M. Goddard

Argus: A universal detector at DORIS II

Abstract The detector ARGUS has been designed as a universal tool to investigate final states from e + e − annihilation processes in the energy range of the ϒ resonances. ARGUS started operation in October 1982 and has since successfully taken data at the ϒ(1S), ϒ(2S) and ϒ(4S) energies, and in the nearby continuum. The detector combines excellent charged particle identification and good photon energy resolution over more than 90% of the full solid angle. A particle originating from the interaction vertex and leaving the beam tube traverses the following components: the vertex drift chamber, the main drift chamber which determines its momentum and specific ionization, the time-of-flight system through which its velocity is determined, and the electromagnetic calorimeter. Muons pass through the magnet coils and the flux return yoke and finally hit the muon chamber system which surrounds the detector. The momentum resolution of ARGUS is σ (p T ) P T = (0.01 2 + (0.009p T [ GeV /c]) 2 ) 1 2 , the photon energy resolution in the barrel shower counters is σ (E) E = ( 0.072 2 +0.065 2 E[ GeV ] ) 1 2 . Combining the information from all p devices, more than 80% of all charged hadrons can be recognized unambiguously. The electron-hadron and muon-hadron rejection rates are 1:200 and 1:50 respectively.

Branching ratio and mass spectrum of the decay ϒ′ → ϒπ+π−

Abstract The reaction e + e − → ϒ ′ → ϒπ + π − , with ϒ → anything, has been measured using the ARGUS detector at DORIS . We obtain a mass difference M ( ϒ ′) − M ( ϒ ) = (562 ± 3) MeV and a decay branching ratio BR( ϒ ′→ ϒπ + π − )=(17.9±0.9±2.1)%. The invariant mass spectrum of the π + π − system differs from phase space, but is well described by a matrix element of the form ( M ππ 2 − λM π 2 ) with λ =2.6±0.5. We also report preliminary results on the exclusive decay ϒ′ → ϒπ + π − , with ϒ → e + e − , and obtain BR( ϒ → e + e − ) = (2.8 ± 0.4 ± 04±0.3)%.

Measurement of tau decays into three charged pions

We report a study of the decay τ−→τ−τ+τ−vτ using the ARGUS detector at the DORIS II storage ring. Tau pairs were produced bye+e− annihilation at centre-of-mass energies near 10 GeV. We have observed about 1,700 events, corresponding to a branching ratio for τ−→τ−τ+τ−vτ of (5.6±0.7)%. The dominant mode for this decay is observed to beρ0π− in aJp=1+ spin state. Theρ0π− mass spectrum shows a broad enhancement near 1.10 GeV/c2, which has the properties expected for theA1.

Direct evidence for W exchange in charmed meson decay

Abstract Using the ARGUS detector at DORIS II, we have observed a signal of 36.7±8.0 events in the decay channel D 0 →K s 0 φ . In the same data sample, we have observed the well established decay D 0 →K s 0 π + π − , and find the ratio, Br(D) 0 → K s 0 φ) Br(D) 0 → K s 0 π + π − ) , to be 0.186±0.052. The substantial value of (0.99±0.32±0.17)% then derived for the branching ratio for D 0 → K 0 φ gives direct evidence that W exchange contributes D 0 decay.

An upper limit on the mass of the tau neutrino

Abstract Using the ARGUS detector at the e+e− storage ring DORIS II, we have measured the vτ energy spectrum in the decay π+π−π±vτ of τ leptons produced near s =10 GeV . From this energy spectrum, we derive an upper limit of m(v τ ) MeV c 2 at the 95% confidence level.

Production and Decay of the F Meson in

Abstract Using the ARGUS detector at DORIS we have observed the prediction of the charged D ∗ meson in e + e − annihilation at a center of mass energy of 10 GeV. The D ∗ fragmentation function has been measured using the decay channels D ∗+ → D 0 π + and D 0 → K − π + and K − π + π + π − . We find σ·Br for the channels D 0 → K − π + and D 0 → K − π + π + π − to be (23.6 ± 2.2 ± 4.7) pb and (51.0 ± 4.6 ± 15.5) pb respectively, and the ratio of branching ratios Br(D 0 → K − π + π + π − )/Br(D 0 → K − π + ) = 2.17 ± 0.28 ± 0.23. In addition we measure the mass difference M( D ∗+ ) − M( D 0 ) to be (145.46 ± 0.07 ± 0.03) MeV, and set an upper limit for D 0 − D 0 mixing of 0.11.

e^+ e^-

Abstract Using the ARGUS detector at the e+e− storage ring DORIS II, we have observed the colour suppressed decay B → J ψ X , with a branching ratio of (1.37+0.6−0.5)% for the mixture of charged and neutral Bs produced on the ϒ(4S). From the momentum distribution of the J ψ we conclude that Br ( B → J ψ X ) CL ) , for recoil masses, mx, less than 1 GeV/c2.

Annihilation at 10-{GeV} Center-of-mass Energy

Abstract Using the ARGUS detector at DORIS we have obtained evidence for a resonance which decays into an F meson and a photon. The observed mass is 2109 ± 9 ± 7 MeV, which is 144 ± 9 ± 7 MeV greater than the F meson mass. Its properties are consistent with those of the F ∗ meson with J P = 1 − .

OBSERVATION OF B MESON DECAY INTO J / psi

Abstract The production of antideuterons has been observed in electron-positron annihilations at center-of-mass energies around 10 GeV. Antideuterons have been identified unambiguously by their energy loss in the drift chamber, their time-of-flight and the pattern of their energy deposition in the shower counters of the ARGUS detector. The production rate in the momentum range (0.6−1.8) GeV/ c is (1.6 −0.7 +1.0 ) × 10 −5 per hadronic event.

Evidence for F∗ meson production in e+e− annihilation at 10 GeV center-of-mass energy

Abstract A search has been made for particles with charge Q = 1 3 , Q = 2 3 and Q = 4 3 produced in e + e − annihilation using the ARGUS detector at the e + e − storage ring DORIS, operating at a centre of mass energy around 10 GeV. No candidate events were found in 84.5 pb −1 of collected data. Upper limits are established for the cross section for the production of fractionally charged particles with masses up to 4 GeV c 2 , improving on previously obtained limits.