Production of Prompt Charmonia in $e^+e^-$ Annihilation at $\sqrt{s}\approx 10.6$ GeV

Abstract

The production of prompt $J/ψ$, $ψ(2S)$, $χ_{c1}$ and $χ_{c2}$ is studied using a $32.4 fb^{-1}$ data sample collected with the Belle detector at the $Υ(4S)$ and 60 MeV below the resonance. The yield of prompt $J/ψ$ mesons in the $Υ(4S)$ sample is compatible with that of continuum production; we set an upper limit ${\cal B}(Υ(4S) \to J/ψX) < 1.9 \times 10^{-4}$ at the 95% confidence level, and find $σ(e^{+}e^{-} \to J/ψX)=1.47\pm 0.10 \pm 0.13$ pb. The cross-sections for prompt $ψ(2S)$ and direct $J/ψ$ are measured. The $J/ψ$ momentum spectrum, production angle distribution and polarization are studied.

Figures (4)

• Figure 1: Mass distributions for the $J/\psi \to e^+ e^-$ (a,c) and $\mu^+ \mu^-$ (b,d) candidates; (a) and (b) are for $\Upsilon (4S)$ data with $p^{*} > 2$ GeV/$c$, (c) and (d) are for off-resonance data. $N_{J/\psi}$ is the number of $J/\psi$ mesons determined by a fit to the dilepton mass distribution, where a Crystall Ball line shape function skwarnicki is used for the signal and the background is described by a polynomial.
• Figure 2: Mass difference distributions for charmonium candidates in the $\Upsilon(4S)$ data: (a) $M_{l^{+}l^{-}\pi^{+}\pi^{-}} - M_{l^{+}l^{-}}$ for $\psi(2S)$ candidates with $p^{*}> 2$ GeV/$c$. (b) $M_{l^{+}l^{-}\gamma} - M_{l^{+}l^{-}}$ for $\chi_{c1,c2}$ candidates with $p^{*}> 2$ GeV/$c$. The curves represent fit results with a Crystall Ball line shape for the signal and a polynomial for the background.
• Figure 3: CM momentum distributions of prompt charmonia, corrected for efficiency : (a) $J/\psi$ (filled points) and $J/\psi$ mesons from $\psi(2S)\to J/\psi\, X$ (open points); (b) $\psi(2S)$.
• Figure 4: The $\cos\theta^{*}$ (a) and $\cos\theta_{H}$ (b) distributions for low and high $p^{*}$. The curves represent fit results, described in the text and summarized in Table \ref{['fits']}.