Double-tag events in two-photon collisions are studied using the L3 detector at LEP centre-of-mass energies from root(s)=189 GeV to 209 GeV. The cross sections of the e+e- -> e+e- hadrons and gamma*gamma* -> hadrons processes are measured as a function of the photon virtualities, Q1^2 and Q2^2, of the two-photon mass, W_gammagamma, and of the variable Y=ln(W_gammagamma^2/(Q1 Q2)), for an average photon virtuality <Q2> = 16 GeV2. The results are in agreement with next-to-leading order calculations for the process gamma*gamma* -> q qbar in the interval 2 <= Y <= 5. An excess is observed in the interval 5 < Y <= 7, corresponding to W_gammagamma greater than 40 GeV . This may be interpreted as a sign of resolved photon QCD processes or the onset of BFKL phenomena.
Differential cross section as a function of the photon virtualities Qi**2. Here Q1 is the virtuality w.r.t the electron vertex, and Q2 w.r.t the positron vertex. Data are given both before and after radiative corrections.
Differential cross section as a function of W, the invariant mas of the virtual GAMMA*GAMMA* system. Data are given both before and after radiative corrections.
Differential cross section as a function of the variable LN(W**2/Q1*Q2). Data are given both before and after radiative corrections.
Measurements of the two-photon interaction e + e − → e + e − + hadrons at s ≃ 91 GeV and s ≃ 183 GeV are presented. The double-tag events, collected with the L3 detector, correspond to interated luminosities of 140 pb −1 at 91 GeV and 52 pb −1 at 183 GeV. The cross-section of γ ∗ γ ∗ collisions has been measured at 〈 Q 2 〉 = 3.5 GeV 2 and 〈 Q 2 〉 = 14 GeV 2 . The data agree well with predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data.
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