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

Measurement of Trilinear Gauge Couplings in e+e−e^+ e^- Collisions at 161 GeV and 172 GeV

Trilinear gauge boson couplings are measured using data taken by DELPHI at 161~GeV and 172~GeV. Values for $WWV$ couplings ($V=Z, \gamma$) are determined from a study of the reactions \eeWW\ and \eeWev, using differential distributions from the $WW$ final state in which one $W$ decays hadronically and the other leptonically, and total cross-section data from other channels. Limits are also derived on neutral $ZV\gamma$ couplings from an analysis of the reaction \eegi

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 ZZ cross-section in e(+)e(-) interactions at 183-189 GeV

Measurements of on-shell ZZ production are described, using data collected by DELPHI in 1997 and 1998, at centre-of-mass energies roots = 182.6 GeV and 188.6 GeV, respectively. Results obtained in each of the final states q (q) over barq (q) over bar, mu (+)mu (-) q (q) over bar e(+)e(-)q (q) over bar, nu&lt;(&lt;nu&gt;)over bar&gt;q (q) over bar, l(+)l(-)l(+)l(-), and nu&lt;(&lt;nu&gt;)over bar&gt;l(+)l(-) are presented. The measured cross-sections for on-shell ZZ production via the tree-level doubly-resonant graphs (NC02) are: sigma (NC02) (182.6 GeV) = 0.38 +/- 0.18 (stat) +/- 0.04 (syst) pb, sigma (NC02) (188.6 GeV) = 0.60+/-0.13 (stat) +/- 0.07 (syst) pb. They are consistent with the Standard Model expectations of 0.25 and 0.65 pb at each energy. (C) 2001 Published by Elsevier Science B.V

Limits on the masses of supersymmetric particles at root s=189 GeV

Searches for charginos, neutralinos and sleptons at LEP2 centre-of-mass energies from 130 GeV to 189 GeV have been used to set lower limits on the mass of the Lightest Supersymmetric Particle and other supersymmetric particles within the MSSM framework. R-parity conservation has been assumed. The lightest neutralino was found to be heavier than GeV/c(2) independent of the m(0) value. The Lightest chargino, the second-to-lightest neutralino, the next-to-heaviest neutralino, the heaviest neutralino, the sneutrino and the right-handed selectron were found to be heavier than 62.4 GeV/c2, 62.4 GeV/c(2), 99.9 GeV/c(2), 116.0 GeV/c(2), 61.0 GeV/c(2), and 87.0 GeV/c(2), respectively. These limits do not depend on m(0) or M-2 and are Valid for 1 less than or equal to tan beta less than or equal to 40, in the mu region where the lightest neutralino is the LSP. If the sneutrino is heavier than the chargino the lightest neutralino has to be heavier than 32.4 GeV/c(2). The effects of mixings in the third family of sfermions on these limits are discussed. The confidence level of all limits given is 95%. (C) 2000 Published by Elsevier Science B.V

Search for SUSY with R-parity violating LL(E)over-bar couplings at root s=189 GeV

Searches for pair production of supersymmetric particles under the assumption that R-parity is not conserved are presented, based on data recorded by the DELPHI detector in 1998 from e(+)e(-) collisions at a centre-of-mass energy of 189 GeV. Only one R-parity violating LL (E) over bar term (i.e. one lambda coupling), which couples scalar leptons to leptons, is considered to be dominant at a time. Moreover, it is assumed that the strength of the R-parity violating couplings is such that the lifetimes can be neglected. The search for pair production of neutralinos, charginos and sleptons has been performed for both direct R-parity violating decays and indirect cascade decays. The results are in agreement with Standard Model expectations, and are used to update the constraints on the MSSM parameter values and the mass limits previously derived at root s = 183 GeV. The present 95% C.L. Limits on supersymmetric particle masses are: m(&lt;(chi)over tilde&gt;0) &gt; 30 GeV/c(2) and m(&lt;(chi)over tilde&gt;+/-) &gt; 94 GeV/c(2); m(&lt;(nu)over tilde&gt;) &gt; 76.5 GeV/c(2) (direct and indirect decays); m((l) over tilde R) &gt; 83 GeV/c(2) (indirect decay only). (C) 2000 Elsevier Science B.V. All rights reserved

Search for the sgoldstino at root s from 189 to 202 GeV

A search for the supersymmetric partner of the goldstino, the sgoldstino S, at LEP2 is presented. The production S gamma followed by S decay into two gluons or into two photons was studied at 189-202 GeV LEP centre-of-mass energies. No evidence for the S production was found and limits on the S mass corresponding to different theory parameters are given. (C) 2000 Elsevier Science B.V. All rights reserved

Measurement and interpretation of fermion-pair production at LEP energies of 183 and 189 GeV

An analysis of the data collected in 1997 and 1998 with the DELPHI detector at e(+)e(-) collision energies close to 183 and 189 GeV was performed in order to extract the hadronic and leptonic fermion-pair cross-sections, as well as the leptonic forward-backward asymmetries and angular distributions. The data are used to put limit on contact interactions between fermions, the exchange of R-parity violating SUSY sneutrinos, Z’ bosons and the existence of gravity in extra dimensions. (C) 2000 Published by Elsevier Science B.V

Determination of the e(+)e(-)-&gt;gamma gamma(gamma) cross-section at centre-of-mass energies ranging from 189 GeV to 202 GeV

A test of the QED process e(+)e(-) –&gt; gamma gamma&gt;(*) over bar *(gamma) is reported. The data analysed were collected with the DELPHI detector in 1998 and 1999 at the highest energies achieved at LEP, reaching 202 GeV in the centre-of-mass. The total integrated luminosity amounts to 375.7 pb(-1). The differential and total cross-sections for the process e(+)e(-) –&gt; gamma gamma were measured, and found to be in agreement with the QED prediction. 95% confidence level (C.L.) lower limits on the QED cut-off parameters of Lambda (+) &gt; 330 GeV and Lambda_ &gt; 320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c(2) (for lambda gamma = 1) was obtained, s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, M-S: M-S &gt; 713 GeV/c(2) (lambda = 1) and M-S &gt; 691 GeV/c(2) (lambda = -1). (C) 2000 Published by Elsevier Science B.V