Lepton flavor conserving Z -> l^+ l^-$ decays in the general two Higgs doublet model

We calculate the new physics effects to the branching ratios of the lepton flavor conserving decays Z -> l^+ l^- in the framework of the general two Higgs Doublet model. We predict the upper limits for the couplings |\bar{\xi}^{D}_{N,\mu\tau}| and |\bar{\xi}^{D}_{N,\tau\tau}| as 3\times 10^2 GeV and 1\times 10^2 GeV, respectively.Comment: 9 pages, 3 figure

Intermittency and Exotic Channels

It is pointed out that accurate measurements of short-range two-particle correlations in like-charge $K\pi$ and in $\pi^ 0\pi^ 0$ channels should be very helpful in determining the origin of the \lq\lq intermittency\rq\rq\ phenomenon observed recently for the like-charge pion pairs.Comment: 5 p., plain tex, preprint T94/078(Saclay), LPTHE 94/58(Orsay

Picosecond laser-pump, x-ray probe spectroscopy of GaAs

A laser-pump, x-ray probe spectroscopic experiment is described, and the results are shown. The Ga KαKα x-ray fluorescence following x-ray absorption, at the Ga K absorption edge was measured, and its increase due to excitation with subpicosecond pulses of laser light at 4.6 eV photon energy was determined. The x-ray absorption, and thus the fluorescence, is increased for about 200 ps after the laser pulse because additional final states for the x-ray absorption are cleared in the valence band by the laser excitation. The technique could eventually lead to a femtosecond pump-probe spectroscopy with an absolute reference energy level and also to a femtosecond x-ray detector. This is of particular importance to future short-pulse x-ray sources, such as free-electron lasers. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69690/2/RSINAK-73-12-4150-1.pd

Picosecond time-resolved x-ray diffraction probe of coherent lattice dynamics (abstract) (invited)

The short pulses of hard x rays from synchrotron and laser based sources are sensitive probes of lattice dynamics on an ultrafast time scale. Using pump–probe time-resolved x-ray diffraction, we are able to follow the propagation of a picosecond coherent acoustic pulse in an ultrafast laser-strained single crystal. Comparison of the data with dynamical diffraction simulations allows for the quantitative determination of both the surface and bulk components of the associated strain. This technique is scalable to femtosecond and shorter time scales as x-ray pulses become shorter in duration, such as in fourth generation light sources. In addition, the diffraction of x rays off of coherent optical phonons may lead to the production of a femtosecond x-ray switch. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69893/2/RSINAK-73-3-1361-1.pd

Proton-antiproton annihilation into massive leptons

We extend previous calculations of polarization observables for the annihilation reaction $\bar p +p\to \ell^{-}+\ell^{+}$ to the case of heavy leptons, such as the $\tau$-lepton. We consider the case when the beam and/or the target are polarized, as well as the polarization of the outgoing leptons. We give the dependence of the unpolarized cross section, angular asymmetry, and various polarization observables on the relevant kinematical variables in the center of mass and in the laboratory system, with particular attention to the effect of the mass induced terms.Comment: 25 pages, 8 figure

Supersonic strain front driven by a dense electron-hole plasma

We study coherent strain in (001) Ge generated by an ultrafast laser-initiated high density electron-hole plasma. The resultant coherent pulse is probed by time-resolved x-ray diffraction through changes in the anomalous transmission. The acoustic pulse front is driven by ambipolar diffusion of the electron-hole plasma and propagates into the crystal at supersonic speeds. Simulations of the strain including electron-phonon coupling, modified by carrier diffusion and Auger recombination, are in good agreement with the observed dynamics.Comment: 4 pages, 6 figure

Production, Decay, and Polarization of Excited Heavy Hadrons

We discuss the production via fragmentation of excited heavy mesons and baryons, and their subsequent decay. In particular, we consider the question of whether a net polarization of the initial heavy quark may be detected, either in a polarization of the final ground state or in anisotropies in the decay products of the excited hadron. The result hinges in part on a nonperturbative parameter which measures the net transverse alignment of the light degrees of freedom in the fragmentation process. We use existing data on charmed mesons to extract this quantity for certain excited mesons. Using this result, we estimate the polarization retention of charm and bottom baryons.Comment: 37 pages, 3 figures available upon request, uses phyzzx forma

Bounds on Vector Leptoquarks

We derive bounds on vector leptoquarks coupling to the first generation, using data from low energy experiments as well as from high energy accelerators. Similarly to the case of scalar leptoquarks, we find that the strongest indirect bounds arise from atomic parity violation and universality in leptonic pi decays. These bounds are considerably stronger than the first direct bounds of HERA, restricting vector leptoquarks that couple with electromagnetic strength to right-handed quarks to lie above 430 GeV or 460 GeV, and leptoquarks that couple with electromagnetic strength to left-handed quarks to lie above 1.3 TeV, 1.2 TeV and 1.5 TeV for the SU(2)_W singlet, doublet and triplet respectively.Comment: 14 Pages (LaTeX), including 1 uufiled postscript figure. WIS-93/119/Dec-P

Phenomenology of BsB_s Decays

Using the QCD sum rules technique we study several aspects of the phenomenology of the b-flavoured strange meson $B_s^0$. In particular, we evaluate the mass of the particle, the leptonic constant and the form factors of the decays $\overline {B_s^0} \to D^{+}_s \ell^- \bar\nu$, $\overline {B_s^0} \to D^{*+}_s \ell^- \bar\nu$, $\overline {B_s^0} \to K^{*+} \ell^- \bar\nu$. We also calculate, in the factorization approximation, a number of two-body non leptonic $\overline {B_s^0}$ decays.Comment: 19 pages, 2 figures (not included) available upon request, LaTex, BARI-TH/93-139, UTS-DFT-93-1