M. Amoretti

Production and detection of cold antihydrogen atoms.

A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem—experimental investigations involving comparisons of particles with antiparticles are numerous. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN) and at Fermilab, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.

Positron plasma diagnostics and temperature control for antihydrogen production

Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss nondestructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed.

Complete nondestructive diagnostic of nonneutral plasmas based on the detection of electrostatic modes

The detection of electrostatic nonneutral plasma modes in the ATHENA (ApparaTus for High precision Experiment on Neutral Antimatter) experiment [M. Amoretti, C. Amsler, G. Bonomi et al., Nature (London) 419, 456 (2002)] is described. A complete nondestructive diagnostic of the plasma based on a fit to the line shape of the function describing the power transmitted through the plasma around the frequency of the fundamental mode is developed and the experimental results are presented and discussed.

Evidence For The Production Of Slow Antiprotonic Hydrogen In Vacuum

We present evidence showing how antiprotonic hydrogen, the quasistable antiproton (p)-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion H2+ in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events, evidence is presented for antiprotonic hydrogen production with sub-eV kinetic energies in states around n=70, and with low angular momenta. The slow antiprotonic hydrogen may be studied using laser spectroscopic techniques.

Production of slow protonium in vacuum

We descrbe how protonium, the quasi-stable antiproton-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion

Producing Slow Antihydrogen for a Test of CPT Symmetry with ATHENA

{\rm H}_2^+

Centrifugal separation of ions and an oppositely charged non-neutral plasma

in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events in the ATHENA experiment, evidence is presented for protonium production with sub-eV kinetic energies in states around n = 70, with low angular momenta. This work provides a new two-body system for studies using laser spectroscopic techniques.

Cold Antihydrogen at ATHENA:Experimental Observation and Beyond

The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported.

Results from ATHENA

The motion of a single ion confined in a Penning-Malmberg trap together with a plasma column of electrons or positrons is described by means of a simple model. The model qualitatively reproduces the basic mechanism of the centrifugal separation for multispecies plasma composed of particles with the same sign of charge. The ion is pushed toward the plasma boundary also when its charge and the plasma charge have opposite signs. An estimation of the characteristic time scale for the separation is obtained and discussed.

Temperature dependence of anti-hydrogen production in the ATHENA experiment

Antihydrogen atoms may become the easiest and most precise way to probe deeply into tests of violation of the CPT (charge conjugation, parity, time reversal) symmetry and the Weak Equivalence Principle (WEP). We review the first production of cold antihydrogen atoms within the ATHENA/AD‐1 experiment at CERN, its motivations and studies henceforth. The ATHENA success was followed almost immediately by the ATRAP group. From the initial claim of production of tens of thousand of these exotic species — by the mixing of cold and trapped positrons and antiprotons — we have evolved to better understand and control the system. The joint production for 2002 and 2003 has been re‐evaluated to about one million antiatoms. We have performed cooling efficiency studies of antiprotons within the positron cloud; developed ways to excite and heat the positron cloud, and probe its number, density and temperature in situ; developed antiproton and antihydrogen imaging tomography. We have also been able to gather information o...