A search for pair-produced charged Higgs bosons was performed in the data collected by the DELPHI detector at LEP II at centre-of-mass energies from 189 GeV to 209 GeV. Five different final states, ...\(\tau^ + \nu_{\tau}\tau^- \bar{\nu}_{\tau}\), \(\mathrm{c}\bar{\mathrm{s}}\bar{\mathrm{c}}\mathrm{s}\), \(\mathrm{c}\bar{\mathrm{s}}{\tau^- \bar{\nu}_{\tau}}\), \(\mathrm{W}^*\!\mathrm{A}\mathrm{W}^*\!\mathrm{A}\) and \(\mathrm{W}^*\!\mathrm{A}\tau^- \bar{\nu}_{\tau}\) were considered, accounting for the major expected decays in type I and type II Two Higgs Doublet Models. No significant excess of data compared to the expected Standard Model processes was observed. The existence of a charged Higgs boson with mass lower than 76.7 GeV/c2 (type I) or 74.4 GeV/c2 (type II) is excluded at the 95% confidence level, for a wide range of the model parameters. Model independent cross-section limits have also been calculated.
A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996-2000). The data sample has an integrated ...luminosity of 660 pb(-1) and was collected over a range of centre-of-mass energies from 161 to 209 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W- -> l (nu) over bar (l) and W+W- -> q (q) over bar'(q) over barq'channels. The W mass result for the combined data set is M-W = 80.336 +/- 0.055(Stat.) +/- 0.028(Syst.) +/- 0.025(FSI) +/- 0.009(LEP) GeV/c(2) , where FSI represents the uncertainty due to final state interaction effects in the q (q) over bar'(q) over barq' channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is Gamma(W) = 2.404 +/- 0.140(Stat.) +/- 0.077(Syst.) +/- 0.065(FSI) GeV/c(2). These results supersede all values previously published by the DELPHI collaboration.
This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the process for centre-of-mass energies above the Z ...resonance, from -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 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 in R-parity violating supersymmetry.This paper is dedicated to the memory of Alan Segar.
An analysis is presented of events containing jets including at least one b-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, ...with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced fourtop-quark production, pair production of chiral b '-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b ' quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models.
Infrared and collinear safe event shape distributions and their mean values are determined in \({\mathrm{e^+e^-}}\) collisions at centre-of-mass energies between 45 and 202GeV. A phenomenological ...analysis based on power correction models including hadron mass effects for both differential distributions and mean values is presented. Using power corrections, \(\alpha_s\) is extracted from the mean values and shapes. In an alternative approach, renormalisation group invariance (RGI) is used as an explicit constraint, leading to a consistent description of mean values without the need for sizeable power corrections. The QCD \(\beta\)-function is precisely measured using this approach. From the DELPHI data on Thrust, including data from low energy experiments, one finds \\beta_0 = 7.86 \pm 0.32\ for the one loop coefficient of the \(\beta\)-function or, assuming QCD, \n_{\mathrm{f}} = 4.75 \pm 0.44 \ for the number of active flavours. These values agree well with the QCD expectation of \(\beta_0=7.67\) and \(n_{\mathrm{f}}=5\). A direct measurement of the full logarithmic energy slope excludes light gluinos with a mass below 5GeV.
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.
This Letter presents the results of a search for a heavy particle decaying into an e±μ∓, e±τ∓, or μ±τ∓ final state in pp collisions at s=7 TeV. The data were recorded with the ATLAS detector at the ...LHC during 2011 and correspond to an integrated luminosity of 4.6 fb−1. No significant excess above the Standard Model expectation is observed, and exclusions at 95% confidence level are placed on the cross section times branching ratio for the production of an R-parity-violating supersymmetric tau sneutrino. For a sneutrino mass of 500 (2000) GeV, the observed limits on the production cross section times branching ratio are 3.2 (1.4) fb, 42 (17) fb, and 40 (18) fb for the eμ, eτ, and μτ modes, respectively. These results considerably extend constraints from Tevatron experiments.
A search for pair-produced doubly charged Higgs bosons has been performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies between 189 and 209 GeV. No excess is ...observed in the data with respect to the Standard Model background. A lower limit for the mass of 97.3 GeV/c2 at the 95% confidence level has been set for doubly charged Higgs bosons in left–right symmetric models for any value of the Yukawa coupling between the Higgs bosons and the τ leptons.
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.
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