Strong Interaction Shift Research Articles

On the way from thermal multifragmentation to dynamical disintegration

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 23P0 hyperfine state could be resolved from the three close-lying states 23P2, 21P1, and 23P1. The hadronic shift was determined to be ϵ23P0=+139±28 meV (attractive). The value found for Γ23P0=120±25 meV is much larger than the spin-averaged 2p-level broadening Γ̄bal2p 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 Γ̄2(3P2,1P1,3P1)=38±9 meV was measured. In deuterium, the spin-averaged hadronic shift and broadening were found to be ϵ̄2p=−243±26 meV (repulsive) and Γ̄2p=489±30 meV.

First measurements at the DAΦNE φ-factory with the DEAR experimental setup

The relevant background for the DEAR experiment – low-energy X rays and ionizing particles – present in the DEAR interaction region of the DAΦNE e +e − collider was investigated using the first-stage DEAR setup and CCD detectors. An extensive Monte Carlo simulation was performed for the present setup and beam conditions. Good quantitative agreement between measurements and simulation was achieved. This is a confirmation that, with respect to the expected background, which gives an important contribution to the statistical precision of the experiment, the configuration chosen to measure the strong interaction shift and width in kaonic hydrogen and kaonic deuterium can indeed reach the planned level of accuracy.

Balmer α transitions in antiprotonic hydrogen and deuterium

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( 3P 2, 1P 1, 3P 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.

Strong interaction effects in kaonic deuterium

High precision measurements of kaonic hydrogen x rays and also, for the first time, of kaonic deuterium are under way within the DEAR project using the ${e}^{+}{e}^{\ensuremath{-}}$ storage ring at Frascati. The values of the strong interaction $1s$ level shift and width in kaonic deuterium cannot be simply predicted by relating them, via the Deser-Trueman formula, to the ${K}^{\ensuremath{-}}d$ scattering length because the latter is not known experimentally: it cannot be obtained by adding the ${K}^{\ensuremath{-}}p$ and ${K}^{\ensuremath{-}}n$ scattering lengths but involves the solution of a complicated multichannel three-body problem. We give results of calculations of the kaonic deuterium strong interaction shift and width using an $(N\overline{K},Y\ensuremath{\pi})$ interaction $(Y=\ensuremath{\Lambda},\ensuremath{\Sigma})$ that fits the available low-energy scattering data. The $1s$ level shift in kaonic deuterium comes out negative and both the shift and the width are estimated to be about 1 keV. The $2p$ capture rate is estimated to be smaller than the $2\stackrel{\ensuremath{\rightarrow}}{p}1s$ x-ray transition rate. This information is of importance for the planned experiment as it indicates that most of the kaons should reach the lowest $1s$ level.

Measurement of strong interaction parameters in antiprotonic hydrogen and deuterium

In the PS207 experiment at CERN, X-rays from antiprotonic hydrogen and deuterium have been measured at low pressure. The strong interaction shift and the broadening of the Kα transition in antiprotonic hydrogen were determined. Evidence was found for the individual hyperfine components of the protonium ground state.

OBSERVATION OF KAONIC HYDROGEN ATOM X-RAY

We successfully observed clear K-series kaonic hydrogen X-rays for the first time taking advantage of two charged pions tagging technique and a gaseous hydrogen target. The strong-interaction energy shift and width of 1s state of K −p atom were determined to be ΔE 1s = -323 ± 63 (statistical) ± 11 (systematic) eV and Г1s = 407 ± 208 ± 100 eV. Our result means that the K −p strong interaction near threshold is repulsive and the long-standing kaonic hydrogen puzzle is solved.

Experiments withΞ−atoms

Experiments with ${\ensuremath{\Xi}}^{\ensuremath{-}}$ atoms are proposed in order to study the nuclear interaction of $\ensuremath{\Xi}$ hyperons. The production of ${\ensuremath{\Xi}}^{\ensuremath{-}}$ in the ${(K}^{\ensuremath{-}}{,K}^{+})$ reaction, the ${\ensuremath{\Xi}}^{\ensuremath{-}}$ stopping in matter, and its atomic cascade are incorporated within a realistic evaluation of the results expected for ${\ensuremath{\Xi}}^{\ensuremath{-}}$ x-ray spectra across the periodic table, using an assumed $\ensuremath{\Xi}$-nucleus optical potential ${V}_{\mathrm{opt}}.$ Several optimal targets for measuring the strong-interaction shift and width of the x-ray transition to the ``last'' atomic level observed are singled out: F, Cl, I, and Pb. The sensitivity of these observables to the parameters of ${V}_{\mathrm{opt}}$ is considered. The relevance of such experiments is discussed in the context of strangeness $\ensuremath{-}2$ nuclear physics and multistrange nuclear matter. Finally, with particular reference to searches for the H dibaryon, the properties of ${\ensuremath{\Xi}}^{\ensuremath{-}}d$ atoms are also discussed. The role of Stark mixing and its effect on S and P state capture of ${\ensuremath{\Xi}}^{\ensuremath{-}}$ by the deuteron together with estimates of the resulting probability for producing the H dibaryon are considered in detail.

New precision measurement of the pionic deuteriums-wave strong interaction parameters

The x rays of the pionic deuterium 2p-1s transition were measured with a high resolution crystal spectrometer including a cyclotron trap (a magnetic device to increase the pion stopping density) and a CCD (charge-coupled device) detector system. The 1s strong interaction shift ${\ensuremath{\epsilon}}_{1s}$ and total width ${\ensuremath{\Gamma}}_{1s}$ were determined from the position and line shape of the x-ray peak. The (complex) pionic deuterium s-wave scattering length ${a}_{{\ensuremath{\pi}}^{\ensuremath{-}}d}$ was deduced. Its real part was related to the pion-nucleon scattering lengths, and the isoscalar coupling constant for ${\ensuremath{\pi}}^{\ensuremath{-}}$ absorption was deduced from the imaginary part.

X-ray spectroscopy of the pionic deuterium atom

The low energy X-rays of the pionic deuterium 3 P-1 S 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 1 S strong interaction shift ϵ 1 S and total decay width Γ 1 S 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 a π − d was deduced: a π −d = −0.0259(±0.0011) + i0.0054(±0.0011)m π −1 . From the real part of a π − d a constraint in terms of the isoscalar and isovector πN′ scattering lengths b 0 and b 1 was deduced. From Im a π − d we determined the isoscalar coupling constant for π − absorption: | g 0| = (2.6 ± 0.3) 10 −2 m π −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.

The DEAR experiment at DAΦNE

DEAR is one of the first experiments at the new DAΦNE O-factory at the Laboratori Nazionali di Frascati dell'INFN. The objective of the DEAR experiment is to perform a precision measurement of the strong interaction shifts and widths of the K-series lines in kaonic hydrogen and the first observation of the same quantities in kaonic deuterium. The aim is to obtain a precise determination of the isospin-dependent kaon-nucleon scattering lengths which will represent a breakthrough in KN low-energy phenomenology and will allow us to determine the kaon-nucleon sigma terms. The sigma terms give a direct measurement of chiral symmetry breaking and are connected to the strangeness content of the proton. First results on background measurements with the DEAR NTP setup installed on DAΦNE are reported.

The strong interaction shift and width of the ground state of pionic hydrogen

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.

Strong interaction shift and width of the 1s level in pionic hydrogen.

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 ${a}_{{\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n}^{h}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.136\ifmmode\pm\else\textpm\fi{}{0.010m}_{\ensuremath{\pi}}^{\ensuremath{-}1}$.

Determination of the S-wave scattering length in pionic deuterium with a high resolution crystal spectrometer.

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}.

Measurement of the strong interaction shift and width of the 1S state in pionic hydrogen

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.

Precision measurement of antiprotonic hydrogen and deuterium X-rays

X-rays from antiprotonic hydrogen and deuterium have been measured at low pressures. Using the cyclotron trap, a 105 MeV/c antiproton beam from LEAR was stopped with an efficiency of 86% in 30 mbar hydrogen gas in a volume of only 100 cm3. The X-rays were measured with Si(Li) detectors and a Xe-CH4 drift chamber. The strong interaction shift and broadening of the Lymanα transition and the spin-averaged 2p width in antiprotonic hydrogen was measured with unprecedented accuracy. The triplet component of the ground state in antiprotonic hydrogen was determined for the first time.

Momentum-space method for pionic atoms.

A new momentum-space method is developed for calculation of the strong-interaction shifts and widths in pionic atoms. The singularity connected with the Coulomb potential is treated by using the Vincent and Phatak prescription. The nuclear and atomic distances are separated in our scheme and this secures numerical stability of the calculation. The latter property makes the method a useful alternative to the earlier algorithms. Sample results for a series of light pionic atoms are shown.

Determination of the strong interaction shift in pionic hydrogen with a high resolution crystal spectrometer system

The 3P-1S X-ray transition energy was measured in pionic hydrogen with a double focussing silicon crystal spectrometer in combination with a cyclotron trap and CCD detectors: E = 2885.98 ± 0.17 (stat.) ± 0.15 (syst.) eV. The corresponding strong intera ction shift ϵ 1S = 7.12 ± 0.32 eV (attractive) yields the scattering length combination 1 3 (2a 1 + a 3) = 0.086 ± 0.004 m π −1 .

Antiprotonic Hydrogen: From Atomic Capture to Annihilation

Antiprotons stopping in H2 form antiprotonic hydrogen, atoms of protons and antiprotons bound by their electromagnetic interaction. Antiprotonic hydrogen atoms are formed in high Rydberg states from which they deexcite by external Auger processes and by radiative transitions to the low-lying energy levels. The levels are shifted and broadened due to strong interactions between the two particles. The strong interaction shift and width of the 1S ground state and the width of the 2P state have been determined in recent experiments at the Low-Antiproton-Ring (LEAR) at CERN. The strong interaction effects can be understood quantitatively by including a meson exchange potential (known from nuclear forces) in the Hamiltonian. This meson exchange potential is known to require the existence of deuteron-like bound states of protons and antiprotons, often called baryonium. Baryonium resonances had beed searched for in numerous experiments but without any conclusive evidence for their existence. It is shown how a detailed understanding of the atomic cascade before annihilation has helped to find a new resonance which is likely such a baryonium resonance.

Annihilation shifts and widths of the p-bar-d atomic levels.

The strong interaction shifts and widths of the antiproton-deuteron atom are calculated within a simple three-body model. The nuclear p\ifmmode\bar\else\textasciimacron\fi{}-d optical potential is obtained from a projected form of the Faddeev equations with rank one, separable, S-wave two-body potentials. The N-N\ifmmode\bar\else\textasciimacron\fi{} potential parameters are fit to the zero-energy scattering results of the Graz potential. The Coulomb potential is combined with the nuclear optical potential to obtain the atomic levels from the Schr\"odinger equation. The truncation of the Faddeev model optical potential to the level of the standard t\ensuremath{\rho} impulse approximation overestimates the shifts and widths by up to 10% and 30%, respectively. The use of first-order perturbation theory for the atomic eigenvalue overestimates the widths by one order of magnitude.

Pionic-atom 3d2p X-ray measurements in 54,56Fe, 59Co, and 58,60,61,62,64Ni

We have measured the strong interaction shifts and widths of the pionic 3d2p transitions in separated isotopes of 54,56Fe, 59Co, and 58,60,61,62,64Ni. We have fitted phenomenological pionnuclear potential parameters to the pionic-atom data employing nuclear structure information from measured charge densities. We have explored the sensitivity of these data to the values of the p-wave terms and have used them to determine the neutron radii. We compare these radii with Hartree-Fock predictions and with the results of other probes.