Search

Using the CELLO detector, we have measured cross sections for the process γγ→ π π in the mass range 0.75-1.9 GeV/c. A partial wave fit to the data indicates the presence of a sizeable S-wave amplitude with signs of resonant behaviour. Values for the γγ width of the f(1270) are given, showing the model-dependence of this quantity. At higher dipion masses, the model of Brodsky and Lepage is found to give an order of magnitude description of the data. [ABSTRACT FROM AUTHOR]

We have measured the cross section and Q-dependence of the reaction γγ→ multihadrons, using the CELLO detector at DESY, for visible final-state masses between 4 and 9 GeV. The data are well fitted by an incoherent sum of Generalised Vector Meson Dominance and Quark Parton Model terms, but at low Q require the addition of a third component which resembles the QPM but is less two-jet-like. With and without this term, the GVDM cross section at Q=0 is found to be 200±20 and 250±25 nb, respectively. [ABSTRACT FROM AUTHOR]

We have studied the reaction e e→ e e using data taken by the CELLO detector at 35 GeV centre of mass energy with an integrated luminosity of 86 pb. The differential cross section is found to agree with the Standard Model and is used to set limits on possible deviations from the pointlike structure of the electron. The lower limits obtained for the compositeness scale Λ range from 0.8 to 6.0 TeV (95% C.L.), depending on the structure of the current. [ABSTRACT FROM AUTHOR]

Differential cross section data of the CELLO experiment on pair production of muons, taus, and heavy quarks in e e-annihilation are presented and analysed, together with our data on Bhabha scattering, in terms of compositeness effects characterized by the mass scale Λ. We discuss difficulties in the combination of limits Λ from different experiments. The appropriate parameter to combine different results turns out to be ɛ=±1/ Λ, which is in contrast to Λ Gaussian distributed. [ABSTRACT FROM AUTHOR]

We present measurement of the πγγ, ηγγ and η′γγ form factors. The π-form factor is for the first time observed in the space-like region. The transition form factor of the η-meson is determined from its decay modes πππ, ππγ and the neutral decay mode γγ. The decay of the η′ is observed in the decay channels ργ, ηππ with η→γγ and in the four charged prong final state stemming from ηππ with the η decaying into ππ(π/γ). All form factors agree well with a simple ρ-pole predicted by the vector meson dominance model and also with the QCD inspired Brodsky-Lepage model. [ABSTRACT FROM AUTHOR]

We have studied the ρ production rate in the reaction ξξ→3π3π in the energy range 1.6≦ W≦7.5 GeV with the CELLO detector at PETRA. Our analysis points to a substantial yield of ρρππ events in particular at W>4.0 GeV. We give cross sections for the ρ2π2π and ρρππ final states and calculate upper limits for the reaction γγ→ρρ (1700) →ρρππ. [ABSTRACT FROM AUTHOR]

The production of b and c quarks in e e annihilation has been studied with the CELLO detector in the range from 35 GeV up to the highest PETRA energies. The heavy quarks have been tagged by their semileptonic decays. The charge asymmetries for b quarks at 35 and 43 GeV have been found to be A=−(22.2±8.1)% and A=−(49.1±16.5)%, respectively, using a method incorporating jet variables and their correlations for the separation of the heavy quarks from the back ground of the lighter quarks. For c quarks we obtain A=−(12.9±8.8)% and A=+(7.7±14.0)%, respectively. The axial vector coupling constants of the heavy quarks c and b are found to be a=+(0.29±0.46) and a=−(1.15±0.41) taking $$B^0 \overline {B^0 } $$ mixing into account. The results are in agreement with the expectations from the standard model. [ABSTRACT FROM AUTHOR]

We present high precision results from an analysis of all major τ branching ratios, determined simultaneously in the same experiment. The results are based on 6064 τ decays observed at $$\sqrt s = 35 GeV$$ , using the CELLO detector at PETRA. The sum of the measured exclusive branching ratios saturates the total τ decay width. In a comparison with the topological branching ratios measured recently by CELLO, the sums of the respective exclusive branching ratios are found to saturate the inclusive fractions. Our results are in good general agreement with existing measurements. However, the decay fractions for τ→πππ v, and π→πππ v are larger than the present world averages. All measured branching ratios are in good agreement with the expectations from a standard τ lepton. [ABSTRACT FROM AUTHOR]

The reaction e e→ e eπππ in the untagged mode has been measured with the CELLO detector at PETRA. The cross section is dominated by exclusive a(1320) production, whose radiative width is determined to be Γ=1.00±0.07(stat.)±0.15(syst.)keV. An angular correlation analysis indicates pure helicity 2 with an upper limit on the helicity 0 contribution of 8.2% (at 95% c.l.). Excitation of the pseudotensor meson π(1670) is observed for the first time in this reaction. The π radiative width and its dependence on interference effects are studied. [ABSTRACT FROM AUTHOR]

We present an analysis of strange particle production from e e annihilation into multihadronic final states. The experiment was performed with the CELLO detector at the PETRA storage ring at DESY, the data was taken at a centre of mass energy of 35 GeV with an integrated luminosity of 86 pb. The particles K, K and Λ have been identified by their characteristic decays, and differential cross sections for their production have been obtained. From a comparison of K and K rates the Lund vector meson suppression parameter V/(V+P) has been determined. [ABSTRACT FROM AUTHOR]