We construct jet observables for energetic top quarks that can be used to determine a short-distance top quark mass from reconstruction in e e ÿ collisions with accuracy better than QCD . Using a sequence of effective field theories we connect the production energy, mass, and top width scales, Q m ÿ, for the top jet cross section, and derive a QCD factorization theorem for the top invariant mass spectrum. Our analysis accounts for s corrections from the production and mass scales, corrections due to constraints in defining invariant masses, nonperturbative corrections from the cross talk between the jets, and s corrections to the Breit-Wigner line shape. This paper mainly focuses on deriving the factorization theorem for hemisphere invariant mass distributions and other event shapes in e e ÿ collisions applicable at a future linear collider. We show that the invariant mass distribution is not a simple Breit-Wigner function involving the top width. Even at leading order it is shifted and broadened by nonperturbative soft QCD effects. We predict that the invariant mass peak position increases linearly with Q=m due to these nonperturbative effects. They are encoded in terms of a universal soft function that also describes soft effects for massless dijet events. In a future paper we compute s corrections to the jet invariant mass spectrum, including a summation of large logarithms between the scales Q, m, and ÿ.
We consider top quarks produced at large energy in e e ÿ collisions, and address the question of what top mass can be measured from reconstruction. The production process is characterized by well-separated scales: the center-of-mass energy Q, the top mass m, the top decay width ÿ t , and also QCD ; scales which can be disentangled with effective theory methods. In particular we show how the mass measurement depends on the way in which soft radiation is treated, and that this can shift the mass peak by an amount of order Q QCD =m. We sum large logs for Q m ÿ t > QCD and demonstrate that the renormalization group ties together the jet and soft interactions below the scale m. Necessary conditions for the invariant mass spectrum to be protected from large logs are formulated. Results for the cross section are presented at next-to-leading order with next-to-leading-log (NLL) resummation, for invariant masses in the peak region and the tail region. Using our results we also predict the thrust distribution for massive quark jets at NLL order for large thrust. We demonstrate that soft radiation can be precisely controlled using data on massless jet production, and that in principle, a short-distance mass parameter can be measured using jets with precision better than QCD .
We derive a factorization theorem for the Higgs boson transverse momentum (p T ) and rapidity (Y ) distributions at hadron colliders, using the Soft Collinear Effective Theory (SCET), for m h p T Λ QCD where m h denotes the Higgs mass. In addition to the factorization of the various scales involved, the perturbative physics at the p T scale is further factorized into two collinear impact-parameter Beam Functions (iBFs) and an inverse Soft Function (iSF). These newly defined functions are of a universal nature for the study of differential distributions at hadron colliders. The additional factorization of the p T -scale physics simplifies the implementation of higher order radiative corrections in α s (p T ). We derive formulas for factorization in both momentum and impact parameter space and discuss the relationship between them. Large logarithms of the relevant scales in the problem are summed using the renormalization group equations of the effective theories. Power corrections to the factorization theorem in p T /m h and Λ QCD /p T can be systematically derived. We perform multiple consistency checks on our factorization theorem including a comparison with known fixed order QCD results. We compare the SCET factorization theorem with the Collins-Soper-Sterman approach to low-p T resummation. *
We prove a factorization theorem in QCD for the color suppressed decays B 0 →D 0 M 0 and B 0 →D* 0 M 0 where M is a light meson. Both the color-suppressed and W-exchange or annihilation amplitudes contribute at lowest order in ⌳ QCD /Q where Qϭ͕m b ,m c ,E ͖, so no power suppression of annihilation contributions is found. A new mechanism is given for generating nonperturbative strong phases in the factorization framework. Model-independent predictions that follow from our results include the equality of the B 0 →D 0 M 0 and B 0 →D* 0 M 0 rates and the equality of nonperturbative strong phases between isospin amplitudes, ␦ (DM) ϭ␦ (D*M ) . Relations between amplitudes and phases for M ϭ, are also derived. These results do not follow from large N c factorization with heavy quark symmetry.
We review the status of precision measurements of weak neutral current interactions, mediated arXiv:1302.6263v2 [hep-ex]
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