Alignment of the ATLAS Inner Detector Tracking System

The ATLAS detector at CERN's Large Hadron Collider (LHC) is equipped with a tracking system at its core (the Inner Detector, ID) consisting of silicon and gaseous straw tube detectors. The physics performance of the ID requires a precision alignment; a challenge involving complex algorithms and significant computing power. The alignment algorithms were already validated on: Combined Test Beam data, Cosmic Ray runs and simulated physics events. The alignment chain was tested on a daily basis in exercises that mimicked ATLAS data taking operations. ID commissioning after final installation into the ATLAS detector has yielded thousands of reconstructed cosmic ray tracks, which have been used for an initial alignment of the ID before the LHC start-up. A hardware system using Frequency Scanning Interferometry will be used to monitor structural deformations. Given the programme outlined here, the ATLAS Inner Detector has had a solid preparation for LHC collisions.Comment: ICHEP0

Searches for Extra Dimensions at the Tevatron

Models in which gravity and/or Standard Model gauge bosons propagate in more than three spatial dimensions have implications that can be tested at current colliders. In this paper, we report on the results from searches for extra dimensions at the two Tevatron experiments, CDF and D0, which utilize up to 200 pb^-1 of proton-antiproton collision data from Run II taken at 1.96 TeV CoM energy, between spring 2002 and fall 2003.Comment: 10 Pages. Proceedings, Hadron Collider Physics (HCP 2004), E. Lansing, Michigan, US

Parallel Computing Studies for the Alignment of the ATLAS Silicon Tracker

The silicon system of the ATLAS Inner Detector consists of about 6000 modules in its Semiconductor Tracker and Pixel Detector. Therefore, the offline global fit alignment algorithm has to deal with solving a problem of up to 36000 degrees of freedom.32-bit single-CPU platforms were foreseen to be unable to handle such large-size operations needed by the algorithm. The proposed solution is to utilize a Beowulfcluster with a 64-bit architecture. We have performed the initial studies on performance of such a system using SCARF RAL cluster, compared with earlier predictions, obtained the first promising results on parallel computing for the ATLAS tracker alignment. After a brief introduction with the motivation, we will describe the hardware and software used and present the results of the studies, using also examples from the ATLAS simulated data

Fourth Family Neutrinos and the Higgs Boson

We evaluate the LHC discovery potential for the fourth family Standard Model neutrinos in the process $pp\to Z/h\to\nu_{4}{\bar{\nu}_{4}}\to W\mu W\mu$. We show that, depending on their masses, the simultaneous discovery of both the Higgs boson and the heavy neutrinos is probable at early stages of LHC operation. Results are presented for both Majorana and Dirac type fourth family neutrinos.Comment: 12 pages, uses axodraw.sty, v2: includes typo fixes, improved analysis, v4: minor modifications in response to the JHEP refere

Multi-W Events at LHC from a Warped Extra Dimension with Custodial Symmetry

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.Comment: 17 pages, 26 figure

Beam Halo Monitoring at CDF

Losses from the proton and antiproton beams of the Fermilab Tevatron have been shown to produce a halo which contribute to backgrounds to physics signals in the Collider Detector at Fermilab (CDF). To provide a measure of the beam halo and losses, we have installed arrays of scintillation counters on both sides of the CDF detector. We describe here the physical configuration of these counters, their implementation and performance within the Fermilab Accelerator Control Network (ACNET). We show correlations between these new devices and the accelerator operating conditions. We point out that the use of these monitors is leading to improvement in the accelerator operations and reduced backgrounds in CDF.Comment: 27 pages, 17 figures, submitted to NIM

Low Scale Gravity Signatures in ATLAS

The ATLAS detector may reveal in the LHC collisions signatures of extra dimensional models which predict quantum gravity at the TeV scale. One of the most dramatic consequences of such models is the copious production of micro blackholes. Micro blackholes can yield distinct signatures with large multiplicity and large energy release in the ATLAS detector. Extra dimensional models also predict the existence of Kaluza-Klein partners of SM gauge bosons, such as the excited graviton and gluon. These particles can be searched for in their two-body decays. The emerging final state particles are highly energetic, thus requiring novel reconstruction techniques, in particular in the heavy quark (t, b) channels. I will summarize the current status of the low scale gravity studies in ATLAS with example signatures

Study of a twisted ATLAS SCT Barrel deformation as revealed by a photogrammetric survey

A photogrammetry survey on the SCT barrels was performed as an engineering check on the structure of the ATLAS Semiconductor Tracker (SCT) shortly after construction. Analysis of the data obtained revealed small scale elliptical deformation as well as a twist of the structure. The results of the survey are presented as well as interpolation of the measured targets to the module positions and a comparison with track based alignment measurements

Inclusive Search for Anomalous Production of High-pT Like-Sign Lepton Pairs in Proton-Antiproton Collisions at sqrt{s}=1.8 TeV

We report on a search for anomalous production of events with at least two charged, isolated, like-sign leptons with pT > 11 GeV/c using a 107 pb^-1 sample of 1.8 TeV ppbar collisions collected by the CDF detector. We define a signal region containing low background from Standard Model processes. To avoid bias, we fix the final cuts before examining the event yield in the signal region using control regions to test the Monte Carlo predictions. We observe no events in the signal region, consistent with an expectation of 0.63^(+0.84)_(-0.07) events. We present 95% confidence level limits on new physics processes in both a signature-based context as well as within a representative minimal supergravity (tanbeta = 3) model.Comment: 15 pages, 4 figures. Minor textual changes, cosmetic improvements to figures and updated and expanded reference

Measurement of the Dipion Mass Spectrum in X(3872) -> J/Psi Pi+ Pi- Decays

We measure the dipion mass spectrum in X(3872)--> J/Psi Pi+ Pi- decays using 360 pb-1 of pbar-p collisions at 1.96 TeV collected with the CDF II detector. The spectrum is fit with predictions for odd C-parity (3S1, 1P1, and 3DJ) charmonia decaying to J/Psi Pi+ Pi-, as well as even C-parity states in which the pions are from Rho0 decay. The latter case also encompasses exotic interpretations, such as a D0-D*0Bar molecule. Only the 3S1 and J/Psi Rho hypotheses are compatible with our data. Since 3S1 is untenable on other grounds, decay via J/Psi Rho is favored, which implies C=+1 for the X(3872). Models for different J/Psi-Rho angular momenta L are considered. Flexibility in the models, especially the introduction of Rho-Omega interference, enable good descriptions of our data for both L=0 and 1.Comment: 7 pages, 4 figures -- Submitted to Phys. Rev. Let