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7.0

Jun 30, 2018
06/18

Jun 30, 2018
by
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 cross-section 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

6
6.0

Jun 30, 2018
06/18

Jun 30, 2018
by
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 process-independent splitting amplitudes, which can be expanded systematically in perturbation theory. Working in conventional dimensional regularisation, we compute the two-loop 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 two-loop...

Topic: High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1411.3587

3
3.0

Jun 30, 2018
06/18

Jun 30, 2018
by
Thomas Gehrmann; Dominik Kara

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We compute the three-loop 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 third-order 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

3
3.0

Jun 30, 2018
06/18

Jun 30, 2018
by
James Currie; Aude Gehrmann-De Ridder; Thomas Gehrmann; Nigel Glover; Joao Pires; Steven Wells

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We report on the calculation of the next-to-next-to-leading order (NNLO) QCD corrections to the production of two gluonic jets at hadron colliders. In previous work, we discussed gluonic dijet production in the gluon-gluon 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 quark-antiquark scattering.

Topic: High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1407.5558

7
7.0

Jun 30, 2018
06/18

Jun 30, 2018
by
Thomas Gehrmann

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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

3
3.0

Jun 30, 2018
06/18

Jun 30, 2018
by
Thomas Gehrmann; Andreas von Manteuffel; Lorenzo Tancredi; Erich Weihs

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We compute the full set of two-loop Feynman integrals appearing in massless two-loop four-point functions with two off-shell legs with the same invariant mass. These integrals allow to determine the two-loop 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 next-to-next-to-leading 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

4
4.0

Jun 30, 2018
06/18

Jun 30, 2018
by
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 next-to-next-to-leading order based on a gauge invariant operator definition. We demonstrate the cancellation of light-cone divergences and show that universal process-independent transverse parton distribution functions can be obtained through a refactorization. Our results serve as the first explicit higher-order calculation of these functions starting from first principles,...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1403.6451

3
3.0

Jun 30, 2018
06/18

Jun 30, 2018
by
Charalampos Anastasiou; Claude Duhr; Falko Dulat; Elisabetta Furlan; Thomas Gehrmann; Franz Herzog; Bernhard Mistlberger

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We present the cross-section for the threshold production of the Higgs boson at hadron-colliders at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. We present an analytic expression for the partonic cross-section at threshold and the impact of these corrections on the numerical estimates for the hadronic cross-section at the LHC. With this result we achieve a major milestone towards a complete evaluation of the cross-section at N3LO which will reduce the theoretical...

Topic: High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1403.4616

4
4.0

Jun 30, 2018
06/18

Jun 30, 2018
by
Thomas Gehrmann; Niklaus Haefliger; Pier Francesco Monni

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We study the application of the Brodsky-Lepage-Mackenzie (BLM) scale setting prescription to event shape distributions in electron-positron 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

6
6.0

Jun 30, 2018
06/18

Jun 30, 2018
by
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 next-to-next-to-leading order based on a gauge invariant operator definition. We demonstrate for the first time that such a definition works beyond the first non-trivial order. We extract the coefficient functions relevant for a next-to-next-to-next-to-leading 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

5
5.0

Jun 29, 2018
06/18

Jun 29, 2018
by
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 forward-backward asymmetry in $e^+e^-\to b{\bar b}$ collisions at the $Z$ boson resonance, taking the non-zero 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

6
6.0

Jun 29, 2018
06/18

Jun 29, 2018
by
James Currie; Thomas Gehrmann; Jan Niehues

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The production of two-jet final states in deep inelastic scattering is an important QCD precision observable. We compute it for the first time to next-to-next-to-leading 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

3
3.0

Jun 29, 2018
06/18

Jun 29, 2018
by
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 CP-even 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 top-quark 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

5
5.0

Jun 29, 2018
06/18

Jun 29, 2018
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 heavy-top-quark 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

3
3.0

Jun 29, 2018
06/18

Jun 29, 2018
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 cross-section in the gluon-fusion 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 top-quark is assumed to be infinitely heavy, while all other Standard Model quarks are massless. We combine this result with QCD corrections to the cross-section where all finite quark-mass effects are included exactly through NLO. In addition, electroweak corrections and the...

Topic: High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1602.00695

4
4.0

Jun 28, 2018
06/18

Jun 28, 2018
by
Taushif Ahmed; Thomas Gehrmann; Prakash Mathews; Narayan Rana; V. Ravindran

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The coupling of a pseudo-scalar 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 three-loop massless QCD corrections to the form factor that describes the coupling of a pseudo-scalar Higgs boson to gluons. Due to the axial anomaly, the pseudo-scalar 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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13

Jun 27, 2018
06/18

Jun 27, 2018
by
Thomas Gehrmann; Sam Guns; Dominik Kara

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The rare Higgs boson decay $H\to Z\gamma$ is forbidden at tree-level. In the Standard Model, it is loop-mediated 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 on-shell renormalization. The small quark mass expansion of the decay matrix element contains only single-logarithmic 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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14

Jun 27, 2018
06/18

Jun 27, 2018
by
Thomas Gehrmann; Andreas von Manteuffel; Lorenzo Tancredi

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We compute the two-loop massless QCD corrections to the helicity amplitudes for the production of two massive vector bosons in quark-antiquark 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 two-loop QCD description of the corresponding electroweak four-lepton production processes. The calculation is performed by projecting the two-loop diagrams onto an appropriate basis of Lorentz...

Topic: High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1503.04812

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88

Sep 24, 2013
09/13

Sep 24, 2013
by
Thomas Gehrmann; Johannes M. Henn; Tobias Huber

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In this paper we study the Sudakov form factor in N=4 super Yang-Mills theory to the three-loop order. The latter is expressed in terms of planar and non-planar 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 three-loop cusp and collinear anomalous dimensions in dimensional regularisation. We find that the...

Source: http://arxiv.org/abs/1112.4524v1

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64

Sep 23, 2013
09/13

Sep 23, 2013
by
Thomas Gehrmann; Lorenzo Tancredi

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The self-couplings 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 next-to-next-to-leading order (NNLO) in QCD, we derive the two-loop 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 parton-level tensor...

Source: http://arxiv.org/abs/1112.1531v3

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49

Sep 23, 2013
09/13

Sep 23, 2013
by
Pier Francesco Monni; Thomas Gehrmann; Gionata Luisoni

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The thrust distribution in electron-positron 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 next-to-next-to-leading logarithmic (NNLL) accuracy. We independently derive the two-loop 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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140

Sep 23, 2013
09/13

Sep 23, 2013
by
Tancredi Carli; Thomas Gehrmann; Stefan Hoeche

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We present an extension of the multi-purpose Monte-Carlo event generator Sherpa for processes in deeply inelastic lepton-nucleon 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 higher-order tree-level matrix elements allows to obtain predictions...

Source: http://arxiv.org/abs/1006.5696v1

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82

Sep 22, 2013
09/13

Sep 22, 2013
by
Rikkert Frederix; Thomas Gehrmann; Nicolas Greiner

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Heading towards a full automation of next-to-leading order (NLO) QCD corrections, one important ingredient is the analytical integration over the one-particle 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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47

Sep 22, 2013
09/13

Sep 22, 2013
by
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 3-jet production and related event-shape 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 event-shape distributions, which are exemplarily discussed here for the thrust distribution at LEP and linear-collider energies, turn out to be at the few-per-cent...

Source: http://arxiv.org/abs/1001.4467v1

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52

Sep 22, 2013
09/13

Sep 22, 2013
by
Alejandro Daleo; Aude Gehrmann-De 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 cross-checked against the known NNLO coefficient functions for deep inelastic...

Source: http://arxiv.org/abs/1001.2397v1

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42

Sep 22, 2013
09/13

Sep 22, 2013
by
Ansgar Denner; Stefan Dittmaier; Thomas Gehrmann; Christian Kurz

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We compute the electroweak ${\cal O}(\alpha^3\alpha_s)$ corrections to three-jet production and related event-shape observables at electron-positron colliders. We properly account for the experimental photon isolation criteria and for the corrections to the total hadronic cross section. Corrections to the three-jet rate and to normalised event-shape distributions turn out to be at the few-per-cent level.

Source: http://arxiv.org/abs/0906.0372v2

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57

Sep 22, 2013
09/13

Sep 22, 2013
by
Thomas Gehrmann; Gionata Luisoni; Pier Francesco Monni

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In the context of the dispersive model for non-perturbative 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 centre-of-mass energy range $\sqrt{s}=14-206$ GeV in view of a simultaneous determination of the strong coupling constant and the non-perturbative parameter $\alpha_0$. The fits are...

Source: http://arxiv.org/abs/1210.6945v2

54
54

Sep 22, 2013
09/13

Sep 22, 2013
by
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 multi-muon events that was found by the CDF experiment....

Source: http://arxiv.org/abs/0812.4240v1

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56

Sep 22, 2013
09/13

Sep 22, 2013
by
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 one-loop 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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68

Sep 21, 2013
09/13

Sep 21, 2013
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 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...

Source: http://arxiv.org/abs/0808.2128v1

52
52

Sep 21, 2013
09/13

Sep 21, 2013
by
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

44
44

Sep 21, 2013
09/13

Sep 21, 2013
by
Aude Gehrmann-De Ridder; Thomas Gehrmann; E. W. N. Glover; Joao Pires

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We report the calculation of next-to-next-to-leading 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

45
45

Sep 20, 2013
09/13

Sep 20, 2013
by
Aude Gehrmann-De 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, initial-initial 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

52
52

Sep 20, 2013
09/13

Sep 20, 2013
by
Thomas Gehrmann; Stefan Hoeche; Frank Krauss; Marek Schonherr; Frank Siegert

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We present a new approach to combine multiple NLO parton-level calculations matched to parton showers into a single inclusive event sample. The method provides a description of hard multi-jet configurations at next-to leading order in the perturbative expansion of QCD, and it is supplemented with the all-orders resummed modelling of jet fragmentation provided by the parton shower. The formal accuracy of this technique is discussed in detail, invoking the example of electron-positron...

Source: http://arxiv.org/abs/1207.5031v2

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46

Sep 18, 2013
09/13

Sep 18, 2013
by
Hannes Jung; Albert De Roeck; Jochen Bartels; Olaf Behnke; Johannes Blumlein; Stanley Brodsky; Amanda Cooper-Sarkar; 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 Schorner-Sadenius; 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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51

Sep 18, 2013
09/13

Sep 18, 2013
by
Thomas Gehrmann; Thomas Lübbert; Li Lin Yang

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We present a calculation of the perturbative quark-to-quark transverse parton distribution function at next-to-next-to-leading order based on a gauge invariant operator definition. We demonstrate for the first time that such a definition works beyond the first non-trivial order. We extract from our calculation the coefficient functions relevant for a next-to-next-to-next-to-leading logarithmic $Q_T$ resummation in a large class of processes at hadron colliders.

Source: http://arxiv.org/abs/1209.0682v2

42
42

Sep 18, 2013
09/13

Sep 18, 2013
by
Aude Gehrmann-De 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 next-to-next-to-leading order. In previous papers, we derived the subtraction terms that rendered (a) the double real radiation tree-level process finite in the single and double unresolved regions of phase space and (b) the mixed single real radiation one-loop 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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30

Sep 17, 2013
09/13

Sep 17, 2013
by
Tancredi Carli; Thomas Gehrmann; Stefan Hoeche

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We extend the multi-purpose Monte-Carlo event generator Sherpa to include processes in deeply inelastic lepton-nucleon 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 higher-order tree-level matrix elements, it is possible...

Source: http://arxiv.org/abs/0912.3715v1

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36

Sep 17, 2013
09/13

Sep 17, 2013
by
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 three-jet production and related event-shape observables at electron--positron colliders. The Z-boson resonance is described within the complex-mass scheme, rendering the calculation valid both in the resonance and off-shell regions. Higher-order initial-state radiation is included in the leading-logarithmic 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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158

Jul 20, 2013
07/13

Jul 20, 2013
by
Thomas Gehrmann

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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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71

Jul 20, 2013
07/13

Jul 20, 2013
by
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, initial-initial antenna functions with both radiators in the initial state are required. In view of extending the antenna subtraction method to next-to-next-to-leading order (NNLO) calculations at...

Source: http://arxiv.org/abs/1107.4037v1