Isolated leptons from heavy flavor decays: Theory and data

Events with isolated leptons play a prominent role in signatures of new physics phenomena at high energy collider physics facilities. In earlier publications, we examine the standard model contribution to isolated lepton production from bottom and charm mesons and baryons through their semileptonic decays (b, c -> l + X), showing that this source can overwhelm the effects of other standard model processes in some kinematic domains. In this paper, we show that we obtain good agreement with recent Tevatron collider data, both validating our simulations and showing that we underestimate the magnitude of the heavy-flavor contribution to the isolated lepton yields. We also show that the isolation requirement acts as a narrow bandpass filter on the momentum of the isolated lepton, and we illustrate the effect of this filter on the background to Higgs boson observation in the dilepton mode. We introduce and justify a new rule of thumb: isolated electrons and muons from heavy flavor decay are produced with roughly the same distributions as b and c quarks, but with 1/200 times the rates of b and c production, respectively.Comment: 12 pg, revtex, 5 fig, corrected typo

Missing heavy flavor backgrounds to Higgs boson production

We investigate characteristics of the signal and backgrounds for Higgs boson decay into WW at the Fermilab Tevatron and CERN Large Hadron Collider. In the the lepton-pair-plus-missing-energy final state, we show that the background receives an important contribution from semileptonic decays of heavy flavors. Lepton isolation cuts provide too little suppression of these heavy flavor contributions, and an additional 4 to 8 orders-of-magnitude suppression must come from physics cuts. We demonstrate that an increase of the minimum transverse momentum of nonleading leptons in multilepton events is one effective way to achieve the needed suppression, without appreciable loss of the Higgs boson signal. Such a cut would impact the efficiency of searches for supersymmetry as well. We emphasize the importance of direct measurement of the lepton background from heavy flavor production.Comment: 23 pgs., 10 figs, revtex4, 1 Ref. added, minor typos corrected, to appear in Phys. Rev.

Mapping the photochemistry of European mid-Latitudes rivers: An assessment of their ability to photodegrade contaminants

The abiotic photochemical reactions that take place naturally in sunlit surface waters can degrade many contaminants that pose concern to water bodies for their potentially toxic and long-term effects. This works aims at assessing the ability of European rivers to photoproduce reactive transient intermediates, such as HO• radicals and the excited triplet states of chromophoric dissolved organic matter (3CDOM*), involved in pollutant degradation. A photochemical mapping of the steady-state concentrations of these transients was carried out by means of a suitable modeling tool, in the latitude belt between 40 and 50°N. Such a map allowed for the prediction of the photochemical lifetimes of the phenylurea herbicide isoproturon (mostly undergoing photodegradation upon reaction with HO• and especially 3CDOM*) across different European countries. For some rivers, a more extensive dataset was available spanning the years 1990–2002, which allowed for the computation of the steady-state concentration of the carbonate radicals (CO3•−). With these data, it was possible to assess the time trends of the photochemical half-lives of further contaminants (atrazine, ibuprofen, carbamazepine, and clofibric acid). The calculated lifetimes were in the range of days to weeks, which might or might not allow for efficient depollution depending on the river-water flow velocity

Properties of 125 GeV Higgs boson in non-decoupling MSSM scenarios

Tantalizing hints of the Higgs boson of mass around 125 GeV have been reported at the LHC. We explore the MSSM parameter space in which the 125 GeV state is identified as the heavier of the CP even Higgs bosons, and study two scenarios where the two photon production rate can be significantly larger than the standard model (SM). In one scenario, $\Gamma(H\to \gamma\gamma)$ is enhanced by a light stau contribution, while the $WW^{\ast}$ ($ZZ^{\ast}$) rate stays around the SM rate. In the other scenario, $\Gamma(H\to b\bar{b})$ is suppressed and not only the $\gamma\gamma$ but also the $WW^{\ast}$ ($ZZ^{\ast}$) rates should be enhanced. The $\tau\bar{\tau}$ rate can be significantly larger or smaller than the SM rate in both scenarios. Other common features of the scenarios include top quark decays into charged Higgs boson, single and pair production of all Higgs bosons in $e^+e^-$ collisions at $\sqrt{s}\lesssim 300$ GeV.Comment: 20 pages, 5 figures, accepted version for publication in JHE

Z-prime Gauge Bosons at the Tevatron

We study the discovery potential of the Tevatron for a Z-prime gauge boson. We introduce a parametrization of the Z-prime signal which provides a convenient bridge between collider searches and specific Z-prime models. The cross section for p pbar -> Z-prime X -> l^+ l^- X depends primarily on the Z-prime mass and the Z-prime decay branching fraction into leptons times the average square coupling to up and down quarks. If the quark and lepton masses are generated as in the standard model, then the Z-prime bosons accessible at the Tevatron must couple to fermions proportionally to a linear combination of baryon and lepton numbers in order to avoid the limits on Z--Z-prime mixing. More generally, we present several families of U(1) extensions of the standard model that include as special cases many of the Z-prime models discussed in the literature. Typically, the CDF and D0 experiments are expected to probe Z-prime-fermion couplings down to 0.1 for Z-prime masses in the 500--800 GeV range, which in various models would substantially improve the limits set by the LEP experiments.Comment: 34 pages, 13 figure