827 research outputs found
Resummed jet rates for heavy quark production in electron-positron annihilation
Expressions for Sudakov form factors for heavy quarks are presented. They are
used to construct resummed jet rates in electron-positron annihilation.
Predictions are given for production of bottom quarks at LEP and top quarks at
the Linear Collider.Comment: Talk given by German Rodrigo at EPS2003 - Aachen, Germany, July 2003;
3 pages, 2 figure
From B Modes to Quantum Gravity and Unification of Forces
It is commonly anticipated that gravity is subject to the standard principles
of quantum mechanics. Yet some (including Einstein) have questioned that
presumption, whose empirical basis is weak. Indeed, recently Freeman Dyson has
emphasized that no conventional experiment is capable of detecting individual
gravitons. However, as we describe, if inflation occurred, the Universe, by
acting as an ideal graviton amplifier, affords such access. It produces a
classical signal, in the form of macroscopic gravitational waves, in response
to spontaneous (not induced) emission of gravitons. Thus recent BICEP2
observations of polarization in the cosmic microwave background will, if
confirmed, provide empirical evidence for the quantization of gravity. Their
details also support quantitative ideas concerning the unification of strong,
electromagnetic, and weak forces, and of all these with gravity.Comment: 4 pages, no figures. v2: minor typos corrected, reference added. v3:
very minor typo corrected. Winning entry in Gravity Research Foundation essay
competitio
Using Cosmology to Establish the Quantization of Gravity
While many aspects of general relativity have been tested, and general
principles of quantum dynamics demand its quantization, there is no direct
evidence for that. It has been argued that development of detectors sensitive
to individual gravitons is unlikely, and perhaps impossible. We argue here,
however, that measurement of polarization of the Cosmic Microwave Background
due to a long wavelength stochastic background of gravitational waves from
Inflation in the Early Universe would firmly establish the quantization of
gravity.Comment: 4 pages, no figures, revised in response to referee's reports.
Accepted for publication in PR
W+n-jet predictions at NLO matched with a parton shower
The MC@NLO method as implemented in the Sherpa MC generator is presented
using the production of W-bosons in conjunction with up to three jets as an
example. Corresponding results computed at next-to leading order in QCD and
including parton shower corrections are compared to recent experimental data
from the Large Hadron Collider.Comment: 4 pages, 2 figures. To appear in the proceedings of DIS 201
Next-to-leading order matrix elements and truncated showers
An algorithm is presented that combines the ME+PS approach to merge sequences
of tree-level matrix elements into inclusive event samples with the POWHEG
method, which combines exact next-to-leading order matrix elements with parton
showers. The quality of the approach and its implementation in Sherpa are
exemplified by results for e+e- annihilation into hadrons at LEP, for Drell-Yan
lepton-pair production at the Tevatron and for Higgs-boson and W+W- production
at LHC energies.Comment: 5 pages, 8 figures; To appear in the proceedings of Physics at the
LHC 2010, DESY, Hamburg, 7-12 June 201
Bottom-quark mass effects in associated production with and bosons
In this study, predictions obtained in the four and in the five flavour
schemes are compared for two important processes involving heavy flavours at
the LHC: the production of a or a Higgs boson in association with
quarks. In particular we obtain predictions with \Sherpa's \MCatNLO
implementation for the four--flavour scheme, treating the 's as massive, and
with multijet merging at leading and next-to leading order for the
five--flavour scheme. While differences between the two schemes, at the
inclusive level, are well understood from resummation of possibly large logs
into the -PDFs, differences in shape present a major problem for
experimental measurements. We make use of data for production at
the TeV LHC to exhibit strengths and weaknesses of the different approaches
and we use these results to validate predictions for -associated Higgs-boson
production at the 13 TeV Run II.Comment: Proceedings of XXV International Workshop on Deep-Inelastic
Scattering and Related Subjects, 3-7 April 2017, University of Birmingham,
UK. 10 pages, 6 figure
Resummed jet rates with heavy quarks in electron-positron collisions
Expressions for Sudakov form factors for heavy quarks are presented. They are
used to construct resummed jet rates in electron-positron annihilation.
Predictions are given for production of bottom quarks at LEP and top quarks at
the Linear Collider.Comment: Talk given by German Rodrigo at QCD@Work 2003 - Conversano, Italy,
June 2003; 6 pages, three figure
Using cosmology to establish the quantization of gravity
While many aspects of general relativity have been tested, and general principles of quantum dynamics demand its quantization, there is no direct evidence for that. It has been argued that development of detectors sensitive to individual gravitons is unlikely, and perhaps impossible. We argue here, however, that measurement of polarization of the Cosmic Microwave Background due to a long wavelength stochastic background of gravitational waves from Inflation in the Early Universe would firmly establish the quantization of gravity
Matching Parton Showers and Matrix Elements
We compare different procedures for combining fixed-order tree-level matrix
element generators with parton showers. We use the case of W-production at the
Tevatron and the LHC to compare different implementations of the so-called CKKW
scheme and one based on the so-called MLM scheme using different matrix element
generators and different parton cascades. We find that although similar results
are obtained in all cases, there are important differences.Comment: Proceedings of the "HERA and the LHC" workshop, CERN/DESY 2004/200
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