47 research outputs found

### Analysis of the $h, H, A \to \tau \mu$ decays induced from SUSY loops within the Mass Insertion Approximation

In this paper we study the lepton favor violating decay channels of the
neutral Higgs bosons of the Minimal Supersymmetric Standard Model into a lepton
and an anti-lepton of different flavor. We work in the context of the most
general flavor mixing scenario in the slepton sector, in contrast to the
minimal flavor violation assumption more frequently used. Our analytic
computation is a one-loop diagrammatic one, but in contrast to the full
one-loop computation which is usually referred to the physical slepton mass
basis, we use here instead the Mass Insertion Approximation (MIA) which uses
the electroweak interaction slepton basis and treats perturbatively the mass
insertions changing slepton flavor. By performing an expansion in powers of the
external momenta in the relevant form factors, we will be able to separate
explicitly in the analytic results the leading non-decoupling (constant at
asymptotically large sparticle masses) and the next to leading decoupling
contributions (decreasing with the sparticle masses). Our final aim is to
provide a set of simple analytic formulas for the form factors and the
associated effective vertices, that we think may be very useful for future
phenomenological studies of the lepton flavor violating Higgs boson decays, and
for their comparison with data. The accuracy of the numerical results obtained
with the MIA are also analyzed and discussed here in comparison with the full
one-loop results. Our most optimistic numerical estimates for the three neutral
Higgs boson decays channels into $\tau$ and $\mu$ leptons, searching for their
maximum rates that are allowed by present constraints from $\tau \to \mu
\gamma$ data and beyond Standard Model Higgs boson searches at the LHC, are
also included.Comment: 37 pages, 16 figures, 3 appendices. This version v3 matches the
manuscript published in JHE

### Study of Polarization in B -> VT Decays

In this paper, we examine B -> VT decays (V is a vector and T is a tensor
meson), whose final-state particles can have transverse or longitudinal
polarization. Measurements have been made of B -> \phi K_2^*, and it is found
that fT/fL is small, where fT (fL) is the fraction of transverse (longitudinal)
decays. We find that the standard model (SM) naively predicts that fT/fL << 1.
The two extensions of the naive SM which have been proposed to explain the
large fT/fL in B -> \phi K^* -- penguin annihilation and rescattering -- make
no firm predictions for the polarization in B -> \phi K_2^*. The two
new-physics scenarios, which explain the data in B -> \pi K and the \phi (\rho)
K^* polarization measurements, can reproduce the fT/fL data in B -> \phi K_2^*
only if the B -> T form factors obey a certain hierarchy. Finally, we present
the general angular analysis which can be used to get helicity information
using two- and three-body decays.Comment: 15 pages, latex, 3 figures (enclosed), several changes made,
conclusions unchanged, publication info adde

### CP Violation in Three-Body Chargino Decays

CP violation in supersymmetry can give rise to rate asymmetries in the decays
of supersymmetric particles. In this work we compute the rate asymmetries for
the three-body chargino decays \tilde\chi^\pm_2 \to \tilde\chi^\pm_1 HH,
\tilde\chi^\pm_2 \to \tilde\chi^\pm_1 ZZ, \tilde\chi^\pm_2 \to \tilde\chi^\pm_1
W^+ W^- and \tilde\chi^\pm_2 \to tilde\chi^\pm_1 ZH. Each of the decays
contains contributions mediated by neutral Higgs bosons that can possibly go on
shell. Such contributions receive a resonant enhancement; furthermore, the
strong phases required for the CP asymmetries come from the widths of the
exchanged Higgs bosons. Our results indicate that the rate asymmetries can be
relatively large in some cases, while still respecting a number of important
low-energy bounds such as those coming from B meson observables and electric
dipole moments. For the parameters that we consider, rate asymmetries of order
10% are possible in some cases.Comment: 17 pages, 4 figures, published versio

### Exploring unsupervised top tagging using Bayesian inference

Recognizing hadronically decaying top-quark jets in a sample of jets, or even
its total fraction in the sample, is an important step in many LHC searches for
Standard Model and Beyond Standard Model physics as well. Although there exists
outstanding top-tagger algorithms, their construction and their expected
performance rely on Montecarlo simulations, which may induce potential biases.
For these reasons we develop two simple unsupervised top-tagger algorithms
based on performing Bayesian inference on a mixture model. In one of them we
use as the observed variable a new geometrically-based observable
$\tilde{A}_{3}$, and in the other we consider the more traditional
$\tau_{3}/\tau_{2}$ $N$-subjettiness ratio, which yields a better performance.
As expected, we find that the unsupervised tagger performance is below existing
supervised taggers, reaching expected Area Under Curve AUC $\sim 0.80-0.81$ and
accuracies of about 69% $-$ 75% in a full range of sample purity. However,
these performances are more robust to possible biases in the Montecarlo that
their supervised counterparts. Our findings are a step towards exploring and
considering simpler and unbiased taggers.Comment: 15 pages, 6 figure

### Model-independent search strategy for the lepton-flavor-violating heavy Higgs boson decay to τμ at the LHC

In this work we present a model-independent search strategy at the LHC for heavy Higgs bosons decaying into a tau and a muon, H/ A→ τμ, showing a plausible tendency to improve the sensitivity obtained by the present experimental limits. This search strategy is performed for the Higgs boson mass range 1–5 TeV and uses as the most relevant kinematical variables, in order to discriminate signal against background, the transverse momenta of the muon and the tau together with the missing transverse energy. We estimate the exclusion limits at 95% CL and the significances for evidence and discovery at s = 14 TeV with L = 300 fb- 1, observing a growth in the sensitivities for high Higgs boson masses. Moreover, since the Higgs boson decay into a tau-lepton pair may mimic our LFV signal, we also study the impact of the ditau channel on the exclusion limits and the significances for evidence and discovery. In particular, the impact on the exclusion limits of LFV heavy Higgs boson decays is significant when the ditau rate begins to compete with the corresponding to the H/ A→ τμ decayThis work has been partially supported by CONICET and ANPCyT under projects PICT 2016-0164 (E. A., N. M., A. S.), PICT 2017-2751 (E. A., N. M., A. S.) and PICT 2017-2765 (E. A.). This work is supported by the European Union through the ITN ELUSIVES H2020-MSCA-ITN-2015//674896 and the RISE INVISIBLE-SPLUS H2020-MSCA-RISE-2015//690575, by the CICYT through the project FPA2016-78645-P, and by the Spanish MINECOs “Centro de Excelencia Severo Ochoa” Programme under Grant SEV-2016-059

### Four tops for LHC

We design a search strategy for the Standard Model t¯tt¯tproduction at the LHC in the same-sign dilepton and trilepton channels. We study different signal features and, given the small expected number of signal events, we scrutinize in detail all reducible and irreducible backgrounds. Our analysis shows that by im-posing a basic set of jet and lepton selection criteria, the SM pp→t¯tt¯tprocess could be evidenced in the near future, within Run-II, when combining both multi-lepton search channels. We argue that this search strategy should also be used as a guideline to test New Physics coupling predominantly to top-quarks. In particular, we show that a non-resonant New Physics enhancement in the four-top final state would be de-tectable through this search strategy. We study two top-philicsimplified models of this kind, a neutral scalar boson and a Z0, and present current and future exclusion limits on their mass and couplings.Instituto de Física La Plat