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Thomas Gehrmann; Stefan Hoeche; Frank Krauss; Marek Schonherr; Frank Siegert
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We present a new approach to combine multiple NLO partonlevel calculations matched to parton showers into a single inclusive event sample. The method provides a description of hard multijet configurations at nextto leading order in the perturbative expansion of QCD, and it is supplemented with the allorders resummed modelling of jet fragmentation provided by the parton shower. The formal accuracy of this technique is discussed in detail, invoking the example of electronpositron...
Source: http://arxiv.org/abs/1207.5031v2
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by
Rikkert Frederix; Thomas Gehrmann; Nicolas Greiner
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Heading towards a full automation of nexttoleading order (NLO) QCD corrections, one important ingredient is the analytical integration over the oneparticle phase space of the unresolved particle that is necessary when adding the subtraction terms to the virtual corrections. We present the implementation of these integrated dipoles in the MadGraph framework. The result is a package that allows an automated calculation for the NLO real emission parts of an arbitrary process.
Source: http://arxiv.org/abs/1004.2905v2
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Thomas Gehrmann; Dominik Kara
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We compute the threeloop QCD corrections to the vertex function for the Yukawa coupling of a Higgs boson to a pair of bottom quarks in the limit of vanishing quark masses. This QCD form factor is a crucial ingredient to thirdorder QCD corrections for the production of Higgs bosons in bottom quark fusion, and for the fully differential decay rate of Higgs bosons to bottom quarks. The infrared pole structure of the form factors agrees with the prediction from infrared factorization in QCD.
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1407.8114
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Ansgar Denner; Stefan Dittmaier; Thomas Gehrmann; Christian Kurz
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We report on a recent calculation of the electroweak O(\alpha^3\alpha_s) corrections to 3jet production and related eventshape observables at e+e colliders. The calculation properly accounts for the experimental photon isolation criteria and for the corrections to the total hadronic cross section. Corrections to the normalised eventshape distributions, which are exemplarily discussed here for the thrust distribution at LEP and linearcollider energies, turn out to be at the fewpercent...
Source: http://arxiv.org/abs/1001.4467v1
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Thomas Gehrmann; Gionata Luisoni; Pier Francesco Monni
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In the context of the dispersive model for nonperturbative corrections, we extend the leading renormalon subtraction to NNLO for the thrust distribution in $e^+e^$ annihilation. Within this framework, using a NNLL+NNLO perturbative description and including bottom quark mass effects to NLO, we analyse data in the centreofmass energy range $\sqrt{s}=14206$ GeV in view of a simultaneous determination of the strong coupling constant and the nonperturbative parameter $\alpha_0$. The fits are...
Source: http://arxiv.org/abs/1210.6945v2
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Tancredi Carli; Thomas Gehrmann; Stefan Hoeche
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We present an extension of the multipurpose MonteCarlo event generator Sherpa for processes in deeply inelastic leptonnucleon scattering. Hadronic final states in this kinematical setting are characterised by the presence of multiple kinematical scales, which were up to now accounted for only by specific resummations in individual kinematical regions. An extension of a known method for merging truncated parton showers with higherorder treelevel matrix elements allows to obtain predictions...
Source: http://arxiv.org/abs/1006.5696v1
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Thomas Gehrmann; Thomas Luebbert; Li Lin Yang
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We present a perturbative calculation of the transverse parton distribution functions in all partonic channels up to nexttonexttoleading order based on a gauge invariant operator definition. We demonstrate for the first time that such a definition works beyond the first nontrivial order. We extract the coefficient functions relevant for a nexttonexttonexttoleading logarithmic $q_T$ resummation in a large class of processes at hadron colliders.
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1401.1222
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Thomas Gehrmann; Thomas Luebbert; Li Lin Yang
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We describe the perturbative calculation of the transverse parton distribution functions in all partonic channels up to nexttonexttoleading order based on a gauge invariant operator definition. We demonstrate the cancellation of lightcone divergences and show that universal processindependent transverse parton distribution functions can be obtained through a refactorization. Our results serve as the first explicit higherorder calculation of these functions starting from first principles,...
Topics: High Energy Physics  Theory, High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1403.6451
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Charalampos Anastasiou; Claude Duhr; Falko Dulat; Elisabetta Furlan; Thomas Gehrmann; Franz Herzog; Bernhard Mistlberger
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In this article, we compute the gluon fusion Higgs boson crosssection at N3LO through the second term in the threshold expansion. This calculation constitutes a major milestone towards the full N3LO cross section. Our result has the best formal accuracy in the threshold expansion currently available, and includes contributions from collinear regions besides subleading corrections from soft and hard regions, as well as certain logarithmically enhanced contributions for general kinematics. We...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1411.3584
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by
Tancredi Carli; Thomas Gehrmann; Stefan Hoeche
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We extend the multipurpose MonteCarlo event generator Sherpa to include processes in deeply inelastic leptonnucleon scattering. Hadronic final states in this kinematical setting are characterised by the presence of multiple kinematical scales, which were up to now accounted for only by specific resummations in individual kinematical regions. Using an extension of the recently introduced method for merging truncated parton showers with higherorder treelevel matrix elements, it is possible...
Source: http://arxiv.org/abs/0912.3715v1
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by
Thomas Gehrmann; Lorenzo Tancredi
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The selfcouplings of the electroweak gauge bosons are probed at hadron colliders through the production of a massive gauge boson and a photon. To extend the theoretical description of this type of final states towards nexttonexttoleading order (NNLO) in QCD, we derive the twoloop QCD corrections to the helicity amplitudes describing the production of a massive gauge boson in association with a real photon. Our results are obtained by applying projectors to the general partonlevel tensor...
Source: http://arxiv.org/abs/1112.1531v3
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In this talk, I review recent developments in perturbative QCD and their applications to collider physics.
Source: http://arxiv.org/abs/1007.2107v2
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by
Charalampos Anastasiou; Claude Duhr; Falko Dulat; Elisabetta Furlan; Thomas Gehrmann; Franz Herzog; Bernhard Mistlberger
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We present the crosssection for the threshold production of the Higgs boson at hadroncolliders at nexttonexttonexttoleading order (N3LO) in perturbative QCD. We present an analytic expression for the partonic crosssection at threshold and the impact of these corrections on the numerical estimates for the hadronic crosssection at the LHC. With this result we achieve a major milestone towards a complete evaluation of the crosssection at N3LO which will reduce the theoretical...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1403.4616
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Ansgar Denner; Stefan Dittmaier; Thomas Gehrmann; Christian Kurz
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We present a complete calculation of the electroweak O(alpha^3 alpha_s) corrections to threejet production and related eventshape observables at electronpositron colliders. The Zboson resonance is described within the complexmass scheme, rendering the calculation valid both in the resonance and offshell regions. Higherorder initialstate radiation is included in the leadinglogarithmic approximation. We properly account for the corrections to the total hadronic cross section and for the...
Source: http://arxiv.org/abs/1003.0986v1
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Thomas Gehrmann; Nicolas Greiner; Pedro Schwaller
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In this letter we discuss a certain class of Hidden Valley models where the dynamics in the hidden sector are close to a strongly coupled conformal fixed point. We show that these models can explain the excess in cosmic ray muon events with high muon multiplicities that has been reported from cosmic ray studies with the ALEPH and DELPHI detectors. We further point out that these models can also at least partially account for the excess in multimuon events that was found by the CDF experiment....
Source: http://arxiv.org/abs/0812.4240v1
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Charalampos Anastasiou; Claude Duhr; Falko Dulat; Elisabetta Furlan; Thomas Gehrmann; Franz Herzog; Achilleas Lazopoulos; Bernhard Mistlberger
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In view of the searches at the LHC for scalar particle resonances in addition to the 125 GeV Higgs boson, we present the cross section for a CPeven scalar produced via gluon fusion at N3LO in perturbative QCD assuming that it couples directly to gluons in an effective theory approach. We refine our prediction by taking into account the possibility that the scalar couples to the topquark and computing the corresponding contributions through NLO in perturbative QCD. We assess the theoretical...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Experiment
Source: http://arxiv.org/abs/1605.05761
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This article summarizes new theoretical developments, ideas and results that were presented at the 2014 Moriond "QCD and High Energy Interactions".
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1406.5379
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Aude GehrmannDe Ridder; Thomas Gehrmann; Mathias Ritzmann
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The antenna subtraction method handles real radiation contributions in higher order corrections to jet observables. The method is based on antenna functions, which encapsulate all unresolved radiation between a pair of hard radiator partons. To apply this method to compute hadron collider observables, initialinitial antenna functions with both radiators in the initial state are required in unintegrated and integrated forms. In view of extending the antenna subtraction method to...
Source: http://arxiv.org/abs/1207.5779v1
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Thomas Gehrmann; Guenter Grindhammer; Vivian O'Dell; Roman Walczak
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A summary of new experimental results and recent theoretical developments discussed in the "Hadronic Final States and QCD" working group is presented.
Source: http://arxiv.org/abs/0808.2616v2
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Thomas Gehrmann; Sam Guns; Dominik Kara
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The rare Higgs boson decay $H\to Z\gamma$ is forbidden at treelevel. In the Standard Model, it is loopmediated through a $W$ boson or a heavy quark. We analytically compute the QCD correction to the heavy quark loop, confirming earlier purely numerical results, that were obtained for onshell renormalization. The small quark mass expansion of the decay matrix element contains only singlelogarithmic contributions at each perturbative order, which is in contrast to the double logarithms...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1505.00561
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by
Charalampos Anastasiou; Claude Duhr; Falko Dulat; Elisabetta Furlan; Thomas Gehrmann; Franz Herzog; Achilleas Lazopoulos; Bernhard Mistlberger
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We present the most precise value for the Higgs boson crosssection in the gluonfusion production mode at the LHC. Our result is based on a perturbative expansion through N$^3$LO in QCD, in an effective theory where the topquark is assumed to be infinitely heavy, while all other Standard Model quarks are massless. We combine this result with QCD corrections to the crosssection where all finite quarkmass effects are included exactly through NLO. In addition, electroweak corrections and the...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1602.00695
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Thomas Gehrmann; Andreas von Manteuffel; Lorenzo Tancredi
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We compute the twoloop massless QCD corrections to the helicity amplitudes for the production of two massive vector bosons in quarkantiquark annihilation, allowing for an arbitrary virtuality of the vector bosons: $q \bar q' \to V_1V_2$. Combining with the leptonic decay currents, we obtain the full twoloop QCD description of the corresponding electroweak fourlepton production processes. The calculation is performed by projecting the twoloop diagrams onto an appropriate basis of Lorentz...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1503.04812
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Thomas Gehrmann; Thomas Lübbert; Li Lin Yang
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We present a calculation of the perturbative quarktoquark transverse parton distribution function at nexttonexttoleading order based on a gauge invariant operator definition. We demonstrate for the first time that such a definition works beyond the first nontrivial order. We extract from our calculation the coefficient functions relevant for a nexttonexttonexttoleading logarithmic $Q_T$ resummation in a large class of processes at hadron colliders.
Source: http://arxiv.org/abs/1209.0682v2
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by
Xuan Chen; Thomas Gehrmann; Nigel Glover; Matthieu Jaquier
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We present the computation of Higgs boson plus one jet production at NNLO at the LHC. The computation is carried out in the heavytopquark approximation and using the antenna subtraction formalism to handle the IR divergent structure of the individual contributions. All channels and all colours are included. We illustrate aspects of the subtraction formalism and present results for the total cross section as well as distributions in the kinematical variables using a realistic experimental...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1604.04085
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James Currie; Aude GehrmannDe Ridder; Thomas Gehrmann; Nigel Glover; Joao Pires; Steven Wells
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We report on the calculation of the nexttonexttoleading order (NNLO) QCD corrections to the production of two gluonic jets at hadron colliders. In previous work, we discussed gluonic dijet production in the gluongluon channel. Here, for the first time, we update our numerical results to include the leading colour contribution to the production of two gluonic jets via quarkantiquark scattering.
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1407.5558
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Aude GehrmannDe Ridder; Thomas Gehrmann; E. W. N. Glover; Joao Pires
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We report the calculation of nexttonexttoleading order (NNLO) QCD corrections in the purely gluonic channel to dijet production and related observables at hadron colliders. Our result represents the first NNLO calculation of a massless jet observable at hadron colliders, and opens the path towards precision QCD phenomenology with the LHC.
Source: http://arxiv.org/abs/1301.7310v1
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by
James Currie; Thomas Gehrmann; Jan Niehues
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The production of twojet final states in deep inelastic scattering is an important QCD precision observable. We compute it for the first time to nexttonexttoleading order (NNLO) in perturbative QCD. Our calculation is fully differential in the lepton and jet variables and allows one to impose cuts on the jets both in the laboratory and the Breit frame. We observe that the NNLO corrections are moderate in size, except at kinematical edges, and that their inclusion leads to a substantial...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1606.03991
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Hannes Jung; Albert De Roeck; Jochen Bartels; Olaf Behnke; Johannes Blumlein; Stanley Brodsky; Amanda CooperSarkar; Michal Deak; Robin Devenish; Markus Diehl; Thomas Gehrmann; Guenter Grindhammer; Gosta Gustafson; Valery Khoze; Albert Knutsson; Max Klein; Frank Krauss; Krzysztof Kutak; Eric Laenen; Leif Lonnblad; Leszek Motyka; Paul R. Newman; Fred Olness; Daniel Pitzl; Marta Ruspa; Agustin Sabio Vera; Gavin P. Salam; Thomas SchornerSadenius; Mark Strikman
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More than 100 people participated in a discussion session at the DIS08 workshop on the topic What HERA may provide. A summary of the discussion with a structured outlook and list of desirable measurements and theory calculations is given.
Source: http://arxiv.org/abs/0809.0549v2
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Ansgar Denner; Stefan Dittmaier; Thomas Gehrmann; Christian Kurz
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We compute the electroweak ${\cal O}(\alpha^3\alpha_s)$ corrections to threejet production and related eventshape observables at electronpositron colliders. We properly account for the experimental photon isolation criteria and for the corrections to the total hadronic cross section. Corrections to the threejet rate and to normalised eventshape distributions turn out to be at the fewpercent level.
Source: http://arxiv.org/abs/0906.0372v2
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by
Rikkert Frederix; Thomas Gehrmann; Nicolas Greiner
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We present the implementation of the dipole subtraction formalism for the real radiation contributions to any nexttoleading 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...
Source: http://arxiv.org/abs/0808.2128v1
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Thomas Gehrmann; Johannes M. Henn; Tobias Huber
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In this paper we study the Sudakov form factor in N=4 super YangMills theory to the threeloop order. The latter is expressed in terms of planar and nonplanar loop integrals. We show that it is possible to choose a representation in which each loop integral has uniform transcendentality. We verify analytically the expected exponentiation of the infrared divergences with the correct values of the threeloop cusp and collinear anomalous dimensions in dimensional regularisation. We find that the...
Source: http://arxiv.org/abs/1112.4524v1
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Thomas Gehrmann; Pier Francesco Monni
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The antenna subtraction method handles real radiation contributions in higher order corrections to jet observables. The method is based on antenna functions, which encapsulate all unresolved radiation between a pair of hard radiator partons. To apply this method to compute hadron collider observables, initialinitial antenna functions with both radiators in the initial state are required. In view of extending the antenna subtraction method to nexttonexttoleading order (NNLO) calculations at...
Source: http://arxiv.org/abs/1107.4037v1
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Thomas Gehrmann; Lorenzo Tancredi; Erich Weihs
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We compute the helicity amplitudes for the processes $gg\to Zg$ and $gg\to Z\gamma$ to two loops in massless QCD. The perturbative expansion of these processes starts only at the oneloop level, such that our results are a crucial ingredient to the NLO corrections to $Z\gamma$ and $Z+$jet production through gluon fusion.
Source: http://arxiv.org/abs/1302.2630v2
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Claude Duhr; Thomas Gehrmann; Matthieu Jaquier
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The factorisation of QCD matrix elements in the limit of two external partons becoming collinear is described by processindependent splitting amplitudes, which can be expanded systematically in perturbation theory. Working in conventional dimensional regularisation, we compute the twoloop splitting amplitudes for all simple collinear splitting processes, including subleading terms in the regularisation parameter. Our results are then applied to derive an analytical expression for the twoloop...
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1411.3587
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Werner Bernreuther; Long Chen; Oliver Dekkers; Thomas Gehrmann; Dennis Heisler
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We compute the order $\alpha_s^2$ QCD corrections to the $b$quark forwardbackward asymmetry in $e^+e^\to b{\bar b}$ collisions at the $Z$ boson resonance, taking the nonzero mass of the $b$ quark into account. We determine these corrections with respect to both the $b$quark axis and the thrust axis definition of the asymmetry. We compute also the distributions of these axes with respect to the electron beam. If one neglects the flavor singlet contributions to the $b$quark asymmetry, as...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Experiment
Source: http://arxiv.org/abs/1611.07942
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Pier Francesco Monni; Thomas Gehrmann; Gionata Luisoni
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The thrust distribution in electronpositron annihilation is a classical precision QCD observable. Using renormalization group (RG) evolution in Laplace space, we perform the resummation of logarithmically enhanced corrections in the dijet limit, $T\to 1$ to nexttonexttoleading logarithmic (NNLL) accuracy. We independently derive the twoloop soft function for the thrust distribution and extract an analytical expression for the NNLL resummation coefficient $g_3$. To combine the resummed...
Source: http://arxiv.org/abs/1105.4560v2
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Aude GehrmannDe Ridder; Thomas Gehrmann; E. W. N. Glover; Joao Pires
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We use the antenna subtraction method to isolate the double virtual infrared singularities present in gluonic scattering amplitudes at nexttonexttoleading order. In previous papers, we derived the subtraction terms that rendered (a) the double real radiation treelevel process finite in the single and double unresolved regions of phase space and (b) the mixed single real radiation oneloop process both finite and well behaved in the unresolved regions of phase space. Here, we show how to...
Source: http://arxiv.org/abs/1211.2710v1
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by
Taushif Ahmed; Thomas Gehrmann; Prakash Mathews; Narayan Rana; V. Ravindran
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The coupling of a pseudoscalar Higgs boson to gluons is mediated through a heavy quark loop. In the limit of large quark mass, it is described by an effective Lagrangian that only admits light degrees of freedom. In this effective theory, we compute the threeloop massless QCD corrections to the form factor that describes the coupling of a pseudoscalar Higgs boson to gluons. Due to the axial anomaly, the pseudoscalar operator for the gluonic field strength mixes with the divergence of the...
Topics: High Energy Physics  Experiment, High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1510.01715
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by
Thomas Gehrmann; Niklaus Haefliger; Pier Francesco Monni
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We study the application of the BrodskyLepageMackenzie (BLM) scale setting prescription to event shape distributions in electronpositron collisions. The renormalization scale is set dynamically according to the BLM method. We study NLO predictions and we discuss extensions of the prescription to NNLO.
Topic: High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1401.6809
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Thomas Gehrmann; Andreas von Manteuffel; Lorenzo Tancredi; Erich Weihs
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We compute the full set of twoloop Feynman integrals appearing in massless twoloop fourpoint functions with two offshell legs with the same invariant mass. These integrals allow to determine the twoloop corrections to the amplitudes for vector boson pair production at hadron colliders, $q \bar{q} \to V V$, and thus to compute this process to nexttonexttoleading order accuracy in QCD. The master integrals are derived using the method of differential equations, employing a canonical...
Topics: High Energy Physics  Theory, High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1404.4853
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Alejandro Daleo; Aude GehrmannDe Ridder; Thomas Gehrmann; Gionata Luisoni
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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 crosschecked against the known NNLO coefficient functions for deep inelastic...
Source: http://arxiv.org/abs/1001.2397v1