Search

The cascade of ( p 4 He) + and ( p 3 He) + has been calculated as a function of the helium density. Collisions between antiprotonic helium ions and helim atoms were simulated, and the strength of Stark mixing transitions and of Auger transitions were derived. The yields of radiative transitions were then calculated by means of a cascade model without use of any free parameter. The results for electromagnetic effects agree fully with results of recent LEAR experiments using helium gas targets with pressures down to 36 mbar and with results of previous experiments stopping antiprotons in liquid helium and in pressurized helium gas. The fractional contribution of pHe annihilations from S, P, and D state have been determined.

We present a model of the cascade of antiprotonic hydrogen ( p p ) atoms. Stark mixing and external Auger rates are calculated by simulation of the collision processes between p p atom and hydrogen. The calculations show that the results are insensitive to variations of the p p velocity which is not calculated within the model. Therefore no free parameter is needed. The model describes the intensities of the characteristic lines, the fractional annihilation of S- and P-states, and the cascade time. The results agree with recent experiment data obtained at LEAR.

Narrow states observable through the emission of monoenergetic charged pions have been searched for in p p annihilation at rest in a gaseous hydrogen target where annihilation from atomic angular momentum L = 1 states dominates. No structure is observed. The 5σ upper limit for the production of narrow states in the mass range 1100–1670 MeV is 2 × 10 −3 of all annihilations.

The magnetic moment of positive muons stopped in liquid bromine has been measured by determining the precession frequency in a magnetic field of sub ppm homogeneity with a stroboscopic method. The diamagnetic shielding of the magnetic field was determined by NMR measurements on analogous chemical compounds. The present result is μ μ / μ p = 3.1833448 (29) (±0.9 ppm).

The importance of approximate isospin selection rules observed inN¯ N annihilation at rest into two strange mesons is emphasized. The selection rules are traced back to a symmetry between amplitudes describing annihilation by the flux of quarks. Presumably the symmetry reflects the symmetry of ¯qq annihilation vertices. The relation of the symmetry to a quark — diquark substructure of the nucleon is discussed.

Antiprotons moderated in H 2 are captured in the Coulomb field of protons forming pp atoms. The time which elapsed between capture into atomic orbits and annihilation has been measured in H 2 at NPT. A cascade time of (5.1±0.7) ns was determined.

Proton-antiproton annihilation at rest into two mesons is analysed in a model describing annihilation by quark lines. The model allows to fit existing data with two parameters. The parameters describe the amplitudes for diagrams with and without rearrangement of quark lines.

It is shown that a previously described method for measuring the spin resonance of free electrons in a trap can also be used to measure their (g-2) anomaly. The electrons are trapped in an electrostatic quadrupole field with a superimposed homogeneous axial magnetic field, and are polarized by spin exchange. The spin and (g-2) resonance are monitored through the spin dependence of the excitation processe+Na (3S)→e+Na(3P). Calculations are made of the energy levels and transition probabilities of the trapped electrons.

We report results of a high resolution search for the tensor glueball candidate ξ(2230) in a p p formation experiment. π0π0 and ηη decay channels were measured in a scan of the mass region 2220 MeV to 2240 MeV. No evidence for the existence of ξ(2230) was found. 95% confidence upper limits for the possible existence of ξ are presented.

The detection of tagged low-energy X-rays in a gas proportional counter is reported in order to demonstrate the capability of the X-ray drift chamber technique to identify low-energy X-rays. The drift-time distributions of X-ray lines of different energies vary because of the strong energy dependence of the X-ray absorption cross-section. Soft X-rays display a drift-time spectrum that is sharply peaked at late drift-times, while X-rays of higher energy show a more uniformly spread drift-time distribution. The drift-time information therefore supplements the amplitude information in the low-energy region where the resolution is poorer. We have used a 54Mn source that emits 0.5–0.65 keV and 5.5 keV X-rays in coincidence with 835 keV γ-rays which are well suited for tagging.

The study of polarization effects in nucleon-nucleon scattering experiments has increased considerably our understanding of the Nuclear forces. Correspondingly it can be expected that the study of polarization phenomena in antiproton-nucleon scattering will also help us to resolve — at least partly — the complicated spin structure of the antiproton-nucleon amplitudes.

The features of the Crystal Barrel Detector which is in preparation for LEAR at CERN, are discussed. The physics aims include qq‐ and exotics‐spectroscopy and a detailed investigation of yet unknown pp‐anihilation channels. An eventual later use on the PSI‐B‐Meson‐Factory is discussed. The paper finishes with a description of the present status of the project.

We have observed the E meson produced in pp annihilation at rest (pp → π+π[E → K+K0π−, K−K0π+) in a H2 gas target at NTP. The mass and width are M=1413±8 MeV and Γ=62±16 MeV. There is strong evidence (3σ) for the production of the f1(1285) in the same final state. The partial‐wave analysis of the E decay Dalitz plot gives no preference for the spin‐parity assignments 0−+ or 1++. The absolute branching ratio for (60±10%) P wave annihlation is (3±0.9) ⋅ 10−4, compared to (7.12m*0.7 ⋅ 10−4 in liquid H2, suggesting that ππE production is strongly suppressed in the P‐wave. This result supports the 0− spin‐parity assignment for the E meson.

The ASTERIX experiment has been designed1) with three main objectives: (a) To study the general features of pp interactions at rest: strong interaction shift and broadening of the atomic levels of the pp atom, branching ratios of the pp annihilation channels from S and P atomic states, spin dependence of shifts, widths and branching ratios; (b) To extend (with comparable resolution, better reconstruction of final states, about 100 times more statistics and data both with P-wave and S-wave initial states) the work done so far in the spectroscopy of light mesons produced in pp annihilations at rest2); (c) To search with high sensitivity for gluonium (gg, ggg bound states), qqqq baryonium structures and NN states bound by strong interactions. These objects are likely to be produced in pp annihilations at rest besides the well-known qq light mesonic structures already seen in bubble chamber experiments.

This enlarged version of the presentation made at the Workshop refers to the general search for boson resonances produced in pp annihilations at rest to be made as part of the ASTERIX experiment at LEAR.

We have observed the Balmer series of antiprotonic hydrogen atoms formed in gaseous hydrogen at 4 atm. The yield of L X-rays was determined to be (6 ± 3)% per stopped antiproton. The 2P state is dominantly depopulated via p p annihilation and not by radiative transitions to the 1S state.

The cascade of muonic helium and its pressure dependence has been calculated over the whole pressure range from 1×10 −2 to 1×10 3 atm. The calculation does not use any free parameter. The results show good agreement with experimental data.

X-ray transitions to the 4F, 3D, and 2P atomic levels of pHe have been observed with antiprotons stopped in He gas at 4 and 1.1 atm NT. The population by radiative transitions of the 3D level in gas Y M (4 atm ) = (28±14)% and Y M (1.1 atm ) = (43±22)% exceeds by more than one order of magnitude that measured in liquid He. The annihilation width of the 3D level Γ a 3D = 2.8±1.0 × 10 −3 eV is determined from the ratio between the numbers of X-rays feeding and depopulating the 3D level. The strong-interaction shift of the 2P level e (2P) = −14±6 eV is obtained by inputting the p He experimental X-ray yields into a cascade calculation, the results of which are in good agreement with well-established data from muonic, pionic, and kaonic helium.

Results on antiproton absorption at rest in gaseous nitrogen and deuterium are presented from an analysis of approximately ${10}^{6}$ events each taken with a magnetic spectrometer. Inclusive features such as pion and proton multiplicities and spectra are presented. Data relating to absorption modes requiring more than one nucleon, such as the \ensuremath{\Lambda} yield, the \ensuremath{\Lambda} spectrum, and the exclusive deuterium channels p\ifmmode\bar\else\textasciimacron\fi{}d\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p, \ensuremath{\Lambda}${K}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ are discussed. The fully reconstructable channels p\ifmmode\bar\else\textasciimacron\fi{}d\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p,${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{+}$ ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p also show a high-energy proton tail unaccounted for by single nucleon rescattering mechanisms.

The ASTERIX experiment has been set up to study \(p\bar p\)-annihilations at rest into \(q\bar q\)-mesons and other boson resonances like glueballs (gg, ggg), hybrids (\(q\bar qq\)), baryonia (\(qq\bar q\bar q\)) and \(N\bar N\) bound states from S and P states of the \(p\bar p\) atom. A detailed description of the apparatus can be found in the proposal1) and in the contributions to the LEAR Erice Workshop 19822, 3)

The ASTERIX spectrometer has been used to study the formation and the ground state of the pp atom and exclusive final states of pp annihilation at rest in a H2 gas target at NTP, using antiprotons from the Low Energy Antiproton Ring (LEAR) at CERN. The article describes the mechanical construction of the apparatus, the trigger logic, the chamber readout, and the data acquisition system. The detector calibration and the offline processing of the 55 million reconstructed events are illustrated. An overview is given about the new physics results obtained by the experiment.

AN analysis is presented of two body final states of collinear charged pions or kaons from antiproton‐proton annihilation at rest in the ASTERIX spectrometer at LEAR. The relative branching ratio of kaons to pions, which is sensitive to the dynamics of quark‐antiquark annihilation and rearrangement, is shown to differ for P and S wave initial states.

Roy's equations are used to check if the scalar-isoscalar pion-pion scattering amplitudes fitted to experimental data fulfill crossing symmetry conditions. It is shown that the amplitudes describing the ``down-flat'' phase shift solution satisfy crossing symmetry below 1 GeV while the amplitudes fitted to the "up-flat'' data do not. In this way the long standing "up-down" ambiguity in the phenomenological determination of the scalar-isoscalar pion-pion amplitudes has been resolved confirming the independent result of the recent joint analysis of the pi+pi- and pi0pi0 data., 6 pages, 2 figures, talk given at Tenth International Conference on Hadron Spectroscopy (Hadron'03), Aschaffenburg, Germany, August 31 - September 6 2003