R. Heller

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)%.

The argus time-of-flight system

The time-of-flight system of the ARGUS detector at the DORIS e+e− storage ring consists of 64 barrel scintillation counters covering 75% of 4π, and 2 × 48 end cap counters, covering 17% of 4π. The barrel counters are viewed by two phototubes each, while the end cap counters have one tube only. The time-of-flight system serves as a part of the fast trigger and identifies charged particles. The time resolution achieved during the first year of ARGUS operation is 210 ps for Bhabhas (which are used for the off-line monitoring of the system), and 220 ps for hadrons, both in barrel and end cap counters. This converts into a three standard deviation mass separation up to 700 MeV/c between pions and kaons and 1200 MeV/c between kaons and protons. Electrons can be separated from heavier particles up to 230 MeV/c.

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 The 1760 shower counter modules of the detector ARGUS at DORIS II are monitored by a laser as the central light source. A lead glass counter, which also detects cosmic muons, and a photodiode serve as reference systems. The paper describes the technical layout, performance and stability of the monitoring system. Algorithms and corrections applied in the calibration procedure are discussed in detail. The monitoring system serves also to control the time-of-flight counter performance and to calibrate their TDCs.

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

Abstract We have investigated the ϒ→γττ using tagged ϒ mesons from the decay ϒ→π + π − ϒ. The photon spectrum exhibits no monochromatic line corresponding to a narrow object decaying into a τ pair and is fully compatible with the expected background contributions. The branching ratio Br(ϒ→τ + τ − is determined to be (3.07±0.46±0.22)%.

Calibration and monitoring of the ARGUS shower counters

Using the ARGUS detector at DORIS, we have investigated the hadronic transitions of the Υ(2S) to the Υ(1S). The decays to Υ(1S)π+π−, Υ(1S)π0π0 and Υ(1S)η where the Υ(1S) subsequently decays intoe+e− and Υ(1S)η have been investigated. The transition via two charged pions has also been studied inclusively. We obtain branching ratios of the Υ(2S) into Υ(1S)π+π− of (18.1±0.5±1.0)%, into Υ(1S)π0π0 of (9.5±1.9±1.9)% and into Υ(1S)η of less than 0.5% with 90% confidence. From the exclusive events we find the leptonic branching ratios of the Υ(1S) to beBee=(2.42±0.14±0.14)% andBμμ=(2.30±0.25±0.13)%. Kinematical parameters of the two pion transitions have been investigated in detail and found to be consistent with current algebra and colour-field multipole expansion.

Search for narrow states coupling to τ pairs in radiative ϒ decays

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 − .

The hadronic transitions from Υ(2S) to Υ(1S)

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.