We give a factorization formula for the e + e − thrust distribution dσ/dτ with τ = 1 − T based on soft-collinear effective theory. The result is applicable for all τ , i.e. in the peak, tail, and fartail regions. The formula includes O(α 3 s ) fixed-order QCD results, resummation of singular partonic α j s ln k (τ )/τ terms with N 3 LL accuracy, hadronization effects from fitting a universal nonperturbative soft function defined in field theory, bottom quark mass effects, QED corrections, and the dominant top mass dependent terms from the axial anomaly. We do not rely on Monte Carlo generators to determine nonperturbative effects since they are not compatible with higher order perturbative analyses. Instead our treatment is based on fitting nonperturbative matrix elements in field theory, which are moments Ωi of a nonperturbative soft function. We present a global analysis of all available thrust data measured at center-of-mass energies Q = 35 to 207 GeV in the tail region, where a two parameter fit to αs(mZ) and the first moment Ω1 suffices. We use a short distance scheme to define Ω1, called the R-gap scheme, thus ensuring that the perturbative dσ/dτ does not suffer from an O(ΛQCD) renormalon ambiguity. We find αs(mZ) = 0.1135 ± (0.0002)expt ± (0.0005) hadr ± (0.0009)pert, with χ 2 /dof = 0.91, where the displayed 1-sigma errors are the total experimental error, the hadronization uncertainty, and the perturbative theory uncertainty, respectively. The hadronization uncertainty in αs is significantly decreased compared to earlier analyses by our two parameter fit, which determines Ω1 = 0.323 GeV with 16% uncertainty.

In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved; apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral K mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral B mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of K, D, and B mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model. In the near future, there will be a transition from the current to a new generation of experiments; thus a review of the status of quark flavor physics is timely. This report is the result of the work of physicists attending the 5th CKM workshop, hosted by the University of Rome "La Sapienza", September 9-13, 2008. It summarizes the results of the current generation of experiments that are about to be completed and it confronts these results with the theoretical understanding of the field which has greatly improved in the past decade. (C) 2010 Elsevier B.V. All rights reserved

This report of the BOOST2012 workshop presents the results of four working groups that studied key aspects of jet substructure. We discuss the potential of firstprinciple QCD calculations to yield a precise description of the substructure of jets and study the accuracy of state-ofthe-art Monte Carlo tools. Limitations of the experiments' ability to resolve substructure are evaluated, with a focus on the impact of additional (pile-up) proton proton collisions on jet substructure performance in future LHC operating scenarios. A final section summarizes the lessons learnt from jet substructure analyses in searches for new physics in the production of boosted top quarks.

The most precise top quark mass measurements use kinematic reconstruction methods, determining the top mass parameter of a Monte Carlo event generator m MC t . Because of hadronization and parton-shower dynamics, relating m MC t to a field theory mass is difficult. We present a calibration procedure to determine this relation using hadron level QCD predictions for observables with kinematic mass sensitivity. The highest precision measurements are based on direct reconstruction methods exploiting kinematic properties related to the top quark mass, and are based on multivariate fits that depend on a maximum amount of information on the top decay final states. This includes template and matrix element fits for distributions such as the measured invariant mass. These observables are highly differential, depending on experimental cuts and jet dynamics. Multipurpose Monte Carlo (MC) event generators are employed to do the analysis, and the results are influenced by both perturbative and nonperturbative QCD effects. Thus, the measured mass is the top mass parameter m MC t contained in the particular MC event generator. Its interpretation may also depend in part on the MC tuning and the observables used in the analysis.The systematic uncertainties from MC modeling are a dominant uncertainty in the above measurements, but do not address how m MC t is related to a mass parameter defined precisely in quantum field theory that can be globally used for higher-order predictions. The relation is nontrivial because it requires an understanding of the interplay between the partonic components of the MC generator (hard matrix elements and parton shower) and the hadronization model. In the context of top quark mass determinations, it is often assumed that MC generators should be considered as models whose partonic components and hadronization models are, through the tuning procedure, capable of describing experimental data to a precision that is higher than that of their partonic input.In the past m MC t has been frequently identified with the pole mass. This is compatible with parton-shower implementations for massive quarks, but a direct identification is disfavored because of sensitivity to nonperturbative effects from below the MC shower cutoff, Λ c ∼ 1 GeV. Also, the pole mass has an OðΛ QCD Þ renormalon ambiguity, while m MC t does not (since partonic information is not employed below Λ c ). It has been argued [4,5] can be calibrated into a field theory mass scheme through a fit of MC predictions to hadron level QCD computations for observables closely related to the distributions that enter the experimental analyses. In this Letter we provide a precise quantitative study on the interpretation of m MC t in terms of the MSR and pole mass schemes based on a hadron level prediction for the variable τ 2 for the production of a boosted top-antitop quark pair in e þ e − annihilation. It is defined aswhere the sum is over the 3-momenta of all final state particles, the maximum defines the thrust axisñ t , and Q is the center-of-ma...

We consider cumulant moments (cumulants) of the thrust distribution using predictions of the full spectrum for thrust including O(α 3 s ) fixed order results, resummation of singular N 3 LL logarithmic contributions, and a class of leading power corrections in a renormalon-free scheme. From a global fit to the first thrust moment we extract the strong coupling and the leading power correction matrix element Ω1. We obtain αs(mZ) = 0.1140 ± (0.0004)exp ± (0.0013) hadr ± (0.0007)pert, where the 1-σ uncertainties are experimental, from hadronization (related to Ω1) and perturbative, respectively, and Ω1 = 0.377 ± (0.044)exp ± (0.039)pert GeV. The n-th thrust cumulants for n ≥ 2 are completely insensitive to Ω1, and therefore a good instrument for extracting information on higher order power corrections, Ω ′ n /Q n , from moment data. We find (Ω ′ 2 ) 1/2 = 0.74 ± (0.11)exp ± (0.09)pert GeV.