122560479
Deuteron and Anti-deuteron Production in e+e- Collisions at the Z Resonance
Deuteron and anti-deuteron production in Z decays has been observed in the ALEPH experiment at LEP. The production rate of anti-deuterons is measured to be 5.9+-1.8+-0.5 10^-6 per hadronic Z decay in the anti-deuteron momentum range 0.62 to 1.03 GeV/c. The coalescence parameter B_2, which characterizes the likelihood of anti-deuteron production, is measured to be 0.0033+-0.0013 GeV^2 in Z dedays. These measurements indicate that the production of anti-deuterons is suppressed in e+e- collisions compared to pp and photoproduction collisions.
16317400
Test of colour reconnection models using three-jet events in hadronic Z decays
Hadronic Z decays into three jets are used to test QCD models of colour reconnection (CR). A sensitive quantity is the rate of gluon jets with a gap in the particle rapidity distribution and zero jet charge. Gluon jets are identified by either energy-ordering or by tagging two b-jets. The rates predicted by two string-based tunable CR models, one implemented in JETSET (the GAL model), the other in ARIADNE, are too high and disfavoured by the data, whereas the rates from the corresponding non-CR standard versions of these generators are too low. The data can be described by the GAL model assuming a small value for the R0 parameter in the range 0.01-0.02.
122387957
Search for pentaquark states in Z decays
Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L., upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N Theta(1535)+ . BR(Theta(1535)^+ -> pK0s xi^- pi^-) Xi^-pi^+ D*-p) D^-p) < 31 x 10^-4.
208865941
Single photon and multiphoton production in $e^{+} e^{-}$ collisions at $\sqrt{s}$ up to 209-GeV
Events containing only energetic photons are analysed in a sample of \(628 \mathrm{pb}^{-1}\) of data recorded from \(\rm e^+e^-\) collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The \(e^+ e^-\to \nu\bar{\nu}\gamma(\gamma)\) and \(e^+ e^-\to \gamma\gamma(\gamma)\) cross sections are measured and found to be in agreement with the standard model predictions. The number of light neutrino generations is determined to be \(N_\nu = 2.86 \pm 0.09\). Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits are also set on the parameters of models with extra spatial dimensions, with contact interactions and with excited electrons.
33921627
Search for neutral Higgs bosons decaying into four taus at LEP2
A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb−1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, $ {\xi^2} = \frac{{\sigma \left( {{\text{e}^{+} }{\text{e}^{-} } \to {\text{Zh}}} \right)}}{{{\sigma_{\text{SM}}}\left( {{\text{e}^{+} }{\text{e}^{-} } \to {\text{Zh}}} \right)}} \times B\left( {h \to {\text{aa}}} \right) \times B{\left( {{\text{a}} \to {\tau^{+} }{\tau^{-} }} \right)^2} $. For mh < 107 GeV/c2 and 4 < ma < 10 GeV/c2, ξ2 > 1 is excluded at the 95% confidence level.
14187092
Inclusive semileptonic branching ratios of b hadrons produced in Z decays
A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct $\bl$ and cascade $\bcl$ dec ays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The results obtained by averaging the two techniques are BR(b->l) = 0.1070 +- 0.0010 +- 0.0023 +- 0.0026 BR(b->c->l) = 0.0818 +- 0.0015 +- 0.0022 + 0.0022 -0.0014
119338939
Highlights from the NA60 experiment
NA60 measured dimuon production in p–A and In–In collisions at the CERN SPS. This paper presents a high statistics measurement of meson production in In–In collisions at 158 A GeV. Both the transverse momentum, rapidity, decay angular distributions and the absolute yield were measured as a function of centrality. The results are compared to previous measurements in order to shed light on the long standing puzzle. In addition, highlights on η meson production and on the dimuon excess below the J/ψ mass are presented.
120476909
Charged particle multiplicity measurements in NA60
The NA60 experiment at the CERN SPS studies dimuon production in nucleusnucleus and proton-nucleus collisions. One of the main detectors in the apparatus is the silicon pixel vertex telescope, which tracks charged particles in the target region. This detector complements the information from the muon spectrometer, improving the dimuon mass resolution and signal-to-noise ratio of the experiment, overcoming the main limitations of its predecessors. The silicon vertex telescope also provides the experiment with the capability of measuring charged particle multiplicities. In this paper we briefly describe the experiment and some preliminary results on charged particle multiplicities for two different colliding systems at different incident beam energies (Pb-Pb at 30 AGeV and In-In at 158 AGeV).
118611860
A comparative measurement of $\phi\rightarrow K^+K^-$ and $\phi\rightarrow \mu^+\mu^-$ in In-In collisions at the CERN SPS
The NA60 experiment at the CERN SPS has studied $\phi$ meson production in In-In collisions at 158A GeV via both the $K^+K^-$ and the $\mu^+\mu^-$ decay channels. The yields and inverse slope parameters of the $m_T$ spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. Possible physics implications are discussed.
3023314
Intermediate mass dimuon production in indium-indium collisions at the CERN SPS
R. Arnaldi 10, R. Averbeck 9, K. Banicz 2,4, J. Castor 3, B. Chaurand 7, C. Cicalò 1, A. Colla 10, P. Cortese 10, S. Damjanovic 4, A. David 2,5, A. De Falco 1, A. Devaux 3, A. Drees 9, L. Ducroux 6, H. En’yo 8, A. Ferretti 10, M. Floris 1, P. Force 3, A. ,Förster 2, N. Guettet 2,3, A. Guichard 6, H. Gulkanian 11, J. Heuser 8, M. Keil 2,5, L. Kluberg 2,7, C. Lourenço 2, J. Lozano 5, F. Manso 3, A. Masoni 1, P. Martins 2,5, A. Neves 5, H. Ohnishi 8, C. Oppedisano 10, P. Parracho 2, P. Pillot 6, G. Puddu 1, E. Radermacher 2, P. Ramalhete 2, P. Rosinsky 2, E. Scomparin 10, J. Seixas 2,5, S. Serci 1, P. Sonderegger 5, H.J. Specht 4, R. Tieulent 6, G. Usai 1, R. Veenhof 2,5, H.K. Wöhri 2,5
119278353
J/ψ production in proton-nucleus collisions at 158 and 400 GeV
Abstract The NA60 experiment has studied J / ψ production in p–A collisions at 158 and 400 GeV, at the CERN SPS. Nuclear effects on the J / ψ yield have been estimated from the A -dependence of the production cross section ratios σ J / ψ A / σ J / ψ Be (A = Al, Cu, In, W, Pb, U). We observe a significant nuclear suppression of the J / ψ yield per nucleon–nucleon collision, with a larger effect at lower incident energy, and we compare this result with previous observations by other fixed-target experiments. An attempt to disentangle the different contributions to the observed suppression has been carried out by studying the dependence of nuclear effects on x 2 , the fraction of the nucleon momentum carried by the interacting parton in the target nucleus.