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.
These final results from DELPHI searches for the Standard Model (SM) Higgs boson, together with benchmark scans of the Minimal Supersymmetric Standard Model (MSSM) neutral Higgs bosons, used data ...taken at centre-of-mass energies between 200 and 209 GeV with a total integrated luminosity of 224 pb-1. The data from 192 to 202 GeV are reanalysed with improved b-tagging for MSSM final states decaying to four b-quarks. The 95% confidence level lower mass bound on the Standard Model Higgs boson is 114.1 GeV/c2. Limits are also given on the lightest scalar and pseudo-scalar Higgs bosons of the MSSM.
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.
The muon spectrometer of the ATLAS detector for the Large Hadron Collider is designed to provide a muon transverse momentum resolution of 2%–10% for momenta between 6
GeV and 1
TeV over a ...pseudo-rapidity range of |
η|⩽2.7. This required the development of precision drift chambers with a track position resolution of
40
μ
m, the Monitored Drift Tube (MDT) chambers. We report about the construction of the three main types of MDT chambers for ATLAS, test results and the first production experience.
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.
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.
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 study of quark jets in e+e− reactions at LEP has demonstrated that the hadronisation process is reproduced well by the Lund string model. However, our understanding of gluon fragmentation is less ...complete. In this study enriched quark and gluon jet samples of different purities are selected in three-jet events from hadronic decays of the Z collected by the DELPHI experiment in the LEP runs during 1994 and 1995. The leading systems of the two kinds of jets are defined by requiring a rapidity gap and their sum of charges is studied. An excess of leading systems with total charge zero is found for gluon jets in all cases, when compared to Monte Carlo simulations with JETSET (with and without Bose–Einstein correlations included) and ARIADNE. The corresponding leading systems of quark jets do not exhibit such an excess. The influence of the gap size and of the gluon purity on the effect is studied and a concentration of the excess of neutral leading systems at low invariant masses (≲2 GeV/c2) is observed, indicating that gluon jets might have an additional hitherto undetected fragmentation mode via a two-gluon system. This could be an indication of a possible production of gluonic states as predicted by QCD.
The production fractions of charged and neutral b-hadrons in b-quark events from Z0 decays have been measured with the DELPHI detector at LEP. An algorithm has been developed, based on a neural ...network, to estimate the charge of the weakly-decaying b-hadron by distinguishing its decay products from particles produced at the primary vertex. From the data taken in the years 1994 and 1995, the fraction of b̄-quarks fragmenting into positively charged weakly-decaying b-hadrons has been measured to be: f+=42.09±0.82(stat)±0.89(syst)%. Subtracting the rates for charged Ξ̄b+ and Ω̄b+ baryons gives the production fraction of B+ mesons: fBu=40.99±0.82(stat)±1.11(syst)%.
DELPHI results are presented on the inclusive production of two (KKπ)0 states in the mass region 1.2–1.6 GeV/c2 in hadronic Z decays at LEP I. The measured masses (widths) are 1274±6 MeV/c2 ...(29±12 MeV/c2) and 1426±6 MeV/c2 (51±14 MeV/c2), respectively. A partial-wave analysis of the (KKπ)0 system shows that the first peak is consistent with the IG(JPC)=0+(1++)/(0−+)a0(980)π and the second with the IG(JPC)=0+(1++)K∗(892)K+c.c. assignments. The total hadronic production rates per hadronic Z decay are (0.165±0.051) and (0.056±0.012), respectively. These measurements are consistent with the two states being the f1(1285) and f1(1420) mesons.
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