SUSY parameter determination

The impact of the LHC, SLHC and the ILC on the precision of the determination of supersymmetric parameters is investigated. In particular, in the point SPS1a the measurements performed at the ILC will improve by an order of magnitude the precision obtained by the LHC alone. The SLHC with respect to the LHC has the potential to reduce the errors by a factor two.Comment: Invited talk at 2005 International Linear Collider Physics and Detector Workshop and Second ILC Accelerator Workshop, Snowmass, CO(Snowmass05) 3 pages, LaTe

ATLAS electromagnetic barrel calorimeter performance in recent testbeams

During the combined testbeam in summer 2004 a slice of the ATLAS barrel detector—including all detector sub systems from the inner tracker, the calorimetry to the muon system—was exposed to particle beams (electrons, pions, photons, muons) with different energies (1–350 GeV). The aim was to study the combined performance of the different detector sub systems in ATLAS-like conditions. We will present studies with different amounts of material in front of the calorimeter, representing various regions in the ATLAS detector, performance results from the electromagnetic calorimetry, including uniformity, resolution, and linearity as well as a discussion of the calibration scheme. The performance in the combined ATLAS-like set-up will be compared to the one obtained in stand-alone testbeams

SFitter: Reconstructing the MSSM Lagrangian from LHC data

Once supersymmetry is found at the LHC, the question arises what are the fundamental parameters of the Lagrangian. The answer to this question should thereby not be biased by assumptions on high-scale models. SFitter is a tool designed for this task. Taking LHC (and possibly ILC) data as input it scans the TeV-scale MSSM parameter space using its new weighted Markov chain technique. Using this scan it determines a list of best-fitting parameter points. Additionally a log-likelihood map is calculated, which can be reduced to lower-dimensional Frequentist's profile likelihoods or Bayesian probability maps.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 4 eps figure

Reconstruction of fundamental SUSY parameters at LHC and at a future linear collider

Presentation par R. LafayeUnveiling the mechanism leading to the breaking of supersymmetry is among the outstanding questions for future colliders. To achieve this goal, models will need to be scrutinized and their parameters assessed. Global fitting tools, like Fittino and SFitter, have been developed and set a robust framework for such analyses. Using the SPS1a snowmass point as an example for the SUSY and Higgs particles that could be observed at the LHC and at a future TeV Linear Collider, we have studied the determination and its precision of MSUGRA parameters from the measurements expected in this point. While the LHC will provide the first measurement of the parameters, the Linear Collider will increase their precision by an order of magnitude. However, when moving to the unconstrained weak-scale MSSM, measurements from the LHC, such as the gluino and squarks masses and couplings, and from the LC, such as charginos and high precision slepton mass measurements, are necessary to reconstruct the Lagrangian with the best available precision. Using a set of hypothetical measurements at LHC and at a future LC, we will show how these colliders probe different sectors of the MSSM Lagrangian and how this complementarity increases our handle on the determination of the weak-scale parameters of the Lagrangian. In fact, the combination of the measurements of the LHC and the LC is essential to probe the complete MSSM weak-scale lagrangian

Higgs look-alikes at the LHC

The discovery of a Higgs particle is possible in a variety of search channels at the LHC. However the true identity of any putative Higgs boson will at first remain ambiguous, until one has experimentally excluded other possible assignments of quantum numbers and couplings. We quantify to what degree one can discriminate a Standard Model Higgs boson from "look-alikes" at, or close to, the moment of discovery at the LHC. We focus on the fully-reconstructible "golden" decay mode to a pair of Z bosons and a four-lepton final state, simulating sPlot-weighted samples of signal and background events. Considering both on-shell and off-shell Z's, we show how to utilize the full decay information from the events, including the distributions and correlations of the five relevant angular variables. We demonstrate how the finite phase space acceptance of any LHC detector sculpts the decay distributions, a feature neglected in previous studies. We use likelihood ratios to discriminate a Standard Model Higgs from look-alikes with other spins or nonstandard parity, CP, or form factors. For a benchmark resonance mass of 200 GeV/c^2, we achieve a median expected discrimination significance of 3 sigma with as few as 19 events, and even better discrimination for the off-shell decays of a 145 GeV/c^2 resonance.Comment: 39 pages, 55 figures, typos fixed, figures added, and minor clarification

Higgs Physics at the Large Hadron Collider

In this talk I will begin by summarising the importance of the Higgs physics studies at the LHC. I will then give a short description of the pre-LHC constraints on the Higgs mass and the theoretical predictions for the LHC along with a discussion of the current experimental results, ending with prospects in the near future at the LHC. In addition to the material covered in the presented talk, I have included in the writeup, a critical appraisal of the theoretical uncertainties in the Higgs cross-sections at the Tevatron as well as a discussion of the recent experimental results from the LHC which have become available since the time of the workshop.Comment: LateX, 12 figures, 15 pages, Presented at the XIth Workshop on High Energy Physics Phenomenology, 2010, Ahmedabad, Indi

Higgs Physics: Theory

I review the theoretical aspects of the physics of Higgs bosons, focusing on the elements that are relevant for the production and detection at present hadron colliders. After briefly summarizing the basics of electroweak symmetry breaking in the Standard Model, I discuss Higgs production at the LHC and at the Tevatron, with some focus on the main production mechanism, the gluon-gluon fusion process, and summarize the main Higgs decay modes and the experimental detection channels. I then briefly survey the case of the minimal supersymmetric extension of the Standard Model. In a last section, I review the prospects for determining the fundamental properties of the Higgs particles once they have been experimentally observed.Comment: 21 pages, 15 figures. Talk given at the XXV International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 11), 22-27 August 2011, Mumbai, Indi

Measuring the Higgs Sector

If we find a light Higgs boson at the LHC, there should be many observable channels which we can exploit to measure the relevant parameters in the Higgs sector. We use the SFitter framework to map these measurements on the parameter space of a general weak-scale effective theory with a light Higgs state of mass 120 GeV. Our analysis benefits from the parameter determination tools and the error treatment used in new--physics searches, to study individual parameters and their error bars as well as parameter correlations.Comment: 45 pages, Journal version with comments from refere