The performance of the High-density Projection Chamber (HPC), the barrel electromagnetic calorimeter of the DELPHI experiment, is described. The detector adopts the time projection technique in order to obtain exceptionally fine spatial granularity in the three coordinates (similar to 2 X 20 mrad(2) in theta x phi with nine samplings along the shower axes), using a limited number of readout channels (18,432). Among the various topics concerning the HPC construction and operation, major emphasis is given to the aspects related to the calibration in energy of the calorimeter, based mainly on the analysis of the detector response to (83)mKr decays, and to the treatment of ageing in the readout proportional counters.

The multiplicities per event of π± and K± are measured separately for e+e- annihilation into cc, bb, and light quark pairs at Ecm=29 GeV. The K± multiplicity is higher for heavy quark events than for light quark events. The π± multiplicity and the π± scaled differential cross section at low x=Ebeam/Ebeam are found to be higher for bb events than for other events.

We present a measurement of the photon structure functionF 2 γ in the reactionee→eeX forQ2 in the range 0.2<Q2<7 GeV2, using 9,200 multihadron events obtained with the TPC/Two-Gamma detector at PEP. The data have been corrected for detector effects using a regularized unfolding procedure and are presented as a function ofx andQ2. The structure function shows scaling in the region 0.3<Q2<1.6 GeV2,x<0.3 and rises for higherQ2. AtQ2=5.1 GeV2 the results are compared with QCD and, within the scheme of Antoniadis and Grunberg, rather conservative bounds for the QCD scale parameter of 133±50<\(\Lambda _{\overline {{\rm M}S} } \)<268±98 MeV are obtained. A study of the final state structure shows that the rise ofF 2 γ is consistent with being entirely due to the pointlike component of the photon.

We compare the pT dependence of pion, kaon and proton production cross sections in the central rapidity region in e+e− annihilation events and in proton-proton collisions at ISR energies. We find similarities both in the pT dependence of cross sections and in the particle composition as a function of pT, in agreement with the hypothesis of a universal mechanism of particle production.

The production of charmed ${D}^{\mathrm{*}}$ mesons in ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ annihilations at a center-of-mass energy of 29 GeV has been studied using the time-projection-chamber (TPC) detector at the SLAC storage ring PEP. The production cross section, fragmentation function, and forward-backward asymmetry due to electroweak effects are measured, and a limit on ${D}^{0}$-D${\ifmmode\bar\else\textasciimacron\fi{}}^{0}$ mixing is determined.

We study long-range correlations between hadrons in opposite jets ine+e− annihilation events at\(\sqrt s \)=29 GeV. We use the data to measure differences between quark and antiquark fragmentation functions into charged hadrons, and to estimate the variation of fragmentation properties among quark flavors. We find large variations in longitudinal fragmentation functions, but universal mean transverse momenta of hadrons in jets.

Three currently used fragmentation models are tested by studying the distribution of particles between jet axes in the 3-jet events ofe+e− annihilation, using data collected by the Time Projection Chamber at PEP. These three models — the Lund String model, the Webber Cluster model and an Independent Fragmentation model (IF) — each implement different Lorentz-frame structures for the fragmentation process of quarks and gluons into hadrons. The Lund model provides a good description of the data, while the IF model does not. The Webber model, which is untuned, does not describe the absolute particle densities between jets, but correctly predicts the ratios of those densities, which are less sensitive to the tuning.

We have measured the inclusive prompt electron cross section over a wide momentum range (P>0.5 GeV/c) with the PEP-4 TPC detector. The semielectronic branching fractions of thec andb quarks are (9.1±0.9 (stat.)±1.3 (syst.))% and (11.0±1.8±1.0)%, respectively. Theb quark fragmentation function peaks at highz with 〈z b 〉=0.74±0.05±0.03. The axial couplings to the neutral current area c =2.3±1.4±1.0 for thec quark anda b =−2.0±1.9±0.5 for theb quark.

We use the time-projection chamber detector to study mechanisms of baryon production in the central rapidity region of jets from ${e}^{+}{e}^{\ensuremath{-}}$ annihilation. On the basis of angular correlations between protons and antiprotons, we exclude the isotropic decay of heavy mesonic clusters as a dominant source of baryons at 95% confidence level. The diquark mechanisms used in string fragmentation models reproduce the data, provided that diquarks are formed in a two-step process which allows mesons to be produced in between the baryon and antibaryon.

Inclusive production cross sections for photons and π0's ine+e− annihilation at a center of mass energy of 29 GeV have been measured. The π0 production spectrum agrees with a corresponding measurement for π±. The ratio of the π0 inclusive rate to the average for π± is 0.92±0.14. The fractions of the total energy carried by photons and π0's are 0.244±0.016 and 0.217±0.033, respectively. The fraction of total energy carried by all stable hadrons, prompt leptons and photons is determined to be 0.938±0.045, leaving 0.062±0.045 for neutrinos.