14 research outputs found
Optimized Variables of the Study of Polarization
The value of the -baryon polarization can be extracted from inclusive data
at LEP with better than 10\% precision based on current statistics. We present
a new variable by which to measure the polarization, which is the ratio of the
average electron energy to the average neutrino energy. This variable is both
sensitive to polarization and insensitive to fragmentation uncertainties.Comment: 10 pages (LaTeX), 2 figures, MIT-CTP-2270, CERN-PPE/94-0
(Borel) convergence of the variationally improved mass expansion and the O(N) Gross-Neveu model mass gap
We reconsider in some detail a construction allowing (Borel) convergence of
an alternative perturbative expansion, for specific physical quantities of
asymptotically free models. The usual perturbative expansions (with an explicit
mass dependence) are transmuted into expansions in 1/F, where
for while for m \lsim \Lambda,
being the basic scale and given by renormalization group
coefficients. (Borel) convergence holds in a range of which corresponds to
reach unambiguously the strong coupling infrared regime near , which
can define certain "non-perturbative" quantities, such as the mass gap, from a
resummation of this alternative expansion. Convergence properties can be
further improved, when combined with expansion (variationally improved
perturbation) methods. We illustrate these results by re-evaluating, from
purely perturbative informations, the O(N) Gross-Neveu model mass gap, known
for arbitrary from exact S matrix results. Comparing different levels of
approximations that can be defined within our framework, we find reasonable
agreement with the exact result.Comment: 33 pp., RevTeX4, 6 eps figures. Minor typos, notation and wording
corrections, 2 references added. To appear in Phys. Rev.
A new measurement of direct CP violation in two pion decays of the neutral kaon
The NA48 experiment at CERN has performed a new measurement of direct CP
violation, based on data taken in 1997 by simultaneously collecting K_L and K_S
decays into pi0pi0 and pi+pi-. The result for the CP violating parameter
Re(epsilon'/epsilon) is (18.5 +/- 4.5(stat)} +/- 5.8 (syst))x10^{-4}.Comment: 18 pages, 6 figure
A new measurement of direct CP violation in the neutral kaon system
A new measurement of the ratio of the CP-violating amplitudes for and is reported. The measured value for is , where the first error is the statistical uncertainty and the second is the estimate of the systematic uncertainty. This gives a value for the parameter describing direct CP violation:
Search for supersymmetry with R-parity violating LL(E)over-bar couplings at root s=183 GeV
Searches for pair production of supersymmetric particles in e(+)e(-) collisions at centre-of-mass energy of 183 GeV have been performed on DELPHI data under the assumption that R- parity is not conserved. Only one R-parity violating coupling of lambda type, which couples the sleptons to the leptons (LL (E) over bar term), is considered to be dominant at a time. Since in models with R-parity violation any supersymmetric particle can be the lightest one, searches for charginos, neutralinos, sleptons and squarks have been performed both for direct R-parity violating decays and for indirect cascade decays. Morever, it is assumed that the strength of the R- parity violating couplings is such that the lifetimes can be neglected. The present study of supersymmetric particle pair production is used to exclude domains of the Minimal Supersymmetric Standard Model parameter space previously explored under the assumption of R-parity conservation
Measurements of the Z partial decay width into c(c)over-bar and multiplicity of charm quarks per b decay
The partial decay width R-c of the Z into c (c) over bar quark pair and the number of charm quarks n(c) per b decay are measured with the DELPHI detector at LEP 1. Particle identification provides clear DO, D+, D-s(+) and Lambda(c)(+) signatures. The charm hadron production rate is measured in each channel by a fit to the scaled energy, impact parameter information and the invariant mass spectrum. Two measurements of R-c are presented, from the D*(+) production rate and from the overall charm counting, including strange charm baryon production, in c (c) over bar events. The multiplicity n(c), which includes hidden c (c) over bar and strange charm baryon production, is inferred from the charm counting in bb events. The final results are R-c = 0.1665 +/- 0.0095 and n(c) = 1.166 +/- 0.086
Measurement and interpretation of fermion-pair production at LEP energies from 130 to 172 GeV
The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995 and 1996, have been used to determine the hadronic and leptonic cross-sections and leptonic forward-backward asymmetries. In addition, the cross-section ratios and forward-backward asymmetries for flavour-tagged samples of light (uds), c and b quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted by performing S-matrix fits to these data and to the data collected previously at the energies near the Z(0) resonance peak (85-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions, R-parity violating SUSY particle exchange and of possible Z' bosons