Dipole Subtraction Research Articles

NLO polarized chargino pair production in electron positron annihilation

We calculate the complete one-loop quantum corrections to the helicity eigenstate chargino pair production cross sections in polarized electron positron collisions, within the Minimal Supersymmetric Standard Model. We calculate the non-QED corrections using the helicity amplitudes formalism, and Dimensional Regularization to deal with ultraviolet divergences. We calculate QED corrections using the dipole subtraction formalism to extract soft and collinear divergences in Bremsstrahlung, canceling them with the infrared divergences from virtual QED corrections. We show numerical results for the Focus Point scenario in mSUGRA, where we find important quantum corrections for differential cross sections with definite chargino helicities.

Assault on the NLO wishlist:pp→tt̄bb̄

We present the results of a next-to-leading order calculation of QCD corrections to the production of an on-shell top-anti-top quark pair in association with two flavored b-jets. Besides studying the total cross section and its scale dependence, we give several differential distributions. Where comparable, our results agree with a previous analysis. While the process under scrutiny is of major relevance for Higgs boson searches at the LHC, we use it to demonstrate the ability of our system built around Helac-Phegas to tackle complete calculations at the frontier of current studies for the LHC. On the technical side, we show how the virtual corrections are efficiently computed with Helac-1Loop, based on the OPP method and the reduction code CutTools, using reweighting and Monte Carlo over color configurations and polarizations. As far as the real corrections are concerned, we use the recently published Helac-Dipoles package. In connection with improvements of the latter, we give the last missing integrated dipole formulae necessary for a complete implementation of phase space restriction dependence in the massive dipole subtraction formalism.

Automatic construction of dipole subtraction

An automatization of the dipole subtraction method is reported. We have completed three essential steps: the creation of the dipole terms, the calculation of the color linked squared Born matrix elements, and the evaluation of different helicity amplitudes. The routines have been tested for a number of complex processes. For example we have compared the output of our program for g g → t t ¯ g g with the results of Refs. [S. Dittmaier, P. Uwer and S. Weinzierl, Phys. Rev. Lett. 98, 262002 (2007), S. Dittmaier, P. Uwer and S. Weinzierl, arXiv:0810.0452 [hep-ph]] and found complete agreement.

Automating dipole subtraction

We report on automating the Catani-Seymour dipole subtraction which is a general procedure to treat infrared divergences in real emission processes at next-to-leading order in QCD. The automatization rests on three essential steps: the creation of the dipole terms, the calculation of the color linked squared Born matrix elements, and the evaluation of different helicity amplitudes. The routines have been tested for a number of complex processes, such as the real emission process gg --> t anti-t ggg.

MadDipole: automation of the dipole subtraction method in MadGraph/MadEvent

We present the implementation of the dipole subtraction formalism for the real radiation contributions to any next-to-leading order QCD process in the MadGraph/MadEvent framework. Both massless and massive dipoles are considered. Starting from a specific (n+1)-particle process the package provides a Fortran code for all possible dipoles to all Born processes that constitute the subtraction term to the (n+1)-particle process. The output files are given in the usual MadGraph StandAlone style using helicity amplitudes. Comment: 14 pages, 4 figures

NLO QCD corrections to tri-boson production

We present a calculation of the NLO QCD corrections for the production of three vector bosons at the LHC, namely ZZZ, W+W−Z, W+ZZ, and W+W−W+ production. The virtual corrections are computed using the recently proposed method of reduction at the integrand level (OPP reduction). Concerning the contributions coming from real emission we used the dipole subtraction to treat the soft and collinear divergences. We find that the QCD corrections for these electroweak processes are in the range between 70 and 100 percent. As such they have to be considered in experimental studies of triple vector boson production at the LHC.

Polarized QED splittings of massive fermions and dipole subtraction for non-collinear-safe observables

Building on earlier work, the dipole subtraction formalism for photonic corrections is extended to various photon–fermion splittings where the resulting collinear singularities lead to corrections that are enhanced by logarithms of small fermion masses. The difference to the earlier treatment of photon radiation is that now no cancellation of final-state singularities is assumed, i.e. we allow for non-collinear-safe final-state radiation. Moreover, we consider collinear fermion production from incoming photons, forward-scattering of incoming fermions, and collinearly produced fermion–antifermion pairs. For all cases we also provide the corresponding formulas for the phase-space slicing approach, and particle polarization is supported for all relevant situations. A comparison of numerical results obtained with the proposed subtraction procedure and the slicing method is explicitly performed for the sample process e − γ → e − μ − μ + .

Automating dipole subtraction for QCD NLO calculations

In this publication the construction of an automatic algorithm to subtract infrared divergences in real QCD corrections through the Catani-Seymour dipole subtraction method [arXiv:hep-ph/9605323] is reported. The resulting computer code has been implemented in the matrix element generator AMEGIC++ [arXiv:hep-ph/0109036]. This will allow for the automatic generation of dipole subtraction terms and their integrals over the one-parton emission phase space for any given process. If the virtual matrix element is provided as well, this then directly leads to an NLO QCD parton level event generator.

A subtraction scheme for computing QCD jet cross sections at NNLO: regularization of real-virtual emission

We present a generalization of the dipole subtraction scheme for computing jet cross sections in electron-positron annihilation at next-to-next-to-leading order accuracy in perturbative QCD. In this second part we deal with the regularization of the real-virtual contribution to the NNLO correction.

Matching parton showers to NLO computations

In this review a new method is presented for attaching parton shower algorithms to NLO partonic jet cross sections in electron-positron annihilation. Our method is based on the Catani-Seymour dipole subtraction method and also uses an adaptation of the matching scheme of Catani, Krauss, Kuhn, and Webber.

Four-fermion production at $\gamma\gamma$ colliders: 2. Radiative corrections in double-pole approximation

The O(alpha) electroweak radiative corrections to gamma gamma --> WW --> 4f within the electroweak Standard Model are calculated in double-pole approximation (DPA). Virtual corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for gamma gamma --> 4f + gamma. Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-space slicing. The radiative corrections are implemented in a Monte Carlo generator called COFFERgammagamma, which optionally includes anomalous triple and quartic gauge-boson couplings in addition and performs a convolution over realistic spectra of the photon beams. A detailed survey of numerical results comprises O(alpha) corrections to integrated cross sections as well as to angular, energy, and invariant-mass distributions. Particular attention is paid to the issue of collinear-safety in the observables.

A new method for real radiation at next-to-next-to-leading order

We propose a new method of computing real emission contributions to hard QCD processes. Our approach uses sector decomposition of the exclusive final-state phase space to enable extraction of all singularities of the real emission matrix elements before integration over any kinematic variable. The exact kinematics of the real emission process are preserved in all regions of phase space. Traditional approaches to extracting singularities from real emission matrix elements, such as phase space slicing and dipole subtraction, require both the determination of counterterms for double real emission amplitudes in singular kinematic limits and the integration of these contributions analytically to cancel the resulting singularities against virtual corrections. Our method addresses both of these issues. The implementation of constraints on the final-state phase space, including various jet algorithms, is simple using our approach. We illustrate our method using ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}$ jets at $O({\ensuremath{\alpha}}_{S}^{2})$ as an example.

NLO QCD corrections to [formula omitted] production in hadron collisions

The Higgs boson H of the Standard Model can be searched for in the channels p p ̄ /pp→t t ̄ H+X at the Tevatron and the LHC. The cross sections for these processes and the final-state distributions of the Higgs boson and top quarks are presented at next-to-leading order QCD. To calculate these QCD corrections, a special calculational technique for pentagon diagrams has been developed and the dipole subtraction formalism has been adopted for massive particles. The impact of the corrections on the total cross sections is characterized by K factors, the ratios of the cross sections in next-to-leading order over leading order QCD. At the central value μ 0=(2 m t + M H )/2 of the renormalization and factorization scales, the K factors are found to be slightly below unity for the Tevatron ( K∼0.8) and slightly above unity for the LHC ( K∼1.2). Including the corrections significantly stabilizes the theoretical predictions for the total cross sections and for the distributions in rapidity and transverse momentum of the Higgs boson and the top quarks.

Fully differential single-top-quark cross section in next-to-leading order QCD

We present a new next-to-leading order calculation for fully differential single-top-quark final states. The calculation is performed using phase space slicing and dipole subtraction methods. The results of the methods are found to be in agreement. The dipole subtraction method calculation retains the full spin dependence of the final state particles. We show a few numerical results to illustrate the utility and consistency of the resulting computer implementations.

The dipole formalism for next-to-leading order QCD calculations with massive partons

The dipole subtraction method for calculating next-to-leading order corrections in QCD was originally only formulated for massless partons. In this paper we extend its definition to include massive partons, namely, quarks, squarks and gluinos. We pay particular attention to the quasi-collinear region, which gives rise to terms that are enhanced by logarithms of the parton masses, M. By ensuring that our subtraction cross section matches the exact real cross section in all quasi-collinear regions we achieve uniform convergence both for hard scales Q∼ M and Q⪢ M. Moreover, taking the masses to zero, we exactly reproduce the previously-calculated massless results. We give all the analytical formulae necessary to construct a numerical program to evaluate the next-to-leading order QCD corrections to arbitrary observables in an arbitrary process.

Comparison of phase space slicing and dipole subtraction methods for $\gamma^* \rightarrow Q\bar{Q}$

We compare the phase space slicing and dipole subtraction methods in the computation of the inclusive and differential next-to-leading order cross sections for heavy quark production in the simple process \(\gamma^* \rightarrow Q\bar{Q}\). For the phase space slicing method we study the effects of improvement terms that remove restrictions on the slicing parameter \(s_{\mathrm{min}}\). For the dipole method our comparison is a first check on some of its counterterms involving massive quarks, derived recently. In our comparison we address issues such as numerical accuracy and efficiency.

Comments on the statistical analysis of excess variance in the COBE differential microwave radiometer maps

view Abstract Citations (116) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Comments on the Statistical Analysis of Excess Variance in the COBE Differential Microwave Radiometer Maps Wright, E. L. ; Smoot, G. F. ; Kogut, A. ; Hinshaw, G. ; Tenorio, L. ; Lineweaver, C. ; Bennett, C. L. ; Lubin, P. M. Abstract Cosmic anisotropy produces an excess variance σ_sky_^2^ in the {DELTA}T maps produced by the Differential Microwave Radiometer (DMR) on CO8E that is over and above the instrument noise. After smoothing to an effective resolution of 10^deg^, this excess, σ_sky_(10^deg^), provides an estimate for the amplitude of the primordial density perturbation power spectrum with a cosmic uncertainty of only 12%. We employ detailed Monte Carlo techniques to express the amplitude derived from this statistic in terms of the universal rms quadrupole amplitude, <Q_RMS_^2^>^0.5^. The effects of monopole and dipole subtraction and the non-Gaussian shape of the DMR beam cause the derived <Q_RMS_^2^>^0.5^ to be 5%-10% larger than would be derived using simplified analytic approximations. We also investigate the properties of two other map statistics: the actual quadrupole and the Boughn-Cottingham statistic. Both the σ_sky_(10^deg^) statistic and the Boughn-Cottingham statistic are consistent with the <Q_RMS_^2^>^0.5^ = 17 +/- 5 microK reported by Smoot et al. (1992) and Wright et al. (1992). Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173537 Bibcode: 1994ApJ...420....1W Keywords: Microwave Radiometers; Monte Carlo Method; Signal To Noise Ratios; Sky Surveys (Astronomy); Variance (Statistics); Anisotropy; Cosmic Background Explorer Satellite; Cosmology; Data Smoothing; Power Spectra; Quadrupoles; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: OBSERVATIONS full text sources ADS |