3,249 research outputs found
A clean signal for a top-like isosinglet fermion at the Large Hadron Collider
We predict a clean signal at the Large Hadron Collider (=14 TeV for
a scenario where there is a top-like, charge +2/3 vectorlike isosinglet
fermion. Such a quark, via mixing with the standard model top, can undergo
decays via both flavour-changing Z-boson coupling and flavour-changing Yukawa
interactions. We concentrate on the latter channel, and study the situation
where, following its pair-production, the heavy quark pair gives rise to two
tops and two Higgs boson. We show that the case where each Higgs decays in the
channel, there can be a rather distinct and background-free signal
that can unveil the existence of the vectorlike isosinglet quark of this kind.Comment: 14 pages, 5 figures, 4 table
Triboson interpretations of the ATLAS diboson excess
The ATLAS excess in fat jet pair production is kinematically compatible with
the decay of a heavy resonance into two gauge bosons plus an extra particle.
This hypothesis would explain the absence of such a large excess in the
analogous CMS analysis of fat dijet final states, as well as the negative
results of diboson resonance searches in the semi-leptonic decay modes. If the
extra particle is the Higgs boson, this hypothesis might also explain
-statistical fluctuations aside- why the CMS search for WH resonances in the
semi-leptonic channel finds some excess while in the fully hadronic one it does
not have a significant deviation.Comment: LaTeX 17 pages. v2: Enlarged discussion to address CMS WH excess. v3:
Added discussion of diboson helicities. Final version to appear in JHE
Dilepton azimuthal correlations in tt production
The dilepton azimuthal correlation, namely the difference phi between the azimuthal
angles of the positive and negative charged lepton in the laboratory frame, provides
a stringent test of the spin correlation in tt production at the Large Hadron Collider. We
introduce a parameterisation of the differential cross section dalpha=dphi in terms of a Fourier
series and show that the third-order expansion provides a su ciently accurate approximation.
This expansion can be considered as a `bridge' between theory and data, making it
very simple to cast predictions in the Standard Model (SM) and beyond, and to report
measurements, without the need to provide the numbers for the whole binned distribution.
We show its application by giving predictions for the coeffcients in the presence of
(i) an anomalous top chromomagnetic dipole moment; (ii) an anomalous tbW interaction.
The methods presented greatly facilitate the study of this angular distribution, which is of
special interest given the 3:2(3:7) deviation from the SM next-to-leading order prediction
found by the ATLAS collaboration in Run 2 data.This work has been supported by MINECO Project FPA 2013-47836-C3-2-P (including
ERDF)
Top quark tensor couplings
We compute the real and imaginary parts of the one-loop electroweak
contributions to the left and right tensorial anomalous couplings of the
vertex in the Standard Model (SM). For both tensorial couplings we find that
the real part of the electroweak SM correction is close to 10 of the leading
contribution given by the QCD gluon exchange. We also find that the electroweak
real and imaginary parts for the anomalous right coupling are almost of the
same order of magnitude. The one loop SM prediction for the real part of the
left coupling is close to the 3 discovery limit derived from
. Besides, taking into account that the predictions of
new physics interactions are also at the level of a few percents when compared
with the one loop QCD gluon exchange, these electroweak corrections should be
taken into account in order to disentangle new physics effects from the
standard ones. These anomalous tensorial couplings of the top quark will be
investigated at the LHC in the near future where sensitivity to these
contributions may be achieved.Comment: 16 pages, 2 figure
Probing Top Anomalous Couplings at the Tevatron and the Large Hadron Collider
Chromomagnetic and chromoelectric dipole interactions of the top quark are
studied in a model independent framework. Limits are set on the scale of new
physics that might lead to such contributions using available Tevatron data.
Prospects at the LHC are reviewed.Comment: Version published in Praman
EFTfitter: A tool for interpreting measurements in the context of effective field theories
Over the past years, the interpretation of measurements in the context of effective field theories has attracted much attention in the field of particle physics. We present a tool for interpreting sets of measurements in such models using a Bayesian ansatz by calculating the posterior probabilities of the corresponding free parameters numerically. An example is given, in which top-quark measurements are used to constrain anomalous couplings at the Wtb-vertex.The authors would like to thank Fabian Bach, Kathrin Becker, Dominic HirschbĂŒhl and Mikolaj Misiak for their help and for the fruitful discussions. In particular, the authors would like to thank Fabian Bach for providing the code for the single-top cross sections. N.C. acknowledges the support of FCT-Portugal through the contract IF/00050/2013/CP1172/CT00
Novel signatures for vector-like quarks
We consider supersymmetric extensions of the standard model with a vector-like doublet (T B) of quarks with charge 2/3 and â1/3, respectively. Compared to non-supersymmetric models, there is a variety of new decay modes for the vector-like quarks, involving the extra scalars present in supersymmetry. The importance of these new modes, yielding multi-top, multi-bottom and also multi-Higgs signals, is highlighted by the analysis of several benchmark scenarios. We show how the triangles commonly used to represent the branching ratios of the âstandardâ decay modes of the vector-like quarks involving W, Z or Higgs bosons can be generalised to include additional channels. We give an example by recasting the limits of a recent heavy quark search for this more general case.The work of J.A. Aguilar-Saavedra has been supported by MINECO Projects FPA 2016-
78220-C3-1-P and FPA 2013-47836-C3-2-P (including ERDF), and by Junta de Andaluc a
Project FQM-101. The work of D.E. L opez-Fogliani has been supported by the Argentinian
CONICET. The work of C. Mu~noz has been supported in part by the Programme SEV-
2012-0249 `Centro de Excelencia Severo Ochoa'. D.E. L opez-Fogliani and C. Mu~noz also
acknowledge the support of the Spanish grant FPA2015-65929-P (MINECO/FEDER, UE),
and MINECO's Consolider-Ingenio 2010 Programme under grant MultiDark CSD2009-
00064
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