152 research outputs found
NA62 sensitivity to heavy neutral leptons in the low scale seesaw model
The sensitivity of beam dump experiments to heavy neutral leptons depends on
the relative strength of their couplings to individual lepton flavours in the
Standard Model. We study the impact of present neutrino oscillation data on
these couplings in the minimal type I seesaw model and find that it
significantly constrains the allowed heavy neutrino flavour mixing patterns. We
estimate the effect that the DUNE experiment will have on these predictions. We
then discuss implication that this has for the sensitivity of the NA62
experiment when operated in the beam dump mode and provide sensitivity
estimates for different benchmark scenarios. We find that the sensitivity can
vary by almost two orders of magnitude for general choices of the model
parameters, but depends only weakly on the flavour mixing pattern within the
parameter range that is preferred by neutrino oscillation data.Comment: 29 pages, 8 figures, 3 tables, version accepted by JHE
Searching for New Long Lived Particles in Heavy Ion Collisions at the LHC
We show that heavy ion collisions at the LHC provide a promising environment
to search for new long lived particles in well-motivated New Physics scenarios.
One advantage lies in the possibility to operate the main detectors with looser
triggers, which can increase the number of observable events by orders of
magnitude if the long lived particles are produced with low transverse
momentum. In addition, the absence of pileup in heavy ion collisions can avoid
systematic nuisances that will be present in future proton runs, such as the
problem of vertex mis-identification. Finally, there are new production
mechanisms that are absent or inefficient in proton collisions. We show that
the looser triggers alone can make searches in heavy ion data competitive with
proton data for the specific example of heavy neutrinos in the Neutrino Minimal
Standard Model, produced in the decay of B mesons. Our results suggest that
collisions of ions lighter than lead, which are currently under discussion in
the heavy ion community, are well-motivated from the viewpoint of searches for
New Physics.Comment: Version accepted by Physical Review Letters for publication as a
Letter. 6 pages, 3 figure
Heavy Higgs Bosons at Low : from the LHC to 100 TeV
We present strategies to search for heavy neutral Higgs bosons decaying to
top quark pairs, as often occurs at low in type II two Higgs
doublet models such as the Higgs sector of the MSSM. The resonant production
channel is unsatisfactory due to interference with the SM background. We
instead propose to utilize same-sign dilepton signatures arising from the
production of heavy Higgs bosons in association with one or two top quarks and
subsequent decay to a top pair. We find that for heavier neutral Higgs bosons
the production in association with one top quark provides greater sensitivity
than production in association with two top quarks. We obtain current limits at
the LHC using Run I data at 8 TeV and forecast the sensitivity of a dedicated
analysis during Run II at 14 TeV. Then we perform a detailed BDT study for the
14 TeV LHC and a future 100 TeV collider.Comment: published version, 22 pages, 15 figures, 3 table
Heavy Higgs Bosons at 14 TeV and 100 TeV
Searching for Higgs bosons beyond the Standard Model (BSM) is one of the most
important missions for hadron colliders. As a landmark of BSM physics, the MSSM
Higgs sector at the LHC is expected to be tested up to the scale of the
decoupling limit of O(1) TeV, except for a wedge region centered around
, which has been known to be difficult to probe. In this
article, we present a dedicated study testing the decoupled MSSM Higgs sector,
at the LHC and a next-generation -collider, proposing to search in channels
with associated Higgs productions, with the neutral and charged Higgs further
decaying into and , respectively. In the case of neutral Higgs we are
able to probe for the so far uncovered wedge region via . Additionally, we cover the the high range with . The combination of these searches with channels dedicated to
the low region, such as and potentially covers the full range. The search for charged
Higgs has a slightly smaller sensitivity for the moderate region,
but additionally probes for the higher and lower regions with even
greater sensitivity, via . While the LHC will be able
to probe the whole range for Higgs masses of O(1) TeV by combining
these channels, we show that a future 100 TeV -collider has a potential to
push the sensitivity reach up to TeV. In order to deal
with the novel kinematics of top quarks produced by heavy Higgs decays, the
multivariate Boosted Decision Tree (BDT) method is applied in our collider
analyses. The BDT-based tagging efficiencies of both hadronic and leptonic
top-jets, and their mutual fake rates as well as the faking rates by other jets
(, , , , etc.) are also presented.Comment: published versio
Testing Naturalness
Solutions to the electroweak hierarchy problem typically introduce a new
symmetry to stabilize the quadratic ultraviolet sensitivity in the self-energy
of the Higgs boson. The new symmetry is either broken softly or collectively,
as for example in supersymmetric and little Higgs theories. At low energies
such theories contain naturalness partners of the Standard Model fields which
are responsible for canceling the quadratic divergence in the squared Higgs
mass. Post the discovery of any partner-like particles, we propose to test the
aforementioned cancellation by measuring relevant Higgs couplings. Using the
fermionic top partners in little Higgs theories as an illustration, we
construct a simplified model for naturalness and initiate a study on testing
naturalness. After electroweak symmetry breaking, naturalness in the top sector
requires at leading order, where and
are the Higgs couplings to a pair of top quarks and top partners, respectively.
Using a multivariate method of Boosted Decision Tree to tag boosted particles
in the Standard Model, we show that, with a luminosity of 30 at a 100
TeV -collider, naturalness could be tested with a precision of 10 % for a
top partner mass up to 2.5 TeV.Comment: 20 pages, 7 figures, 2 table
Proximity Induced Superconductivity in CdTe-HgTe Core-Shell Nanowires
In this letter we report on proximity superconductivity induced in CdTe-HgTe
core-shell nanowires, a quasi-one-dimensional heterostructure of the
topological insulator HgTe. We demonstrate a Josephson supercurrent in our
nanowires contacted with superconducting Al leads. The observation of a sizable
product, a positive excess current and multiple Andreev reflections
up to fourth order further indicate a high interface quality of the junctions.Comment: Accepted for publication in Nano Letter
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