arXiv subjects

Thomas Gehrmann

Publications and source records attributed to Thomas Gehrmann.

At least 73 records · Page 4Linked to original sources

arXiv2019

Triple Differential Dijet Cross Section at the LHC

The measurement of the triple-differential dijet production cross section as a function of the average transverse momentum $p_{T,\textrm{avg}}$, half the rapidity separation $y^{*}$, and the boost $y_{b}$ of the two leading jets in the event enables a kinematical scan of the underlying parton momentum distributions. We compute for the first time the second-order perturbative QCD corrections to this triple-differential dijet cross section, at leading color in all partonic channels, thereby enabling precision studies with LHC dijet data. A detailed comparison with experimental CMS 8 TeV data is performed, demonstrating how the shape of this differential cross section probes the parton densities in different kinematical ranges.

hep-ph↗

arXiv2019

Master integrals for the NNLO virtual corrections to $q \bar{q} \rightarrow t \bar{t}$ scattering in QCD: the non-planar graphs

We complete the analytic evaluation of the master integrals for the two-loop non-planar box diagrams contributing to the top-pair production in the quark-initiated channel, at next-to-next-to-leading order in QCD. The integrals are determined from their differential equations, which are cast into a canonical form using the Magnus exponential. The analytic expressions of the Laurent series coefficients of the integrals are expressed as combinations of generalized polylogarithms, which we validate with several numerical checks. We discuss the analytic continuation of the planar and the non-planar master integrals, which contribute to $q {\bar q} \to t {\bar t}$ in QCD, as well as to the companion QED scattering processes $ e e \to μμ$ and $e μ\to e μ$.

hep-ph↗

arXiv2019

Jet cross sections at the LHC and the quest for higher precision

We perform a phenomenological study of $Z$ plus jet, Higgs plus jet and di-jet production at the Large Hadron Collider. We investigate in particular the dependence of the leading jet cross section on the jet radius as a function of the jet transverse momentum. Theoretical predictions are obtained using perturbative QCD calculations at the next-to and next-to-next-to-leading order, using a range of renormalization and factorization scales. The fixed order predictions are compared to results obtained from matching next-to-leading order calculations to parton showers. A study of the scale dependence as a function of the jet radius is used to provide a better estimate of the scale uncertainty for small jet sizes. The non-perturbative corrections as a function of jet radius are estimated from different generators.

hep-ph↗

arXiv2019

Higgs boson production at the LHC using the $q_T$ subtraction formalism at N$^3$LO QCD

We consider higher-order QCD corrections to Higgs boson production through gluon-gluon fusion in the large top quark mass limit in hadron collisions. We extend the transverse-momentum ($q_T$) subtraction method to next-to-next-to-next-to-leading order (N$^3$LO) and combine it with the NNLO Higgs-plus-jet calculation to numerically compute differential infrared-safe observables at N$^3$LO for Higgs boson production in gluon fusion. To cancel the infrared divergences, we exploit the universal behaviour of the associated $q_T$ distributions in the small-$q_T$ region. We document all the necessary ingredients of the transverse-momentum subtraction method up to N$^3$LO. The missing third order collinear functions, which contribute only at $q_T$ =0, are approximated using a prescription which uses the known result for the total Higgs boson cross section at this order. As a first application of the third-order $q_T$ subtraction method, we present the N$^3$LO rapidity distribution of the Higgs boson at the LHC.

hep-ph↗

arXiv2018

Precise QCD Description of the Higgs Boson Transverse Momentum Spectrum

The transverse momentum ($p_T$) distribution of Higgs bosons at hadron colliders enables a detailed probe of its production dynamics and is a key ingredient to precision studies of Higgs boson properties, but receives very large QCD corrections. We obtain a precision prediction for the $p_T$ spectrum by matching second-order (NNLO) QCD corrections at large $p_T$ with resummation of third-order logarithmic (N$^3$LL) corrections at small $p_T$. We achieve significantly improved results for $p_T< 35\,{\rm GeV}$ with perturbative uncertainties $\lesssim \pm 6\%$, and thus a convergent perturbative series for all values of $p_T$.

hep-ph↗

arXiv2018

Two-loop massless QCD corrections to the $g+g \rightarrow H+H$ four-point amplitude

We compute the two-loop massless QCD corrections to the four-point amplitude $g+g \rightarrow H+H$ resulting from effective operator insertions that describe the interaction of a Higgs boson with gluons in the infinite top quark mass limit. This amplitude is an essential ingredient to the third-order QCD corrections to Higgs boson pair production. We have implemented our results in a numerical code that can be used for further phenomenological studies.

hep-ph↗

arXiv2018

Infrared sensitivity of single jet inclusive production at hadron colliders

Jet production at hadron colliders is a benchmark process to probe the dynamics of the strong interaction and the structure of the colliding hadrons. One of the most basic jet production observables is the single jet inclusive cross section, which is obtained by summing all jets that are observed in an event. Our recent computation of next-to-next-to-leading order (NNLO) QCD contributions to single jet inclusive observables uncovered large corrections in certain kinematical regions, which also resulted in a sizeable ambiguity on the appropriate choice of renormalization and factorization scales. We now perform a detailed investigation of the infrared sensitivity of the different ingredients to the single jet inclusive cross section. We show that the contribution from the second jet, ordered in transverse momentum $p_{T}$, in the event is particularly sensitive to higher order effects due to implicit restrictions on its kinematics. By investigating the second-jet transverse momentum distribution, we identify large-scale cancellations between different kinematical event configurations, which are aggravated by certain types of scale choice. Taking perturbative convergence and stability as selection criteria enables us to single out the total partonic transverse energy $\hat{H}_{T}$ and twice the individual jet transverse momentum $2\,p_{T}$ (with which $\hat{H}_{T}$ coincides in Born kinematics) as the most appropriate scales in the perturbative description of single jet inclusive production.

hep-ph↗

arXiv2018

Applications of integrand reduction to two-loop five-point scattering amplitudes in QCD

We review the current state-of-the-art in integrand level reduction for five-point scattering amplitudes at two loops in QCD. We present some benchmark results for the evaluation of the leading colour two-loop five-gluon amplitudes in the physical region as well as the partonic channels for two quarks and three gluons and four quarks and one gluon.

hep-ph↗

arXiv2018

Systematic approximation of multi-scale Feynman integrals

An algorithm for the systematic analytical approximation of multi-scale Feynman integrals is presented. The algorithm produces algebraic expressions as functions of the kinematical parameters and mass scales appearing in the Feynman integrals, allowing for fast numerical evaluation. The results are valid in all kinematical regions, both above and below thresholds, up to in principle arbitrary orders in the dimensional regulator. The scope of the algorithm is demonstrated by presenting results for selected two-loop three-point and four-point integrals with an internal mass scale that appear in the two-loop amplitudes for Higgs+jet production.

hep-ph↗

arXiv2018

NNLO QCD Corrections to W+jet Production in NNLOJET

We give an overview of our calculation of the next-to-next-to-leading order (NNLO) QCD corrections to W + jet production in hadronic collisions. Phenomenological results for multiple differential distributions are compared to CMS data for 8 TeV proton-proton collisions. We further discuss the application of the calculation to the transverse momentum spectrum of inclusive W boson production, again accompanied by a comparison to 8 TeV CMS data. In both cases, the inclusion of NNLO QCD effects give an improved agreement between theory and data with considerably reduced scale uncertainties with respect to the next-to-leading order (NLO) results.

hep-ph↗

arXiv2018

NNLO corrections to VBF Higgs boson production

This talk expands on recently published results for the factorising next-to-next-to-leading order (NNLO) QCD corrections to Higgs boson production in the vector boson fusion (VBF) channel. The calculation is fully differential in the kinematics of the Higgs boson and the final state jets and is implemented in the NNLOJET framework for computing higher-order QCD corrections. We find the NNLO corrections to be limited in magnitude to about $\pm 5$\% with a weak kinematical dependence in the transverse momenta and rapidity separation of the two tagging jets.

hep-ph↗

arXiv2018

Jet cross sections at the LHC with NNLOJET

We review the status of NNLO calculations for jet cross sections at the LHC. In particular, we describe how perturbative stability and convergence can be used as criteria to select the most appropriate scales in the theoretical description of di-jet and single jet inclusive production.

hep-ph↗

arXiv2017

NNLO predictions for dijet production in diffractive DIS

Cross sections for inclusive dijet production in diffractive deep-inelastic scattering are calculated for the first time in next-to-next-to-leading order (NNLO) accuracy. These cross sections are compared to several HERA measurements published by the H1 and ZEUS collaborations. We computed the total cross sections, 49 single-differential and five double-differential distributions for six HERA measurements. The NNLO corrections are found to be large and positive. The normalization of the resulting predictions typically exceeds the data, while the kinematical shape of the data is described better at NNLO than at next-to-leading order (NLO). Our results use the currently available NLO diffractive parton distributions, and the discrepancy in normalization highlights the need for a consistent determination of these distributions at NNLO accuracy.

hep-ph↗

arXiv2017

NNLO QCD corrections to event orientation in e+e- annihilation

We present a new implementation of the NNLO QCD corrections to three-jet final states and related event-shape observables in electron--positron annihilation. Our implementation is based on the antenna subtraction method, and is performed in the NNLOJET framework. The calculation improves upon earlier results by taking into account the full kinematical information on the initial state momenta, thereby allowing the event orientation to be computed to NNLO accuracy. We find the event-orientation distributions at LEP and SLC to be very robust under higher order QCD corrections.

hep-ph↗

arXiv2017

Precise predictions for dijet production at the LHC

We present the calculation of dijet production, doubly-differential in dijet mass, $m_{jj}$ and rapidity difference, $|y^{*}|$, at leading colour in all partonic channels at next-to-next-to-leading order (NNLO) in perturbative QCD. We consider the long-standing problems associated with scale choice for dijet production at next-to-leading order (NLO) and investigate the impact of including the NNLO contribution. We find that the NNLO theory provides reliable predictions, even when using scale choices which display pathological behaviour at NLO. We choose the dijet invariant mass as the theoretical scale on the grounds of perturbative convergence and residual scale variation and compare the predictions to the ATLAS 7 TeV 4.5 fb$^{-1}$ data.

hep-ph↗

arXiv2017

Differential single jet inclusive production at Next-to-Next-to-Leading Order in QCD

In this talk we present the recent calculation in all partonic channels of the fully differential single jet inclusive cross section at Next-to-Next-to-Leading Order in QCD. We discuss the size and shape of the perturbative corrections as a function of the functional form of the renormalisation and factorisation scales and compare the predictions at NLO and NNLO to the available ATLAS 7 TeV data. We find significant effects at low-$p_T$ due to changes in the functional form of the scale choice whereas at high-$p_T$ the two most common scale choices in the literature give identical results and the perturbative corrections lead to a substantial reduction in the scale dependence of the theoretical prediction at NNLO.

hep-ph↗

arXiv2017

AWEsome: An open-source test platform for airborne wind energy systems

In this paper we present AWEsome (Airborne Wind Energy Standardized Open-source Model Environment), a test platform for airborne wind energy systems that consists of low-cost hardware and is entirely based on open-source software. It can hence be used without the need of large financial investments, in particular by research groups and startups to acquire first experiences in their flight operations, to test novel control strategies or technical designs, or for usage in public relations. Our system consists of a modified off-the-shelf model aircraft that is controlled by the pixhawk autopilot hardware and the ardupilot software for fixed wing aircraft. The aircraft is attached to the ground by a tether. We have implemented new flight modes for the autonomous tethered flight of the aircraft along periodic patterns. We present the principal functionality of our algorithms. We report on first successful tests of these modes in real flights.

eess.SY↗

arXiv2017

Single jet inclusive production for the individual jet $p_{T}$ scale choice at the LHC

We study the single jet inclusive cross section up to next-to-next-to leading order in perturbative QCD, implemented in the parton-level event generator NNLOJET . Our results are fully differential in the jet transverse momentum and rapidity and we apply fiducial cuts for comparison with the available ATLAS 7 TeV 4.5 fb$^{-1}$ data for jet radius $R=0.4$. For the theoretical calculation we employ the antenna subtraction method to reliably cancel all infrared divergences present at intermediate stages of the calculation. We present all results using the individual jet transverse momentum $μ_{R}=μ_{F}\sim p_{T}$ as the renormalization and factorization scale for each jet's contribution to the single jet inclusive cross section. Finally, we consider the differences between our predictions using this scale choice to those for the leading jet transverse momentum scale choice, $μ_{R}=μ_{F}\sim p_{T_{1}}$, used in [14], with reference to the ATLAS data.

hep-ph↗