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CTEQ parton distributions: NNLO, heavy quarks, and LHC data30m
The Les Houches NNLO wishlist/extending NLO predictions30m
The Les Houches NLO wishlist is a compilation of NLO calculations that are both needed by the experimental community and practical from the theoretical perspective. The wish list was started in 2005,
and added to in 2007 and 2009. In 2011, given the advances in automatic NLO calculations, we have closed the wish list, and instead have added a similar list for calculations needed at NNLO. I will discuss this NNLO list and why the calculations are crucial. I will also discuss multi-partonic NLO calculations such as those from Blackhat+Sherpa, show comparisons to data from ATLAS, and indicate kinematic regions/variables where the pure NLO prediction does not agree with the data, but the NLO prediction, augmented by additional NLO information from higher partonic multiplicities, does provide a better agreement. I will discuss the technical problems with such an approach and how they may be overcome.
(Michigan State University (US))
(University of Wisconsin-Madison)
The 4-dimensional helicity scheme beyond one-loop30m
(Brookhaven National Lab)
NNLO and N3LO DIS structure functions in ACOT scheme30m
We analyze the properties of the ACOT scheme for heavy quark production
and make use of the higher-order massless results at NNLO and N3LO
for the structure functions F2 and FL in neutral current
deep-inelastic scattering to estimate the higher order corrections.
For this purpose we decouple the heavy quark mass entering the phase space
from the one entering the dynamics of the short distance cross section.
We show numerically that the phase space mass is generally more important.
Therefore, the dominant heavy quark mass effects at higher orders
can be taken into account using the massless Wilson coefficients together with
an appropriate slow-rescaling prescription implementing the phase space constraints.
Combining the exact ACOT scheme at NLO with these expressions provides
a very good approximation to the missing full calculation in the ACOT scheme
at NNLO and N3LO.
I will discuss how the charge of a jet can be calculated and discuss some of its potentially interesting LHC applications, such as separating a W' from a Z'. I will give a field-theoretic description of the jet charge and establish its relationship with fragmentation functions. A comparison with Pythia will be presented.
QCD corrections in VBFNLO30m
(Department of Physics)
(University of Pittsburgh)
Alternative subtraction scheme using Nagy Soper Dipoles30m
We present a new subtraction scheme, where the subtraction terms have been derived from an improved shower algorithm including quantum interferences. We discuss recent progress in the development of the scheme and show several examples, where the scheme has been applied to processes at lepton and hadron colliders.
(IKTP, TU Dresden)
Forward Branching Phase Space Generators for NLO Monte Carlos30m
The Matrix Element Method at NLO30m
The Matrix element method (MEM) is a widely used tool in experimental analyses since it optimizes the maximal theoretical information (from the Matrix element) and combines this in a meaningful way with detector effects to obtain a likelihood that a particular experimental data set is described by an underlying theoretical model. Most famously the MEM was used in the discovery of the top quark and measure its mass at the Tevatron. However the major drawback of the method is its limitation to leading order matrix elements. This work will illustrate how NLO corrections can be calculated on an event by event basis, providing the ability to define the MEM at NLO.
Towards a more accurate prediction of W+b jet production with an automatized approach to one-loop calculations30m
We present results for the O(alpha_s) virtual corrections to qg ->W b bbar q' obtained with a new automatized approach to the evaluation of one-loop amplitudes in terms of Feynman diagrams. Together with the O(alpha_s) corrections to q qbar' -> W b bbar g, which can be obtained from our results by crossing symmetry, this represents the bulk of the next-to-leading order virtual QCD corrections to W b bbar + j and W b + j hadronic production, calculated in a fixed-flavor scheme with four light flavors. Furthermore, these corrections represent a well defined and independent subset of the 1-loop amplitudes needed for the NNLO calculation of W b bbar. Our approach was tested against several
existing results for NLO amplitudes including selected O(alpha_s) one-loop corrections to W + 3j hadronic production. We discuss the efficiency of our method both with respect to evaluation time and numerical stability.
One-loop scattering amplitudes from Integrand Reduction30m
Scattering Amplitudes with Open Loops30m
I will present a numerical one-loop algorithm, introduced in arXiv:1111.5206 [hep-ph], which is based on the recursive construction of loop-momentum polynomials called open loops. This novel approach permits to generate one-loop scattering amplitudes for multi-particle processes in a fully automatic and highly efficient way.
Renormalization Group Equations of the Gauge Couplings in the Standard Model at Three-Loop Order30m
We present the renormalization group equations of the gauge couplings
in the Standard Model at three-loop order in the minimal substraction scheme. We
take into account all contributions involving the Standard Model gauge
couplings, the top-, bottom- and tau-Yukawa couplings and the Higgs
self-coupling. We discuss our prescription of the gamma_5-matrix along with
other details of the calculation.
(Karlsruher Institut für Technologie)
I'll present new results for the NNLO corrections to the top-pair production cross-section at the Tevatron.
Alexander Dimitrov Mitov
Towards jet cross sections at NNLO for LHC30m
Aude Gehrmann-De Ridder
A subtraction scheme for NNLO hadronic cross sections30m
(Argonne National Laboratory)
BR( B -> Xs gamma) in 2HDMs to NNLO in QCD30m
The rare decay rate B -> Xs gamma provides the strongest bound on the mass of the charged Higgs boson in Two-Higgs Doublet Models (2HDM).
In this talk results for the three-loop corrections to the matching coefficients C7 and C8 are presented. They constitute building blocks for the NNLO prediction of BR( B -> Xs gamma) within 2HDM. We describe the calculation in detail and provide numerical results for the branching ratio.
W-boson pair production has been studied extensively during the LEP era
and has led to a precise determination of the W-mass, width and its
couplings. At the LHC, vector-boson pair production will be of similar
importance. Due to the high energies accessable at the LHC, combined
with high luminosity, the process is a perfect candidate to probe the
non-Abelian structure of the Standard Model at the highest energies.
Obviously accurate theoretical predictions are need to profit from
these experimental possibilities.
Results for the full one-loop electroweak corrections to W-boson pair
production at hadron colliders will be presented. These corrections
bocome large at high transverse momenta. In addiction, photon-induced
processes are discussed in detail which contribute with surprisingly
large cross sections at high invariant masses of the W-W system. In
total, modifications of rates and distributions by several tens of
percent are predicted.
(Karlsruher Institut fuer Technologie)
A Formalism for the Systematic Treatment of Rapidity Logarithms in Quantum Field Theory30m
We present a formalism for the systematic resummation of a class of logarithms relevant for jet observables in QCD. The logarithms are associated with the rapidities of factorized partons (which are either soft or collinear to specified directions) diverging under certain phase space constraints. The resummation is necessary for a consistent formulation of the perturbation series, and cannot be captured by standard renormalization group techniques. The formalism allows for a consistent merging of resummed corrections with the low energy matrix elements, with full control of the errors in the resummation scheme. Applications to the jet broadening observable and the Higgs transverse momentum cross-sections are outlined.
Multi-parton next-to-leading order calculations30m
Numerical evaluation of multi-loop integrals30m
In this talk the new version of the public program SecDec 2.0 for the
numerical evaluation of multi-loop integrals with several mass scales
The program is based on sector decomposition to extract dimensionally
regulated singularities. To deal with integrable singularities
due to mass thresholds, the integration contour is deformed into the
complex plane. As applications, numerical results for several two-loop
integrals are given, including non-planar two-loop four-point functions
entering heavy quark pair production at NNLO.
Sophia Carola Borowka
(MPI for Physics Munich)
Higher-order numerical integration using subtraction terms30m
I report on recent progress in NLO predictions for multi-jet observables at the LHC, and describe their role in aiding new physics searches.
W/Z+jets production at NLO matched with a parton shower30m
A promenade through MadGolem30m
With the outstanding performance of the first LHC running stage at 7 TeV,
searches for New Physics have started to constrain the
allowed parameter space of many of the proposed
predictions for the major New Physics discovery channels
has therefore become a most pressing request to
particle phenomenologists these days.
MadGolem is a new computational tool that automates
the calculation of next-to-leading order (NLO) QCD corrections
for heavy particle production in the MadEvent/Golem framework.
In this talk we will describe the structure of our code,
with particular emphasis on the generation of the renormalized one-loop amplitudes and
the automatized subtraction of infrared and on-shell divergences.
We will survey the many dedicated tests of all these aspects. Finally,
we will describe the user's interface and illustrate
how the tool performs in practice.
In this presentation we will review two recent applications of the fully automized MadGolem package:
1) Squark-Neutralino at NLO QCD: This process has the interesting feature to be a source of monojet signatures, consisting in the production of one hard jet associated with missing transverse energy, been one of the major LHC search channels motivated by many scenarios of physics Beyond the Standard Model. The NLO transverse momentum distributions we have compared with a MLM merged computation and find good agreement for the heavy particles produced.
2) Sgluon pair at NLO QCD: Sgluons are an example of scalar color octet states which arise in a variety of extensions of the Standard Model. They can be fundamental or composite degrees of freedom. In this study we examine the features and quantitative impact of the QCD quantum eﬀects on the production rates and sgluon distributions for the LHC. The NLO sgluon distributions we compare to the matched results for the combined process pp → sgluon pair + jets.
(University of Pittsburgh)
The VINCIA parton shower - present and future30m
NLL soft and Coulomb resummation for squark and gluino production at the LHC.30m
We present predictions of the total production cross sections of pairs of squarks and gluinos at the LHC, which incorporate a combined resummation of soft logarithms and Coulomb singularities, including bound-state contributions. These terms dominate the threshold region of the partonic cross section and are resummed directly in momentum space using an effective-theory framework based on SCET and pNRQCD. This differs from the more conventional approach where soft logarithms are exponentiated in Mellin-moment space. The combined resummation of soft and Coulomb corrections can lead to much bigger effects than soft resummation alone, with corrections of up to 120% to the fixed-order NLO result for gluino-gluino production at 7 TeV, and smaller (but still sizeable) effects for the other production processes. The theoretical uncertainty of the cross sections is typically reduced to about \pm 10%.
HERWIRI 1 and 2: Amplitude-Based Resummation in Precision Hadron Scattering30m
We present comparisons of HERWIRI1 to experimental data showing the effect of its IR-improved kernels in both HERWIG6.5 and MC@NLO environments. We also present the first complete implementation of HERWIRI2, which incorporates the order-alpha electroweak corrections and coherent exclusive exponentiation structure of the KK Monte Carlo in a HERWIG environment for Z production. We discuss its current status and results, and sketch future upgrades.
Summary and Outlook30m
(Univ. of California Los Angeles (US))