16 research outputs found
On power corrections to the event shape distributions in QCD
We study power corrections to the differential thrust, heavy jet mass and
C-parameter distributions in the two-jet kinematical region in e^+e^-
annihilation. We argue that away from the end-point region, e>>
\Lambda_{QCD}/Q, the leading 1/Q-power corrections are parameterized by a
single nonperturbative scale while for e \Lambda_{QCD}/Q one encounters a novel
regime in which power corrections of the form 1/(Qe)^n have to be taken into
account for arbitrary n. These nonperturbative corrections can be resummed and
factor out into a universal nonperturbative distribution, the shape function,
and the differential event shape distributions are given by convolution of the
shape function with perturbative cross-sections. Choosing a simple ansatz for
the shape function we demonstrate a good agreement of the obtained QCD
predictions for the distributions and their lowest moments with the existing
data over a wide energy interval.Comment: 18 pages, LaTeX style, 4 figure
The Qt distribution of the Breit current hemisphere in DIS as a probe of small-x broadening effects
We study the distribution 1/sigma dsigma/dQt, where Qt is the modulus of the
transverse momentum vector, obtained by summing over all hadrons, in the
current hemisphere of the DIS Breit frame. We resum the large logarithms in the
small Qt region, to next-to--leading logarithmic accuracy, including the
non-global logarithms involved. We point out that this observable is simply
related to the Drell-Yan vector boson and predicted Higgs Qt spectra at hadron
colliders. Comparing our predictions to existing HERA data thus ought to be a
valuable source of information on the role or absence of small-x (BFKL)
effects, neglected in conventional resummations of such quantities.Comment: 16 pages, 3 figures, uses JHEP3.cl
Nonperturbative contributions to a resummed leptonic angular distribution in inclusive boson production
We summarize a new analysis of the distribution of charged
leptons produced in decays of and bosons in the
Collins-Soper-Sterman (CSS) formalism for transverse momentum resummation. By
comparing the distribution measured at the Tevatron with the
resummed CSS cross section with approximate Wilson
coefficients, we constrain the magnitude of the nonperturbative Gaussian
smearing factor and analyze its uncertainty caused by variations in scale
parameters. We find excellent agreement between the data and
our theoretical prediction, provided by the \textsc{ResBos} resummation
program. The nonperturbative factor that we obtained can be used to update
resummed QCD predictions for precision measurements in inclusive and
production and for comparisons to various models of nonperturbative dynamics.Comment: 8 pages, 3 figures. Presented at conference: "The QCD Evolution
Workshop", May 14-17 2012, Thomas Jefferson National Accelerator Facility,
Newport News, V
Instanton Contribution to the Quark Form Factor
The nonperturbative effects in the quark form factor are considered in the
Wilson loop formalism. The properties of the Wilson loops with cusp
singularities are studied taking into account the perturbative and
nonperturbative contributions, where the latter are considered within the
framework of the instanton liquid model. For the integration path corresponding
to this form factor -- the angle with infinite sides -- the explicit expression
for the vacuum expectation value of the Wilson operator is found to leading
order. The calculations are performed in the weak-field limit for the instanton
vacuum contribution and compared with the one- and two-loop order results for
the perturbative part. It is shown that the instantons produce the powerlike
corrections to the perturbative result, which are comparable in magnitude with
the perturbative part at the scale of order of the inverse average instanton
size. It is demonstrated that the instanton contributions to the quark form
factor are exponentiated to high orders in the small instanton density
parameter.Comment: Version coincident with the journal publication. LaTeX, 15 pages, 1
figur
Joint resummation in electroweak boson production
We present a phenomenological application of the joint resummation formalism
to electroweak annihilation processes at measured boson momentum Q_T. This
formalism simultaneously resums at next-to-leading logarithmic accuracy large
threshold and recoil corrections to partonic scattering. We invert the impact
parameter transform using a previously described analytic continuation
procedure. This leads to a well-defined, resummed perturbative cross section
for all nonzero Q_T, which can be compared to resummation carried out directly
in Q_T space. From the structure of the resummed expressions, we also determine
the form of nonperturbative corrections to the cross section and implement
these into our analysis. We obtain a good description of the transverse
momentum distribution of Z bosons produced at the Tevatron collider.Comment: 27 pages, LaTeX, 8 figures as eps files. Some additions to earlier
version, this version as published in Phys. Rev. D66 (2002) 01401
Instanton Corrections to Quark Form Factor at Large Momentum Transfer
Within the Wilson integral formalism, we discuss the structure of
nonperturbative corrections to the quark form factor at large momentum transfer
analyzing the infrared renormalon and instanton effects. We show that the
nonperturbative effects determine the initial value for the perturbative
evolution of the quark form factor and attribute their general structure to the
renormalon ambiguities of the perturbative series. It is demonstrated that the
instanton contributions result in the finite renormalization of the
next-to-leading perturbative result and numerically are characterized by a
small factor reflecting the diluteness of the QCD vacuum within the instanton
liquid model.Comment: Version coincident with the journal publication, 9 pages; REVTe