The charmed strange baryon Xi(c)(0) was searched for in the decay channel Xi(c)(0) -> Xi(-)pi(+), and the beauty strange baryon Xi(b) in the inclusive channel Xi(b) -> Xi(-)l(-)(nu) over barX, using ...the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992-1995. The Xi(-) was reconstructed through the decay AT, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Xi(c)(0) and Xi(b) selection. The production rates were measured to be f(Xi c)(0) x BR(Xi(c)(0) -> Xi(-)pi(+) = (4.7 +/- 1.4(stat.) +/- 1.1(syst.)) x 10(-4) per hadronic Z decay, and BR(b -> Xi(b))xBR(Xi(b) -> Xi(-)l(-)X) = (3.0 +/- 1.0(stat.) +/- 0.3(syst.)) x 10(-4) for each lepton species (electron or muon). The lifetime of the Xi(b) baryon was measured to be tau(Xi b) = 1.45(-0.43)(+0.55)(stat.)+/- 0.13(syst.) ps. A combination with the previous DELPHI lifetime measurement gives tau(Xi b) = 1.48(-0.31)(+0.40)(stat.)+/- 0.12(syst.) ps.
This paper presents the final interpretation of the results from DELPHI on the searches for Higgs bosons in the minimal supersymmetric extension of the Standard Model (MSSM). A few representative ...scenarios are considered, that include CP conservation and explicit CP violation in the Higgs sector. The experimental results encompass the searches for neutral Higgs bosons at LEP1 and LEP2 in final states as expected in the MSSM, as well as LEP2 searches for charged Higgs bosons and for neutral Higgs bosons decaying into hadrons independent of the quark flavour. The data reveal no significant excess with respect to background expectations. The results are translated into excluded regions of the parameter space in the various scenarios. In the CP-conserving case, these lead to limits on the masses of the lightest scalar and pseudoscalar Higgs bosons, h and A, and on tanβ. The dependence of these limits on the top quark mass is discussed. Allowing for CP violation reduces the experimental sensitivity to Higgs bosons. It is shown that this effect depends strongly on the values of the parameters responsible for CP violation in the Higgs sector.
These final results on e(+) e(-) W+ W- production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total ...cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |V-cs| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.
Measurements are presented of
R
b
, the ratio of the
cross-section to the
cross-section in e
+
e
−
collisions, and the forward-backward asymmetry
A
FB
b
at twelve energy points in the range
–207 GeV. ...These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.
Di-jet production in γ γ collisions at LEP2 Adam, W.; Allmendinger, T.; Amaldi, U. ...
The European physical journal. C, Particles and fields,
12/2008, Letnik:
58, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The production of two high-pT jets in the interactions of quasi-real photons in e+e− collisions at \(\sqrt{s_{ee}}\) from 189 GeV to 209 GeV is studied with data corresponding to an integrated e+e− ...luminosity of 550 pb−1. The jets reconstructed by the k⊥-cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, pT, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum \(\overline{p_{T}}\) of the jets and is compared to perturbative QCD calculations.
Searches for pair-production of supersymmetric particles under the assumption of non-conservation of R-parity with a dominant LL (E) over bar or (U) over bar(D) over bar(D) over bar term have been ...performed using the data collected by the DELPHI experiment at LEP in e(+)e(-) collisions at centre-of-mass energies from 192 up to 208 GeV. No excess of data above Standard Model expectations was observed. The results were used to constrain the MSSM parameter space and to derive limits on the masses of supersymmetric particles.
In a study of the reaction e(-)e(+)-> W-W+ with the DELPHI detector, the probabilities of the two W particles occurring in the joint polarisation states transverse-transverse (T T), ...longitudinal-transverse plus transverse-longitudinal (LT) and longitudinal-longitudinal (LL) have been determined using the final states WW -> lvq (q) over bar (l = e, mu). The two-particle joint polarisation probabilities, i.e. the spin density matrix elements rho T T, rho LT, rho LL, are measured as functions of the W- production angle, theta(W-), at an average reaction energy of 198.2 GeV. Averaged over all cos.W-, the following joint probabilities are obtained: (rho) over barT T = (67 +/- 8)%, (rho) over barL T = (30 +/- 8)%, (rho) over barL T = (3 +/- 7)%. These results are in agreement with the Standard Model predictions of 63.0%, 28.9% and 8.1%, respectively. The related polarisation cross-sections sigma(TT), sigma(LT) and sigma(LL) are also presented.
The pseudoscalar meson eta(b) has been searched for in two-photon interactions at LEP II. The data sample corresponds to a total integrated luminosity of 617 pb(-1) at centre-of-mass energies ranging ...from 161 to 209 GeV. Upper limits at a confidence level of 95% on the product Gamma(gamma gamma) (eta(b)) x BR(eta(b)) are 190, 470 and 660 eV/c(2) for the eta(b) decaying into 4, 6 and 8 charged particles, respectively.
The pseudoscalar meson ηb has been searched for in two-photon interactions at LEP II. The data sample corresponds to a total integrated luminosity of 617 pb−1 at centre-of-mass energies ranging from ...161 to 209 GeV. Upper limits at a confidence level of 95% on the product Γγγ(ηb)×BR(ηb) are 190, 470 and 660 eV/c2 for the ηb decaying into 4, 6 and 8 charged particles, respectively.
The quark model does not exclude states composed of more than three quarks, like pentaquark systems. Controversial evidence for such states has been published in the last years, in particular: for a ...strange pentaquark
Θ
(
1540
)
+
; for a double-strange state, the
Ξ
(
1862
)
−
−
, subsequently called
Φ
(
1860
)
−
−
; and for a charmed state, the
Θ
c
(
3100
)
0
. If confirmed, a full pentaquark family might exist; such pentaquark states could be produced in
e
+
e
−
annihilations near the Z energy. In this Letter a search for pentaquarks is described using the DELPHI detector at LEP, characterized by powerful particle identification sub-systems crucial in the separation of the signal from the background for these states. At 95% CL, upper limits are set on the production rates
〈
N
〉
of such particles and their charge-conjugate state per Z decay:
〈
N
Θ
+
〉
×
Br
(
Θ
+
→
p
K
S
0
)
<
5.1
×
10
−4
,
〈
N
Θ
+
+
〉
<
1.6
×
10
−3
,
〈
N
Φ
(
1860
)
−
−
〉
×
Br
(
Φ
(
1860
)
−
−
→
Ξ
−
π
−
)
<
2.9
×
10
−4
,
〈
N
Θ
c
(
3100
)
0
〉
×
Br
(
Θ
c
(
3100
)
0
→
D
∗
+
p
¯
)
<
8.8
×
10
−4
.
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