95 research outputs found
Simulated NNLO for high-pT observables in vector boson + jets production at the LHC
We present a study of higher order QCD corrections beyond NLO to processes
with an electroweak vector boson, W or Z, in association with jets. We focus on
the regions of high transverse momenta of commonly used differential
distributions. We employ the LoopSim method to merge NLO samples of different
multiplicity obtained from MCFM and from BLACKHAT+SHERPA in order to compute
the dominant part of the NNLO corrections for high-pT observables. We find that
these corrections are indeed substantial for a number of experimentally
relevant observables. For other observables, they lead to significant reduction
of scale uncertainties.Comment: 16 pages, 8 figures; v2: expanded discussion in a few places, added
and corrected references, version accepted by Eur. Phys. J.
Efficient negative-weight elimination in large high-multiplicity Monte Carlo event samples
We demonstrate that cell resampling can eliminate the bulk of negative event
weights in large event samples of high multiplicity processes without
discernible loss of accuracy in the predicted observables. The application of
cell resampling to much larger data sets and higher multiplicity processes such
as vector boson production with up to five jets has been made possible by
improvements in the method paired with drastic enhancement of the computational
efficiency of the implementation.Comment: 15 pages, 4 figure
High multiplicity processes at NLO with BlackHat and Sherpa
In this contribution we review recent progress with fixed-order QCD
predictions for the production of a vector boson in association with jets at
hadron colliders, using the programs BlackHat and SHERPA. We review general
features of next-to-leading-order (NLO) predictions for the production of a
massive vector boson in association with four jets. We also discuss how precise
descriptions of vector-boson production can be applied to the determination of
backgrounds to new physics signals. Here we focus on data-driven backgrounds to
a missing-energy-plus-jets search performed by CMS. Finally, we review recent
progress in developing theoretical tools for high-multiplicity loop-computation
within the BlackHat-library. In particular, we discuss methods for handling the
color degrees of freedom in multi-jet predictions at NLO.Comment: 12 pages, contribution to the proceedings of Loops and Legs 201
Unweighting multijet event generation using factorisation-aware neural networks
In this article we combine a recently proposed method for factorisation-aware matrix element surrogates with an unbiased unweighting algorithm. We show that employing a sophisticated neural network emulation of QCD multijet matrix elements based on dipole factorisation can lead to a drastic acceleration of unweighted event generation. We train neural networks for a selection of partonic channels contributing at the tree-level to Z+4,5 jets and t¯t + 3, 4 jets production at the LHC which necessitates a generalisation of the dipole emulation model to include initial state partons as well as massive final state quarks. We also present first steps towards the emulation of colour-sampled amplitudes. We incorporate these emulations as fast and accurate surrogates in a two-stage rejection sampling algorithm within the SHERPA Monte Carlo that yields unbiased unweighted events suitable for phenomenological analyses and post-processing in experimental workflows, e.g. as input to a time-consuming detector simulation. For the computational cost of unweighted events we achieve a reduction by factors between 16 and 350 for the considered channels
Direct Evidence for Tautomerization of the Uracil Moiety within the Pb2+/Uridine-5′-monophosphate Complex: A Combined Tandem Mass Spectrometry and IRMPD study
International audienc
On one master integral for three-loop on-shell HQET propagator diagrams with mass
An exact expression for the master integral I_2 arising in three-loop
on-shell HQET propagator diagrams with mass is derived and its analytical
expansion in the dimensional regularization parameter epsilon is given.Comment: 6 pages, 1 figure; v3: completely re-written, 2 new authors, many new
results, additional reference
Antenna subtraction with hadronic initial states
The antenna subtraction method for the computation of higher order
corrections to jet observables and exclusive cross sections at collider
experiments is extended to include hadronic initial states. In addition to the
already known antenna subtraction with both radiators in the final state
(final-final antennae), we introduce antenna subtractions with one or two
radiators in the initial state (initial-final or initial-initial antennae). For
those, we derive the phase space factorization and discuss the allowed phase
space mappings at NLO and NNLO. We present integrated forms for all antenna
functions relevant to NLO calculations, and describe the construction of the
full antenna subtraction terms at NLO on two examples. The extension of the
formalism to NNLO is outlined.Comment: 33 pages, 3 figure
Symmetric qubits from cavity states
Two-mode cavities can be prepared in quantum states which represent symmetric
multi-qubit states. However, the qubits are impossible to address individually
and as such cannot be independently measured or otherwise manipulated. We
propose two related schemes to coherently transfer the qubits which the cavity
state represents onto individual atoms, so that the qubits can then be
processed individually. In particular, our scheme can be combined with the
quantum cloning scheme of Simon and coworkers [C. Simon et al, PRL 84, 2993
(2000)] to allow the optimal clones which their scheme produces to be spatially
separated and individually utilized.Comment: 8 pages, 4 figures, minor typographical errors correcte
Interstitial fluid osmolarity modulates the action of differential tissue surface tension in progenitor cell segregation during gastrulation
The segregation of different cell types into distinct tissues is a fundamental process in metazoan development. Differences in cell adhesion and cortex tension are commonly thought to drive cell sorting by regulating tissue surface tension (TST). However, the role that differential TST plays in cell segregation within the developing embryo is as yet unclear. Here, we have analyzed the role of differential TST for germ layer progenitor cell segregation during zebrafish gastrulation. Contrary to previous observations that differential TST drives germ layer progenitor cell segregation in vitro, we show that germ layers display indistinguishable TST within the gastrulating embryo, arguing against differential TST driving germ layer progenitor cell segregation in vivo. We further show that the osmolarity of the interstitial fluid (IF) is an important factor that influences germ layer TST in vivo, and that lower osmolarity of the IF compared with standard cell culture medium can explain why germ layers display differential TST in culture but not in vivo. Finally, we show that directed migration of mesendoderm progenitors is required for germ layer progenitor cell segregation and germ layer formation
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