L. M. Simons

Determination of the πN scattering lengths from pionic hydrogen

Abstract 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 .

Balmer α transitions in antiprotonic hydrogen and deuterium

Abstract The strong-interaction shifts ϵ and broadenings Γ of the 2p levels in antiprotonic hydrogen and deuterium have been measured for the first time with a crystal spectrometer. In hydrogen, the 2 3 P 0 hyperfine state could be resolved from the three close-lying states 2 3 P 2 , 2 1 P 1 , and 2 3 P 1 . The hadronic shift was determined to be ϵ 2 3 P 0 =+139±28 meV (attractive). The value found for Γ 2 3 P 0 =120±25 meV is much larger than the spin-averaged 2p-level broadening Γ bal 2p as determined from earlier experiments measuring the intensity balance. The average shift of the three unresolved states is consistent with zero and a mean broadening of Γ 2( 3 P 2 , 1 P 1 , 3 P 1 ) =38±9 meV was measured. In deuterium, the spin-averaged hadronic shift and broadening were found to be ϵ 2p =−243±26 meV (repulsive) and Γ 2p =489±30 meV.

A large area CCD X-ray detector for exotic atom spectroscopy

A large area, position and energy sensitive detector has been developed to study the characteristic X-radiation of exotic atoms in the few keV range. The detector, built up from an array of six high-resistivity CCDs, is used as the focal plane of a reflection-type crystal spectrometer. A large detection area is necessary because of the need to detect simultaneously two or more lines close in energy as well as broad structures like fluorescence X-rays from electronic atoms. The fine pixel structure provides accurate determination of the X-ray line position while the excellent background rejection capabilities of the CCD, using both energy and topographical discrimination, are essential in the high background environment of a particle accelerator.

Measurement of the strong interaction parameters in antiprotonic hydrogen and probable evidence for an interference with inner bremsstrahlung

Abstract The spin-averaged values of the 1s strong interaction parameters in antiprotonic hydrogen were measured with good statistics. The results are: shift (ϵ 1s ) = −712.5 ± 20.3 eV and width (Γ 1s ) = 1054± 65 eV . These values are compatible and have approximately the same precision as the world average before this experiment. With some additional constraints, both the triplet and singlet components could be extracted from the same spectrum. The results are: 3 S 1 shift: −785 ± 35 eV , 3 S 1 width: 940 ± 80 eV , 1 S 0 width: 1200 ± 250 eV . In addition, precise values for the K α L α and Ltotal L α yields at low pressure (20 mbar) were obtained: 0.0176 ± 0.0016 and 1.45 ± 0.05 . Furthermore, the 2p mean absorption width of 30.8 ± 3.0 meV was deduced, also compatible with and of similar precision as the world average before this experiment. An indication of interference between the measured Lyman (Ki) x-ray series and the process of inner bremsstrahlung due to charged meson production after annihilation was seen because of the low background conditions of this experiment.

The cyclotron trap for antiprotons

The cyclotron trap is a device to increase the stop density of negatively charged particles. Its working principle is to wind up the range of a stopping particle in a weak focusing magnetic field. Its main application in the past was the spectroscopy of exotic atoms. A modern application is the production of low energy muon or antiproton beams.

Electromagnetic cascade and chemistry of exotic atoms

This Workshop was organized to bring once more tagether the scientists of the rather heterogeneaus field of exotic atoms. At present the main topic of the field seems to be the study of the atomic cascade. There are some who study it intentionally -Iet us call them cascadeurs -and others who think they investigate other features of the exotic atoms (like Coulomb capture, particle transfer, muon catalyzed fusion, chemical effects, fundamental properties, etc.) -users-while in fact they study some special consequences of the same atomic cascade. We decided to get cascadeurs and users discuss the problems of exotic atoms at wonderful Erice, at the 5th Course of the International School of Physics of Exotic Atoms. Our Workshop was quite successful, we have heard excellent talks from participants from a dozen countfies and most of them have prepared written contributions for this volume. The Organizers express their gratitude to all participants for their contributions, especially to David Measday for bis concluding remarks (not printed here) and to James Cohen for jumping in for Leonid Ponomarev who had to leave unexpectedly in the middle of the meeting. We greatly appreciate the enthusiastic help of Marianne Signer in every stage of the organization work. Am!, of course, the Workshop could not happen at all without the incredibly efficient organization by the Ettore Majorana Centre of Scientific Culture. Leopold M. Simons Dezso Horvath Gabriele Torelli V CONTENTS OPENING ADDRESS ...xi ...

On the characterisation of a Bragg spectrometer with X-rays from an ECR source

Narrow X-ray lines from helium-like argon emitted from a dedicated ECR source have been used to determine the response function of a Bragg crystal spectrometer equipped with large area spherically bent silicon (111) or quartz (10¯ crystals. The measured spectra are compared with simulated ones created by a ray-tracing code based on the expected theoretical crystal’s rocking curve and the geometry of the experimental set-up.

Laser spectroscopy of the Lamb shift in muonic hydrogen

The muonic hydrogen atom in the 2s state provides the possibility of achieving high precision laser spectroscopy experiments from which a high precision value of the proton radius can be deduced. This will ultimately allow an increased precision in the test of QED in bound systems. Important progress has been made in recent years in the ability to stop muons in a low pressure gas target and in the understanding of the 2s-metastability in muonic hydrogen. As a consequence the 2s–2p laser spectroscopy experiment is now feasible and we present here the basic experimental concept considered by our collaboration.

X-ray spectroscopy of the pionic deuterium atom

Abstract 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.

Measurement of the strong interaction parameters in antiprotonic deuterium

Abstract Antiprotonic deuterium K α X-rays were seen for the first time. Their analysis resulted in spin-averaged 1s strong interaction parameters, namely −1050±250 eV (repulsive) for the 1s shift and 1100±750 eV for the 1s width. The large errors are mainly due to low statistics. In addition, values for the K α /L α and L total /L α yields at low pressure (20 mbar) were obtained: 0.005±0.003 and 1.34±0.05. Furthermore, a 2p mean absorption width of 80 ≤ Γ 2p ≤ 350 meV was deduced. The results for the 1s ground state are somewhat surprising, especially the narrow 1s width which is similar to the spin-averaged antiprotonic hydrogen 1s width. However, our 1s width is in agreement with low-energy scattering data [A. Zenoni et al., Phys. Lett. B 461 (1999) 413] (see preceding paper).