Search for supersymmetric particles in scenarios with a gravitino LSP and stau NLSP

Sleptons, neutralinos and charginos were searched for in the context of scenarios where the lightest supersymmetric particle is the gravitino. It was assumed that the stau is the next-to-lightest supersymmetric particle. Data collected with the DELPHI detector at a centre-of-mass energy near 189 GeV were analysed combining the methods developed in previous searches at lower energies. No evidence for the production of these supersymmetric particles was found. Hence, limits were derived at 95% confidence level.Comment: 31 pages, 14 figure

Study of B0_s anti-B0_s oscillations and B0_s lifetimes using hadronic decays of B0_s mesons

Oscillations of B0s mesons have been studied in samples selected from about 3.5 million hadronic Z decays detected by DELPHI between 1992 and 1995. One analysis uses events in the exclusive decay channels: B0s -> Ds- pi+ or Ds- a1+ and B0s -> anti-D0 K- pi+ or anti-D0 K- a1+, where the D decays are completely reconstructed. In addition, B0s anti-B0s oscillations have been studied in events with an exclusively reconstructed Ds accompanied in the same hemisphere by a high momentum hadron of opposite charge. Combining the two analyses, a limit on the mass difference between the physical B0s states has been obtained: Delta(m_B0s) > 4.0 ps^{-1} at the 95% C.L. with a sensitivity of Delta(m_B0s) = 3.2 ps^{-1}. Using the latter sample of events, the B0s lifetime has been measured and an upper limit on the decay width difference between the two physical B0s states has been obtained: tau(B0s) = 1.53^{+0.16}_{-0.15}(stat.) +/- {0.07}(syst.) ps \Delta\Gamma(B0s)/\Gamma(B0s) < 0.69 at the 95% C.L. The combination of these results with those obtained using Ds+- lepton-+ sample gives: Delta(m_B0s) > 4.9 ps^{-1} at the 95% C.L. with a sensitivity of Delta(m_B0s) = 8.7 ps^{-1}. tau(B0s) = 1.46 +/- 0.11 ps and \Delta\Gamma(B0s)/\Gamma(B0s) < 0.45 at the 95% C.L.Comment: 42 pages, 13 figure

Measurement of the (B)over-bar -&gt; D-(*)pi l(nu)over-bar(l) branching fraction

A study of b semileptonic decays into D, D pi(+/-) and D*pi(+/-) final states is presented. The D-0, D+ and D*(+) mesons are exclusively reconstructed in Z decay data recorded from 1992 to 1995 in the DELPHI experiment at LEP. The overall branching fractions are measured to be: BR(b –&gt; D(0)l(-)&lt;(upsilon)over bar&gt;X-l) = (7.04 +/- 0.34(stat) +/- 0.36 (syst.exp) +/- 0.17(BRD))%, BR(b –&gt; D(+)l(-)&lt;(upsilon)over bar&gt;X-l) = (2.72 +/- 0.19(stat) +/- 0.16(syst.exp) +/- 0.18(BRD))%, BR(b –&gt; D*(+)l(-)&lt;(upsilon)over bar&gt;X-l) = (2.75 +/- 0.17(stat) +/- 0.13 (syst.exp) +/- 0.09 (BRD))%, where the D-0 and D+ results include also contributions from D*(0) and D*(+) decays. A fit to the distribution of the pi(+/-) impact parameter to the primary interaction vertex provides a measurement of the b semileptonic branching fractions into the D(0)pi(+/-)X, D(+)pi(+/-)X and D*(+)pi(+/-)X final states. Assuming that single pion decay modes of B mesons dominate, the partial rates for (B) over bar –&gt; D pi l(-)&lt;(upsilon)over bar&gt;(l) and (B) over bar –&gt; D*pi l(-)&lt;(upsilon)over bar&gt;(l) have been obtained, corresponding to a total branching fraction: BR((B) over bar –&gt; D pi l(-)&lt;(upsilon)over bar&gt;(l)) + BR((B) over bar –&gt; D*pi l(-)&lt;(upsilon)over bar&gt;(l)) = (3.40 +/- 0.52 (stat) +/- 0.32 (syst))%. This result agrees well with the observed difference between the total B semileptonic branching fraction and the sum of the (B) over bar –&gt; Dl(-) upsilon(l) and D* l(-)&lt;(upsilon)over bar&gt;(l) branching fractions. (C) 2000 Elsevier Science B.V. All rights reserved

W pair production cross-section and W branching fractions in e(+)e(-) interactions at 189 GeV

{The cross-section for the process e(+)e(-) --&gt; W+ W- has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 189 GeV and corresponding to an integrated luminosity of 155 pb(-1). Based on the 2392 events selected as WW candidates, the cross-section for the doubly resonant process e(+)e(-) --&gt; W+W- has been measured to be 15.83 +/- 0.38 (stat) +/- 0.20(syst)pb. The branching fractions of the W decay were also measured and found to be in good agreement with the Standard Model expectation. From these a value of the CKM mixing matrix element \textbackslash{} V-cs\textbackslash{} = 1.001 +/- 0.040 (stat) +/- 0.020(syst) was derived. (C) 2000 Elsevier Science B.V. All rights reserved.