766 research outputs found
Inclusive Displaced Vertex Searches for Heavy Neutral Leptons at the LHC
The inclusion of heavy neutral leptons to the Standard Model particle content
could provide solutions to many open questions in particle physics and
cosmology. The modification of the charged and neutral currents from
active-sterile mixing of neutral leptons can provide novel signatures in
Standard Model processes. We revisit the displaced vertex signature that could
occur in collisions at the LHC via the decay of heavy neutral leptons with
masses of a few GeV emphasizing the implications of flavor, kinematics,
inclusive production and number of these extra neutral fermions. We study in
particular the implication on the parameter space sensitivity when all mixings
to active flavors are taken into account. We also discuss alternative cases
where the new particles are produced in a boosted regime.Comment: 24 pages, 10 figures. Extended analysis. Published versio
Probing new physics with displaced vertices: muon tracker at CMS
Long-lived particles can manifest themselves at the LHC via "displaced
vertices" - several charged tracks originating from a position separated from
the proton interaction point by a macroscopic distance. Here we demonstrate a
potential of the muon trackers at the CMS experiment for displaced vertex
searches. We use heavy neutral leptons and Chern-Simons portal as two examples
of long-lived particles for which the CMS muon tracker can provide essential
information about their properties.Comment: Journal versio
Collider Searches for Long-Lived Particles Beyond the Standard Model
Experimental tests of the Standard Model of particle physics (SM) find
excellent agreement with its predictions. Since the original formation of the
SM, experiments have provided little guidance regarding the explanations of
phenomena outside the SM, such as the baryon asymmetry and dark matter. Nor
have we understood the aesthetic and theoretical problems of the SM, despite
years of searching for physics beyond the Standard Model (BSM) at particle
colliders. Some BSM particles can be produced at colliders yet evade being
discovered, if the reconstruction and analysis procedures not matched to
characteristics of the particle. An example is particles with large lifetimes.
As interest in searches for such long-lived particles (LLPs) grows rapidly, a
review of the topic is presented in this article. The broad range of
theoretical motivations for LLPs and the experimental strategies and methods
employed to search for them are described. Results from decades of LLP searches
are reviewed, as are opportunities for the next generation of searches at both
existing and future experiments.Comment: 79 pages, 36 figures, submitted to Progress in Particle and Nuclear
Physic
Looking for the left sneutrino LSP with displaced-vertex searches
We analyze a displaced dilepton signal expected at the LHC for a tau left
sneutrino as the lightest supersymmetric particle with a mass in the range
- GeV. The sneutrinos are pair produced via a virtual , or
in the channel and, given the large value of the tau Yukawa
coupling, their decays into two dileptons or a dilepton plus missing transverse
energy from neutrinos can be significant. The discussion is carried out in the
SSM, where the presence of -parity violating couplings involving
right-handed neutrinos solves the problem and can reproduce the neutrino
data. To probe the tau left sneutrinos we compare the predictions of the SSM with the ATLAS search for long-lived particles using displaced lepton
pairs in collisions at TeV, allowing us to constrain the
parameter space of the model. We also consider an optimization of the trigger
requirements used in existing displaced-vertex searches by means of a High
Level Trigger that exploits tracker information. This optimization is
generically useful for a light metastable particle decaying into soft charged
leptons. The constraints on the sneutrino turn out to be more stringent. We
finally discuss the prospects for the TeV LHC searches as well as further
potential optimizations.Comment: Version published in PRD, discussions expanded, references added, LEP
and LHC constraints discussed in more detail, 29 pages, 9 figures, 9 table
The experimental status of direct searches for exotic physics beyond the standard model at the Large Hadron Collider
The standard model of particle physics is an extremely successful theory of
fundamental interactions, but it has many known limitations. It is therefore
widely believed to be an effective field theory that describes interactions
near the TeV scale. A plethora of strategies exist to extend the standard
model, many of which contain predictions of new particles or dynamics that
could manifest in proton-proton collisions at the Large Hadron Collider (LHC).
As of now, none have been observed, and much of the available phase space for
natural solutions to outstanding problems is excluded. If new physics exists,
it is therefore either heavy (i.e. slightly above the reach of current
searches) or hidden (i.e. currently indistinguishable from standard model
backgrounds). We summarize the existing searches, and discuss future directions
at the LHC.Comment: 33 pages, 7 figure
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Search for long-lived, massive particles decaying into dimuon vertices in pp collisions at 13 TeV with the ATLAS detector at the LHC
A search for long-lived, massive particles decaying into dimuon pairs, in 32.9 fb-1 of data analyzed from the ATLAS detector is presented. Two signal models are considered: GGM SUSY, where the long lived particle mass is between 300-1000 GeV, and the dark photon model, where the ZD mass is between 20-60 GeV. An excess over the predicted background is observed in the GGM channel, however the angular/kinematic distributions of the excess vertices are consistent with a detec- tor/conditions related issue. A modified selection is used for the GGM channel which increases the signal sensitivity. 95% confidence level (CL) upper limits on the signal cross sections times branching fraction are set as a function of cτ for both benchmark models. The cτ limits for the GGM channel extend from 2.57-1050 cm, and the cτ limit for the ZD channel extends from 0.32-1572 cm. 95% CL upper limits on the ZD cross section are also set in the coupling-cτ plane, for a range of BF(H→ ZDZD)
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