Inelastic Photoproduction at HERA: a Second Charmonium Crisis?

The measurement of the inelastic photoproduction of charmonium at HERA seems to have ignited a new charmonium crisis. The (already discredited) color singlet model fits the data for large charmonium energy fraction z, where the NRQCD model qualitatively fails. We here point out that by the straightforward inclusion of color singlet and octet processes in the soft color (color evaporation) scheme, the HERA data can be accommodated for all z. We anticipate that the color singlet model will fail at low z, as it does in hadroproduction.Comment: 10 pages, Revtex, uses epsfig.sty to include 4 postscript figures. Also available from the UW-Madison Phenomenology preprint archives at http://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1045.ps.Z or at ftp://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1045.ps.

Searching for Leptoquarks in electron-photon Collisions

We study the production of composite scalar leptoquarks in $e\gamma$ colliders, and we show that an $e^+e^-$ machine operating in its $e\gamma$ mode is the best way to look for these particles in $e^+e^-$ collisions, due to the hadronic content of the photon.Comment: 12 pages in REVTeX3. 6 figures appended as postcript files. Report: IFT-P.014/93 and IFUSP-P 104

Prospects for CP-violation searches in the future experiment with RF-separated K+/- beam at U-70

The first description of the experimental program "OKA" with RF-separated K+/- beam at Protvino U-70 PS is presented. The parameters of the beam as well as the potential for CP-violation searches are discussed.Comment: 8 pages, 6 figures, submitted to proceedings of International Conference on CP Violation, Sep 18-22, 2000, Ital

Colorless States in Perturbative QCD: Charmonium and Rapidity Gaps

We point out that an unorthodox way to describe the production of rapidity gaps in deep inelastic scattering, recently proposed by Buchm\"uller and Hebecker, suggests a description of the production of heavy quark bound states which is in agreement with data. The approach questions the conventional treatment of the color quantum number in perturbative QCD.Comment: 14 pages, plain Latex, 9 postscript figures included. Uses epsf.sty. Postscript file of paper with figures also available at http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-919.ps.Z or at ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-919.ps.

Doubly charged Higgs from ee-γ\gamma scattering in the 3-3-1 Model

We studied the production and signatures of doubly charged Higgs bosons in the process $\gamma e^- \rightarrow H^{--}E^+$, where $E^+$ is a heavy lepton, at the $e^-e^+$ International Linear Collider (ILC) and CERN Linear Collider (CLIC). The intermediate photons are given by the Weizs$\ddot{a}$cker-Williams and laser backscattering distributions. We found that significant signatures are obtained by bremsstrahlung and backward Comptom scattering of laser. A clear signal can be obtained for doubly charged Higgs bosons, doubly charged gauge bosons and heavy leptons

Excited Leptons at the CERN Large Hadron Collider

We analyze the potential of the CERN Large Hadron Collider (LHC) to search for excited spin-1/2 electrons and neutrinos. Assuming a SU(2)_L X U(1)_Y invariant model, we study in detail the single production of excited electrons and neutrinos and respective backgrounds through the reactions p p -> e+ e- V and e+- \nu V with V=photon, W, or Z. We show that the LHC will be able to tighten considerably the direct constraints on these possible new states, probing excited lepton masses up to 1-2 TeV depending on their couplings to fermions and gauge bosons.Comment: 15 pages, 7 figure

Lepton flavor violating signals of a little Higgs model at the high energy linear e+e−e^{+}e^{-} colliders

Littlest Higgs $(LH)$ model predicts the existence of the doubly charged scalars $\Phi^{\pm\pm}$, which generally have large flavor changing couplings to leptons. We calculate the contributions of $\Phi^{\pm\pm}$ to the lepton flavor violating $(LFV)$ processes $l_{i}\to l_{j}\gamma$ and $l_{i}\to l_{j}l_{k}l_{k}$, and compare our numerical results with the current experimental upper limits on these processes. We find that some of these processes can give severe constraints on the coupling constant $Y_{ij}$ and the mass parameter $M_{\Phi}$. Taking into account the constraints on these free parameters, we further discuss the possible lepton flavor violating signals of $\Phi^{\pm\pm}$ at the high energy linear $e^{+}e^{-}$ collider $(ILC)$ experiments. Our numerical results show that the possible signals of $\Phi^{\pm\pm}$ might be detected via the subprocesses $e^{\pm}e^{\pm}\to l^{\pm}l^{\pm}$ in the future $ILC$ experiments.Comment: 16 pages, 7 figures. Discussions and references added, typos correcte

Explaining the Higgs Decays at the LHC with an Extended Electroweak Model

We show that the recent discovery of a new boson at the LHC, which we assume to be a Higgs boson, and the observed enhancement in its diphoton decays compared to the SM prediction, can be explained by a new doublet of charged vector bosons from an extended electroweak gauge sector model with SU(3)_C\otimesSU(3)_L\otimesU(1)_X symmetry. Our results show a good agreement between our theoretical expected sensitivity to a 126--125 GeV Higgs boson and the experimental significance observed in the diphoton channel at the 8 TeV LHC. Effects of an invisible decay channel for the Higgs boson are also taken into account, in order to anticipate a possible confirmation of deficits in the branching ratios into $ZZ^*$, $WW^*$, bottom quarks, and tau leptons.Comment: 16 pages, 5 figure

b-Jet Identification in the D0 Experiment

Algorithms distinguishing jets originating from b quarks from other jet flavors are important tools in the physics program of the D0 experiment at the Fermilab Tevatron p-pbar collider. This article describes the methods that have been used to identify b-quark jets, exploiting in particular the long lifetimes of b-flavored hadrons, and the calibration of the performance of these algorithms based on collider data.Comment: submitted to Nuclear Instruments and Methods in Physics Research

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging

We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($\sigma_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $\sigma_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let