Search results for "STANDARD MODEL"
showing 10 items of 1206 documents
Results of the NA31 Experiment on K0Decays
1989
Decays of neutral kaons are of high interest in high energy physics. The discovery of CP violation1 opened up a field of new physics. Today, interest is concentrated on precision measurements of CP-violating parameters as well as on searches for rare decays that are suppressed or forbidden in the standard model.
Measurement of the e+e- → ZZ production cross section at centre-of-mass energies of 183 and 189 GeV
1999
The ee -> ZZ cross section at sqrt(s)=182.7 and 188.6 GeV has been measured using the ALEPH detector. The analysis covers all of the visible ZZ final states and yields cross section measurements of sigma_ZZ(182.7 GeV) = 0.11 +- (0.16,0.11) (stat.) +- 0.04 (syst.) pb and sigma_ZZ(188.6 GeV) = 0.67 +- 0.13 (stat.) +- 0.04 (syst.) pb consistent with the Standard Model expectations.
Towards high-precision mass measurements on 74Rb for a test of the CVC hypothesis and the unitarity of the CKM matrix
2004
At the highest possible precisions, atomic-mass measurements can be used to perform fundamental studies. Examples for such studies are a check of the conserved-vector-current (CVC) hypothesis and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, both postulates of the Standard Model. The comparative half-lives Ft of superallowed β decays constitute the nuclear-physics access to these tests. The Q value of the β decay of 74 Rb, one of the three experimentally accessible parameters that enter into the Ft values, has been measured with the ISOLTRAP experiment at ISOLDE/CERN. The ultimate mass precision requirement and the way to achieve it are outlined.
Cosmological promising parameters of stau in the minimal supersymmetric standard model
2009
We find that we can account for the possible descrepancy of the primordial abundance of 7 Li between the observation and the prediction of the Big-Bang Nucleosynthesis in a scenario of the Big-Bang Nucleosynthesis with the Minimal Supersymmetric Standard Model. This scenario is consistent with a stau-neutralino coannihilation scenario to explain the relic abundance of dark matter. The solution to the discrepancy is given by taking the values of parameters; the mass of the neutralino as 300 GeV and the mass difference between the stau and the neutralino as (100 – 120) MeV.
Search for a light Higgs resonance in radiative decays of theϒ(1S)with a charm tag
2015
A search is presented for the decay Υ(1S)→ γA^0, A^0 → cc[bar], where A^0 is a candidate for the CP-odd Higgs boson of the next-to-minimal supersymmetric standard model. The search is based on data collected with the BABAR detector at the Υ(2S) resonance. A sample of Υ(1S) mesons is selected via the decay Υ(2S)→π + π − Υ(1S). The A^0 → cc[bar] decay is identified through the reconstruction of hadronic D^0, D^+, and D^∗ (2010)^+ meson decays. No significant signal is observed. The measured 90% confidence-level upper limits on the product branching fraction B(Υ(1S) → γA^0 ) × B(A^0 → cc[bar] ) range from 7.4×10^(−5) to 2.4×10^(−3) for A^0 masses from 4.00 to 8.95 GeV/c^2 and 9.10 to 9.25 Ge…
Constraints to new physics models for the proton charge radius puzzle from the decayK+→μ++ν+e−+e+
2014
A possible explanation for the discrepancy between electronic and muonic hydrogen measurements of the proton charge radius are new, lepton-universality violating interactions. Several new couplings and particles have been suggested that account for this discrepancy. At present, these explanations are poorly constrained. Experiments such as the upcoming kaon decay experiment at JPARC may constrain or eliminate some explanations by sensitivity to the decay channel $K^+ \rightarrow \mu^+ +\nu + e^- + e^+$. We calculate the predicted contributions of the various explanations to this channel. The predicted signals, if present, should be large enough to be resolved in the experiment.
Search for new physics in beta-neutrino correlations with the WITCH spectrometer
2002
The WITCH (Weak Interaction Trap for CHarged particles) experiment is a retardation spectrometer coupled to a Penning trap and measures the beta-neutrino angular correlation via the shape of the recoil energy spectrum. The present form of the Standard Model describes weak processes in terms of vector and axial-vector type interactions, but the possible presence of scalar and tensor interactions is not yet ruled out. The main aim of this experiment is a test of the Standard Model for possible admixture of scalar and tensor currents. (C) 2002 Elsevier Science B.V. All rights reserved.
Inclusive B ¯ → X s ℓ + ℓ − $$ \overline{B}\to {X}_s{\ell}^{+}{\ell}^{-} $$ : complete angular analysis and a thorough study of collinear photons
2015
We investigate logarithmically enhanced electromagnetic corrections of all angular observables in inclusive $$ \overline{B}\to {X}_s{\ell}^{+}{\ell}^{-} $$ . We present analytical results, which are supplemented by a dedicated Monte Carlo study on the treatment of collinear photons in order to determine the size of the electromagnetic logarithms. We then give the Standard Model predictions of all observables, considering all available NNLO QCD, NLO QED and power corrections, and investigate their sensitivity to New Physics. Since the structure of the double differential decay rate is modified in the presence of QED corrections, we also propose new observables which vanish if only QCD correc…
Leptons and QCD
2015
Three important QCD-related aspects of the τ and μ dynamics are reviewed: the determination of the strong coupling from the hadronic tau decay width, leading to the updated value αs(mτ2)=0.331±0.013; the measurement of |Vus| through the Cabibbo-suppressed decays of the τ, and the Standard Model prediction for the muon anomalous magnetic moment.
Search for flavor-changing neutral current and lepton-flavor violating decays of D-0 -> l(+)l(-)
2004
We report on a search for the flavor-changing neutral current decays $\Dz\to e^+e^-$ and $\Dz\to\mu^+\mu^-$, and the lepton-flavor violating decay $\Dz\to e^\pm\mu^\mp$. The measurement is based on $122 {fb}^{-1}$ of data collected by the \babar detector at the PEP-II asymmetric $e^+e^-$ collider. No evidence is found for any of the decays. The upper limits on the branching fractions, at the 90 % confidence level, are $1.2\times 10^{-6}$ for $\Dz\to e^+e^-$, $1.3\times 10^{-6}$ for $\Dz\to\mu^+\mu^-$, and $8.1\times 10^{-7}$ for $\Dz\to e^\pm\mu^\mp$.