The forward-backward asymmetry in e + e − → b b at s = 57.9 GeV and the b-quark branching ratio to muons have been measured using neural networks. Unlike previous methods for measuring the b b forward-backward asymmetry where the estimated background from c -quark decays and other sources are subtracted, here events are categorized as either b b or non- b b events by neural networks based on event-by-event characteristics. The determined asymmetry is −0.429 ± 0.044 (stat) ± 0.047 (sys) and is consistent with the prediction of the standard model. The measured B B mixing parameter is 0.136 ± 0.037 (stat) ± 0.040 (sys) ± 0.002 (model) and the measured b-quark branching ratio to muons is 0.122 ± 0.006 (stat) ± 0.007 (sys).
.
The Michel parameters ϱ, η, ξ, and ξδ, the chirality parameter ξ h and the τ polarization P τ are measured using 32012 τ pair decays. Their values are extracted from the energy spectra of leptons and hadrons in τ − → l − ν l ν τ and τ − → π − ν τ decays, the energy and decay angular distributions in τ − → ϱ − ν τ decays, and the correlations in the energy spectra and angular distributions of the decay products. Assuming universality in leptonic and semileptonic τ decays, the results are ϱ = 0.794±0.039±0.031, η = 0.25±0.17±0.11, ξ = 0.94±0.21±0.07, ξδ = 0.81±0.14±0.06, ξ h = −0.970±0.053±0.011, and P τ = −0.154±0.018±0.012. The measurement is in agreement with the V-A hypothesis for the weak charged current.
No description provided.
We present a measurement of the forward-backward charge asymmetry of the process pp¯→Z0/γ+X,Z0/γ→e+e− at Mee>MZ, using 110pb−1 of data at s=1.8TeV collected at the Collider Detector at Fermilab. The measured charge asymmetries are 0.43±0.10 in the invariant mass region Mee>105GeV/c2, and 0.070±0.016 in the region 75<Mee<105GeV/c2. These results are consistent with the standard model values of 0.528±0.009 and 0.052±0.002, respectively.
The forward-backward asymmetry resuts from angular differential cross section : D(SIG)/D(COS(THETA*) = A*(1 + COS(THETA*)**2) + B*COS(THETA*), where THETA * is the emission angle of the E- relative to the quark momentum in the rest frame of the E+ E- pair.
We present the first experimental study of the ratio of cumulant to factorial moments of the charged-particle multiplicity distribution in high-energy particle interactions, using hadronic Z$^0$ decays collected by the SLD experiment at SLAC. We find that this ratio, as a function of the moment-rank $q$, decreases sharply to a negative minimum at $q=5$, which is followed by quasi-oscillations. These features are insensitive to experimental systematic effects and are in qualitative agreement with expectations from next-to-next-to-leading-order perturbative QCD.
CONST is the cumulant to factorial moments ratio. See text for definition.
The p+p→π++d reaction is studied at excess energies between 0.275 and 3.86 MeV. Differential and total cross section were measured employing a magnetic spectrometer with nearly 4π acceptance in the center of mass system. The measured anisotropies between 0.008 and 0.29 indicate that the p wave is not negligible even so close to threshold. The data are compared to other data offering no evidence for charge symmetry breaking or time reversal violation. The s-wave and p-wave contributions at threshold are deduced.
The CONST is p-wave contribution to the cross section. The differential cross section is fitted usig the relations 4*pi*D(SIG)/D(OMEGA) = SIG + CONST*P2(COS(THETA)), where P2 denotes the Legendre polynomial.
Using the ARGUS detector at the e + e − storage ring DORIS II at DESY, we have made two measurements of the mixing parameter χ d using kaons as flavour tags. Using D ∗+ K ± correlations we found χ d = 0.20 ± 0.13 ± 0.12 and from the study of (D ∗+ ℓ − ) K ± correlations we obtained χ d = 0.19 ± 0.07 ± 0.09. The branching ratio for B → D ∗+ X has been updated: Br( B → D ∗+ X) = (19.6 ± 1.9) %. We have also determined the average multiplicity of charged kaons in B 0 decays to be 0.78 ± 0.08.
Mixing parameter from counting kaon events. First (...,C=D*+K+-) and second(...,C=(D*+LEPTON-)K+-) value are obtained from a study of D*+K+- and (D*+LEPTO N-)K+- correlations respectively. Second value and the value, reported in Phys.Lett. 324B (1994) 249, were averaged, result third value (...,C=COMBINED) of the mixing parameter in the table (see text for details). In the second value (...,C=(D*+LEPTON-)K+-) the first systematic error is due to the background estimation, the branching ratio for the process B --> K+(K-) X, experimental cuts, and the second one is due to to the uncertainty on the branching ratio for the processes D0 --> K+- X.
No description provided.
We have analysed a sample of 2.36 million minimum bias events produced in p p collisions at s =630 GeV in the UA1 experiment at the CERN collider. We have studied the production of charged particles with transverse momenta ( p T ) up to 25 GeV/c. The results are in agreement with QCD predictions. The rise of 〈 p T 〉 with charged particle multiplicity may be related to changing production of low p T particles.
No description provided.
No description provided.
No description provided.
From a sample of 2.36 million minimum bias events produced in p p collisions at s =630 GeV in the UA1 experiment and from other published data at the CERN S p p S collider we have estimated the relative production of π ± , π 0 , K ± , K S 0 , Λ, Λ , p and p . We obtain a meson over baryon ratio M B = 6.4 ± 1.1 . From the K S 0 π ± ratio we measure the strangeness suppression factor λ = 0.29 ± 0.02 ± 0.01 which, combining with other available data provides a new world average of 0.29 ± 0.015. Both the K S 0 π ± ratio and the strangeness suppression factor λ as a function of s are investigated, and an extrapolation to the LHC energy is performed.
Extrapolation to pt=0.
CONST is strangeness suppression factor, extracted from KS/PI+- ratio (see text).
CP violation has been observed as a time-dependent rate asymmetry between the decays ${⩈erline K}^0 ⌝ghtarrow ≪^{0} ≪^{0}$ and K0 → π0π{0}, where the neutral kaons are produced with definite and individually known strangeness in ${⋏r p}p ⌝ghtarrow{⩈erline K}^0 K^+≪^- $ or p̅p → K0 K− π+. A special technique for the data analysis has been developed. The values obtained for ϕ00 and ¦ η00¦ are in agreement with those of previous measurements of CP violation.
No description provided.
The Compton scattering cross section on the proton has been measured at laboratory angles of 90$~\circ$ and 135$~\circ$ using tagged photons in the energy range 70--100 MeV and simultaneously using untagged photons in the range 100--148MeV. With the aid of dispersion relations, these cross sections were used to extract the electric and magnetic polarizabilities, $\bar{\alpha}$ and $\bar{\beta}$ respectively, of the proton. We find $$\bar{\alpha}+\bar{\beta} = ( 15.0 \pm 2.9 \pm 1.1 \pm 0.4 ) \times 10~{-4} \: {\rm fm}~3,$$ in agreement with a model-independent dispersion sum rule, and $$\bar{\alpha}-\bar{\beta} = ( 10.8 \pm 1.1 \pm 1.4 \pm 1.0 ) \times 10~{-4} \: {\rm fm}~3,$$ where the errors shown are statistical, systematic, and model-dependent, respectively. A comparison with previous experiments is given and global values for the polarizabilities are extracted.
Tagged photons.
Untagged photons.
No description provided.
Forum