Can extended objects explain the GSI e+ e? lines?

Abstract

The anomalous electron-positron coincidences observed in heavy-ion collisions have been interpreted as signal for the pair decay of hitherto unknown neutral objects with masses around 1.8 MeV. We discuss the decay modes of such extended composite particles when they are bound to a nucleus. In particular we investigate the angular correlation of the emitted pair and the competing single-photon decay channel. We confront the particle hypothesis with recent negative results from experiments searching for resonances in Bhabha scattering. The induced pair decay of a metastable 1 § § state in secondary collisions with target atoms is discussed as a possible explanation. PACS: 14.80.Pb; 12.90. +b; 23.20.Nx This is the characteristics of a two-body decay of a (slowly moving) particle-like object X~ § +e-with mass in the 1.8 MeV region. This has led to a large diversity of models and speculations on the nature of the object X ~ [9]. Meanwhile the situation has become even more complex since several line structures have been found which do not all confirm with the two-body decay scenario [10,11].In this paper we will briefly summarize the experimental situation (Sect. 2) and then concentrate on a particular model for a composite X ~ particle [12,13] which was devised to give a comprehensive description of the data (Sect. 3). In Sect. 4 we investigate the decay modes of X ~ bound to a nucleus. Section 5 confronts the particle hypothesis with recent data from Bhabha scattering experiments.

Bound states of composite particles and the GSI lines

“…The Coulomb force repells the f+ particle to a large distance so that it feels an effective spherically symmetric interaction exerted by the (nucleus +f-)-system. Using this simple approach it was found [12] that although the binding energy can be brought into reasonable agreement with the observed level spacing the disturbance of the back-to-back correlation turns out to be too small.…”

“…(i) The calculated angular correlation of electron and positron [12] deviates from the pure back-to-back behaviour characteristic of a free two-body decay. However, this deviation is too small to explain the experimentally observed forward correlation.…”

“…V(rl) is the interaction potential between thef +-and f--particles. To agree with earlier work [10,12] we simply will use a linearly rising confining potential V(rO = ~r: (2) and neglect the Coulomb interaction between the constituents.…”

Two-particle bound states in the field of a heavy nucleus

“…V(rx) describes any additional interaction potential between the light particles which, from a calculational point of view, can be chosen quite freely. In the example of thef +f-model [10,11] we will use a linearly rising confining potential V(q)= o-r~. We treat the problem nonrelativistically and neglect the spin of the particles.…”

Induced decay of compositeJPC=1++Stein1, Reinhardt2, Schäfer3 et al. 1994Phys. Rev. ASelf Cite2000View full textAdd to dashboardCite

“…Assuming that the dominant decay channel is the e + echannel, the most sensitive Grenoble measurements rule out all resonances with lifetimes < 10-'' s, which is the time scale set by the heavy-ion experiments [5,8]. However, the fact that low-Z solid-state targets had to be used may provide a loophole for the particle interpretation as already outlined in [9].…”