Search

Physical review letters 108(18), 181805 (1-5) (2012). doi:10.1103/PhysRevLett.108.181805, Motivated by evidence for the existence of dark matter, many new physics models predict the pair production of new particles, followed by the decays into two invisible particles, leading to a momentum imbalance in the visible system. For the cases where all four components of the vector sum of the two `missing' momenta are measured from the momentum imbalance, we present analytic solutions of the final state system in terms of measureable momenta, with the mass shell constraints taken into account. We then introduce new variables which allow the masses involved in the new physics process, including that of the dark matter particles, to be extracted. These are compared with a selection of variables in the literature, and possible applications at lepton and hadron colliders are discussed., Published by APS, College Park, Md.

Universität Hamburg, Diplomarbeit, 2003; 62 pp., (2003). doi:10.3204/DESY-THESIS-2003-001, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

22 pp. (2003)., If there is no light Higgs boson, the interaction among the gauge bosons becomes strong at high energies [∼ 1TeV]. The effects of strong electroweak symmetry breaking (EWSB) could manifest them- selves indirectly as anomalous couplings before they give rise to new physical states like resonances. Here we present a study of the mea- surement of trilinear gauge couplings looking at the hadronic decay channel of W boson production at an $e\gamma$ - collider. A sensitivity in the range of $10^{−3}$ to $10^{−4}$ can be reached depending on the coupling under consideration.

Universität Hamburg, Diss., 2002; 136 pp., (2002). doi:10.3204/DESY-THESIS-2002-054, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

Physical review / D 63(3), 035003 (2001). doi:10.1103/PhysRevD.63.035003, We calculate total and differential cross sections for the production of sfermion pairs in photon-photon collisions, including contributions from resolved photons and arbitrary photon polarization. Sfermion production in photon collisions depends only on the sfermion mass and charge. It is thus independent of the details of the SUSY breaking mechanism, but highly sensitive to the sfermion charge. We compare the total cross sections for bremsstrahlung, beamstrahlung, and laser backscattering photons to those in $e^+e^-$ annihilation. We find that the total cross section at a polarized photon collider is larger than the $e^+e^-$ annihilation cross section up to the kinematic limit of the photon collider., Published by Inst., Woodbury, NY

Physical review / D 63(7), 074502 (2001). doi:10.1103/PhysRevD.63.074502, We present the next-to-leading-order cross sections of the heavy quark-antiquark pair production in polarized photon-photon collision for the general case of photon polarizations. The numerical results for top-antitop production cross sections together with production asymmetries are obtained for linearly polarized photon-photon collisions, including one-loop QCD radiative corrections., Published by Inst., Woodbury, NY

14 pp. (2000).

29 pp. (2000)., We consider the possibility that after operations at the LHC and $e^+e^-$ Linear Colliders a Higgs boson will be discovered, but no signal of New Physics will be found (Standard-Model-like scenario). This can occur in the Standard Model (SM) as well as in other models, including the Two-Higgs-Doublet Model (2HDM), the MSSM, etc. Experiments at a Photon Collider can resolve these cases. In this paper we compare the SM and the 2HDM~(II). In the analysis we use as independent quantities the ratios, to the SM values, of couplings of the observed Higgs boson to gauge bosons, and to up and down-type quarks (basic couplings). We derive a relation between these ratios within the 2HDM~(II), a pattern relation. With the aid of this relation, different possible realizations of an SM-like scenario are found. For these realizations, we calculate the loop couplings of the Higgs boson with $\gamma\gamma$ and $Z \gamma$, and also with gluons, taking into account the expected accuracy in the measurements of the basic couplings. The obtained deviation of the two-photon width from its SM value is generally higher than the expected inaccuracy in the measurement of $\Gamma_{\gamma \gamma}$ at a Photon Collider. The result is sensitive to the parameters of the Higgs self interaction.

8 pp. (2000)., We briefly present the motivation for studying the processes mediated by the QCD pomeron at high energy $e^+e^-$ colliders. We describe the behaviour of the cross-section for the reaction $\gamma \gamma \to J/\psi J/\psi$ obtained from the BFKL equation with dominant non-leading corrections. We give the predictions for the rates of anti-tagged $e^+e^- \to e^+e^- J/\psi J/\psi$ events in TESLA and conclude that such reactions may be excellent probes of the hard pomeron.

Zeitschrift für Physik / C 74, 469-477 (1997)., Published by Springer, Berlin

11 pp. (1996)., A maximum likelihood analysis of ARGUS data on two-photon production of π + π + π 0 π 0 π − π − is presented. A small fraction of events is due to the production of omega pairs. The γγ → ωω cross section has its maximum value close to threshold.

In two-photon collisions at LEP2 and a future e + e − linear collider heavy quarks (mainly charm) will be pair-produced rather copiously. The production via direct and resolved photons can be distinguished experimentally via a remnant-jet tag. We study correlations of the heavy quarks at next-to-leading order in QCD in the direct channel, which is free from phenomenological parton densities in the photon. These correlations are therefore directly calculable in perturbative QCD and provide a stringent test of the production mechanism.

22 pp. (1991)., The reactionγγ→3π+3π- has been studied usig the JADE detector at PETRA. The topological cross sectionσ(γγ→3π+3π-) was measured in the CM energy range 1.5–5.5 GeV. The production ofρ0,s was observed and the average number ofρ0,s per event measured. The contributions of the subprocessesγγ→ρ02π+2π-,γγ→ρ0ρ0π+2π- andγγ→ 3π+3π- (phase space) were studied and 95% C.L. upper limits for the cross sectionσ(γγ→ρ0ρ0π+π- determined. Finally the Bose-Einstein correlation for pairs of like signed pions was observed. A fit to a standard parametrization gave results consistent with other studies of this effect in pion systems.

42 pp. (1990).

Universität Hamburg, Diss., 1989; 86 pp. (1989). = Universität Hamburg, Diss., 1989

113 pp. (1986)., This paper summarizes experimental results on exclusive hadron production in two-photon collisions at electron-positron storage rings and attempts some interpretation. Experimental know-how is described and new suggestions are made for future analyses. New model calculations on resonance form factors and pair production amplitudes are presented. The two-photon vertex is decomposed such that experiments can be parameterized with the minimal number of free parameters. Selection rules for off-shell photon collisions are given in addition to Yang’s theorems.

Physical review / D 38(5), 1365 - 1376 (1988). doi:10.1103/PhysRevD.38.1365, The Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reaction e+e−→e+e−γ*γ*→e+e−γγ, where X is a narrow resonance with mass between 100 and 3000 MeV. Formation of π0, η, and η’ mesons is observed, and the following meson partial widths are obtained: Γπ0Γ0→γγ=7.7±0.5±0.5 eV, Γη−γγ=0.514±0.017±0.035 keV, and Γη’→γγ=4.7±0.5±0.5 keV. No other narrow resonances are observed, and upper limits are given for the product ΓX→γγBX→γγ. .AE, Published by Inst., Woodbury, NY

229 pp. (1987).

11 pp. (1984).