Anomalous Quartic Couplings in ννˉγγ\nu \bar{\nu} \gamma \gamma Production via WW-Fusion at LEP2

The production of $\nu \bar{\nu} \gamma \gamma$ in high-energy $e^+e^-$ collisions offers a window on anomalous quartic gauge boson couplings. We investigate the effect of two possible anomalous couplings on the cross section for $\nu \bar{\nu} \gamma \gamma$ production via $WW$-fusion at LEP2 ($\sqrt{s} = 200$ GeV).Comment: 7 pages, 3 figures, LaTex, clarifying definition adde

Summary of the Structure Function Session at Dis01

The status and ongoing developments in the field of deep inelastic scattering presented at the DIS01 workshop in Bologna are discussed from both the experimental and the theoretical perspective.Comment: Invited talk presented at the 9th International Workshop on Deep Inelastic Scattering (DIS 2001), Bologna, Italy, 27 Apr - 1 May 2001, to appear in the Proceedings. (30 pages, 17 figures

Like-Sign W Boson Production at the LHC as a Probe of Double Parton Scattering

Double parton scattering, i.e. two parton hard scattering processes in the same hadron-hadron collision, may constitute an important background for Higgs and other new particle searches at the LHC. We point out that like-sign W pair production provides a relatively clean way of searching for, and calibrating, double parton scattering at the LHC.Comment: 10 pages, LaTeX, 5 figures, epsfi

Update of MRST parton distributions.

We discuss the latest update of the MRST parton distributions in response to the most recent data. We discuss the areas where there are hints of difficulties in the global fit, and compare to some other updated sets of parton distributions, particularly CTEQ6. We briefly discuss the issue of uncertainties associated with partons

MRST global fit update.

We discuss the impact of the most recent data on the MRST global analysis - in particular the new high-ET jet data and their implications for the gluon and the new small x structure function data. In the light of these new data we also consider the uncertainty in predictions for physical quantities depending on parton distributions, concentrating on the W cross-section at hadron colliders

Radiation Zeros in W^+W^-\gamma Production at High-Energy Colliders

The vanishing of the cross section for particular points in phase space - radiation zeros - is examined for the process $q \bar q \to W^+W^- \gamma$ at high energy. Unlike the process $q \bar q' \to W^\pm \gamma$, actual zeros only occur in the soft-photon limit. However, for photon energies that are not too large, the cross section does exhibit deep dips in regions of phase space corresponding to the position of the actual zeros. We show that in these regions the sensitivity to possible anomalous quartic couplings is very large.Comment: 19 pages, 7 figures, LaTe

Heavy Quark Production at a γγ\gamma \gamma Collider: the Effect of Large Logarithmic Perturbative Corrections

We present quantitative results on the cross section for $\gamma + \gamma (J_z=0) \to b \bar{b}\to two b$-jets based on the recently achieved all orders resummation of large soft (Sudakov) and hard (non-Sudakov) double logarithms. The next-to-leading order QCD perturbative corrections are included exactly. We find that one needs to include at least four loops for the novel hard leading logarithms, on the cross section level, in order to be safe from large opposite sign cancellations that plagued earlier phenomenological studies. We find that the background to intermediate mass Higgs boson production at a future photon linear collider (PLC) is thus reasonably well under control and should allow the direct determination of the partial Higgs width $\Gamma (H \to \gamma + \gamma)$. Assuming high efficiency $b$-tagging, the total Higgs width measurement at a PLC is thus a realistic goal.Comment: 14 pages, 5 eps-figures, uses LateX2e. Submitted to Phys. Rev. Let

MRST partons and uncertainties.

We discuss uncertainties in the extraction of parton distributions from global analyses of DIS and related data. We present conservative sets of partons, at both NLO and NNLO, which are stable to x,Q2,W2 cuts on the data. We give the corresponding values of S(M2 Z) and the cross sections for W production at the Tevatron

Sudakov Logarithm Resummation in Transverse Momentum Space for Electroweak Boson Production at Hadron Colliders

A complete description of W and Z boson production at high-energy hadron colliders requires the resummation of large Sudakov double logarithms which dominate the transverse momentum (q_T) distribution at small q_T. We compare different prescriptions for performing this resummation, in particular implicit impact parameter space resummation versus explicit transverse momentum space resummation. We argue that the latter method can be formulated so as to retain the advantages of the former, while at the same time allowing a smooth transition to finite order dominance at high q_T.Comment: 32 pages, Latex, epsfig, 17 figure