Search for gauge mediated SUSY breaking topologies at $S^(1/2)$ similar to 189-GeV
Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 \(\mathrm{pb}^{-1}\) of data collected at \(\sqrt s\) = 188.6 GeV with the ALEPH detector. These topologies include acoplanar photons, non-pointing single photon, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing energy final states. No evidence for these new phenomena is observed and limits on production cross sections and sparticle masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/\(c^2\) on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter \(\Lambda\) are derived, independently of the NLSP lifetime.

title: Charm counting in b decays
abstract: The inclusive production of charmed particles in decays has been measured from the yield of D0, D+, Ds+ and Λc+ decays in a sample of events with high b purity collected with the ALEPH detector from 1992 to 1995. From these measurements, adding the charmonia production rate and an estimate of the charmed strange baryon contribution, the average number of charm quarks per b decay is determined to be nc = 1.230 ± 0.036 ± 0.038 ± 0.053, where the uncertainties are due to statistics, systematic effects and branching ratios, respectively.

title: A precise determination of the number of families with light neutrinos and of the Z boson partial widths
abstract: More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z decays collected with the ALEPH detector at LEP we find Mz=91.182±0.026 (exp.) ±0.030 (beam) GeV, Γz=2.541±0.056 GeV and σhad0=41.4±0.8 nb. The partial widths for the hadronic and leptonic channels are Γhad=1804±44 MeV, Γe+e−=82.1±3.4 MeV, Γμ+μ−=87.9±6.0 MeV and Γτ+τ−=86.1±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width Γl+l−=83.9±2.2 MeV, the effective weak mixing angle is found to be sin2θw(Mz)=0.231±0.008. Usin g the partial widths calculated in the standard model, the number of light neutrino families is Nν=3.01±0.15 (exp.)±0.05 (theor.).

title: Production of D**s mesons in hadronic Z decays
abstract: The production rates of the orbitally excited Ds** mesons, Ds1 and Ds2*, are measured with the 4.1 million hadronic Z decays recorded by the ALEPH detector during 1991--1995. The Ds** mesons are reconstructed in the decay modes Ds1+ -> D*+ K0, Ds1+ -> D*0 K+ and Ds2*+ -> D0 K+. The production rate of the Ds1 is measured to be n(Z->Ds1+-)=(0.52+-0.09+-0.06)%, under the assumption that the two considered decay modes of the Ds1 saturate the branching ratio. The production rate of the Ds2* is determined to be n(Z->Ds2*+-)=(0.83+-0.29+0.07-0.13)%, assuming that the branching fraction of the decay Ds2*+ -> D0 K+ is 45%. The production rates in Z->cc and Z->bbar decays are measured separately.

title: Measurement of the tau lepton lifetime
abstract: The mean lifetime of the lepton is measured in a sample of 25700 pairs collected in 1992 with the ALEPH detector at LEP. A new analysis of the 1-1 topology events is introduced. In this analysis, the dependence of the impact parameter sum distribution on the daughter track momenta is taken into account, yielding improved precision compared to other impact parameter sum methods. Three other analyses of the oneand three-prong decays are updated with increased statistics. The measured lifetime is 293:5 3:1 1:7 fs. Including previous (1989{1991) ALEPH measurements, the combined lifetime is 293:7 2:7 1:6 fs.

title: Measurement of W pair production in e+ e- collisions at 183-GeV
abstract: The production of W + W − pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 182.7 GeV, corresponding to an integrated luminosity of 57 pb −1 . Cross sections are given for different topologies of W decays into leptons or hadrons. Under Standard Model assumptions for the W-pair production and decay, the W-pair cross section is measured to be 15.57±0.62 (stat.) ±0.29 (syst.) pb . Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching ratio of the W boson into hadrons is measured to be B(W→hadrons) =68.93±1.21 (stat.) ±0.51 (syst.) % , allowing a determination of the CKM matrix element |V cs |=1.043±0.058 (stat.) ±0.026 (syst.) . The agreement of the cross sections with the Standard Model prediction allows a limit to be set on the W decay rate to undetectable final states.

title: The Birth of strange stars and their dynamo - originated magnetic fields
abstract: It is shown that protostrange stars (PSSs) can be convective and that there are two possible scenarios describing their turbulence. Besides the local turbulence on the scale which is less than the mean free path of neutrinos, large-scale (1 km) convection also may occur with properties that are similar to those of convection in protoneutron stars (PNSs). We thus suggest that strange stars can also create dynamo-originated magnetic elds during the deleptonization episode soon after a supernova explosion. Further detailed investigations are needed to see whether or not strange stars and neutron stars can be distinguished according to the dierences in dynamo actions in strange quark matter and in neutron matter. The magnetic elds of strange stars and neutron stars may also behave very dierently during the accretion-phase when the elds decay.

title: Possible evidence that pulsars are quark stars
abstract: It is a pity that the real state of matter in pulsar‐like stars is still not determined confidently because of the uncertainty about cold matter at supranuclear density, even 40 years after the discovery of pulsar. Nuclear matter (related to neutron stars) is one of the speculations for the inner constitution of pulsars even from the Landau's time more than 70 years ago, but quark matter (related to quark stars) is an alternative due to the fact of asymptotic freedom of interaction between quarks as the standard model of particle physics develops since 1960s. Therefore, one has to focus on astrophysical observations in order to answer what the nature of pulsars is. In this presentation, I would like to summarize possible observational evidence/hints that pulsar‐like stars could be quark stars, and to address achievable clear evidence for quark stars in the future experiments.

title: Lower bounds of altitudes for pulsar $\gamma$-ray radiation
abstract: Determining radiation location observationally plays a very important role in testing the pulsar radiation models. One-photon pair production in the strong magnetic field, $\gamma-e^{+}e^{1}$, is one of the important physical processes in pulsar radiation mechanisms. Photons near pulsar surface with sufficient energy will be absorbed in the magnetosphere and the absorption optical depth for these GeV $\gamma$-ray photons is usually large. In this paper, we include the aberrational, rotational and general relativistic effects and calculate the $\gamma$-B optical depth for $\gamma$-ray photons. Then we use the derived optical depth to determine the radiation altitude lower bounds for photons with given energies. As a case study, we calculate the lower bounds of radiation altitudes of Crab pulsar for photons with energy from 5 GeV to 1 TeV.

title: Towards the properties of long gamma-ray burst progenitors with Swift data
abstract: We investigate the properties of both the prompt and X-ray afterglows of gamma-ray bursts (GRBs) in the burst frame with a sample of 33 Swift GRBs. Assuming that the steep decay segment in the canonical X-ray afterglow light curves is due to the curvature effect, we fit the light curves with a broken power law to derive the zero time of the last emission epoch of the prompt emission (t 1 ) and the beginning as well as the end time of the shallow decay segment (t 2 and t 3 ). We show that both the isotropic peak gamma-ray luminosity (L peak,γ ) and gamma-ray energy (E iso,γ ) are correlated with the isotropic X-ray energy (E iso,γ ) of the shallow decay phase and the isotropic X-ray luminosity at t 2 (L x ,t 2 ). We infer the properties of the progenitor stars based on a model proposed by Kumar et al. who suggested that both the prompt gamma-rays and the X-ray afterglows are due to the accretions of different layers of materials of the GRB progenitor star by a central black hole (BH). We find that most of the derived masses of the core layers are M c = 0.1 ~ 5 M ☉ , and their average accretion rates in the prompt gamma-ray phase are M c = 0.01~ 1 M ☉ s -1 , with a radius of r c = 10 8 ~ 10 10 cm. The rotation parameter is correlated with the burst duration, being consistent with the expectation of collapsar models. The estimated radii and the masses of the fall-back materials for the envelope layers are r e = 10 10 ~ 10 12 cm and M e = 10 -3 ~ 1 M ☉ , respectively. The average accretion rates in the shallow decay phase are correlated with those in the prompt gamma-ray phase, but they are much lower, i.e. M e = 10 -8 ~ 10 -4 M ☉ s -1 . The r e values are smaller than the photospheric radii of Wolf-Rayet stars. In our calculation, we assume a uniform mass of the central BH (M BH = 10M ☉ ). Therefore, we may compare our results with simulation results. It is interesting that the assembled mass density profile for the bursts in our sample is well consistent with the simulation for a pre-supernova star with mass M = 25M ☉ .

title: Possible re-acceleration regions above the inner gap and pulsar gamma-ray emission
abstract: We propose that the violent breakdown of the Ruderman-Sutherland type vacuum gap above the pulsar polar cap region may produce copious primary particles and make the charge density above the gap in excess of the Goldreich-Julian density. Such an excess residue of charge density may arise some re-acceleration regions above the gap due to the space-charge-limited flow mechanism. Such re-acceleration regions, if exist, may accelerate particles to carry away more spin-down energy, and may have some implications for pulsar $\gamma$-ray emission.