3,349 research outputs found

    Status and startup for physics with the ATLAS experiment

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    The LHC accelerator is going to produce the first proton-proton collisions in one year from now. The ATLAS experiment at the LHC entered in a new phase, dedicated to the detector commissioning. This paper is focused on the ATLAS physics commissioning, which will proceed through four different stages. We describe here the strategy which will be followed to understand the detector and undertake the first physics measurements, from beam tests to cosmic run and from pre-collision to collision events

    Special Supersymmetric features of large invariant mass unpolarized and polarized top-antitop production at LHC

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    We consider the top-antitop invariant mass distributions for production of unpolarized and polarized top quark pairs at LHC, in the theoretical framework of the MSSM. Assuming a "moderately" light SUSY scenario, we derive the leading logarithmic electroweak contributions at one loop in a region of large invariant mass, Mttˉ≃1M_{t\bar t}\simeq1 TeV, for the unpolarized differential cross section dσ/dMttˉd\sigma/dM_{t\bar t} and for the differential longitudinal top polarization asymmetry At(Mttˉ)A_t(M_{t\bar t}). We perform a realistic evaluation of the expected uncertainties of the two quantities, both from a theoretical and from an experimental point of view, and discuss the possibility of obtaining, from accurate measurements of the two mass distributions, stringent consistency tests of the model, in particular identifications of large tan⁥ÎČ\tan\beta effects.Comment: 23 pages, 9 eps figure

    Top quark rare three-body decays in the littlest Higgs model with T-parity

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    In the littlest Higgs model with T-parity (LHT), the mirror quarks have flavor structures and will contribute to the top quark flavor changing neutral current. In this work, we perform an extensive investigation of the top quark rare three-body decays t→cVV(V=Îł,Z,g)t\to cVV (V=\gamma,Z,g) and t→cffˉ(f=b,τ,ÎŒ,e)t\to cf\bar{f} (f=b,\tau,\mu,e) at one-loop level. Our results show that the branching ratios of t→cggt\to cgg and t→cbbˉt\to cb\bar{b} could reach O(10−3)\mathcal {O}(10^{-3}) in the favorite parameter space of the littlest Higgs model with T-parity, which implies that these decays may be detectable at the LHC or ILC, while for the other decays, their rates are too small to be observable at the present or future colliders.Comment: 12 pages, 10 figure

    Rare Decay of the Top t -> cgg in the Standard Model

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    We calculate the one-loop flavor changing neutral current top quark decay t -> cgg in the Standard Model. We demonstrate that the rate for t -> cgg exceeds the rate for a single gluon emission t -> cg by about two orders of magnitude, while the rate for t -> cq barq (q=u) is slightly smaller than for t -> cg.Comment: 22 pages, 4 figures and 2 tables. Typo in Eq.2.1 corrected, text slightly modified, references added. Version to appear in Phys.Rev.

    Running a typical ROOT HEP analysis on Hadoop MapReduce

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    We evaluate how a typical ROOT High Energy Physics (HEP) analysis can be executed on Hadoop MapReduce. We take into account several aspects and we propose a method to perform the analysis in a completely transparent way to ROOT, the data and the user: the goal is to let ROOT run without any modifications and to store the data in its original format. The solutions which has been found to solve the encountered problems can be easily ported to any HEP code, and in general to any code working on binary data relying on independent sub-problems like HEP particle collision events. We tested the method by running an analysis code for the top quark pair production cross section measurement with the ATLAS experiment at the Large Hadron Collider in the CERN laboratory

    Prototype ATLAS IBL Modules using the FE-I4A Front-End Readout Chip

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    The ATLAS Collaboration will upgrade its semiconductor pixel tracking detector with a new Insertable B-layer (IBL) between the existing pixel detector and the vacuum pipe of the Large Hadron Collider. The extreme operating conditions at this location have necessitated the development of new radiation hard pixel sensor technologies and a new front-end readout chip, called the FE-I4. Planar pixel sensors and 3D pixel sensors have been investigated to equip this new pixel layer, and prototype modules using the FE-I4A have been fabricated and characterized using 120 GeV pions at the CERN SPS and 4 GeV positrons at DESY, before and after module irradiation. Beam test results are presented, including charge collection efficiency, tracking efficiency and charge sharing.Comment: 45 pages, 30 figures, submitted to JINS