HP2.3rd - The 3rd International Workshop on High Precision for Hard Processes at the LHC

14 Sept 2010, 09:00 → 17 Sept 2010, 14:30 Europe/Rome

GGI - Florence

The LHC physics programme has successfully started. It is expected to give answers to fundamental questions in high-energy physics, such as those on the origin of Electro Weak (EW) symmetry breaking, the existence of supersymmetry, and the nature of dark matter.

Since the LHC is a hadron collider, all the interesting high-pT new reactions are driven by QCD hard scattering. To claim for new-physics signals, a good control over known Standard Model (SM) processes is thus necessary. The series of Workshops "High Precision for Hard Processes" (HP2) was started to discuss advances in the field of QCD and EW radiative corrections to both SM and BSM processes at hadron colliders. The first workshop of the series was held in Zürich in 2006, and it was followed by a second workshop in Buenos Aires in 2008. The third workshop, HP2.3rd, takes place in Florence from 14 to 17 september 2010.

We plan to discuss:

• Phenomenological results on hard-scattering cross sections at high perturbative orders
• Methods to compute multi-leg loop amplitudes at tree and loop levels
• Monte Carlo event generators, parton showers, merging with matrix elements, matching with NLO computations

Furthermore, we plan to have status reports on the first LHC physics results, on the latest Tevatron results and on new developments in Beyond the Standard Model physics.

Tuesday 14 September

09:00 Registration

09:25 Opening

Morning I

Convener: Massimiliano Grazzini (CERN)

1 Vector-Boson + Multi-Jet Production with BlackHat

Speaker: David Kosower (IPhT, CEA-Saclay)

Slides kosower.pdf kosower.pptx

2 NLO calculations with SAMURAI

TBA

Speaker: Francesco Tramontano (CERN)

Slides Tramontano.pdf

10:30 Coffee Break

Morning II

Convener: Giuseppe Marchesini (Dipartimento di Fisica "Macedonio Melloni")

3 Recent Progress in the Golem Project

The status of the Golem project will be reviewed and some recent results will be presented.

Speaker: Mr Gavin Cullen (University of Edinburgh)

Slides cullen.pdf

4 MadFKS: automation of the FKS subtraction method

In this talk, recent progress on the automation of the FKS subtraction method for NLO computations in QCD (within the MadGraph/MadEvent framework) will be discussed.

Speaker: Rikkert Frederix (University of Zurich)

Slides frederix.pdf

5 NLO QCD corrections to processes with electroweak bosons in the final state.

Speaker: Giuseppe Bozzi (Universita' degli Studi di Milano)

Slides bozzi.pdf

6 A Duality Relation between Loops and Trees at Two Loops and Beyond

I present an extension of the duality relation between one-loop integrals and phase-space integrals, developed by S. Catani et al., to higher-order loops. This duality relation is realized by a modification of the customary +i0 prescription of the Feynman propagators and compensates for the absence of multiple-cut contributions that appear in the Feynman tree theorem. I will report on a rederivation of the duality theorem at one-loop order in a form which is more suitable for its iterative extension to higher loop orders and show explicitly its application to the two- and three-loop scalar master integrals, for which the structure of the occurring cuts and results are discussed in detail.

Speaker: Isabella Bierenbaum (IFIC Valencia)

Slides Bierenbaum.pdf

13:00 Lunch

Afternoon I

Convener: Daniele Dominici (Universita di Firenze)

7 ATLAS and CMS: status and first results

Speaker: Andrea Di Simone (Rome University, Tor Vergata)

Slides disimone.odp disimone.pdf

8 Single-cut spinor integration and tadpole coefficients

I report on work done in collaboration with Ruth Britto. I will present the extension of the spinor integration formalism for one-loop amplitudes from the double-cut to the single-cut case. I will show how this technique can be applied for the computation of tadpole coefficients, which arise in a master integral expansion if massive particles circulate in the loop. When massive particles are present in the loop, single-cut spinor integration can be used for the full reconstruction of the cut-constructible part of the one-loop amplitudes. Indeed, double (and optionally triple and quadruple) cuts fix the coefficients of box, triangle and bubble integrals but cannot determine the tadpole coefficients, which are free of cuts in physical channels.

Speaker: Edoardo Mirabella (Institut de Physique Théorique, CEA)

Slides mirabella.pdf

9 Z-boson pair + 1-jet production at NLO QCD

A fully differential calculation of the next-to-leading order QCD corrections to the production of $Z$-boson pairs in association with a hard jet at the Tevatron and LHC is presented. This process is an important background for Higgs particle and new physics searches at hadron colliders. We find sizable corrections for cross sections and differential distributions, particularly at the LHC. Residual scale uncertainties are typically at the 10\% level and can be further reduced by applying a veto against the emission of a second hard jet. Our results confirm that NLO corrections do not simply rescale LO predictions. [Phys.Lett.B683:154-159,2010] + successful comparison with ZZj calculation of Dittmaier, Kallweit, Uwer [Les Houches Workshop SM and NLO Multileg WG procs., arXiv:1003.1241] + additional work: - additional differential distributions - comparison of dynamic with fixed scale definitions - comparison of Kt and SISCone jet algorithms investigate source of large residual scale uncertainty at LHC: - contributions of different initial state channels - independent variation of \mu_R and \mu_F [in progress]

Speaker: Nikolas Kauer (RHUL)

Slides kauer.pdf

16:15 Coffee Break

Afternoon II

Convener: Stefano Catani (Unknown)

10 Top Quark Physics with D-Dimensional Generalized Unitarity

I will talk about results of a NLO QCD calculation to top quark pair production and decay at the LHC. The inclusion of top quark decays in the prediction allows for a fully realistic description of the final state at NLO QCD. In particular, I will point out the importance of spin correlations and corrections to the decay. I will also focus on results for top quark pair production in association with a hard jet. This process constitutes the major background to Higgs production in vector boson fusion. I will present distributions that are important for this search, corrected through NLO QCD. Another interesting topic that I would like to talk about is the forward-backward asymmetry in top quark production. All results for the virtual corrections have been obtained with the method of D-dimensional generalized unitarity.

Speaker: Markus Schulze (Johns Hopkins University)

Slides talk_2noextras.infn2010.schulze.pdf

11 Electroweak corrections to W/Z + jet production at the LHC

In this talk we present the calculation of the next-to-leading-order electroweak corrections to W/Z-boson + jet production including leptonic W/Z-boson decays. The vector-boson resonances are treated consistently using the complex-mass scheme, and all off-shell effects are taken into account. The corresponding next-to-leading-order QCD corrections have also been recalculated. All the results are implemented in a flexible Monte Carlo code.

Speaker: Dr Alexander Mück (RWTH Aachen)

Slides mueck.pdf

18:00 Welcome Apero

Wednesday 15 September

Morning I

Convener: Ruth Britto (University of Amsterdam)

12 Massive Quarks in Vincia

We report on the extension of Vincia, a parton shower based on the dipole-antenna picture of QCD, to massive quarks.

Speaker: Mathias Ritzmann (ETH Zuerich)

Slides ritzmann.pdf

13 Bound-state effects on top-quarks kinematical distributions at hadron colliders

We present a theoretical framework to compute the fully differential cross sections for the top-quark productions and their subsequent decays at hadron colliders, incorporating the bound-state effects which are important in the t\bar{t} threshold region. We include the bound-state effects such that the cross sections are correct in the LO approximation both in the threshold and high-energy regions. Then, based on this framework we compute various kinematical distributions of top quarks as well as of their decay products at the LHC, by means of Monte-Carlo event-generation. These are compared with the corresponding predictions based on conventional perturbative QCD. In particular, we find a characteristic bound-state effect on the (bW^+)-(\bar{b}W^-) double-invariant-mass distribution, which is deformed to the lower invariant-mass side in a correlated manner.

Speaker: Dr Hiroshi Yokoya (CERN PH-TH)

Slides Yokoya_HP2.3rd.pdf

10:30 Coffee Break

Morning II

Convener: Dimitri Colferai (Unknown)

14 Wilson loops and amplitudes in N=4 SYM

In the planar N=4 supersymmetric Yang-Mills theory, we discuss two-loop amplitudes and Wilson loops at weak coupling, and compare them to the two-loop Wilson loops at strong coupling, which are available in the literature.

Speaker: Dr Claude Duhr (IPPP, Durham)

Slides HP2_Duhr.pdf

15 Gauge invariance in effective theories of QCD

In this talk I will discuss the properties of effective theories of QCD in singular gauges. Light-cone gauges in fact are useful in QCD and in the discussion of TMDPDF. I will discuss how these kind of gauges affect the matrix elements in SCET.

Speaker: Ignazio Scimemi (UCM)

Slides Scimemi.pdf

16 Simulating NNLO QCD corrections for processes with giant K factors

I will present a method, called LoopSim, designed to obtain approximate predictions of the NNLO QCD corrections to the processes with K factors >> 1. The method is based on unitarity and makes use of combining NLO results for different final state multiplicities. After validating the LoopSim procedure against known NNLO results for Drell-Yan lepton $p_t$ spectra I will show approximate NNLO results for the Z+jet observables. Finally, I will conclude with our predictions for dijets that can be compared to early LHC.

Speaker: Sebastian Sapeta (LPTHE)

Slides sapeta.pdf

17 Towards jet cross sections at NNLO for hadron colliders

We present the extension of the NNLO antenna subtraction formalism to jet observables at hadron colliders.

Speaker: Aude Gehrmann-De Ridder (ETH Zurich)

Slides hp2.pptx.pdf

13:00 Lunch

Afternoon I

Convener: David Kosower

18 NNLO jet cross sections by subtraction

We report on recent progress in integrating the approximate cross sections over the phase space of unresolved partons of the general NNLO subtraction scheme of Del Duca, Somogyi and Trocsanyi. In particular, we discuss the computation of a class of integrals that arise when integrating the so-called iterated singly-unresolved approximate cross section. The integrated cross section can be written as the product of an insertion operator in colour space times the Born cross section. We give an overview of the methods used to calculate the integrals and show selected results for the insertion operator for processes with two and three hard partons in the final state.

Speaker: Gabor Somogyi (DESY, Zeuthen)

Slides HP2.3-Somogyi.pdf

19 NNLO antenna subtraction with one hadronic initial state

In this talk we present the extension of the antenna subtraction method to include initial states containing one hadron at NNLO. We sketch the requirements for the different necessary subtraction terms, and we explain how the antenna functions are integrated over the appropriate phase space by reducing the integrals to a small set of master integrals. Where applicable, our results for the integrated antennae were cross-checked against the known NNLO coefficient functions for deep inelastic scattering processes.

Speaker: Gionata Luisoni (Universität Zürich)

Slides Luisoni_hp2_3.pdf

15:30 Coffee Break

Afternoon II

Convener: Giancarlo Ferrera (University of Florence)

20 Top-Antitop Production at Hadron Colliders

We review the status of the theoretical predictions for the top-anti top production in hadronic collisions, paying particular attention to the pair production at the LHC. We stress the need for a complete theoretical analysis that includes higher-order quantum corrections and we discuss recent theoretical calculations at the level of NNLO.

Speaker: Roberto Bonciani (LPSC, Grenoble)

Slides Bonciani.pdf

21 Higgs boson from gluon fusion

Latest theoretical predictions on gluon fusion initiated Higgs production and decay, for Tevatron and LHC, using the fully differential NNLO package FeHiPro.

Speaker: Dr Achilleas Lazopoulos (ETH Zurich)

Slides Lazopoulos.pdf

Thursday 16 September

Morning I

Convener: Aude Gehrmann-De Ridder (ETH Zurich)

22 Threshold resummation of 1/N-suppressed QCD quantities via mass factorization

We analyze the iterative structure of unfactorized partonic cross sections in the threshold (large-x) limit of massless perturbative QCD, and present all-order expressions for, at least, the leading- and next-to-leading logarithmic off-diagonal splitting functions P_gq and P_qg and the corresponding coefficient functions C_phi,q and C_2,g in Higgs- and gauge-boson exchange deep-inelastic scattering. The application of this approach to other coefficient functions is discussed.

Speaker: Prof. Andreas Vogt (University of Liverpool)

Slides av-hp210.pdf

23 Event shapes at hadron colliders

We present results for event-shape differential distributions at the Tevatron and at the LHC. Theoretical predictions are obtained by combining next-to-leading order (NLO) calculations with all-order resummation of logarithmic enhanced contributions at next-to-leading logarithmic (NLL) accuracy. We show that event shapes have significant scope in validating and tuning parton shower event generators, as well as for testing models for hadronisation and underlying event. We also discuss how event shapes can be exploited to distinguish between QCD and New Physics events.

Speaker: Andrea Banfi (ETH Zürich)

Slides banfi_HP23.pdf

10:30 Coffee Break

Morning II

Convener: Thomas Becher (University of Bern)

24 High-energy resummation for rapidity distributions

Speaker: Fabrizio Caola (Universita' di Milano and INFN)

Slides Caola.pdf

25 Mueller-Navelet Jets at LHC

Speaker: Dimitri Colferai (University of Firenze)

Slides colferai.pdf

26 Threshold resummation for Drell-Yan production: theory and phenomenology

We present a phenomenological study of vector boson production at hadron colliders based on NNLO fixed order calculation and on resummation of threshold logarithms. We compare different prescriptions for the calculation of resummed quantities, we study the ambiguity related to the resummation prescription, and we compare it to that coming from scales variation.

Speaker: Dr Marco Bonvini (INFN, Sezione di Genova)

Slides bonvini__hp23.pdf

12:30 Lunch

Afternoon I

Convener: Prof. Matthias Steinhauser (TTP Karlsruhe)

27 Results from the Tevatron

Speaker: Gregorio Bernardi (LPNHE Paris)

Slides bernardi.pdf

28 The ttbar total cross section at hadron colliders at NNLL

Using the SCET--formalism, we perform threshold resummation in x--space for top--quark pair production at hadron colliders. Our analysis extends to NNLL, including soft and coulomb gluon resummation. Results for the total cross section of t-tbar production at the LHC and the Tevatron are presented.

Speaker: Mr Sebastian Klein (RWTH Aachen)

Slides Se_Klein_Florenz.pdf

15:15 Coffee Break

Afternoon II

Convener: Andreas Vogt (University of Liverpool)

29 Transverse-Momentum Resummation in DY Production from Effective Field Theory

Using Soft-Collinear Effective Theory, a closed-form, all-order expression for the Drell-Yan cross section at small transverse momentum is derived, which is free of large perturbative logarithms. The anomalous dimensions and matching coefficients necessary for resummation at next-to-next-to-leading logarithmic order are given explicitly. The precise relation between the effective-theory result and the Collins-Soper-Sterman formula is discussed, and as a by-product the three-loop coefficient $A^{(3)}$ is obtained. Contrary to what is assumed in the literature, this coefficient differs from the three-loop cusp anomalous dimension. A nontrivial feature of the resummation is that the naive factorization of the cross section at small transverse momentum is broken by a collinear anomaly, which prevents a process-independent definition of $x_\perp$-dependent parton distribution functions. Studying the all-order form of this anomaly, a factorization theorem is derived for the product of two such functions, in which the dependence on the hard momentum transfer is separated out. The remainder factors into a product of two universal functions of longitudinal momentum variables and $x_\perp^2$. Their renormalization-group evolution is obtained and solved in closed form. The necessary anomalous dimensions are known to three-loop order. The matching of these functions at small $x_\perp$ onto standard parton distributions is calculated at one-loop order.

Speaker: Thomas Becher (University of Bern)

Slides becher_HP2.3.pdf

30 Transverse-momentum resummation for Drell-Yan production at NNLL accuracy

We consider the transverse-momentum (q_T) distribution of Drell--Yan lepton pairs produced in hadron collisions. At small values of q_T, we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-next-to-leading logarithmic accuracy. At intermediate and large values of q_T, we consistently combine resummation with the known next-to-leading order perturbative result. All perturbative terms up to order alpha_S^2 are included in our computation which, after integration over q_T, reproduces the known next-to-next-to-leading order result for the Drell--Yan total cross section. We show and discuss the reduction in the scale dependence of the results with respect to lower-order calculations, estimating the corresponding perturbative uncertainty. We present a preliminary comparison with Tevatron Run II data.

Speaker: Dr Giancarlo Ferrera (University of Florence)

Slides ferrera-hp23.pdf

20:00 Social Dinner

Friday 17 September

Morning I

Convener: Yukinari Sumino (Tohoku University)

31 Status of BSM

Speaker: Riccardo Barbieri (SNS Pisa)

Slides barbieri.pdf

32 Precise Higgs boson masses in the MSSM

Three-loop corrections to the light CP even Higgs boson mass are considered within the MSSM. The calculation is based on the proper approximations and their combination in various regions of the parameter space and the results are implemented in the computer code H3m. The three-loop effects to $M_h$ are typically of the order of a few hundred MeV and opposite in sign to the two-loop corrections.

Speaker: Prof. Matthias Steinhauser (KIT)

Slides steinhauser.pdf

10:45 Coffee Break

Morning II

Convener: Charalampos Anastasiou (Unknown)

33 Study of anomalous top quark FCNC interactions via single top events by using the charge asymmetry

The potential of the LHC for investigation of anomalous top quark interactions with gluon (tug, tcg) through the production of tW-channel of single top quark is studied. In the Standard Model, the single top quarks in the tW-channel mode are charge symmetric meaning that (pp ! t + W−) = (pp ! ¯t + W+). However, the presence of anomalous FCNC couplings leads to charge asymmetry. In this paper a method is proposed in which this charge asymmetry may be used to constrain anomalous FCNC couplings. The strength of resulting constraints is estimated for the LHC for the center of mass energies of 7 and 14 TeV.

Speaker: Mr Seyed Mohsen Etesami (Isfahan University of Technology and IPM - Institute for studies in theoretical Physics and Mathematics)

34 Precise prediction for Higgs production via gluon fusion in BSM scenarios

The search for the Higgs boson is a primary objective at the Tevatron and the LHC. The dominant production mechanism is gluon fusion, for which new physics effects can lead to significant deviations from the standard model predictions. We consider an extension of the Standard Model in which an arbitrary number of heavy quarks is introduced, and their coupling to the Higgs boson is arbitrary. We present the construction of an effective Lagrangian where the heavy particles are integrated out and the computation of the corresponding Wilson coefficient at three-loops. We analyze the deviations of the Higgs production cross-section from the Standard Model predictions.

Speaker: Elisabetta Furlan (ETH Zurich)

Slides Furlan_HP2.pdf

35 Higgs Pseudo-Observables

Starting from the gauge invariant definition of complex pole, the relation between physical observables measured at LHC and Tevatron and standard model Higgs pseudo-observables is analyzed. This leads to new definitions for the production cross section and the partial decay width, which do not violate first principles. Their computation requires the analytical continuation of Feynman loop integrals from real to complex internal masses and complex Mandelstam invariants. The numerical relevance of the result is shown for Higgs masses up to $600\,$GeV.

Speaker: Sandro Uccirati (Institut für Theoretische Teilchenphysik (TTP) - KIT)

Slides uccirati.pdf

36 Gluino Pair Production at the LHC

We present new results for the production of gluino pairs at the LHC. Binding effects can make an impact on the cross section around threshold depending on the decay width of a single gluino. Next-to-leading order corrections for the various subprocesses are presented in analytic form together with numerical results. Furthermore, assuming a stable constituent particle the formation of gluino-gluino boundstates is investigated as far as the separation of its signal from the background.

Speaker: Mr Matthias Kauth (KIT)

Slides kauth.pdf

13:15 Lunch