Prospects for b-tagging in ATLAS and tracking commissioning results with cosmic rays

The ability to identify jets containing B hadrons is important for the high-pT physics program of a general-purpose experiment at the LHC such as ATLAS. This capability relies on the very accurate measurements of the parameters of charged tracks provided by the ATLAS Inner Detector. Using millions of cosmic-ray tracks collected during the automn 2008, the ATLAS Inner Detector has been aligned and its tracking performance assessed. Some of the very encouraging results which have been obtained and are relevant for b-tagging are discussed, notably the current level of alignment of the detector and the resolution on the transverse impact parameter of tracks. The various b-tagging algorithms are then described, and their anticipated performance discussed in the light of the cosmic-ray data results. Finaly,the expected accuracy with which the b-tagging performance will be measured in data is mentioned

Signals of Models with Large Extra Dimensions in ATLAS

The generic missing transverse energy signals at LHC for theories having large extra dimensions are discussed. Final states of jets plus missing energy and photons plus missing energy are simulated in the ATLAS detector. The discovery limit of LHC and the methods to determine the parameters of the underlying model are discussed

Spectra of Field Fluctuations in Braneworld Models with Broken Bulk Lorentz Invariance

We investigate five-dimensional braneworld setups with broken Lorentz invariance continuing the developments of our previous paper (arXiv:0712.1136), where a family of static self-tuning braneworld solutions was found. We show that several known braneworld models can be embedded into this family. Then we give a qualitative analysis of spectra of field fluctuations in backgrounds with broken Lorentz invariance. We also elaborate on one particular model and study spectra of scalar and spinor fields in it. It turns out that the spectra we have found possess very peculiar and unexpected properties.Comment: 30 pages, 8 figures, minor corrections, references added, note adde

Search for the radion using the ATLAS detector

The possibility of observing the radion using the ATLAS detector at LHC is investigated. Studies on searches for the Standard Model Higgs with the ATLAS detector are re-interpreted to obtain limits on radion decay to gamma-gamma and ZZ(*). The observability of radion decays into Higgs pairs, which subsequently decay into gamma-gamma+b-bbar or tau-tau+b-bbar is then estimate

Prospects for b-tagging with ATLAS and tracking results with cosmics

b-tagging is a important tool for a large fraction of the physics program of ATLAS. In addition it is specially important for rediscovering the top quark at a 7 TeV center-of-mass energy, where the signal over background is less favourable than at higher energies. The ATLAS Inner Detector is working extremely well and some results obtained with cosmic muons are presented, showing that most parameters are already very close to the nominal expected values. In addition the cosmic muons were used to align the detector with a relatively good accuray. Therefore it is not unrealistic to start commissioning the b-tagging capability with the first ATLAS data. The tagging algorithms which will be used in early data are then described, as well as their expected performance. Finally the measurement of the b-tagging performance directly in data is discussed

Unsupervised Polygonal Reconstruction of Noisy Contours by a Discrete Irregular Approach

International audienceIn this paper, we present an original algorithm to build a polygonal reconstruction of noisy digital contours. For this purpose, we first improve an algorithm devoted to the vectorization of discrete irregular isothetic objects. Afterwards we propose to use it to define a reconstruction process of noisy digital contours. More precisely, we use a local noise detector, introduced by Kerautret and Lachaud in IWCIA 2009, that builds a multi-scale representation of the digital contour, which is composed of pixels of various size depending of the local amount of noise. Finally, we compare our approach with previous works, by con- sidering the Hausdorff distance and the error on tangent orientations of the computed line segments to the original perfect contour. Thanks to both synthetic and real noisy objects, we show that our approach has interesting performance, and could be applied in document analysis systems

Large extra dimension effects in Higgs boson production at linear colliders and Higgs factories

In the framework of quantum gravity propagating in large extra dimensions, the effects of virtual Kaluza-Klein graviton and graviscalar interference with Higgs boson production amplitudes are computed at linear colliders and Higgs factories. The interference of the almost-continuous spectrum of the KK gravitons with the standard model resonant amplitude is finite and predictable in terms of the fundamental D-dimensional Plank scale M_D and the number of extra dimensions \delta. We find that, for M_D ~ 1 TeV and \delta=2, effects of the order of a few percent could be detected for heavy Higgs bosons (m_H>500 GeV) in Higgs production both via WW fusion in e^+e^- colliders and at \mu^+\mu^- Higgs-boson factories.Comment: 16 pages, 2 figures ; a few comments and references added ; version to appear in JHE

Interaction of a TeV Scale Black Hole with the Quark-Gluon Plasma at LHC

If the fundamental Planck scale is near a TeV, then parton collisions with high enough center-of-mass energy should produce black holes. The production rate for such black holes has been extensively studied for the case of a proton-proton collision at \sqrt s = 14 TeV and for a lead-lead collision at \sqrt s = 5.5 TeV at LHC. As the parton energy density is much higher at lead-lead collisions than in pp collisions at LHC, one natural question is whether the produced black holes will be able to absorb the partons formed in the lead-lead collisions and eventually `eat' the quark-gluon plasma formed at LHC. In this paper, we make a quantitative analysis of this possibility and find that since the energy density of partons formed in lead-lead collisions at LHC is about 500 GeV/fm^3, the rate of absorption for one of these black holes is much smaller than the rate of evaporation. Hence, we argue that black holes formed in such collisions will decay very quickly, and will not absorb very many nearby partons. More precisely, we show that for the black hole mass to increase via parton absorption at the LHC the typical energy density of quarks and gluons should be of the order of 10^{10} GeV/fm^3. As LHC will not be able to produce such a high energy density partonic system, the black hole will not be able to absorb a sufficient number of nearby partons before it decays. The typical life time of the black hole formed at LHC is found to be a small fraction of a fm/c.Comment: 7 pages latex (double column), 3 eps figure