We present a new high-statistics measurement of the cross section for the process e+e~e+e m. +m at a center-of-mass energy of 29 GeV for invariant pion-pair masses M(m+m ) between 350 MeV/c' and 1.6 GeV/c2. We observe the f~( 1270) and measure its radiative width to be 3. 15+0.0420. 39 keV. We also observe an enhancement in the~+~spectrum near 1 GeV. General agreement is found with unitarized models of the yy~m m. reaction that include finalstate interactions.

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We have investigated methods of reconstructing beam profiles in the penumbral region using a set of axially symmetric chambers, differing only in the detector radius. In principal, the transfer functions, or kernels, of such chambers should be functions of radius only. Three chambers of radii 0.297, 0.556, and 0.714 cm have been used. The transfer functions of the chambers can be determined by deconvolving the profiles measured with each detector with the PPMC profile. The results indicate that the transfer functions can be parametrized accurately as a Gaussian cutoff at 1.75(r), with (r) the average radius of the chamber. Deconvolution of the measured profiles with the transfer functions yields a profile that agrees with the PPMC profile to +/- 0.5 mm over the 20-80% penumbra.

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The charged-particle multiplicities of hadronic events deriving from produced bottom or charm quarks have been measured in the Mark II detector at PEP in e+e annihilation at 29 GeV. For events containing one semileptonic and one hadronic weak decay, we find multiplicities of 15.2+0.5+0.7 for bottom and 13.0+0.5+0.8 for charm. The corresponding multiplicities of charged particles accompanying the pair of heavy hadrons are 5.2+0.5+0.9 for bottom, and 8.1 + 0.5 + 0.9 for charm.PACS numbers: 13.65. +i, 13.85.Qk, 14.80.oq The properties of hadronic events produced in e+ e annihilation have generally been studied as averages over all flavors weighted by the relative flavor populations. There is little reason to assume much difference between hadronic jets from up, down, and strange quarks, but for charm and especially bottom, the weak decay products and quark fragmentation properties play an important role. We present in this Letter measurements of the charged-particle multiplicities in events containing bottom jets, -and in events with charm jets. Prompt The effect of background in both the b and c regions has been simulated by the application to real hadron data of lepton misidentification probability tables, binned by p and pT. The muon misidentification tables include the effects of hadron punchthrough and nonprompt muons due to pion and kaon decays, while the electron tables take account of the effect of showering hadrons and the overlap of showers and charged tracks. This procedure is designed to model correctly the correlation between higher multiplicity and the probability that a given event contains a fake lepton.We obtain the unfolded mean multiplicities for the overall hadronic sample, and for the b and c regions,