QCD Interconnection Studies at Linear Colliders

Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider energies.Comment: 1+7 pages, 6 figure

QCD Interconnection Effects

Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider energies.Comment: 1+4 pages, no figures, to appear in the Proceedings of the International Workshop on Linear Colliders, Sitges (Barcelona), Spain, April 28 - May 5, 199

A scenario for high-energy gamma-gamma interactions

A real photon has a complicated nature, whereby it may remain unresolved or fluctuate into a vector meson or a perturbative q-qbar pair. In gamma-gamma events, this gives three by three combinations of the nature of the two incoming photons, and thus six distinct event classes. The properties of these classes are partly constrained by the choices already made in our related gamma-p model. It is therefore possible to predict the energy-dependence of the cross section for each of the six components separately. The total cross section gives support to the idea that a simple factorized ansatz with a pomeron and a reggeon term can be a good approximation. Event properties undergo a stepwise evolution from p-p to gamma-p to gamma-gamma events, with larger charged multiplicity, more transverse energy flow and a higher jet rate in the latter process.Comment: 1+27 pages, LaTeX2e, 20 ps/eps figures included in file using filecontents environment

Forward-Backward Correlations and Event Shapes as probes of Minimum-Bias Event Properties

Measurements of inclusive observables, such as particle multiplicities and momentum spectra, have already delivered important information on soft-inclusive ("minimum-bias") physics at the Large Hadron Collider. In order to gain a more complete understanding, however, it is necessary to include also observables that probe the structure of the studied events. We argue that forward-backward (FB) correlations and event-shape observables may be particulary useful first steps in this respect. We study the sensitivity of several different types of FB correlations and two event shape variables - transverse thrust and transverse thrust minor - to various sources of theoretical uncertainty: multiple parton interactions, parton showers, colour (re)connections, and hadronization. The power of each observable to furnish constraints on Monte Carlo models is illustrated by including comparisons between several recent, and qualitatively different, PYTHIA 6 tunes, for pp collisions at sqrt(s) = 900 GeV.Comment: 13 page

Tevatron Discovery Potential for Fourth Generation Neutrinos: Dirac, Majorana and Everything in Between

We analyze the power of the Tevatron dataset to exclude or discover fourth generation neutrinos. In a general framework, one can have mixed left- and right-handed neutrinos, with Dirac and Majorana neutrinos as extreme cases. We demonstrate that a single Tevatron experiment can make powerful statements across the entire mixing space, extending LEP's mass limits of 60-80 GeV up to 150-175 GeV, depending on the mixing.Comment: 4 pages, pdflate

Revisiting Constraints on Fourth Generation Neutrino Masses

We revisit the current experimental bounds on fourth-generation Majorana neutrino masses, including the effects of right handed neutrinos. Current bounds from LEPII are significantly altered by a global analysis. We show that the current bounds on fourth generation neutrinos decaying to eW and mu W can be reduced to about 80 GeV (from the current bound of 90 GeV), while a neutrino decaying to tau W can be as light as 62.1 GeV. The weakened bound opens up a neutrino decay channel for intermediate mass Higgs, and interesting multi-particle final states for Higgs and fourth generation lepton decays.Comment: 7 pages 1 fi

Energy Scaling of Minimum-Bias Tunes

We propose that the flexibility offered by modern event-generator tuning tools allows for more than just obtaining "best fits" to a collection of data. In particular, we argue that the universality of the underlying physics model can be tested by performing several, mutually independent, optimizations of the generator parameters in different physical regions. For regions in which these optimizations return similar and self-consistent parameter values, the model can be considered universal. Deviations from this behavior can be associated with a breakdown of the modeling, with the nature of the deviations giving clues as to the nature of the breakdown. We apply this procedure to study the energy scaling of a class of minimum-bias models based on multiple parton interactions (MPI) and pT-ordered showers, implemented in the Pythia 6.4 generator. We find that a parameter controlling the strength of color reconnections in the final state is the most important source of non-universality in this model.Comment: 17 pages, 3 figures, 4 table

Resonance-free Region in scattering by a strictly convex obstacle

We prove the existence of a resonance free region in scattering by a strictly convex obstacle with the Robin boundary condition. More precisely, we show that the scattering resonances lie below a cubic curve which is the same as in the case of the Neumann boundary condition. This generalizes earlier results on cubic poles free regions obtained for the Dirichlet boundary condition.Comment: 29 pages, 2 figure

Inverse Slope Systematics in High-Energy p+p and Au+Au Reactions

We employ the Monte-Carlo PYTHIA to calculate the transverse mass spectra of various hadrons and their inverse slopes T* at m_T-m=1.5-2 GeV in p+p reactions at sqrt(s)=200 GeV. Due to (multiple) minijet production T* increases as a function of the hadron mass. Moreover, the T*(m) systematics has a ``discontinuity'' at the charm threshold, i.e. the inverse slope of D-mesons is much higher than that of non-charmed hadrons and even of the heavier Lambda_C baryon. The experimental observation of this characteristic behaviour in Au+Au collisions would indicate the absence of c-quark rescattering. In contrast, the assumption of thermalized partons and hydrodynamical evolution would lead to a smoothly increasing T*(m), without discontinuity at the charm threshold. The degree of collective transverse flow, indicated by the slope of the T*(m) systematics, depends strongly on whether kinetic equilibrium is maintained for some time after hadronization or not.Comment: 14 pages, 2 figures, REVTEX; mistake in plot of c-quark mt-distribution corrected, some references adde

On the Exponential Decay of the n-point Correlation Functions and the Analyticity of the Pressure

The goal of this paper is to provide estimates leading to a direct proof of the exponential decay of the n-point correlation functions for certain unbounded models of Kac type. The methods are based on estimating higher order derivatives of the solution of the Witten Laplacian equation on one forms associated with the hamiltonian of the system. We also provide a formula for the Taylor coefficients of the pressure that is suitable for a direct proof the analyticity