Exclusive production of π and K meson pairs in two photon collisions is measured with ALEPH data collected between 1992 and 2000. Cross-sections are presented as a function of cos θ ∗ and invariant mass, for | cos θ ∗ |<0.6 and invariant masses between 2.0 and 6.0 GeV/ c 2 (2.25 and 4.0 GeV/ c 2 ) for pions (kaons). The shape of the distributions are found to be well described by QCD predictions but the data have a significantly higher normalization.
Measured angular distribution for pion production.
Measured angular distribution for kaon production.
Measured cross section for pion production as a function of W.
We present a new high-statistics measurement of the cross section for the process e+e−→e+e−π+π− at a center-of-mass energy of 29 GeV for invariant pion-pair masses M(π+π−) between 350 MeV/c2 and 1.6 GeV/c2. We observe the f2(1270) and measure its radiative width to be 3.15±0.04±0.39 keV. We also observe an enhancement in the π+π− spectrum near 1 GeV. General agreement is found with unitarized models of the γγ→π+π− reaction that include final-state interactions.
No description provided.
Statistical errors only.
The cross section for the production of π+π− or K+K− pairs in γγ interactions is measured for mππ between 1.7 and 3.5 GeV/c2 and for two intervals of γγ center-of-mass scattering angle. Results are compared with predictions of a QCD model.
Data read off graph.
Data read off graph.
We have studied several features of the production of charged-hardon pairs by γγ collisions. We have measured the f0 partial width Γf0→γγ(Q2) for Q2 in the range 0<Q2<1.4 GeV2/c2, and obtained Γf0→γγ=2.52±0.13±0.38 keV at Q2≈0. The measured Q2 dependence is in agreement with the generalized vector-dominance model. The cross section for γγ→(π+π−+K+K−) in the mass region 1.6≤Mππ≤2.5 GeV/c2 has also been measured and the result compared with that expected from the QCD continuum.
Data read from graph.. Both statistical and systematic errors included.
We report a measurement of the cross section for the process γγ → π + π − at invariant masses 500 MeV/ c 2 < m ππ <2000 MeV/ c 2 . A value for the radiative width of the f(1270) tensor meson Γ f→ γγ = 3.6 ± 0.3 ± 0.5 KeV (helicity λ = 2) has been obtained from a fit to the observed ππ mass spectrum.
DATA REQUESTED FROM AUTHORS.