0000000000106218
AUTHOR
O. Kouznetsov
showing 78 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.
Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Sivers asymmetries
2012
The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Sivers asymmetry of the proton has been extracted in the Bjorken x range 0.003 0.03. The asymmetry is different from zero and positive also in the low x region, where sea-quarks dominate. The kinematic dependence of the asymmetry has also been investigated and results are given for various intervals of hadron and virtual photon fractional energy. In contrast to the case of the Collins asymmetry, the results on the Sivers asymmetry suggest a strong depende…
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…
Measurement of the forward-backward asymmetry of e(+)e(-)-]z-]b(b)over-bar using prompt leptons and a lifetime tag
1995
The forward-backward asymmetry of the process e+e-→Z→b {Mathematical expression} has been measured using events collected by the DELPHI experiment during the 1991 and 1992 LEP runs. This data sample corresponded to 884 000 hadronic Z decays at a centre-of-mass energy {Mathematical expression}. The tagging of b-quark events was performed using two approaches; the first was based on the semileptonic decay channels b→X+μ and b→X+e, the second used a lifetime tag with jet-charge reconstruction. The results of these two methods were combined to give {Mathematical expression} With the semileptonic sample, the forward-backward asymmetry of the process e+e-→Z→ {Mathematical expression} was also mea…
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 theBs0Lifetime in the Exclusive Decay ChannelBs0→J/ψϕ
2005
Using the exclusive decay B-s(0)-->J/psi(mu(+)mu(-))phi(K+K-), we report the most precise single measurement of the B-s(0) lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb(-1) collected with the D0 detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B-s(0) lifetime, tau(B-s(0))=1.444(-0.090)(+0.098)(stat)+/-0.020(sys) ps. We also report a measurement for the lifetime of the B-0 meson using the exclusive decay B-0-->J/psi(mu(+)mu(-))K-*0(892)(K(+)pi(-)). We reconstruct 1370 signal candidates, obtaining tau(B-0)=1.473(-0.050)(+0.052)(stat)+/-0.023(sys) ps, and the ratio of lifetimes, …
Measurement of Dijet Azimuthal Decorrelations at Central Rapidities inpp¯Collisions ats=1.96 TeV
2005
Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the D0 detector in p (p) over bar collisions at a center-of-mass energy root s=1.96 TeV. The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of 150 pb(-1). Azimuthal correlations are stronger at larger transverse momenta. These are well described in perturbative QCD at next-to-leading order in the strong coupling constant, except at large azimuthal differences where contributions with low transverse momentum are significant.
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.
Evidence for B$^{0}_{s}$ meson production in Z$^0$ decays
1992
Seven unambiguous events out of a sample of 270 000 Z0 decays, contain in tile same jet a D(s) meson and a muon at large transverse momentum relative to the et axis. These events are direct evidence for B(s)0 meson production in hadronic Z0 decays. The production rate of these events, relative to all hadronic Z0 decays is ( 18 +/- 8) x 10(-5) this number including the relevant branching fractions of the B(s)0 and D(s). The value of the B(s)0 meson lifetime relative to the average B meson lifetime is measured to be 0.8 +/- 0.4.
Observation of orbitally excited B mesons
1995
Experimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the BÏ and B*Ï distribution of Q = m(B**) - m(B(*)) - m(Ï) using Z0decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B**â B(*)Ï is measured to be 284 ± 5 (stat.) ± 15 (syst.) MeV/c2, and the Gaussian width of the signal is 79 ± 5 (stat.) ± 8 (syst.) MeV/c2. This signal can be described as a single resonance of mass m = 5732 ± 5 (stat.) ± 20 (syst.) MeV/c2and full width Î = 145 ± 28 MeV/c2. The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-…
FIRST MEASUREMENT OF THE STRANGE QUARK ASYMMETRY AT THE Z(0) PEAK
1995
A measurement of the strange quark forward-backward asymmetry at the Z0 peak was performed using 718,000 multihadronic Z0 decays collected by the DELPHI detector at LEP in 1992. The s-quark was tagged by the presence of high momentum charged kaons identified by the Ring Imaging Cherenkov detector and by Λ0;s decaying into pπ-. The s-quark purity obtained was estimated for the two hadrons to be 43%. The average s-quark asymmetry was found to be 0.131±0.035 (stat.) ±0.013 (syst.). The forward-backward asymmetry was measured for unresolved d-and s-quarks, tagged by the detection of a high energy neutron or neutral kaon in the Hadron Calorimeter. The combined d-and s-quark purity was 69% and th…
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…
Search for supersymmetry with gauge-mediated breaking in diphoton events at D0
2004
We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider in 2002--2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-lightest SUSY particle.
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…
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.
The spin structure functiong1pof the proton and a test of the Bjorken sum rule
2016
New results for the double spin asymmetry A(1)(p) and the proton longitudinal spin structure function g(1)(p) are presented. They were obtained by the COMPASS Collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH3 target. The data were collected in 2011 and complement those recorded in 2007 at 160 GeV, in particular at lower values of x. They improve the statistical precision of g(1)(p)(x) by about a factor of two in the region x less than or similar to 0.02. A next-to-leading order QCD fit to the g(1) world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, Delta Sigma, ranging from 0.26 to 0.36, and to 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)
The upgraded DO detector
2006
The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of s…
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.
Leading order determination of the gluon polarisation from DIS events with high-pThadron pairs
2013
We present a determination of the gluon polarisation Delta g/g in the nucleon, based on the longitudinal double-spin asymmetry of DIS events with Q(2) > 1 (GeV/c)(2) including a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam scattering off a polarised (LiD)-Li-6 target. The gluon polarisation is evaluated by a Neural Network approach for three intervals of the gluon momentum fraction x(g) covering the range 0.04 < x(g) < 0.27. The values obtained at leading order in QCD do not show any significant dependence on x(g). Their average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (sy…
Exclusive muoproduction on transversely polarised protons and deuterons
2012
The transverse target spin azimuthal asymmetry A(UT)(sin(phi-phi s)) in hard exclusive production of rho(0) mesons was measured at COMPASS by scattering 160 GeV/c muons off transversely polarised protons and deuterons. The measured asymmetry is sensitive to the nucleon helicity-flip generalised parton distributions E-q, which are related to the orbital angular momentum of quarks in the nucleon. The Q(2), x-B-j and p(T)(2) dependence of A(UT)(sin(phi-phi s)) is presented in a wide kinematic range: 1 (GeV/c)(2) < Q(2) < 10 (GeV/c)(2), 0.003 < xB(j) < 0.3 and 0.05 (GeV/c)(2) < p(T)(2) < 0.5 (GeV/c)(2) for protons or 0.10 (GeV/c)(2) < p(T)(2) < 0.5 (GeV/c)(2) for deuterons. Results for deuteron…
Search for the sgoldstino at √s = 189 to 202 GeV.
2000
A search for the supersymmetric partner of the goldstino, the sgoldstino S, at LEP2 is presented. The production Sgamma followed by S decay into two gluons or into two photons was studied at 189 - 202 GeV LEP centre-of-mass energies. No evidence for the S production was found and limits on the S mass corresponding to different theory parameters are given.
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…
Observation of a New Narrow Axial-Vector Mesona1(1420)
2015
The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV/c pions into the π(-)π(-)π(+) final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of 3π mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow peak is observed in the f0(980)π channel with spin, parity and C-parity quantum numbers J(PC)=1(++). We present a resonance-model study of a subset of the spin-density matrix selecting 3π states with J(PC)=2(++) and 4(++) decaying into ρ(770)π and with J(PC)=1(++) decaying into f0(980)π. We identify a new a1 meson with mass (1414(-13)(+15)) MeV/c2 and wid…
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.
The spin-dependent structure function of the proton g1p and a test of the Bjorken sum rule
2010
Abstract The inclusive double-spin asymmetry, A 1 p , has been measured at COMPASS in deep-inelastic polarised muon scattering off a large polarised NH3 target. The data, collected in the year 2007, cover the range Q 2 > 1 ( GeV / c ) 2 , 0.004 x 0.7 and improve the statistical precision of g 1 p ( x ) by a factor of two in the region x 0.02 . The new proton asymmetries are combined with those previously published for the deuteron to extract the non-singlet spin-dependent structure function g 1 NS ( x , Q 2 ) . The isovector quark density, Δ q 3 ( x , Q 2 ) , is evaluated from a NLO QCD fit of g 1 NS . The first moment of Δ q 3 is in good agreement with the value predicted by the Bjorken su…
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$
2015
We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$. We measured the longi…
Observation and Properties of theX(3872)Decaying toJ/ψπ+π−inpp¯Collisions ats=1.96 TeV
2004
We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in p (p) over bar collisions at roots=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.
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…
Erratum to: Hadron transverse momentum distributions in muon deep inelastic scattering at 160 GeV/ $$c$$ c
2015
Author(s): Adolph, C; Alekseev, MG; Alexakhin, VY; Alexandrov, Y; Alexeev, GD; Amoroso, A; Andrieux, V; Austregesilo, A; Badelek, B; Balestra, F; Barth, J; Baum, G; Bedfer, Y; Berlin, A; Bernhard, J; Bertini, R; Bicker, K; Bieling, J; Birsa, R; Bisplinghoff, J; Boer, M; Bordalo, P; Bradamante, F; Braun, C; Bravar, A; Bressan, A; Buchele, M; Burtin, E; Capozza, L; Chiosso, M; Chung, SU; Cicuttin, A; Crespo, ML; Dalla Torre, S; Dasgupta, SS; Dasgupta, S; Denisov, OY; Donskov, SV; Doshita, N; Duic, V; Dunnweber, W; Dziewiecki, M; Efremov, A; Elia, C; Eversheim, PD; Eyrich, W; Faessler, M; Ferrero, A; Filin, A; Finger, M; Finger Jr, M; Fischer, H; Franco, C; du Fresne von Hohenesche, N; Friedri…
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 …
Study of Σ(1385) and Ξ(1321) hyperon and antihyperon production in deep inelastic muon scattering
2013
Large samples of \Lambda, \Sigma(1385) and \Xi(1321) hyperons produced in deep-inelastic muon scattering off a ^6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of \Sigma(1385)^+, \Sigma(1385)^-, \bar{\Sigma}(1385)^-, \bar{\Sigma}(1385)^+, \Xi(1321)^-, and \bar{\Xi}(1321)^+ hyperons decaying into \Lambda(\bar{\Lambda})\pi were measured. The heavy hyperon to \Lambda and heavy antihyperon to \bar{\Lambda} yield ratios were found to be in the range 3.8% to 5.6% with a relative uncertainty of about 10%. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator.
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.
The COMPASS experiment at CERN
2007
The COMPASS experiment makes use of the CERN SPS high-intensitymuon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing particles are detected in coincidence with the incoming muon or hadron. A large polarized target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a two-stage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both…
The Deuteron Spin-dependent Structure Function g1(d) and its First Moment
2007
We present a measurement of the deuteron spin-dependent structure function g1d based on the data collected by the COMPASS experiment at CERN during the years 2002-2004. The data provide an accurate evaluation for Gamma_1^d, the first moment of g1d(x), and for the matrix element of the singlet axial current, a0. The results of QCD fits in the next to leading order (NLO) on all g1 deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function Delta G positive or negative, which describe the data equally well. In both cases, at Q^2 = 3 (GeV/c)^2 the first moment of Delta G is found to be of the order of 0.2 - 0.3 in absolute value.
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 new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target
2007
New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.
Determination of |Vub|/|Vcb| with DELPHI at LEP
2001
The ratio of the CKM quark-mixing matrix elements |Vub|/|Vcb| has been measured using B hadron semileptonic decays. The analysis uses the reconstructed mass M_X of the secondary hadronic system produced in association with an identified lepton. Since B -> X_u lepton anti-nu transitions are characterised by hadronic masses below those of the D mesons produced in B -> X_c lepton anti-nu transitions, events with a reconstructed value of M_X significantly below the D mass are selected. Further signal enrichments are obtained using the topology of reconstructed decays and hadron identification. A fit to the numbers of decays in the b -> u enriched and depleted samples with M_X above and…
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 Doubly Charged Higgs Boson Pair Production in the Decay toμ+μ+μ−μ−inpp¯Collisions ats=1.96 TeV
2004
A search for pair production of doubly charged Higgs bosons in the process p (p) over bar -->H++H---->mu(+)mu(+)mu(-)mu(-) is performed with the D0 run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive dimuon data collected at an energy of roots=1.96 TeV, corresponding to an integrated luminosity of 113 pb(-1). In the absence of a signal, 95% confidence level mass limits of M(H-L(+/-+/-))>118.4 GeV/c(2) and M(H-R(+/-+/-))>98.2 GeV/c(2) are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs.
Corrigendum to “Odd and even partial waves of ηπ− and η′π− in π−p → η(′)π−p at 191 GeV/c” [Phys. Lett. B 740 (2015) 303–311]
2020
Abstract In Fig. 5 on p. 311 of our Phys. Lett. B 740 (2015) 303 an adjustment by 180 ∘ is required for the phases with respect to the L = 2 , M = 1 wave, of the following waves: L = 1 , 3 , 5 with M = 1 , and L = 2 with M = 2 . After this correction (Fig. 5 (corrected) below), the extracted partial waves describe the angular distribution of the η ( ′ ) in the Gottfried-Jackson (GJ) frame, using Eq. (4) with implicit Condon-Shortley phase convention. The other results of our paper are not affected. The right-handed GJ coordinate system was defined by the z-axis pointing in the direction of the beam in the η ( ′ ) π − center-of-mass system and the y-axis pointing in the direction of p recoil…
MEASUREMENT OF THE FORWARD-BACKWARD ASYMMETRY OF CHARM AND BOTTOM QUARKS AT THE Z-POLE USING D-ASTERISK(+/-)-MESONS
1995
The forward-backward asymmetries for the processes $$e^ + e^ - \to c\bar c$$ and $$e^ + e^ - \to b\bar b$$ at theZ resonance are measured using identifiedD *± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D *+→D 0π+ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be: $$\begin{gathered} A_{FB}^{c\bar c} = 0.077 \pm 0.029(stat) \pm 0.012(sys), \hfill \\ A_{FB}^{b\bar b} = 0.059 \pm 0.062(stat) \pm 0.024(sys). \hfill \\ \end{gathered} $$ Constraining theb asymmetry to the value measured by DELPHI using independent analyses, the charm asymmetry is determined to be: $$A_{FB}^{c,const} = 0.068 \pm…
Measurements of the trilinear gauge boson couplings WWV (V = $\gamma$ Z) in e$^+$e$^-$ collisions at 183 GeV
1999
Measurements of the trilinear gauge boson couplings WWγ and WWZ are presented from data taken by DELPHI in 1997 at an energy of 183 GeV. From a study of the reactions e + e − → W + W − , e + e − → Weν and e + e − → ννγ , values are obtained for Δg 1 Z and Δκ γ , the differences of the WWZ charge coupling and of the WWγ dipole couplings from their Standard Model values, and for λ γ , the WWγ quadrupole coupling. The observations are consistent with the predictions of the Standard Model. (Elsevier)
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.
Search for composite and exotic fermions at LEP 2
1999
A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48~pb$^{-1}$ at an $e^+e^-$ centre-of-mass energy of 183~GeV and about 20~pb$^{-1}$ equally shared between the centre-of-mass energies of 172~GeV and 161~GeV. The search for pair-produced new leptons establishes 95\% confidence level mass limits in the region between 70~GeV/$c^2$ and 90~GeV/$c^2$, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermio…
Search for Z0 decays to two leptons and a charged particle-antiparticle pair
1993
Based on a sample equivalent to 365 000 hadronic Z0 decays, the search in DELPHI data for pairs of leptons accompanied by a pair of charged particles is described. A total of 11 events were found in the electron channel, 9 in the muon channel and 7 in the tau channel. Results on lepton pairs with a radiated photon are also presented. The data from all channels are compatible with the expectations from standard processes. However, one event was found in the tau channel with an unusually high mass of the charged particle pair.
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.}
Improved measurements of cross sections and asymmetries at the Z0 resonance
1994
During the 1992 running period of the LEP e+e- collider, the DELPHI experiment accumulated approximately 24 pb-1 of data at the Z0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass m(t) = 157(-48)+36(expt.)-20(+19)(Higgs) GeV, and for the effective mixing angle sin2 …
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.
A search for $\eta'_c$ production in photon-photon fusion at LEP
1998
A search for the production of the $\eta'_c$ meson, the first radial excitation of the ground state of charmonium $\eta_c$(2980), in the photon-photon fusion reaction at LEP has been performed using the data collected by the DELPHI detector during 1992-1996. No evidence of $\eta'_c$ production is found in the mass region 3520--3800 MeV/c^2. An upper limit for the ratio of the two-photon widths of the $\eta'_c$ and $\eta_c$ is obtained.
Identified charged particles in quark and gluon jets
2000
A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at LEP during 1994-1995 was used for an improved measurement of inclusive distributions of pi+, K+ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, xi^*, of the xi-distributions for kaons in gluon and quark jets are observed to be different.
Measurement of inclusive K*(0)(892), phi(1020) and K-2*(0)(1430) production in hadronic Z decays
1996
The inclusive production of the neutral vector mesons K-*0(892) and phi(1020), and of the tensor meson K-2(*0)(1430), in hadronic decays of the Z has been mea sured by the DELPHI detector at LEP. The average production rates per hadronic Z decay have been determined to be 0.77 +/- 0.08 K-2(*0)(892), 0.104 +/- 0.008 phi(1020) and 0.079 +/- 0.040 K-2(*0)(1430). The ratio of the tensor-to-vector meson production yields, [K-2(*0)(1430)]/[K-*0(892)] = 0.10 +/- 0.05, is smaller than the [f(2)(1270)]/[rho(0)(770)] and [f'(2)(1525)]/[phi(1020)] ratios measured by DELPHI. The production rates and differential cross sections are compared with the predictions of JETSET 7.4 tuned to the DELPHI data and…
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…
Update of the search for charginos nearly mass-degenerate with the lightest neutralino
2000
The 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 \Delta M = 3 GeV/c^2 are considered. No excess of events with respect to the Standard Model expectation has been observed, and exclusions in the plane of \Delta M versus chargino mass are given. The new \Delta M independent lower limit on the mass of the chargino is 62.4 GeV/c^2 in the higgsino scenario (which includes the gaugino mass unification scenario), if all sfermions are heavier than the lightest chargino. In the approximat…
Lifetime of Charged and Neutral B-hadrons Using Event Topology
1995
The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic \PZz decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1\pm0.3\%, and 83\% (70\%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be \TAUBC\pm\ERRBC\;(stat.)\pm\SYSBC\;(syst.)~ps and \TAUBN\pm\ERRBN\;(stat.)\pm\SYSBN\;(syst…
Search for neutral and charged Higgs bosons in $e^+ e^-$ collisions at $\sqrt{s}$= 161 GeV and 172 GeV
1998
A search for neutral and charged Higgs bosons has been performed in the data collected by the {\sc DELPHI} detector at centre-of-mass energies of 161~GeV and 172~GeV. The analysis assumes either the pair-production of charged Higgs bosons, ${\mathrm H}^{\pm}$, or the production of the lightest neutral Higgs boson, h, with either a Z or a neutral pseudoscalar Higgs boson, A. All final state topologies expected from the decay of h and A %neutral Higgs particles into hadrons or a pair of $\tau$ leptons, and from the decay of ${\mathrm H}^{\pm}$ %charged Higgs bosons into a pair of quarks or a $\tau \nu_{\tau}$ pair have been considered. %In the case of the associated production with a Z boson,…
Measurement of trilinear gauge boson couplings WWV, (V Z,gamma) in e(+)e(-) collisions at 189 GeV
2001
Measurements of the trilinear gauge boson couplings WWgamma and WWZ are presented using the data taken by DELPHI in 1998 at a centre-of-mass energy of 189 GeV and combined with DELPHI data at 183 GeV. Values are determined for Delta(g_1^Z) and Delta(kappa_gamma), the differences of the WWZ charge coupling and of the WWgamma dipole coupling from their Standard Model values, and for lambda_gamma, the WWgamma quadrupole coupling. A measurement of the magnetic dipole and electric quadrupole moment of the W is extracted from the results for Delta(kappa_gamma) and lambda_gamma. The study uses data from the final states jjlv, jjjj, lX, jjX and gammaX, where j represents a quark jet, l an identifie…
A measurement of the mean lifetimes of charged and neutral B-hadrons
1993
The decays of B-hadrons have been reconstructed using the charged particles recorded in the DELPHI silicon microstrip detector. The sum of the charges of the secondaries determines the charge of the B-hadron parent. Some 232 114 multihadronic Z0 decays recorded during the 1991 run of LEP at centre-of-mass energies between 88.2 GeV and 94.2 GeV yield 253 B-hadron candidates with well-measured charge. From these the mean lifetimes of neutral and charged B-hadrons are found to be 1.44 +/- 0.21(stat.) +/- 0.14(syst.) ps and 1.56 +/- 0.19(stat.) +/- 0.13(syst.) ps respectively. The ratio of their lifetimes is 1.09(-0.23)+0.28 (Stat.) +/- 0.11 (syst.). Under some assumptions on the abundance and …
Search for supersymmetric particles in scenarios with a gravitino LSP and stau NLSP
2000
Sleptons, neutralinos and charginos were searched for in the context of scenarios where the lightest supersymmetric particle is the gravitino. It was assumed that the stau is the next-to-lightest supersymmetric particle. Data collected with the DELPHI detector at a centre-of-mass energy near 189 GeV were analysed combining the methods developed in previous searches at lower energies. No evidence for the production of these supersymmetric particles was found. Hence, limits were derived at 95% confidence level.
Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
2001
Muon pair production in the process e+e- -> e+e-mu+mu- is studied using the data taken at LEP1 (sqrt(s) \simeq m_Z) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb^{-1}. The QED predictions have been tested over the whole Q^2 range accessible at LEP1 (from several GeV^2/c^4 to several hundred GeV^2/c^4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function F_2^\gamma. Azimuthal correlations are used to obtain information on additional structure functions, F_A^\gamma and F_B^\gamma, which orig…
Single intermediate vector boson production in e(+)e(-) collisions at root s=183 and 189 GeV
2001
The cross sections for the production of single charged and neutral intermediate vector bosons were measured using integrated luminosities of 52 pb-1 and 154 pb-1 collected by the experiment at centre-of-mass energies of 182.6 GeV and 188.6 GeV, respectively. The cross sections for the reactions were determined in limited kinematic regions. The results found are in agreement with the Standard Model predictions for these channels. © 2001 Elsevier Science B.V.
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.
Multiplicity fluctuations in hadronic final states from the decay of the Z0
1992
An analysis of the fluctuations in the phase space distribution of hadrons produced in the decay of 78829 Z0 has been carried out, using the method of factorial moments. The high statistics collected by the DELPHI experiment at LEP during 1990 allowed studies of the event sample both globally and in intervals of p(t) and multiplicity, and for different jet topologies and for single jets. A large contribution to the factorial moments of the one-dimensional data on rapidity with respect to the event axis comes from hard gluons. Details of factorial moments in two and three dimensions are presented. Influences of resonance decays have been studied by Monte Carlo simulation: one-dimensional fac…
Classification of the hadronic decays of the Z$^0$ into b and c quark pairs using a neural network
1992
A classifier based on a feed-forward neural network has been used for separating a sample of about 123 500 selected hadronic decays of the Z 0 , collected by DELPHI during 1991, into three classes according to the flavour of the original quark pair: u u +d d +s s (unresolved), c c and b b . The classification has been used to compute the partial widths of the Z 0 into b and c quark pairs. This gave Γ c c /Γ h = 0.151 ± 0.008 ( stat. ) ± 0.041 ( syst. ) , Γ b b /Γ h = 0.232±0.005 ( stat. )±0.017 ( syst. ) .
A study of the Lorentz structure in tau decays
2000
This paper describes a measurement of the Michel parameters, \eta, \rho, \xi, \xi\delta, and the average \nu_{\tau} helicity, h_{\nu_{\tau}}, in tau lepton decays together with the first measurement of the tensor coupling in the weak charged current. The tau+tau- pairs were produced at the LEP e+e- collider at CERN from 1992 through 1995 in the DELPHI detector. Assuming lepton universality in the decays of the tau the measured values of the parameters were: \eta = -0.005 +/- 0.036 +/- 0.037, \rho = 0.775 +/- 0.023 +/- 0.020, \xi = 0.929 +/- 0.070 +/- 0.030, \xi\delta = 0.779 +/- 0.070 +/- 0.028, h_{\nu_{\tau}} = -0.997 +/- 0.027 +/- 0.011. The strength of the tensor coupling was measured to…
Search for a fermiophobic Higgs at LEP 2
2001
Higgs bosons predicted by the fermiophobic scenario within Two Higgs Doublets Models were searched for in the data collected by the DELPHI detector at centre-of-mass energies between 189 GeV and 202 GeV, corresponding to a total integrated luminosity of 380 pb^{-1}. No signal was found and confidence limits were derived in the framework of possible extensions of the Standard Model Higgs sector.
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…
Measurement of the mass of the W boson using direct reconstruction at √s = 183 GeV
1999
From data corresponding to an integrated luminosity of 53.5 pb(-1) taken during the 183 GeV run in 1997, DELPHI has measured the W mass from direct reconstruction of WW --> lq (q) over bar and WW --> q (q) over bar q (q) over bar events. Combining these channels, a value of m(w) = 80.238 +/- 0.154(stat) +/- 0.035(syst) +/- 0.035(fsi) +/- 0.021 (LEP) GeV/c(2) is obtained, where fsi denotes final state interaction. Combined with the W mass obtained by DELPHI from the WW production cross-section and with the direct measurement at 172 GeV this leads to a measured value of m(w) = 80.270 +/- 0.137(stat) +/- 0.031(syst) +/- 0.030(fsi) +/- 0.021(LEP)GeV/c(2), in good agreement with the Standard Mod…
Limits on the production of scalar leptoquarks from $Z^0$ decays at LEP
1993
A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equ…
Measurement of the Charged-Pion Polarizability
2015
The COMPASS collaboration at CERN has investigated pion Compton scattering, $\pi^-\gamma\rightarrow \pi^-\gamma$, at centre-of-mass energy below 3.5 pion masses. The process is embedded in the reaction $\pi^-\mathrm{Ni}\rightarrow\pi^-\gamma\;\mathrm{Ni}$, which is initiated by 190\,GeV pions impinging on a nickel target. The exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, $Q^2<0.0015$\,(GeV/$c$)$^2$. From a sample of 63\,000 events the pion electric polarisability is determined to be $\alpha_\pi\ =\ (\,2.0\ \pm\ 0.6_{\mbox{\scriptsize stat}}\ \pm\ 0.7_{\mbox{\scriptsize syst}}\,) \times 10^{-4}\,\mbox{fm}^3$ under the …
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…