Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks

A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at root s = 8 TeV. The data correspond to an integrated luminosity of 19.7 fb(-1). The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t (t) over bar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95 confidence level for the product of the production cross section and branching fraction sigma(gg -> X) B(X -> HH -> b (b) over barb (b) over bar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with amass scale Lambda(R) = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV

Correction of Field Rotator-Induced Flat-Field Systematics--A Case Study Using Archived VLT-FORS Data

ESO's two FOcal Reducer and low dispersion Spectrographs (FORS) are the primary optical imaging instruments for the VLT. They are not direct-imaging instruments, as there are several optical elements in the light path. In particular, both instruments are attached to a field rotator. Obtaining truly photometric data with such instruments present a significant challenge. In this paper, we investigate in detail twilight flats taken with the FORS instruments. We find that a large fraction of the structure seen in these flatfields rotates with the field rotator. We discuss in detail the methods we use to determine the cause of this effect. The effect was tracked down to be caused by the Linear Atmospheric Dispersion Corrector (LADC). The results are thus of special interest for designers of instruments with LADCs and developers of calibration plans and pipelines for such instruments. The methods described here to find and correct it, however, are of interest also for other instruments using a field rotator. If not properly corrected, this structure in the flatfield may degrade the photometric accuracy of imaging observations taken with the FORS instruments by adding a systematic error of up to 4% for broad band filters. We discuss several strategies to obtain photometric images in the presence of rotating flatfield pattern.Comment: resolution of some figures reduce

Towards Precision Photometry with FORS: A Status Report

The two FOcal Reducer and low-dis-persion Spectrographs (FORS) are the primary imaging instruments for the VLT. Because they are not direct imaging instruments, the accuracy of photometry which can routinely be obtained is limited by significant sky concentration and other effects. This article reports on the progress of a long-term project to improve the photometric calibration of the FORS instruments

FORS1 is getting Blue: New Blue Optimised Detectors and High Throughput Filters

Ground-based observations in the ultraviolet part of the electromagnetic spectrum are notoriously difficult owing to absorption of the atmosphere, of optical elements and the poorer efficiency of detectors. Now that CCD detectors with excellent UV response and cosmetic quality have become available, it was time to optimise FORS1 for imaging, low-resolution spectroscopic and polarimetric observations in the blue-UV. As a bonus, a new set of broadband filters with very high trans-mission and carefully defined filter bands were installed

Personalbestand an Hochschulen der ehemaligen DDR 1989 und 1990

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