Results from the commissioning of the ATLAS Pixel detector

The ATLAS Pixel detector is a high-resolution, low-noise silicon-based device designed to provide tracking and vertexing information within a distance of 12 cm from the LHC beam axis. It consists of approximately 80 million pixel channels with radiation-hard front-end electronics connected through optical fibers to a custom-controlled DAQ system away from the detector. Following the successful installation of the detector in June 2007, an intense commissioning period was conducted in the year 2008 and more than 400,000 cosmic-ray tracks were recorded in conjunction with other ATLAS sub-detectors. By the end of the year, 96% of the detector was tuned, calibrated, and taking data at 99.8% tracking hit efficiency and with noise occupancy at the 10^-10 level. We present here the results of the commissioning, calibration, and data-taking as well as the outlook for future performance with LHC collision-based data.Comment: 3 pages. Part of the proceedings of the TIPP09 conference, held at Tsukuba, Japan. Updated the figures in v.2 to reflect the version published in NIM A

Composite Models for the 750 GeV Diphoton Excess

We present composite models explaining the diphoton excess of mass around 750 GeV recently reported by the LHC experiments.Comment: 7 pages, 1 figure; matches the published versio

Status of ATLAS and Preparation for the Pb-Pb Run

The ATLAS experiment took its first beam data in September 2008 and is actively preparing for the planned start of LHC collision data-taking in 2009. This preparation includes hardware and software commissioning, as well as calibration and cosmic data analysis. The status and performance of the ATLAS detector will be discussed, with a view towards the Pb+Pb run expected in 2010.Comment: 8 pages, 14 figures, corrected typos, added references, figures corrected for better legibility in B&W - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

ATLAS IBL Pixel Upgrade

The upgrade for ATLAS detector will undergo different phase towards super-LHC. The first upgrade for the Pixel detector will consist of the construction of a new pixel layer which will be installed during the first shutdown of the LHC machine (LHC phase-I upgrade). The new detector, called Insertable B-Layer (IBL), will be inserted between the existing pixel detector and a new (smaller radius) beam-pipe at a radius of 3.3 cm. The IBL will require the development of several new technologies to cope with increase of radiation or pixel occupancy and also to improve the physics performance which will be achieved by reducing the pixel size and of the material budget. Three different promising sensor technologies (planar-Si, 3D-Si and diamond) are currently under investigation for the pixel detector. An overview of the project with particular emphasis on pixel module is presented in this paper.Comment: 3 pages, 3 figures, presented at the 12th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD10) 7 - 10 June 2010, Siena (IT). Accepted by Nuclear Physics B (Proceedings Supplements) (2011

On the reproducing kernel of a Pontryagin space of vector valued polynomials

We give necessary and sufficient conditions under which the reproducing kernel of a Pontryagin space of $d \times 1$ vector polynomials is determined by a generalized Nevanlinna pair of $d \times d$ matrix polynomials.Comment: 33 page

Search for a heavy gauge boson decaying to a charged lepton and a neutrino in 1 fb^(−1) of pp collisions at √s = 7 TeV using the ATLAS detector

The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W'), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 1.04 fb^(−1). No excess above Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 2.15 Te

Implications of QCD radiative corrections on high-pT Higgs searches

We discuss the effect of next-to-leading order (NLO) QCD corrections to the Higgsstrahlung process, where the Higgs boson decays to bottom quarks, using a partonic-level fully differential code. First we evaluate the impact of initial- and final-state gluon radiation on the reconstruction of a mass peak with the fat-jet analysis in the boosted regime at the LHC with sqrt(s) = 14 TeV as proposed in Butterworth et al. (2008) [1]. Finally we study the current CMS search strategy for this channel and compare it to the fat-jet procedure at the LHC with sqrt(s) = 8 TeV. Both show that final-state QCD radiation has a sizable effect and should be taken properly into account.Comment: 16 pages, 5 figures, version accepted for publicatio

Higgs boson search significance deformations due to mixed-in scalars

The existence of exotic scalars that mix with the Standard Model (SM) Higgs boson can affect Higgs boson phenomenology in a multitude of ways. We consider two light Higgs bosons with shared couplings to SM fields and with masses close to each other, in the range where the h \to WW \to l \nu l \nu is an important search channel. In this channel, we do not find the dilution of significance of the `SM-like' Higgs boson that is naively expected because of the mixing. This is because of leakage of events from the decay of the other scalar into its signal region. Nevertheless, we show that the broadening of the h\to WW \to l \nu l \nu significance plots of Standard Model Higgs boson searches could indicate the first evidence of the the extra scalar state.Comment: 6 pages, 6 figures; v2: all plots now made with the lighter Higgs mass equal to 125 GeV and other minor corrections made, to be published in Physics Letters