0000000000134976
AUTHOR
J. M. Lopez
showing 48 related works from this author
Identified particles in quark and gluon jets
1997
A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K+, K-0, p, Lambda and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity. (C) 1997 Published by Elsevier Science B.V.
Updated precision measurement of the average lifetime of B hadrons
1996
The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.}
Search for neutral heavy leptons produced in Z decays
1997
Weak isosinglet Neutral Heavy Leptons ($\nu_m$) have been searched for using data collected by the DELPHI detector corresponding to $3.3\times 10^{6}$ hadronic~Z$^{0}$ decays at LEP1. Four separate searches have been performed, for short-lived $\nu_m$ production giving monojet or acollinear jet topologies, and for long-lived $\nu_m$ giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio $BR($Z$^0\rightarrow \nu_m \overline{\nu})$ of about $1.3\times10^{-6}$ at 95\% confidence level for $\nu_m$ masses between 3.5 and 50 GeV/$c^2$. Outside this range the limit weakens rap…
Rapidity correlations in Lambda baryon and proton production in hadronic Z0 decays
1998
In an analysis of multihadronic events recorded at LEP by DELPHI in the years 1992 through 1994, charged hadrons are identified using the measurement of their energy loss and their Cherenkov angle. Rapidity correlations of \La-\La, proton-proton, and \La-proton pairs are compared. The agreement with the string and cluster fragmentation models is tested. For those pairs that frame a meson in terms of rapidity the compensation of strangeness is studied. For \La{}$\overline{\mathrm{p}}$ pairs the additional correlation with respect to charged kaons is analysed.
Measurement of trilinear gauge couplings in e(+)e(-) collisions at 161 GeV and 172 GeV
1998
Trilinear gauge boson couplings are measured using data taken by DELPHI at 161 GeV and 172 GeV, Values for WWV couplings (V = Z,gamma) are determined from a study of the reactions e(+)e(-) --> W+W- and e(+)e(-) --> We nu, using differential distributions from the WW final state in which one W decays hadronically and the other leptonically, and total cross,section data from other channels, Limits are also derived on neutral ZV gamma couplings from an analysis of the reaction e(+)e(-) --> gamma + invisible particles. (C) 1998 Elsevier Science B.V.
Performance of the DELPHI detector
1996
DELPHI (DEtector with Lepton, Photon and Hadron Identification) is a detector for e(+)e(-) physics, designed to provide high granularity over a 4 pi solid angle, allowing an effective particle identification, It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989. This article reviews its performance.
A measurement of the Tau topological branching ratios
2001
Using data collected in the DELPHI detector at LEP-1, measurements of the inclusive tau branching ratios for decay modes containing one, three, or five charged particles have been performed, giving the following results: B_1 = B(\tau^- -> (particle)^- \geq 0pi^0 \geq 0K^0 \nu_\tau(\bar{\nu})) = (85.316 +/- 0.093 +/- 0.049)%; B_3 = B(\tau^- -> 2h^-h^+ \geq 0pi^0 \geq 0K^0 \nu_\tau) = (14.569 +/- 0.093 +/- 0.048)%; B_5 = B(\tau^- -> 3h^-2h^+ \geq 0pi^0 \geq 0K^0 \nu_\tau) = (0.115 +/- 0.013 +/- 0.006)%, where h is either a charged pi or K meson. The first quoted uncertainties are statistical and the second systematic.
Search for exclusive decays of the Lambda_b baryon and measurement of its mass
1996
A search for fully reconstructed \lb beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the \lc\ppm channel and one in the \lc\a1m channel over a small background. The \lb beauty baryon mass is measured to be (~ 5668 \pm 16~ ({\rm stat.}) \pm 8~({\rm syst.})~)~ \mv.
Tuning and test of fragmentation models based on identified particles and precision event shape data
1996
Event shape and charged particle inclusive distributions are measured using 750000 decays of the $Z$ to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.
Measurement and interpretation of the $W$-pair cross-section in $e^+e^-$ interactions at 161 GeV
1997
In 1996 LEP ran at a centre-of-mass energy of 161~GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of $9.93 {\mathrm{~pb^{-1}}}$, and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant $e^+e^-\to\mathrm{WW}$ process of $3.67~^{+0.97}_{-0.85} \pm 0.19{\mathrm{~pb}}$ has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of ${\mathrm{80.40~\pm~0.44~(stat.)~\pm~0.09~(syst.) ~\pm 0.03~(LEP)~GeV}}/c^2$. Alternatively, if $m_{\mathrm{W}}$ is held fixed at its current value determined by other experiments, t…
Novel method for determination of tritium depth profiles in metallic samples
2019
Tritium accumulation in fusion reactor materials is considered a serious radiological issue, therefore a lot of effort has been concentrated on the development of radiometric techniques. A novel method, based on gradual dissolution, for the determination of the total tritium content and its depth profiles in metallic samples is demonstrated. This method allows for the measurement of tritium in metallic samples after their exposure to a hydrogen and tritium mixture, tritium containing plasma or after irradiation with neutrons resulting in tritium formation. In this method, successive layers of metal are removed using an appropriate etching agent in the controlled regime and the amount of evo…
Measurements of the tau polarisation in Z0 decays
1995
A sample of Z0→τ+τ- events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the τ polarisation in the exclusive decay channels {Mathematical expression}, {Mathematical expression}, πν, ρν and a1ν. The τ polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the τ polarisation as a function of production angle yields the values for the mean τ polarisation 〈P〉τ=-0.148±0.022 and for the Z0 polarisation PZ=-0.136±0.027. These results are used to determin…
Overview of the JET results
2015
Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in…
Search for exclusive charmless b meson decays with the Delphi detector at Lep
1995
Charmless hadronic decays of beauty mesons have been searched for using the data collected with the DELPHI detector at the LEP collider. Several two, three and four-body decay modes have been investigated. Particle identification was used to distinguish the final states with protons, kaons and pions. Three candidate events selected in two-body decay modes are interpreted as evidence for charmless B decays. No excess has been found in higher multiplicity modes and improved upper limits for some of the branching ratios are given. © 1995.
Measurement of the inclusive charmless and double-charm B branching ratios
1998
The DELPHI experiment at LEP has measured the inclusive charmless B hadron decay branching ratio, the B branching ratio into two charmed particles, and the total number of charmed particles per B decay, using the hadronic Z data taken between 1992 and 1995. The results are extracted from a fit to the b-tagging probability distribution based on the precise impact parameter measurements made using the microvertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm (c (c) over bar), is measured to be 0.033 +/- 0.021. The B branching ratio into two open charmed particles is 0.136 +/- 0.042. The mean number of charmed particles per B decay (including hidden …
First evidence for a charm radial excitation, D
1998
Using D*+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66 +/- 14(stat.) events is observed in the D(*+)pi(+)pi(-) final state with a mass of 2637 +/- 2(stat.) +/- 6(syst.) MeV/c(2) and a full width smaller than 15 MeV/c(2) (95% C.L.). This signal is compatible with the expected decay of a radially excited D*' (J(P) = 1(-))meson. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
Search for pair production of heavy objects in 4-jet events at sqrt {s}$=130-136 GeV
1996
Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, hA or H$^+$H$^-$, using a data sample of $5.9\,$pb$^{-1}$ of $e^+ e^-$ collisions at $\sqrt{s}=130$-$136\,{\mathrm {GeV}}$ collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on $b$-tagging finds no hA candidate with high mass. A study optimized to search for H$^+$H$^-$ events with mass in the 40-50$\,{\mathrm{GeV}}/c^2$ range also finds no candidate. Finally a comparison is made with a recent ALEPH a…
First measurement of f′2 (1525) production in Z0 hadronic decays
1996
The inclusive production of the f(2)'(1525) in hadronic Z(0) decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f(2)'(1525) --> K+K-. The average number of f(2)(')(1525) produced per hadronic Z decay, [f(2)'] = 0.020 +/- 0.005 (stat) +/- 0.006 (syst), and the momentum distribution of the f(2)'(1525) have both been measured. The mass and width of the f(2)'(1525) are found to be [M(f2)'] = 1535 +/- 5 (stat) +/- 4 (syst) MeV/c(2). [Gamma(f2)'] = 60 +/- 20 (stat) +/- 19 (syst) MeV/c(2)
Energy dependence of inclusive spectra in e+ e- annihilation
1999
Inclusive charged hadron distributions as obtained from the DELPHI measurements at 130, 136, 161, 172 and 183 GeV are presented as a function of the variables rapidity, xi(p), p and transversal momenta. Data are compared with event generators and with MLLA calculations, in order to examine the hypothesis of local parton hadron duality. The differential momentum spectra show an indication for coherence effects in the production of soft particles. The relation between the energy dependence of the charged multiplicity and the rapidity distribution is examined. (C) 1999 Elsevier Science B.V. All rights reserved.
Search for promptly produced heavy quarkonium states in hadronic Z decays
1996
A search has been made for direct production of heavy quarkonium states in more than 3 million hadronic Z^{0} decays in the 1991-1994 DELPHI data. Prompt J/\psi, \psi(2S) and \Upsilon candidates have been searched for through their leptonic decay modes using criteria based on the kinematics and decay vertex positions. New upper limits are set at the 90 \% confidence level for {Br( Z^0 \rightarrow \left( Q \bar{Q} \right) X ) / Br( Z^0 \rightarrow \mbox{hadrons})} for various strong production mechanisms of J/\psi and \Upsilon; these range down to 0.9 \times 10^{-4}. The limits are set in the presence of a small excess (\sim 1 \% statistical probability of a background fluctuation) in the su…
A Precise Measurement of the Tau Lepton Lifetime
1996
The tau lepton lifetime has been measured using three different methods with the DELPHI detector. Two measurements of one-prong decays are combined, accounting for correlations, giving a result of \tau_\tau = 291.8 \pm 3.3 \mbox{ (stat.)} \pm 2.0 \mbox{(sys.) fs} while the decay length distribution of three-prong decays gives the result \tau_{\tau} = 286.7 \pm 4.9 \mbox{ (stat.)} \pm 3.3 \mbox{ (sys.) fs}. Combining the results presented here with previous DELPHI measurements, we get \tau_{\tau} = 291.4 \pm 3.0 fs and find that the ratio of the coupling constant for tau decay relative to that for muon decay is 0.990 \pm 0.009, compatible with lepton universality.
A search for invisible Higgs bosons produced in e+e- interactions at LEP 2 energies
1999
Searches for HZ production with the Higgs boson decaying into an invisible final state have been performed with the data collected by the DELPHI experiment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pair final states of the Z boson were analysed. From the absence of signal, upper limits on the cross-section and the corresponding Higgs boson mass limits were set at 95% confidence level. The results are interpreted as excluded parameter regions in the framework of the minimal supersymmetric standard model and in the simplest Majoron model with one Higgs doublet and one Higgs singlet field. (C) 1999 Elsevier Science B.V. All rights reserved.
Strange baryon production in Z hadronic decays
1995
A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the ∑± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models. © 1995 Springer-Verlag.
Search for chargino pair production in scenarios with gravitino LSP and stau NLSP at GeV at LEP
1999
Promptly decaying lightest charginos were searched for in the context of scenarios with gravitino LSP. It was assumed that the stau is the next to lightest supersymmetric particle (NLSP). Data collected with the DELPHI detector at a centre-of-mass energy near 183~{~mbox{${mathrm{GeV}}$}}\nwere analysed combining the methods developed in previous searches. No evidence for the production of these particles was found. Hence, limits were derived at 95% confidence level. The mass of charginos was found to be greater than 85.5~GeV/$c^2$ for $m_{ ilde{chi}^+_1}-m_{ ilde{ au}_1}geq 0.3 {mathrm{GeV}}/c^2$, independently of the mass of the gravitino.
Masses, lifetimes and production rates of Ξ− and Ξ¯+ at LEP 1
2006
Measurements of the Xi(-) and (Xi) over bar (+) masses, mass differences, lifetimes and lifetime differences are presented. The (Xi) over bar (+) sample used is much larger than those used previously for such measurements. In addition, the S production rates in Z -> b (b) over bar and Z -> q (q) over bar events are compared and the position xi* of the maximum of the distribution in Z -> q (q) over bar events is measured.
Comparison of the structure of the plasma-facing surface and tritium accumulation in beryllium tiles from JET ILW campaigns 2011-2012 and 2013-2014
2019
In this study, beryllium tiles from Joint European Torus (JET) vacuum vessel wall were analysed and compared regarding their position in the vacuum vessel and differences in the exploitation conditions during two campaigns of ITER-Like-Wall (ILW) in 2011-2012 (ILW1) and 2013-2014 (ILW2) Tritium content in beryllium samples were assessed. Two methods were used to measure tritium content in the samples - dissolution under controlled conditions and tritium thermal desorption. Prior to desorption and dissolution experiments, scanning electron microscopy and energy dispersive x-ray spectroscopy were used to study structure and chemical composition of plasma-facing-surfaces of the beryllium sampl…
Measurement of the Λb0 decay form factor
2004
The form factor of Λb0 baryons is estimated using 3.46×106 hadronic Z decays collected by the DELPHI experiment between 1992 and 1995. Charmed Λc+ baryons fully reconstructed in the pK-π+, pK S0, and Λπ+π+π - modes, are associated to a lepton with opposite charge in order to select Λb0→Λc+l-ν̄l decays. From a combined likelihood and event rate fit to the distribution of the Isgur-Wise variable w, and using the Heavy Quark Effective Theory (HQET), the slope of the b-baryon form factor is measured to be ρ̂2=2.03±0.46(stat) -1.00+0.72(syst). The exclusive semileptonic branching fraction Br(Λb0→Λc+l-ν̄l) can be derived from ρ̂2 and is found to be (5.0-0.8+1.1(stat)-1.2+1.6(syst))%. Limits on ot…
A measurement of the \(\tau\) leptonic branching fractions
1995
Abstract: A sample of 25000 Z(0) --> tau(-)tau(+) events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the tau lepton. The results are B(tau --> e nu) = (17.51+/-0.39)% and B(tau --> mu nu) = (17.02+/-0.31)%. The ratio of the muon and electron couplings to the weak charged current is measured to be g(mu)/g(e) = 1.000+/-0.013, satisfying e-mu universality. The average leptonic branching fraction corrected to the value for a massless lepton, assuming e-mu universality, is found to be B(tau --> l nu) = (17.50+/-0.25)%.
A measurement of αs from the scaling violation in e+e- annihilation
1997
The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from $\zz$ decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is \begin{displaymath} \alpha_s(M_Z) = 0.124^{+0.006}_{-0.007}(exp)\pm 0.009 (theory) \end{displaymath} where the first error represents the experimental uncertainty and the second error is due to the factorization a…
Energy dependence of event shapes and of $\alpha_s$ at LEP 2
1999
Infrared and collinear safe event shape distributions and their mean values are determined using the data taken at five different centre of mass energies above M-Z with the DELPHI detector at LEP. From the event shapes, the strong coupling alpha(s) is extracted in O(alpha(s)(2)), NLLA and a combined scheme using hadronisation corrections evaluated with fragmentation model generators as well as using an analytical power ansatz. Comparing these measurements to those obtained at M-Z, the energy dependence (running) of alpha(s) is accessible. The logarithmic energy slope of the inverse strong coupling is measured to be d alpha(s)(-1)/d log(E-cm) = 1.39 +/- 0.34 (stat) +/- 0.17(syst), in good ag…
Charged particle multiplicity in e^{+}e_{-}$ → q[L:q] events at 161 and 172 GeV and from the decay of the W boson
1998
The data collected by DELPHI in 1996 have been used to measure the average charged particle multiplicities and dispersions in $q\bar{q}$ events at centre-of-mass energies of $\sqrt{s}=161$~GeV and $\sqrt{s}=172$~GeV, and the average charge multiplicity in WW events at $\sqrt{s}=172$~GeV. The multiplicities in $q\bar{q}$ events are consistent with the evolution predicted by QCD. The dispersions in the multiplicity distributions are consistent with Koba-Nielsen-Olesen (KNO) scaling. The average multiplicity of charged particles in hadronic W decays has been measured for the first time; its value, $19.23 \pm 0.74 (stat+syst)$, is consistent with that expected for an $e^+e^-$ interaction at a c…
A measurement of the branching fractions of the b quark into charged and neutral b hadrons
2003
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 bbar-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 Xibar_b^+ and Omegabar_b^+ baryons gives the production fraction of B^+ mesons: f_Bu = (40.99 +/- 0.82 (stat.)…
Measurement of the transverse spin correlation in Z → τ+ τ- decays
1997
The measurement of the correlation between the transverse spin components of tau(+)tau(-) pairs collected during 1992 to 1994 with the DELPHI detector at LEP1 is presented. A value C-TT = 0.87 +/- 0.20 (stat.)(-0.12)(+0.10) (syst.) was obtained for the correlation parameter, in agreement with the Standard Model expectation. (C) 1997 Published by Elsevier Science B.V.
Measurement of the spin density matrix for the rho(0), K*(0)(892) and phi produced in Z(0) decays
1997
The spin density matrix elements for the rho(0), K-*0(892) and phi produced in hadronic Z(0) decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K-*0(892) and phi, in the region x(p) less than or equal to 0.3 (x(p) = p/p(beam)), where rho(00) = 0.33 +/- 0.05 and rho(00) = 0.30 +/- 0.04, respectively. In the fragmentation region, x(p) greater than or equal to 0.4, there is some indication for spin alignment of the rho(0) and K-*0(892), since rho(00) = 0.43 +/- 0.05 and rho(00) = 0.46 +/- 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the phi, rho(00) = 0.30 +/- 0.04 for x(p) greater than or equal …
Measurement of $\Delta^{++}$(1232) production in hadronic Z decays
1995
A measurement of the \Delta^{++}(1232) inclusive production in hadronic decays of the Z at LEP is presented, based on 1.3 million hadronic events collected~ by the DELPHI~ detector in the 1994 LEP running~ period. The DELPHI ring imaging Cherenkov counters are used for identifying hadrons. The average \Delta^{++}(1232) multiplicity per hadronic event is 0.079 \pm 0.015 which is more than a factor of two below the JETSET, HERWIG and UCLA model predictions. It agrees with a recently proposed universal mass dependence of particle production rates in e^{+}e^- annihilations.
Measurement of correlations between pions from different W's in e+e- → W+W- events
1997
Correlations between pions from different W's in e(+)e(-) --> W+W- events are studied using data collected by the DELPHI detector at LEP running at a centre-of-mass energy of 172 GeV in 1996. At the present level of statistics, no enhancement of the correlation function above that expected from a pair of uncorrelated W's is observed at small values of the four-momentum difference of the pions. (C) 1997 Published by Elsevier Science B.V.
Two-particle angular correlations in e(+)e(-) interactions compared with QCD predictions
1998
Two-particle angular correlations in jet cones have been measured in e(+)e(-) annihilation into hadrons at LEP energies (root s = 91 and 183 GeV) and are compared with QCD predictions using the LPHD hypothesis. Two different functions have been tested. While the differentially normalized correlation function shows substantial deviations from the predictions, a globally normalized correlation function agrees well. The size of alpha(s)(eff) land other QCD parameters) and its running with the relevant angular scale, the validity of LPHD, and problems due to non-perturbative effects are discussed critically. (C) 1998 Elsevier Science B.V. All rights reserved.
Energy dependence of the differences between the quark and gluon jet fragmentation
1996
Three jet events arising from decays of the Z beson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is [ r ] = 1.241 +/- 0.015 (stat.) +/- 0.025 (syst.). Gluon jets are broa…
A Search for Heavy Stable and Long-Lived Squarks and Sleptons in $e^+ e^-$ Collisions at Energies from 130 to 183 GeV
1998
A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the ionization loss measured in the Time Projection Chamber identify heavy particles from masses of 2 to nearly 89 GeV/c$^2$. Upper limits are given on the production cross-section and masses of sleptons, free squarks with a charge of $q = \pm 2/3e$ and hadronizing squarks. A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the io…
Study of the four-jet anomaly observed at LEP centre-of-mass energies of 130 and 136 GeV
1999
The four-jet events collected by DELPHI during the special LEP run at centre-of-mass energies of 130 and 136 GeV in 1997 with an integrated luminosity of 5.9 pb(-1) are analysed. Their rate and the distributions of their di-jet masses, their smallest jet charges, and their di-jet charge separations all agree well with Standard Model predictions. Thus the hypothesis of pair production of a new particle with a sum of di-jet masses around 105 GeV/c(2) is not supported. The combined result of the four LEP collaborations refuting this hypothesis at over 99% confidence level is also given. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Search for $B^0_s-\overline{B^0_s}$ oscillations and a measurement of $B^0_d-\overline{B^0_d}$ oscillations using events with an inclusively reconstr…
2003
Neutral B meson oscillations in the B-s(0) - , and B-d(0) - systems were studied using a sample of about 4.0 million hadronic Z decays recorded by the DELPHI detector between 1992 and 2000. Events with a high transverse momentum lepton were removed and a sample of 770 k events with an inclusively reconstructed vertex was selected. The mass difference between the two physical states in the B-d(0) - system was measured to be: Deltam(d) = (0.531 +/- 0.025(stat.) +/- 0.007(syst.))ps(-1). The following limit on the width difference of these states was also obtained: DeltaGamma(Bd)/Gamma(Bd) oscillations was found, a limit on the mass difference of the two physical states was given:, Deltam(s) > …
Measurement of inclusive ρ0, f0(980), f2(1270), K and f′2(1525) production in Z0 decays
1999
DELPHI results are presented on the inclusive production of the neutral mesons ρ0, f0(980), f2(1270), KView the MathML source and f′2(1525) in hadronic Z0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z0 decay have been determined to be: 1.19±0.10 for ρ0; 0.164±0.021 for f0(980); 0.214±0.038 for f2(1270); 0.073±0.023 for KView the MathML source; and 0.012±0.006 for f′2(1525). The total production rates for all mesons and differential cross-sections for …
Lifetime and production rate of beauty baryons from Z decays
1995
The 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)\%…
Search for charged Higgs bosons in e^{+}e^{-}$ collisions at √s=172 GeV
1998
This paper presents results on charged Higgs boson production, based on LEP data collected at √s = 172 GeV, that complement the previous DELPHI results obtained at centre of mass energies up to 161 GeV. The charged Higgs bosons are assumed to be pair produced and to decay either into a quark pair or into τVτ. The three different possible final states are included in the analysis. Data from ring imaging Cherenkov and microvertex detectors are used to identify the quarks as a cs pair. The number of candidates found is compatible with the background expected from standard processes. Combining the results of the present analysis with those of the previous analysis at lower energies, a new lower…
Search for neutral MSSM Higgs bosons at LEP
2006
The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of "benchmark" models, including CP-conserving and CP-violating scenarios. Thes…
Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating
2018
International audience; During the 2015--2016 JET campaigns, many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for DT operation in JET. In this paper, we review various key recent hybrid discharges and model the combined ICRF NBI heating. These deuterium discharges with deuterium beams had the ICRF antenna frequency tuned to match the cyclotron frequency of minority H at the centre of the tokamak coinciding with the second harmonic cyclotron resonance of D. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of D beam ions, allowing us to assess its impact on the neutron rate…
mb at MZ
1998
Abstract The value of the b quark mass at the M Z scale defined in the MS renormalization scheme, m b ( M Z ), was determined using 2.8 million hadronic Z decays collected during 1992-1994 by the DELPHI detector to be m b (M Z )=2.67±0.25 ( stat. )±0.34 ( frag. )±0.27 ( theo. ) GeV/c 2 . The analysis considers NLO corrections to the three-jet production rate including mass effects, and the result obtained agrees with the QCD prediction of having a running b quark mass at an energy scale equal to M Z . This is the first time that such a measurement is performed far above the b b production threshold. The study also verifies the flavour independence of the strong coupling constant for b and l…
A measurement of the photon structure function F-2(gamma) at an average Q(2) of 12 GeV2/c(4)
1995
The hadronic photon structure function F_{2}^{gamma} has been measured in the Q^{2} range from 4 to 30~GeV^2/c^{4} and down to x values of order 0.001, using data taken with the DELPHI detector at LEP between 1991 and 1993. A comparison is made with several F_{2}^{gamma} parameterizations with special emphasis on their low x behaviour. A result on the Q^{2} evolution of F_{2}^{gamma} is presented.