3,531 research outputs found
Perturbative QCD analysis of near-to-planar three jet events
We present the all-order resummed thrust minor distribution as a measure of
aplanarity in three-jet events.Comment: 5 pages, 2 figures, Talk presented by Andrea Banfi at QCD 00
Euroconference, Montpellier, July 200
On soft gluon effects in deep-inelastic structure functions
The behaviour of the quark coefficient functions in deep-inelastic scattering
is investigated for large values of the Bjorken variable x. By combining
results of soft-gluon resummation and fixed-order calculations, we determine
the coefficients of the four leading large-x logarithms, alpha_s^k
[{ln(1-x)}^{2k-l}/(1-x)]_+, l = 1, ...4, to all orders in the strong coupling
constant alpha_s. This result includes two more terms for the three-loop
coefficient functions than previously specified in the literature. The effect
of the fifth logarithmic contribution is approximately evaluated. The terms
derived here are required, but also seem to be sufficient, for a reliable
representation of the coefficient functions at large x.Comment: 10 pages, 3 figures, misprints in third line of eq. (15) correcte
Next-to-next-to-leading logarithmic threshold resummation for deep-inelastic scattering and the Drell-Yan process
The soft-gluon resummation exponents G^N in moment space are investigated for
the quark coefficient functions in deep-inelastic structure functions and the
quark-antiquark contribution to the Drell-Yan cross section dsigma/dM.
Employing results from two- and three-loop calculations we obtain the
next-to-next-to-leading logarithmic terms alpha_s (alpha_s ln N)^n of G^N to
all orders in the strong coupling constant alpha_s. These new contributions
facilitate a reliable assessment of the numerical effect and the stability of
the large-N expansion.Comment: 9 pages, LaTeX, 2 eps-figure
Measurement of triple differential photon plus jet cross section by D0
We report on a new measurement of triple differential cross section for the
process ppbar -> photon + jet + X in ppbar collisions at sqrt(s)=1.96 TeV by
the D0 Collaboration at Fermilab based on a dataset corresponding to an
integrated luminosity of 1.1 fb-1.Comment: 3 pages, 1 figure, To appear in the Proceedings of the 2007
Europhysics Conference on High Energy Physics, Manchester, UK. Accepted for
publication in Journal of Physics : Conference Serie
Phenomenological studies in QCD resummation
We study applications of QCD soft-gluon resummations to electroweak
annihilation cross sections. We focus on a formalism that allows to resum
logarithmic corrections arising near partonic threshold and at small transverse
momentum simultaneously.Comment: 7 pages, LaTeX, 3 figures as eps files. Talk presented by W.
Vogelsang at the "XVI International Conference on Particles and Nuclei
(PaNic02)", Osaka, Japan, September 200
Transverse-momentum resummation for heavy-quark hadroproduction
We consider the production of a pair of heavy quarks () in
hadronic collisions. When the transverse momentum of the heavy-quark pair
is much smaller than its invariant mass, the QCD perturbative expansion is
affected by large logarithmic terms that must be resummed to all-orders. This
behavior is well known from the simpler case of hadroproduction of colourless
high-mass systems, such as vector or Higgs boson(s). In the case of
production, the final-state heavy quarks carry colour charge and are
responsible for additional soft radiation (through direct emission and
interferences with initial-state radiation) that complicates the evaluation of
the logarithmically-enhanced terms in the small- region. We present the
all-order resummation structure of the logarithmic contributions, which
includes colour flow evolution factors due to soft wide-angle radiation.
Resummation is performed at the completely differential level with respect to
the kinematical variables of the produced heavy quarks. Soft-parton radiation
produces azimuthal correlations that are fully taken into account by the
resummation formalism. These azimuthal correlations are entangled with those
that are produced by initial-state collinear radiation. We present explicit
analytical results up to next-to-leading order and next-to-next-to-leading
logarithmic accuracy.Comment: Some comments expanded and references added. Version published on NP
Infrared-Finite Amplitudes for Massless Gauge Theories
We present a method to construct infrared-finite amplitudes for gauge
theories with massless fermions. Rather than computing -matrix elements
between usual states of the Fock space we construct order-by-order in
perturbation theory dressed states that incorporate all long-range
interactions. The -matrix elements between these states are shown to be free
from soft and collinear singularities. As an explicit example we consider the
process jets at next-to-leading order in the strong coupling. We
verify by explicit calculation that the amplitudes are infrared finite and
recover the well-known result for the total cross section hadrons.Comment: 46 page
Problems in resumming interjet energy flows with k_t clustering
We consider the energy flow into gaps between hard jets. It was previously
believed that the accuracy of resummed predictions for such observables can be
improved by employing the clustering procedure to define the gap energy
in terms of a sum of energies of soft jets (rather than individual hadrons) in
the gap. This significantly reduces the sensitivity to correlated soft
large-angle radiation (non-global leading logs), numerically calculable only in
the large limit. While this is the case, as we demonstrate here, the use
of clustering spoils the straightforward single-gluon Sudakov
exponentiation that multiplies the non-global resummation. We carry out an
calculation of the leading single-logarithmic terms
and identify the piece that is omitted by straightforward exponentiation. We
compare our results with the full result from the
program EVENT2 to confirm our conclusions. For jets and DIS
(1+1) jets one can numerically resum these additional contributions as we show,
but for dijet photoproduction and hadron-hadron processes further studies are
needed.Comment: 11 pages, 5 figure
Threshold resummation for high-transverse-momentum Higgs production at the LHC
We study the resummation of large logarithmic QCD corrections for the process
pp ->H+ X when the Higgs boson H is produced at high transverse momentum. The
corrections arise near the threshold for partonic reaction and originate from
soft gluon emission. We perform the all-order resummation at next-to-leading
logarithmic accuracy and match the resummed result with the next-to-leading
order perturbative predictions. The effect of resummation on the Higgs
transverse momentum distribution at the LHC is discussed.Comment: 19 pages, 3 figure
Near-to-planar 3-jet events in and beyond QCD perturbation theory
We present the results of QCD analysis of out-of-event-plane momentum
distribution in 3-jet e+e- annihilation events. We consider the all-order
resummed perturbative prediction and the leading power suppressed
non-perturbative corrections to the mean value and the distribution and
explain their non-trivial colour structure. The technique we develop aims at
improving the accuracy of the theoretical description of multi-jet ensembles,
in particular in hadron-hadron collisions.Comment: 11 pages, 2 figure
- …