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).
A search for sleptons, neutralinos, charginos, sgoldstinos and heavy stable charged sleptons in the context of scenarios where the lightest supersymmetric particle is the gravitino, is presented. ...Data collected during 2000 with the DELPHI detector at centre-of-mass energies from 204 to 208 GeV were analysed and combined with all the data collected from 1995 to 1999 at lower energies. No evidence for the production of sleptons, neutralinos and charginos has been found, therefore new limits on the mass of these supersymmetric particles and on the model parameter space are set. The search for heavy stable charged sleptons also updates the stable sleptons mass limit. The absence of evidence for sgoldstino production allows limits to be set on its mass and on the scale of supersymmetry breaking.
Low-energy particle production perpendicular to the event plane in three-jet events produced in Z decays in e+e− annihilation is measured and compared to that perpendicular to the event axis in ...two-jet events. The topology dependence of the hadron production ratio is found to agree with a leading-order QCD prediction. This agreement and especially the need for the presence of a destructive interference term gives evidence for the coherent nature of gluon radiation. Hadron production in three-jet events is found to be directly proportional to a single topological scale function of the inter-jet angles. The slope of the dependence of the multiplicity with respect to the topological scale was measured to be 2.211±0.014(stat.)±0.053(syst.) in good agreement with the expectation given by the colour-factor ratio CA/CF=9/4. This result strongly supports the assumption of local parton–hadron duality, LPHD, at low hadron momentum.
A precise measurement of the tau lifetime Abdallah, J.; Abreu, P.; Adam, W. ...
European physical journal. C, Particles and fields,
08/2004, Letnik:
36, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The tau lepton lifetime has been measured with the \({\rm e}^ + {\rm e}^- \rightarrow {\rm\tau}^ + {\rm\tau}^-\) events collected by the DELPHI detector at LEP in the years 1991-1995. Three different ...methods have been exploited, using both one-prong and three-prong \(\tau\) decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave \(\tau_\tau \mbox{(1 prong)} = 291.8\pm 2.3_{\mathrm{stat}} \pm 1.5_{\mathrm{sys}} \mathrm{fs}\). A third measurement using taus which decayed to three charged particles yielded \(\tau_\tau \mbox{(3 prong)} = 288.6\pm 2.4_{\mathrm{stat}} \pm 1.3_{\mathrm{sys}} \mathrm{fs}. \) These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be \(\tau_\tau = 290.9\pm 1.4_{\mathrm{stat}} \pm 1.0_{\mathrm{sys}} \mathrm{fs}\).
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.
In some supersymmetric models, the gluino (\(\tilde {\rm g}\)) is predicted to be light and stable. In that case, it would hadronize to form R-hadrons. In these models, the missing energy signature ...of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved. Therefore, such a gluino is not constrained by hadron collider results, which looked for the decay \(\tilde {\rm g}\to{\rm q \bar q}\tilde \chi^0_1\). Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for \({\rm q \bar q}\tilde {\rm g}\tilde {\rm g}\) events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c2 is excluded at the 95% confidence level in these models. Then, R-hadrons produced in the squark decays were searched for in the data collected by DELPHI at the centre-of-mass energies of 189 to 208 GeV, corresponding to an overall integrated luminosity of 609 Pb-1. The observed number of events is in agreement with the Standard Model predictions. Limits at 95% confidence level are derived on the squark masses from the excluded regions in the plane (\(m_{\tilde {\rm q} 1}, m_{\tilde {\rm g}}\))\(m_{\tilde {\rm t}1}>90\) GeV/c2, and \(m_{\tilde {\rm b}1}>96\) GeV/c2 for purely left squarks. \(m_{\tilde {\rm t}1}>87\) GeV/c2, and \(m_{\tilde {\rm b}1}>82\) GeV/c2 independent of the mixing angle.
The production of wrong sign charmed mesons b→D(s)X, D(s)=(D0,D+,Ds), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995.
Charmed mesons in Z→bb̄ events are ...exclusively reconstructed by searching for the decays D0→K−π+, D+→K−π+π+ and Ds+→φπ+→K+K−π+. The wrong sign contribution is extracted by using two discriminant variables: the charge of the b-quark at decay time, estimated from the charges of identified particles, and the momentum of the charmed meson in the rest frame of the b-hadron.
The inclusive branching fractions of b-hadrons into wrong sign charm mesons are measured to be: B(b→D0X)+B(b→D−X)=(9.3±1.7(stat)±1.3(syst)±0.4(B))%, B(b→Ds−X)=(10.1±1.0(stat)±0.6(syst)±2.8(B))% where the first error is statistical, the second and third errors are systematic.
Search for technicolor with DELPHI Abdallah et al, J.
European physical journal. C, Particles and fields,
09/2001, Letnik:
22, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Technicolor represents a viable alternative to the Higgs mechanism for generating gauge boson masses. Searches for technicolor particles \(\rho_T\) and \(\pi_T\) have been performed in the data ...collected by the DELPHI experiment at LEP at centre-of-mass energies between 192 and 208 GeV corresponding to an integrated luminosity of 452 pb\(^{-1}\). Good agreement is observed with the SM expectation in all channels studied. This is translated into an excluded region in the \((M_{\pi_T},M_{\rho_T})\) plane. The \(\rho_T\) production is excluded for all \(90 < M_{\rho_T}<206.7\) GeV/c\(^2\). Assuming a point-like interaction of the \(\pi_T\) with gauge bosons, an absolute lower limit on the charged \(\pi_T\) mass at 95% CL is set at 79.8 GeV/c\(^2\), independently of other parameters of the technicolor model.
Brain injuries such as trauma and stroke lead to glial scar formation by reactive astrocytes which produce and secret axonal outgrowth inhibitors. Chondroitin sulfate proteoglycans (CSPG) constitute ...a well-known class of extracellular matrix molecules produced at the glial scar and cause growth cone collapse. The CSPG glycosaminoglycan side chains composed of chondroitin sulfate (CS) are responsible for its inhibitory activity on neurite outgrowth and are dependent on RhoA activation. Here, we hypothesize that CSPG also impairs neural stem cell migration inhibiting their penetration into an injury site. We show that DCX+ neuroblasts do not penetrate a CSPG-rich injured area probably due to Nogo receptor activation and RhoA/ROCK signaling pathway as we demonstrate in vitro with neural stem cells cultured as neurospheres and pull-down for RhoA. Furthermore, CS-impaired cell migration in vitro induced the formation of large mature adhesions and altered cell protrusion dynamics. ROCK inhibition restored migration in vitro as well as decreased adhesion size.
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