Standard Model Higgs boson searches with the ATLAS detector at the Large Hadron Collider

The investigation of the mechanism responsible for electroweak symmetry breaking is one of the most important tasks of the scientific program of the Large Hadron Collider. The experimental results on the search of the Standard Model Higgs boson with 1 to 2 fb^-1 of proton proton collision data at sqrt s=7 TeV recorded by the ATLAS detector are presented and discussed. No significant excess of events is found with respect to the expectations from Standard Model processes, and the production of a Higgs boson is excluded at 95% Confidence Level for the mass regions 144-232, 256-282 and 296-466 GeV.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in "Pramana - journal of phsyics". 11 pages, 13 figure

Measurement of Jets and Jet Suppression in sqrt(s_NN)=2.76 TeV Lead-Lead Collisions with the ATLAS detector at the LHC

The first results of single jet observables in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented. Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4, using an event-by-event subtraction procedure to correct for the effects of the underlying event including elliptic flow. The geometrically-scaled ratio of jet yields in central and peripheral events,Rcp, indicates a clear suppression of jets with ET >100 GeV. The transverse and longitudinal distributions of jet fragments is also presented. We find little no substantial change to the fragmentation properties and no significant change in the level of suppression when moving to the larger jet definition.Comment: 5 pages, 6 figures, proceedings for Quark Matter 2011, Annecy, France, May 23-28, 201

LHC Coverage of RPV MSSM with Light Stops

We examine the sensitivity of recent LHC searches to signatures of supersymmetry with R-parity violation (RPV). Motivated by naturalness of the Higgs potential, which would favor light third-generation squarks, and the stringent LHC bounds on spectra in which the gluino or first and second generation squarks are light, we focus on scenarios dominated by the pair production of light stops. We consider the various possible direct and cascade decays of the stop that involve the trilinear RPV operators. We find that in many cases, the existing searches exclude stops in the natural mass range and beyond. However, typically there is little or no sensitivity to cases dominated by UDD operators or LQD operators involving taus. We propose several ideas for searches which could address the existing gaps in experimental coverage of these signals.Comment: 41 pages, 12 figures; v2: included new searches (see footnote 10), minor corrections and improvement

First global analysis of SEASAT scatterometer winds and potential for meteorological research

The first global wind fields from SEASAT-A scatterometer (SASS) data were produced. Fifteen days of record are available on tape, with unique wind directions indicated for each observation. The methodology of the production of this data set is described, as well as the testing of its validity. A number of displays of the data, on large and small scales, analyzed and gridded, are provided

Multiple Parton Interactions, top--antitop and W+4j production at the LHC

The expected rate for Multiple Parton Interactions (MPI) at the LHC is large. This requires an estimate of their impact on all measurement foreseen at the LHC while opening unprecendented opportunities for a detailed study of these phenomena. In this paper we examine the MPI background to top-antitop production, in the semileptonic channel, in the early phase of data taking when the full power of $b$--tagging will not be available. The MPI background turns out to be small but non negligible, of the order of 20% of the background provided by W+4j production through a Single Parton Interaction. We then analyze the possibility of studying Multiple Parton Interactions in the W+4j channel, a far more complicated setting than the reactions examined at lower energies. The MPI contribution turns out to be dominated by final states with two energetic jets which balance in transverse momentum, and it appears possible, thanks to the good angular resolution of ATLAS and CMS, to separate the Multiple Parton Interactions contribution from Single Parton Interaction processes. The large cross section for two jet production suggests that also Triple Parton Interactions (TPI) could provide a non negligible contribution. Our preliminary analysis suggests that it might be indeed possible to investigate TPI at the LHC.Comment: Typos fixed. Published in JHE

Monthly mean forecast experiments with the GISS model

The GISS general circulation model was used to compute global monthly mean forecasts for January 1973, 1974, and 1975 from initial conditions on the first day of each month and constant sea surface temperatures. Forecasts were evaluated in terms of global and hemispheric energetics, zonally averaged meridional and vertical profiles, forecast error statistics, and monthly mean synoptic fields. Although it generated a realistic mean meridional structure, the model did not adequately reproduce the observed interannual variations in the large scale monthly mean energetics and zonally averaged circulation. The monthly mean sea level pressure field was not predicted satisfactorily, but annual changes in the Icelandic low were simulated. The impact of temporal sea surface temperature variations on the forecasts was investigated by comparing two parallel forecasts for January 1974, one using climatological ocean temperatures and the other observed daily ocean temperatures. The use of daily updated sea surface temperatures produced no discernible beneficial effect

Constraining SUSY Dark Matter with the ATLAS Detector at the LHC

In the event that R-Parity conserving supersymmetry (SUSY) is discovered at the LHC, a key issue which will need to be addressed will be the consistency of that signal with astrophysical and non-accelerator constraints on SUSY Dark Matter. This issue is studied for the SPS1a mSUGRA benchmark model by using measurements of end-points and thresholds in the invariant mass spectra of various combinations of leptons and jets in ATLAS to constrain the model parameters. These constraints are then used to assess the statistical accuracy with which quantities such as the Dark Matter relic density and direct detection cross-section can be measured. Systematic effects arising from the use of different mSUGRA RGE codes are also estimated. Results indicate that for SPS1a a statistical(systematic) precision on the relic abundance ~ 2.8% (3 %) can be obtained given 300 fb-1 of data.Comment: 11 pages, 10 encapsulated postscript figures. Minor modification to ref

Searching for the Kaluza-Klein Graviton in Bulk RS Models

The best-studied version of the RS1 model has all the Standard Model particles confined to the TeV brane. However, recent variants have the Standard Model fermions and gauge bosons located in the bulk five-dimensional spacetime. We study the potential reach of the LHC in searching for the lightest KK partner of the graviton in the most promising such models in which the right-handed top is localized very near the TeV brane and the light fermions are localized near the Planck brane. We consider both detection and the establishment of the spin-2 nature of the resonance should it be found.Comment: 17 pages, 6 figures - JHEP published version, figures added, branching ratio correcte

Macroscopic Strings and "Quirks" at Colliders

We consider extensions of the standard model containing additional heavy particles ("quirks") charged under a new unbroken non-abelian gauge group as well as the standard model. We assume that the quirk mass m is in the phenomenologically interesting range 100 GeV--TeV, and that the new gauge group gets strong at a scale Lambda < m. In this case breaking of strings is exponentially suppressed, and quirk production results in strings that are long compared to 1/Lambda. The existence of these long stable strings leads to highly exotic events at colliders. For 100 eV < Lambda < keV the strings are macroscopic, giving rise to events with two separated quirk tracks with measurable curvature toward each other due to the string interaction. For keV < Lambda < MeV the typical strings are mesoscopic: too small to resolve in the detector, but large compared to atomic scales. In this case, the bound state appears as a single particle, but its mass is the invariant mass of a quirk pair, which has an event-by-event distribution. For MeV < Lambda < m the strings are microscopic, and the quirks annihilate promptly within the detector. For colored quirks, this can lead to hadronic fireball events with 10^3 hadrons with energy of order GeV emitted in conjunction with hard decay products from the final annihilation.Comment: Added discussion of photon-jet decay, fixed minor typo