A
bstract
The production of high-mass, color-singlet particles in hadron collisions is universally accompanied by initial state QCD radiation that is predominantly soft with respect to the hard ...process scale
Q
and/or collinear with respect to the beam axis. At TeV-scale colliders, this is in contrast to top quark and multijet processes, which are hard and central. Consequently, vetoing events with jets possessing transverse momenta above
p
T
Veto
in searches for new color-singlet states can efficiently reduce non-singlet backgrounds, thereby increasing experimental sensitivity. To quantify this generic observation, we in-vestigate the production and leptonic decay of a Sequential Standard Model
W
′
boson at the 13 TeV Large Hadron Collider. We systematically consider signal and background processes at next-to-leading-order (NLO) in QCD with parton shower (PS) matching. For color-singlet signal and background channels, we resum Sudakov logarithms of the form
α
s
j
(
p
T
Veto
) log
k
(
Q
/
p
T
Veto
) up to next-to-next-to-leading logarithmic accuracy (NNLL) with NLO matching. We obtain our results using the M
ad
G
raph
5_
a
MC@NLO and M
ad
G
raph
5_
a
MC@NLO-SCET frameworks, respectively. Associated Universal F
eyn
-R
ules
Output model files capable of handling NLO+PS- and NLO+NNLL-accurate computations are publicly available. We find that within their given uncertainties, both the NLO+PS and NLO+NNLL(veto) calculations give accurate and consistent predictions. Consequently, jet vetoes applied to color-singlet processes can be reliably modeled at the NLO+PS level. With respect to a
b
-jet veto of
p
T
Veto
= 30 GeV, flavor-agnostic jet vetoes of
p
T
Veto
= 30 − 40 GeV can further reduce single top and
t
t
¯
rates by a factor of 2-50 at a mild cost of the signal rate. Jet vetoes can increase the signal-to-noise ratios by roughly 10% for light
W
′
boson masses of 30 − 50 GeV and 25%-250% for masses of 300-800 GeV.
Abstract Leptoquarks are prime candidates for explaining the intriguing hints for lepton flavour universality violation. In particular, the SU(2) L doublet of scalar leptoquarks S 2 is capable of ...providing an explanation for the tensions between the measurements and the Standard Model predictions in (g − 2) μ , b → sℓ + ℓ − and b → cτν processes, as well as in non-resonant di-electron production. However, in the minimal setup with a single leptoquark generation, a common explanation for all these issues is not possible as this would lead to unacceptably large charged lepton flavour violation. We therefore propose a model with three generations of S 2, each coupling exclusively to a single lepton flavour, i.e. a model extending the Standard Model particle content by an electroquark, a muoquark and a tauquark. We show that after taking into account other constraints, such as those originating from electroweak precision observables and ∆F = 2 processes, it is possible to provide a combined explanation for all these hints of lepton flavour universality violation. Moreover, we find that the presence of the tauquark can generate a dimension-six O 9 U $$ {\mathcal{O}}_9^U $$ operator via off-shell photon penguin diagrams, which, together with the muoquark contribution, further improves the global fit to b → sℓ + ℓ − data.
We present the DMSimpt model implementation in
FeynRules
, which aims to offer a unique general framework allowing for all simulations relevant for simplified
t
-channel dark matter models at ...colliders and for the complementary cosmology calculations. We describe how to match next-to-leading-order QCD fixed-order calculations with parton showers to derive robust bounds and predictions in the context of LHC dark matter searches, and moreover validate two model restrictions (relevant for Dirac and Majorana fermionic dark matter respectively) to exemplify how to evaluate dark matter observables to constrain the model parameter space. More importantly, we emphasise how to achieve these results by using a combination of publicly available automated tools, and discuss how dark matter predictions are sensitive to the model file and software setup. All files, together with illustrative
Mathematica
notebooks, are available from the URL
http://feynrules.irmp.ucl.ac.be/wiki/DMsimpt
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Vector-like quarks are featured by a wealth of beyond the Standard Model theories and are consequently an important goal of many LHC searches for new physics. Those searches, as well as most related ...phenomenological studies, however, rely on predictions evaluated at the leading-order accuracy in QCD and consider well-defined simplified benchmark scenarios. Adopting an effective bottom-up approach, we compute next-to-leading-order predictions for vector-like-quark pair production and single production in association with jets, with a weak or with a Higgs boson in a general new physics setup. We additionally compute vector-like-quark contributions to the production of a pair of Standard Model bosons at the same level of accuracy. For all processes under consideration, we focus both on total cross sections and on differential distributions, most these calculations being performed for the first time in our field. As a result, our work paves the way to precise extraction of experimental limits on vector-like quarks thanks to an accurate control of the shapes of the relevant observables and emphasise the extra handles that could be provided by novel vector-like-quark probes never envisaged so far.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
The Higgs discovery and the lack of any other hint for new physics favor a description of non-standard Higgs physics in terms of an effective field theory. We present an implementation of a ...general Higgs effective Lagrangian containing operators up to dimension six in the framework of F
eyn
R
ules
and provide details on the translation between the mass and interaction bases, in particular for three- and four-point interaction vertices involving Higgs and gauge bosons. We illustrate the strengths of this implementation by using the UFO interface of F
eyn
R
ules
capable to generate model files that can be understood by the M
ad
G
raph
5 event generator and that have the specificity to contain all interaction vertices, without any restriction on the number of external legs or on the complexity of the Lorentz structures. We then investigate several new physics effects in total rates and differential distributions for different Higgs production modes, including gluon fusion, associated production with a gauge boson and di-Higgs production. We finally study contact interactions of gauge and Higgs bosons to fermions.
Simplified fast detector simulation in MadAnalysis 5 Araz, Jack Y.; Fuks, Benjamin; Polykratis, Georgios
The European physical journal. C, Particles and fields,
04/2021, Letnik:
81, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We introduce a new simplified fast detector simulator in the
MadAnalysis 5
platform. The
Python
-like interpreter of the programme has been augmented by new commands allowing for a detector ...parametrisation through smearing and efficiency functions. On run time, an associated C++ code is automatically generated and executed to produce reconstructed-level events. In addition, we have extended the
MadAnalysis 5
recasting infrastructure to support our detector emulator, and we provide predefined LHC detector configurations. We have compared predictions obtained with our approach to those resulting from the usage of the
Delphes 3
software, both for Standard Model processes and a few new physics signals. Results generally agree to a level of about 10% or better, the largest differences in the predictions stemming from the different strategies that are followed to model specific detector effects. Equipped with these new functionalities,
MadAnalysis 5
now offers a new user-friendly way to include detector effects when analysing collider events, the simulation of the detector and the analysis being both handled either through a set of intuitive
Python
commands or directly within the C++ core of the platform.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The existence of colour-octet scalar states, often dubbed sgluons, is predicted in many extensions of the Standard Model of particle physics, such as supersymmetric realisations featuring Dirac ...gauginos. Such states have a large pair-production rate at hadron colliders and mainly decay into pairs of jets and top quarks. Consequently, they represent a primary target for experimental searches for new resonances in the multijet and multitop channels at the Large Hadron Collider. Adopting a phenomenologically-motivated simplified model, we reinterpret the results of a recent experimental search for the four-top-quark Standard Model signal, from which we constrain the sgluon mass to be larger than about 1.06 TeV. We additionally consider how modifications of the existing four-top-quark studies could enhance our ability to unravel the presence of scalar octets in data.
The Higgs potential consists of an unexplored territory in which the electroweak symmetry breaking is triggered, and it is moreover directly related to the nature of the electroweak phase transition. ...Measuring the Higgs boson cubic and quartic couplings, or getting equivalently information on the exact shape of the Higgs potential, is therefore an essential task. However, direct measurements beyond the cubic self-interaction of the Higgs boson consist of a huge challenge, even for a future proton–proton collider expected to operate at a center-of-mass energy of 100 TeV. We present a novel approach to extract model-independent constraints on the triple and quartic Higgs self-coupling by investigating triple Higgs-boson hadroproduction at a center-of-mass energy of 100 TeV, focusing on the ττbb¯bb¯ channel that was previously overlooked due to a supposedly too large background. It is thrown into sharp relief that the assist from transverse variables such as mT2 and a boosted configuration ensures a high signal sensitivity. We derive the luminosities that would be required to constrain given deviations from the Standard Model in the Higgs self-interactions, showing for instance that a 2σ sensitivity could be achieved for an integrated luminosity of 30 ab−1 when Standard Model properties are assumed. With the prospects of combining these findings with other triple-Higgs search channels, the Standard Model Higgs quartic coupling could in principle be reached with a significance beyond the 3σ level.
We describe the
Resummino
package, a
C++
and
Fortran
program dedicated to precision calculations in the framework of gaugino and slepton pair production at hadron colliders. This code allows to ...calculate transverse-momentum and invariant-mass distributions as well as total cross sections by combining the next-to-leading order predictions obtained by means of perturbative QCD with the resummation of the large logarithmic contributions arising in the small transverse-momentum region and close to the production threshold. The results computed in this way benefit from reduced theoretical uncertainties, compared to a pure next-to-leading order approach as currently employed in the experimental analyses searching for sleptons and gauginos at hadron colliders. This is illustrated by using
Resummino
in the context of a typical supersymmetric benchmark point dedicated to superpartner searches at the Large Hadron Collider.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
We analyse scalar leptoquark pair production at the LHC with predictions including
t
-channel lepton exchange contributions up to next-to-leading order (NLO) in QCD. In particular, we ...calculate NLO-QCD predictions for off-diagonal production channels, i.e. channels that involve two different leptoquark eigenstates and are driven solely by diagrams involving Standard Model leptons in the
t
-channel at leading order, as opposed to diagonal channels where a pair of the same leptoquark eigenstate is produced. We find that reliable theoretical predictions for both channels require NLO accuracy. The relative importance of the off-diagonal modes depends strongly on the considered scenario. In a generic model involving
R
2
and
S
3
leptoquarks, at large values of the Yukawa couplings off-diagonal contributions initiated by valence quarks can be up to an order of magnitude higher than the diagonal production. However, we also find that in phenomenologically viable scenarios addressing the flavour anomalies off-diagonal production is generally negligible, with a few exceptions of 10%–30% of the total rate depending on the treatment of the charm density in the proton.
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