30 research outputs found
Measurement of the rate of b anti-b b anti-b events in hadronic Z decays and the extraction of the gluon splitting into b anti-b
No full textThe rate was measured using about hadronic decays collected by the DELPHI experiment in 1994 and 1995. Events were forced into 3-jets with and a b-tag was required for every jet. The rate was measured to be: where the invariant mass of every system is above twice the b quark mass. Using the value of the probability of secondary production of a pair from a gluon per hadronic decay, , was extracted and found to be:
A precise measurement of the partial decay width ratio R-b(0) = Gamma(b(b)over-bar)/Gamma(had)
No full textThe partial decay width of the Z to \bb quark pairs has beenmeasured by the DELPHI detector at LEP using data taken in the years1992 to 1995.Decays of b-hadrons were tagged by several methods usingtracks with large impact parameters and/or reconstructed secondary vertices, complemented by event shape variables.Combining these methods in a multivariate analysis the value\frac{\Gamma({\mathrm Z \rightarrow \bb}) }{ \Gamma({\mathrm {Z \rightarrow had}}) } = 0.21634 \pm 0.00067({\mathrm {stat}}) \pm 0.00060 ({\mathrm {syst}})was obtained, where the production fractionwas fixed to its Standard Model value
Measurement of the rate of b(b)over-bar-b(b)over-bar events in hadronic Z decays and the extraction of the gluon splitting into b(b)over-bar
No full textThe rate Z –> b (b) over bar b (b) over bar was measured using about 2 x 10(6) hadronic decays collected by the DELPHI experiment in 1994 and 1995. Events were forced into 3-jets with y(min) > 0.06 and a b-tag was required for every jet. The rate was measured to be: R-4b = BR(Z –> b (b) over bar b (b) over bar/BR(Z –> hadrons), = (6.0 +/- 1.9(stat.) +/- 1.4(syst.)) x 10(-4) where the invariant mass of every b (b) over bar system is above twice the b quark mass. Using the value of R-4b the probability of secondary production of a b (b) over bar pair from a gluon per hadronic Z decay, g(bb), was extracted and found to be: g(bb) = (3.3 +/- 1.0(stat.) +/- 0.8(syst.)) x 10(-3). (C) 1999 Published by Elsevier Science B.V. All rights reserved
A study of bb production in e+e− collisions at s=130 –207 GeV
No full textMeasurements are presented of R b, the ratio of the bb cross-section to the qq cross-section in e+e− collisions, and the forward-backward asymmetry A FBb at twelve energy points in the range s=130 –207 GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.
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Measurement of A(FB)(b anti-b) in hadronic Z decays using a jet charge technique
No full textThe \BB forward-backward asymmetry %, \AFBbb, has been determined from the average charge flow %, , measured in a sample of 3,500,000 hadronic Z decays collected with the DELPHI detector in 1992 - 1995. The measurement is performed in an enriched \BB sample selected using an impact parameter tag and results in the following values for the \BB forward-backward asymmetry: \begin {center} \begin{tabular}{ccl} \AFBbb (89.55 GeV) & = & 0.068\,\ \pm0.018\,\ (\mbox{stat.})\pm0.0013 (\mbox{syst.}) \\ \AFBbb (91.26 GeV) & = & 0.0982\pm0.0047(\mbox{stat.})\pm0.0016(\mbox{syst.}) \\ \AFBbb (92.94 GeV) & = & 0.123\,\ \pm0.016\,\ (\mbox{stat.})\pm0.0027(\mbox{ syst.}) \\ \end{tabular} \end{center} %at an average center of mass energy of 91.251\, GeV . % The \BB charge separation %, \db, required for this analysis is directly measured in the b tagged sample, while the other charge separations %, \ddusc, are obtained from a fragmentation model precisely calibrated to data. % The effective weak mixing angle %, \sweff, is deduced from the measurement to be: \begin {center} \begin{tabular}{ccl} \sweff & =& \end{tabular} \end{center
Inclusive b decays to wrong sign charmed mesons
No full textThe production of wrong sign charmed mesons b → D (s)X, D (s) = (D 0, D +, D s), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995. Charmed mesons in Z → bb events are exclusively reconstructed by searching for the decays D 0 → K -π +, D + → K -π +π + and D s + 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 → D 0X) + B(b → D -X) = (9.3 ± 1.7(stat) ± 1.3(syst) ± 0.4(B))%, B(b → D s -X) = (10.1 ± 0.4(B))%, B(b → D s -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. © 2003 Published by Elsevier Science B.V.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Lifetime and production rate of beauty baryons from Z decays
No full textThe production and decay of beauty baryons (b-baryons) have been studied using 1.7 \times 10^6 Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify the b-baryons. The first method used pairs of a \Lambda and a lepton to tag the b-baryon decay. The second method associated fully reconstructed \Lambda_c baryons with leptons. The third analysis reconstructed the b-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured: \begin{eqnarray*} f(\qb \ra \Bb) \times \BR(\Bb \ra \mLs \ell\bar{\nu}_{\ell}\X) & = & (0.30 \pm 0.06 \pm0.04)\% , \\ f(\qb \ra \Bb) \times \BR(\Bb \ra \mLc \ell\bar{\nu}_{\ell}\X) & = & (1.18 \pm 0.26^{+0.31}_{-0.21})\% , \\ f(\qb \ra \Bb) \times \BR(\Bb \ra \prot\mu\bar{\nu}_{\mu}\X) & = & (0.49\pm0.11\pm^{+0.15}_{ -0.11})\% . \end{eqnarray*} The average b-baryon lifetime was determined to be:\par \vspace{0.4cm} \centerline {\tau = 1.21 ^{+.21}_{-.18}(stat.)\pm0.04(exp.syst.) ^{+.02}_{-.07}(th.syst.) ps.
Measurement of A(FB)(b(b)over-bar) in hadronic Z decays using a jet charge technique
No full textThe bb forward-backward asymmetry has been determined from the average charge how measured in a sample of 3,500,000 hadronic Z decays collected with the DELPHI detector in 1992 - 1995. The measurement is performed in an enriched b (b) over bar sample selected using an impact parameter tag and results in the following values for the bl; forward-backward asymmetry: A(FB)(b (b) over bar) (89.55 GeV) = 0.068 +/- 0.016 (stat.) +/- 0.0013(syst.) A(FB)(b (b) over bar)(91.26 GeV) = 0.0982 +/- 0.0047(stat.) +/- 0.0016(syst.) A(FB)(b (b) over bar)(92.94 GeV) = 0.123 +/- 0.016 (stat.) +/- 0.0027(syst.) The b (b) over bar charge separation required for this analysis is directly measured in the b tagged sample, while the other charge separations are obtained from a fragmentation model precisely calibrated to data. The effective weak mixing angle is deduced from the measurement to be: sin(2)theta(eff)1 = 0.23186 +/- 0.00063. RI De Angelis, Alessandro/B-5372-2009; Gonzalez Caballero, Isidro/E-7354-2010; Krammer, Manfred/A-6508-2010; Muresan, Raluca-Anca/C-3725-2011; Katsanevas, Stavros/A-4297-2011; Ruiz, Alberto/E-4473-2011; Marti-Garcia, Salvador/F-3085-2011; Verzi, Valerio/B-1149-2012; branchini, paolo/A-4857-2011; Shellard, Ronald/G-4825-2012; Monge, Maria Roberta/G-9127-2012; Petrolini, Alessandro/H-3782-2011; Fruhwirth, Rudolf/H-2529-201
Breeding drought tolerant cowpea: constraints, accomplishments, and future prospects
No full textThis review presents an overview of accomplishments on different aspects of cowpea breeding for drought tolerance. Furthermore it provides options to enhance the genetic potential of the crop by minimizing yield loss due to drought stress. Recent efforts have focused on the genetic dissection of drought tolerance through identification of markers defining quantitative trait loci (QTL) with effects on specific traits related to drought tolerance. Others have studied the relationship of the drought response and yield components, morphological traits and physiological parameters. To our knowledge, QTLs with effects on drought tolerance have not yet been identified in cowpea. The main reason is that very few researchers are working on drought tolerance in cowpea. Some other reasons might be related to the complex nature of the drought stress response, and partly to the difficulties associated with reliable and reproducible measurements of a single trait linked to specific molecular markers to be used for marker assisted breeding. Despite the fact that extensive research has been conducted on the screening aspects for drought tolerance in cowpea only very few¿like the `wooden box¿ technique¿have been successfully used to select parental genotypes exhibiting different mechanisms of drought tolerance. Field and pot testing of these genotypes demonstrated a close correspondence between drought tolerance at seedling and reproductive stages. Some researchers selected a variety of candidate genes and used differential screening methods to identify cDNAs from genes that may underlie different drought tolerance pathways in cowpea. Reverse genetic analysis still needs to be done to confirm the functions of these genes in cowpea. Understanding the genetics of drought tolerance and identification of DNA markers linked to QTLs, with a clear path towards localizing chromosomal regions or candidate genes involved in drought tolerance will help cowpea breeders to develop improved varieties that combine drought tolerance with other desired traits using marker assisted selection
Measurement of A(FB)(b(b)over-bar) in hadronic Z decays using a jet charge technique
No full textThe bb forward-backward asymmetry has been determined from the average charge how measured in a sample of 3,500,000 hadronic Z decays collected with the DELPHI detector in 1992 - 1995. The measurement is performed in an enriched b (b) over bar sample selected using an impact parameter tag and results in the following values for the bl; forward-backward asymmetry: A(FB)(b (b) over bar) (89.55 GeV) = 0.068 +/- 0.016 (stat.) +/- 0.0013(syst.) A(FB)(b (b) over bar)(91.26 GeV) = 0.0982 +/- 0.0047(stat.) +/- 0.0016(syst.) A(FB)(b (b) over bar)(92.94 GeV) = 0.123 +/- 0.016 (stat.) +/- 0.0027(syst.) The b (b) over bar charge separation required for this analysis is directly measured in the b tagged sample, while the other charge separations are obtained from a fragmentation model precisely calibrated to data. The effective weak mixing angle is deduced from the measurement to be: sin(2)theta(eff)1 = 0.23186 +/- 0.00063
