Search results for "annihilation"
showing 10 items of 1016 documents
Tau leptonic branching ratios
1996
A sample of 62249 tau-pair events is selected from data taken with the ALEPH detector in 1991, 1992 and 1993. The measurement of the branching fractions for tau decays into electrons and muons is presented with emphasis on the study of systematic effects from selection, particle identification and decay classification. The results obtained are: B-e=17.79+/-0.12(stat)+/-0.06(syst)(%) and B-mu=17.31+/-0.11(stat)+/-0.05(syst)(%). Combined with the most recent ALEPH determination of the tau lifetime, these results provide a relative measurement of the leptonic couplings in the weak charged current for transverse W bosons: g(mu)/g(e)=1.0002+/-0.0051 and g(tau)/g(mu)=0.9943+/-0.0065. RI ANTONELLI…
A Search for Sleptons and Gauginos in Z0 Decays
1990
Using a data sample corresponding to 10 000 hadronic Z0 decays, we have searched for the production of sleptons and gauginos in the two-prong decays of Z0. No candidate remains after straightforward selections. For neutralinos, we use selection methods developed in our previous search for neutral Higgs particles. The negative results are translated into improved mass limits and parameter constraints on the minimal supersymmetric extension of the standard model.
The coannihilation codex
2015
We present a general classification of simplified models that lead to dark matter (DM) coannihilation processes of the form DM + X $\rightarrow$ SM$_1$ + SM$_2$, where X is a coannihilation partner for the DM particle and SM$_1$, SM$_2$ are Standard Model fields. Our classification also encompasses regular DM pair annihilation scenarios if DM and X are identical. Each coannhilation scenario motivates the introduction of a mediating particle M that can either belong to the Standard Model or be a new field, whereby the resulting interactions between the dark sector and the Standard Model are realized as tree-level and dimension-four couplings. We construct a basis of coannihilation models, cl…
Inclusive production of the η and ω mesons in Z decays, and the muonic branching ratio of the ω
2002
AbstractThe inclusive production of the η and ω(782) mesons is measured in the π+π−π0 decay mode in hadronic Z decays and compared to model predictions. The analysis is based on 4 million hadronic Z decays recorded by the ALEPH detector between 1991 and 1995. The η production rate for xp=pmeson/pbeam>0.10 is found to be 0.355±0.011stat±0.024sys per event, and the ω production rate for xp>0.05 is measured as 0.585±0.019stat±0.033sys per event. The branching ratio for ω→μ+μ− is investigated. A total of 18.1±5.9 events are observed, from which the muonic branching ratio is measured for the first time to be BR(ω→μ+μ−)=(9.0±2.9stat±1.1sys)×10−5.
Search for Single Top Production in $e^{+} e^{-}$ Collisions at $\sqrt{s}$ up to 209 GeV
2002
Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c, \bar{t}u is searched for within the 214 pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209 GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> ��c)+BR(t -> ��u)= 0 and mt=174 GeV/c2.
Precision Measurement of theB→XsγPhoton Energy Spectrum, Branching Fraction, and DirectCPAsymmetryACP(B→Xs+dγ)
2012
The photon spectrum in the inclusive electromagnetic radiative decays of the B meson, B → X_sγ plus B → X_dγ, is studied using a data sample of (382.8±4.2)×10^6Υ(4S) → BB decays collected by the BABAR experiment at SLAC. The spectrum is used to extract the branching fraction B(B → X_sγ)=(3.21±0.33)×10^(-4) for E_γ > 1.8 GeV and the direct CP asymmetry A_(CP)(B → X_(s+d)γ)=0.057±0.063. The effects of detector resolution and Doppler smearing are unfolded to measure the photon energy spectrum in the B meson rest frame.
The radiative return at $\phi$ - and B-factories: small-angle photon emission at next-to-leading order
2002
The radiative return offers the unique possibility for a measurement of the cross section of electron--positron annihilation into hadrons over a wide range of energies. The large luminosity of present phi- and B-factories easily compensates for the additional factor of alpha due to the emission of a hard photon. Final states with photons at large angles can be easily identified. The rate for events with collinear photons, however, is enhanced by a large logarithm and allows, in particular at lower energies, for a complementary measurement. The Monte Carlo generator PHOKHARA, which includes next to leading order corrections from virtual and real photon emission, has been extended from large …
Measurement of W-pair production in $e^{+}e^{-}$ collisions at centre-of-mass energies from 183 to 209 GeV
2004
The W + W- production cross section is measured from a data sample corresponding to a total integrated luminosity of 683 pb-1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 183 to 209 GeV. Individual cross sections for the different topologies arising from W decays into leptons or hadrons, as well as the total W-pair cross section are given at eight centre-of-mass energies. The results are found to be in agreement with recently developed Standard Model calculations at the one percent level. The hadronic branching fraction of the W boson is measured to be B(W→qq¯) = 67.13 ± 0.37(stat.) ± 0.15(syst.)%, from which the CKM matrix element |\ensuremathVcs| is determined…
Search for $B^0_s-\overline{B^0_s}$ oscillations and a measurement of $B^0_d-\overline{B^0_d}$ oscillations using events with an inclusively reconstr…
2003
Neutral B meson oscillations in the B-s(0) - , and B-d(0) - systems were studied using a sample of about 4.0 million hadronic Z decays recorded by the DELPHI detector between 1992 and 2000. Events with a high transverse momentum lepton were removed and a sample of 770 k events with an inclusively reconstructed vertex was selected. The mass difference between the two physical states in the B-d(0) - system was measured to be: Deltam(d) = (0.531 +/- 0.025(stat.) +/- 0.007(syst.))ps(-1). The following limit on the width difference of these states was also obtained: DeltaGamma(Bd)/Gamma(Bd) oscillations was found, a limit on the mass difference of the two physical states was given:, Deltam(s) > …
MEASUREMENT OF TAU BRANCHING RATIOS
1992
著者人数：112名