Neutrons and the crystal ball experiments.

Abstract

The Crystal Ball detector, as originally constructed, consisted of a set of 672 optically-isolated NaI crystals, forming an approximately spherical shell and each crystal viewed by a photomultiplier, a charged-particle tracker within the NaI shell, and two endcaps to cover angles close to two colliding beams. The detector geometry subtends a solid angle of about 93% of 4{pi} st (20{degree} {le} {theta} {le} 160{degree} and 0{degree} {le} {phi} {le} 360{degree}) from the center. The Crystal Ball detector was used for two long series of experiments at the e{sup +}e{sup {minus}} colliding beam accelerators SPEAR [1, 2, 3, 4] at SLAC and DORIS [5, 6, 7, 8] at DESY. A new set of measurements using the Crystal Ball detector is planned at the Brookhaven National Laboratory Alternating Gradient Synchrotrons (BNL AGS). These new experiments will use the 672 NaI crystals from the original detector, but neither the tracker nor endcaps. The ''Crystal Ball'' in this note will refer only to the set of NaI crystals. Initially, the reactions to be studied will include {pi}{sup {minus}}p{r_arrow} neutrals with pion beam momenta {approximately}400-750 MeV/c and K{sup {minus}} p{r_arrow} neutrals with kaon beam momenta {approximately}600-750 MeV/c. Each of these reactions will include a neutron in the final state. whereas the fraction of e{sup +}e{sup {minus}} interactions with neutrons at SLAC or DESY was quite small. Consequently, there is relatively little experience understanding the behavior of neutrons in the Crystal Ball.