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tector is a large-solid-angle magnetic spectrometer that consists of a silicon vertex detector (SVD), a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters (ACC), a barrel-like arrangement of time-of-flight scintillation counters (TOF), and an electromagnetic calorimeter (ECL) comprised of CsI(Tl) crystals located inside a su- perconducting solenoid coil that provides a 1.5 T magnetic field. An iron flux return located outside the coil (KLM) is instrumented to detect K 0 L mesons and to identify muons. The detector is described in detail elsewhere [14]. 

## SELECTION OF EVENTS 

Three-prong decays of the τ are selected from candidate τ $^{+}$τ − pair events as follows. We use events where the number of charged tracks is four and the sum of their charges is zero; the transverse momentum of each track in the laboratory frame is required to be larger than 0.1 GeV/ c , and the tracks should extrapolate back to the interaction point within ± 5 cm along the beam direction and ± 1 cm in the transverse plane. The sum of the reconstructed 

