0000000000125355
AUTHOR
Johnson Sd
showing 7 related works from this author
Production of Charmed Mesons In Z Decays
1994
The production of charmed mesons $$\mathop {D^0 }\limits^{( - )} $$ ,D ± , andD *± is studied in a sample of 478,000 hadronicZ decays. The production rates are measured to be $$\begin{gathered} \frac{{\Gamma ({\rm Z} \to D^{* \pm } X)}}{{\Gamma _{had} }} = 0.187 \pm 0.015(\exp .) \pm 0.013(BR), \hfill \\ \frac{{\Gamma ({\rm Z} \to D^ \pm X)}}{{\Gamma _{had} }} = 0.251 \pm 0.026(\exp .) \pm 0.025(BR), \hfill \\ \frac{{\Gamma ({\rm Z} \to \mathop {D^0 }\limits^{( - )} X)}}{{\Gamma _{had} }} = 0.518 \pm 0.052(\exp .) \pm 0.035(BR), \hfill \\ \end{gathered} $$ where the errors from this analysis are separated from those coming from theD branching ratios (BR). TheD *± momentum distribution is ex…
Search for CP violation in the decay Z → τ+τ−
1995
Data collected by ALEPH in the years 1990, 1991 and 1992 have been used to update a previous search for CP violation in the decay of the Z into tau(+)tau(-). The measurement of the weak dipole form factor of the tau lepton has been performed by studying correlations between the tau leptons. No signal of CP violation was found. The weak dipole form factor is found to be ($) over tilde d(tau) = (+0.15 +/- 0.58(stat) +/- 0.38(sys)) 10(-17)e . cm, obtained with 19628 identified tau(+)tau(-) events. This gives an upper limit on the weak dipole form factor of j\($) over tilde d(tau)\ < 1.5 . 10(-17)e . cm at the 95% confidence level.
Production ofK 0 and Λ in hadronic Z decays
1994
Measurements of the inclusive cross-sections forK 0 and Λ production in hadronic decays of the Z are presented together with measurements of two-particle correlations within pairs of Λ andK 0. The results are compared with predictions from the hadronization models Jetset, based on string fragmentation, and Herwig, based on cluster decays. TheK 0 spectrum is found to be harder than predicted by both models, while the Λ spectrum is softer than predicted. The correlation measurements are all reproduced well by Jetset, while Herwig misses some of the qualitative features and overestimates the size of the $$\Lambda \bar \Lambda $$ correlation. Finally, the possibility of Bose-Einstein correlatio…
Observation of monojet events and tentative interpretation
1994
Abstract A data sample corresponding to almost two million hadronic Z decays collected by the ALEPH detector at LEP has been searched for monojet events. Three events were found, in agreement with the expectation from the process e + e − → γ * v v ¯ , with γ * → f f ¯ . Two events are hadronic, the third one being an e + e − pair. All monojet masses are in excess of 3 GeV/ c 2 , and two of the event have large transverse momenta: 18.5 and 20.3 GeV/ c . These kinematic characteristics are quite unlikely in the process e + e − → γ * v v ¯ . The probability of their occurence increases substantially when processes involving further Z or W exchanges are taken into account, but still remains at …
Heavy Flavor Production and Decay With Prompt Leptons In the Aleph Detector
1994
In 431 000 hadronicZ decays recorded with the ALEPH detector at LEP, the yields of electrons and muons in events with one or more prompt leptons have been analysed to give information on the production and decay of heavy quarks. The fractions of $$b\bar b$$ and $$c\bar c$$ events are measured to be 0.219±0.006±0.005 and 0.165±0.005±0.020, and the corresponding forward-backward asymmetries at theZ mass are measured to be 0.090±0.013±0.003 and 0.111±0.021±0.018, after QED and QCD corrections. Measurements for the semileptonic branching ratios BR $$(b \to \ell ^ - \bar vX)$$ and BR (b→cl+ vX) yield 0.114±0.003±0.004 and 0.082±0.003±0.012, respectively. The dilepton events enable measurement of…
Study of the subjet structure of quark and gluon jets
1995
Measurements of the subjet structure of quark and gluon jets in hadronic Z decays are presented. The analysis is based on one million hadronic events recorded by the ALEPH detector. Roughly symmetric three-jet events are selected with a coarse jet-resolution cut-off, y(1). Gluon jets are identified with a purity of 94.6% in those events where evidence of long-lived heavy-flavour hadrons in the other two jets is found. The jets are then analyzed using a smaller cut-off y(0) (< y(1)) so that subjets are resolved. The properties of the jets (subjet multiplicities [N-q], [N-g] and rates R(n)(g(q)) for n = 1,2,3,4) are determined and are found to be in good agreement with the expectations of per…
Michel Parameters and tau neutrino Helicity From Decay Correlations In Z->tau+tau-
1995
The Michel parameters and the average tau-neutrino helicity are measured using correlations between the decays of the tau(+) and tau(-) produced on the Z resonance and observed in the ALEPH detector at LEP. The Michel parameters, rho(e), eta(e), xi(e), (delta xi)(e), are determined from tau --> e ($) over bar upsilon(e) upsilon(tau) with e = (e, mu), and the average tau neutrino helicity, (h(upsilon(tau))), from tau --> h tau with h = (pi, rho, a(1)). The results obtained with e-mu universality are: rho(e) = 0.751 +/- 0.039 +/- 0.022, eta(e) = -0.04 +/- 0.15 +/- 0.11, xi(e) = 1.18 +/- 0.15 +/- 0.06, (delta xi)(e) = 0.88 +/- 0.11 +/- 0.07, and the average tau neutrino helicity (h(upsilon(tau…