LoopFest XI

10 May 2012, 08:20 → 12 May 2012, 16:20 US/Eastern

157 Benedum Hall (U. Pittsburgh)

Ayres Freitas (University of Pittsburgh)

LoopFest XI will be held at the University of Pittsburgh, sponsored jointly by the Pittsburgh Particle physics, Astrophysics and Cosmolgy Center (Pitt-PACC) and by the Physics Department of Carnegie-Mellon University.

Note: Workshop registration will close on April 29

Thursday, 10 May

1 Welcome

Speaker: Sally Dawson (BNL)

Morning 1

Convener: Tao Han

2 Atlas EW/Higgs

Speaker: Marc-Andre Pleier

Slides Pleier-Loopfest2012.pdf

3 CTEQ parton distributions: NNLO, heavy quarks, and LHC data

Speaker: Pavel Nadolsky

Slides 2-Nadolsky.pdf

4 The Les Houches NNLO wishlist/extending NLO predictions

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.

Speaker: Prof. Joey Huston (Michigan State University (US))

Slides loopfest_huston.pdf

10:00 Coffee break

Eat Drink Be Merry

Morning 2

Convener: Prof. Frank Petriello (University of Wisconsin-Madison)

5 The 4-dimensional helicity scheme beyond one-loop

Speaker: William Kilgore (Brookhaven National Lab)

Slides LoopFestXI-Kilgore.pdf

6 NNLO and N3LO DIS structure functions in ACOT scheme

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.

Speaker: Dr Aleksander Kusina (Southern Methodist University)

Slides kusina_LoopFest2012.pdf

7 The Charge of a Jet

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.

Speaker: Wouter Waalewijn (UCSD)

Slides jetcharge_loopfest.pdf

8 QCD corrections in VBFNLO

Speaker: Dieter Zeppenfeld (Department of Physics)

Slides 7-zeppenfeld.pdf

12:20 Lunch

Afternoon 1

Convener: Prof. Adam Leibovich (University of Pittsburgh)

9 Alternative subtraction scheme using Nagy Soper Dipoles

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.

Speaker: Dr Tania Robens (IKTP, TU Dresden)

Slides trobens_loopfest.pdf

10 Forward Branching Phase Space Generators for NLO Monte Carlos

Speaker: Walter Giele

Slides giele_LoopFest2012.pdf

11 The Matrix Element Method at NLO

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.

Speaker: Ciaran Williams (Fermilab)

Slides Loopfest2012.pdf

12 Towards a more accurate prediction of W+b jet production with an automatized approach to one-loop calculations

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.

Speaker: Dr Laura Reina (CERN)

Slides loopfest12.pdf

16:00 Coffee Break

Afternoon 2

Convener: Dr Laura Reina (CERN)

13 One-loop scattering amplitudes from Integrand Reduction

Speaker: Edoardo Mirabella

Slides mirabella.pdf

14 Scattering Amplitudes with Open Loops

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.

Speaker: Stefano Pozzorini (Universitaet Zuerich (CH))

Slides openloops_loopfest12.pdf

15 Renormalization Group Equations of the Gauge Couplings in the Standard Model at Three-Loop Order

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.

Speaker: Dr Jens Salomon (Karlsruher Institut für Technologie)

Slides salomon.pdf

16 Assisting LHC Searches Using BlackHat & Sherpa

Speaker: David Kosower

Slides 4-Kosower.pdf 4-Kosower.pptx

19:00 Banquet

Friday, 11 May

Morning 1

Convener: Ambar Jain (Carnegie Mellon University)

17 ATLAS Top

Speaker: James Alfred Mueller (University of Pittsburgh (US))

Slides Mueller_LoopFest.pdf

18 ttbar+jet: QCD corrections in production and decay

Speaker: Markus Schulze (Argonne National Laboratory)

Slides 2-Schulze.pdf

19 NLO QCD corrections to pp/ppbar->WWbb

Speaker: Prof. Stefan Dittmaier (Albert-Ludwigs-Universitaet Freiburg (DE))

Slides wwbb_loopfest12.pdf

10:00 Coffee

Morning 2

Convener: Johann Kuehn

20 Top-pair production at NNLO QCD

I'll present new results for the NNLO corrections to the top-pair production cross-section at the Tevatron.

Speaker: Alexander Dimitrov Mitov (CERN)

Slides AlexanderMitov-Loopfest-2012.pdf

21 Towards jet cross sections at NNLO for LHC

Speaker: Aude Gehrmann-De Ridder (ETH Zurich)

Slides loopfest12.pdf

22 A subtraction scheme for NNLO hadronic cross sections

Speaker: Radja Boughezal (Argonne National Laboratory)

Slides 6-Boughezal.pdf

23 BR( B -> Xs gamma) in 2HDMs to NNLO in QCD

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.

Speaker: Thomas Hermann (TTP Karlsruhe)

Slides loopfest_2012.pdf

12:20 Lunch

Afternoon 1

Convener: Stefan Dittmaier (MPI fuer Physik)

24 Beyond the SM at the intensity frontier

Speaker: Michael Ramsey-Musolf (U. Wisconsin-Madison)

Slides Loopfest12_MRM.pdf

25 News from the Electroweak SM Fit and Constraints on SM Extensions within Gfitter

Speaker: Dorthe Kennedy (Deutsches Elektronen-Synchrotron (DE))

Slides Kennedy_Gfitter_Loopfest.pdf

26 W-boson pair production at the LHC

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.

Speaker: Johann Kuehn (Karlsruher Institut fuer Technologie)

Slides loopfest_2012_jk.pdf

27 A Formalism for the Systematic Treatment of Rapidity Logarithms in Quantum Field Theory

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.

Speaker: Mr Duff Neill (Carnegie Mellon University)

Slides Rap_Renorm_Group.pdf

16:00 Coffee

Afternoon 2

Convener: Radja Boughezal (Wuerzburg University)

28 Higgs + 1-jet at the LHC at NNLL order

Speaker: Iain Stewart (MIT)

Slides Higgs1Jet_Stewart_p2.pdf

29 Multi-parton next-to-leading order calculations

Speaker: Sebastian Becker

Slides LoopFest2012.pdf

30 Numerical evaluation of multi-loop integrals

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 is presented. 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.

Speaker: Sophia Carola Borowka (MPI for Physics Munich)

Slides sborowka.pdf

31 Higher-order numerical integration using subtraction terms

Speaker: Ayres Freitas (University of Pittsburgh)

Slides talk.pdf

Saturday, 12 May

Morning 1

Convener: Sally Dawson (BNL)

32 HELAC-NLO: recent developments and phenomenological results

Speaker: Dr Giuseppe Bevilacqua (RWTH Aachen)

Slides bevilacqua_loopfestXI.pdf

33 Automated one-loop calculations with GoSam

Speaker: Giovanni Ossola (New York City College of Technology (CUNY))

Slides 2-Ossola.pdf

34 Recent progress in aMC@NLO

Speakers: Rikkert Frederix, Rikkert Frederix (Universitaet Zuerich (CH))

Slides frederix.pdf

10:00 Coffee

Morning 2

Convener: Prof. Doreen Wackeroth (SUNY Buffalo)

35 Multi-jet physics at the LHC with Blackhat

I report on recent progress in NLO predictions for multi-jet observables at the LHC, and describe their role in aiding new physics searches.

Speaker: Kemal Ozeren (UCLA)

Slides ozeren.pdf

36 W/Z+jets production at NLO matched with a parton shower

Speaker: Stefan Hoeche

Slides stefan_pittsburgh_12-05.pdf

37 A promenade through MadGolem

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 beyond-the-Standard-Model scenarios. Providing accurate 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.

Speaker: Dr David Lopez-Val (Heidelberg University)

Slides lopezval.pdf

38 MadGolem: applications to New Physics

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.

Speaker: Dorival Goncalves Netto (Heidelberg University)

Slides dori_loopfest2012.pdf

12:20 Lunch

Afternoon 1

Convener: Ayres Freitas (University of Pittsburgh)

39 The VINCIA parton shower - present and future

Speaker: Mathias Ritzmann

Slides 1-Ritzmann 1-Ritzmann.key

40 NLL soft and Coulomb resummation for squark and gluino production at the LHC.

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%.

Speaker: Christopher Wever (University Utrecht)

Slides ChrisLoopfest2012.pdf

41 HERWIRI 1 and 2: Amplitude-Based Resummation in Precision Hadron Scattering

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.

Speaker: Scott Yost (The Citadel)

Slides yost-loopfest-2012-v1.pdf

42 Summary and Outlook

Speaker: Zvi Bern (Univ. of California Los Angeles (US))

Slides loopfest_12.pdf