W. Lockman

Production of π0π0 and π0η in photon-photon collisions☆

Abstract We investigate the four-photon final state produced in γγ colissions. In the π 0 π 0 channel we observe f(1270) production with predominantly helicity 2 and measure a partial width Γ γγ 2.9 +0.6 −0.4 ± keV (independent of assumptions on the helicity). We observe A 2 (1310) production in the π 0 η channel and find a partial width Γ γγ = 0.77 ± 0.18 ± 0.27 KeV (assuming helicity 2). We give an upper limit for f ≈ ηη .

Limits on axion and light Higgs boson production in ϒ (1S) decays

Abstract We have searched for axion and light Higgs boson production in the channel ϒ (1 S ) → (a 0 or h 0 ) + γ , where the non-interacting axion a 0 and the Higgs boson h 0 do not decay in the detector. We find no evidence for an axion and give an upper limit, Br( ϒ (1S) → a 0 γ ) −5 (90% CL), for long-lived axions. Combining our limit with the previous search in J / ψ decays, we are able to rule out the axion in the standard model with first order QCD corrections. Our ϒ (1S) data also rule out a Higgs boson with mass m h

Search for exotic tau decays

Abstract The Crystal Ball detector at the Doris II storage ring at DESY was used to search for the exotic decay processes τ →e γ , τ →e π 0 , and τ →e η . No signal was observed. We obtained the following 90% CL upper limits on the branching fractions: B ( τ →e γ ) −4 , B ( τ →e π 0 ) −4 , B ( τ →e η ) −4 .

Analysis of the 33-133-133-1final state in photon-photon collisions

The reactione+e- →e+e- ηπ0π0→e+e- 6γ has been analysed using the full data sample taken with the Crystal Ball detector at the DORIS II storage ring at DESY. The ηπ0π0 invariant mass spectrum is dominated by the η, for which we determine the radiative width Γγγ(η) to be (4.5±0.3±0.5)keV. Near 1.9 GeV/c2 we observe a second enhancement in the ηπ0π0 mass distribution. Assuming that these events are created by the production and subsequent decay of a wide resonanceX(1900), we have investigated the decay modes, the invariant mass distributions of the ηπ0 and π0π0 subsystems and the angular distributions of the final state mesons. We find that the data is best described byJPC=2∓. For thisJP assignment the resonance parameters are Γγγ(X) BR(X→ηππ)=(0.95±0.27±0.20) keV Γtot (X)=(221±92±44)MeV, andM(X)=(1881±32±40) MeV/c2.

Observation of a new ηπ0π0 resonance at 1900 MeV/c2 in two-photon scattering

Abstract Using the Crystal Ball detector at the DORIS II e + e − storage ring, we measure the ηπ 0 π 0 mass spectrum in the reaction e + e − →e + e − ηπ 0 π 0 →e + e − 6 γ from the ηπ 0 π 0 threshold to about 2500 MeV/ c 2 . The spectrum is dominated by the η′, for which we determine Γ γγ ( η ′)BR( η →6 γ )=0.36±0.02±0.03 keV. In addition, we observe an enhancement in the cross section near 1900 MeV/ c 2 which we attribute to the two-photon production of a new resonance X(1900). The angular distributions and the invariant mass distribution of the ηπ 0 subsystem are consistent with those expected for the hypothetical η 2 meson with J PC =2 −+ . For this J P assignment the resonance parameters are M (X) = 1876 ±35±50 MeV/ c 2 , Γ tot (X)=228±90±34 MeV/ c 2 and Γ γγ (X)BR(X→ ηππ ) = 0.9±0.2±0.3 keV.

The Michel parameter for the decay τ→eνν

Abstract The Crystal Ball detector at the Doris II storage ring at DESY has been used to study the electron energy spectrum of the decay τ→evv. In the standard model the Lorentz structure of the decay matrix element is of the well known V-A type, resulting in a Michel parameter of p =0.75. Our spectrum is found to be consistent with this value. A fit yields the value of 0.64±0.07.

Search for radiative ϒ(1S) decays into light mesons

We have searched for radiative decays of the ϒ(1S) resonance, ϒ(1S)→γX, whereX is one of the mesons η, η′f2 (1270),f2 (1720), or a narrow resonance with mass less than 3 GeV/c2 which decays into either π0π0 or ηη. The mesons are identified in their all-neutral decay modes. Since we do not find any such decays, we calculate upper limits on the corresponding branching ratios. These limits are compared to theoretical predictions and to the corresponding branching ratios measured in radiativeJ/Ψ decays.

InclusiveJ/ψ production in decays ofB mesons

The production ofJ/ψ inB meson decays has been measured on the Γ(4S) resonance using the Crystal Ball detector at thee+e− storage ring DORIS II. TheJ/ψ is identified by itse+e− decay mode. We obtain a branching ratio of BR(B→J/ψX)=(1.12±0.33±0.25)% in good agreement with theoretical predictions based on color suppression. TheJ/ψ momentum distribution is observed to be peaked at high values. This implies a substantial contribution from directB meson decays to theJ/ψ. In addition upper limits onJ/ψ production in Γ(1S) and Γ(2S) decays and in continuum processes are determined.

Measurement of the decay of the Υ(1S) and Υ(2S) resonances to muon pairs

AbstractUsing the Crystal Ball detector at thee+e− storage ring DORIS II, we have measured the branching fraction to muon pairsBμμ of the Υ(1S) and Υ(2S) resonances and for the first time the product of the muonic partial widthΓμμ and the branching fraction to electronsBee for both resonances. We obtainn