L. Boldizsar

Muon-pair and tau-pair production in two-photon collisions at LEP

The QED processes e^+ e^- ->e^+ e^- \mu^+ \mu^- and e^+ e^- ->e^+ e^- \tau^+ \tau^- are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV<sqrt{s}<209 GeV. The tau-pairs are observed through the associated decay of one tau into e\nu\nu and the other into \pi\pi\nu . The cross sections are measured as a function of sqrt{s}. For muon pairs, the cross section of the \gamma\gamma ->\mu^+\mu^- process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV<W_{\gamma\gamma}<40 GeV. Good agreement is found between these measurements and the O(\alpha^4) QED expectations. In addition, limits on the anomalous magnetic and electric dipole moments of the tau lepton are extracted.

Measurement of the Z-boson mass using e+e- →Zγ events at centre-of-mass energies above the Z pole

Events from the e + e − → Zγ process with hard initial-state radiation collected with the L3 detector at centre-of-mass energies between 183 GeV and 209 GeV are used to measure the mass of the Z boson. Decays of the Z boson into hadrons or muon pairs are considered and the Z mass is determined to be 91.272±0.032 (stat.)± 0.033 (syst.) GeV, in agreement with the value measured at the Z resonance. Alternatively , assuming this measured value of the Z mass, the method determines the LEP centre-of-mass energy, found to be 175 ± 68 (stat.) ± 68 (syst.) MeV lower than the nominal value.

Search for colour singlet and colour reconnection effects in hadronic Z decays at LEP

A search is performed in symmetric 3-jet hadronic Z-decay events for evidence of colour singlet production or colour reconnection effects. Asymmetries in the angular separation of particles are found to be sensitive indicators of such effects. Upper limits on the level of colour singlet production or of colour reconnection effects are established for a variety of models.  2003 Published by Elsevier B.V. Open access under CC BY license. 22 L3 Collaboration / Physics Letters B 581 (2004) 19–30

A new SPS programme

A new experiemntal program to study hadron production in hadron-nucleus and nucleus-nucleus collisions at the CERN SPS has been recently proposed by the NA49-future collaboration. The physics goals of the program are: -Search for the critical point of strongly interacting matter and a study of the properties of the onset of deconfinemnt in nucleus-nucleus collisions, -Measurements of correlations, fluctuations and hadron spectra at high pT in proton-nucleus collisions needed as for better understanding of nucleus-nucleus results, -Measurements of hadron production in hadron-nucleus interactions needed for neutrino (T2K) and cosmic-ray (Pierre Auger Observatory and KASCADE) expriments. The physics of the nucleus-nucleus program is reviewed in this presentation.

A very high momentum particle identification detector

Abstract.A new detector concept has been investigated to extend the capabilities of heavy-ion collider experiments, represented here through the ALICE detector, in the high transverse momentum (pT region. The resulting Very High Momentum Particle Identification Detector (VHMPID) performs charged hadron identification on a track-by-track basis in the 5 GeV/c < p < 25 GeV/c momentum range and provides heavy-ion experiments with new opportunities to study parton-medium interactions at RHIC and LHC energies, where the creation of deconfined quark-gluon matter has been established. The detector is based on novel advances to the pressurized gaseous ring imaging Cherenkov (RICH) concept, which yield a very compact, high resolution addition to existing heavy-ion experiments. We conclude that in order for the device to yield statistically significant results not only for single particle measurements, but also for di-hadron and jet-tagged correlation studies, it has to cover contiguously up to 30% of a central barrel detector in radial direction. This will allow, for the first time, identified charged hadron measurements in jets. In this paper we summarize the physics motivations for such a device, as well as its conceptual design, layout, and integration into ALICE.

Inclusive Lambda production in two-photon collisions at LEP

The reactions e^+e^- ->e^+e^- Lambda X and e^+e^- ->e^+e^- Lambda X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 209 GeV. Inclusive differential cross sections are measured as a function of the lambda transverse momentum, p_t, and pseudo-rapidity, eta, in the ranges 0.4 GeV<p_t<2.5 GeV and |\eta|<1.2. The data are compared to Monte Carlo predictions. The differential cross section as a function of p_t is well described by an exponential of the form A exp (- p_t /<p_t>)

VHMPID RICH prototype using pressurized C4F8O radiator gas and VUV photon detector

.