We describe the universal Monte-Carlo (parton-level) event generator WHIZARD (
http://whizard.event-generator.org
), version 2. The program automatically computes complete tree-level matrix elements, ...integrates them over phase space, evaluates distributions of observables, and generates unweighted partonic event samples. These are showered and hadronized by calling external codes, either automatically from within the program or via standard interfaces. There is no conceptual limit on the process complexity; using current hardware, the program has successfully been applied to hard scattering processes with up to eight particles in the final state. Matrix elements are computed as helicity amplitudes, so spin and color correlations are retained. For event generation, processes can be concatenated with full spin correlation, so factorized approximations to cascade decays are possible when complete matrix elements are not desired. The Standard Model, the MSSM, and many alternative models such as Little Higgs, anomalous couplings, or effects of extra dimensions or noncommutative SM extensions have been implemented. Using standard interfaces to parton shower and hadronization programs, WHIZARD covers physics at hadron, lepton, and photon colliders.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Weak vector-boson W, Z scattering at high energy probes the Higgs sector and is most sensitive to any new physics associated with electroweak symmetry breaking. We show that in the presence of the ...125 GeV Higgs boson, a conventional effective-theory analysis fails for this class of processes. We propose to extrapolate the effective-theory ansatz by an extension of the parameter-free K-matrix unitarization prescription, which we denote as direct T-matrix unitarization. We generalize this prescription to arbitrary nonperturbative models and describe the implementation as an asymptotically consistent reference model matched to the low-energy effective theory. We present exemplary numerical results for full six-fermion processes at the LHC.
We describe a new parallel approach to the evaluation of phase space for Monte-Carlo event generation, implemented within the framework of the
Whizard
package. The program realizes a twofold ...self-adaptive multi-channel parameterization of phase space and makes use of the standard OpenMP and MPI protocols for parallelization. The modern MPI3 feature of asynchronous communication is an essential ingredient of the computing model. Parallel numerical evaluation applies both to phase-space integration and to event generation, thus covering computing-intensive parts of physics simulation for a realistic collider environment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We study in a bottom-up approach the theoretically consistent description of additional resonances in the electroweak sector beyond the discovered Higgs boson as simplified models. We focus on scalar ...and tensor resonances. Our formalism is suited for strongly coupled models, but can also be applied to weakly interacting theories. The spurious degrees of freedom of tensor resonances that would lead to bad high-energy behavior are treated using a generalization of the Stuckelberg formalism. We calculate scattering amplitudes for vector-boson and Higgs boson pairs. The high-energy region is regulated by the T-matrix unitarization procedure, leading to amplitudes that are well behaved on the whole phase space. We present numerical results for complete partonic processes that involve resonant vector-boson scattering for the current and upcoming runs of LHC
A
bstract
We explore the sensitivity of directly testing the muon-Higgs coupling at a high-energy muon collider. This is strongly motivated if there exists new physics that is not aligned with the ...Standard Model Yukawa interactions which are responsible for the fermion mass generation. We illustrate a few such examples for physics beyond the Standard Model. With the accidentally small value of the muon Yukawa coupling and its subtle role in the high-energy production of multiple (vector and Higgs) bosons, we show that it is possible to measure the muon-Higgs coupling to an accuracy of ten percent for a 10 TeV muon collider and a few percent for a 30 TeV machine by utilizing the three boson production, potentially sensitive to a new physics scale about Λ ∼ 30
−
100 TeV.
We present a new study of quasi-elastic
W
and
Z
scattering processes in high-energy
e
+
e
-
collisions, based on and extrapolating the low-energy effective theory which extends the standard model ...with a
125
GeV
Higgs boson. We parameterize deviations in the low-energy range in terms of the dimension-eight operators that arise in the effective theory. Smoothly extending this to higher energy, we study a set of simplified models of new physics in
W
/
Z
scattering, (1) a structureless extrapolation of the effective theory, and (2) scalar and tensor resonance multiplets. The high-energy asymptotics of all models is regulated by a universal unitarization procedure. This enables us to provide benchmark scenarios which can be meaningfully evaluated off shell and in exclusive event samples, and to determine the sensitivity of an
e
+
e
-
collider to the model parameters. We analyze the longitudinal vector-boson scattering modes, where we optimize the cuts for the fiducial cross section for different collider scenarios. Here, we choose energy stages of 1.0, 1.4 and 3 TeV, as motivated by the extendability of the ILC project and the staging scenario of the CLIC project.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Neutrinos are the most elusive particles known. Heavier sterile neutrinos mixing with the standard neutrinos might solve the mystery of the baryon asymmetry of the universe. In this letter, we show ...that among all future energy frontier accelerators, muon colliders will provide the farthest search reach for such neutrinos for mass ranges above the Z pole into the multi-TeV regime, becoming the optimal machine for this kind of studies. We compare the performance of muon with electron colliders of the same machine energy and briefly discuss the complementarity in flavor space between the two types of accelerators.
A
bstract
We present results on NLO electroweak (EW) corrections to multiple massive boson production processes at a future muon collider. Inclusive cross sections with
O
(
α
) corrections for ...processes for up to four bosons in the final state as well as differential distributions for
HZ
production are computed for
s
= 3, 10 and 14 TeV by using FKS subtraction in the NLO EW automated Monte-Carlo framework WHIZARD+RECOLA. Large logarithmic effects due to collinear ISR and EW virtual correction factors as well as the impacts of an energy cut on hard photons are discussed with an emphasis on the properties of Higgsstrahlung. The potential of a proposed muon collider for studying physics of the EW sector is underlined by the EW corrections significantly affecting observables for processes at high energies and boson multiplicities.
Heavy neutrinos at future linear e+e− colliders Mękała, Krzysztof; Reuter, Jürgen; Żarnecki, Aleksander Filip
The journal of high energy physics,
06/2022, Letnik:
2022, Številka:
6
Journal Article
Recenzirano
Odprti dostop
A
bstract
Neutrinos are among the most mysterious particles in nature. Their mass hierarchy and oscillations, as well as their antiparticle properties, are being intensively studied in experiments ...around the world. Moreover, in many models of physics beyond the Standard Model, the baryon asymmetry or the dark matter density in the Universe are explained by introducing new species of neutrinos. Among others, heavy neutrinos of Dirac or Majorana nature were proposed to solve open questions in High Energy Physics. Such neutrinos with masses above the electroweak (EW) scale could be produced at future linear e
+
e
−
colliders, like the Compact LInear Collider (CLIC) or the International Linear Collider (ILC).
We studied the possibility of observing decays of heavy Dirac and Majorana neutrinos in the
qqℓ
final state with ILC running at 500 GeV and 1 TeV, and CLIC at 3 TeV. The analysis is based on the W
hizard
event generation and fast simulation of detector response with Delphes. Neutrinos with masses from 200 GeV to 3.2 TeV were considered. We estimated the limits on the production cross sections, interpreted them in terms of the neutrino-lepton coupling parameter
V
ℓ
N
2
(effectively the neutrino mixing angle) and compared them with current limits coming from the LHC running at 13 TeV, as well as the expected limits from future hadron colliders. The limits for the future lepton colliders, extending down to the coupling values of 10
−
7
−
10
−
6
, are stricter than any other limit estimates published so far.
Processes where
W
and
Z
bosons scatter into pairs of electroweak bosons
W
,
Z
, and Higgs, are sensitive probes of new physics in the electroweak sector. We study simplified models that describe ...typical scenarios of new physics and parameterize the range of possible LHC results between the standard-model prediction and unitarity limits. Extending the study beyond purely longitudinal scattering, we investigate the role of transversally polarized gauge bosons. Unitarity becomes an essential factor, and limits on parameters matched to the naive perturbative low-energy effective theory turn out to be necessarily model-dependent. We discuss the implications of our approach for the interpretation of LHC data on vector-boson scattering and Higgs-pair production.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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