arXiv subjects

Christoph Englert

Publications and source records attributed to Christoph Englert.

143 records · Page 8Linked to original sources

arXiv2012

Higgs self-coupling measurements at the LHC

Both the ATLAS and CMS collaborations have reported a Standard Model Higgs-like excess at around $m_h = 125$ GeV. If an SM-like Higgs particle is discovered in this particular mass range, an important additional test of the SM electroweak symmetry breaking sector is the measurement of the Higgs self-interactions. We investigate the prospects of measuring the Higgs self-coupling for $m_h=125 \gev$ in the dominant SM decay channels in boosted and unboosted kinematical regimes. We further enhance sensitivity by considering dihiggs systems recoiling against a hard jet. This configuration exhibits a large sensitivity to the Higgs self-coupling which can be accessed in subjet-based analyses. Combining our analyses allows constraints to be set on the Higgs self-coupling at the LHC.

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arXiv2012

Measuring Higgs CP and couplings with hadronic event shapes

Experimental falsification or validation of the Standard Model of Particle Physics involves the measurement of the CP quantum number and couplings of the Higgs boson. Both ATLAS and CMS have reported an SM Higgs-like excess around m_H=125 GeV. In this mass range the properties of the Higgs boson can be extracted from an analysis of the azimuthal angle distribution of the two jets in pp->Hjj events. This channel is also important to measure the couplings of the Higgs boson to electroweak gauge bosons and fermions, hereby establishing the exceptional role of the Higgs boson in the Standard Model. Instead of exploiting the jet angular correlation, we show that hadronic event shapes exhibit substantial discriminative power to separate a CP even from a CP odd Higgs. Some event shapes even show an increased sensitivity to the Higgs CP compared to the azimuthal angle correlation. Constraining the Higgs couplings via a separation of the weak boson fusion and the gluon fusion Higgs production modes can be achieved applying similar strategies.

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arXiv2012

From Jet Counting to Jet Vetoes

The properties of multi-jet events impact many LHC analysis. The exclusive number of jets at hadron colliders can be described in terms of two simple patterns: staircase scaling and Poisson scaling. In photon plus jets production we can interpolate between the two patterns using simple kinematic cuts. The associated theoretical errors are well under control. Understanding such exclusive jet multiplicities significantly impacts Higgs searches and searches for supersymmetry at the LHC.

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arXiv2012

Unconstraining the Unhiggs

We investigate whether or not perturbative unitarity is preserved in the Unhiggs model for the scattering process of heavy quarks and longitudinal gauge bosons $\bar q q \to V_L^+ V_L^-$. With the Yukawa coupling given in the original formulation of the Unhiggs model, the model preserves unitarity for Unhiggs scaling dimensions $d\leq 1.5$. We examine the LHC phenomenology that is implied by the Unhiggs model in this parameter range in detail and discuss to what extent the LHC can test $d$ if an excess is measured in the phenomenologically clean $ZZ$ channel in the future or if the LHC measurement remains consistent with the background. We then make use of the AdS/CFT correspondence to derive a new Yukawa coupling that is conformally invariant at high energies, and show that with this Yukawa coupling the theory is unitary for $1 \leq d < 2$.

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arXiv2012

The Higgs Portal from LHC to ILC

Interpretations of searches for the Higgs boson are governed by model-dependent combinations of Higgs production cross sections and Higgs branching ratios. Mixing of the Higgs doublet with a hidden sector captures modifications from the Standard Model Higgs phenomenology in the standard search channels in a representative way, in particular because invisible Higgs decay modes open up. As a consequence, LHC exclusion bounds, which disfavor a heavy Standard Model Higgs can be consistently understood in terms of a standard-hidden mixed Higgs system. Shedding light on the possible existence of such an admixture with a hidden sector and quantifying the resemblance of an eventually discovered scalar resonance with the Standard Model Higgs crucially depends on measurement of invisible decays. This task will already be tackled at LHC, but eventually requires the clean environment of a future linear collider to be ultimately completed.

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arXiv2012

Establishing Jet Scaling Patterns with a Photon

Staircase and Poisson scaling are two typical patterns we observe for the exclusive number of jets at high energy hadron colliders. We examine these scaling properties for photon plus jets production at the LHC and find that this channel is well suited to study these features. We illustrate and discuss when to expect each of the two patterns, how to induce a transition through kinematic cuts, and how photons are related to heavy gauge bosons. Measurements of photon+jets production is therefore providing valuable information on exclusive jet scaling, which is going to help to eventually understand the theoretical origin of exclusive jet scaling properties in more detail.

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arXiv2012

Evasive Higgs Maneuvers at the LHC

Non-standard decays of the Higgs boson produced at the Large Hadron Collider can lead to signatures which can easily be missed due to non-adapted trigger or search strategies. Keeping electroweak symmetry breaking Standard Model-like we classify the phenomenology of an evasive Higgs boson into three categories and discuss how they can be described in an effective field theory. We comment on how one can improve the search strategies to also detect such an evasive Higgs.

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arXiv2012

LHC: Standard Higgs and Hidden Higgs

Interpretations of Higgs searches critically involve production cross sections and decay probabilities for different analysis channels. Mixing effects can reduce production rates, while invisible decays can reduce decay probabilities. Both effects can transparently be quantified in Higgs systems where a visible Higgs boson is mixed with a hidden sector Higgs boson. Recent experimental exclusion bounds can be re-interpreted in this context as a sign for non-standard Higgs properties. Should a light Higgs boson be discovered, then our analysis will quantify how closely it may coincide with the Standard Model.

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arXiv2011

Results in Precision Multiboson+Jet Phenomenology

We review recent results in precision multiboson+jet phenomenology at the LHC. We discuss strategies how to compute these processes at NLO QCD and examine the impact of the perturbative corrections on the expected phenomenology, especially in the context of anomalous gauge boson couplings searches.

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arXiv2011

W+jets, Z+jets, multijets and new physics searches

W+jets, Z+jets and QCD multijet production processes at hadron colliders are backgrounds to many searches for physics beyond the Standard Model which involve leptons and missing energy in the final state. We review the current theoretical and experimental status of these processes at the LHC. Furthermore, we discuss several methods that allow for reliable predictions for these processes in the context of new-physics searches.

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arXiv2011

Ditau jets in Higgs searches

Understanding and identifying ditau jets -- jets consisting of pairs of tau particles, can be of crucial importance and may even turn out to be a necessity if the Higgs boson decays dominantly to new light scalars which, on the other hand, decay to tau pairs. As often seen in various models of BSM such as in the NMSSM, Higgs portals etc., the lightness of these new states ensures their large transverse momenta and, as a consequence, the collinearity of their decay products. We show that the non-standard signatures of these objects, which can easily be missed by standard analysis techniques, can be superbly exploited in an analysis based on subjet observables. When combined with additional selection strategies, this analysis can even facilitate an early discovery of the Higgs boson. To be specific, a light Higgs can be found with $S/\sqrt{B} \gtrsim 5$ from $\mathcal {L} \simeq 12 fb^{-1}$ of data. We combine all these observables into a single discriminating likelihood that can be employed toward the construction of a realistic and standalone ditau tagger.

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arXiv2011

Exploring the Higgs portal

We study the Higgs portal from the Standard-Model to a hidden sector and examine which elements of the extended theory can be discovered and explored at the LHC. Our model includes two Higgs bosons covering parameter regions where the LHC will be sensitive to two, one or none of the particles at typical discovery luminosities for Standard Model Higgs production.

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arXiv2011

Precise predictions for W γγ+jet production at hadron colliders

In this letter we report on a calculation of W gamma gamma + jet production at next-to-leading order QCD. We include the leptonic decays of the W and take into account all off-shell and finite width effects. This is the first computation which falls into the category of triboson+jet production at next-to-leading order QCD. In total we find sizable corrections with nontrivial phase space dependencies. Therefore, our results are important for phenomenological analyses such as the extraction of anomalous electroweak quartic couplings from inclusive hadron collider data.

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arXiv2011

Precise predictions for (non-standard) W+photon+jet production

We report on a detailed investigation of the next-to-leading order (NLO) QCD corrections to $Wγ$+jet production at the Tevatron and the LHC using a fully-flexible parton-level Monte Carlo program. We include the full leptonic decay of the $W$, taking into account all off-shell and finite width effects, as well as non-standard $WWγ$ couplings. We find particularly sizable corrections for the currently allowed parameter range of anomalous couplings imposed by LEP data. In total the NLO differential distributions reveal a substantial phase space dependence of the corrections, leaving considerable sensitivity to anomalous couplings beyond scale uncertainty at large momentum transfers in the anomalous vertex.

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arXiv2011

Jets plus Missing Energy with an Autofocus

Jets plus missing transverse energy is one of the main search channels for new physics at the LHC. A major limitation lies in our understanding of QCD backgrounds. Using jet merging we can describe the number of jets in typical background channels in terms of a staircase scaling, including theory uncertainties. The scaling parameter depends on the particles in the final state and on cuts applied. Measuring the staircase scaling will allow us to also predict the effective mass for Standard Model backgrounds. Based on both observables we propose an analysis strategy avoiding model specific cuts which returns information about the color charge and the mass scale of the underlying new physics.

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arXiv2010

Measuring spin and CP from semi-hadronic ZZ decays using jet substructure

We apply novel jet techniques to investigate the spin and CP quantum numbers of a heavy resonance X, singly produced in pp -> X -> ZZ -> l(+)l(-)jj at the LHC. We take into account all dominant background processes to show that this channel, which has been considered unobservable until now, can qualify under realistic conditions to supplement measurements of the purely leptonic decay channels X -> ZZ -> 4l. We perform a detailed investigation of spin- and CP-sensitive angular observables on the fully-simulated final state for various spin and CP quantum numbers of the state X, tracing how potential sensitivity communicates through all the steps of a subjet analysis. This allows us to elaborate on the prospects and limitations of performing such measurements with the semihadronic final state. We find our analysis particularly sensitive to a CP-even or CP-odd scalar resonance, while, for tensorial and vectorial resonances, discriminative features are diminished in the boosted kinematical regime.

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arXiv2010

QCD corrections to non-standard WZ+jet production with leptonic decays at the LHC

We discuss the impact of anomalous WW$γ$ and WWZ couplings on WZ+jet production at next-to-leading order QCD, including full leptonic decays of the electroweak gauge bosons. While the inclusive hadronic cross sections do not exhibit any particular sensitivity to anomalous couplings once the residual QCD scale uncertainties are taken into account, the transverse momentum distributions show substantial deviations from the Standard Model, provided that the anomalous vertices are probed at large enough momentum transfers.

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