Measurement of angular correlations in Drell-Yan lepton pairs to probe Z/gamma* boson transverse momentum at sqrt(s)=7 TeV with the ATLAS detector

A measurement of angular correlations in Drell-Yan lepton pairs via the phi(eta)* observable is presented. This variable probes the same physics as the Z/gamma* boson transverse momentum with a better experimental resolution. The Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decays produced in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb(-1). Normalised differential cross sections as a function of phi(eta)* are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is also measured double differentially as a function of phi(eta)* for three independent bins of the Z boson rapidity. The results are compared to QCD calculations and to predictions from different Monte Carlo event generators. The data are reasonably well described, in all measured Z boson rapidity regions, by resummed QCD predictions combined with fixed-order perturbative QCD calculations or by some Monte Carlo event generators. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties.

Search for the neutral Higgs bosons of the Minimal Supersymmetric Standard Model in pp collisions at sqrts=7 TeV with the ATLAS detector

A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb(-1) to 4.8 fb(-1). Higgs boson decays into oppositely-charged in muon or tau lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits are for the production cross-section of a generic neutral Higgs boson, phi, as a function of the Higgs boson mass and for h/A/H production in the MSSM as a function of the parameters m(A) and tan beta in the m(h)(max) scenario for m(A) in the range of 90 GeV to 500 GeV.

Search for new phenomena in events with three charged leptons at a center-of-mass energy of 7 TeV with the ATLAS detector

A generic search for anomalous production of events with at least three charged leptons is presented. The search uses a pp-collision data sample at a center-of-mass energy of root s = 7 TeV corresponding to 4.6 fb(-1) of integrated luminosity collected in 2011 by the ATLAS detector at the CERN Large Hadron Collider. Events are required to contain at least two electrons or muons, while the third lepton may either be an additional electron or muon, or a hadronically decaying tau lepton. Events are categorized by the presence or absence of a reconstructed tau-lepton or Z-boson candidate decaying to leptons. No significant excess above backgrounds expected from Standard Model processes is observed. Results are presented as upper limits on event yields from non-Standard-Model processes producing at least three prompt, isolated leptons, given as functions of lower bounds on several kinematic variables. Fiducial efficiencies for model testing are also provided. The use of the results is illustrated by setting upper limits on the production of doubly charged Higgs bosons decaying to same-sign lepton pairs.

A search for prompt lepton-jets in pp collisions at sqrts=7 TeV with the ATLAS detector

We present a search for a light (mass < 2 GeV) boson predicted by Hidden Valley supersymmetric models that decays into a final state consisting of collimated muons or electrons, denoted "lepton-jets". The analysis uses 5 fb(-1) of root s = 7 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider to search for the following signatures: single lepton-jets with at least four muons; pairs of lepton-jets, each with two or more muons; and pairs of lepton-jets with two or more electrons. This study finds no statistically significant deviation from the Standard Model prediction and places 95% confidence-level exclusion limits on the production cross section times branching ratio of light bosons for several parameter sets of a Hidden Valley model.

Search for displaced muonic lepton jets from light Higgs boson decay in proton-proton collisions at sqrts TeV with the ATLAS detector

A search is performed for collimated muon pairs displaced from the primary vertex produced in the decay of long-lived neutral particles in proton-proton collisions at root s = 7 TeV centre-of-mass energy, with the ATLAS detector at the LHC. In a 1.9 fb(-1) event sample collected during 2011, the observed data are consistent with the Standard Model background expectations. Limits on the product of the production cross section and the branching ratio of a Higgs boson decaying to hidden-sector neutral long-lived particles are derived as a function of the particles' mean lifetime.

A search for ttbar resonances in the lepton plus jets final state with ATLAS using 4.7 fb⁻¹ of collisions at sqrt(s) = 7 TeV

A search for new particles that decay into top quark pairs (t (t) over bar) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 4.7 fb(-1) of proton-proton (pp) collision data collected at a center-of-mass energy root s = 7 TeV. In the t (t) over bar) -> WbWb decay, the lepton plus jets final state is used, where one W boson decays leptonically and the other hadronically. The t (t) over bar) system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the t (t) over bar) invariant mass spectrum is performed. No evidence for a t (t) over bar) resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow Z' resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor Z' resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with m 15.3%. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.07 TeV.

Search for supersymmetry using final states with one lepton, jets, and missing transverse momentum with the ATLAS detector in √s=7 TeV pp collisions

This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from √s=7  TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35  pb(-1). No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for A(0)=0 GeV, tanβ=3, and μ>0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.

Alternative DNA base-pairs: from efforts to expand the genetic code to potential material applications

The complementary Watson-Crick base-pairs, A:T and G:C, have long been recognized as pivotal to both the stability of the DNA double helix and replication/transcription. Recently, the replacement of the Watson-Crick base-pairs with other molecular entities has received considerable attention. In this tutorial review we highlight different approaches used to replace natural base-pairs and equip them with novel function. We also discuss the advantages that non-natural base-pairs convey with respect to practical applications.