Search results for "physics beyond the Standard Model"
showing 10 items of 449 documents
A search for new physics in dijet mass and angular distributions in pp collisions at [subscript √s=7] TeV measured with the ATLAS detector
2011
A search for new interactions and resonances produced in LHC proton–proton (pp) collisions at a centre-of-mass energy ps = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb−1, dijet mass and angular distributions were measured up to dijet masses of 3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space–time dimensions for quantum gravity…
Inclusive search for same-sign dilepton signatures in pp collisions at $ sqrt {s} = 7 $ TeV with the ATLAS detector
2011
An inclusive search is presented for new physics in events with two isolated leptons (e or mu) having the same electric charge. The data are selected from events collected from p p collisions at root s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb(-1). The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, e mu and mu mu channels. Four models predic…
Vacuum Induced CP Violation Generating a Complex CKM Matrix with Controlled Scalar FCNC
2018
We propose a viable minimal model with spontaneous CP violation in the framework of a two Higgs doublet model. The model is based on a generalised Branco–Grimus–Lavoura model with a flavoured Z2 symmetry, under which two of the quark families are even and the third one is odd. The lagrangian respects CP invariance, but the vacuum has a CP violating phase, which is able to generate a complex CKM matrix, with the rephasing invariant strength of CP violation compatible with experiment. The question of scalar mediated flavour changing neutral couplings is carefully studied. In particular we point out a deep connection between the generation of a complex CKM matrix from a vacuum phase and the ap…
Vector-like quarks and New Physics in the flavour sector
2013
We present a detailed analysis of recent flavour data in the framework of a simple extension of the Standard Model, where a Q = 2/3 vector-like isosinglet quark is added to the spectrum. Constraints from all the relevant quark flavour sectors are used. Important deviations from Standard Model expectations in different observables such as the semileptonic asymmetry in Bd decays, AdSL, the time-dependent CP asymmetry in Bs ? J/??, and rare decays such as K+ ? ?+? can be obtained.
Top physics studies at the LHC in the standard model and beyond with the ATLAS detector
2009
The LHC will be a Top quark factory, producing large numbers of Top quarks even at the initial low luminosities. This will enable a rich program of Top quark Physics to be explored, both within the Standard Model and using Top quarks as probes of Physics Beyond the Standard Model. Recent studies from ATLAS will be presented, including prospects for the measurements of the production of Top pairs and single Top production, angular correlations in the Top decay, and the precision measurement of the Top quark mass. The search for Physics beyond the Standard Model will be illustrated with searches for rare Top decays involving Flavour Changing Neutral Currents, and the reconstruction of tt-bar …
The $Z$ boson in the Framed Standard Model
2018
The framed standard model (FSM), constructed initially for explaining the existence of three fermion generations and the hierarchical mass and mixing patterns of quarks and leptons, suggests also a "hidden sector" of particles including some dark matter candidates. It predicts in addition a new vector boson $G$, with mass of order TeV, which mixes with the $\gamma$ and $Z$ of the standard model yielding deviations from the standard mixing scheme, all calculable in terms of a single unknown parameter $m_G$. Given that standard mixing has been tested already to great accuracy by experiment, this could lead to contradictions, but it is shown here that for the three crucial and testable cases s…
Search for squark production in events with jets, hadronically decaying tau leptons and missing transverse energy at s=1.96 TeV
2009
A search for supersymmetric partners of quarks is performed in the topology of multijet events accompanied by at least one tau lepton decaying hadronically and large missing transverse energy. Approximately 1 fb(-1) of p (p) over bar collision data from the Fermilab Tevatron Collider at a center of mass energy of 1.96 TeV recorded by the D detector is analyzed. Results are combined with the previously published DO inclusive search for squarks and gluinos. No evidence of physics beyond the Standard Model is found and lower limits on the squark mass up to 410 GeV are derived in the framework of minimal supergravity with tan beta = 15, A(0) = -2m(0) and mu < 0, in the region where decays to ta…
Search for scalar leptoquarks and T-odd quarks in the acoplanar jet topology using of collision data at
2008
A search for new physics in the acoplanar jet topology has been performed in 2.5 fb(-1) of data from p (p) over bar collisions at root s = 1.96 TeV, recorded by the DO detector at the Fermilab Tevatron Collider. The numbers of events with exactly two acoplanar jets and missing transverse energy are in good agreement with the Standard Model expectations. The result of this search has been used to set a lower mass limit of 205 GeV at the 95% C.L. on the mass of a scalar leptoquark when this particle decays exclusively into a quark and a neutrino. In the framework of the Little Higgs model with T-parity, limits have also been obtained on the T-odd quark mass as a function of the T-odd photon m…
Nonstandard Yukawa couplings and Higgs portal dark matter
2015
We study the implications of non-standard Higgs Yukawa couplings to light quarks on Higgs-portal dark matter phenomenology. Saturating the present experimental bounds on up-quark, down-quark, or strange-quark Yukawa couplings, the predicted direct dark matter detection scattering rate can increase by up to four orders of magnitude. The effect on the dark matter annihilation cross section, on the other hand, is subleading unless the dark matter is very light -- a scenario that is already excluded by measurements of the Higgs invisible decay width. We investigate the expected size of corrections in multi-Higgs-doublet models with natural flavor conservation, the type-II two-Higgs-doublet mode…
New physics effects in tree-level decays and the precision in the determination of the quark mixing angle γ.
2015
We critically review the assumption that no new physics is acting in tree-level B-meson decays and study the consequences for the ultimate precision in the direct determination of the Cabibbo-Kobayashi-Maskawa (CKM) angle γ. In our exploratory study we find that sizeable universal new physics contributions, ΔC1,2, to the tree-level Wilson coefficients C1,2 of the effective Hamiltonian describing weak decays of the b quark are currently not excluded by experimental data. In particular, we find that ImΔC1 and ImΔC2 can easily be of order ±10% without violating any constraints from data. Such a size of new physics effects in C1 and C2 corresponds to an intrinsic uncertainty in the CKM angle γ …