Estimation of Power Corrections to Hadronic Event Shapes

Power corrections to hadronic event shapes are estimated using a recently suggested relationship between perturbative and non-perturbative effects in QCD. The infrared cutoff dependence of perturbative calculations is related to non-perturbative contributions with the same dependence on the energy scale $Q$. Corrections proportional to $1/Q$ are predicted, in agreement with experiment. An empirical proportionality between the magnitudes of perturbative and non-perturbative coefficients is noted.Comment: 5 pages, LaTeX (no figures

Jet Rates in Deep Inelastic Scattering at Small xx

The recent results of Forshaw and Sabio Vera on small-$x$ jet rates to order $\alpha_s^3$ are extended to all orders, for any number of jets. A simple generating function is obtained.Comment: 8 pages, LaTeX, no figure

Herwig++ 2.2 Release Note

A new release of the Monte Carlo program Herwig++ (version 2.2) is now available. This version includes a number of improvements including: matrix elements for the production of an electroweak gauge boson, W and Z, in association with a jet; several new processes for Higgs production in association with an electroweak gauge boson; and the matrix element correction for QCD radiation in Higgs production via gluon fusion

A Positive-Weight Next-to-Leading-Order Monte Carlo for e+e- Annihilation to Hadrons

We apply the positive-weight Monte Carlo method of Nason for simulating QCD processes accurate to Next-To-Leading Order to the case of e+e- annihilation to hadrons. The method entails the generation of the hardest gluon emission first and then subsequently adding a `truncated' shower before the emission. We have interfaced our result to the Herwig++ shower Monte Carlo program and obtained better results than those obtained with Herwig++ at leading order with a matrix element correction.Comment: 21 pages, 11 figures, 2 tables Reason for replacement: minor corrections, typos and 1 changed referenc

Fragmentation Function Method for Charge Asymmetry Measurements in \e^+e^- Collisions

We propose a method for measuring the hadron charge asymmetry in \ee collisions which is based upon the fragmentation function formalism, and is largely independent of modelling of fragmentation effects. Furthermore, in this method, QCD radiative corrections can be accounted for in a systematic way.Comment: 11 pages, 4 figures, Latex, CERN-TH.7212/9

HERBVI - a program for simulation of baryon- and lepton- number violating processes

We describe a Monte Carlo event generator for the simulation of baryon- and lepton-number violating processes at supercolliders. The package, {\HERBVI}, is designed as a hard-process generator interfacing to the general hadronic event simulation program {\HW}. In view of the very high multiplicity of gauge bosons expected in such processes, particular attention is paid to the efficient generation of multiparticle phase space. The program also takes account of the expected colour structure of baryon-number violating vertices, which has important implications for the hadronization of the final state.Comment: 19 pages, standard LaTeX, no figure

Naturalness Reach of the Large Hadron Collider in Minimal Supergravity

We re-analyse the prospects of discovering supersymmetry at the LHC, in order to re-express coverage in terms of a fine-tuning parameter and to extend the analysis to scalar masses (m_0) above 2 TeV. We use minimal supergravity (mSUGRA) unification assumptions for the SUSY breaking parameters. Such high values of m_0 have recently been found to have a focus point, leading to relatively low fine-tuning. In addition, improvements in the simulations since the last study mean that this region no longer lacks radiative electroweak symmetry breaking. The best fine tuning reach is found in a mono-leptonic channel, where for mu>0, A_0=0 and tan beta=10 (corresponding to the focus point), all points in mSUGRA with m_0 < 4000 GeV, with a fine tuning measure up to 300 (570) are covered by the search, where the definition of fine-tuning excludes (includes) the contribution from the top Yukawa coupling. Even for arbitrarily high m_0, mSUGRA does not evade detection provided the gaugino mass parameter M_{1/2} < 460 GeV

Renormalon Phenomena in Jets and Hard Processes

The `renormalon' or `dispersive' method for estimating non-perturbative corrections to QCD observables is reviewed. The corrections are power-suppressed, i.e. of the form $A/Q^p$ where $Q$ is the hard process momentum scale. The renormalon method exploits the connection between divergences of the QCD perturbation series and low-momentum dynamics to predict the power, $p$. The further assumption of an approximately universal low-energy effective strong coupling leads to relationships between the coefficients $A$ for different observables. Results on $1/Q^2$ corrections to deep inelastic structure functions and $1/Q$ corrections to event shapes are presented and compared with experiment. Shape variables that could be free of $1/Q$ and \as(Q^2)/Q corrections are suggested.Comment: 17 pages, LaTeX, 5 figures, uses epsfig. Talk at XXVII International Symposium on Multiparticle Dynamics, Frascati, Italy, 8-12 September 199

Measuring Supersymmetric Particle Masses at the LHC in Scenarios with Baryon-Number R-Parity Violating Couplings

The measurement of sparticle masses in the Minimal Supersymmetric Standard Model at the LHC is analysed, in the scenario where the lightest neutralino decays into three quarks. Such decays, occurring through the baryon-number violating coupling lambda"\_ijk, pose a severe challenge to the capability of the LHC detectors since the final state has no missing energy signature and a high jet multiplicity. We focus on the case of non-zero lambda"\_212 which is the most difficult experimentally. The proposed method is valid over a wide range of SUGRA parameter space with lambda"\_212 between 10^{-5}-0.1. Simulations are performed of the ATLAS detector at the Large Hadron Collider. Using the lightest neutralino from the decay chain left-squark to quark + next-to-lightest neutralino to right-slepton + lepton + quark and finally to lightest neutralino + lepton pair + quark, we show that the lightest and next-to-lightest neutralino masses can be measured by 3-jet and 3-jet + lepton pair invariant mass combinations. At the SUGRA point M_0=100 GeV, M_{1/2}=300 GeV, A_0=300 GeV, tan beta=10, sign of mu positive and with lambda"\_212=0.005, we achieve statistical (systematic) errors of 3 (3), 3 (3), 0.3 (4) and 5 (12) GeV respectively for the masses of the lightest neutralino, next-to-lightest neutralino, right-slepton and left-squark, with an integrated luminosity of 30 fb^{-1}

Local charge compensation from colour preconfinement as a key to the dynamics of hadronization

If, as is commonly accepted, the colour-singlet, `preconfined', perturbative clusters are the primary units of hadronization, then the electric charge is necessarily compensated locally at the scale of the typical cluster mass. As a result, the minijet electric charge is suppressed at scales that are greater than the cluster mass. We hence argue, and demonstrate by means of Monte Carlo simulations using HERWIG, that the scale at which charge compensation is violated is close to the mass of the clusters involved in hadronization, and its measurement would provide a clue to resolving the nature of the dynamics. We repeat the calculation using PYTHIA and find that the numbers produced by the two generators are similar. The cluster mass distribution is sensitive to soft emission that is considered unresolved in the parton shower phase. We discuss how the description of the splitting of large clusters in terms of unresolved emission modifies the algorithm of HERWIG, and relate the findings to the yet unknown underlying nonperturbative mechanism. In particular, we propose a form of $\alpha_S$ that follows from a power-enhanced beta function, and discuss how this $\alpha_S$ that governs unresolved emission may be related to power corrections. Our findings are in agreement with experimental data.Comment: 37 pages, 20 figure