J. Pielorz

Measurement and QCD analysis of the photon structure function F2(x, Q2)

Abstract We present a measurement of the hadronic structure function F2γ(x, Q2) of the photon in the Q2 range from 10 to 100 GeV2. Data were taken with the PLUTO detector at the e+e- storage ring PETRA. This measurement and previous PLUTO measurements in the Q2 range of 1.5 to 16 GeV2 are compared with higher order QCD calculations. The structure function is consistent with the predicted log Q2 behaviour when charm contributions are subtracted. The x dependence can be well described for 0.1 Λ MS = 183 + 65/ −40( stat. ) + 46/ −36( sys. ) MeV for the QCD scale parameter.

Pion pair production in photon-photon interactions

The processγγπ+π− has been measured with complete particle identification. Cross-sections are presented from near threshold up to the region of thef(1270). In the mass range 0.5–0.7 GeV, crosssections are lower than the Born term predictions and show no evidence for an ε(600). The two-photon width of thef(1270) is found to be in agreement with previous results.

Measurement of the total photon-photon cross section for the production of hadrons at small Q2

The total photon-photon cross section for the production of hadrons, σγγ(W, Q2), has been measured in the single-tag condition for 0.1 < Q2 < 1.0 GeV2 and 1.5 < W < GeV. The results are based on 2929 multihadron events obtained with the PLUTO detector at PETRA. The Q2 dependence of σγγ average over W can be described by GVDM. The dependence of σγγ on the mass W of the hadronic final state has been extracted at Q2 = 0.44 GeV2 by unfolding the effects of experimental resolution and acceptance. The cross section is found to rise at small W. The result is compared with VDM and the parton model.

Measurement of exclusive η′ production in γγ reactions

Abstract We observe γγ → η′ production in the reaction e + e − → e + e − π + π − γ. We measure the product γ γγ ( η ′) B ( η ′ → ϱ 0 γ ) to be 1.14 ± 0.08 ± 0.11 keV. A first measurement of the γγ → η′ transition form factor is made for Q 2 up to 1 GeV 2 .

Tests of the standard model with lepton pair production ine+e− reactions

The differential cross section of the reactione+e−→e+e− at a c.m. energy of 34.7 GeV has been measured. The result, together with our previously measurede+e−→α+α− data, are compared with the standard model predictions. We obtain for the weak neutral current couplings the valuesgv2=0.09×0.06,ga2=0.38×0.08. A fit of the Weinberg mixing angle gives the valuegv2=0.09×0.06,ga2=0.038×0.08. The data are also used to set limits on possible deviations from the pointlike structure of leptons. An upper limit for thee+e− coupling to a heavy spin 0 boson is also given.

Measurement and analysis of the reactionγγ→3π+3π-

We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded.

Tensor meson excitation in the reaction γγ→K S 0 K S 0

AbstractIn the analysis of the reactione+e−→e+e−KS0Ks0 clear evidence for exclusive γγ→f2′ resonance production is observed. The productΓγγ ·B(f2′→K

TheQ 2 and transverse momentum dependence of jet production in photon-photon interactions

\bar K