119236927
The Beam Thrust Cross Section for Drell-Yan at NNLL Order
At the LHC and Tevatron strong initial-state radiation (ISR) plays an important role. It can significantly affect the partonic luminosity available to the hard interaction or contaminate a signal with additional jets and soft radiation. An ideal process to study ISR is isolated Drell-Yan production, pp → Xll without central jets, where the jet veto is provided by the hadronic event shape beam thrust τB . Most hadron collider event shapes are designed to study central jets. In contrast, requiring τB ≪ 1 provides an inclusive veto of central jets and measures the spectrum of ISR. For τB ≪ 1 we carry out a resummation of α n s ln mτB corrections at next-to-next-to-leading-logarithmic order. This is the first resummation at this order for a hadron-hadron collider event shape. Measurements of τB at the Tevatron and LHC can provide crucial tests of our understanding of ISR and of τB ’s utility as a central jet veto.
39006374
Extracting short distance information from b->s l+ l-effectively
We point out that in inclusive $B\ensuremath{\rightarrow}{X}_{s}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay an angular decomposition provides a third (${q}^{2}$ dependent) observable sensitive to a different combination of Wilson coefficients than the rate and the forward-backward asymmetry. Since a precise measurement of ${q}^{2}$ dependence requires large data sets, it is important to consider the data integrated over regions of ${q}^{2}$. We develop a strategy to extract all measurable Wilson coefficients in $B\ensuremath{\rightarrow}{X}_{s}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ from a few simple integrated rates in the low ${q}^{2}$ region. A similar decomposition in $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$, together with the $B\ensuremath{\rightarrow}{K}^{*}\ensuremath{\gamma}$ rate, also provides a determination of the Wilson coefficients, without reliance on form factor models and without having to measure the zero of the forward-backward asymmetry.
118502076
Treating the b quark distribution function with reliable uncertainties
The parton distribution function for a b quark in the B meson (called the shape function) plays an important role in the analysis of the B -> X_s gamma and B -> X_u l nu data, and gives one of the dominant uncertainties in the determination of |Vub|. We introduce a new framework to treat the shape function, which consistently incorporates its renormalization group evolution and all constraints on its shape and moments in any short distance mass scheme. At the same time it allows a reliable treatment of the uncertainties. We develop an expansion in a suitable complete set of orthonormal basis functions, which provides a procedure for systematically controlling the uncertainties due to the unknown functional form of the shape function. This is a significant improvement over fits to model functions. Given any model for the shape function, our construction gives an orthonormal basis in which the model occurs as the first term, and corrections to it can be studied. We introduce a new short distance scheme, the "invisible scheme", for the kinetic energy matrix element, lambda_1. We obtain closed form results for the differential rates that incorporate perturbative corrections and a summations of logarithms at any order in perturbation theory, and present results using known next-to-next-to-leading order expressions. The experimental implementation of our framework is straightforward.
17505545
Theory uncertainties for Higgs mass and other searches using jet bins
Bounds on the Higgs mass from the Tevatron and LHC are determined using exclusive jet bins to maximize sensitivity. Scale variation in exclusive fixed-order predictions underestimates the perturbative uncertainty for these cross sections, due to cancellations between the perturbative corrections leading to large K factors and those that induce logarithmic sensitivity to the jet-bin boundary. To account for this, we propose that scale variation in the fixed-order calculations should be used to determine theory uncertainties for inclusive jet cross sections, whose differences yield exclusive jet cross sections. This yields a theory correlation matrix for the jet bins such that the additional uncertainty from large logarithms due to the jet boundary cancels when neighboring bins are added. This procedure is tested for H + 0, 1 jets, WW + 0 jets, and W + 0, 1, 2 jets, and found to be generally applicable. For a case where the higher-order resummation of the jet boundary corrections is known, we show that this procedure yields fixed-order uncertainties which are theoretically consistent with those obtained in the resummed calculation.
119267678
Factorization for generic jet production
Factorization is the central ingredient in any theoretical prediction for collider experiments. We introduce a factorization formalism that can be applied to any desired observable, like event shapes or jet observables, for any number of jets and a wide range of jet algorithms in leptonic or hadronic collisions. This is achieved by using soft-collinear effective theory to prove the formal factorization of a generic fully differential cross section in terms of a hard coefficient, and generic jet and soft functions. In this formalism, whether a given observable factorizes in the usual sense, depends on whether it is inclusive enough, so the jet functions can be calculated perturbatively. The factorization formula for any such observable immediately follows from our general result, including the precise definition of the jet and soft functions appropriate for the observable in question. As examples of our formalism, we work out several results in two-jet production for both e{sup +}e{sup -} and pp collisions. For the latter, we also comment on how our formalism allows one to treat underlying events and beam remnants.
119059119
Next-to-leading-order uncertainties in Higgs+2 jets from gluon fusion
A central ingredient in establishing the properties of the newly discovered Higgs-like boson is to isolate its production via vector boson fusion (VBF). With the typical experimental selection cuts, the VBF sample is contaminated by a 25% fraction from Higgs + 2 jet production via gluon fusion (ggF) which has large perturbative uncertainties. We perform a detailed study of the perturbative uncertainties in the NLO predictions for pp -> H+2 jets via ggF used by the ATLAS and CMS collaborations, with the VBF selection cuts of their current H -> gamma gamma analyses. We discuss in detail the application of the so-called "ST method" for estimating fixed-order perturbative uncertainties in this case, and also consider generalizations of it. Qualitatively, our results apply equally to other decay channels with similar VBF selection cuts. Typical VBF selections include indirect restrictions or explicit vetoes on additional jet activity, primarily to reduce non-Higgs backgrounds. We find that such restrictions have to be chosen carefully and are not necessarily beneficial for the purpose of distinguishing between the VBF and ggF production modes, since a modest reduction in the relative ggF contamination can be easily overwhelmed by its quickly increasing perturbative uncertainties.
9063079
The Physics of the B Factories
This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C.