ar X iv : 0 90 6 . 42 14 v 1 [ he p - ex ] 2 3 Ju n 20 09

The cross sections for the reactions ee → φη, φη, ρη, ρη have been measured using a data sample of 516 fb collected with the Belle detector at the KEKB asymmetric-energy ee collider. The corresponding values of the cross sections are: 1.4± 0.4± 0.1 fb (φη), 5.3± 1.1± 0.4 fb (φη), 3.1± 0.5± 0.1 fb (ρη) and 3.3± 0.6± 0.2 fb (ρη). The energy dependence of the cross sections is presented using Belle measurements together with those of CLEO and BaBar. High-statistics data samples accumulated at B-factories allow a study of rare exclusive two-body processes in ee annihilation. An example of such a highly suppressed process is the reaction ee → V P , where V and P stand for Vector and Pseudoscalar mesons, respectively. It has been observed [1, 2] that double charm production in ee → J/ψηc has an unexpectedly high cross section. The basic diagram for double charm production is very similar to the one describing ee → φη(η) where c quarks are replaced by s quarks. Thus, comparison of the two reactions may contribute to better understanding of the underlying physics. In addition, we investigate the processes ee → ρη(η), which also belong to the V P class with a different isospin configuration and light quarks only. Some of the ee → V P reactions have previously been measured at different center-of-mass (CM) energies: in the DM1 experiment at √ s between 1.4 and 2.18GeV [3], in the CLEO experiment at √ s = 3.67GeV [4] and by the BaBar collaboration at √ s between 1 and 3GeV using initial-state radiation (ISR) [5] and at √ s = 10.58GeV [6]. The cross section of the process ee → ρη was also measured by the BES collaboration at √ s = 3.65GeV [7]. The reaction ee → φη has not yet been observed, nevertheless the upper limit on its cross section set by CLEO [4] can be useful for discrimination between models that predict different energy dependences. The QCD-based models predict the energy dependence for the process ee → V P to be 1/s [8, 9] while the cross section for the process ee → φη measured by CLEO and BaBar favors a 1/s dependence. The form factor for the process ee → V P is expected to have a 1/s dependence [10]. Recently theoretical calculations of ee → V P cross sections have been published, which use the light cone approach [11, 12]. Predictions are given for two values of √ s: 3.67 and 10.58GeV. The authors of Ref. [11] claim that their results favor a 1/s dependence. In Ref. [12] σ ∼ 1/s is expected in the limit s→ ∞. The analysis presented here is based on data taken at the Υ(4S) ( √ s = 10.58GeV) with the Belle detector at the KEKB asymmetric-energy ee collider [13]. The total integrated luminosity of the onresonance sample used in the analysis is 516 fb. To check that the processes ee → V P are due to a single-photon annihilation and that the hadronic decay of the Υ(4S) does not give a significant contribution, we use a 58 fb data sample collected 60 MeV below the resonance peak. All the observed off-resonance signals are consistent with those at the Υ(4S) resonance within statistical errors. We use these data to set upper limits for the branching ratios of Υ(4S) → V P .