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Abstract:

We present a comprehensive black-hole event generator, BlackMax, which simulates the experimental signatures of microscopic and Planckian black-hole production and evolution at the LHC in the context of brane world models with low-scale quantum gravity. The generator is based on phenomenologically realistic models free of serious problems that plague low-scale gravity, thus offering more realistic predictions for hadron-hadron colliders. The generator includes all of the black-hole graybody factors known to date and incorporates the effects of black-hole rotation, splitting between the fermions, non-zero brane tension and black-hole recoil due to Hawking radiation (although not all simultaneously). The generator can be interfaced with Herwig and Pythia.

Abstract:

The challenges for the tracking detector systems at the LHC are unprecedented in terms of the number of channels, the required read-out speed and the expected radiation levels. The ATLAS Semiconductor Tracker (SCT) end-caps have a total of about 3 million electronics channels each reading out every 25 ns into its own on-chip 3.3 μ s buffer. The highest anticipated dose after 10 years operation is 1.4 × 10¹⁴ cm^{- 2} in units of 1 MeV neutron equivalent (assuming the damage factors scale with the non-ionising energy loss). The forward tracker has 1976 double-sided modules, mostly of area ∼ 70 cm², each having 2 × 768 strips read out by six ASICs per side. The requirement to achieve an average perpendicular radiation length of 1.5% X0, while coping with up to 7 W dissipation per module (after irradiation), leads to stringent constraints on the thermal design. The additional requirement of 1500 e^- equivalent noise charge (ENC) rising to only 1800 e^- ENC after irradiation, provides stringent design constraints on both the high-density Cu/Polyimide flex read-out circuit and the ABCD3TA read-out ASICs. Finally, the accuracy of module assembly must not compromise the 16 μ m (r φ) resolution perpendicular to the strip directions or 580 μ m radial resolution coming from the 40 mrad front-back stereo angle. A total of 2210 modules were built to the tight tolerances and specifications required for the SCT. This was 234 more than the 1976 required and represents a yield of 93%. The component flow was at times tight, but the module production rate of 40-50 per week was maintained despite this. The distributed production was not found to be a major logistical problem and it allowed additional flexibility to take advantage of where the effort was available, including any spare capacity, for building the end-cap modules. The collaboration that produced the ATLAS SCT end-cap modules kept in close contact at all times so that the effects of shortages or stoppages at different sites could be rapidly resolved. © 2007 Elsevier B.V. All rights reserved.

Abstract:

We present the first observation of the baryon decay Λb0→ Λc+π- followed by Λc+→pK-π+ in 106pb-1 pp̄ collisions at s=1.96TeV in the CDF experiment. In order to reduce systematic error, the measured rate for Λb0 decay is normalized to the kinematically similar meson decay B̄0→D+π- followed by D+→π+K-π+. We report the ratio of production cross sections (σ) times the ratio of branching fractions (B) for the momentum region integrated above pT>6GeV/c and pseudorapidity range |η|<1.3: σ(pp̄→Λb0X)/ σ(pp̄→B̄0X)×B(Λb0→Λc+π-)/ B(B̄0→D+π-)=0.82±0.08(stat)±0.11(syst)±0. 22[B(Λc+→pK-π+)]. © 2007 The American Physical Society.

Abstract:

Randall-Sundrum models based on SU(2)_L * SU(2)_R with custodial symmetry are compelling frameworks for building alternative models of electroweak symmetry breaking. A particular feature of these models is the likely presence of light Kaluza-Klein fermions related to the right-handed top quark. These can be as light as a few hundred GeV and still compatible with EW precision constraints. In this article, we study the detectability of four-W final states at the LHC, which arise from the pair-production and tW decay of light Kaluza-Klein bottom quarks as well as light Kaluza-Klein quarks carrying electric charge 5/3.