J C Chollet

Search for decays of the W± and Z bosons into quark-antiquark pairs

Abstract The invariant mass distribution of jet pairs observed in the UA2 central calorimeter is examined in the search for an excess of events in the region of the W ± and Z bosons, which would reveal their decays into quark-antiquark pairs. We give a detailed account of the methods of analysis used to optimize the mass resolution achieving ≅±10%. A structure is observed at the level of ≅ 3 standard deviations in the mass region of W ± and Z with shape and position consistent with expectation from their qqdecays. It contains 632 ± 190 events, 1.4 standard deviations above the standard model prediction of 340 ± 80 events.

Observation of the interference between KLo and KSo in the πoπo decay mode

Data obtained with a copper regenerator on the interference between the decays KLo → 2πo and KSo → 2π o are presented. The analysis leads to the results: φoo = 510 ± 30o, |ηoo| = (1.23 ± 0.24) (|ƒ − ƒko) × 10−3 where (ƒ−ƒ)ko is the regeneration amplitude for copper at 2 GeV/c in fm2. Present experimental data suggest (ƒ−ƒ)ko = 2.7 ± 0.3.

Further results on the interference between the πoπo decay of KLo and KSo

The experiment of Chollet et al. has been continued with a similar set up. The analysis of these new data leads to 56 free decay events KLo→πoπo and 1481 interference events KS, Lo, → πoπo behind a 20 cm thick copper regenerator. The results are ϕoo = 38o ± 25o and |ηoo|/(|f−f|/k) = (1.13 ± 0.12) × 10−3 where |f−f|/k is the regeneration amplitude for copper at 2 GeV/c in fm2.

Measurement of the KL0 → 2γ branching ratio and search for KS0 → 2γ decays

Abstract Using an optical spark chamber set-up, we have measured the two photon decay rate of neutral K mesons behind a regenerator. K L 0 → 2 γ decays are normalized to K S 0 → 2 π 0 events, so the result depends on the K 0 regeneration in copper at 2 GeV/ c and has a value of Γ( K L 0 → 2γ) Γ( K L 0 → all ) = (5.0 ± 1.0) × 10 −4 [22 mb /(|ƒ− ƒ |/k)] 2 . K S 0 → 2 γ events are not observed, and from the normalization to K S 0 → 2 γ 0 we get Γ( K S 0 → 2γ) Γ( K S 0 → all ) −3 with 90% conf