The phi-phi analysis
Eta_c energy
The data taken thanks to the phiphi trigger
have been analyzed, for the eta_c energy and eta_c'.
At the eta_c energy have been analyzed 280.2 nb^-1 on the peak
(2985-2990)MeV, 139.6 nb^-1 below the resonance (2950,2957)MeV and
145.5 above the resonance (3004,3009)MeV.
Since the apparatus doesn't distinguish between different kind
of hadronic decays a special method has been used:
the value of the phi mass (M_phi=1019 MeV/c^2) is changed in the kinameatic
fit from 999 MeV to 1059 MeV, with 5MeV steps.
For each step the fit is applied to the data and the number of events with
P(chi^2)> K (K=0.4, 0.5, 0.6) is counted.
The real phi-phi events pass the cut only with the right value of M_phi,
while the background events pass the above cut even for different value
of M_phi. From the difference between the number of phi-phi events for
M_phi=1019 MeV and the the mean number of background events for M_phi
not equal to 1019 MeV we can calculate the number of real phi-phi events.
The results can be seen clicking here .
The total number of phi-phi events is about 30, corresponding to a cross
section of (3.3+-1.5)nb, on the eta_c peak. In the
off-resonance region there is no evidence of phi-phi signal.
Eta_c' energy
At the eta_c' energy 4 points have been analyzed:
Ecm=3620 MeV
Ecm=3625 MeV
Ecm=3630 MeV
Ecm=3644 MeV
The analysis method is the same described above. In all the points there is
no evidence of phi-phi signal click
here to see an eta_c' point),
due to a background too high.