M. Tonutti

Observation of the radiative transition ψ → γE(1420)

Abstract We have observed a radiative transition from the ψ to a state decaying into K S K ± π ∓ , with mass M = 1.44 −0.015 +0.01 GeV/ c 2 and width Γ = 0.05 −0.02 +0.03 GeV/ c 2 . We tentatively identify this state as the E(1420). Assuming that this state is an isospin singlet, we have determined the branching fraction product B(ψ → γ E ) × B( E × K K π) = (3.6 ± 1.4) × 10 −3 .

A measurement of the cross section for four-pion production in λλ collisions at spear☆

Abstract We present a measurement of the cross section for the reaction e + e − → e + e − π + π − π + π − at SPEAR. This channel is found to be large and dominated by the process γγ → ϱ 0 ϱ 0 → π + π − π + π − . The cross section, which is small just above the four-pion threshold, exhibits a large enhancement near the ϱ 0 ϱ 0 threshold.

Pion pair production in photon-photon collisions at spear

Abstract We report a measurement of the cross section for the process γγ → π + π − at invariant masses 500 MeV/ c 2 m ππ c 2 . A value for the radiative width of the f(1270) tensor meson Γ f→ γγ = 3.6 ± 0.3 ± 0.5 KeV (helicity λ = 2) has been obtained from a fit to the observed ππ mass spectrum.

Observations of S∗ → π+π−in ψ decay

Abstract Copious production of S ∗ decaying into π + π − is observed in ψ decay. (974 ± 4 - i 14 ± 5) MeV, consistent with the parameters extracted from couplede channel; fits to pheripheral π + π − and K + K − production experiments. The inclusive branching ratio for ψ → S ∗ + X is found to be (0.42 ± 0.08)%.

A study of the decayτ−→π−μτ

We present a high statistics measurement of the branching ratio for the decay τ-→π-μτ using data obtained with the Mark II detector at the SLAC e+e- storage ring SPEAR. We have used events from the center-of-mass energy region 3.52 to 6.7 GeV to determine that B(τ-→π-μτ)=0.117±0.004±0.018. From electron-muon events in the same data sample, we have determined that B(τ-→π-μτ) B(τ-→e--μeμτ)=0.66±0.03±0.11. We present measurements of the mass and spin of the τ and the mass of the τ neutrino based, for the first time, on a hadronic decay mode of the τ.

A search for stable particles heavier than the proton and for q = 2/3 quarks produced in e+ e- annihilation

Abstract We have searched 1.4 × 10 6 e + e − annihilation events for particles with 1–3 GeV/ c 2 mass and charge Q = − 2 3 from the processes e + e − →q q X and e + e − → q q . Upper limits of RQ ∼ 10 −4 for each process are presented which improve the previous limits on free quark production in electromagnetic interactions by 2 orders of magnitude.

Results on two-photon interactions from Mark II at SPEAR

Two-photon interactions have been studied with the SLAC-LBL Mark II magnetic detector at SPEAR. The cross-section for η′ production by the reaction e+e− → e+e−η′ has been measured over the beam energy range from 2 to 4 GeV. The radiative width Tγγ(η′) has been determined to be 5.8 ± 1.1 keV (±20% systematic uncertainty). Upper limits on the radiative widths of the f(1270), A2(1310), and f′(1515) mesons have been determined. The two-prong final state events show a signal for the f(1270) decaying into η+π− . The current status of this analysis has been discussed.