beam, of an intensity comparable to the intensity of the neutron beam in the Ann experiment, was scattered at 24° (lab.) from the frozen-spin target at energies of 468 and 501 MeV. From the measured left-right asymmetries and knowledge of the proton-proton analyzing powers, Ay(24°, 468 MeV) = 0.4087±0.0060 and Ay(24°, 501 MeV) = 0.4204±0.0059, the target polarizations could be deduced. The weighted average of the ratios of the target polarization deduced in the scattering experiment and obtained from nuclear magnetic resonance measurements was found to be Pt(scattering)/Pt(NMR) = 0.962±0.008(stat)±0.021(sys)±0.014(sys) at 468 MeV and 0.950±0.005(stat)±0.020(sys)±0.013(sys) at 501 MeV. By dividing the target cell holding the butanol beads, as illuminated by the incident proton beam, in three parts (top, middle, and bottom), a determination of the average polarization for each of the three parts was made. A clear decrease of the polarization going from the top to the bottom of the target cell was found.

We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 = 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 2-gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments., 5 pages, 3 figures, submitted to Physical Review Letters; shortened to meet PRL length limit, clarified some text after referee's comments

Elastic and inelastic scattering of unpolarized and polarized protons by {sup 40}Ar nuclei for incident energies between 20 and 50 MeV has been studied by reanalyzing experimental scattering spectra for the 2{sup +}(1.46 MeV) and 3{sup -}(3.68 MeV) levels in the angular range 30 degree sign -160 degree sign for incident protons of energies of 25.1, 32.5, and 40.7 MeV. An isospin dependent soft-rotator coupled-channels optical model with the potential containing a dispersive term with a nonlocal contribution is used to analyze the data.

TRIUMF experiment 497 has measured the parity violating longitudinal analyzing power, A_z, in pp elastic scattering at 221.3 MeV incident proton energy. This paper includes details of the corrections, some of magnitude comparable to A_z itself, required to arrive at the final result. The largest correction was for the effects of first moments of transverse polarization. The addition of the result, A_z=(0.84 \pm 0.29 (stat.) \pm 0.17 (syst.)) \times 10^{-7}, to the pp parity violation experimental data base greatly improves the experimental constraints on the weak meson-nucleon coupling constants h^{pp}_\rho and h^{pp}_\omega, and has implications for the interpretation of electron parity violation experiments., Comment: 17 pages RevTeX, 14 PostScript figures. Revised version with additions suggested by Phys. Rev. C

TRIUMF experiment E497 is a study of parity violation in pp scattering at an energy where the leading term in the analyzing power is expected to vanish, thus measuring a unique combination of weak-interaction flavour conserving terms. It is desired to reach a level of sensitivity of 2x10^-8 in both statistical and systematic errors. The leading systematic errors depend on transverse polarization components and, at least, the first moment of transverse polarization. A novel polarimeter that measures profiles of both transverse components of polarization as a function of position is described., 19 pages LaTeX, 10 PostScript figures. To appear in Nuclear Instruments and Methods in Physics Research, Section A

Parity violation in proton-proton elastic scattering provides a unique window on the hadronic weak interaction. At low and intermediate energies, the coupling constants of an effective meson exchange model provide an appropriate parametrization. Measurements at different beam energies permit the lowest partial wave amplitudes to be determined in a model independent framework. The TRIUMF cyclotron provides a unique opportunity to measure the 3P2−1D2 contribution to proton-proton parity violation at 221 MeV beam energy. This partial wave in turn isolates the weak ρ meson exchange contribution, which is only known to within a factor of 2 from theoretical estimates. An experiment underway for many years at TRIUMF completed data taking in 1999, and the analysis is now nearing completion. Preliminary results, based on half of the acquired data sample, are consistent with the meson exchange model prediction at this beam energy.

Experimental data for deuteron breakup by protons in collinear geometry at 25.00 MeV are compared with the predictions of rigorous Faddeev calculations using the Paris potential and with those of the Doleschall code. The Paris potential significantly underdetermines the breakup cross section in collinear geometry. The explanation for this discrepancy is not entirely clear at this time.

Measurements of parity-violating longitudinal analyzing powers (normalized asymmetries) in polarized proton-proton scattering provide a unique window on the interplay between the weak and strong interactions between and within hadrons. Several new proton-proton parity violation experiments are presently either being performed or are being prepared for execution in the near future: at TRIUMF at 221 MeV and 450 MeV and at COSY (Kernforschungsanlage Juelich) at 230 MeV and near 1.3 GeV. These experiments are intended to provide stringent constraints on the set of six effective weak meson-nucleon coupling constants, which characterize the weak interaction between hadrons in the energy domain where meson exchange models provide an appropriate description. The 221 MeV is unique in that it selects a single transition amplitude (3P2-1D2) and consequently constrains the weak meson-nucleon coupling constant h_rho{pp}. The TRIUMF 221 MeV proton-proton parity violation experiment is described in some detail. A preliminary result for the longitudinal analyzing power is Az = (1.1 +/-0.4 +/-0.4) x 10^-7. Further proton-proton parity violation experiments are commented on. The anomaly at 6 GeV/c requires that a new multi-GeV proton-proton parity violation experiment be performed., Comment: 13 Pages LaTeX, 5 PostScript figures, uses espcrc1.sty. Invited talk at QULEN97, International Conference on Quark Lepton Nuclear Physics -- Nonperturbative QCD Hadron Physics & Electroweak Nuclear Processes --, Osaka, Japan May 20--23, 1997

Precision measurements of parity violation in proton-proton scattering impose very stringent requirements on the polarized beam quality. The contributions of random and spin-correlated beam modulations to the experimental accuracy are discussed. This analysis for the TRIUMF optically pumped polarized ion source and H− ion cyclotron with multiturn extraction is quite different from previous experiments at LAMPF, PSI and Bonn. The required beam quality is obtained by combining efforts at every stage: reduction of modulations at the source, minimization of transfer coefficients in the injection line and cyclotron, feedback systems for injected and accelerated beam stabilization, precision measurements of the beam energy, intensity and polarization profiles, and reduction of the sensitivities of the experimental apparatus to these modulations.

An experiment (E497) is underway at TRIUMF to measure the angle-integrated, parity violating longitudinal analyzing power, A{sub z}, in proton-proton elastic scattering, to a precision of {plus_minus}0.2{times}10{sup {minus}7}. The experiment uses a 221 MeV longitudinally polarized proton beam incident on a 40 cm liquid hydrogen target. The beam energy is carefully chosen so that the contribution to A{sub z} from the J=0 parity mixed partial wave ({sup 1}S{sub 0}{minus}{sup 3}P{sub 0}) integrates to zero over the acceptance of the apparatus, leaving the experiment sensitive mainly ({gt}95{percent}) to A{sub z} arising from the {sup 3}P{sub 2}{minus}{sup 1}D{sub 2}, J=2 wave. To minimize sources of systematic error, the TRIUMF ion source and cyclotron parameters have been refined to the extent that helicity correlated beam changes are at an extremely low level, and specialized instrumentation on the E497 beamline is able to measure residual helicity correlated modulations to a precision consistent with the goals of the experiment. A data taking run in February-March, 1997 logged approximately 12{percent} of the desired data and produced a preliminary result, A{sub z}=(1.1{plus_minus}0.4{plus_minus}0.4){times}10{sup {minus}7}, where the error is statistical only. {copyright} {ital 1997 American Institute of Physics.}

TRIUMF Experiment 369, a measurement of charge symmetry breaking in np elastic scattering at 350 MeV, has completed data taking. Scattering asymmetries were measured with a polarized (unpolarized) neutron beam incident on an unpolarized (polarized) frozen spin target. Coincident scattered neutrons and recoil protons were detected by a mirror symmetric detection system in the center‐of‐mass angle range from 50°–90°. A preliminary result for the difference of the zero‐crossing angles, where analyzing powers cross zero, is Δθcm =0.445°±0.054°(stat.)±0.051°(syst.) based on fits over the angle range 53.4°≤θcm≤86.9°. The difference of the analyzing powers ΔA≡An−Ap, where the subscripts denote polarized nucleons, was deduced with dA/dθcm=(−1.35±0.05)×10−2 deg−1 to be [60±7(stat.)±7(syst.)±2(syst.)] ×10−4.

TRIUMF experiment 369, a measurement of charge symmetry breaking in np elastic scattering at 350 MeV, has completed data taking. Scattering asymmetries were measured with a polarized (unpolarized) neutron beam incident on an unpolarized (polarized) frozen spin target. Coincident scattered neutrons and recoil protons were detected by a mirror symmetric detection system in the center of mass angle range from 50°–90°. A preliminary result for the difference of the zero‐crossing angles, where analyzing powers cross zero, is Δθcm=0.48°±0.08°(stat.)±0.08°(syst.) based on fits over the angle range 55.8°≤θcm≤85.4°. The difference of the analyzing powers ΔA≡An−Ap, where the subscripts denote polarized nucleons, was deduced with dA/dθcm=−1.47×10−2 deg−1 from phase shift analyses to be [71±12(stat.)±12(syst.)]×10−4. It is expected that when all data are analyzed a statistical accuracy of about 7×10−4 in ΔA will be achieved.

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)

The zero point of the analyzing power for neutron‐proton scattering has been measured as a function of scattering angle for 4 incident neutron energies, 174.3, 202.4, 216.5, and 260.3 MeV. The accuracy is ±0.25°. (AIP)

We measured the relative differential cross section and analyzing powers A SO, A NO and A LO for the reaction np→ppπ− at an incident neutron energy of 443 MeV. The geometry of our detector allowed us to sample almost all the available phase-space. We reconstructed the full kinematics of each event from the measured trajectories of at least two of the three final state particles. Cuts based on the vertex reconstruction and kinematic χ2 allowed us to remove most background, primarily nn→npπ− from the target walls and other materials. These cuts gave a signal-to-noise ratio of 22:1, but fewer than 3% of the total data survived the cuts. The resulting ~400,000 np→ppπ− were binned against p-p invariant mass and angles which are most suited to partial waves analysis. Comparisons are made to predictions of the model of Kloet and Lomon. These observables represent the first measurements of their kind at this energy and it is hoped that their determination will allow us to extract the role of isospin-0 amplitudes in the process of pion production.

The validity of charge symmetry has long been of fundamental interest and much circumstantial evidence has accumulated over the years favoring charge symmetry breaking (CSB) on the order of a fraction of a percent. Although low energy nucleon-nucleon scattering studies have shown a slight inequality of the nn and pp scattering lengths[1], it has proved very difficult to remove experimental and theoretical uncertainties to isolate charge symmetry breaking interactions unequivocally. Evidence of CSB is present in π scattering from 3 H and 3 He and in π — d total and differential cross section measurements[2],[3],[4],[5]. The π — d results have been interpreted in terms of mass splittings in the Δ system. Differences in the binding energies of mirror nuclei (the Nolen-Schiffer effect) hint at the presence of charge symmetry breaking terms in the interaction but, again, the isolation and removal of electromagnetic (EM) effects has proved difficult[6],[7].

Differential cross sections for proton elastic scattering from $^{42}$,44,48Ca have been measured at seven energies in the laboratory energy range from 21.0 to 48.4 MeV, and for $^{40}\mathrm{Ca}$ at six energies between 25.0 and 45.0 MeV. Measurements were made at 2.5\ifmmode^\circ\else\textdegree\fi{} intervals from 10\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{} (laboratory angles), and at 5.0\ifmmode^\circ\else\textdegree\fi{} intervals between 90\ifmmode^\circ\else\textdegree\fi{} and 170\ifmmode^\circ\else\textdegree\fi{}. Relative errors in the data are typically between 3% and 4%; the scale errors are also 3%. The data have been analyzed by both nonrelativistic and relativistic optical models. The optical potential parameters were used to calculate nuclear matter radius information for the calcium isotopic series, which is compared to previous results.

Analyzing power data A/sub y/(theta) have been obtained for p+ /sup 3/He elastic scattering at 11 energies between 21.4 and 49.6 MeV for laboratory angles between 20/sup 0/ and 160/sup 0/. Errors typically are less than 0.01. These data are compared with fits obtained in a single energy phase-shift analysis and R-matrix predictions.

An experiment resulting in the first measurement of the isospin-mixing, charge-symmetry violating component of the n-italic-p-italic interaction has been performed. The experiment determined the difference in the angles of the zero crossing of the neutron and proton analyzing powers A-italic/sub n-italic/ and A-italic/sub p-italic/ at 477 MeV. In terms of the laboratory scattering angle of the neutron, the measured difference t-italich-italice-italict-italica-italic/sub 0//sub n-italic/(A/sub n/)= -t-italich-italice-italict-italica-italic/sub 0//sub n-italic/(A/sub p/) = +0.13X(de +- 0.06 X(de( +- 0.03X(de) where the second error is a worst case estimate of systematic error. The resulting difference in the analyzing powers at the zero-crossing angle A-italic/sub n-italic/-A/sub p/ = +0.0037 +- 0.0017( +- 0 .0008).

Proton total reaction cross sections have been measured for the nuclei 159 Tb, 181 Ta and 197 Au at seven proton energies between 20 and 48 MeV using an attenuation technique. The experimentally determined energy dependence of the total reaction cross sections is compared with results obtained for black nucleus and optical model calculations.

The polarized neutron beam facility at TRIUMF has been upgraded for use in high precision neutron scattering experiments. Polarized neutrons are produced via transverse polarization transfer in the D(p,n)2p reaction at 9° in the lab. Proton beam position on the LD2 production target is stabilized to better than ±0.2 mm using a feedback system controlling beam line elements. The region of uniform neutron beam intensity at the experimental target location is a rectangular area 56 mm wide and 40 mm high. In that area the neutron beam intensity is 9 × 103 (100 nA cm2 s) and the neutron polarization is 50%. The facility is being used to determine charge symmetry breaking in n−p elastic scattering, to study neutron radiative capture by hydrogen, and a measurement of the spin correlation parameter Ann.

Differential cross-section and analyzing power angular distributions have been measured for the elastic scattering of polarized protons on 24 Mg, 27 Al and 32 S between 13 and 27 MeV. An optical model analysis has been performed and the spin-orbit potentials display significant variations in the giant resonance region of 25 Al, 28 Si and 33 C1. The 24 Mg and 32 S data have been examined in a phase-shift analysis.

A selection of problems that remain to be resolved in elastic and inelastic nucleon-nucleon systems is presented.

We have measured the 116 Sn( d , p) 117 Sn differential cross section and vector analysing power at 12.22 and 15.09 MeV incident deuteron energy, and the cross section and proton analysing power in the inverse 117 Sn( p , d) 116 Sn reaction at the same c.m. energy (16.83 and 19.75 MeV incident proton energies). We have analysed these data together with the earlier data of Cadmus on the same reaction at 8.22 MeV. We were successful in obtaining several global potentials that fit the elastic scattering of deuterons by the target nucleus and of protons by the recoil nucleus. These global potentials were used in DWBA calculations in attempts to reproduce the reaction data. In all cases they failed completely. DWBA calculations performed using a deuteron potential deduced from the adiabatic prescription of Johnson and Soper (1970) had some success. A method proposed by Johnson (1962) was used to determine whether the proton or the deuteron potential was primarily at fault. In this method, the vector analysing power and proton polarisation in a ( d , p) reaction are combined to give the quantities Sp and Sd, where Sp and Sd, each proportional to the strength of the spin-orbit potential in the channel indicated by the subscript, are independent of the spin-orbit potential in the other channel. A failure of the DWBA to reproduce Sp or Sd would reveal that the shortcomings of the model are primarily confined to one or the other of these two channels. Unfortunately, Johnson's method was not very helpful in establishing which potential is at fault as it did not provide separation of the effects due to the central potentials.

Detection equipment has been developed to allow precision measurements of n−p elastic scattering of 150 to 500 MeV polarized neutron beams at TRIUMF. The apparatus permits a determination of the difference in angle, ‡θ, at which the neutron and proton analyzing powers An and Ap cross zero with a precision of ±0.04° lab at 500 MeV. From this difference in ‡θ the difference between An and Ap can be obtained to a precision of ±0.001.

The experiment in progress at TRIUMF measures the difference ƊA between the neutron and proton analyzing powers An, and Ap in n-p elastic scattering at 480 MeV.

Angular distributions have been calculated for the parity-violating longitudinal analyzing power A/sub z/ from 15 to 800 MeV, based on the parity-violating mixings between phases such as /sup 1/S/sub 0/-/sup 3/P/sub 0/, /sup 3/P/sub 2/-/sup 1/D/sub 2/, etc. At low energies the angular distributions are isotropic (except for the Coulomb region) and only the /sup 1/S/sub 0/-/sup 3/P/sub 0/ phases are important. At energies greater than 100 MeV, the angular distributions show structure due to the importance of higher-J mixings. At 800 MeV the higher-J mixings give contributions to the angular distribution which oscillate around zero and contribute little to the value of the angle-integrated A/sub Z/, even though these contributions may have relatively large maxima at 90/sup 0/ (c.m.). The reversal in the sign of the angle-integrated A/sub Z/ between low energies and 800 MeV comes about naturally from the phase shifts; thus this sign reversal is due solely to the strong-interaction contribution to the parity-violating interaction. Angular-dependence information will be required to separate the various contributions to A/sub Z/ from the possible parity-violating mixings.

A technique is presented for the calculation of the efficiency of detection of two coincident particles. The technique has been applied to the interpretation of the results of bremsstrahlung experiments, but is sufficiently flexible to be easily applied to other cases. Various detection geometries are considered. The dependence of the bremsstrahlung cross-section on the noncoplanarity of the detected particles is included explicitly in the efficiency calculation.

A measurement of the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\alpha}$ bremsstrahlung cross section at 9.35 MeV has established the upper limit 5.1 ${\mathrm{\ensuremath{\mu}}\mathrm{b}/\mathrm{s}\mathrm{r}}^{2}$ with 90% probability. We give a comparison with predictions, including only single-scattering terms.

A description of the polarimeter and its performance is given. It surpasses all other polarimeters in efficiency at comparable energy resolutions for protons of energies larger than 20 MeV. The scattering yield Y is 3 × 10−3 at 29 MeV with an anlysing power P of −0.3, giving a figure of merit 〈PY 1 2 〉 of 1.6 × 10−2.

For deuteron break-up by protons at kinematic conditions far from two-body enhancements, a region of sensitivity to higher partial wave components of the two-body interaction has been found. In particular, using two different nucleon-nucleon tensor forces, three-body calculations of break-up cross sections show statistically significant differences as compared with measured cross sections. Calculated tensor analyzing powers are seen to be highly sensitive to the tensor force. Experimental investigation of these is encouraged.

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%.