The CDF MiniPlug Calorimeters at the Tevatron

Two MiniPlug calorimeters, designed to measure the energy and lateral position of particles in the pseudorapidity region of 3.6<|eta|<5.1 of the CDF detector, have been installed as part of the Run II CDF upgrade at the Tevatron collider. Detector performance and first results from $\bar pp$ collision data are presented.Comment: Presented at `Frontier Detectors for Frontier Physics; 9th Pisa Meeting on Advanced Detectors', Biodola, Italy, 25-31 May 2003. 2 page

Towards an optimized all lattice-matched InAlAs/InGaAsP/InGaAs multijunction solar cell with efficiency >50%

An approach for an all lattice-matched multijunction solar cell optimized design is presented with 5.807 Å lattice constant, together with a detailed analysis of its performance by means of full device modeling. The simulations show that a (1.93 eV)In_(0.37)Al_(0.63)As/(1.39 eV)In_(0.38)Ga_(0.62)As_(0.57)P_(0.43)/(0.94 eV)In_(0.38)Ga_(0.62)As 3-junction solar cell can achieve efficiencies >51% under 100-suns illumination (with V_(oc) = 3.34 V). As a key proof of concept, an equivalent 3-junction solar cell lattice-matched to InP was fabricated and tested. The independently connected single junction solar cells were also tested in a spectrum splitting configuration, showing similar performance to a monolithic tandem device, with V_(oc) = 1.8 V

GaInP/GaAs dual junction solar cells on Ge/Si epitaxial templates

In this study, we report synthesis of large area (> 2 cm^2) crack-free GaInP/GaAs double junction solar cells on 50 mm diameter Ge/Si templates fabricated using wafer bonding and ion implantation induced layer transfer techniques. Defect removal from the template film and film surface prior to epitaxial growth was found to be critical to achievement of high open circuit voltage and efficiency. Cells grown on templates prepared with chemical mechanical polishing in addition a wet chemical etch show comparable performance to control devices grown on bulk Ge substrates. Current-voltage (I–V) data under AM 1.5 illumination indicate that the short circuit current is comparable in templated and control cells, but the open circuit voltage is slightly lower (2.08V vs. 2.16V). Spectral response measurements indicate a drop in open circuit voltage due to a slight lowering of the top GaInP cell band gap. The drop in band gap is due to a difference in the indium composition in the two samples caused by the different miscut (9° vs. 6°) of the two kinds of substrates

Partons and Jets at the LHC

I review some issues related to short distance QCD and its relation to the experimental program of the Large Hadron Collider (LHC) now under construction in Geneva.Comment: Talk at the conference QCD2002 at IIT Kanpur, India, November 2002. Ten pages with 12 figure

Search for the Supersymmetric Partner of the Top-Quark in ppˉp \bar{p} Collisions at s=1.8TeV\sqrt{s} = 1.8 {\rm TeV}

We report on a search for the supersymmetric partner of the top quark (stop) produced in $t \bar{t}$ events using $110 {\rm pb}^{-1}$ of $p \bar{p}$ collisions at $\sqrt{s} = 1.8 {\rm TeV}$ recorded with the Collider Detector at Fermilab. In the case of a light stop squark, the decay of the top quark into stop plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with Standard Model $t \bar{t}$ production and decay. Hence, we set limits on the branching ratio of the top quark decaying into stop plus LSP, excluding branching ratios above 45% for a LSP mass up to 40 {\rm GeV/c}$^{2}$.Comment: 11 pages, 4 figure

Combined search for the standard model Higgs boson decaying to a bb pair using the full CDF data set

We combine the results of searches for the standard model Higgs boson based on the full CDF Run II data set obtained from sqrt(s) = 1.96 TeV p-pbar collisions at the Fermilab Tevatron corresponding to an integrated luminosity of 9.45/fb. The searches are conducted for Higgs bosons that are produced in association with a W or Z boson, have masses in the range 90-150 GeV/c^2, and decay into bb pairs. An excess of data is present that is inconsistent with the background prediction at the level of 2.5 standard deviations (the most significant local excess is 2.7 standard deviations).Comment: To be published in Phys. Rev. Lett (v2 contains minor updates based on comments from PRL

Measurements of branching fraction ratios and CP-asymmetries in suppressed B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^- decays

We report the first reconstruction in hadron collisions of the suppressed decays B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^-, sensitive to the CKM phase gamma, using data from 7 fb^-1 of integrated luminosity collected by the CDF II detector at the Tevatron collider. We reconstruct a signal for the B^- -> D(-> K^+ pi^-)K^- suppressed mode with a significance of 3.2 standard deviations, and measure the ratios of the suppressed to favored branching fractions R(K) = [22.0 \pm 8.6(stat)\pm 2.6(syst)]\times 10^-3, R^+(K) = [42.6\pm 13.7(stat)\pm 2.8(syst)]\times 10^-3, R^-(K)= [3.8\pm 10.3(stat)\pm 2.7(syst]\times 10^-3, as well as the direct CP-violating asymmetry A(K) = -0.82\pm 0.44(stat)\pm 0.09(syst) of this mode. Corresponding quantities for B^- -> D(-> K^+ pi^-)pi^- decay are also reported.Comment: 8 pages, 1 figure, accepted by Phys.Rev.D Rapid Communications for Publicatio

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV

We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with the Collider Detector at Fermilab. We select ttbar decays into the final states e nu + jets and mu nu + jets, in which at least one b quark from the t-quark decays is identified using a secondary vertex-finding algorithm. Assuming a top quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat) +1.1-0.9 (syst) pb. We also report the first observation of ttbar with significance greater than 5 sigma in the subsample in which both b quarks are identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3 (syst) pb.Comment: Accepted for publication in Physics Review Letters, 7 page