The number of women and underrepresented individuals working in science, technology, engineering and mathematics (STEM) fields does not reflect the diversity of our societies. Even if children have ...an interest in STEM, they may not consider choosing a study or career in that direction if their perception is that they would not belong in science. This study examines the effects of a STEM lesson series aimed at inclusivity and diversity on children's perception and sense of belonging in space science. Before and after the lesson series, children filled out a questionnaire aimed at eliciting their perception of space science and space scientists. After the lessons, a subsample of children was interviewed about the effects of the lesson series on the children's perception and sense of belonging regarding space science. Six months after the last lesson took place, children from two classes filled out a short survey with open questions to measure retention. The results of this study showed that the lesson series had a significant impact on children's perception of space scientists, and that the implementation of the lessons facilitated thinking about (a future in) space science. This lesson series has succeeded in changing children's perception of space scientists as a diverse and international group of people.
Searches for neutral Higgs bosons produced at LEP in association with Z bosons, in pairs and in the Yukawa process are presented in this paper. Higgs boson decays into b quarks, \(\tau\) leptons, or ...other Higgs bosons are considered, giving rise to four-b, four-b + jets, six-b and four-\(\tau\) final states, as well as mixed modes with b quarks and \(\tau\) leptons. The whole mass domain kinematically accessible at LEP in these topologies is searched. The analysed data set covers both the LEP1 and LEP2 energy ranges and exploits most of the luminosity recorded by the DELPHI experiment. No convincing evidence for a signal is found, and results are presented in the form of mass-dependent upper bounds on coupling factors (in units of model-independent reference cross-sections) for all processes, allowing interpretation of the data in a large class of models.
A determination of the single W spin density matrix (SDM) elements in the reaction e
+
e
-
→W
+
W
-
→lνqq̄(l=e/μ) is reported at centre-of-mass energies between 189 and 209 GeV. The data sample used ...corresponds to an integrated luminosity of 520 pb
-1
taken by DELPHI between 1998 and 2000. The single W SDM elements, ρ
ττ’
W±
(τ,τ’=± 1 or 0), are determined as a function of the W
-
production angle with respect to the e
-
beam direction and are obtained from measurements of the W decay products by the application of suitable projection operators, Λ
ττ’
, which assume the V-A coupling of the W-boson to fermions. The measured SDM elements are used to obtain the fraction of longitudinally polarised Ws, with the result:
at a mean energy of 198 GeV. The SDM elements are also used to determine the triple gauge couplings Δg
1
Z
,Δκ
γ
,λ
γ
and g
4
Z
,
and
. For the CP-violating couplings the results of single parameter fits are:
The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model.
Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2<
E
γ
≤1 GeV and transverse momentum with ...respect to the parent muon
p
T
<40 MeV/
c
, and 1<
E
γ
≤10 GeV and
p
T
<80 MeV/
c
. A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic
Z
0
decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06±0.12±0.07 in the photon energy range 0.2<
E
γ
≤1 GeV and 1.04±0.09±0.12 in the photon energy range 1<
E
γ
≤10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.
The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and ...light quark jets (ℓ=uds) in events with n=2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, R
n
bℓ
, have been measured with a double-tag technique using the CAMBRIDGE jet-clustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R
4
bℓ
, a measurement of the b-quark mass using massive leading-order calculations gives:
This result is compatible with previous three-jet determinations at the M
Z
energy scale and with low energy mass measurements evolved to the M
Z
scale using QCD renormalisation group equations.
Electroweak measurements performed with data taken at the electron–positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total ...luminosity of about 3 fb−1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.
Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron–positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose–Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, mW and ΓW, the branching fraction of W decays to hadrons, B(W→had), and the trilinear gauge-boson self-couplings g1Z, κγ and λγ are determined to be: mW=80.376±0.033GeVΓW=2.195±0.083GeVB(W→had)=67.41±0.27%g1Z=0.984−0.020+0.018κγ=0.982±0.042λγ=−0.022±0.019.
A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle pT ...distribution and the differential charged hadrons dσ/dpT cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.
The exclusive and semi-exclusive branching ratios of the τ lepton hadronic decay modes (, , , , , , , , and ) were measured with data from the DELPHI detector at LEP.
In the reaction e+e-→WW→(q1q̄2)(q3q̄4) the usual hadronization models treat the colour singlets q1q̄2 and q3q̄4 coming from two W bosons independently. However, since the final state partons may ...coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as colour reconnection. In this article the results of the investigation of colour reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its κ parameter most compatible with the data was found to be: κSK-I=2.2+2.5-1.3 corresponding to the probability of reconnection \(\mathcal{P}_{\text{reco}}\) to be in the range \(0.31 <\mathcal{P}_{{\text{reco}}} < 0.68\) at 68% confidence level with its best value at 0.52.
The charged particle multiplicity in hadronic three-jet events from Z decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading ...logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio CA/CF with the result in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios \(r = N_{gg}(s)/N_{q\bar q}(s)\) of the gluon and quark multiplicities and \(r^{(1)} = N_{gg}'(s)/N_{q\bar q}'(s)\) of their derivatives are compared with perturbative calculations. While a good agreement between calculations and data is observed for r(1), larger deviations are found for r indicating that non-perturbative effects are more important for r than for r(1).
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