Search results for "Standard"
showing 10 items of 3299 documents
Flavour Symmetries and SUSY Soft Breaking in the LHC Era
2007
The so-called supersymmetric flavour problem does not exist in isolation to the Standard Model flavour problem. We show that a realistic flavour symmetry can simultaneously solve both problems without ad hoc modifications of the SUSY model. Furthermore, departures from the SM expectations in these models can be used to discriminate among different possibilities. In particular we present the expected values for the electron EDM in a flavour model solving the supersymmetric flavour and CP problems.
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 …
Searches for sleptons and squarks in e(+)e(-) collisions at 189 GeV
1999
The data collected at a centre-of-mass energy of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 173.6 pb$^{-1}$, are analysed in a search for the scalar partners of quarks and leptons predicted in supersymmetric models. No evidence for any such particles was found in the decay channels $\sle \to \ell \chi$, $\stop \rightarrow \mathrm{c}\neu$, $\stop \rightarrow \mathrm{b}\ell\snu$, $\sbot \rightarrow \mathrm{b}\neu$, and $\mathrm{\tilde{q}} \rightarrow \mathrm{q}\neu$. Improved mass lower limits have been obtained in the framework of the Minimal Supersymmetric Standard Model.
Review of Particle Properties
2002
This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 2205 new measurements from 667 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations. For the fir…
Search for W′ boson production in the W′→tb¯ decay channel
2006
We present a search for the production of a new heavy gauge boson W' that decays to a top quark and a bottom quark. We have analyzed 230 pb(-1) of data collected with the DO detector at the Fermilab Tevatron collider at a center-of-mass energy of 1.96 TeV. No significant excess of events above the standard model expectation is found in any region of the final state invariant mass distribution. We set upper limits on the production cross section of W' bosons times branching ratio to top quarks at the 95% confidence level for several different W, boson masses. We exclude masses between 200 and 610 GeV for a W' boson with standard-model-like couplings, between 200 and 630 GeV for a W, boson wi…
Two-loop gluino corrections to the inclusive decayB→Xsγin theCPviolating MSSM with largetanβ
2004
We investigate two-loop gluino corrections to the effective Lagrangian for b{yields}s+{gamma}(g) in the minimal supersymmetric extension of the standard model (MSSM) at large tan{beta}, including the contributions in which quark flavor change is mediated by charginos. Using the translation invariance of loop momenta and the Ward-Takahashi identities that are required by the SU(3){sub c}xU(1){sub em} gauge invariance, we simplify our expressions to concise forms. As an example, we discuss two-loop gluino corrections to the CP asymmetry of inclusive B{yields}X{sub s}{gamma} decay in CP violating MSSM.
Search for new particles leading toZ+jetsfinal states inpp¯collisions ats=1.96 TeV
2007
We present the results of a search for new particles that lead to a Z boson plus jets in p{bar p} collisions at {radical}s = 1.96 TeV using the Collider Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 fb{sup -1} collected using Z boson decays to ee and {mu}{mu} is used. We describe a completely data-based method to predict the dominant background from standard-model Z+jet events. This method can be similarly applied to other analyses requiring background predictions in multi-jet environments, as shown when validating the method by predicting the background from W+jets in t{bar t} production. No significant excess above the background prediction is observed, and a limi…
Quark mixing in the discrete dark matter model
2011
We consider a model in which dark matter is stable as it is charged under a Z2 symmetry that is residual after an A4 flavour symmetry is broken. We consider the possibility to generate the quark masses by charging the quarks appropriately under A4. We find that it is possible to generate the CKM mixing matrix by an interplay of renormalisable and dimension-six operators. In this set-up, we predict the third neutrino mixing angle to be large and the dark matter relic density to be in the correct range. However, low energy observables - in particular meson-antimeson oscillations - strongly limit the available parameter space.
Two-Higgs leptonic minimal flavour violation
2011
We construct extensions of the Standard Model with two Higgs doublets, where there are flavour changing neutral currents both in the quark and leptonic sectors, with their strength fixed by the fermion mixing matrices $V_{CKM}$ and $V_{PMNS}$. These models are an extension to the leptonic sector of the class of models previously considered by Branco, Grimus and Lavoura, for the quark sector. We consider both the cases of Dirac and Majorana neutrinos and identify the minimal discrete symmetry required in order to implement the models in a natural way.
Search for scalar top quarks in the acoplanar charm jets and missing transverse energy final state in pp¯ collisions at s=1.96 TeV
2008
We present a search for the pair production of scalar top quarks, $\tilde{t}$, using 995 pb$^{-1}$ of data collected in $p\bar{p}$ collisions with the D0 detector at the Fermilab Tevatron Collider at $\sqrt{s} = 1.96$ TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino ($\tilde{\chi}^{0}_{1}$), where $\tilde{\chi}^{0}_{1}$ is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. We find the yield of such events to be consistent with the standard model expectation, and exclude sets of $\tilde{t}$ and $\tilde{\chi}^{0}_{1} $ masses at the 95% C.L. that substantially extend the domain excl…