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Several methods for the determination of the mass of the top quark with the ATLAS detector at the LHC are presented. All dominant decay channels of the top quark can be explored. The measurements are in most cases dominated by systematic uncertainties. New methods have been developed to control those related to the detector. The results indicate that a total error on the top mass at the level of 1 GeV should be achievable
A new pixel Front-End (FE) IC is being developed in a 130 nm technology for use in the upgraded ATLAS pixel detector. The new pixel FE will be made of smaller pixels (50 x 250 mu m vs. 50 x 400 mu m for the present FE, FE-13), a much improved active area over inactive area ratio, and a new analog pixel chain tuned for low power and new detector input capacitance. The higher luminosity for which this IC is tuned implies a complete redefinition of the digital architecture logic, which will not be based on End-of-Column data buffering but on local pixel logic and local pixel data storage. An overview of the new FE is given with particular emphasis on the new digital logic architecture and possible architecture variations.
Measurements of on-shell ZZ production are described, using data collected by DELPHI in 1997 and 1998, at centre-of-mass energies roots = 182.6 GeV and 188.6 GeV, respectively. Results obtained in each of the final states q (q) over barq (q) over bar, mu (+)mu (-) q (q) over bar e(+)e(-)q (q) over bar, nu[([nu])over bar]q (q) over bar, l(+)l(-)l(+)l(-), and nu[([nu])over bar]l(+)l(-) are presented. The measured cross- sections for on-shell ZZ production via the tree-level doubly- resonant graphs (NC02) are: sigma (NC02) (182.6 GeV) = 0.38 +/- 0.18 (stat) +/- 0.04 (syst) pb, sigma (NC02) (188.6 GeV) = 0.60+/-0.13 (stat) +/- 0.07 (syst) pb. They are consistent with the Standard Model expectations of 0.25 and 0.65 pb at each energy.
Searches for pair production of supersymmetric particles in e(+)e(-) collisions at centre-of-mass energy of 183 GeV have been performed on DELPHI data under the assumption that R- parity is not conserved. Only one R-parity violating coupling of lambda type, which couples the sleptons to the leptons (LL (E) over bar term), is considered to be dominant at a time. Since in models with R-parity violation any supersymmetric particle can be the lightest one, searches for charginos, neutralinos, sleptons and squarks have been performed both for direct R-parity violating decays and for indirect cascade decays. Morever, it is assumed that the strength of the R- parity violating couplings is such that the lifetimes can be neglected. The present study of supersymmetric particle pair production is used to exclude domains of the Minimal Supersymmet...
Searches for the Standard Model Higgs boson have been performed in the data collected by the. DELPHI experiment at LEP in the year 2000 at centre-of-mass energies between 200 and 209 GeV corresponding to a total integrated luminosity of 224 pb(-1). No evidence for a Higgs signal is observed in the kinematically accessible mass range, and a 95% CL lower mass limit of 114.3 GeV/c(2) is set, to be compared with an expected median limit of 113.5 GeV/c(2) for these data.
Searches for pair production of supersymmetric particles under the assumption that R-parity is not conserved are presented, based on data recorded by the DELPHI detector in 1998 from e(+)e(-) collisions at a centre-of-mass energy of 189 GeV. Only one R-parity violating LL (E) over bar term (i.e. one lambda coupling), which couples scalar leptons to leptons, is considered to be dominant at a time. Moreover, it is assumed that the strength of the R-parity violating couplings is such that the lifetimes can be neglected. The search for pair production of neutralinos, charginos and sleptons has been performed for both direct R-parity violating decays and indirect cascade decays. The results are in agreement with Standard Model expectations, and are used to update the constraints on the MSSM parameter values and the mass limits previously de...
During 1993 and 1995 LEP was run at 3 energies near the Z(0) peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP operated only at the Z(0) peak. In total DELPHI accumulated data corresponding to an integrated luminosity of approximately 116 pb(-1). Analyses of the hadronic cross-sections and of the cross-sections and forward-backward asymmetries in the leptonic channels used the most precise evaluations of the LEP energies. In the dimuon channel, events with a photon radiated horn the initial state have been used to probe the cross-sections and asymmetries down to PETRA energies. Model independent fits to all DELPHI lineshape and asymmetry data horn 1990 to 1995 have been carried out giving values of the resonance parameters: M-Z = 91.1863 +/- 0.0028 GeV Gamma(Z) = 2.4876 +/- 0.0041 GeV ...
Searches for neutral Higgs bosons in the Standard Model and the MSSM have been performed using data collected by the DELPHI experiment at a centre-of-mass energy of 188.7 GeV, corresponding to an integrated luminosity of 158 pb(-1). These analyses are used, in combination with our results from lower energies, to set new 95% confidence level lower mass bounds on the Standard Model Higgs boson (94.6 GeV/c(2)) and on the lightest neutral scalar (82.6 GeV/c(2)) and neutral pseudoscalar (84.1 GeV/c(2)) Higgs bosons in a representative scan of the MSSM parameters. The results are also interpreted in the framework of a general two-Higgs doublet model.
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