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High Precision for Hard Processes at the LHC
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ETH Zurich
ETH Zurich
Description
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Day 1
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10:30
Coffee
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5
Can we find a computationally efficient loop algorithm?Even disregarding the intrinsic necessity of some new algorithm for numerical evaluation of one-loop diagrams, and even in case it has no intrinsic necessity at all, a probable decision about its goodness is possible inductively by studying its success. Success here means fruitfulness in consequences, in particular in verifiable consequences, i.e., consequences demonstrable without the new algorithm, whose proofs with the help of the new algorithm, however, are considerably simpler and easier to discover, and make it possible to contract into one proof many different proofs.Speaker: Giampiero Passarino (Torino)
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6
Precise predictions for the Higgs-boson decay H -> WW/ZZ -> 4 fermionsThe decay of the Standard Model Higgs boson into four fermions via a virtual W-boson or Z-boson pair is one of the most important decay modes in the Higgs-boson search at the LHC. We present a calculation of the first order radiative corrections to these processes, including higher order improvements. The intermediate W- and Z-boson resonances are consistently described using the complex mass scheme, which is explained in the talk. Numerical results for partial decay widths and angular and invariant-mass distributions are shown.Speaker: Ansgar Denner (PSI Zurich)
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12:15
Lunch
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8
Automated QCD calculations at NLOI will discuss various technical aspects related to automated QCD calculations at NLO: - the recursive calculation of amplitudes, - the organization of the colour structures, - the automated generation of subtraction terms, - the numerical tensor reduction of loop integrals.Speaker: Stefan Weinzierl (Mainz)
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15:15
Coffee
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11
Exclusive Drell-Yan production at NN LOI describe a parton-level Monte Carlo calculation of Drell-Yan production at next-to-next-to-leading order. The calculation is performed with a subtraction scheme in which the subtraction term is the squared matrix element itself.Speaker: William Kilgore (Brookhaven)
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16:50
Coffee
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13
Computing one-loop amplitudes at the integrand levelWe show how to extract the coefficients of the 4-, 3-, 2- and 1-point one-loop scalar integrals from the full one-loop amplitude of arbitrary scattering processes. In a similar fashion, also the rational terms can be derived. Basically no information on the analytical structure of the amplitude is required, making our method appealing for an efficient numerical implementation.Speaker: Roberto Pittau (Torino)
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14
Higgs Production via Gluon Fusion: QCD corrections to Squark LoopsThe loop-induced processes gg -> h,H,A provide the dominant Higgs boson production mechanisms at the Tevatron and LHC in a large range of the minimal supersymmetric extension of the Standard Model. For squark masses below ~400 GeV squark loop contributions become important in addition to the top and bottom quark loops. The two-loop QCD corrections to the squark contributions of these processes are determined including the full squark and Higgs mass dependences. They turn out to be of O(10-100%) and thus important for the Tevatron and LHC experiments. Squark mass effects of the K factors can be of O(20-30%).Speaker: Michael Spira (PSI)
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Day 2
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16
Prospects for measurements of hard scattering processes at the LHCAfter a very brief report on the status of the LHC preparations (machine and detectors) I will try to summarize the current understanding of how well specific hard scattering processes can be measured at the LHC, and what the relevance of these measurements is. Examples are the Drell-Yan process, top production, W/Z + jet as well as inclusive jet production.Speaker: Guenther Dissertori (ETH Zurich)
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The two-loop anomalous dimension matrix for soft gluon exchangeResummation of soft-gluon exchange for QCD hard scattering requires an anomalous dimension matrix in color space. We compute this matrix directly for arbitrary massless processes for the first time at two loops, and show that it is proportional to the one-loop matrix. This result reproduces the 1/eps pole terms in previous explicit two-loop computations, and predicts such terms for arbitrary processes. The proportionality of the one- and two-loop matrices also makes it possible to resum in closed form the next-to-next-to-leading logarithms for arbitrary processes.Speaker: Lance Dixon (SLAC)
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10:30
Coffee
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12:15
Lunch
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22
Techniques for one-loop tensor integrals in many-particle processesIn the calculation of NLO corrections to multi-leg processes serious numerical problems arise in the commonly used Passarino-Veltman reduction of tensor to scalar integrals in exceptional phase-space configurations. In this talk two alternative methods are discussed solving this problem. One of the methods relies on a seminumerical approach, in which a specific tensor coefficient is evaluated numerically, replacing the standard scalar integral in the list of basis integrals. The other method makes use of expansions in terms of small Gram and (if needed) other kinematical determinants. Both procedures have been successfully applied to the NLO electroweak corrections to e+e- --> 4fermions.Speaker: Stefan Dittmaier (MPI, Munich)
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15:15
Coffee
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The GOLEM project: status and applicationsIn this talk I review the status of our GOLEM project. The acronym stands for "General One-Loop Evaluator of Matrix-elements". This tool is designed to allow for an efficient and numerically stable evaluation of multi-particle one-loop amplitudes which are needed for the precise description of numerous processes relevant for the upcoming LHC. First applications are presented.Speaker: Thomas Binoth (Edinburgh)
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16:50
Coffee
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28
Soft-gluon effects in WW production at hadron collidersSpeaker: Massimiliano Grazzini (INFN, Firenze)
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29
Madgraph beyond the Standard ModelMadgraph and Madevent are a well established tool to evaluate tree-level amplitudes and create unweighted events for processes with a large number of external particles at the LHC. For the Madgraph collaboration I review the status, some physics complications and recent calculations of Madgraph/Madevent for physics beyond the Standard Model.Speaker: Tilman Plehn (Edinburgh)
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16
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Day 3
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10:30
Coffee
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33
Twistor Inspired Higgs PhenomenologyWe discuss how the twistor inspired methods can be used to derive compact expressions for multi-parton amplitudes involving Higgs bosons (in the limit that the top quark mass is heavy producing an effective Higgs-gluon interaction).Speaker: Nigel Glover (Durham)
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12:15
Lunch
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36
All-multiplicity amplitudes in QCDI will discuss the construction of amplitudes at one-loop in QCD using the unitarity bootstrap approach. I will detail the techniques needed to build the rational contributions to these amplitudes as well as highlighting not only their application to fixed-multiplicity amplitudes but also to all-multiplicity amplitudes.Speaker: Darren Forde (Saclay)
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15:15
Coffee
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Techniques and Results for Supergravity CalculationsThe recent progress for calculating gauge theory amplitudes may also be applied to gravity calculations. We find surprising similarities between the perturbative expansions of maximally supersymmetric Yang-Mills and gravity theories. We discuss possible implications of these results for the UV behaviour of supergravity in D=4.Speaker: David Dunbar (Swansea)
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16:50
Coffee
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