Antideuteron production in ${\rm Y}(nS)$ decays and the nearby continuum

Using CLEO data, we study the production of the antideuteron, $\overline{d}$, in ${\rm Y}(nS)$ resonance decays and the nearby continuum. The branching ratios obtained are ${\mathcal{B}}^{\mathrm{dir}}({\rm Y}(1S)\to \overline{d}X)=(3.36\pm 0.23\pm 0.25)\times {10}^{-5}$, $\mathcal{B}({\rm Y}(1S)\to \overline{d}X)=(2.86\pm 0.19\pm 0.21)\times {10}^{-5}$, and $\mathcal{B}({\rm Y}(2S)\to \overline{d}X)=(3.37\pm 0.50\pm 0.25)\times {10}^{-5}$, where the “dir” superscript indicates that decays produced via reannihilation of the $b\overline{b}$ pair to a ${\gamma }^{*}$ are removed from both the signal and the normalizing number of ${\rm Y}(1S)$ decays in order to isolate direct decays of the ${\rm Y}(1S)$ to $ggg$, $gg\gamma$. Upper limits at 90% C.L. are given for $\mathcal{B}({\rm Y}(4S)\to \overline{d}X)<1.3\times {10}^{-5}$, and continuum production $\sigma (e^{+}{e}^{-}\to \overline{d}X)<0.031\mathrm{pb}$. The ${\rm Y}(2S)$ data is also used to extract a limit on ${\chi }_{bJ}\to \overline{d}X$. The results indicate enhanced deuteron production in $ggg$, $gg\gamma$ hadronization compared to ${\gamma }^{*}\to q\overline{q}$. Baryon number compensation is also investigated with the large ${\rm Y}(1S)\to \overline{d}X$ sample.

Figure 1

The ${\chi }_d$ distribution in the momentum range $0.45–1.45\mathrm{GeV}/c$ fit to a Gaussian antideuteron signal and a falling background function. The background estimation employs the area of the triangular region between the dashed cuts, as detailed in the text.

Figure 2

Deuteron ${\chi }_d$ distributions ($dE/dx$ normalized deviation) in different deuteron momentum bins.

Figure 3

Momentum dependence of antideuteron production in ${\rm Y}(1S)$ decays observed by CLEO (filled circles) and ARGUS (open diamonds). The solid line shows the fit described in the text; the dashed portion is an extrapolation beyond the momentum range which we observe.

Figure 4

Antideuteron and deuteron sample distributions for the momentum range $0.6–1.1\mathrm{GeV}/c$ in the ${\rm Y}(1S)$ data. Top row: $\Delta r$ and $\Delta z$ for antideuterons. Middle row: $\Delta r$ and $\Delta z$ for deuterons. Bottom left: $\Delta z$ for deuterons in $\Delta r$ sidebands. Bottom right: Fit to $\Delta z$ for deuterons after subtraction of the $\Delta r$ sidebands in the previous panel. The signal Gaussian width is fixed to the antideuteron signal width from the fit to data in the upper right panel.

Figure 5

$d$ and $\overline{d}$ yields in the momentum range $0.45–1.45\mathrm{GeV}/c$ with additional criteria as described. Top row: ${\chi }_d$ for deuterons (left) and antideuterons (right) with all standard cuts, including $-2<{\chi }_d<+3$. Second row: As above, but requiring at least one antiproton (left) or proton (right) candidate in addition. Third row: As above, but requiring two antiproton (left) or two proton (right) candidates instead. Fourth row: $\Delta r$ and $\Delta z$ for deuterons with $n_p>0$. The curve on the left shows a fit to a signal Gaussian plus a polynomial background. Fifth row: $\Delta r$ and $\Delta z$ for deuterons with $n_p=2$.

Figure 6

An ${\rm Y}(1S)\to 3{\pi }^{+}3{\pi }^{-}d\overline{d}X$ candidate event in the CLEO detector, viewed along the beam axis. The $d$ track ($p=0.55\mathrm{GeV}/c$) is highlighted. The $\overline{d}$ track ($p=0.84\mathrm{GeV}/c$) is the one with most energetic calorimeter shower; the circle size is proportional to the shower energy. The difference between the center-of-mass energy and the total energy of observed particles, based on tracking and particle identification, is about 120 MeV.