101 research outputs found
A study of intermittency in Hadronic Z Decays
No full textA study on the modifications of the relation between author and lector due to the translation from text to hypertex
Study of b-quark mass effects in multijet topologies with the DELPHI detector at LEP
No full textThe 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, Rn 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 R4 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 MZ energy scale and with low energy mass measurements evolved to the MZ scale using QCD renormalisation group equations
Search for single top quark production via contact interactions at LEP2
No full textSingle top quark production via four-fermion contact interactions associated to flavour-changing neutral currents was searched for in data taken by the DELPHI detector at LEP2. The data were accumulated at centre-ofmass energies ranging from 189 to 209 GeV, with an integrated luminosity of 598.1 pb−1. No evidence for a signal was found. Limits on the energy scale Λ, were set for scalar-, vector- and tensor-like coupling scenarios. © The Author(s) 2011
A study of the b-quark fragmentation function with the DELPHI detector at LEP I and an averaged distribution obtained at the Z Pole
No full textThe nature of b-quark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementarymethods are used to reconstruct the energy of weakly decaying b-hadrons, EweakB. The average value of xweakB = EweakB/Ebeam is measured to be 0.699 ± 0.011. The resulting xweakB distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of bhadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA 6.156 from DELPHI data: a=1.84+0.23-0.21 and b=0.642+0.073-0.063 GeV-2, with a correlation factor ρ=92.2%. Combining the data on the b-quark fragmentation distributions with those obtained at the Z peak by ALEPH, OPAL and SLD, the average value of xweakB is found to be 0.7092 ± 0.0025 and the non-perturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a = 1.48+0.11-0.10 and b = 0.509+0.024-0.023 GeV-2, with a correlation factor ρ 92.6%. © The Author(s) 2011
Update of the search for charginos nearly mass-degenerate with the lightest neutralino
No full textThe data collected by DELPHI in 1998 at the centre-of-mass energy of 189 GeV have been used to update the search for charginos nearly mass-degenerate with the lightest supersymmetric particle, which is assumed to be the lightest neutralino. Mass differences below ΔM = 3 GeV/c2 are considered. No excess of events with respect to the Standard Model expectation has been observed, and exclusions in the plane of ΔM versus chargino mass are given. The new ΔM independent lower limit on the mass of the chargino is 62.4 GeV/c2 in the higgsino scenario (which includes the gaugino mass unification scenario), if all sfermions are heavier than the lightest chargino. In the approximation of large sfermion masses the limit is 59.8 GeV/c2, independently of the field content.0info:eu-repo/semantics/publishe
Study of the dependence of direct soft photon production on the jet characteristics in hadronic Z0 decays
No full textAn analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behavior to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones. © 2010 The Author(s)
Searches for invisibly decaying Higgs bosons with the DELPHI detector at LEP
No full textGeneral rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 29 Jun 2019 Digital Object Identifier (DOI) 10.1140/epjc/s2003-01469-8 Eur. Phys. J. C 32, 475-492 (2004) Abstract. Searches for HZ production with the Higgs boson decaying into an invisible final state were performed using the data collected by the DELPHI experiment at centre-of-mass energies between 188 GeV and 209 GeV. Both hadronic and leptonic final states of the Z boson were analysed. In addition to the search for a heavy Higgs boson, a dedicated search for a light Higgs boson down to 40 GeV/c 2 was performed. No signal was found. Assuming the Standard Model HZ production cross-section, the mass limit for invisibly decaying Higgs bosons is 112.1 GeV/c 2 at 95% confidence level. An interpretation in the Minimal Supersymmetric extension of the Standard Model (MSSM) and in a Majoron model is also given
Search for lepton flavor violating τ− decays with a KS0 meson
No full textAbstractWe have searched for the lepton flavor violating decays τ−→ℓ−KS0 (ℓ=e or μ), using a data sample of 281 fb−1 collected with the Belle detector at the KEKB e+e− asymmetric-energy collider. No evidence for a signal was found in either of the decay modes, and we set the following upper limits for the branching fractions: B(τ−→e−KS0)<5.6×10−8 and B(τ−→μ−KS0)<4.9×10−8 at the 90% confidence level. These results improve the previously published limits set by the CLEO Collaboration by factors of 16 and 19, respectively
Measurement of phi(3) with a Dalitz plot analysis of B+->(DK(*)+)-K-(*) decay
No full textWe present a measurement of the unitarity triangle angle phi(3) using a Dalitz plot analysis of the K-S(0)pi(+)pi(-) decay of the neutral D meson from the B-+/-->(DK(*)+/-)-K-(*) process. The method exploits the interference between D-0 and (D) over bar (0) to extract the angle phi(3), strong phase delta and the ratio r of suppressed and allowed amplitudes. We apply this method to a 357 fb(-1) data sample collected by the Belle experiment. The analysis uses three modes: B+-> DK+, B+->(DK+)-K-* with D-*-> D pi(0), and B+-> DK*+ with K*+-> K-S(0)pi(+), as well as the corresponding charge-conjugate modes. From a combined maximum likelihood fit to the three modes, we obtain phi(3)=53 degrees(+15 degrees s)(-18 degrees)(stat)+/- 3 degrees(syst)+/- 9 degrees(model). The corresponding 2 standard deviation interval is 8 degrees <phi(3)< 111 degrees.Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)62ARTICLE11null7
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