Measurement of ZZ production in leptonic final states at {\surd}s of 1.96 TeV at CDF

In this paper we present a precise measurement of the total ZZ production cross section in pp collisions at {\surd}s= 1.96 TeV, using data collected with the CDF II detector corresponding to an integrated luminosity of approximately 6 fb-1. The result is obtained by combining separate measurements in the four-charged (lll'l'), and two-charged-lepton and two-neutral-lepton (llvv) decay modes of the Z. The combined measured cross section for pp {\to} ZZ is 1.64^(+0.44)_(-0.38) pb. This is the most precise measurement of the ZZ production cross section in 1.96 TeV pp collisions to date.Comment: submitted to Phys. Rev. Let

Insights into the High-energy γ-ray Emission of Markarian 501 from Extensive Multifrequency Observations in the Fermi Era

We report on the γ-ray activity of the blazar Mrk501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) -ray spectrum of Mrk501 can be well described by a single power-law function with a photon index of 1.78 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 0.14, and the softest one is 2.51 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15August 1) on Mrk501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size r0.1pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (C1044ergs1) constitutes only a small fraction (<103) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude

Analysis of hard X- and gamma-rays and microwave emissions during the flare of July 18, 2002

The Nobeyama Radioheliograph observation results and data from the KONUS-Wind spectrometer mounted at the Wind and RHESSI satellites on several solar flares are jointly analyzed. The analysis results for data on the flare of July 18, 2002 are described. The hard X-rays were measured in the 18 keV-15 MeV range (KONUS-Wind), and spectroheliograph measurements were carried out in the radio range at frequencies of 17 and 34 GHz. Spatial distributions of the radio brightness were calculated for the flare of July 18, 2002; they show the presence of two sources at the footpoints and one source at the top of the supposed flaring loop. The energy spectra of hard X-rays, energy flux, and the total number of accelerated electrons were found from the KONUS spectrometer data. The number of accelerated X-ray emitted electrons was estimated as N a parts per thousand yen 10(36), and the maximum X-ray energy flux was estimated as 5 x 10(-6) erg cm(-2) s(-1). The spectrum index varies in time from -4.6 to -3.6, i.e., the soft-hard-harder trend is implemented. The spectral index of the radio waves is alpha a parts per thousand -0.3 at the flare start, attains the value alpha a parts per thousand -0.5 at the flux maximum, and even change the sign further. The accelerated electron transport model in the flare loop plasma is suggested for interpretation of relationships between parameters of the radio emission and hard X-rays