Search results for "Electron–positron annihilation"
showing 10 items of 705 documents
Lifetime and production rate of beauty baryons from Z decays
1995
The production and decay of beauty baryons (b-baryons) have been studied using 1.7 \times 10^6 Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify the b-baryons. The first method used pairs of a \Lambda and a lepton to tag the b-baryon decay. The second method associated fully reconstructed \Lambda_c baryons with leptons. The third analysis reconstructed the b-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured: \begin{eqnarray*} f(\qb \ra \Bb) \times \BR(\Bb \ra \mLs \ell\bar{\nu}_{\ell}\X) & = & (0.30 \pm 0.06 \pm0.04)\%…
MEASUREMENT OF THE GAMMA(B-B-OVER-BAR)/GAMMA(HAD) BRANCHING RATIO OF THE Z BY DOUBLE HEMISPHERE TAGGING
1995
Two measurements of {Mathematical expression} are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, {Mathematical expression} is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018 {Mathematical expression}. © 1995 Springer-Verlag.
Measurement of inclusive pi(0) production in hadronic Z(0) decays
1996
An analysis is presented of inclusive \pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \pi^0 decays are reconstructed by \linebreak using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to x_p = 2 \cdot p_{\pi}/\sqrt{s} = 0.75) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for {q\overline q} and {b \bar b} events. The number of \pi^0's per hadronic Z^0 event is N(\pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{(stat)} \…
Lifetime of Charged and Neutral B-hadrons Using Event Topology
1995
The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic \PZz decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1\pm0.3\%, and 83\% (70\%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be \TAUBC\pm\ERRBC\;(stat.)\pm\SYSBC\;(syst.)~ps and \TAUBN\pm\ERRBN\;(stat.)\pm\SYSBN\;(syst…
Strange baryon production in Z hadronic decays
1995
A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the ∑± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models. © 1995 Springer-Verlag.
Fermion pair production in e+e- collisions at 189-209 GeV and constraints on physics beyond the Standard Model
2006
Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e+e- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e+e-, mu+mu-, tau+tau-, qq, bb and cc production are in agreement with the Standard Model predictions. Constraints are set on scenarios of new physics such as four-fermion contact interactions, leptoquarks, Z' bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos.
Improved limits on the lepton-flavor violating decays tau(-) -> l(-)l(+)l(-)
2007
A search for the neutrinoless, lepton-flavor violating decay of the tau lepton into three charged leptons has been performed using 376fb-1 of data collected at an e+e- center-of-mass energy around 10.58 GeV with the BABAR detector at the SLAC PEP-II storage rings. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (4-8)×10-8 at 90% confidence level. © 2007 The American Physical Society.
Measurement of the D→K−π+ strong phase difference in ψ(3770)→D0D¯0
2014
Abstract We study D 0 D ¯ 0 pairs produced in e + e − collisions at s = 3.773 GeV using a data sample of 2.92 fb−1 collected with the BESIII detector. We measured the asymmetry A K π CP of the branching fractions of D → K − π + in CP-odd and CP-even eigenstates to be ( 12.7 ± 1.3 ± 0.7 ) × 10 − 2 . A K π CP can be used to extract the strong phase difference δ K π between the doubly Cabibbo-suppressed process D ¯ 0 → K − π + and the Cabibbo-favored process D 0 → K − π + . Using world-average values of external parameters, we obtain cos δ K π = 1.02 ± 0.11 ± 0.06 ± 0.01 . Here, the first and second uncertainties are statistical and systematic, respectively, while the third uncertainty arises …
Measurements of the absolute branching fractions forDs+→ηe+νeandDs+→η′e+νe
2016
By analyzing 482 pb(-1) of e(+)e(-) collision data collected at root s = 4.009 GeV with the BESIII detector at the BEPCII collider, we measure the absolute branching fractions for the semileptonic decays D-s(+) -> eta e(+)nu(e) and D-s(+) -> eta ' e(+)nu(e) to be B(D-s(+) -> eta e(+)nu(e)) = (2.30 +/- 0.31 +/- 0.08)% and B(D-s(+) -> eta ' e(+)nu(e)) = (0.93 +/- 0.30 +/- 0.05)%, respectively, and their ratio B(D-s(+) -> eta ' e(+)nu(e)) / B(D-s(+) -> eta ' e(+)nu(e)) = 0.40 +/- 0.14 +/- 0.02, where the first uncertainties are statistical and the second ones are systematic. The results are in good agreement with previous measurements within uncertainties; they can be used to determine the eta…
Amplitude Analysis of theB±→φK*(892)±Decay
2007
We perform an amplitude analysis of B-+/-->phi(1020)K-*(892)(+/-) decay with a sample of about 384x10(6) B (B) over bar pairs recorded with the BABAR detector. Overall, twelve parameters are measured, including the fractions of longitudinal f(L) and parity-odd transverse f(perpendicular to) amplitudes, branching fraction, strong phases, and six parameters sensitive to CP violation. We use the dependence on the K pi invariant mass of the interference between the J(P)=1(-) and 0(+) K pi components to resolve the discrete ambiguity in the determination of the strong and weak phases. Our measurements of f(L)=0.49 +/- 0.05 +/- 0.03, f(perpendicular to)=0.21 +/- 0.05 +/- 0.02, and the strong phas…