Comparing fragmentation of strange quark in Z decays and K+p reactions

The ratios of the production rates K*(892)/K, phi/K, rho^0/pi, omega/pi, Delta^{++}/p, Sigma+(1385)/Lambda, Xi^-/Lambda and their x_p dependences obtained from results of the LEP and SLD experiments in Z hadronic decays are analysed. The corresponding ratios for promptly produced mesons are estimated at x_p -> 1. A comparison of the LEP results with those from the Mirabelle and BEBC K+p experiments at 32 and 70 GeV/c shows striking similarity in fragmentation of the strange valence quark of the incident K+ and strange quarks produced in Z decays. The JETSET model describes the LEP, Mirabelle and BEBC results. The model of Pei is consistent with the data for mesons, but presumably underestimates the fractions of primary octet baryons. The quark combinatorics model of Anisovich et al.is incompatible with the data.Comment: tex and sty files and 6 eps-figure

Experimental Summary on Hadronic Decays: A TAU98 Review

Selected results on hadronic decays of the tau lepton from the TAU98 Workshop are reviewed. A comprehensive picture emerges for strange particle branching fractions, and exploration of resonant substructure of both strange and non-strange decays is seen to have matured substantially.Comment: 10 pages, postscript file also available through http://w4.lns.cornell.edu/public/CLN

Parton Content of Real and Virtual Photons

Parameter-free and perturbatively stable leading order (LO) and next-to-leading order (NLO) parton densities for real and virtual photons are presented.Comment: Talk given at the International Conference on the Structure and Interactions of the Photon, PHOTON99, Freiburg im Breisgau, Germany, May 23 - 27, 1999. To appear in the Proceedings, 5 page

Limits on Low Scale Gravity from e+e−→W+W−,ZZe^+ e^- \to W^+ W^-, ZZ and γγ\gamma \gamma

It has been proposed recently that the scale of quantum gravity (``the string scale'') can be $M_S \sim$ few TeV with $n \geq 2$ extra dimensions of size $R \stackrel{<}{\sim}$ mm so that, at distances greater than $R$, Newtonian gravity with $M_{Pl} \sim 10^{18}$ GeV is reproduced if $M_{Pl}^2 \sim R^n M_S^{n+2}$. Exchange of virtual gravitons in this theory generates higher-dimensional operators involving SM fields, suppressed by powers of $M_S$. We discuss constraints on this scenario from the contribution of these operators to the processes $e^+ e^- \to W^+ W^-, ZZ, \gamma \gamma$. We find that LEP2 can place a limit $M_S \approx 1$ TeV from $e^+ e^- \to W^+ W^-, ZZ, \gamma \gamma$.Comment: Replacing an earlier version. A discussion of using polarized electron beams and some minor comments have been adde

Measurements of Fragmentation Photons with the PHENIX Detector

Direct photons associated with jets provide a direct measurement of the effects of energy loss on the fragmentation of the parton as it propagates through the medium. Perturbative QCD calculations describe the direct photon cross section well at next-to-leading order, predicting a significant contribution from photons produced through parton fragmentation. Non-perturbative quantities such as the photon fragmentation function, which is poorly constrained, lead to large theoretical uncertainties. The measurement of photons correlated with jets in p+p collisions serves as an important test of these calculations and is an essential baseline measurement for comparison to A+A collisions. A natural way of selecting such photons is to study hadron-photon correlations. Results for the production of photons associated with high pT hadron triggers are presented for PHENIX p+p data at 200 GeV center-of-mass energy.Comment: 4 pages, 4 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee Corrected typos, changed conten

Cross Sections and Lorentz Violation

The derivation of cross sections and decay rates in the Lorentz-violating standard-model extension is discussed. General features of the physics are described, and some conceptual and calculational issues are addressed. As an illustrative example, the cross section for the specific process of electron-positron pair annihilation into two photons is obtained.Comment: 17 page

Vector-to-Pseudoscalar and Meson-to-Baryon Ratios in Hadronic Z Decays at LEP

Mass dependences of the total production rates per hadronic Z decay of all light-flavour hadrons measured so far at LEP are extrapolated to the zero mass limit (m=0) using phenomenological laws of hadron production related to the spin, isospin, strangeness content and mass of the particles. The vector-to-pseudoscalar and meson-to-baryon ratios at m=0 are found to be: rho^+ / 3 pi^+ = 1.2 +/- 0.3 and pi^+ / p = 2.9 +/- 0.3, in good agreement with the predictions of quark combinatorics.Comment: LaTeX with sprocl.sty; 6 pages with 2 eps-figures; minor Editor's corrections. Talk given at the 30th International Symposium on Multiparticle Dynamics, Tihany, Lake Balaton, Hungary, October 9-15, 2000. To be published in the Proceedings (World Scientific, Singapore