Top Quark Measurements at the Fermilab Tevatron

The top quark, discovered at the Tevatron in 1995, is a very interesting particle. Precise measurement of the top properties using large data samples will allow stringent tests of the Standard Model and offer a unique window on new physics. In this report will be reviewed the status of the current knowledge of the top quark as provided by the Run I results of the CDF and D0 experiment. A first look at various preliminary measurements obtained with data collected during Run II will be also presented.Comment: 10 pages, 14 figures Proceeding of Lepton-Photon 2003, Fermilab Batavia (IL), August 200

On the scattering length of the K^- d system

Multiple-scattering approximations to Faddeev calculations of the K^- d scattering length are reviewed and compared with published Kbar-N-N pi-Y-N fully reactive Faddeev calculations. A new multiple-scattering approximation which goes beyond the `fixed-center' assumption for the nucleons is proposed, aiming at accuracies of 5-10%. A precise value of the K^- d scattering length from the measurement of the K^- d 1s atomic level shift and width, planned by the DEAR/SIDDHARTA collaboration, plus a precise value for the K^- p scattering length by improving the K^- p atom measurements, are essential for extracting the K^- n scattering length, for resolving persistent puzzles in low-energy Kbar-N phenomenology and for extrapolating into Kbar-nuclear systems.Comment: Invited talk at MESON 2006, Krakow, June 2006. To be published in International Journal of Modern Physics A. Requires use of ws-ijmpa.cl

On Measuring the top quark mass using the dilepton decay modes

We demonstrate a new likelihood method for extracting the top quark mass from events of the type ttbar-->bW(l+nu)bW(l+nu) This method estimates the top quark mass correctly from an ensemble of dilepton events. The method proposed by Dalitz and Goldstein [1] is shown to result in a systematic underestimation of the top quark mass. Effects due to the spin correlations between the top and anti-top quarks are shown to be unimportant in estimating the mass of the top quark.Comment: To appear in the proceedings of the 1996 DPF/DPB study on new directions for High Energy Physics, Snowmass, Colorad

Test of Analysis Method for Top-Antitop Production and Decay Events

We have carried out Monte Carlo calculations on two sets of randomly generated QCD events due to $p\bar{p} \to t \bar{t}$ with top mass $m_t = 170$ GeV, one set leading to $e^+e^-$ or $e^{\pm}\mu^{\mp}$ or $\mu^+\mu^-$ 2jets (dilepton) and the other leading to $e^{\pm}$ or $\mu^{\pm}$ 4jets (unilepton) configurations, in order to test the likelihood methods we have proposed for determining the top mass by analyses of these two sets of configurations. For the set of unilepton events, our method gives a very efficient and quite sharp measure of the top mass lying several GeV below the input mass. For the dilepton set, our method gives a much broader and markedly asymmetric distribution for the top mass estimates, 75% of them lying below 170 GeV, but the dilepton data will have much lower background than unilepton data. We then illustrate these methods by applying them to the data available from CDF in 1995 and discuss the results obtained in relation to the results for the sets of Monte Carlo events. The dilepton events yield masses spread widely, over 140 to 180 GeV, generally lower than the unilepton events, which cluster around $175\pm 8$ GeV. In an appendix, we discuss the nature of the additional ``slow'' $\mu^{+}$ observed in one CDF dilepton event, concluding that it is most probably a ``tertiary lepton'' resulting from the decay sequence $b\to c + hadrons$, followed by $c\to s \mu^{+} \nu$.Comment: 31 pages from PostScript file (Latex2e and 11 PostScript figures used rspublic.sty, eps.sty). Submitted to Proc. Royal Society Londo

On Observing Top Quark Production at the Tevatron

A technique for separating top quark production from Standard Model background events is introduced. It is applicable to the channel in which one top quark decays semi-leptonically and its anti-quark decays hadronically into three jets, or vice versa. The method is shown to discriminate dramatically between Monte Carlo generated events with and without simulated top quarks of mass around 120 GeV and above. The simulations were performed with CDF detector characteristics incorporated, showing that the method is applicable to existing data.Comment: 8 pages, TUFTS-TH-92-G01 (Two minor TeX mistakes corrected

The permutation group S_N and large Nc excited baryons

We study the excited baryon states for an arbitrary number of colors Nc from the perspective of the permutation group S_N of N objects. Classifying the transformation properties of states and quark-quark interaction operators under S_N allows a general analysis of the spin-flavor structure of the mass operator of these states, in terms of a few unknown constants parameterizing the unknown spatial structure. We explain how to perform the matching calculation of a general two-body quark-quark interaction onto the operators of the 1/Nc expansion. The inclusion of core and excited quark operators is shown to be necessary. Considering the case of the negative parity L=1 states transforming in the MS of S_N, we discuss the matching of the one-gluon and the Goldstone-boson exchange interactions.Comment: 38 pages. Final version to be published in Physical Review

Liquid-gas Phase Transition in Strange Hadronic Matter with Weak Y-Y Interaction

The liquid-gas phase transition in strange hadronic matter is reexamined by using the new parameters about the $\Lambda - \Lambda$ interaction deduced from recent observation of $^{6}_{\Lambda\Lambda}He$ double hypernucleus. The extended Furnstahl-Serot-Tang model with nucleons and hyperons is utilized. The binodal surface, the limit pressure, the entropy, the specific heat capacity and the Caloric curves are addressed. We find that the liquid-gas phase transition can occur more easily in strange hadronic matter with weak Y-Y interaction than that of the strong Y-Y interaction.Comment: 10 pages, 7 figure

Structure and three-body decay of 9^9Be resonances

The complex-rotated hyperspherical adiabatic method is used to study the decay of low-lying $^9$Be resonances into one neutron and two $\alpha$-particles. We investigate the six resonances above the break-up threshold and below 6 MeV: $1/2^\pm$, $3/2^\pm$ and $5/2^\pm$. The short-distance properties of each resonance are studied, and the different angular momentum and parity configurations of the $^8$Be and $^5$He two-body substructures are determined. We compute the branching ratio for sequential decay via the $^8$Be ground state which qualitatively is consistent with measurements. We extract the momentum distributions after decay directly into the three-body continuum from the large-distance asymptotic structures. The kinematically complete results are presented as Dalitz plots as well as projections on given neutron and $\alpha$-energy. The distributions are discussed and in most cases found to agree with available experimental data.Comment: 12 pages, 10 figures. To appear in Physical Review