2,949 research outputs found

    Suche nach Sleptonen und leptonisch zerfallenden Charginos in e+e‚ąíe^+ e^- Kollisionen bei Schwerpunktsenergien bis zu 184 GeV mit dem ALEPH-Detektor

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    In den Jahren 1996 und 1997 konnte der ALEPH--Detektor bei Schwerpunktsenergien zwischen 161 GeV und 184 GeV Daten mit einer integrierten Luminosit"at von mehr als 80 pb^-1 aufzeichnen. Diese Daten wurden nach einem "Uberschu"s an Ereignissen mit acoplanaren Leptonen untersucht. Da sowohl deren Anzahl als auch deren Ereignisgr"o"sen mit der Standardmodell- erwartung gut vertr"aglich sind, kann die Produktion von Selektronen, Smyonen und Charginos, falls diese leptonisch zerfallen, f"ur bestimmte Massenkombi- nationen mit einem Vertrauensinterval von 95%95\% ausgeschlossen werden: - Rechtsh"andige Selektronen m"ussen schwerer als 81 GeV/c^2 sein, falls die Massendifferenz zum leichtesten Neutralino Delta m mindestens 10 GeV/c^2 gro"s ist. - F"ur Selektronen mit Delta m > 5 GeV/c^2 (Delta m > 3 GeV/c^2) wird eine untere Grenze von 74 GeV/c^2 (68 GeV/c^2) gefunden. - Rechtsh"andige Smyonen m"ussen schwerer als 71 GeV/c^2 sein, falls die Massendifferenz mindestens 5 GeV/c^2 betr"agt. Hierbei wird ein Verzweigungs- verh"altnis von 100% in ein Myon und das leichteste Neutralino vorausgesetzt. - Betr"agt die Massendifferenz zwischen Smyon und dem leichtesten Neutralino mindestens 3 GeV/c^2, so wird eine untere Schranke auf die Smyonmasse von 56 GeV/c^2 erreicht. - Falls es kinematisch erlaubt ist, so zerfallen Charginos haupts"achlich in ein Sneutrino und ein Lepton. F"ur eine Massendifferenz gr"o"ser als 8 GeV/c^2 kann eine untere Massengrenze von 86 GeV/c^2 f"ur leptonisch zerfallende Charginos gesetzt werden. - Charginos mit einer Massendifferenz zum Sneutrino von mehr als 5 GeV/c^2 m"ussen mindestens 75 GeV/c^2 schwer sein. Hierbei gelten f"ur Selektronen und Charginos die SUSY--Parameter: mu = -200 GeV/c^2, tan(beta) = 2. Die Ausschlu"sgrenzen der Smyonen sind unabh"angig von diesen Parametern. Au"serdem wurde nach Ereignissen mit einzelnen Elektronen gesucht. Auch hier sind die Anzahl und die Verteilungen der Ereignisgr"o"sen gut mit dem Standard- modell vertr"aglich, so da"s sich daraus Ausschlu"sgrenzen f"ur die assoziierte Produktion von ~e_{R}~e_{L} berechnen lassen. Diese werden zusammen mit der Suche nach acoplanaren Leptonen zu einer Massengrenze f"ur rechtsh"andige Sleptonen kombiniert. Falls eine universelle Gauginomasse m1/2 und eine gemeinsamen Masse m0 f"ur die skalaren Teilchen bei einer Vereinheitlichungsskala M(GUT) existieren, so gel- ten folgende Ausschlu"sgrenzen (CL = 95%): - F"ur tan(beta) = 35 m"ussen Sleptonen schwerer als 78 GeV/c^2 sein. - Bei kleineren Werten von tan(beta) ist die Ausschlu"sgrenze f"ur Sleptonen weniger restriktiv. F"ur tan(beta) = 2 (tan(beta) = sqrt(2)) wird eine untere Massenschranke von 64 GeV/c^2 (52 GeV/c^2) erreicht. - F"ur tan(beta) = 1 kann eine untere Massengrenze auf Sleptonen von 61 GeV/c^2 gesetzt werden. Diese Massengrenzen sind nur von tan(beta) abh"angig. Sie sind unabh"angig von $ mu und gelten f"ur alle Massendifferenzen. Durch die Kombination der Suchen nach Sleptonen und leptonisch zerfallenden Charginos wird unter GUT--Annahmen folgende Massenschranke (CL = 95%) erreicht: - Sleptonen m"ussen schwerer als 48 GeV/c^2 sein. Diese Massengrenze gilt unabh"angig von den SUSY--Parametern und der Massen- differenz zwischen Sleptonen und den leichtesten Neutralinos

    1,1,3,3-Tetratriflylpropene (TTP): A Strong, Allylic C‚ÄďH Acid for Br√łnsted and Lewis Acid Catalysis

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    Tetratrifylpropene (TTP) has been developed as a highly acidic, allylic C‚ÄďH acid for Br√łnsted and Lewis acid catalysis. It can readily be obtained in two steps and consistently shows exceptional catalytic activities for Mukaiyama aldol, Hosomi‚ÄďSakurai, and Friedel‚ÄďCrafts acylation reactions. X-ray analyses of TTP and its salts confirm its designed, allylic structure, in which the negative charge is delocalized over four triflyl groups. NMR experiments, acidity measurements, and theoretical investigations provide further insights to rationalize the remarkable reactivity of TTP

    Report of the AOD Format Task Force

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    The Analysis Object Data (AOD) are produced by ATLAS reconstruction and are the main input for most analyses. AOD, like the Event Summary Data (ESD, the other main output of reconstruction) are written as POOL files and are readable from Athena, and, to a limited extent, from ROOT. The AOD typical size, processing speed, and their relatively complex class structure and package dependencies, make them inconvenient to use for most interactive analysis. According to the computing model, interactive analysis will be based on Derived Physics Data (DPD), a user-defined format commonly produced from the AOD. As of release 12.0.3 it is common practice to write DPD as Athena-aware Ntuples (AANT) in ROOT. In an effort to organize and standardize AANT, we introduced the Structured Athena-aware Ntuple (SAN), an AANT containing objects that behave, as much as it is allowed by ROOT interpreter limitations, as their AOD counterparts. Recently it was proposed to extend SAN functionality beyond DPD implementation. SAN objects would be used as AOD objects. The TOB formed our task force with the mandate to "perform a technical evaluation of the two proposals, one based upon the existing AOD classes and architecture, the other upon Structured Athena-Aware Ntuples. [...] Criteria for the evaluation should include I/O performance, support for schema evolution, suitability for end user analysis and simplicity.

    Search for CP Violation in the Decay Z -> b (b bar) g

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    About three million hadronic decays of the Z collected by ALEPH in the years 1991-1994 are used to search for anomalous CP violation beyond the Standard Model in the decay Z -> b \bar{b} g. The study is performed by analyzing angular correlations between the two quarks and the gluon in three-jet events and by measuring the differential two-jet rate. No signal of CP violation is found. For the combinations of anomalous CP violating couplings, h^b=h^AbgVb‚ąíh^VbgAb{\hat{h}}_b = {\hat{h}}_{Ab}g_{Vb}-{\hat{h}}_{Vb}g_{Ab} and hb‚ąó=h^Vb2+h^Ab2h^{\ast}_b = \sqrt{\hat{h}_{Vb}^{2}+\hat{h}_{Ab}^{2}}, limits of \hat{h}_b < 0.59and and h^{\ast}_{b} < 3.02$ are given at 95\% CL.Comment: 8 pages, 1 postscript figure, uses here.sty, epsfig.st

    Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

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    A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure

    Search for Electroweak Production of Single Top Quarks in ppbar Collisions

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    We present a search for electroweak production of single top quarks in the electron+jets and muon+jets decay channels. The measurements use ~90 pb^-1 of data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with the DZero detector between 1992 and 1995. We use events that include a tagging muon, implying the presence of a b jet, to set an upper limit at the 95% confidence level on the cross section for the s-channel process ppbar->tb+X of 39 pb. The upper limit for the t-channel process ppbar->tqb+X is 58 pb.Comment: 11 pages, 2 figures. This is the published versio

    Search for Large Extra Dimensions in Dielectron and Diphoton Production

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    We report a search for effects of large extra spatial dimensions in ppbar collisions at a center-of-mass energy of 1.8 TeV with the DZero detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% confidence level, on the effective Planck scale between 1.0 TeV and 1.4 TeV for several formalisms and numbers of extra dimensions.Comment: 6 pages, 2 figures, submitted to Phys. Rev. Let

    A Quasi-Model-Independent Search for New Physics at Large Transverse Momentum

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    We apply a quasi-model-independent strategy ("Sleuth") to search for new high p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron. Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X exclusive final states are systematically analyzed for hints of physics beyond the standard model. Simultaneous sensitivity to a variety of models predicting new phenomena at the electroweak scale is demonstrated by testing the method on a particular signature in each set of final states. No evidence of new high p_T physics is observed in the course of this search, and we find that 89% of an ensemble of hypothetical similar experimental runs would have produced a final state with a candidate signal more interesting than the most interesting observed in these data.Comment: 28 pages, 17 figures. Submitted to Physical Review
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