New QCD results from LEP

I review recent QCD results from LEP. The emphasis is on results that represent new studies and on puzzling disagreements of theory and experiment. Further results are nevertheless mentioned by reference. The new studies discussed in more detail are the most precise measurement of unbiased gluon jets to date, strong evidence of color coherence in 3-jet events, and an, albeit unsuccessful, search for penta-quarks. As yet unexplained disagreements are observed in photon-photon collisions for high momentum charged particle and single jet production, and for the total cross section of b-quark production.Comment: To appear in the proceedings of the 39th Rencontres De Moriond On QCD And High Energy Hadronic Interactions 28 March - 4 April 2004, La Thuile, Ital

Jet production in two-photon collisions at LEP

Jet and di-jet production are studied in collisions of quasi-real photons collected during the LEP2 program at e+e- center-of-mass energies from 189 to 209 GeV. OPAL reports good agreement of NLO perturbative QCD with the measured differential di-jet cross sections, which reach a mean transverse energy of the di-jet system of 25 GeV. L3, on the other hand, finds drastic disagreement of the same calculation with single jet production for transverse jet momenta larger than about 25 GeV.Comment: 3 pages, 4 figures, Talk presented at the EPS'03 conference in Aachen, Germany, to be published in the proceedings (EPJ direct

Highlights from ATLAS

The ATLAS experiment has been taking data efficiently since LHC collisions started, first at the injection energy of 450 GeV/beam and at 1.18 TeV/beam in 2009, then at 3.5 TeV/beam in 2010. Many results have already been obtained based on this data demonstrating the performance of the detector, as well as first physics measurements. Only a selection of highlights will be presented here.Comment: 12 pages, 9 figures, proceedings of talk presented at XVIII International Workshop on Deep-Inelastic Scattering and Related Subjects, April 19 -23, 2010, Convitto della Calza, Firenze, Ital

Forward pi^0-meson production at HERA

The production of high transverse momentum piz^0-mesons has been measured in deep-inelastic e-p scattering events at low Bjorken-$x$ taken with the H1 detector at HERA. The production of high p_T particles is strongly correlated to the emission of hard partons in QCD and is therefore sensitive to the dynamics of the strong interaction. For the first time the measurement of single particles has been extended to the region of small angles w.r.t. the proton remnant (forward region) and down to very low values of x ~ 5x10^-5. This region is expected to be particularly sensitive to QCD evolution effects in final states. Differential cross sections of inclusive pi^0-meson production have been measured as a function of Bjorken-x and the four-momentum transfer Q^2, and also as a function of the transverse momentum and the polar angle of the pi^0-mesons. A recent BFKL calculation and QCD models based on the DGLAP splitting functions are compared to the data. The best description of the data is achieved by the BFKL calculation.Comment: 3 pages, 2 figures, talk given on behalf of the H1 collaboration at DIS99, Zeuthe

Determination of the strong coupling constant at LEP

Multi-hadronic events produced in e+e- collisions provide an excellent laboratory to study QCD, the theory of strong interactions, and in particular to determine the strong coupling parameter alpha_s and demonstrate its predicted behavior as a function of the energy scale. Determinations of alpha_s at LEP will be reviewed with emphasis on event shape variables and jet rates in 3-jet and 4-jet events.Comment: Proceedings of DIS06, XIV International Workshop on Deep Inelastic Scattering, Tsukuba, Japan, 20-24 April 2006, 4 pages, 2 figure

High momentum particle and jet production in photon-photon collisions

Jet and particle production have been studied in collisions of quasi-real photons collected during the LEP2 program. OPAL and DELPHI report good agreement of NLO perturbative QCD with the measured differential di-jet cross sections, which reach a mean transverse energy of the di-jet system of 25 GeV. L3, on the other hand, finds drastic disagreement of the same calculation with single jet production for transverse jet momenta larger than about 25 GeV. L3 observes similar disagreement between data and NLO QCD in their measurements of charged and neutral particle production at high transverse momenta of the particles. A recent measurement performed by DELPHI of the same quantities does not confirm this observation.Comment: 7 pages, 3 figures, to appear in the proceedings of PHOTON200

The Hadronic Picture of the Photon

The hadronic interactions of the photon are studied in terms of new measurements of the total hadronic cross section and di-jet production in photon-photon collisions at LEP2.Comment: 3 pages, 3 figures, 1 table, to be published in proceedings ICHEP2000, Osaka, Japa

Submillimeter wave detection with superconducting tunnel diodes

Superconductor-Insulator-Superconductor (SIS) diodes are the detector elements in the most sensitive heterodyne receivers available from 100 to 500 GHz. SIS mixers are the front end of radio astronomical systems around the world. SIS mixer technology is being extended to 1 THz and higher frequencies for eventual use on spaceborne astronomical experiments. Here is a short review of submillimeter SIS mixers. The role of impedance matching in the proper design of an SIS mixer is described. A variety of methods for achieving good impedance match at submillimeter frequencies are presented. The experimental state of the submillimeter SIS mixer art is described and summarized

Parallel arrays of Josephson junctions for submillimeter local oscillators

In this paper we discuss the influence of the DC biasing circuit on operation of parallel biased quasioptical Josephson junction oscillator arrays. Because of nonuniform distribution of the DC biasing current along the length of the bias lines, there is a nonuniform distribution of magnetic flux in superconducting loops connecting every two junctions of the array. These DC self-field effects determine the state of the array. We present analysis and time-domain numerical simulations of these states for four biasing configurations. We find conditions for the in-phase states with maximum power output. We compare arrays with small and large inductances and determine the low inductance limit for nearly-in-phase array operation. We show how arrays can be steered in H-plane using the externally applied DC magnetic field