1,471 research outputs found
Measurement of the decays tau/sup -/. -->. rho/sup -/. nu. /sub tau/ and tau/sup -/. -->. K*/sup -/(892). nu. /sub tau/ using the Mark II detector at SPEAR
No full textMeasurements of the branching fractions for the Cabibbo-favored decay tau/sup -/ ..-->.. rho/sup -/..nu../sub tau/ and the Cabibbo-suppressed decay tau/sup -/ ..-->.. K*/sup -/(892)..nu../sub tau/ are presented. The energy dependence of the tau/sup +/tau/sup -/ production cross section is measured with the aid of the decay tau/sup -/ ..-->.. rho/sup -/..nu../sub tau/, which yields a measurement M/sub tau/ = (1790 +- 40) MeV. A 2 sigma upper limit for the forbidden decay tau/sup -/ ..-->.. K*/sup -/(1430)..nu../sub tau/ is also presented. 3 figures
Fragmentation of quarks and gluons, tests of QCD in e/sup +/e/sup -/ annihilation
No full textThis report covers the topics of fragmentation of quarks and gluons and tests of QCD in e/sup +/e/sup -/ annihilation and is a summary of a rapporteur talk given at the 1983 International Symposium on Lepton and Photon Interactions at High Energies. New data on the general characteristics of the e/sup +/e/sup -/ environment at the UPSILON and at PETRA and PEP are discussed. For the first time there is a lot of data on resonance production - eta, K*, rho, phi, ..xi... There is more data on c quark fragmentation from tagged D/sup *+-/ and direct observation of D/sup +/ and D/sup 0/. There are four experiments using high P/sub t/ leptons to measure the b quark fragmentation function - agreement amongst the experiments is very good. All these measurements can usefully be incorporated in the Monte Carlo simulation models. QCD tests are discussed. ..cap alpha../sub 3/ has been measured using the energy dependence of the total hadronic cross section. Unfortunately this method is not very precise. Other measurements of ..cap alpha../sub 3/ from shape analyses and energy-energy correlations have been done including the effects of all second order QCD diagrams. The results seem to depend both on the procedure and the models used to extract ..cap alpha../sub 3/. The evidence for differences in gluon and quark fragmentation are reviewed. There is now evidence that baryon conservation occurs locally in a jet rather than globally in an event. Multiplicity and jet mass correlations are presented as well as data on KNO scaling. 46 references
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Study of the Baryon - Anti-Baryon Decays of the J/psi
No full textThe Mark III collaboration presents results on the decays J/psi ..-->.. B/sub 8/ anti B/sub 8/, and J/psi ..-->.. B/sub 8/ anti B/sub 10/ using 5.8 x 10/sup 6/ produced J/psi's collected at SPEAR. Branching ratios have been determined for the decays J/psi ..-->.. ..sigma../sup +/ anti ..sigma../sup -/ (1385) + c.c., J/psi ..-->.. ..xi../sup -/ anti ..xi../sup +/ (1530) + c.c. and J/psi ..-->.. ..xi../sup -/ anti ..xi../sup +/. An upper limit on the branching ratios for the decay J/psi ..-->.. ..xi../sup 0/ anti ..xi../sup 0/ (1530) + c.c. has also been determined. These indicate large isospin violation in the decay patterns for J/psi ..-->.. ..xi.. anti ..xi..*. 7 refs., 9 figs
Dalitz Plot Analyses of J/ψ→π+π−π0 , J/ψ→K+K−π0 , and J/ψ→Ks0K±π∓ Produced via E+e− Annihilation with Initial-State Radiation
No full textWe study the processes e+e-→γISRJ/ψ, where J/ψ→π+π-π0, J/ψ→K+K-π0, and J/ψ→KS0K±π∓ using a data sample of 519 fb-1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e+e- collider at center-of-mass energies at and near the Υ(nS) (n=2,3,4) resonances. We measure the ratio of branching fractions R1=B(J/ψ→K+K-π0)B(J/ψ→π+π-π0) and R2=B(J/ψ→KS0K±π∓)B(J/ψ→π+π-π0). We perform Dalitz plot analyses of the three J/ψ decay modes and measure fractions for resonances contributing to the decays. We also analyze the J/ψ→π+π-π0 decay using the Veneziano model. We observe structures compatible with the presence of ρ(1450) in all three J/ψ decay modes and measure the relative branching fraction: R(ρ(1450))=B(ρ(1450)→K+K-)B(ρ(1450)→π+π-)=0.307±0.084(stat)±0.082(sys)
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Experimental tests of quantum chromodynamics
No full textExperimental tests of quantum chromodynamics are discussed in the e/sup +/e/sup -/ continuum, in pp and anti p p collisions, in measurements of ..cap alpha../sub s/ from UPSILON decays, in deep inelastic lepton scattering, and in the measurement of the photon structure function. A large body of data relating to the testing of quantum chromodynamics is reviewed, showing qualitative agreement between the data from a wide range of processes and QCD. 66 refs., 79 figs. (LEW
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e/sup +/e/sup -/ interactions at very high energy: searching beyond the standard model
No full textThese lectures discuss e/sup +/e/sup -/ interactions at very high energies with a particular emphasis on searching the standard model which we take to be SU(3)/sub color/..lambda.. SU(2) ..lambda.. U(1). The highest e/sup +/e/sup -/ collision energy exploited to date is at PETRA where data have been taken at 38 GeV. We will consider energies above this to be the very high energy frontier. The lectures will begin with a review of the collision energies which will be available in the upgraded machines of today and the machines planned for tomorrow. Without going into great detail, we will define the essential elements of the standard model. We will remind ourselves that some of these essential elements have not yet been verified and that part of the task of searching beyond the standard model will involve experiments aimed at this verification. For if we find the standard model lacking, then clearly we are forced to find an alternative. So we will investigate how the higher energy e/sup +/e/sup -/ collisions can be used to search for the top quark, the neutral Higgs scalar, provide true verification of the non-Abelian nature of QCD, etc. Having done this we will look at tests of models involving simple extensions of the standard model. Models considered are those without a top quark, those with charged Higgs scalars, with multiple and/or composite vector bosons, with additional generations and possible alternative explanations for the PETRA three jet events which don't require gluon bremsstrahlung. From the simple extensions of the standard model we will move to more radical alternatives, alternatives which have arisen from the unhappiness with the gauge hierarchy problem of the standard model. Technicolor, Supersymmetry and composite models will be discussed. In the final section we will summarize what the future holds in terms of the search beyond the standard model
Status of PEP-II and BaBar
No full textThe SLAC B Factory asymmetric B-factories was approved by President Clinton in October 1993. B-factories The inaugural meeting of the detector collaboration was held at SLAC in December 1993, at which time the 9 nation BaBar collaboration began. First funding for the machine construction was released in January 1994
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Measurements of the decays tau/sup -/. -->. rho/sup -/. nu. /sub tau/, tau/sup -/. -->. pi. /sup -/. nu. /sub tau/ and tau/sup -/. -->. K*-(892). nu. /sub tau/ using the MARK II detector at SPEAR
No full textMeasurements of the branching fractions for the Cabibbo favored decays tau/sup -/ ..-->.. rho/sup -/ ..-->.. ..pi../sup -/..nu../sub tau/ and the Cabibbo suppressed decay mode tau/sup -/ ..-->.. K*/sup -/ (892)..nu../sub tau/ are presented. The energy dependence of the tau/sup +/tau/sup -/ production cross section is obtained for the decays tau/sup -/ ..-->.. rho/sup -/..nu../sub tau/ and these spectra agree well with the classification of the tau/sup -/ as a spin-1/2 point particle. Fits to the production cross section yield a measurement of M/sub tau/ = (1787 +- 10) MeV/c/sup 2/ for the tau mass. Ninety-five percent confidence upper limits for the forbidden decay tau/sup -/ ..-->.. K*/sup -/(1430)..nu../sub tau/ and the tau neutrino mass are presented
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Recent results from the MAC and MARK II detectors at PEP
No full textData from PEP are presented for the MAC and MARK II detectors. All data are at a center-of-mass energy of 29 GeV and correspond to a data set varying from 15 to 30 pb/sup -1/. R = sigma/sub hadronic//sigma/sub ..mu mu../ is presented by both groups, and inclusive momentum distributions (S(d sigma/dx)) for SPEAR and PEP energies are presented by the MARK II. The S(d sigma/dx) distributions exhibit sizeable scaling violations. Both groups have measured energy-energy correlations. The measurements yield ..cap alpha../sub s/ = 0.20 +- 0.01 +- 0.02 (MAC) and ..cap alpha../sub s/ = 0.19 +- 0.01 +- 0.03 (MARK II) where ..cap alpha../sub s/ is the strong coupling constant to first order. It is stressed however that this measurement of ..cap alpha../sub s/ is a very sensitive to nonperturbative (fragmentation) effects. The MARK II group has observed a clean D/sup *+-/ signal from which they obtain sigma(D/sup *+-/) = 0.25 +- 0.10 as the cross section for producing a charged D* at 29 GeV. The charm fragmentation function is measured and it appears to be fairly hard with an average fractional energy for the D*/sup + -/ of approx. 0.6. The MAC group has measured the tau lifetime and finds a value t/sub tau/ = (4.9 +- 2.0) x 10/sup -13/ secs. The MARK II group has measured the tau branching fractions into one (B/sub 1/) and three B/sub 3/ = 1 - B/sub 1/) charged prongs. They find B/sub 1/ = (86 +- 3 +- 1)%. They also find B/sub 5/ < 0.5% at the 90% confidence level. Also presented from the MARK II group are limits on the production of charged scalar particles (Higgs or technipions; H +-) which couple to tau's. For 2 < H +- mass < 10 GeV/c/sup 2/, the branching fraction for H +- to decay to tau nu/sub tau/ is found to be less than 5% at the 90% confidence level. 32 references
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