J.M. Scarr

RHO PRODUCTION BY VIRTUAL PHOTONS

The reaction 3,vp -+ pcr+Tr - was studied in the W, Q2 region 1.3-2.8 GeV, 0.3-1.4 GeV 2 using tile streamer chamber at DESY. A detailed analysis of rho production via ~,vp ~ p 0p is presented. Near threshold rho production has peripheral and non-peripheral contributions of comparable magnitude. At higher energies (14/> 2 GeV) the peripheral component is dominant. The Q2 dependence of o(q, vp ~ o 0p) follows that of the rho propagator as predicted by VDM. The slope of do/dt at ~ Qz ) = 0.4 and 0.8 GeV 2 is within errors equal to its value at Q2 = 0. The overall shape of thep ° is t dependent as in photoproduction, but is independent of Q2. The decay angular distribution shows that longitudinal rhos dominate in the threshold region. At higher energies transverse rhos are dominant. Rho prod)~ction by transverse photons proceeds almost exclusively by natural parity exchange, o T ~ (0.83 -+ 0.06) e T for 2.2 2 GeV.

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.

First measurement of the photon structure function F2

Abstract Using data taken at PETRA we present results on deep inelastic electron photon scattering at momentum transfers 1 Q 2 2 . The results are expressed in terms of the photon structure function F 2 and are compared with QCD predictions and “hadronic” models of the photon. The pointlike component of the photon is found to be dominant.

Search for new heavy quarks in

Abstract The total e + e − annihilation onto hadron has been measured at CM energies between 33.00 and 36.72 GeV and between 38.66 and 46.78 GeV in steps of 20 and 30 MeV respectively. The average of the ratio R = σ ( e + e − → hadrons )/ σ is 〈 R 〉=3.85±0.12 and 〈 R 〉=4.04±0.10 for the two energy ranges. The systematic error on 〈 R 〉 is 0.31. Both values are consistent with the expectation for the known coloured quarks u, d, s, c and b. No evidence was found for the production of new quarks. If the largest fluctuation in R is interpreted as a narrow resonance, it corresponds to a product of the electronic width and the hadronic branching ratio Γ ee B had >2.9 keV at the 95% confidence level, well below the value expected for the toponium vector ground state with charge 2 3 e . The observed number of aplanar final states rules out the continuum production of a a new heavy flavour with pointlike cross section up to a CM energy of 45.4 GeV for a quarck charge of 1 3 e . and up to 46.6 GeV for 2 3 e at the 95% confidence level.

e^+e^-

Abstract The reaction e + e − → τ + τ − has been studied at centre of mass energies between 14.0 and 46.8 GeV with the CELLO detector at the PETRA e + e − collider. We present results for the cross section σ τ and the charge asymmetry A τ . The results are in good agreement with the standard model. We have also measured the topological decay rates BR 1 , BR 3 and BR 5 for the inclusive decay of the τ lepton into one, three and five charge particles. The results confirm and improve earlier CELLO measurements at other energies. We find for the combined values at all energies BR 1 = (84.9 ± 0.4 ± 0.3)%, BR 3 = (15.0 ± 0.4 ± 0.3)% and BR 5 = (0.16 ± 0.13 ± 0.04)%.

collisions up to 46.78 GeV cm energy

Abstract An event from e+e− annihilation at √s = 43.450 GeV containing two topologically isolated energetic muons and two hadronic jets has been observed. The masses of the μ−μ, jet-jet and μ-jet combinations are all large. The expected number of such events from known processes is about 10−3.

τ Production and decay with the cello detector at petra

Abstract Using the CELLO detector at PETRA a search has been made for excited leptons by studying e + e − interactions which yield l + l − γγ, l + l − γ and γγ final states, where l =e,μ or τ . Good agreement with QED is observed and new limits are set on e ∗ , μ ∗ , and τ ∗ production.

Observation of a multiparticle event with two isolated energetic muons in e+e- interactions

Abstract A search for single photons, produced in e + e − collisions together with particles interacting only weakly with matter, has been performed using the CELLO detector operating at the PETRA storage ring. From the absence of any signal, an upper limit is set at 15 (90% CL) on the number of light neutrino species, and lower limits on various supersymmetric particle masses are derived. For massless photinos, mass degenerate scalar partners of the left- and right-handed electrons are excluded below 37.7 GeV/ c 2 (90% CL).

EXCITED LEPTON SEARCH

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.

A search for single photons at petra

A search for single photons, produced in e+e− collisions together with particles interacting only weakly with matter, has been performed using the CELLO detector at the PETRA storage ring. We report on results from data taken at 35 GeV < √s<46.57 GeV. An upper limit of 8.7 (90% CL) on the number of light neutrino species is set. Combining our result with published results from other e+e− experiments the number of light neutrinos is limited to Nv < 4.6 at 90% CL. We also set lower limits on the masses of supersymmetric particles.