Search results for " Standard Model"
showing 10 items of 645 documents
Search for massive long-lived highly ionising particles with the ATLAS detector at the LHC
2011
A search is made for massive highly ionising particles with lifetimes in excess of 100 ns, with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb-1 of pp collision data taken at √s = 7TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e ≤ |q| ≤ 17e and masses 200 GeV ≤ m ≤ 1000 GeV are set in the range 1–12 pb for different hypotheses on the production mechanism.
A road map to solar neutrino fluxes, neutrino oscillation parameters, and tests for new physics
2003
We analyze all available solar and related reactor neutrino experiments, as well as simulated future 7Be, p-p, pep, and ^8B solar neutrino experiments. We treat all solar neutrino fluxes as free parameters subject to the condition that the total luminosity represented by the neutrinos equals the observed solar luminosity (the `luminosity constraint'). Existing experiments show that the p-p solar neutrino flux is 1.02 +- 0.02 (1 sigma) times the flux predicted by the BP00 standard solar model; the 7Be neutrino flux is 0.93^{+0.25}_{-0.63} the predicted flux; and the ^8B flux is 1.01 +- 0.04 the predicted flux. The neutrino oscillation parameters are: Delta m^2 = 7.3^{+0.4}_{-0.6}\times 10^{-…
Atmospheric neutrino oscillations and new physics
2004
We study the robustness of the determination of the neutrino masses and mixing from the analysis of atmospheric and K2K data under the presence of different forms of phenomenologically allowed new physics in the nu_mu--nu_tau sector. We focus on vector and tensor-like new physics interactions which allow us to treat, in a model independent way, effects due to the violation of the equivalence principle, violations of the Lorentz invariance both CPT conserving and CPT violating, non-universal couplings to a torsion field and non-standard neutrino interactions with matter. We perform a global analysis of the full atmospheric data from SKI together with long baseline K2K data in the presence of…
Resolving the octant of theta(23) with T2K and NOvA
2013
Preliminary results of MINOS experiment indicate that theta(23) is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for theta(23): one in the lower octant (LO: theta(23) 45 degrees). v(mu) -> v(e) oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NOvA experiments. Because of the hierarchy-delta(CP) degeneracy and the octant delta(CP) degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of delta(CP) fo…
Minimal flavor violation in the see-saw portal
2020
We consider an extension of the Standard Model with two singlet leptons, with masses in the electroweak range, that induce neutrino masses via the see-saw mechanism, plus a generic new physics sector at a higher scale, $\Lambda$. We apply the minimal flavor violation (MFV) principle to the corresponding Effective Field Theory ($\nu$SMEFT) valid at energy scales $E \ll \Lambda$. We identify the irreducible sources of lepton flavor and lepton number violation at the renormalizable level, and apply the MFV ans\"atz to derive the scaling of the Wilson coefficients of the $\nu$SMEFT operators up to dimension six. We highlight the most important phenomenological consequences of this hypothesis in…
Probes of the Standard Model effective field theory extended with a right-handed neutrino
2019
If neutrinos are Dirac particles and, as suggested by the so far null LHC results, any new physics lies at energies well above the electroweak scale, the Standard Model effective field theory has to be extended with operators involving the right-handed neutrinos. In this paper, we study this effective field theory and set constraints on the different dimension-six interactions. To that aim, we use LHC searches for associated production of light (and tau) leptons with missing energy, monojet searches, as well as pion and tau decays. Our bounds are generally above the TeV for order one couplings. One particular exception is given by operators involving top quarks. These provide new signals in…
New global fits to $b \to s$ data with all relevant parameters
2018
The LHCb experiment has made several measurements in $b \to s$ transitions which indicate tensions with the Standard Model predictions. Assuming the source of these tensions to be new physics, we present new global fits to all Wilson coefficients which can effectively receive beyond the Standard Model contributions. While the theoretically clean ratios $R_{K^{(*)}}$ which are sensitive to lepton flavour non-universality may unambiguously establish lepton non-universal new physics in the near future, most of the other tensions with the SM in the $b \to s$ data, in particular in the angular observables of the $B\to K^* \mu\mu$ decay and in the branching ratio of the $B_s \to \phi \mu\mu$ deca…
Search for Neutral Higgs Bosons in Events with Multiple Bottom Quarks at the Tevatron
2012
The combination of searches performed by the CDF and D0 collaborations at the Fermilab Tevatron Collider for neutral Higgs bosons produced in association with b quarks is reported. The data, corresponding to 2.6fb -1 of integrated luminosity at CDF and 5.2fb -1 at D0, have been collected in final states containing three or more b jets. Upper limits are set on the cross section multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson. Significant enhancements to the production of Higgs bosons can be found in theories beyond the standard model, for example, in supersymmetry. The results are int…
Measuring the top energy asymmetry at the LHC: QCD and SMEFT interpretations
2020
The energy asymmetry in top-antitop-jet production is an observable of the top charge asymmetry designed for the LHC. We perform a realistic analysis in the boosted kinematic regime, including effects of the parton shower, hadronization and expected experimental uncertainties. Our predictions at particle level show that the energy asymmetry in the Standard Model can be measured with a significance of $3\sigma$ during Run 3, and with more than $5\sigma$ significance at the HL-LHC. Beyond the Standard Model the energy asymmetry is a sensitive probe of new physics with couplings to top quarks. In the framework of the Standard Model Effective Field Theory, we show that the sensitivity of the en…
Multilepton dark matter signals
2020
The signatures of dark matter at the LHC commonly involve, in simplified scenarios, the production of a single particle plus large missing energy, from the undetected dark matter. However, in $Z'$-portal scenarios anomaly cancellation requires the presence of extra dark leptons in the dark sector. We investigate the signatures of the minimal scenarios of this kind, which involve cascade decays of the extra $Z'$ boson into the dark leptons, identifying a four-lepton signal as the most promising one. We estimate the sensitivity to this signal at the LHC, the high-luminosity LHC upgrade, a possible high-energy upgrade, as well as a future circular collider. For $Z'$ couplings compatible with c…