J. Eades

Hyperfine structure of antiprotonic helium revealed by a laser-microwave-laser resonance method.

Using a newly developed laser-microwave-laser resonance method, we observed a pair of microwave transitions between hyperfine levels of the (n,L)=(37,35) state of antiprotonic helium. This experiment confirms the quadruplet hyperfine structure arising from the interaction of the antiproton orbital angular momentum, the electron spin and the antiproton spin as predicted by Bakalov and Korobov. The measured frequencies of nu(+)(HF)=12.895 96+/-0.000 34 GHz and nu(-)(HF)=12.924 67+/-0.000 29 GHz agree with recent theoretical calculations on a level of 6x10(-5).

Spin-parity analysis of the E meson centrally produced in the reactions π+ p → π+ (K01K±K±) p and pp → p(K01K±π ±)p at 85 GeV/c

Results are presented of a spin-parity analysis on a sample of ∼ 1000 E mesons centrally produced in the reactions (π+/p) p → (π+/p) (K01K±π∓) p at 85 GeV/c. The E quantum numbers are determined to be JPC = 1++. Its decay in this channel is consistent with being 100% into K∗K + c.c. and no evidenceis seen for a δ π decay mode where δ → KK. The mass and width were determined to be M = (1425 ± 2) MeV and Γ = (62 ± 5) MeV.

Hyperfine structure of the metastable p̄He+ atomcule revealed by a laser-induced (n, l) = (37, 35) → (38, 34) transition

Abstract A precise scan of the previously discovered laser-induced transition ( n, l ) = (37, 35) → (38, 34) in pHe + revealed a doublet structure with a separation of Δ ν HF = 1.70 ± 0.05 GHz. This new type of “hyperfine” splitting is ascribed to the interaction of the antiproton orbital angular momentum and the electron spin.

The design of the optical components and gas control systems of the CERN Omega ring imaging Cherenkov detector

Abstract A large ring imaging Cherenkov detector (RICH) has been commissioned for use at the CERN Omega spectrometer. In the first of a series of reports we begin by discussing the general design of the device and illustrate the dependence of the attainable spatial resolution and range of particle identification on its optical parameters. We then describe in detail the construction and performance of the major optical components and gas systems of the detector.

A Ring Imaging Cherenkov detector for the CERN Omega Spectrometer — the design and recent performance

Abstract A large acceptance Ring Imaging Cherenkov detector has been constructed for use at the CERN Omega Spectrometer. The design of the detector is discussed, with attention paid to its principal components, and preliminary results are given which show that the detector is capable of identifying pions, kaons and protons at 80 GeV c .

Antihydrogen production and precision experiments

The study of CPT invariance with the highest achievable precision in all particle sectors is of fundamental importance for physics. Equally important is the question of the gravitational acceleration of antimatter. In recent years, impressive progress has been achieved in capturing antiprotons in specially designed Penning traps, in cooling them to energies of a few milli-electron volts, and in storing them for hours in a small volume of space. Positrons have been accumulated in large numbers in similar traps, and low energy positron or positronium beams have been generated. Finally, steady progress has been made in trapping and cooling neutral atoms. Thus the ingredients to form antihydrogen at rest are at hand. Once antihydrogen atoms have been captured at low energy, spectroscopic methods can be applied to interrogate their atomic structure with extremely high precision and compare it to its normal matter counterpart, the hydrogen atom. Especially the 1S-2S transition, with a lifetime of the excited state of 122 msec and thereby a natural linewidth of 5 parts in 10{sup 16}, offers in principle the possibility to directly compare matter and antimatter properties at a level of 1 part in 10{sup 16}.

Inclusive photoproduction of single charged particles at highp T

Single charged-particle inclusive cross sections for photon, pion and kaon beams on hydrogen at the CERN-SPS are presented as functions ofpT andxF. Data cover the range 0.0<pT<5.0 GeV/c and 0.0<xF<1.0 at incident momenta from 70 to 170 GeV/c. The comparison between photon- and hadron-induced data indicates a relative excess of particles withpT>1.6 GeV/c for the photon-induced data. Using the hadron-induced data to estimate the hadronic behaviour of the photon, the difference distributions and ratios of cross sections are a measure of the contribution of the point-like photon interactions. The data are compared with QCD calculations and show broadly similar features.

Laser resonance studies of the interactions of metastable antiprotonic helium atomcules p4He+ with surrounding H2 molecules

Abstract We have employed a laser resonance method to study the interactions of individual states of metastable antiprotonic atomcules p He + with surrounding H 2 molecules. We have found that the lifetimes of the ( n , 1) = (37,34) and (39,35) states are shortened by small admixtures of H 2 molecules in quite different ways; the observed quenching cross section for the upper (39,35) state in helium medium at 1 bar and 30 K is (2.4 ± 1.0) × 10 −15 cm 2 , a factor of 24 larger than that for the lower (37,34) state.

QUENCHING OF METASTABLE STATES OF ANTIPROTONIC HELIUM ATOMS BY COLLISIONS WITH H2 MOLECULES

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were induced making use of state dependent quenching effects caused by trace admixtures of H2 to the target helium gas. With this method of “H2-assisted inverse resonances” the decay rates of the states (n,l)=(39,l),l=36,37,38, and (38,l),l=35,36,37 of pHe+ were determined as a function of the H2 admixture. The quenching cross sections at 30 K deduced therefrom for the states with n=39 were found to be of the order of the geometrical cross section for pHe+–H2 collisons (2⋅10−15 cm2), with a moderate decrease with increasing l. Within a given cascade with constant v=n−l−1, the quenching cross sections for states with n=38 are smaller by a factor of 4–6 than those for states with n=39.

Analog measurement of delayed antiproton annihilation time spectra in a high intensity pulsed antiproton beam

Abstract An analog detection system has been developed to measure delayed antiproton annihilation time spectra for laser resonance spectroscopy of metastable antiprotonic helium atoms using the high-intensity pulsed beam of antiprotons from LEAR at CERN.