Search results for "Standard Model"
showing 10 items of 1206 documents
New opportunities at the next-generation neutrino experiments I: BSM neutrino physics and dark matter
2020
Abstract The combination of the high intensity proton beam facilities and massive detectors for precision measurements of neutrino oscillation parameters including the charge-parity violating (CPV) phase will open the door to help make beyond the standard model (BSM) physics reachable even in low energy regimes in the accelerator-based experiments. Large-mass detectors with highly precise tracking and energy measurements, excellent timing resolution, and low energy thresholds will enable the searches for BSM phenomena from cosmogenic origin, as well. Therefore, it is also conceivable that BSM topics in the next-generation neutrino experiments could be the dominant physics topics in the fore…
Can we probe intrinsic CP and T violations and nonunitarity at long baseline accelerator experiments?
2017
One of the fundamental parameters entering the neutrino oscillation framework is the leptonic $CP$ phase ${\ensuremath{\delta}}_{13}$, and its measurement is an important goal of the planned long baseline experiments. It should be noted that ordinary matter effects complicate the determination of this parameter, and there are studies in the literature that deal with separation of intrinsic vs extrinsic $CP$ violation. It is important to investigate the consequences of new physics effects that can not only hamper the measurement of ${\ensuremath{\delta}}_{13}$ but also impact the consequences of discrete symmetries such as $CP$, $T$, and unitarity in different oscillation channels. In the pr…
R-Parity Breaking in Minimal Supergravity
1999
We consider the Minimal Supergravity Model with universality of scalar and gaugino masses plus an extra bilinear term in the superpotential which breaks R-Parity and lepton number. We explicitly check the consistency of this model with the radiative breaking of the electroweak symmetry. A neutrino mass is radiatively induced, and large Higgs-Lepton mixings are compatible with its experimental bound. We also study briefly the lightest Higgs mass. This one-parameter extension of SUGRA-MSSM is the simplest way of introducing R-parity violation.
Search for the Scalar Top Quark inpp¯Collisions ats=1.8TeV
2002
We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of p (p) over bar events corresponding to 108.3 pb (-1) of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, (t) over tilde-->b (χ) over tilde (+)(1) and (t) over tilde-->bl (ν) over tilde , no evidence for signal is found. We derive cross-section limits as a function of stop ((t) over tilde), chargino ((χ) over tilde (+)(1)), and sneutrino ((ν) …
Charged Higgs signals in tt¯H searches
2017
New scalars from an extended Higgs sector could have weak scale masses and still have escaped detection. In a type I two Higgs doublet model, for instance, even the charged Higgs can be lighter than the top quark. Because electroweak production of these scalars is modest, the greatest opportunity for their detection might come from rare top decays. For mass hierarchies of the type ${m}_{t}g{m}_{{H}^{+}}g{m}_{{A}^{0},{H}^{0}}$, the natural signal can arise from top quark pair production, followed by the decay chain $t\ensuremath{\rightarrow}b{H}^{+}$, ${H}^{+}\ensuremath{\rightarrow}{W}^{+(*)}{\ensuremath{\phi}}^{0}$, ${\ensuremath{\phi}}^{0}\ensuremath{\rightarrow}b\overline{b},{\ensuremath…
Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying into W±W∓ or ZZ in Fully Hadronic Final States from s=13 TeV pp Coll…
2021
Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W^{±}W^{∓} or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb^{-1} of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The s→V(qq[over ¯])V(qq[over ¯]) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with m_{s}>160 GeV are excluded.
The W and Z boson spin observables as messengers of New Physics at LHC
2017
The successful LHC operation suggests going beyond the search of excess of events for the quest of new physics. We demonstrate that the eight multipole parameters describing the spin state of the W or Z bosons are able to disentangle their hidden production mechanism. They can be separately extracted from well defined angular asymmetries in the leptonic distribution of boson decays. The discriminating power of this analysis is well illustrated by: (i) polarised top quark decays, (ii) two body decay of heavy resonances, (iii) Drell-Yan production of Z plus jets, (iv) Z boson plus missing transverse energy.
Perturbative Unitarity Constraints on Charged/Colored Portals
2015
Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak or QCD phase transitions. This implies a new scale of physics and mediator particles needed to facilitate dark matter annihilations. In this work, we consider scenarios where thermal dark matter annihilates via scalar mediators that are colored and/or electrically charged. We show how partial wave unitarity places upper bounds on the masses and couplings on both the dark matter and mediators. To do this, we employ effective field theories with dark matter as well as three flavors of sleptons or squarks with minimum flavor violation. For Dirac (…
Perturbative unitarity constraints on the NMSSM Higgs Sector
2018
Abstract We place perturbative unitarity constraints on both the dimensionful and dimensionless parameters in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) Higgs Sector. These constraints, plus the requirement that the singlino and/or Higgsino constitutes at least part of the observed dark matter relic abundance, generate upper bounds on the Higgs, neutralino and chargino mass spectrum. Requiring higher-order corrections to be no more than 41% of the tree-level value, we obtain an upper bound of 20 TeV for the heavy Higgses and 12 TeV for the charginos and neutralinos outside defined fine-tuned regions. If the corrections are no more than 20% of the tree-level value, the bounds …
Probing CP violation with non-unitary mixing in long-baseline neutrino oscillation experiments: DUNE as a case study
2016
When neutrino masses arise from the exchange of neutral heavy leptons, as in most seesaw schemes, the effective lepton mixing matrix $N$ describing neutrino propagation is non-unitary, hence neutrinos are not exactly orthonormal. New CP violation phases appear in $N$ that could be confused with the standard phase $\delta_{\text{CP}}$ characterizing the three neutrino paradigm. We study the potential of the long-baseline neutrino experiment DUNE in probing CP violation induced by the standard CP phase in the presence of non-unitarity. In order to accomplish this we develop our previous formalism, so as to take into account the neutrino interactions with the medium, important in long baseline…