Understanding SUSY limits from LEP

LEP results have constrained heavily the Minimal Supersymmetric Standard Model, while providing hints for light Higgs boson and for ``SUSY-assisted'' gauge couling unification. In this paper the results obtained at LEP within two scenarios, the gravity-mediated MSSM framework and the minimal SUGRA scenario are presented. Model-dependence and coverage of LEP results is discussed.Comment: Prepared for 3nd International Conference on Physics Beyond the Standard Model, Beyond the Desert 02, Oulu, Finland, 2-7 June 200

The LHC, shining light on the Dark Side

Starting in the summer of 2007, the Large Hadron Collider (LHC) will collide proton beams at center-of-mass energies of 14 TeV exceeding by a factor of ten what was previously achieved. It will be located in the 27km long underground tunnel, in which the Large Electron Positron collider (LEP) was working until the year 2000. The Large Hadron Collider is a part of the accelerator complex of the European Laboratory of Particle Physics (CERN), situated on the Franco-Swiss border close to Geneva.Comment: 7pages, 5 figure

Machine Learning Classification of Sphalerons and Black Holes at the LHC

In models with large extra dimensions, "miniature" black holes (BHs) might be produced in high-energy proton-proton collisions at the Large Hadron Collider (LHC). In the semi-classical regime, those BHs thermally decay, giving rise to large-multiplicity final states with jets and leptons. On the other hand, similar final states are also expected in the production of electroweak sphaleron/instanton-induced processes. We investigate whether one can discriminate these scenarios when BH or sphaleron-like events are observed in the LHC using Machine Learning (ML) methods. Classification among several BH scenarios with different numbers of extra dimensions and the minimal BH masses is also examined. In this study we consider three ML models: XGBoost algorithms with (1) high- and (2) low-level inputs, and (3) a Residual Convolutional Neural Network. In the latter case, the low-level detector information is converted into an input format of three-layer binned event images, where the value of each bin corresponds to the energy deposited in various detector subsystems. We demonstrate that only a few detected events are sufficient to effectively discriminate between the sphaleron and BH processes. Separation among BH scenarios with different minimal BH masses is also possible with a reasonable number of events, that can be collected in the LHC Run-2, -3 and the high-luminosity LHC (HL-LHC). We find, however, that a large number of events is needed to discriminate between BH hypotheses with the same minimal BH mass, but different numbers of extra dimensions.Comment: 18 pages, 5 figure

The scientific case for eInfrastructure in Norway

The scientific case for eInfrastructure in NorwaypublishedVersio

Charged-particle multiplicities in pppp interactions at s\sqrt{s} = 900 GeV measured with the ATLAS detector at the LHC

The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |eta|500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at eta = 0 is measured to be 1.333 +/- 0.003 (stat.) +/- 0.040 (syst.), which is 5-15% higher than the Monte Carlo models predict.publishedVersio

Measurement of the b-hadron production cross section using decays to D*+ μ − X final states in pp collisions at √s = 7 TeV with the ATLAS detector

The b-hadron production cross section is measured with the ATLAS detector in pp collisions at √s = 7 TeV, using 3.3 pb−1 of integrated luminosity, collected during the 2010 LHC run. The b-hadrons are selected by partially reconstructing D*+μ−X final states. Differential cross sections are measured as functions of the transverse momentum and pseudorapidity. The measured production cross section for a b-hadron with pT > 9 GeV and |η| < 2.5 is 32.7±0.8(stat.)+4.5−6.8(syst.) μb, higher than the next-to-leadingorder QCD predictions but consistent within the experimental and theoretical uncertainties

Charged-particle multiplicities in pppp interactions at s\sqrt{s} = 900 GeV measured with the ATLAS detector at the LHC

The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |eta|500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at eta = 0 is measured to be 1.333 +/- 0.003 (stat.) +/- 0.040 (syst.), which is 5-15% higher than the Monte Carlo models predict.publishedVersio

Measurement of distributions sensitive to the underlying event in inclusive Z-boson production in pp collisions at √s = 7 TeV with the ATLAS detector

A measurement of charged-particle distributions sensitive to the properties of the underlying event is presented for an inclusive sample of events containing a TeX -boson, decaying to an electron or muon pair. The measurement is based on data collected using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of TeX TeV with an integrated luminosity of TeX fb TeX . Distributions of the charged particle multiplicity and of the charged particle transverse momentum are measured in regions of azimuthal angle defined with respect to the TeX -boson direction. The measured distributions are compared to similar distributions measured in jet events, and to the predictions of various Monte Carlo generators implementing different underlying event models