[show abstract][hide abstract] ABSTRACT: An update of the search for sleptons, neutralinos and charginos in the context of scenarios where the lightest supersymmetric particle is the gravitino and the next-to-lightest supersymmetric particle is a slepton, is presented, together with the update of the search for heavy stable charged particles in light gravitino scenarios and Minimal Supersymmetric Standard Models. Data collected in 1999 with the DELPHI detector at centre-of-mass energies around 192, 196, 200 and 202 GeV were analysed. No evidence for the production of these supersymmetric particles was found. Hence, new mass limits were derived at 95\% confidence level.
[show abstract][hide abstract] ABSTRACT: Searches for spontaneous R-parity-violating signals at GeV and GeV have been performed using the 1997 and 1998 DELPHI data, under the assumption of R-parity breaking in the third lepton family. The expected topology for the decay of a pair of charginos into two acoplanar taus plus missing energy was investigated and no evidence for a signal was found. The results were used to derive a limit on the chargino mass and to constrain the allowed domains of the MSSM parameter space.
[show abstract][hide abstract] ABSTRACT: Searches for pair production of gauginos and squarks in e+e− collisions at a centre-of-mass energy of 189 GeV have been performed on data corresponding to an integrated luminosity of 158 pb−1 collected by the DELPHI detector at LEP. The data were analyzed under the assumption of non-conservation of R-parity through a single dominant coupling between squarks and quarks. Typical final states contain between 4 and 10 jets with or without additional leptons. No excess of data above Standard Model expectations was observed. The results were used to constrain domains of the MSSM parameter space and derive limits on the masses of supersymmetric particles. The following mass limits at 95% CL were obtained from these searches: neutralino mass: GeV; chargino mass: GeV; stop and sbottom mass (indirect decay) with ΔM>5 GeV: GeV for Φmix=0 rad, GeV for Φmix=0.98 rad, GeV for Φmix=0 rad. The angle φmix is the mixing angle between left and right handed quarks.
[show abstract][hide abstract] ABSTRACT: A new precise measurement of |Vcb| and of the branching ratio BR) has been performed using a sample of about 5000 semileptonic decays , selected by the DELPHI detector at LEP I by tagging the soft pion from D∗+→D0π+. The results are: , . The analytic dependencies of the differential cross-section and of the Isgur–Wise form factor as functions of the variable have also been obtained by unfolding the experimental resolution.
[show abstract][hide abstract] ABSTRACT: The rapidity-rank structure of pp¯ pairs is used to analyze the
mechanism of baryon production in hadronic Z0 decay. The
relative occurrence of the rapidity-ordered configuration pMp¯,
where /M is a meson, and that of pp¯ adjacent pairs is compared.
The data are found to be consistent with predictions from a mechanism
producing adjacent-rank pp¯ pairs, without requiring
`string-ordered' pMp¯ configurations. An upper limit of 15% at 90%
confidence is determined for the pMp¯ contribution.
Physics Letters B 08/2000; 490:61-70. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: A study of b semileptonic decays into D, Dπ+/- and
D*π+/- final states is presented. The
D0, 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
D0 and D+ results include also contributions from
D*0 and D*+ decays. A fit to the distribution of
the π+/- impact parameter to the primary interaction
vertex provides a measurement of the b semileptonic branching fractions
into the D0π+/-X,
D+π+/-X and D*+π+/-X
final states. Assuming that single pion decay modes of B mesons
dominate, the partial rates for
B¯-->D*πl-νl¯ have been
obtained, corresponding to a total branching
0.32(syst))%.This result agrees well with the observed difference
between the total B semileptonic branching fraction and the sum of the
D*l-νl¯ branching fractions.
Physics Letters B 02/2000; 475:407-428. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: The rapidity-rank structure of pairs is used to analyze the mechanism of baryon production in hadronic Z0 decay. The relative occurrence of the rapidity-ordered configuration , where M is a meson, and that of adjacent pairs is compared. The data are found to be consistent with predictions from a mechanism producing adjacent-rank pairs, without requiring `string-ordered' configurations. An upper limit of 15% at 90% confidence is determined for the contribution.
[show abstract][hide abstract] ABSTRACT: A test of the QED process e+e−→γγ(γ) 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−→γγ 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 Λ+>330 GeV and Λ−>320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c2 (for λγ=1) was obtained. s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, MS: MS>713 GeV/c2 (λ=1) and MS>691 GeV/c2 (λ=−1).
[show abstract][hide abstract] ABSTRACT: Production of Σ− and Λ(1520) in hadronic Z decays has been measured using the Delphi detector at Lep. The Σ− is directly reconstructed as a charged track in the Delphi microvertex detector and is identified by its Σ→nπ decay leading to a kink between the Σ− and π-track. The reconstruction of the Λ(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 beThe production rate of the Λ(1520) suggests that a large fraction of the stable baryons descend from orbitally excited baryonic states. It is shown that the baryon production rates in Z decays follow a universal phenomenological law related to isospin, strangeness and mass of the particles.
[show abstract][hide abstract] ABSTRACT: An update of the searches for charginos and gravitinos is presented, based on a data sample corresponding to the 158 pb−1 recorded by the DELPHI detector in 1998, at a centre-of-mass energy of 189 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/c2 higher than those obtained at a centre-of-mass energy of 183 GeV. The (μ, M2) MSSM domain excluded by combining the chargino searches with neutralino searches at the Z resonance implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 31.0 GeV/c2 for tanβ≥ 1.
[show abstract][hide abstract] ABSTRACT: The cross-section for the process
e+e--->W+W- has been
measured with the data sample collected by DELPHI at an average
centre-of-mass energy of 182.65 GeV and corresponding to an integrated
luminosity of 53 pb-1. Based on the 770 events selected as WW
candidates, the cross-section for the doubly resonant process
)=15.86 +/-0.69 (stat) +/-0.26 (syst) pb has been measured and
found to be in good agreement with the Standard Model expectation. The
branching fractions of the W decay were also measured. From these a
value of the CKM mixing matrix element Vcs=0.985+/-0.073
(stat)+/-0.025 (syst) was derived. Our previously published WW
cross-section measurements and the derived measurement of mW
have been revised and updated with the present cross-section measurement
to yield mW=80.49+/-0.43(stat)+/-0.09(syst)+/-0.03(LEP)
Physics Letters B 05/1999; 456:310-321. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between
130 GeV and 183 GeV have been studied to search for processes of the type e+e- → YY with the subsequent decay Y → X7, where X is an undetectable neutral particle. Reactions of this kind are expected in
supersymmetric models, where the Y particle can be either the lightest neutralino, decaying to a photon and a gravitino, or
the next-to-lightest neutralino, decaying to a photon and the lightest neutralino. To study the case of long-lived Y particles,
a search for single-photon events with the reconstructed photon axis pointing far from the beam interaction region has also
been performed. No evidence for a deviation from Standard Model expectations has been observed in the data and upper limits
have been derived on the signal cross-section as a function of the the X and Y masses and of the Y mean decay path.
European Physical Journal C 04/1999; 6(3):371-384. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: Data taken by DELPHI during the 1995 and 1996 LEP runs have been used to search for the supersymmetric partners of electron,
muon and tau leptons and of top and bottom quarks. The observations are in agreement with standard model predictions. Limits
are set on sfermion masses. Searches for long lived scalar leptons from low scale supersymmetry breaking models exclude stau
masses below 55 GeV/c2 at the 95% confidence level, irrespective of the gravitino mass.
European Physical Journal C 04/1999; 6(3):385-401. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector. These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 pb−1. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from to for electromagnetic type couplings) and couplings of the leptoquark states. A search for top-charm flavour changing neutral currents ( or charge conjugate) used the semileptonic decay channel. A limit on the flavour changing cross-section via neutral currents was set at 0.55pb (95% confidence level).
[show abstract][hide abstract] ABSTRACT: Measurements of the trilinear gauge boson couplings WWγ and WWZ are presented from data taken by DELPHI in 1997 at an energy of 183 GeV. From a study of the reactions e+e−→W+W−, e+e−→Weν and e+e−→ννγ, values are obtained for Δg1Z and Δκγ, the differences of the WWZ charge coupling and of the WWγ dipole couplings from their Standard Model values, and for λγ, the WWγ quadrupole coupling. The observations are consistent with the predictions of the Standard Model.
[show abstract][hide abstract] ABSTRACT: Decays of W± bosons, produced at LEP2, have been used to measure the |Vcs| element of the Cabibbo-Kobayashi-Maskawa matrix. Values for |Vcs| were extracted both from the measured hadronic branching ratio of W± decays and by tagging the flavour of hadronic jets produced in W± decays. Applying the two methods to the data collected during 1996 at energies of 161 and 172 GeV, DELPHI obtains |Vcs|=0.91+0.15−0.14(stat)±0.05(syst).
[show abstract][hide abstract] ABSTRACT: In an analysis of multihadronic events recorded at LEP by DELPHI in the years 1992 through 1994, rapidity correlations of Λ-Λ, proton-proton, and Λ-proton pairs are compared with each other and with the predictions of the string fragmentation model. For Λ pairs, the additional correlation with respect to charged kaons is also analysed.
[show abstract][hide abstract] ABSTRACT: The total and the differential cross-sections for the reaction e+e−→γγ(γ) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb−1. The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z0 energies) on the QED cutoff parameters are Λ+>253 GeV and Λ−>225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant λγ=1 is 231 GeV/c2. All the limits are at the 95% confidence level.
[show abstract][hide abstract] ABSTRACT: This paper presents results on charged Higgs boson production, based on LEP data collected at GeV, that complement the previous DELPHI results obtained at centre of mass energies up to 161 GeV. The charged Higgs bosons are assumed to be pair produced and to decay either into a quark pair or into τντ. The three different possible final states are included in the analysis. Data from ring imaging Cherenkov and microvertex detectors are used to identify the quarks as a cs pair. The number of candidates found is compatible with the background expected from standard processes. Combining the results of the present analysis with those of the previous analysis at lower energies, a new lower mass limit for the charged Higgs boson is set at 54.5 GeV/c2.
[show abstract][hide abstract] ABSTRACT: Oscillations of B0s mesons were studied in events
with a large transverse momentum lepton selected from 3.2 million
hadronic Z0 decays registered by DELPHI between 1991 and
1994. A limit on the mass difference between the physical
B0s stateswas obtained by combining the results
obtained in three channels.
Physics Letters B 10/1997; 414:382-400. · 4.57 Impact Factor