104 research outputs found
Faddeev study of heavy baryon spectroscopy
We investigate the structure of heavy baryons containing a charm or a bottom
quark. We employ a constituent quark model successful in the description of the
baryon-baryon interaction which is consistent with the light baryon spectra. We
solve exactly the three-quark problem by means of the Faddeev method in
momentum space. Heavy baryon spectrum shows a manifest compromise between
perturbative and nonperturbative contributions. The flavor dependence of the
one-gluon exchange is analyzed. We assign quantum numbers to some already
observed resonances and we predict the first radial and orbital excitations of
all states with or 3/2. We combine our results with heavy quark
symmetry and lowest-order SU(3) symmetry breaking to predict the masses and
quantum numbers of six still non-measured ground-state beauty baryons.Comment: 22 pages, 4 figures, 8 tables. Accepted for publication in J. Phys.
Measurement and Interpretation of Fermion-Pair Production at LEP energies above the Z Resonance
This paper presents DELPHI measurements and interpretations of
cross-sections, forward-backward asymmetries, and angular distributions, for
the e+e- -> ffbar process for centre-of-mass energies above the Z resonance,
from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are
consistent with the predictions of the Standard Model and are used to study a
variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering
and several models which include physics beyond the Standard Model: the
exchange of Z' bosons, contact interactions between fermions, the exchange of
gravitons in large extra dimensions and the exchange of sneutrino in R-parity
violating supersymmetry.Comment: 79 pages, 16 figures, Accepted by Eur. Phys. J.
A Determination of the Centre-of-Mass Energy at LEP2 using Radiative 2-fermion Events
Using e+e- -> mu+mu-(gamma) and e+e- -> qqbar(gamma) events radiative to the
Z pole, DELPHI has determined the centre-of-mass energy, sqrt{s}, using energy
and momentum constraint methods. The results are expressed as deviations from
the nominal LEP centre-of-mass energy, measured using other techniques. The
results are found to be compatible with the LEP Energy Working Group estimates
for a combination of the 1997 to 2000 data sets.Comment: 20 pages, 6 figures, Accepted by Eur. Phys. J.
A Measurement of the Tau Hadronic Branching Ratios
The exclusive and semi-exclusive branching ratios of the tau lepton hadronic
decay modes (h- v_t, h- pi0 v_t, h- pi0 pi0 v_t, h- \geq 2pi0 v_t, h- \geq 3pi0
v_t, 2h- h+ v_t, 2h- h+ pi0 v_t, 2h- h+ \geq 2pi0 v_t, 3h- 2h+ v_t and 3h- 2h+
\geq 1pi0 v_t) were measured with data from the DELPHI detector at LEP.Comment: 53 pages, 18 figures, Accepted by Eur. Phys. J.
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 the electron structure function F2e at LEP energies
The hadronic part of the electron structure function F2e has been measured for the first time, using e+e−e+e− data collected by the DELPHI experiment at LEP, at centre-of-mass energies of √s=91.2-209.5 GeV. The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function View the MathML sourceF2e data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function View the MathML sourceF2γ analyses and help in refining existing parameterisations
Study of double-tagged gamma gamma events at LEPII
Double-tagged interactions of photons with virtualities Q^2 between 10 GeV^2
and 200 GeV^2 are studied with the data collected by DELPHI at LEPII from 1998
to 2000, corresponding to an integrated luminosity of 550 pb^{-1}. The gam*
gam* -> mu+mu- data agree with QED predictions. The cross-section of the
reaction gam* gam* -> hadrons is measured and compared to the LO and NLO BFKL
calculations.Comment: 17 pages, 9 figures, Accepted by Eur. Phys. J.
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
Study of the Dependence of Direct Soft Photon Production on the Jet Characteristics in Hadronic Z^0 Decays
40 pages, 10 figures, Accepted by Eur. Phys. J. CAn analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behaviour to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.Peer reviewe
Measurements of CP-conserving trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at LEP2
The data taken by Delphi at centre-of-mass energies between 189 and 209 GeV are used to place limits on the CP-conserving trilinear gauge boson couplings , λ γ and Δκ γ associated to W + W − and single W production at Lep2. Using data from the jj ℓ ν, jjjj, jjX and ℓ X final states, where j, ℓ and X represent a jet, a lepton and missing four-momentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by Delphi. This paper is dedicated to the memory of Professor Paul Booth who was Delphi Deputy Spokesperson from 1989 to 1994. He played a key role in the final installation and commissioning of the Delphi detector as well as leading the Liverpool group for many years thereafter.Peer reviewe
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