1,960 research outputs found
Exotic Higgs decays in the golden channel
The Higgs boson may have decay channels that are not predicted by the
Standard Model. We discuss the prospects of probing exotic Higgs decays at the
LHC using the 4-lepton final state. We study two specific scenarios, with new
particles appearing in the intermediate state of the 4-lepton Higgs decay. In
one, Higgs decays to a Z boson and a new massive gauge boson, the so-called
hidden photon. In the other, Higgs decays to an electron or a muon and a new
vector-like fermion. We argue that the upcoming LHC run will be able to explore
a new parameter space of these models that is allowed by current precision
constraints. Employing matrix element methods, we use the full information
contained in the differential distribution of the 4-lepton final state to
extract the signal of exotic decays. We find that, in some cases, the LHC can
be sensitive to new physics even when the correction to the total 4-lepton
Higgs rate is of the order of a percent. In particular, for the simplest
realization of the hidden photon with the mass between 15 and 65 GeV, new
parameter space can be explored in the LHC run-II.Comment: 16 pages; v2: minor corrections, references adde
Directly Measuring the Tensor Structure of the Scalar Coupling to Gauge Bosons
Kinematic distributions in the decays of the newly discovered resonance to
four leptons can provide a direct measurement of the tensor structure of the
particle's couplings to gauge bosons. Even if the particle is shown to be a
parity even scalar, measuring this tensor structure is a necessary step in
determining if this particle is responsible for giving mass to the Z. We
consider a Standard Model like coupling as well as coupling via a dimension
five operator to either ZZ or Z\gamma. We show that using full kinematic
information from each event allows discrimination between renormalizable and
higher dimensional coupling to ZZ at the 95% confidence level with O(50) signal
events, and coupling to Z\gamma can be distinguished with as few as 20 signal
events. This shows that these measurements can be useful even with this year's
LHC data.Comment: 7 pages, 5 figures; typos corrected, references adde
The Virtual Diphoton Excess
Interpreting the excesses around 750 GeV in the diphoton spectra to be the
signal of a new heavy scalar decaying to photons, we point out the possibility
of looking for correlated signals with virtual photons. In particular, we
emphasize that the effective operator that generates the diphoton decay will
also generate decays to two leptons and a photon, as well as to four leptons,
independently of the new resonance couplings to and . Depending
on the relative sizes of these effective couplings, we show that the virtual
diphoton component can make up a sizable, and sometimes dominant, contribution
to the total and partial widths. We also discuss
modifications to current experimental cuts in order to maximize the sensitivity
to these virtual photon effects. Finally, we briefly comment on prospects for
channels involving other Standard Model fermions as well as more exotic decay
possibilities of the putative resonance.Comment: 8 pages, 6 figures; v2 figure 2 and references adde
Golden Probe of the Top Yukuwa
We perform a preliminary study of the ability of the Higgs decay to four
leptons to shed light on the top quark Yukawa couplings. In particular we
examine whether the `golden channel' is sensitive to the
properties of the top quark couplings to the Higgs boson. We show that
kinematic distributions are sensitive to interference of the next-to-leading
order electroweak corrections with the tree level contribution. This
translates into a sensitivity to the top quark Yukawa couplings such that
meaningful constraints on their properties can begin to be obtained once
fb of data has been collected at TeV, with
significant improvements at higher luminosity or with a higher energy hadron
collider. This makes the channel a useful probe of the top quark
Yukawa couplings that is qualitatively different from already established
searches in two body decays, , and . We also
briefly discuss other potential possibilities for probing the top Yukawa
properties in and .Comment: references and footnote adde
Light (and darkness) from a light hidden Higgs
We examine light diphoton signals from extended Higgs sectors possessing (approximate) fermiophobia with Standard Model (SM) fermions as well as custodial symmetry. This class of Higgs sectors can be realized in various beyond the SM scenarios and is able to evade many experimental limits, even at light masses, which are otherwise strongly constraining. Below the WW threshold, the most robust probes of the neutral component are di and multi-photon searches. Utilizing the dominant Drell-Yan Higgs pair production mechanism and combining it with updated LHC diphoton data, we derive robust upper bounds on the allowed branching ratio for masses between 45 − 160 GeV. Furthermore, masses ≲ 110 GeV are ruled out if the coupling to photons is dominated by W boson loops. We then examine two simple ways to evade these bounds via cancellations between different loop contributions or by introducing decays into an invisible sector. This also opens up the possibility of future LHC diphoton signals from a light hidden Higgs sector. As explicit realizations, we consider the Georgi-Machacek (GM) and Supersymmetric GM (SGM) models which contain custodial (degenerate) Higgs bosons with suppressed couplings to SM fermions and, in the SGM model, a (neutralino) LSP. We also breifly examine the recent ∼ 3σ CMS diphoton excess at ∼ 95 GeV.We thank Andrew Akeroyd, Filippo Sala, Jose Santiago, Daniel Stolarski, and Lorenzo
Ubaldi for useful comments and discussions. The work of R.V.M. is supported by
MINECO, FPA 2016-78220-C3-1-P, FPA 2013-47836-C3-2/3-P (including ERDF), and the
Juan de la Cierva program, as well as by Junta de Andalucia Project FQM-101. The work
of R.V. is partially supported by the Sam Taylor fellowship. K.X. is supported by U. S.
Department of Energy under Grant No. DE-SC0010129. K.X. also thanks Fermilab for
their hospitality and partial support during this work
New vector bosons and the diphoton excess
We consider the possibility that the recently observed diphoton excess at
GeV can be explained by the decay of a scalar particle ()
to photons. If the scalar is the remnant of a symmetry-breaking sector of some
new gauge symmetry, its coupling to photons can be generated by loops of the
charged massive vectors of the broken symmetry. If these new vector
bosons carry color, they can also generate an effective coupling to gluons. In
this case the diphoton excess could be entirely explained in a simplified model
containing just and . On the other hand if
does not carry color, we show that, provided additional colored particles exist
to generate the required to gluon coupling, the diphoton excess could
be explained by the same commonly invoked to explain the diboson
excess at TeV. We also explore possible connections between the
diphoton and diboson excesses with the anomalous forward-backward
asymmetry.Comment: Latex 8 pages, 1 figure. Extended discussion, new references. Matches
published versio
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