We present a measurement of direct photon pair production cross sections using 4.2 fb(-1) of data collected with the DO detector at the Fermilab Tevatron p (p) over bar Collider. We measure single ...differential cross sections as a function of the diphoton mass, the transverse momentum of the diphoton system, the azimuthal angle between the photons, and the polar scattering angle of the photons. In addition, we measure double differential cross sections considering the last three kinematic variables in three diphoton mass bins. The results are compared with different perturbative QCD predictions and event generators. (C) 2010 Elsevier B.V. All rights reserved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We present a search for flavor changing neutral currents via quark-gluon couplings in a sample of single top quark final states corresponding to 2.3 fb(-1) of integrated luminosity collected with the ...DO detector at the Fermilab Tevatron Collider. We select events containing a single top quark candidates with an additional jet, and obtain separation between signal and background using Bayesian neural networks. We find consistency between background expectation and observed data, and set limits on flavor changing neutral current gluon couplings of the top quark to up quarks (tgu) and charm quarks (tgc). The cross section limits at the 95% C.L. are sigma(tgu) < 0.20 pb and sigma(tgc) < 0.27 pb. These correspond to limits on the top quark decay branching fractions of B(t -> gu) < 2.0 x 10(-4) and B(t -> gc) < 3.9 x 10(-3).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We have performed a new search for radio pulsars in archival data of the intermediate and high Galactic latitude parts of the Southern High Time Resolution Universe pulsar survey. This is the first ...time the entire dataset has been searched for binary pulsars, an achievement enabled by GPU-accelerated dedispersion and periodicity search codes nearly 50 times faster than the previously used pipeline. Candidate selection was handled entirely by a Machine Learning algorithm, allowing for the assessment of 17.6 million candidates in a few person-days. We have also introduced an outlier detection algorithm for efficient radio-frequency interference (RFI) mitigation on folded data, a new approach that enabled the discovery of pulsars previously masked by RFI. We discuss implications for future searches, particularly the importance of expanding work on RFI mitigation to improve survey completeness. In total we discovered 23 previously unknown sources, including 6 millisecond pulsars and at least 4 pulsars in binary systems. We also found an elusive but credible redback candidate that we have yet to confirm.
We show that the rate of association between terrestrial gamma ray flashes (TGFs) observed by the Fermi gamma ray burst monitor and VLF discharges detected by the World Wide Lightning Location ...Network (WWLLN) depends strongly on the duration of the TGF, with the shortest TGFs having associated WWLLN events over 50% of the time, and the longest TGFs showing a less than 10% match rate. This correlation is stronger if one excludes the WWLLN discharges that are not simultaneous (within 200 µs) with the TGF. We infer that the simultaneous VLF discharges are from the relativistic electron avalanches that are responsible for the flash of gamma rays and the nonsimultaneous VLF discharges are from related intracloud lightning strokes. The distributions of far‐field radiated VLF stroke energy measured by WWLLN for the simultaneous and nonsimultaneous discharges support the hypothesis of two discrete populations of VLF signals associated with TGFs, with the simultaneous discharges among the strongest measured by WWLLN.
Key PointsShort TGFs have high match rate with WWLLN. TGF electrons emit radio signalTGFs are also associated with lightning events, less often seen by WWLLNThe TGF radio signal is much more powerful than the lightning signal
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We present the first measurements at a hadron collider of differential cross sections for Z/gamma* + jet + X production in Delta phi(Z. jet), vertical bar Delta y(Z, jet)vertical bar and vertical bar ...y(boost)(Z + jet)vertical bar. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Europium dibenzoylmethide triethylammonium (EuD
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TEA) is one of the brightest known triboluminescent (TL) materials. First synthesized in 1966, emission from EuD
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TEA is bright enough to be seen in ...daylight. In this paper we report the synthesis of Eu(
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) tetrakis compounds using different solvents, and their influence on the appearance, TL yield, and decay time. The physical appearance of Eu compounds changed with the solvent type. Further, the solvents influenced the time for nucleation and completion of the reaction. TL measurements show that Eu tetrakis compounds derived from acetone solvent had the largest emission, while the smallest emission with the shortest decay time was obtained for the product from chloroform solvent. Photoluminescent emission spectra for the compounds from different solvents show the
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peaks which are consistent with previously reported results for EuD
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TEA. However the intensity of the
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transition shows the 613.5 nm is larger than the 611.7 nm for the products from 1-butanol and methylene chloride. Eu compound from 1-butanol shows a more intense 616.5 nm and 624.2 nm peaks, of which the later peak is almost merged into the background for Eu compounds obtained from the other solvents.
The measured photoluminescent emission spectra for samples made with a selection of solvents were consistent with what was previously measured for EuD
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TEA.
Studying the gravitational-wave sky with pulsar timing arrays (PTAs) is a key science goal for the Square Kilometre Array (SKA) and its pathfinder telescopes. With current PTAs reaching ...sub-microsecond timing precision, making accurate measurements of interstellar propagation effects and mitigating them effectively has become increasingly important to realise PTA goals. As these effects are much stronger at longer wavelengths, low-frequency observations are most appealing for characterizing the interstellar medium (ISM) along the sight lines toward PTA pulsars. The Murchison Widefield Array (MWA) and the Engineering Development Array (EDA), which utilizes MWA technologies, present promising opportunities for undertaking such studies, particularly for PTA pulsars located in the southern sky. Such pulsars are also the prime targets for PTA efforts planned with the South African MeerKAT, and eventually with the SKA. In this paper we report on observations of two bright southern millisecond pulsars PSRs J0437-4715 and J2145-0750 made with these facilities; MWA observations sampling multiple frequencies across the 80-250 MHz frequency range, while the EDA providing direct-sampled baseband data to yield a large instantaneous usable bandwidth of \(\sim\)200 MHz. Using these observations, we investigate various aspects relating to pulsar emission and ISM properties, such as spectral evolution of the mean pulse shape, scintillation as a function of frequency, chromaticity in interstellar dispersion, and flux density spectra at low frequencies. Systematic and regular monitoring observations will help ascertain the role of low-frequency measurements in PTA experiments, while simultaneously providing a detailed characterization of the ISM toward the pulsars, which will be useful in devising optimal observing strategies for future PTA experiments.
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