72 research outputs found
Hadroproduction of t anti-t pair with two isolated photons with PowHel
We simulate the hadroproduction of a t anti-t pair in association with two
isolated hard photons at 13 TeV LHC using the PowHel package. We use the
generated events, stored according to the Les-Houches event format, to make
predictions for differential distributions formally at the next-to-leading
order (NLO) accuracy. We present predictions at the hadron level employing the
cone-type isolation of the photons used by experiments. We also compare the
kinematic distributions to the same distributions obtained in the t anti-t H
final state when the Higgs-boson decays into a photon pair, to which the
process discussed here is an irreducible background.Comment: 18 pages, 11 figures, minor changes, version submitted for
publicatio
Hadroproduction of t anti-t pair in association with an isolated photon at NLO accuracy matched with parton shower
We simulate the hadroproduction of a t anti-t pair in association with a hard
photon at LHC using the PowHel package. These events are almost fully inclusive
with respect to the photon, allowing for any physically relevant isolation of
the photon. We use the generated events, stored according to the Les-Houches
event format, to make predictions for differential distributions formally at
the next-to-leading order (NLO) accuracy and we compare these to existing
predictions accurate at NLO using the smooth isolation prescription of
Frixione. We also make predictions for distributions after full parton shower
and hadronization using the standard experimental cone-isolation of the photon.Comment: 21 pages, 17 figures, version accepted for publication in JHE
Energy-energy correlation in electron-positron annihilation at NNLL+NNLO accuracy
We present the computation of energy-energy correlation in
collisions in the back-to-back region at next-to-next-to-leading logarithmic
accuracy matched with the next-to-next-to-leading order perturbative
prediction. We study the effect of the fixed higher order corrections in a
comparison of our results to LEP and SLC data. The next-to-next-to-leading
order correction has a sizable impact on the extracted value of
, hence its inclusion is mandatory for a precise
measurement of the strong coupling using energy-energy correlation.Comment: 24 pages, 7 figures and 1 table, published versio
Precise determination of from a global fit of energy-energy correlation to NNLO+NNLL predictions
We present a comparison of the computation of energy-energy correlation in
collisions in the back-to-back region at next-to-next-to-leading
logarithmic accuracy matched with the next-to-next-to-leading order
perturbative prediction to LEP, PEP, PETRA, SLC and TRISTAN data. With these
predictions we perform an extraction of the strong coupling constant taking
into account non-perturbative effects modelled with Monte Carlo event
generators. The final result at NNLO+NNLL precision is
.Comment: 35 pages, 10 figures, 2 table
Three-jet production in electron-positron collisions using the CoLoRFulNNLO method
We introduce a subtraction method for jet cross sections at
next-to-next-to-leading order (NNLO) accuracy in the strong coupling and use it
to compute event shapes in three-jet production in electron-positron
collisions. We validate our method on two event shapes, thrust and C-parameter,
which are already known in the literature at NNLO accuracy and compute for the
first time oblateness and the energy-energy correlation at the same accuracy.Comment: 5 pages, 6 figure
Determination of beyond NNLO using event shape averages
We consider a method for determining the QCD strong coupling constant using
fits of perturbative predictions for event shape averages to data collected at
the LEP, PETRA, PEP and TRISTAN colliders. To obtain highest accuracy
predictions we use a combination of perturbative
calculations and estimations of the perturbative
coefficients from data. We account for non-perturbative effects using modern
Monte Carlo event generators and analytic hadronization models. The obtained
results show that the total precision of the determination cannot
be improved significantly with the higher order perturbative QCD corrections
alone, but primarily requires a deeper understanding of the non-perturbative
effects.Comment: 29 pages, 4 figures, 4 tables, journal versio
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