160 research outputs found
Precision top pair production at hadron colliders
We demonstrate the impact of recent NNLO calculations on precision top quark
phenomenology.Comment: Based on talks given at the 11th DESY Workshop "Loops and Legs in
Quantum Field Theory 2012", the 7th International Workshop on the CKM
Unitarity Triangle "CKM 2012" and the 5th International Workshop on Top Quark
Physics "Top 2012
Determination of the top quark mass from leptonic observables
We present a procedure for the determination of the mass of the top quark at
the LHC based on leptonic observables in dilepton events. Our
approach utilises the shapes of kinematic distributions through their few
lowest Mellin moments; it is notable for its minimal sensitivity to the
modelling of long-distance effects, for not requiring the reconstruction of top
quarks, and for having a competitive precision, with theory errors on the
extracted top mass of the order of 0.8 GeV. A novel aspect of our work is the
study of theoretical biases that might influence in a dramatic way the
determination of the top mass, and which are potentially relevant to all
template-based methods. We propose a comprehensive strategy that helps minimise
the impact of such biases, and leads to a reliable top mass extraction at
hadron colliders.Comment: 29 pages, 3 figure
Final state interactions in single- and multi-particle inclusive cross sections for hadronic collisions
We study the role of low momentum transfer (soft) interactions between
high-transverse momentum heavy particles and beam remnants (spectators) in
hadronic collisions. Such final-state interactions are power suppressed for
single-particle inclusive cross sections whenever that particle is accompanied
by a recoiling high-p_T partner whose momentum is not fixed. An example is the
single-top inclusive cross section in top pair production. Final-state soft
interactions in multi-particle inclusive cross sections, including transverse
momentum distributions, however, produce leading power corrections in the
absence of hard recoiling radiation. Nonperturbative corrections due to
scattering from spectators are generically suppressed by powers of
\Lambda/p'_T, where \Lambda is a hadronic scale, and p'_T is the largest
transverse momentum of radiation recoiling against the particles whose momenta
are observed.Comment: 18 pages, 6 figure
Top++: a program for the calculation of the top-pair cross-section at hadron colliders
We present the program Top++ for the numerical evaluation of the total
inclusive cross-section for producing top quark pairs at hadron colliders. The
program calculates the cross-section in a) fixed order approach with exact
next-to-next-to leading order (NNLO) accuracy and b) by including soft-gluon
resummation for the hadronic cross-section in Mellin space with full
next-to-next-to-leading logarithmic (NNLL) accuracy. The program offers the
user significant flexibility through the large number (29) of available
options. Top++ is written in C++. It has a very simple to use interface that is
intuitive and directly reflects the physics. The running of the program
requires no programing experience from the user.Comment: v2.0: Major update: includes full NNLO result; functionality updates.
Program webpage: http://www.alexandermitov.com/softwar
NNLO corrections to top pair production at hadron colliders: the quark-gluon reaction
We compute the next-to-next-to-leading order QCD correction to the total
inclusive top pair production cross-section in the reaction qg \to t\bar t + X.
We find moderate O(1%) correction to central values at both Tevatron and LHC.
The scale variation of the cross-section remains unchanged at the Tevatron and
is significantly reduced at the LHC. We find that recently introduced
approximation based on the high-energy limit of the top pair cross-section
significantly deviates from the exact result. The results derived in the
present work are included in version 1.4 of the program Top++. Work towards
computing the reaction gg\to t\bar t+X is ongoing.Comment: 17+1 pages, 6 figure
Diagrammatic Exponentiation for Products of Wilson Lines
We provide a recursive diagrammatic prescription for the exponentiation of
gauge theory amplitudes involving products of Wilson lines and loops. This
construction generalizes the concept of webs, originally developed for eikonal
form factors and cross sections with two eikonal lines, to general soft
functions in QCD and related gauge theories. Our coordinate space arguments
apply to arbitrary paths for the lines.Comment: 16 pages, 4 figures; minor corrections, version to appear in Phys.
Rev.
Bump-hunting in LHC ttbar events
We demonstrate that a purposefully normalised NNLO top pair invariant mass
differential spectrum can have very small theoretical uncertainty and, in
particular, a small sensitivity to the top quark mass. Such observable can thus
be a very effective bump-hunting tool for resonances decaying to top pair
events during LHC Run II and beyond. To illustrate how the approach works, we
concentrate on one specific example of current interest, namely, the possible
750 GeV di-gamma excess resonance Phi. Considering only theoretical
uncertainties, we demonstrate that it is possible to distinguish pp -> Phi ->
tt signals studied in the recent literature [Hespel, Maltoni and Vryonidou,
arXiv:1606.04149] from the pure SM background with very high significance.
Alternatively, in case of non-observation, a strong upper limit on the decay
rate Phi -> tt can be placed.Comment: 8 pages, 6 figures, analytic fits attached, plot on top-mass
sensitivity for the invariant mass distribution added, appendix on top-mass
sensitivity of differential distributions added, minor additional changes and
comments, matches published versio
Resolving the Tevatron Top Quark Forward-Backward Asymmetry Puzzle: Fully Differential Next-to-Next-to-Leading-Order Calculation
We determine the dominant missing Standard Model (SM) contribution to the top
quark pair forward-backward asymmetry at the Tevatron. Contrary to past
expectations, we find a large, around 27%, shift relative to the well-known
value of the inclusive asymmetry in next-to-leading order (NLO) QCD. Combining
all known Standard Model corrections, we find that AFB^{SM} = 0.095 +- 0.007.
This value is in agreement with the latest D0 measurement [V. M. Abazov et al.
(D0 Collaboration), Phys. Rev. D 90, 072011 (2014)] AFB^{D0} = 0.106+- 0.03 and
about 1.5 sigma below that of CDF [T. Aaltonen et al. (CDF Collaboration),
Phys. Rev. D 87, 092002 (2013)] AFB^{CDF} =0.164 +- 0.047. Our result is
derived from a fully differential calculation of the next-to-next-to leading
order (NNLO) QCD corrections to inclusive top pair production at hadron
colliders and includes - without any approximation - all partonic channels
contributing to this process. This is the first complete fully differential
calculation in NNLO QCD of a two-to-two scattering process with all coloured
partons.Comment: 6 pages, 4 figures. Published journal version: title extended and few
clarifications adde
Percent level precision physics at the Tevatron: first genuine NNLO QCD corrections to q qbar -> t tbar + X
We compute the Next-to-Next-to-Leading Order (NNLO) QCD corrections to the
partonic reaction that dominates top-pair production at the Tevatron. This is
the first ever NNLO calculation of an observable with more than two colored
partons, and/or massive fermions, at hadron colliders. Augmenting our fixed
order calculation with soft-gluon resummation through Next-to-Next-to-Leading
Logarithmic (NNLL) accuracy, we observe that the predicted total inclusive
cross-section exhibits a very small perturbative uncertainty, estimated at
+-2.7%. We expect that once all sub-dominant partonic reactions are accounted
for, and work in this direction is ongoing, the perturbative theoretical
uncertainty for this observable could drop below +-2%. Our calculation
demonstrates the power of our computational approach and proves it can be
successfully applied to all processes at hadron colliders for which
high-precision analyses are needed.Comment: 4 pages, 4 figure
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