E. Boudinov

Operation, optimisation, and performance of the DELPHI RICH detectors

The Ring Imaging Cherenkov detectors of DELPHI represent a large-scale particle identification system which covers almost the full angular acceptance of DELPHI. The combination of liquid and gas radiators (C4F10, C5F12, and C6F14) provides particle identification over the whole secondary particle momentum spectrum at LEP I and LEP II. Continuing optimisation on the hardware as well as on the online and offline software level have resulted in a stable operation of the complete detector system for more than five years at full physics performance.

Measurement of trilinear gauge boson couplings WWV, (V Z,gamma) in e(+)e(-) collisions at 189 GeV

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 identified lepton and X missing four-momentum. The observations are consistent with the predictions of the Standard Model.

Inclusive

Production of Sigma- and Lambda(1520) in hadronic Z decays has been measured using the DELPHI detector at LEP. The Sigma- is directly reconstructed as a charged track in the DELPHI microvertex detector and is identified by its Sigma -> n pi decay leading to a kink between the Sigma- and pi-track. The reconstruction of the Lambda(1520) resonance relies strongly on the particle identification capabilities of the barrel Ring Imaging Cherenkov detector and on the ionisation loss measurement of the TPC. Inclusive production spectra are measured for both particles. The production rates are measured to be = 0.081 +/- 0.002 +/- 0.010, = 0.029 +/- 0.005 +/- 0.005. The production rate of the Lambda(1520) suggests that a large fraction of the stable baryons descend from orbitally excited baryonic states. It is shown that the baryon production rates in Z decays follow a universal phenomenological law related to isospin, strangeness and mass of the particles.

\Sigma^-

From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be 〈nch〉 = 23.84 ± 0.51 (stat) ± 0.52 (syst). When compared to lower energy data, the value measured is consistent with the evolution predicted by QCD with corrections at next-to-leading order, for a value αs(130 GeV) = 0.105 ± 0.003 (stat) ± 0.008 (syst).

and

The DELPHI detector at LEP has collected 54 pb(-1) of data at a centre-of-mass energy around 183 GeV during 1997, 158 pb(-1) around 189 GeV during 1998, and 187 pb(-1) between 192 and 200 GeV during 1999. These data were used to measure the average charged particle multiplicity in e(+)e(-)→b (b) over bar events: (n)(b (b) over bar), and the difference delta(hl) between (n)(b (b) over bar) and the multiplicity, (n)(l (l) over bar), in generic light quark (u,d,s) events: delta(hl)(183 GeV) = 4.55 +/- 1.31(stat) +/- 0.73(syst), delta(hl)(189 GeV) = 4.43 +/- 0.85(stat) +/- 0.61(syst), delta(hl)(200 GeV) = 3.39 +/- 0.89(stat) +/- 1.01 (syst). This result is consistent with QCD predictions, while it is inconsistent with calculations assuming that the multiplicity accompanying the decay of a heavy quark is independent of the: mass of the quark itself.

\Lambda(1520)

Abstract A search for stable or long-lived heavy charged particles in e + e − interactions at energies of 130–136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ± e and ± 2 3 e particles in the range of 0.4–2.3 pb for masses from 45 to 84 GeV/ c 2 . Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/ c 2 for high (low) sneutrino masses can be excluded at 95% confidence level. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65) GeV/ c 2 can be excluded at 95% confidence level.

production in hadronic Z decays

Searches for pair production of gauginos and squarks in e(+)e(- ) collisions at a centre-of-mass energy of 189 GeV have been performed on data corresponding to an integrated luminosity of 158 pb(-1) collected by the DELPHI detector at LEP. The data were analyzed under the assumption of non-conservation of R- parity through a single dominant (U) over bar(D) over bar(D) over bar coupling between squarks and quarks. Typical final states contain between 4 and 10 jets with or without additional leptons. No excess of data above Standard Model expectations was observed. The results were used to constrain domains of the MSSM parameter space and derive limits on the masses of supersymmetric particles. The following mass limits at 95% CL were obtained from these searches: neutralino mass: m([([chi])over tilde]1)(0) greater than or equal to 32 GeV; chargino mass: m([([chi])over tilde]1)(+) greater than or equal to 94 GeV; stop and sboctom mass (indirect decay) with DeltaM gt 5 GeV: m((t) over tilde1) greater than or equal to 74 GeV for Phi (mix) = 0 rad, m((t) over tilde1) greater than or equal to 59 GeV for Phi (mix) = 0.98 rad, m((b) over tilde1) greater than or equal to 72 GeV for Phi (mix) = 0 rad. The angle phi (mix) is the mixing angle between left and right handed quarks.Searches for pair production of gauginos and squarks in e+e- collisions at a centre-of-mass energy of 189 GeV have been performed on data corresponding to an integrated luminosity of 158 pb-1 collected by the DELPHI detector at LEP. The data were analyzed under the assumption of non-conservation of R-parity through a single dominant Ū D D coupling between squarks and quarks. Typical final states contain between 4 and 10 jets with or without additional leptons. No excess of data above Standard Model expectations was observed. The results were used to constrain domains of the MSSM parameter space and derive limits on the masses of supersymmetric particles. The following mass limits at 95% CL were obtained from these searches: neutralino mass: mx1/0 ≥ 32 GeV; chargino mass: mx1/+ ≥ 94 GeV; stop and sbottom mass (indirect decay) with δAM > 5 GeV: mt1 ≥ 74 GeV for φmix = 0 rad, mt1 ≥ 59 GeV for φmix = 0.98 rad, mb1 ≥ 72 GeV for φmix = 0 rad. The angle φmix is the mixing angle between left and right handed quarks.

Charged particle multipicity in e+e- interactions at sqrt{s}=130 GeV

Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb\(^{-1}\) have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (\({\mathrm {\tilde \ell}}\rightarrow\ell{\mathrm{\tilde \chi_1^0}}\)), producing acoplanar lepton pairs plus missing energy, and the cascade decay (\({\mathrm {\tilde \ell}} \rightarrow \ell{\mathrm{\tilde \chi_2^0}}\rightarrow \ell\gamma{\mathrm{\tilde \chi_1^0}}\)), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are \(m_{\tilde e} \le 87 \mathrm{GeV}/c^2, m_{\tilde{\mu}} \le 80 \mathrm{GeV}/c^2\) and \(m_{\tilde{\tau}} \le 75 \mathrm{GeV}/c^2\), respectively, for values of \(\mu=-200 \mathrm{GeV}/c^2\) and tan\(\beta\)=1.5.Abstract. Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb

Hadronization properties of b quarks compared to light quarks in e(+)e(-)→ q(q)over-bar from 183 to 200 GeV

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Search for stable heavy charged particles in e(+)e(-) collisions at root s=130-136, 161 and 172 GeV

have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (