305 research outputs found

    Determination of the QCD color factor ratio CA/CF from the scale dependence of multiplicity in three jet events

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    I examine the determination of the QCD color factor ratio CA/CF from the scale evolution of particle multiplicity in e+e- three jet events. I fit an analytic expression for the multiplicity in three jet events to event samples generated with QCD multihadronic event generators. I demonstrate that a one parameter fit of CA/CF yields the expected result CA/CF=2.25 in the limit of asymptotically large energies if energy conservation is included in the calculation. In contrast, a two parameter fit of CA/CF and a constant offset to the gluon jet multiplicity, proposed in a recent study, does not yield CA/CF=2.25 in this limit. I apply the one parameter fit method to recently published data of the DELPHI experiment at LEP and determine the effective value of CA/CF from this technique, at the finite energy of the Z0 boson, to be 1.74+-0.03+-0.10, where the first uncertainty is statistical and the second is systematic.Comment: 20 pages including 6 figures Version 2 corrects typographical error in equation (2

    Tevatron Mass Limits for Heavy Quarks Decaying via Flavor Changing Neutral Current

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    The dimuon and dielectron data from the Tevatron pˉp\bar pp collider are used to probe for heavy quarks, which decay dominantly via flavour changing neutral current. Depending on whether the FCNCFCNC decay occurs at the tree or loop level, one gets a lower mass limit of 85 or 75 GeV. The former applies to singlet, vector doublet and mirror type quarks while the latter applies to a lefthanded quark doublet of the fourth generation.Comment: 13 pages, TIFR/TH/92-58, Two figures to be supplied on reques

    Flavor mixing in the gluino coupling and the nucleon decay

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    Flavor mixing in the quark-squark-gluino coupling is studied for the minimal SU(5) SUGRA-GUT model and applied to evaluation of the nucleon lifetime. All off-diagonal (generation mixing) elements of Yukawa coupling matrices and of squark/slepton mass matrices are included in solving numerically one-loop renormalization group equations for MSSM parameters, and the parameter region consistent with the radiative electroweak symmetry breaking condition is searched. It is shown that the flavor mixing in the gluino coupling for a large tanβ\tan\beta is of the same order of magnitude as the corresponding Kobayashi-Maskawa matrix element in both up-type and down-type sector. There exist parameter regions where the nucleon decay amplitudes for charged lepton modes are dominated by the gluino dressing process, while for all the examined regions the neutrino mode amplitudes are dominated by the wino dressing over the gluino dressing.Comment: 24 pages, LaTeX, figures are available upon request. ICRR-Report-317-94-1

    Quark-Gluon Jet Differences at LEP

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    A new method to identify the gluon jet in 3-jet ``{\bf Y}'' decays of Z0Z^0 is presented. The method is based on differences in particle multiplicity between quark jets and gluon jets, and is more effective than tagging by leptonic decay. An experimental test of the method and its application to a study of the ``string effect'' are proposed. Various jet-finding schemes for 3-jet events are compared.Comment: 11 pages, LaTeX, 4 PostScript figures availble from the author ([email protected]), MSUTH-92-0

    Collider discovery limits for supersymmetric Higgs bosons

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    The prospects for discovery of the five Higgs bosons of the minimal supersymmetric standard model are assessed for existing and planned future colliders, including LEP\,I, LEP\,II, LHC and SSC. As a benchmark for comparisons, we take a top-quark mass mt=150m_t= 150\,GeV and squark mass parameter m~=1\tilde m= 1\,TeV in evaluating one-loop radiative corrections; some results for other mtm_t values are also given. Searches based on the most promising production and decay channels are taken into account. For large regions in parameter space, detectable signals are predicted for one or more of the Higgs bosons, but there remains a region for which no signals would be visible at the above colliders.Comment: 24 pages, 23 postscript figures available on request. MAD/PH/69

    Diphoton Production at Hadron Colliders and New Contact Interactions

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    We explore the capability of the Tevatron and LHC to place limits on the possible existence of flavor-independent qqˉγγq \bar q \gamma\gamma contact interactions which can lead to an excess of diphoton events with large invariant masses. Assuming no departure from the Standard Model is observed, we show that the Tevatron will eventually be able to place a lower bound of 0.5-0.6 TeV on the scale associated with this new contact interaction. At the LHC, scales as large as 3-6 TeV may be probed with suitable detector cuts and an integrated luminosity of 100fb1100 fb^{-1}.Comment: LaTex, 12pages plus 5 figures(available on request), SLAC-PUB-657

    A study of the nuclear medium influence on transverse momentum of hadrons produced in deep inelastic neutrino scattering

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    The influence of nuclear effects on the transverse momentum (pT)(p_T) distributions of neutrinoproduced hadrons is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with EνE_{\nu} = 3-30 GeV) at Serpukhov accelerator. Dependences of onthekinematicalvariablesofinclusivedeepinelasticscatteringandoftheproducedhadronsaremeasured.Ithasbeenobserved,thatthenucleareffectscauseanenhancementof on the kinematical variables of inclusive deep-inelastic scattering and of the produced hadrons are measured. It has been observed, that the nuclear effects cause an enhancement of of hadrons (more pronounced for the positively charged ones) produced in the target fragmentation region at low invariant mass of the hadronic system (2 <W<< W < 4 GeV) or at low energies transferred to the current quark (2 <ν<9< \nu < 9 GeV). At higher WW or ν\nu, no influence of nuclear effects on is observed. Measurement results are compared with predictions of a simple model, incorporating secondary intranuclear interactions of hadrons (with a formation length extracted from the Lund fragmentation model), which qualitatively reproduces the main features of the data.Comment: 23 pages, 7 figure

    SIGNALS FOR MINIMAL SUPERGRAVITY AT THE CERN LARGE HADRON COLLIDER: MULTI-JET PLUS MISSING ENERGY CHANNEL,

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    We use ISAJET to perform a detailed study of the missing transverse energy \eslt plus multi-jet signal expected from superparticle production at the CERN LHC. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. We delineate the region of parameter space where the \eslt supersymmetry signal should be observable at the LHC and compare it to the regions explorable via searches for sleptons and for chargino/neutralino production. We confirm that, given a data sample of 10~\fb^{-1}, mtg1300m_{\tg}\sim 1300 GeV can be explored if m_{\tq}\gg m_{\tg}, while mtg2000m_{\tg}\sim 2000 GeV can be probed if m_{\tq}\simeq m_{\tg}. We further examine what information can be gleaned from scrutinizing this event sample. For instance, the multi-jet multiplicity yields information on whether squark production makes a significant contribution to the observed \eslt sample. Furthermore, reconstructing hemispheric masses may yield a measure of mtgm_{\tg} to 1525%\sim 15-25\%. Finally, for favourable ranges of parameters, by reconstructing masses of tagged bbˉb\bar{b} jet pairs, it may be possible to detect Higgs bosons produced via sparticle cascade decay chains.Comment: 22 pages (REVTEX); a PS text file (etmiss.ps) and 12 figures (etlhc.uu or etlhc.ps) can be obtained via anonymous ftp at ftp://hep.fsu.edu/anonymous.bae

    A Precision Calculation of the Next-to-Leading Order Energy-Energy Correlation Function

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    The O(alpha_s^2) contribution to the Energy-Energy Correlation function (EEC) of e+e- -> hadrons is calculated to high precision and the results are shown to be larger than previously reported. The consistency with the leading logarithm approximation and the accurate cancellation of infrared singularities exhibited by the new calculation suggest that it is reliable. We offer evidence that the source of the disagreement with previous results lies in the regulation of double singularities.Comment: 6 pages, uuencoded LaTeX and one eps figure appended Complete paper as PostScript file (125 kB) available at: http://www.phys.washington.edu/~clay/eecpaper1/paper.htm

    Constraints on a Massive Dirac Neutrino Model

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    We examine constraints on a simple neutrino model in which there are three massless and three massive Dirac neutrinos and in which the left handed neutrinos are linear combinations of doublet and singlet neutrinos. We examine constraints from direct decays into heavy neutrinos, indirect effects on electroweak parameters, and flavor changing processes. We combine these constraints to examine the allowed mass range for the heavy neutrinos of each of the three generations.Comment: latex, 29 pages, 7 figures (not included), MIT-CTP-221
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