Search

The hadronic part of the electron structure function F2e has been measured for the first time, using e+e− data collected by the DELPHI experiment at LEP, at centre-of-mass energies of s=91.2–209.5 GeV . The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function F2e data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function F2γ analyses and help in refining existing parameterisations.

Physical review / D 70(11), 115007 (2004). doi:10.1103/PhysRevD.70.115007, In models where the gravitino is the lightest supersymmetric particle (LSP), the next-to-lightest supersymmetric particle (NLSP) is long-lived. We consider an important charged NLSP candidate, the scalar tau $\tilde{\tau}$. Slow charged NLSPs may be produced at future colliders and they may be stopped in a massive stopper which simultaneously serves as a detector for the NLSP and its decay products. We found the number of events at a 1 kton to O(10) kton detector could be significant enough to study the NLSP decays with lifetime shorter than $10^{10}$ sec at the LHC. The performance of existing 1 kton detectors may be good enough to do such studies at the LHC, if they can be placed close to the ATLAS/CMS detectors. At a future $e^- e^-$ collider, scalar electrons $\tilde{e}^-$s are copiously produced. Slow NLSPs may be produced from the $\tilde{e}^-$ decay. The number of stopped NLSPs at a future linear collider could be large enough to study rare decay modes of the NLSP., Published by Inst., Woodbury, NY

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

We present theoretical predictions for the transverse-momentum distribution of J/psi mesons promptly produced in gamma gamma collisions within the factorization formalism of nonrelativistic quantum chromodynamics, including the contributions from both direct and resolved photons, and we perform a conservative error analysis. The fraction of J/psi mesons from decays of bottom-flavoured hadrons is estimated to be negligibly small. New data taken by the DELPHI Collaboration at LEP2 nicely confirm these predictions, while they disfavour those obtained within the traditional colour-singlet model.

14 pp. (2002)., We consider $J/\psi$ photoproduction in $e^+ e^-$ as well as linear photon colliders. We find that the process is dominated by the resolved photon channel. Both the once-resolved and twice-resolved cross-sections are sensitive to (different combinations of) the colour octet matrix elements. Hence, this may be a good testing ground for colour octet contributions in NRQCD. On the other hand, the once-resolved J/psi production cross-section, particularly in a linear photon collider, is sensitive to the gluon content of the photon. Hence these cross-sections can be used to determine the parton distribution functions, especially the gluon distribution, in a photon, if the colour octet matrix elements are known.

5 pp. (2001)., A comparison of the potentials of ep and $e^+e^-$machines to probe the structure of the photon is performed. In particular, the kinematic reach of a proposed future ep facility, THERA, is compared with those of current colliders, LEP and HERA, and with the proposed linear collider, TESLA. THERA like HERA will use a proton beam of 920 GeV but with an increased electron beam energy of 250 GeV allowing higher scales, $Q^2$, and lower values of parton momentum fraction in the photon, x_\gamma, to be probed.

11 pp. (2001).

18 pp. (2001)., A realistic study of the sensitivity to signals of strong electroweak symmetry breaking at Tesla energies using $ee→WW\nu\nu$ and $ee→ZZ\nu\nu$ processes is presented. Limits on α4 and α5, parameters of the electroweak chiral lagrangian, are given and discussed.

13 pp. (2001)., The measurement of forward jets in DIS eγ events is studied for a future linear $e^+e^−$ collider, both for the $ee$ mode and the $e\gamma$ mode. These measurements are sensitive to BFKL effects, as was demonstrated by HERA.

Universität Hamburg, Diss., 2001; 127 pp. (2001). = Universität Hamburg, Diss., 2001

11 pp. (2001)., Previous studies of the kinematic coverage for measuring the photon structure function $F_2^\gamma$ at a future 500 GeV $e^+e^−$ linear collider [1, 2] are updated using current estimates of luminosities and important detector parameters. A simple illustration is given of the sensitivity of the photonic structure functions on the strong coupling constant $\alpha_s$.

7 pp. (2000).

8 pp. (2000)., A high energy linear $e^+e^-$ collider (LC) can also be used as a Photon Collider (PC), using Compton scattering of laser photons on the $e^+/e^-$ beams. The leading order cross-section for the production of heavy quarks, $e^+e^- -> e^+e^- Q(\bar{Q}) X$, at high transverse momenta is calculated for both LC and PC modes. The sensitivity of this process to the parton distribution parametrizations of real photons, especially the gluon content, is tested for both modes.

8 pp. (2000)., A parametrization of the real photon structure function $F_2^\gamma$ in the low $Q^2$, low $x$ region is formulated. It includes both the vector meson dominance (VMD) and the QCD components, the latter suitably extrapolated to the low $Q^2$ region and based on arbitrary parton distributions in the photon. The parametrization used together with the Gluck, Reya, and Vogt (GRV) and Gluck, Reya, and Schienbein (GRS) parton densities describes reasonably well the existing high energy data on $F_2^\gamma$, $\sigma_{\gamma\gamma}$, and the low $Q^2$ data on $\sigma_{\gamma^* \gamma}$. Predictions for $\sigma_{\gamma\gamma}$ and for $\sigma_{\gamma^*\gamma}$ for energies which may become accessible in future linear colliders are also given.

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.

12 pp. (1999)., We calculate the total cross-section for $\gamma^* \gamma^*$ collisions and for the process $e^+ e^− → e^+ e^−$ +hadrons with two tagged leptons assuming dominance of the QCD pomeron exchange. We solve the BFKL equation including the dominant subleading effects generated by the consistency constraint which restricts the available phase-space of the emitted gluons to the region in which the virtuality of the exchanged gluons is dominated by their transverse momentum squared. Estimate of the possible soft pomeron contribution to the $\gamma^* \gamma^*$ cross-section is also presented. At very high CM energies W the calculated total $\gamma^* \gamma^*$ cross-section exhibits effective power-law $(W^2)^λ$ behaviour with $\lambda \tilde{} 0.3$. We confront our results with the recent measurements at LEP and give predictions for the energies which can be accessible at TESLA and at other future linear e + e − colliders.

5 pp. (1999)., We examine the prospects for studying the diffractive production of high $p_t$ photons in the process $\gamma+\gamma -> \gamma+X$ at a future linear collider operating in both ee and gamma-gamma modes. The high luminosity associated with a linear collider make it the ideal place to measure this process.

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.

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.

The reaction $e^+e^−→e^+e^−π^0π^0$ has been analyzed using 97pb$^{−1}$ of data taken with the Crystal Ball detector at the DESY $e^−e^+$ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for $γγ→π^0π^0$ for π0π0 mvariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for W=$mπ^0π^0

77 pp. (1983).

120 pp. (1988).

6 pp. (1987)., The final state K$^+K^− \pi^+\pi ^-$ has been studied in γγ interactions using the ARGUS detector at the e+e− storage ring DORIS II at DESY. Production of the vector meson pair K$^{∗0}$(892)K$^{∗0}$(892) is observed for the first time. The cross section for K$^+K^− \pi^+\pi^-$, K$^∗0K^−\pi^+$c.c. and K$^{∗0}$K$^{∗0}$ are all found to be of the order of a few nb. In the W$_{\gamma\gamma}$ range accessible, a mean upper limit of 0.5 n$_b$ at 95% CL is derived for φ$\rho^0$ production.

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.

155841 (1980)., The analysis of two photon physics at the e+e− storage ring PETRA is reviewed. Higher order QED processes e+e−→e+e−e+e−(e+e−μ+μ−) have been measured in good agreement with the QED calculations. The production of the f0 resonance has been invstigated and the radiative width has been determined. The total cross section σ(Q2,W) of the inelastic electron photon scattering has been studied in some detail. Evidence for the production of large PT jets in the reaction γγ→qq̄ is reported and a first measurement of the photon structure function in deep inelastic eγ scattering is discussed.

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(1982). doi:10.1051/jphyscol:1982313, Without abstract

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Universität Hamburg, Diplomarbeit, 1989; 67 pp. (1989). = Universität Hamburg, Diplomarbeit, 1989

19 pp. (1983).

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

30 pp. (1983).

61 pp. (1981).

34 pp. (1983)., A total of 26 papers have been contributed to the experimental discussion session. I will discuss some of the tools needed for 2γ experimentation and then point to highlights and regions of particular

229 pp. (1987).

11 pp. (1984).

(1982). doi:10.1088/0031-8949/25/1B/011, Selected topics of recent experimental results from the high-energy electron-position storage rings are presented. The topics include some of the τ and charm physics from SPEAR, the upsilon physics from DORIS and CESR, and the γγ physics and quark and gluon physics from the PLUTO and TASSO Collaborations at PETRA. Related data from the JADE and MARK J Collaborations at PETRA are discussed in separate papers at this School.

17 pp. (1983)., I review experimental results on the reactions e+e− → e+e−e+e− and e+e− → e+e− μ+μ− from PETRA and PEP. Recent high statistics measurements are compared to QED predictions in the form of diagrammatic