Search

The final results from the pionic hydrogen X-ray experiment at PSI are presented. With this experiment the strong interaction energy level shift e 1s and the total decay width Γ 1s of the 1s state of pionic hydrogen were obtained from a precise measurement of the 3p–1s X-ray line: e 1s =−7.108±0.013(stat.)±0.034(syst.) eV (attractive) and Γ 1s = 0.868±0.040(stat.)±0.038(syst.) eV. The corresponding hadronic π N s-wave scattering lengths for elastic scattering and single charge exchange are: a π − p→π − p =0.0883±0.0008 m −1 π and a π − p→π 0 n =−0.128±0.006 m −1 π . Combining the results of the pionic hydrogen and deuterium measurements, the isoscalar ( b 0 ) and isovector ( b 1 ) scattering lengths, corresponding to an isospin symmetric interaction, can be calculated: b 0 =0.0016±0.0013 m −1 π and b 1 =−0.0868±0.0014 m −1 π .

The energy and time distributions of the decay X-rays of excited, metastable, molecular (dµHe)*-resonances were measured. The comparison of the observed energy spectra with calculated ones suggests that decay from the rotational state J = 1 dominates at the investigated conditions. The muon transfer rates from ground state deuterium to the helium isotopes 3He and 4He at low temperatures were determined from the time distributions of these spectra. Additionally, the temperature dependence of the muon transfer rate was clearly established in deuterium / 4He mixtures.

We have performed an experiment to investigate various processes induced by muons in hydrogen-deuterium mixtures. Preliminary results are given for cascade X-ray yields, q1s, relative yields of conversion muons and fusion γ-rays, molecular formation and hyperfine transition rates.

We report our investigations of X rays emitted during the muonic cascade in hydrogen employing charge coupled devices as X-ray detectors. The density dependence of the relative X-ray yields for the muonic hydrogen lines (K_alpha, K_beta, K_gamma) has been measured at densities between 0.00115 and 0.97 of liquid hydrogen density. In this density region collisional processes dominate the cascade down to low energy levels. A comparison with recent calculations is given in order to demonstrate the influence of Coulomb deexcitation., Comment: 5 pages, Tex, 4 figures, submitted to Physical Review Letters

The low energy X-rays of the pionic deuterium 3P-1S transition were measured using a high resolution crystal spectrometer, together with a cyclotron trap (a magnetic device to increase the pion stopping density) and a CCD (charge-coupled device) detector system. The spectrometer resolution was 0.65 eV FWHM for a measured energy of approximately 3075 eV. This energy was measured with a precision of 0.1 eV. Compared to conventional methods, the cyclotron trap allowed for a gain in stopping density of about an order of magnitude. The CCDs had excellent spatial and energy resolutions. Non-X-ray background could therefore be almost completely eliminated. The 1S strong interaction shift ϵ1S and total decay width Γ1S were determined from the position and line shape of the X-ray peak. They are ϵ 1S ( shift ) = 2.43 ± 0.10 eV ( repulsive ), Γ 1S ( width ) = 1.02 ± 0.21 eV , where the statistical and systematic errors were added linearly. The total (complex) pionic deuterium S-wave scattering length aπ−d was deduced: a π − d = −0.0259(±0.0011) + i 0.0054(±0.0011)m π −1 . From the real part of aπ−d a constraint in terms of the isoscalar and isovector πN′ scattering lengths b0 and b1 was deduced. From Im aπ−d we determined the isoscalar coupling constant for π− absorption: |g0| = (2.6 ± 0.3) 10−2mπ−2. The experiments of the pionic hydrogen and deuterium S-wave scattering lengths were analyzed within the framework of a search for i isospin symmetry violation. The data are still compatible with isospin conservation. The scattering lengths deduced from the Karlsruhe-Helsinki phase shift analysis disagree with the present results.

Muon transfer from hydrogen isotopes to helium is of importance in muon-catalyzed fusion and serves as a unique tool for the direct observation of the mesomolecular ion (pµHe)*. During two data-taking runs in 1994 and 1995 at PSI, measurements of the transfer from protium to helium were carried out using CCD's and Ge-diodes as independent X-ray detectors to obtain information on the time distribution and intensity of the 7 keV decay X-ray of the mesomolecular ion. Dual1H2 +4 He and triple1H2 + Ne +3,4He gas mixtures at low temperatures were investigated to extract transfer rates. Protium of high purity was available. For the first time a transfer rate from muonic protium to3He was measured. A general survey of our measurements and preliminary analysis is presented.

The 3p-1s transition in pionic hydrogen was investigated with a high-resolution crystal spectrometer system. From the precisely measured transition energy, together with the (calculated) electromagnetic energy, the strong interaction shift of the 1s state was obtained as ϵ 1s = −7.127 ± 0.028(stat.)± 0.036(syst.) eV (attractive). From the natural line width, measured for the first time, we determine the decaywidth of the 1s state: Γ 1s (decay) = 0.97 ± 0.10(stat.)± 0.05(syst.) eV. With the recently calculated electromagnetic corrections the s-wave scattering lengths of an isospin symmetric strong interaction are deduced. The scattering length for elastic scattering of a negative pion on a proton is a π − p → π − p h = 0.0885±0.00003(stat.)±0.0006(syst.) m π −1 . The scattering lengthe for single charge exchange is found to be a π − p → π 0 n h = −0.136 ± 0.007(stat.) ± 0.003(syst.) m π −1 . The experiment was performed at the Paul Scherrer Institute (PSI) in Switzerland. A focussing crystal spectrometer with an array of bent crystals, the cyclotron trap (a magnetic system designed to increase the particle stop density) and a CCD (charge-coupled device) detector system were employed. The results from the pionic hydrogen experiment — together with those from the pionic deuterium experiment — were used to test the isospin symmetry of the strong interaction. The present data are still consistent with isospin sysmmetry.

We report the first direct observation of excited state muon transfer in hydrogen/deuterium mixtures by direct measurement of q_1s, the probability that a mu-p atom, which is initially formed in an excited state, reaches the 1s ground state. The dependence of q_1s on deuterium concentration c_d was measured for two different densities at cryogenic temperatures using charge coupled devices (CCDs) to detect the muonic X rays. First results based on the analysis of the K_alpha-lines of the two isotopes are presented., 4 figures

The pionic deuterium 3{ital P}{minus}1{ital S} x-ray transition was measured with a quartz crystal spectrometer in combination with a cyclotron trap and charge coupled device detectors. The strong interaction shift and total decay width of the 1{ital S} level are {epsilon}{sub 1{ital S}}(shift)=2.48{plus_minus}0.10 eV (repulsive), {Gamma}{sub 1{ital S}}(width)=1.02{plus_minus}0.21 eV, where the statistical and systematic errors were added linearly. They yield the total pionic deuterium {ital S}-wave scattering length: {ital a}{sub {pi}{sup {minus}}{ital d}}= {minus}0.0264({plus_minus}0.0011)+{ital i}0.0054({plus_minus}0.0011){ital m}{sub {pi}}{sup {minus}1}.

The energy and line shape of the 3P-1S transition in pionic hydrogen have been measured with a reflecting crystal spectrometer combined with a cyclotron trap and Charge Coulped Devices (CCDs). The instrumental resolution was 0.7 eV (FWHM) at 2.9 keV. Results for the strong interaction energy shift and broadening of the ground state and the corresponding πN s-wave scattering lengths will be presented soon.

A reflecting crystal spectrometer consisting of three cylindrically bent quartz (110) crystals is described, it was designed to measure the 3 keV Kβ X-rays from pionic hydrogen and deuterium. Charge coupled devices (CCDs) were used as X-ray detectors. Projecting the reflexes of all three crystals on one common focus, an instrumental energy resolution below 1 eV was obtained at an energy of 2.9 keV.

An experiment is described which aims to determine the pion mass to 1 ppm or better, from which a new determination of the upper limit of the muon neutrino mass is anticipated. The approach utilizes spectroscopy of X-ray emissions from pionic atoms formed in gaseous targets. The spectroscopy is performed with a Bragg crystal spectrometer, with an energy resolution of approximately 300 meV, using an array of X-ray CCDs mounted at the focus to measure the spectral line structure of the 4 keV pionic nitrogen transition. To achieve sub-ppm accuracy, as energy calibration a muonic oxygen transition is used. It is known with a precision of 0.3 ppm and almost coincides in energy with the pionic transition.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Measurements of the K X-ray transitions of muonic hydrogen (μ−p and μ−d) were performed at H2 or D2 gas pressures between 17 and 533 hPa (T ≈ 293 K). The intensity ratios K α K total and K β K total depend on the gas density because the strength of excited state collisional interactions increases at higher densities. The data are compared with the results of a cascade calculation. They are sensitive to the collisional Stark mixing rates at the main quantum levels n = 4, …,8.

The $3p\ensuremath{-}1s$ x-ray line of pionic hydrogen was measured with a reflecting bent crystal spectrometer. The strong interaction energy level shift and the total decay width of the $1s$ state, obtained from the transition energy and the linewidth, are ${\ensuremath{\varepsilon}}_{1s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}7.127\ifmmode\pm\else\textpm\fi{}0.028\left(\mathrm{stat}\right)\ifmmode\pm\else\textpm\fi{}0.036(\mathrm{syst})\phantom{\rule{0ex}{0ex}}\mathrm{eV}$ (attractive) and ${\ensuremath{\gamma}}_{1s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.97\ifmmode\pm\else\textpm\fi{}0.10\left(\mathrm{stat}\right)\ifmmode\pm\else\textpm\fi{}0.05\left(\mathrm{syst}\right)\phantom{\rule{0ex}{0ex}}\mathrm{eV}$. The corresponding hadronic $\ensuremath{\pi}N$ s-wave scattering lengths for elastic scattering and single charge exchange are ${a}_{{\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}p}^{h}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.0885\ifmmode\pm\else\textpm\fi{}{0.0009m}_{\ensuremath{\pi}}^{\ensuremath{-}1}$ and ${a}_{{\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n}^{h}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.136\ifmmode\pm\else\textpm\fi{}{0.010m}_{\ensuremath{\pi}}^{\ensuremath{-}1}$.

FIRST PREFACE - 'The most important experiment to be carried out in low energy K-meson physics today is the definitive determination of the energy level shift in the K-p atoms, because of their direct connection with the physics of KN interaction and their complete independence from all other kinds of measurements which bear on this interaction'.

In spite of its low absorption coefficient for X-rays, amorphous Silicon can be an interesting alternative approach for X-ray detection because of its low cost, its potential for large-area deposition and the possibility to deposit on a curved surface. For this application, basically two approaches have been proposed up to now: either a thick solar cell type n-i-p structure (the i-layer as to be sufficiently thick i.e typically 50 μm or more), or a normal solar cell type n-i-p structure (with a relatively thin i-layer, i.e (typically 1 to 2 μm) together with a fluorescent layer emitting visible light composed e.g. of CsJ. In this paper, we present first results of a X-ray detectors with thick i-layers (15 to 100 μm) prepared by the high deposition rate VHF-GD technique introduced at our laboratory. Detectors with low leakage currents (2) under high reverse bias voltages (about 100 V) could be fabricated at rates as high as 22 Å/s. As substrates, aluminium as well as TCO-coated glass substrates were used. The detectors have a n-i-p structure, where highly conductive (100 S/cm) n-doped μc-Si:H was first deposited. For the substrate preparation, a high energy Ar plasma was applied before the first deposition step; in this way excellent sticking conditions could be achieved, although in the thicker detectors considerable curvature due to the internal mechanical stress could be observed. A medical X-ray radiation source was used, where the detector was exposed to a continuous X-ray spectrum at acceleration voltages between 80 kV and 240 kV. The paper presents measurements on the linearity of the detector, as well as on the value of the reverse current in the dark, which must be as small as possible to have the best signal to noise ratio.

We present differential cross-sections for pp elastic scattering at eight laboratory momenta from 1.50 to 2.06 GeV/c. The data are analysed using an 8-parameter optical modela la Frahn and Venter. However, the best representation of the differential cross-sections is obtained by combining the glory model with a parametrization of the scattering amplitude in terms of coherent exponentials. Both representations show the dominance of the partial wave with orbital angular momentum equal to four.

Antiproton-proton annihilations into final states containing one or two K10-mesons are studied on the basis of 450 000 pictures from the CERN 2 m HBC. The experiment covers the domain of antiproton incident momentum from 1.50 to 2.04 GeV/c. The resonance production rates are computed for the most abundant channels. The K10K10 threshold effect is explained through the inelastic channel π+π− → K10K10. The decay modes D, E → δ±(975)π∓, δ±(975) → K10K± are pointed out. The strange mesons C and C′ are observed in these annihilations and come mainly from the two-body channels \(p\bar p\) → (C, C′)K and\(p\bar p\) → (C, C′)K*.

A study of nonequilibrium phonon propagation in a low-temperature bolometric detector with a Monte Carlo code is presented. The simulation of the thermalization process allows us to predict the temperature pulse in a 1 cm3 germanium bolometer detecting 5 MeV alpha-particles.

Experimental results for the cross-sections, the effectivemass distributions, the angular distributions and correlations are presented for the reaction\(\bar p\)p → 3π−3π+. All the multipion mass distributions and the ππ angular correlations are described in terms of a final-state interaction model including theδ00 andδ11 ππ phase shifts, as well as an A2 effect.

We present the results of a study of the exclusive reactions π + 4 He → π − 4 p (double charge exchange, DCE) and π + 4 He → π + π − 3 pn (one-pion production). The experiment was performed with the Oxford/RHEL helium bubble chamber irradiated with a 1.7 GeV/c π+ beam. A general review of DCE models is presented and experimental results at other energies are discussed in the light of these models. None of the existing theoretical models is compatible with out data at 1.7 GeV/c. We propose a new mechanism for DCE, involving three nucleons, which reproduces the integrated as well as the differential cross sections. Some consequences for other models are also discussed.

The reaction\(\bar pp \to \bar \Lambda \Lambda \) has been studied in a bubble chamber experiment at eight incident momenta between 1.50 and 2.06 GeV/c. The differential cross-section, the polarization and the spin correlation coefficients have been measured. They have been compared with the prediction of two theoretical models: the K-meson conspiracy and the exchange of the K*K** degenerate trajectory associated with a Regge cut. The latter model gives the best representation of the data.

The reaction pp → nn has been studied at an incident antiproton laboratory momentum of 1.13 GeV/c. The antineutron was identified through a subsequent annihilation on a proton. In all, 2601 identified events were obtained. Total and differential cross sections are presented. Comparison is made with the predictions of the Bryan and Phillips model which, in this energy range, is succesful in describing the related reaction pp → pp. Here, the agreement is less good.

The analysis of exclusive neutral strange particle production in the reactions π−p → K°Λ + K°Σ° and pp → ΛΛ + ΛΣ° + c.c. at 3.15, 4.95, 7.9 and 12 GeV/c yielded the differential cross section distributions up to about 90° c.m.s. scattering angle and the Λ-particle polarization at large transverse momentum. Applying a fit to dσ/dt ∞ s−n resulted in n = 8.6 ± 0.9 for the K° Λ + K° Σ° final state which is compatible with the quark counting rule n = 8 for meson-baryon reactions. The average Λ polarization around t = −1.6 (GeV/c)2 was PΛ = 0.79 ± 0.17 at 3.15 GeV/c beam energy.

n p annihilations with ⩾ 3 prongs with an incident antineutron momentum between 0.5 and 0.8 GeV/c are analysed. We present the topological branching ratios and cross sections, the resonance production rates and possible ϱ-ω interference effects.

Based on a sample of about 3500 events, we have measured the total and differential cross sections of p p → n n in the 700–760 MeV/c incident momentum region. It is found that σCE = 10.7 ± 0.2 mb at the average momentum of 730 MeV/c. The differential angular distribution is characterised by a sharp peak and a dip in the forward direction followed by a secondary maximum. The position of the dip corresponds to |t| ≈ mπ2. These results are compared with the predictions of the model of Bryan-Phillips. On the other hand, this dip-bump structure can be well understood on a simple picture involving a π exchange and a constant background (for |t| ≲ 3 mπ2).

Muon transfer from the ground state of muonic deuterium to a helium atom proceeds mainly via the formation of a muonic molecule in an excited state. A large number of decay X rays (∼ 6.8 keV) from these (dµHe)* molecules were observed for the4He as well as for the3He case. The time distributions of these X rays allow the determination of the ground state transfer rate. The simultaneous employment of Ge/Si-detectors and CCDs for the same target conditions allows the determination of the branching ratio of radiative to nonradiative decay for the first time.