Particle Physics and Cosmology

Today, both particle physics and cosmology are described by few parameter Standard Models, i.e. it is possible to deduce consequence of particle physics in cosmology and vice verse. The former is examined in this lecture, in light of the recent systematic exploration of the electroweak scale by the LHC experiments. The two main results of the first phase of the LHC, the discovery of a Higgs-like particle and the absence so far of new particles predicted by "natural" theories beyond the Standard Model (supersymmetry, extra-dimension and composite Higgs) are put in a historical context to enlighten their importance and then presented extensively. To be complete, a short review from the neutrino physics, which can not be probed at LHC, is also given. The ability of all these results to resolve the 3 fundamental questions of cosmology about the nature of dark energy and dark matter as well as the origin of matter-antimatter asymmetry is discussed in each case.Comment: 32 pages, 47 figures, Proceeding from the 100th Les Houches Summer School on Post-Planck Cosmology, July 8th - Aug 2nd 2013. Update with recently published ATLAS/CMS 8 TeV result

Lessons for SUSY from the LHC after the first run

A review of direct searches for new particles predicted by Supersymmetry after the first run of the LHC is proposed. This review is based on the results provided by the ATLAS and CMS experiments.Comment: 31 pages, 41 figures, Appear in the special issue of the EPJ C journal entitled "SUSY after the Higgs discovery

Commissioning of the ATLAS electromagnetic calorimeter with minimum bias events

This note presents the potentiality to commission the ATLAS EM calorimeter during the (very) first days of data taking, prior to be able to trig and identify correctly electrons. For this purpose, a very simple analysis using the $\phi$ symmetry of the abundant minimum bias events and computing the energy accumulated in the EM calorimeter is proposed. No input from the Monte Carlo is necessary, and only information from the calorimeter is used. To cope with the high number of events, simulation and analysis are performed using the GRID technology. Adopting a simple energy reconstruction scheme based on the cosmic muon experience should allow to spot intrinsic problems of the EM calorimeter in a few days. It should also give first hints on the $\phi$ dispersion of the Inner Detector material, if the excess is sizeable >10\% X$_0$ in a region $\Delta \eta \times \Delta \phi=0.1\times 0.1$. Ultimately, a first flavor of systematics coming from the EM calorimeter $\phi$~non-uniformity and its positionning (in the ATLAS framework or with respect to the beam) could be possible

Comparison between full and fast simulations in top physics

All analyses performed in the top quark sector with a full simulation of the ATLAS detector show a good agreement with fast simulation results. The purpose of this note is to understand why detailed detector effects are not so crucial in these studies. A systematic comparison, based on a ``Rome'' Data Challenge fully simulated data sample and an ATLFAST simulated one, is done on all top event objects, electrons, muons, neutrinos, light and b-jets. A very good agreement on reconstructed top kinematics variables is shown. This assess the robustness of the results obtained with fast simulations in the top quark sector, and more particularly the detailed estimates of the related systematic uncertainties, which are the key points of most of these analyses

Signal reconstruction in the EM end-cap calorimeter and check with cosmic data in the region 0< eta <3.2

In 2007, the electromagnetic end-cap calorimeter joined the ATLAS commissioning effort. Since then, calibration and cosmic muon runs are taken regularly, allowing to set-up, debug and test in situ the signal reconstruction. These are the first data in the 1.4500 MeV) have been used to perform a systematic and quantitative comparison between data and predicted physics pulse shapes in a coherent way over the entire calorimeter coverage, 0< eta <3.2. This represents the first attempt to unify barrel and end-cap in situ data in a common analysis. Results are similar in the barrel and the end-cap, only slightly worse for the latter as expected from its more complex geometry. This is the first proof of the quality of an ATLAS-like signal reconstruction in the end-caps, despite its challenging aspect, and gives confidence that the energy reconstruction is in good control over the complete electromagnetic calorimeter coverage 0< eta <3.2

Position resolution and particle identification with the ATLAS EM calorimeter

In the years between 2000 and 2002 several pre-series and series modules of the ATLAS EM barrel and end-cap calorimeter were exposed to electron, photon and pion beams. The performance of the calorimeter with respect to its finely segmented first sampling has been studied. The polar angle resolution has been found to be in the range 50-60 mrad/sqrt(E (GeV)). The neutral pion rejection has been measured to be about 3.5 for 90% photon selection efficiency at pT=50 GeV/c. Electron-pion separation studies have indicated that a pion fake rate of (0.07-0.5)% can be achieved while maintaining 90% electron identification efficiency for energies up to 40 GeV.Comment: 32 pages, 22 figures, to be published in NIM

In situ commissioning of the ATLAS electromagnetic calorimeter with cosmic muons

In 2006, ATLAS entered the {\it in situ} commissioning phase. The primary goal of this phase is to verify the detector operation and performance with cosmic muons. Using a dedicated cosmic muon trigger from the hadronic Tile calorimeter, a sample of approximately $120\,000$ events was collected in several modules of the barrel electromagnetic (EM) calorimeter between August 2006 and March 2007. As cosmic events are generally non-projective and arrive asynchronously with respect to the trigger clock, methods to improve the standard signal reconstruction for this situation are presented. Various selection criteria for projective muons and clustering algorithms have been tested, leading to preliminary results on calorimeter uniformity in $\eta$ and timing performance

Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb−1 of s√=7TeV proton-proton collisions

Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb−1 of pp collision data at s√=7TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m 0, gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV

Measurement of inclusive two-particle angular correlations in pp collisions with the ATLAS detector at the LHC

We present a measurement of two-particle angular correlations in proton- proton collisions at s√=900 GeV and 7 TeV. The collision events were collected during 2009 and 2010 with the ATLAS detector at the Large Hadron Collider using a single-arm minimum bias trigger. Correlations are measured for charged particles produced in the kinematic range of transverse momentum p T  > 100 MeV and pseudorapidity |η| < 2.5. A complex structure in pseudorapidity and azimuth is observed at both collision energies. Results are compared to pythia 8 and herwig++ as well as to the AMBT2B, DW and Perugia 2011 tunes of pythia 6. The data are not satisfactorily described by any of these models