Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the ...inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of |V_cb| from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: m_b(1 GeV) = 4.591 +/- 0.062 +/- 0.039 +/- 0.005 GeV/c^2 m_c(1 GeV) = 1.170 +/- 0.093 +/- 0.055 +/- 0.005 GeV/c^2 mu_{pi}^2(1 GeV) = 0.399 +/- 0.048 +/- 0.034 +/- 0.087 GeV^2 \tilde{\rho}_D^3 = 0.053 +/- 0.017 +/- 0.011 +/- 0.026 GeV^3, and include corrections at order 1/m_b^3. Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of |V_cb| is obtained: |V_cb| = 0.0421 x (1 +/- 0.014 (meas.) +/- 0.014 (fit) +/- 0.015 (th.)).
Performance of the DELPHI detector Abreu, P.; Ajinenko, I.; Aleksan, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
1996, Letnik:
378, Številka:
1
Journal Article
Recenzirano
Odprti dostop
DELPHI (DEtector with Lepton, Photon and Hadron Identification) is a detector for e
+e
− physics, designed to provide high granularity over a 4π solid angle, allowing an effective particle ...identification. It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989. This article reviews its performance.
Neutral triple-gauge-boson couplings ZZZ, ZZγ and Zγγ have been studied with the DELPHI detector using data at energies between 183 and 208 GeV. Limits are derived on these couplings from an analysis ...of the reactions e + e - →Zγ, using data from the final states γff̄, with f=q or ν, from e + e - →ZZ, using data from the four-fermion final states qq̄qq̄, qq̄μ + μ - , qq̄e + e - , qq̄νν̄, μ + μ - νν̄ and e + e - νν̄, and from e + e - →Zγ * , in which the final state γ is off mass-shell, using data from the four-fermion final states qq̄e + e - and qq̄μ + μ - . No evidence for the presence of such couplings is observed, in agreement with the predictions of the Standard Model.
Infrared and collinear safe event shape distributions and their mean values are determined using the data taken at five different centre of mass energies above
M
Z with the DELPHI detector at LEP. ...From the event shapes, the strong coupling
α
s
is extracted in
O
(
α
s
2), NLLA and a combined scheme using hadronisation corrections evaluated with fragmentation model generators as well as using an analytical power ansatz. Comparing these measurements to those obtained at
M
Z, the energy dependence (running) of
α
s
is accessible. The logarithmic energy slope of the inverse strong coupling is measured to be
d
α
−1
s
d
log(E
cm
)
=1.39±0.34(
stat)±0.17(
syst)
,
in good agreement with the QCD expectation of 1.27.
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.
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
.
PDF
