arXiv subjects

Tuomas Hapola

Publications and source records attributed to Tuomas Hapola.

12 recordsLinked to original sources

arXiv2019

HEJ 2: High Energy Resummation for Hadron Colliders

We present HEJ 2, a new implementation of the High Energy Jets formalism for high-energy resummation in hadron-collider processes as a flexible Monte Carlo event generator. In combination with a conventional fixed-order event generator, HEJ 2 can be used to obtain greatly improved predictions for a number of phenomenologically important processes by adding all-order logarithmic corrections in $\hat{s}/p_\perp^2$. A prime example for such a process is the gluon-fusion production of a Higgs boson in association with widely separated jets, which constitutes the dominant background to Higgs boson production in weak-boson fusion.

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arXiv2018

Higgs-boson plus Dijets: Higher-Order Matching for High-Energy Predictions

Several important processes and analyses at the LHC are sensitive to higher-order perturbative corrections beyond what can currently be calculated at fixed order. The formalism of High Energy Jets (HEJ) calculates the corrections systematically enhanced for a large ratio of the centre-of-mass energy to the transverse momentum of the observed jets. These effects are relevant in the analysis of e.g. Higgs-boson production in association with dijets within the cuts devised to enhance the contribution from Vector Boson Fusion (VBF). HEJ obtains an all-order approximation, based on logarithmic corrections which are matched to fixed-order results in the cases where these can be readily evaluated. In this paper we present an improved framework for the matching utilised in HEJ, which for merging of tree-level results is mathematically equivalent to the one used so far. However, by starting from events generated at fixed order and supplementing these with the all-order summation, it is computationally simpler to obtain matching to calculations of high multiplicity. We demonstrate that the impact of the higher-multiplicity matching on predictions is small for the gluon-fusion (GF) contribution of Higgs-boson production in association with dijets in the VBF-region, so perturbative stability against high-multiplicity matching has been achieved within HEJ. We match the improved HEJ prediction to the inclusive next-to-leading order (NLO) cross section and compare to pure NLO in the h->photon photon channel with standard VBF cuts.

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arXiv2018

Higgs Boson Plus Dijets: Higher Order Corrections

The gluon fusion component of Higgs-boson production in association with dijets is of particular interest because it both (a) allows for a study of the CP-structure of the Higgs-boson couplings to gluons, and (b) provides a background to the otherwise clean study of Higgs-boson production through vector-boson fusion. The degree to which this background can be controlled, and the CP-structure of the gluon-Higgs coupling extracted, both depend on the successful description of the perturbative corrections to the gluon-fusion process. High Energy Jets (HEJ) provides all-order, perturbative predictions for multi-jet processes at hadron colliders at a fully exclusive, partonic level. We develop the framework of HEJ to include the process of Higgs-boson production in association with at least two jets. We discuss the logarithmic accuracy obtained in the underlying all-order results, and calculate the first next-to-leading corrections to the framework of HEJ, thereby significantly reducing the corrections which arise by matching to and merging fixed-order results. Finally, we compare predictions for relevant observables obtained with NLO and HEJ. We observe that the selection criteria commonly used for isolating the vector-boson fusion component suppresses the gluon-fusion component even further than predicted at NLO.

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arXiv2015

Custodial Vector Model

We analyze the Large Hadron Collider (LHC) phenomenology of heavy vector resonances with a $SU(2)_L\times SU(2)_R$ spectral global symmetry. This symmetry partially protects the electroweak S-parameter from large contributions of the vector resonances. The resulting custodial vector model spectrum and interactions with the standard model fields lead to distinct signatures at the LHC in the diboson, dilepton and associated Higgs channels.

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arXiv2014

Higgs Boson with Multiple Jets

The High Energy Jets (HEJ) framework accounts for large logarithms arising from the wide angle hard gluon emissions. The resummation in HEJ is based on an approximation to allow fast evaluation for arbitrary multiplicity. The approximation is motivated by the high energy limit and as such captures the leading logarithmic corrections in large invariant mass between the partons. These corrections are important when there is a large separation in rapidity between the produced jets. This situation arises in a Higgs boson plus jets analysis. Furthermore, HEJ includes matching to full tree level accuracy up to four jets. This talk will introduce the HEJ framework and discuss advances in the formal accuracy attained within HEJ, and the application to predictions for the production of Higgs boson plus jets.

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arXiv2014

Constraints on Majorana Dark Matter from a Fourth Lepton Family

We study the possibility of dark matter in the form of heavy neutrinos from a fourth lepton family with helicity suppressed couplings such that dark matter is produced thermally via annihilations in the early Universe. We present all possible constraints for this scenario coming from LHC and collider physics, underground direct detectors, neutrino telescopes, and indirect astrophysical searches. Although we embed the WIMP candidate within a model of composite dynamics, the majority of our results are model independent and applicable to all models where heavy neutrinos with suppressed couplings account for the dark matter abundance.

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arXiv2013

Warped Extra Dimensional Benchmarks for Snowmass 2013

The framework of a warped extra dimension with the Standard Model (SM) fields propagating in it is a very well-motivated extension of the SM since it can address both the Planck-weak and flavor hierarchy problems of the SM. We consider signals at the 14 and 33 TeV large hadron collider (LHC) resulting from the direct production of the new particles in this framework, i.e.,Kaluza-Klein (KK) excitations of the SM particles. We focus on spin-1 (gauge boson) and spin-2 (graviton) KK particles and their decays to top/bottom quarks (flavor-conserving) and W/Z and Higgs bosons, in particular. We propose two benchmarks for this purpose, with the right-handed (RH) or LH top quark, respectively, being localized very close to the TeV end of the extra dimension. We present some new results at the 14 TeV (with 300 fb$^-1$ and 3000 fb$^-1$) and 33 TeV LHC. We find that the prospects for discovery of these particles are quite promising, especially at the high-luminosity upgrade.

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arXiv2013

Perturbative extension of the standard model with a 125 GeV Higgs and Magnetic Dark Matter

We introduce a perturbative extension of the standard model featuring a new dark matter sector together with a 125 GeV Higgs. The new sector consists of a vector-like heavy electron E, a complex scalar electron S and a standard model singlet Dirac fermion χ. The interactions among the dark matter candidate χand the standard model particles occur via loop-induced processes involving the operator SEχy, with y being the Yukawa-like coupling. The model is an explicit underlying realization of the light magnetic dark matter effective model introduced earlier to alleviate the tension among several direct dark matter search experiments. We further constrain the parameters of the underlying theory using results from the Large Hadron Collider. The extension can accommodate the recently observed properties of the Higgs-like state and leads to interesting predictions. Finally we show that the model's collider phenomenology and constraints nicely complement the ones coming from dark matter searches.

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arXiv2012

W Plus Multiple Jets at the LHC with High Energy Jets

We study the production of a W boson in association with n hard QCD jets (for n>=2), with a particular emphasis on results relevant for the Large Hadron Collider (7 TeV and 8 TeV). We present predictions for this process from High Energy Jets, a framework for all-order resummation of the dominant contributions from wide-angle QCD emissions. We first compare predictions against recent ATLAS data and then shift focus to observables and regions of phase space where effects beyond NLO are expected to be large.

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arXiv2012

Pseudo Goldstone Bosons Phenomenology in Minimal Walking Technicolor

We construct the non-linear realized Lagrangian for the Goldstone Bosons associated to the breaking pattern of SU(4) to SO(4). This pattern is expected to occur in any Technicolor extension of the standard model featuring two Dirac fermions transforming according to real representations of the underlying gauge group. We concentrate on the Minimal Walking Technicolor quantum number assignments with respect to the standard model symmetries. We demonstrate that for, any choice of the quantum numbers, consistent with gauge and Witten anomalies the spectrum of the pseudo Goldstone Bosons contains electrically doubly charged states which can be discovered at the Large Hadron Collider.

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arXiv2011

W' and Z' limits for Minimal Walking Technicolor

We interpret the recent data on non-observation of Z'- and W'-bosons, reported by CMS, within Minimal Walking Technicolor models and use them to constrain the couplings and spectrum of the theory. We provide the reach for both exclusion and possible observation for the LHC with 5 fb^-1 at 7 TeV in the centre of mass energy, and 100 fb^-1 at 13 TeV.

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arXiv2011

Composite Higgs to two Photons and Gluons

We introduce a simple framework to estimate the composite Higgs boson coupling to two-photon in Technicolor extensions of the standard model. The same framework allows us to predict the composite Higgs to two-gluon process. We compare the decay rates with the standard model ones and show that the corrections are typically of order one. We suggest, therefore, that the two-photon decay process can be efficiently used to disentangle a light composite Higgs from the standard model one. We also show that the Tevatron results for the gluon-gluon fusion production of the Higgs either exclude the techniquarks to carry color charges to the 95% confidence level, if the composite Higgs is light, or that the latter must be heavier than around 200 GeV.

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