Di-jet production in γ γ collisions at LEP2

The production of two high-p T jets in the interactions of quasi-real photons in e + e − collisions at from 189 GeV to 209 GeV is studied with data corresponding to an integrated e + e − luminosity of 550 pb−1. The jets reconstructed by the k ⊥ -cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, p T , above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum of the jets and is compared to perturbative QCD calculations

Direct Observation of the Strange b Baryon Xi(b)-.

We report the first direct observation of the strange b baryon (). We reconstruct the decay J/-, with J/µ+µ-, and --p-- in p collisions at =1.96 TeV. Using 1.3 fb-1 of data collected by the D0 detector, we observe 15.2±4.4(stat)(syst) candidates at a mass of 5.774±0.011(stat)±0.015(syst) GeV. The significance of the observed signal is 5.5, equivalent to a probability of 3.3×10-8 of it arising from a background fluctuation. Normalizing to the decay bJ/, we measure the relative rate =0.28±0.09(stat)(syst)

Observation of the Doubly Strange b Baryon &#937;b&#8722;

We report the observation of the doubly strange b baryon Omega(-)(b) in the decay channel Omega(-)(b) -> J/psi Omega(-), with J/psi -> mu(+)mu(-) and Omega(-) -> Lambda K- -> (p pi(-))K-, in p (p) over bar collisions at root s = 1.96 TeV. Using approximately 1.3 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider, we observe 17.8 +/- 4.9(stat) +/- 0.8(syst) Omega(-)(b) signal events at a mass of 6.165 +/- 0.010(stat) +/- 0.013(syst) GeV. The significance of the observed signal is 5.4 sigma, corresponding to a probability of 6.7 x 10(-8) of it arising from a background fluctuation.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Direct observation of the strange b baryon Xib-.

We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- --&gt;J/psiXi-, with J/psi--&gt;mu+mu-, and Xi---&gt;Lambdapi---&gt;ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)--&gt;J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- --&gt;J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)--&gt;J/psiLambda) = 0.28+/-0.09(stat)(-0.08)(+0.09)(syst)

Search for pair production of second generation scalar leptoquarks

We report on a search for the pair production of second generation scalar leptoquarks (LQ) in ppbar collisions at the center of mass energy sqrt(s)=1.96 TeV using a data set corresponding to an integrated luminosity of 1.0 fb-1 collected with the D0 experiment at the Fermilab Tevatron Collider. Topologies arising from the LQLQbar->muqnuq and LQLQbar->muqmuq decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction beta for the decay LQ->muq. These are interpreted as lower limits on the leptoquark mass as a function of beta. For beta=1 (0.5), scalar second generation leptoquarks with masses up to 316 GeV (270 GeV) are excluded