10,699 research outputs found
Initial state radiation effects in inclusive production at B factories
Based on Monte Carlo techniques, we analyze the initial state radiation (ISR)
effects in prompt \jpsi inclusive production at B factories. ISR enhances
cross section \sigma(e^-e^+\to\jpsi+gg+X) by about , which is almost
the same size as the QCD and relativistic correction. Moreover, ISR slightly
changes \sigma(e^-e^+\to\jpsi+c\bar{c}+X). The \jpsi momentum spectrum in
e^-e^+\to\jpsi+gg+X and in e^-e^+\to\jpsi+c\bar{c}+X is softer after the
photon showering from the initial beam radiation. After combining the
QCD,relativistic, and ISR corrections,a more precise theoretical result is
obtained. The new result provides a more stringent constraint of the
color-octet contribution to \sigma(e^-e^+\to\jpsi+X_{\rm{non-}c\bar{c}}).Comment: journal version;16 pages, 9 figures, 4 table
Colored Particle Production in New Physics at NLO QCD and Its Matching to Parton Showers
In this talk, I show the automated Monte Carlo simulations at next-to-leading
order in QCD as well as its matching to parton showers are already feasible
within the framework of \MG5aMC. I briefly overview the recent activities and
take the colored particle production at the LHC as examples. The tools and the
models are ready for using by both phenomenologists and experimentalists.Comment: 12 pages, 3 figures, 2 tables, contribution to proceedings of XXIII
Cracow EPIPHANY Conference, 9-12 January 2017, IFJ PAN, Cracow, Polan
Boosting perturbative QCD stability in quarkonium production
The aim of this paper is to introduce a general way to stabilize the
perturbative QCD computations of heavy quarkonium production in the boosted or
high-momentum transferring region with tree-level generators only. Such an
approach is possible by properly taking into account the power-enhanced
perturbative contributions in a soft and collinear safe manner without
requiring any complete higher-order computations. The complicated NLO results
for inclusive quarkonium hadroproduction can be well reproduced within our
approach based on a tree-level generator {\sc\small HELAC-Onia}. We have
applied it to estimate the last missing leading-twist contribution from the
spin-triplet color-singlet S-wave production at ,
which is a NNLO term in the expansion for the quarkonium
spectrum. We conclude that the missing NNLO contribution will not change the
order of the magnitude of the short-distance coefficient. Such an approach is
also quite appealing as it foresees broad applications in quarkonium-associated
production processes, which are mostly absent of complete higher-order
computations and fragmentation functions.Comment: 40 pages, 26 figures, 3 tables; v2: journal version, fix a few typos
fixed, add two figures, reorganize the figure
HELAC-Onia: an automatic matrix element generator for heavy quarkonium physics
By the virtues of the Dyson-Schwinger equations, we upgrade the published
code \mtt{HELAC} to be capable to calculate the heavy quarkonium helicity
amplitudes in the framework of NRQCD factorization, which we dub
\mtt{HELAC-Onia}. We rewrote the original \mtt{HELAC} to make the new program
be able to calculate helicity amplitudes of multi P-wave quarkonium states
production at hadron colliders and electron-positron colliders by including new
P-wave off-shell currents. Therefore, besides the high efficiencies in
computation of multi-leg processes within the Standard Model, \mtt{HELAC-Onia}
is also sufficiently numerical stable in dealing with P-wave quarkonia (e.g.
) and P-wave color-octet intermediate states. To the best
of our knowledge, it is a first general-purpose automatic quarkonium matrix
elements generator based on recursion relations on the market.Comment: Published version. 24 pages,1 figure, 7 tables, HELAC-Onia is
available from http://helac-phegas.web.cern.ch/helac-phega
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