Antideuteron Yield at the AGS and Coalescence Implications

We present Experiment 864's measurement of invariant antideuteron yields in $11.5A$ GeV/c Au+Pt collisions. The analysis includes 250×10⁶ triggers representing 14×10⁹ $10%$ central interactions sampled for events with high mass candidates. We find $(1/2{π}{p}ₜ){d}²N/{dydp}ₜ{{0ex}{0ex}}={{0ex}{0ex}}3.5±{}1.5(stat{)}_{{-}0.5}+0.9(syst)×{}{10}^{{-}8}{GeV}^{{-}2}{c}²$ for $1.8<y<2.2$, $〈{p}ₜ〉{{0ex}{0ex}}={{0ex}{0ex}}0.35GeV/c$ ( ${y}c.m.{{0ex}{0ex}}={{0ex}{0ex}}1.6$) and $3.7±{}2.7(stat{)}_{{-}1.5}+1.4(syst)×{}{10}^{{-}8}$ ${GeV}^{{-}2}{c}²$ for $1.4<y<1.8$, $〈{p}ₜ〉{{0ex}{0ex}}={{0ex}{0ex}}0.26GeV/c$, and a coalescence parameter ${{B}₂}$ of $4.1±{}2.9(stat{)}_{{-}2.4}+2.3(syst)×{}{10}^{{-}3}{GeV}²{c}^{{-}3}$. Implications for coalescence and antimatter annihilation are discussed.