Setting limits on supersymmetry using simplified models

Experimental limits on supersymmetry and similar theories are difficult to set because of the enormous available parameter space and difficult to generalize because of the complexity of single points. Therefore, more phenomenological, simplified models are becoming popular for setting experimental limits, as they have clearer physical implications. The use of these simplified model limits to set a real limit on a concrete theory has not, however, been demonstrated. This paper recasts simplified model limits into limits on a specific and complete supersymmetry model, minimal supergravity. Limits obtained under various physical assumptions are comparable to those produced by directed searches. A prescription is provided for calculating conservative and aggressive limits on additional theories. Using acceptance and efficiency tables along with the expected and observed numbers of events in various signal regions, LHC experimental results can be re-cast in this manner into almost any theoretical framework, including non-supersymmetric theories with supersymmetry-like signatures.Comment: 14 pages, 11 figure

Measurement of the W charge asymmetry in the W→μν decay mode in pp collisions at √s = 7 TeV with the ATLAS detector

This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton–proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the W→μν decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb^(−1). The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton

A search for new physics in dijet mass and angular distributions in pp collisions at √s = 7 TeV measured with the ATLAS detector

A search for new interactions and resonances produced in LHC proton–proton (pp) collisions at a centre-of-mass energy √s = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb^(−1), dijet mass and angular distributions were measured up to dijet masses of ~3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space–time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale Λ below 9.5 TeV

Search for Diphoton Events with Large Missing Transverse Energy in 7 TeV Proton-Proton Collisions with the ATLAS Detector

A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at √s = 7  TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3.1  pb^(-1). No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R < 729  GeV are excluded at 95% C.L., providing the most sensitive limit on this model to date

Search for a Heavy Particle Decaying into an Electron and a Muon with the ATLAS Detector in √s = 7 TeV pp collisions at the LHC

This Letter presents the first search for a heavy particle decaying into an e^±μ^∓ final state in √s=7  TeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35  pb^(-1). No excess above the standard model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming all R-parity violating couplings are zero except λ'_(311)=0.11 and λ_(312)=0.07. In a lepton flavor violating model, a Z′-like vector boson with masses of 0.70–1.00 TeV and corresponding cross sections times branching ratios of 0.175–0.183 pb is excluded. These results extend to higher mass R-parity violating sneutrinos and lepton flavor violating Z’s than previous constraints from the Tevatron

Search for a heavy neutral particle decaying into an electron and a muon using 1 fb^(−1) of ATLAS data

A search is presented for a high mass neutral particle that decays directly to the e^± μ^∓ final state. The data sample was recorded by the ATLAS detector in √s=7~TeV pp collisions at the LHC from March to June 2011 and corresponds to an integrated luminosity of 1.07 fb^(−1). The data are found to be consistent with the Standard Model background. The high e^± μ^∓ mass region is used to set 95% confidence level upper limits on the production of two possible new physics processes: tau sneutrinos in an R-parity violating supersymmetric model and Z′-like vector bosons in a lepton flavor violating model

Search for new physics in the dijet mass distribution using 1 fb^(−1) of pp collision data at √s = 7 TeV collected by the ATLAS detector

Invariant mass distributions of jet pairs (dijets) produced in LHC proton–proton collisions at a centre-of-mass energy √s=7TeV have been studied using a data set corresponding to an integrated luminosity of 1.0 fb^(-1) recorded in 2011 by ATLAS. Dijet masses up to ∼4 TeV are observed in the data, and no evidence of resonance production over background is found. Limits are set at 95% C.L. for several new physics hypotheses: excited quarks are excluded for masses below 299 TeV, axigluons are excluded for masses below 3.32 TeV, and colour octet scalar resonances are excluded for masses below 1.92 TeV

Search for charged Higgs bosons decaying via H^± → τν in tt events using pp collision data at √s = 7 TeV with the ATLAS detector

The results of a search for charged Higgs bosons are presented. The analysis is based on 4.6fb^(−1) of proton-proton collision data at √s=7TeV collected by the ATLAS experiment at the Large Hadron Collider, using top quark pair events with a τ lepton in the final state. The data are consistent with the expected background from Standard Model processes. Assuming that the branching ratio of the charged Higgs boson to a τ lepton and a neutrino is 100 %, this leads to upper limits on the branching ratio of top quark decays to a b quark and a charged Higgs boson between 5% and 1% for charged Higgs boson masses ranging from 90 GeV to 160 GeV, respectively. In the context of the m_h^(max) scenario of the MSSM, tan β above 12-26, as well as between 1 and 2-6, can be excluded for charged Higgs boson masses between 90 GeV and 150 GeV

Measurements of the electron and muon inclusive cross-sections in proton–proton collisions at √s = 7 TeV with the ATLAS detector

This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton–proton collisions at a centre-of-mass energy of √s = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4 < pT < 100 GeV and within pseudorapidity |η| < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < pT < 26 GeV and within |η| < 2.0, excluding 1.37 < |η| < 1.52. Integrated luminosities of 1.3 pb^(−1) and 1.4 pb^(−1) are used for the electron and muon measurements, respectively. After subtraction of the W/Z/γ^∗ contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-pT resummation, and to be sensitive to the effects of NLL resummation

Measurement of the azimuthal anisotropy for charged particle production in √s_(NN) = 2.76 TeV lead-lead collisions with the ATLAS detector

Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at √s_(NN)=2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 μb^(−1). This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients v_n denoting the magnitude of the anisotropy. Significant v_2–v_6 values are obtained as a function of transverse momentum (0.52) and one particle with p_T<3 GeV, the v_(2,2)–v_(6,6) values are found to factorize as v_(n,n)(p_T^a,p_T^b)≈v_n(p_T^a)v_n(p_T^b) in central and midcentral events. Such factorization suggests that these values of v_(2,2)–v_(6,6) are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the v_(1,1)(p_T^a,p_T^b) data are consistent with the combined contributions from a rapidity-even v_1 and global momentum conservation. A two-component fit is used to extract the v_1 contribution. The extracted v_1 is observed to cross zero at p_T≈1.0 GeV, reaches a maximum at 4–5 GeV with a value comparable to that for v_3, and decreases at higher p_T