CERN Accelerating science

noimg: The estimated inclusive, $\epem$ and $\rm h^+h^-$ backgrounds in each $\wgg$ bin.: The number of events, estimated background and $\gamma \gamma \ra \ppbar$ cross section as a function of $ W_{\gamma \gamma}$ for $ |\cos \theta^*| < 0.6$. The average value $\langle W_{\gamma \gamma} \rangle$ of each bin corresponds to a weighted average according to a $W_{\gamma \gamma}^{-12}$ distribution. The first uncertainty is statistical, the second systematic.: The differential cross section as a function of $|\cos\theta^*|$ for the different $\wgg$ ranges. The first uncertainty is statistical, the second systematic.: $\gamma \gamma \ra \ppbar$ cross section as a function of $ W_{\gamma \gamma}$ for $ |\cos \theta^*| < 0.3$ and $ 0.3 < |\cos \theta^*| < 0.6$. The average value $\langle W_{\gamma \gamma} \rangle$ of each bin corresponds to a weighted average according to a $W_{\gamma \gamma}^{-12}$ distribution. The first uncertainty is statistical, the second systematic.

The ratio between the transverse energy deposited in the electromagnetic calorimeter, $E_t$, and the transverse momentum, $p_t$, for the proton candidate after the antiproton selection. The $\epem \ra \epem \epem$ Monte Carlo prediction is superimposed on the data.

The effective mass of the $\rm p \overline{p}$ pair, $\wgg$, for the 989 selected events. The 938 events at the right of the cut are used in the subsequent analysis.

The selection efficiency as a function of a) $\wgg$ for $| \cos \theta^* | < 0.6$ and b) $\cos \theta^*$ (full circles) for 2.1 GeV $ < \wgg <$ 4.5 GeV. The full squares indicate the efficiency for detecting two charged tracks of opposite charge in the detector, with no further requirements.

The selection efficiency as a function of a) $\wgg$ for $| \cos \theta^* | < 0.6$ and b) $\cos \theta^*$ (full circles) for 2.1 GeV $ < \wgg <$ 4.5 GeV. The full squares indicate the efficiency for detecting two charged tracks of opposite charge in the detector, with no further requirements.

The $\gamma \gamma \rightarrow \ppbar$ cross sections as a function of $W_{\gamma\gamma}$ for $|\cos \theta^*| < 0.6$ compared to the three-quark model calculation {\protect \cite{th3}} and to the recent quark-diquark model prediction {\protect \cite{th6}}, available for $W_{\gamma \gamma} >2.5$ GeV. Statistical and systematic uncertainties are added in quadrature.

The differential cross section as a function of $|\cos\theta^*|$ for a) $2.1 < W_{\gamma \gamma} < 2.5$ GeV, b) $2.5< W_{\gamma \gamma}< 3.0 $ GeV and c) $3.0 < W_{\gamma \gamma} < 4.5 $ GeV. The data are compared to the predictions of the quark-diquark model. The fit in a) is described in the text.

The differential cross section as a function of $|\cos\theta^*|$ for a) $2.1 < W_{\gamma \gamma} < 2.5$ GeV, b) $2.5< W_{\gamma \gamma}< 3.0 $ GeV and c) $3.0 < W_{\gamma \gamma} < 4.5 $ GeV. The data are compared to the predictions of the quark-diquark model. The fit in a) is described in the text.

The differential cross section as a function of $|\cos\theta^*|$ for a) $2.1 < W_{\gamma \gamma} < 2.5$ GeV, b) $2.5< W_{\gamma \gamma}< 3.0 $ GeV and c) $3.0 < W_{\gamma \gamma} < 4.5 $ GeV. The data are compared to the predictions of the quark-diquark model. The fit in a) is described in the text.

a) The $\gamma \gamma \rightarrow \ppbar$ cross section as a function of $W_{\gamma\gamma}$ for the large angle region, $|\cos \theta^*|<0.3$ (full circle), and the small angle region, $0.3<|\cos \theta^*|<0.6$ (open circle). b) The small angle and c) the large angle cross section with the quark-diquark model predictions and the fit described in text.

a) The $\gamma \gamma \rightarrow \ppbar$ cross section as a function of $W_{\gamma\gamma}$ for the large angle region, $|\cos \theta^*|<0.3$ (full circle), and the small angle region, $0.3<|\cos \theta^*|<0.6$ (open circle). b) The small angle and c) the large angle cross section with the quark-diquark model predictions and the fit described in text.

a) The $\gamma \gamma \rightarrow \ppbar$ cross section as a function of $W_{\gamma\gamma}$ for the large angle region, $|\cos \theta^*|<0.3$ (full circle), and the small angle region, $0.3<|\cos \theta^*|<0.6$ (open circle). b) The small angle and c) the large angle cross section with the quark-diquark model predictions and the fit described in text.