High LEP Research Articles

Determination of the top quark mass through the measurement of the $$\frac{{\Gamma ({\rm Z} \to b\bar b)}}{{\Gamma _{hadr} - \Gamma (Z \to b\bar b)}}$$ ratio at high luminosity LEP

We introduce the ratio ofb \(\bar b\) events to the hadronic nonb \(\bar b\) ones as an excellent quantity to determine indirectly the top quark mass at high luminosity LEP. Assuming a realistic impact parameter resolution we conclude that with a few million Z's the top quark mass can be fixed with a precision of about 15 GeV.

StandardSU(5) supergravity grand unification model and predictions

A review is given of the StandardSU(5) supergravity model. This model has passed an important check regarding unification of the electro-weak and the strong couplings using high precision LEP data. It is shown that for a significant domain of the parameter space the model also satisfies constraints on the SUSY spectrum from CDF and LEP, as well as proton stability and cosmological relic density constraints.

Updated analysis of high precision LEP data

The precision electroweak data presented by the LEP Collaborations at La Thuile and Moriond Conferences in March 1993 are analyzed in a multiparameter framework that allows inclusion of a large category of extensions of the minimal SU(2) L×U(1) Standard Model. The main conclusion are: 1. (i) The data agree well with the Minimal Standard Model (MSM); 2. (ii) The best fit to the top quark and Higgs boson masses in the MSM is M t =143± 18 19 GeV, M H =73± 13 178 GeV. The positive error on M H is gaussian in log ( M H ). The data favor somewhat the lighter Higgs boson mass range but still agrees with M H =1000 GeV within less than two standard deviations. 3. (iii) The new results on Γ b / Γ had now play a fundamental role in deriving a Δϱ and M H -independent top quark mass limit from the Z→b b vertex correction. So far this limit was mostly obtained from R had and was intimately dependent on the value chosen for the strong coupling constant. With all data we find, for α s ( M Z 2)=0.117 ± 0.005, M t <185 GeV at 95% CL, Δϱ and M H independent. As a consequence of this new precision on Γ b / Γ had, it is possible to derive from electroweak measuremnts a value of α s ( M Z 2), even with all the electroweak parameters left free outside the MSM range: α s ( M Z 2)=0.111±0.015.

The radiative B0→ γ+ X decays

The photon spectrum of radiative decays B 0→ γ+ X is calculated in a relativistic treatment. The branching ratio BR ( B 0→ γ+ X)=(0.8−8)×10 −5 is obtaines. This makes the radiative decays B 0→ γ+ X detectable ast the high luminosity LEP. If the future experimental branching ratio turns out to be of the same order, this will show that B 0→ γ+ X decays are highly suppressed by QCD short-distance corrections. Comparisons of this result with other groups' are also provided.

Extraction and neutron activation analysis of humic substances

Methods are described for the isolation of humaic substances from a soil samples. The produres and based on extractions with sodium hydroxide or sodium pyrophosphate. Four of the humic samples were dried and then analysed by thermal neutron activation analysis. The humic samples along with three standard rocks were irradiated for 15 hours in a flux of ∼1012 n·cm−2·s−1. Counting was carried out using both a large volume Ge(Li) detector and a high resolution LEP detertor. Quantitative analysis was based on the known element concentrations in the standard rocks. The elements determined were Sc, Cr, Fe, Co, As, Se, Br, Mo, Sb, La, Ce, Eu, Hf, Ta, Th, and U. concentrations ranged from 0.02 ppm (La) to 7900 ppm (Fe).