Search results for "partícules"
showing 10 items of 522 documents
Inclusive Sigma(-) and Lambda(1520) production in hadronic Z decays
2000
Production of Sigma- and Lambda(1520) in hadronic Z decays has been measured using the DELPHI detector at LEP. The Sigma- is directly reconstructed as a charged track in the DELPHI microvertex detector and is identified by its Sigma -> n pi decay leading to a kink between the Sigma- and pi-track. The reconstruction of the Lambda(1520) resonance relies strongly on the particle identification capabilities of the barrel Ring Imaging Cherenkov detector and on the ionisation loss measurement of the TPC. Inclusive production spectra are measured for both particles. The production rates are measured to be = 0.081 +/- 0.002 +/- 0.010, = 0.029 +/- 0.005 +/- 0.005. The production rate of the Lambda(1…
Charged particle multiplicity in e(+)e(-) interactions at root s=130 GeV
1996
From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be = 23:84 0:51(stat) 0:52(syst). When compared to lower energy data, the value measured is consistent with the evolution predicted by QCD with corrections at next-to-leading order, for a value s(130GeV) = 0:105 0:003(stat) 0:008(syst).
Rapidity-rank structure of p(p)over-bar pairs in hadronic Z(0) decays
2000
The rapidity-rank structure of p pbar pairs is used to analyze the mechanism of baryon production in hadronic Z0 decay. The relative occurrence of the rapidity-ordered configuration p M pbar, where M is a meson, and that of p pbar adjacent pairs is compared. The data are found to be consistent with predictions from a mechanism producing adjacent-rank p pbar pairs, without requiring `string-ordered' p M pbar configurations. An upper limit of 15% at 90% confidence is determined for the p M pbar contribution.
Measurement of the forward backward asymmetry of c and b quarks at the Z pole using reconstructed D mesons
1999
A measurement of the forward--backward asymmetry of e+e−→cc¯ and e+e−→bb¯ on the Z resonance is performed using about 3.5 million hadronic Z decays collected by the DELPHI detector at LEP in the years 1992 to 1995. The heavy quark is tagged by the exclusive reconstruction of several D meson decay modes. The forward--backward asymmetries for c and b quarks at the Z resonance are determined to be: \renewcommand{\arraystretch}{1.6} \begin{array}{rcr@{}l} \Afbc(\sqrt{s} = 91.235 {\rm GeV}) &=& &#;0659 \pm 0.0094 (stat) \pm 0.0035 (syst) \Afbb (\sqrt{s} = 91.235 {\rm GeV}) &=& &#;0762 \pm 0.0194 (stat) \pm 0.0085 (syst) \Afbc(\sqrt{s} = 89.434 {\rm GeV}) &=&-&#;0496 \pm 0.0368 (stat) \pm 0.0053 …
Charged and identified particles in the hadronic decay of W bosons and in e(+)e(-) -> q(q)over-bar from 130 to 200 GeV
2000
Inclusive distributions of charged particles in hadronic W decays are experimentally investigated using the statistics collected by the DELPHI experiment at LEP during 1997, 1998 and 1999, at centre-of-mass energies from 183 to around 200 GeV. The possible effects of interconnection between the hadronic decays of two Ws are not observed. Measurements of the average multiplicity for charged and identified particles in q qbar and WW events at centre-of-mass energies from 130 to 200 GeV and in W decays are presented. The results on the average multiplicity of identified particles and on the position xi^* of the maximum of the xi_p = -log(2p/sqrt(s)) distribution are compared with predictions o…
Search for heavy stable and long-lived particles in e(+)e(-) collisions at root s=189 GeV
2000
A search for stable and long-lived heavy charged particles was performed using the data taken by the DELPHI experiment at an energy of 189 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the ionisation loss measured in the Time Projection Chamber were used to identify heavy particles passing through the detector. No evidence for the production of such particles has been found, therefore exclusion limits at 95% confidence level were derived on the masses of left and right handed smuons and staus. The results were combined with previous DELPHI searches in this channel. Including previous DELPHI results, masses of left (right) handed stable smuons and staus can be …
Observation of short-range 3-particle correlations in e(+)e(-) annihilations at lep energies
1995
\def\tpc{three-particle correlation} \def\twopc{two-particle correlation} Measurements are presented of short range three-particle correlations in e^+ e^- annihilations at LEP using data collected by the DELPHI detector. %The jet structure is studied using three-particle correlation functions. At small values of the four-momentum difference, strong three-particle correlations are observed for like-sign (+++ and ---) and for unlike-sign (++- and +--) pion combinations which are not a consequence of two-particle correlations. A possible explanation of the observed effects in like-sign combinations is the existence of higher order Bose-Einstein interference, which significantly changes the par…
Search for stable heavy charged particles in e(+)e(-) collisions at root s=130-136, 161 and 172 GeV
1997
A search for stable or long-lived heavy charged particles in e+e− interactions at energies of 130¿136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ±e and View the MathML source particles in the range of 0.4¿2.3 pb for masses from 45 to 84 GeV/c2. Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/c2 for high (low) sneutrino masses can be excluded at 9…
Upper limits on the branching ratios tau-]mu-gamma and tau-]e-gamma
1995
The DELPHI collaboration has searched for lepton flavour violating decays tau -> mugamma and tau -> egamma using a data sample of about 70 pb-1 of integrated luminosity corresponding to 81 000 produced tau+tau- events. No candidates were found for either of the two modes. This yields branching ratio upper limits of B(tau -> egamma) mugamma) < 6.2 × 10-5 at 90% confidence level.
Observation of B-c(+) -> J/ psi D-s(+) and B-c(+) -> J/ psi D-s*(+) decays
2013
The decays B-c(+) -> J/ psi D-s(+) and B-c(+) -> J/ psi D-s*(+) are observed for the first time using a dataset, corresponding to an integrated luminosity of 3 fb(-1), collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of root s = 7 and 8 TeV. The statistical significance for both signals is in excess of 9 standard deviations. The following ratios of branching fractions are measured to be 'B(B-c(+) -> J/ psi D-s(+))/B(B-c(+) -> J/ psi pi(+)) = 2.90 +/- 0.57 +/- 0.24, B(B-c(+) -> J/psi D-s*(+))/B(B-c(+) -> J/ psi D-s(+)) = 2.37 +/- 0.56 +/- 0.10, where the first uncertainties are statistical and the second systematic. The mass of the B-c(+) meson is measu…