One-loop SQCD corrections to the decay of top squarks to charm and neutralino in the generic MSSM

In this article we calculate the one-loop supersymmetric QCD (SQCD) corrections to the decay u˜1→cχ˜01 in the minimal supersymmetric standard model with generic flavor structure. This decay mode is phenomenologically important if the mass difference between the lightest squark u˜1 (which is assumed to be mainly stoplike) and the neutralino lightest supersymmetric particle χ˜01 is smaller than the top mass. In such a scenario u˜1→tχ˜01 is kinematically not allowed and searches for u˜1→Wbχ˜01 and u˜1→cχ˜01 are performed. A large decay rate for u˜1→cχ˜01 can weaken the LHC bounds from u˜1→Wbχ01 which are usually obtained under the assumption Br[u˜1→Wbχ01]=100%. We find the SQCD corrections enhance Γ[u˜1→cχ˜01] by approximately 10% if the flavor violation originates from bilinear terms. If flavor violation originates from trilinear terms, the effect can be ±50% or more, depending on the sign of At. We note that connecting a theory of supersymmetry breaking to LHC observables, the shift from the DR¯¯¯¯¯ to the on-shell mass is numerically very important for light stop decays.

Flavour-violation in two-Higgs-doublet models

In these proceedings we review the flavour phenomenology of 2HDMs with generic Yukawa structures [1]. We first consider the quark sector and find that despite the stringent constraints from FCNC processes large effects in tauonic B decays are still possible. We then consider lepton flavour observables, show correlations between m →eg and m− →e−e+e− in the 2HDM of type III and give upper bounds on the lepton flavour violating B decay Bd →me.

Folate Receptor Targeted Alpha-Therapy Using Terbium-149

Terbium-149 is among the most interesting therapeutic nuclides for medical applications. It decays by emission of short-range α-particles (Eα = 3.967 MeV) with a half-life of 4.12 h. The goal of this study was to investigate the anticancer efficacy of a 149Tb-labeled DOTA-folate conjugate (cm09) using folate receptor (FR)-positive cancer cells in vitro and in tumor-bearing mice. 149Tb was produced at the ISOLDE facility at CERN. Radiolabeling of cm09 with purified 149Tb resulted in a specific activity of ~1.2 MBq/nmol. In vitro assays performed with 149Tb-cm09 revealed a reduced KB cell viability in a FR-specific and activity concentration-dependent manner. Tumor-bearing mice were injected with saline only (group A) or with 149Tb-cm09 (group B: 2.2 MBq; group C: 3.0 MBq). A significant tumor growth delay was found in treated animals resulting in an increased average survival time of mice which received 149Tb-cm09 (B: 30.5 d; C: 43 d) compared to untreated controls (A: 21 d). Analysis of blood parameters revealed no signs of acute toxicity to the kidneys or liver in treated mice over the time of investigation. These results demonstrated the potential of folate-based α-radionuclide therapy in tumor-bearing mice.

Search for long-lived neutral particles decaying into lepton jets in proton-proton collisions at √s=8 TeV with the ATLAS detector

Several models of physics beyond the Standard Model predict neutral particles that decay into final states consisting of collimated jets of light leptons and hadrons (socalled “lepton jets”). These particles can also be long-lived with decay length comparable to, or even larger than, the LHC detectors’ linear dimensions. This paper presents the results of a search for lepton jets in proton-proton collisions at the centre-of-mass energy of √s = 8TeV in a sample of 20.3 fb−1 collected during 2012 with the ATLAS detector at the LHC. Limits on models predicting Higgs boson decays to neutral long-lived lepton jets are derived as a function of the particle’s proper decay length.

Measurement of Higgs boson production in the diphoton decay channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5  fb −1 of proton-proton collisions data at s √ =7  TeV and 20.3  fb −1 at s √ =8  TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be μ=1.17±0.27 at the value of the Higgs boson mass measured by ATLAS, m H =125.4  GeV . The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m H . They are found to be μ ggF =1.32±0.38 , μ VBF =0.8±0.7 , μ WH =1.0±1.6 , μ ZH =0.1 +3.7 −0.1 , and μ tt ¯ H =1.6 +2.7 −1.8 , for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a W or Z boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.

Electron and photon energy calibration with the ATLAS detector using LHC Run 1 data

This paper presents the electron and photon energy calibration achieved with the ATLAS detector using about 25 fb−1 of LHC proton–proton collision data taken at centre-of-mass energies of √s = 7 and 8 TeV. The reconstruction of electron and photon energies is optimised using multivariate algorithms. The response of the calorimeter layers is equalised in data and simulation, and the longitudinal profile of the electromagnetic showers is exploited to estimate the passive material in front of the calorimeter and reoptimise the detector simulation. After all corrections, the Z resonance is used to set the absolute energy scale. For electrons from Z decays, the achieved calibration is typically accurate to 0.05% in most of the detector acceptance, rising to 0.2% in regions with large amounts of passive material. The remaining inaccuracy is less than 0.2–1% for electrons with a transverse energy of 10 GeV, and is on average 0.3% for photons. The detector resolution is determined with a relative inaccuracy of less than 10% for electrons and photons up to 60 GeV transverse energy, rising to 40% for transverse energies above 500 GeV.

Measurement of the muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton-proton collision data

This paper presents the performance of the ATLAS muon reconstruction during the LHC run with pp collisions at √s = 7–8 TeV in 2011–2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of J/ψ → μμ, Z → μμ and ϒ → μμ decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon |η| < 2.7 and 5 ≲ pT ≲ 100 GeV) the efficiency is above 99% and is measured with per-mille precision. The momentum resolution ranges from 1.7% at central rapidity and for transverse momentum pT ≅ 10 GeV, to 4% at large rapidity and pT ≅ 100 GeV. The momentum scale is known with an uncertainty of 0.05% to 0.2% depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.

Search for supersymmetry in events with large missing transverse momentum, jets, and at least one tau lepton in 20 fb⁻¹ of √s= 8 TeV proton-proton collision data with the ATLAS detector

A search for supersymmetry (SUSY) in events with large missing transverse momentum, jets, at least one hadronically decaying tau lepton and zero or one additional light leptons (electron/muon), has been performed using 20.3 fb−1 of proton-proton collision data at √s = 8TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed in the various signal regions and 95% confidence level upper limits on the visible cross section for new phenomena are set. The results of the analysis are interpreted in several SUSY scenarios, significantly extending previous limits obtained in the same final states. In the framework of minimal gauge-mediated SUSY breaking models, values of the SUSY breaking scale ʌ below 63TeV are excluded, independently of tan β. Exclusion limits are also derived for an mSUGRA/CMSSM model, in both the R-parity-conserving and R-parity-violating case. A further interpretation is presented in a framework of natural gauge mediation, in which the gluino is assumed to be the only light coloured sparticle and gluino masses below 1090GeV are excluded.

Search for strong production of supersymmetric particles in final states with missing transverse momentum and at least three b-jets at √s= 8 TeV proton-proton collisions with the ATLAS detector

This paper reports the results of a search for strong production of supersymmetric particles in 20.1 fb−1 of proton-proton collisions at a centre-of-mass energy of 8TeV using the ATLAS detector at the LHC. The search is performed separately in events with either zero or at least one high-pT lepton (electron or muon), large missing transverse momentum, high jet multiplicity and at least three jets identified as originated from the fragmentation of a b-quark. No excess is observed with respect to the Standard Model predictions. The results are interpreted in the context of several supersymmetric models involving gluinos and scalar top and bottom quarks, as well as a mSUGRA/CMSSM model. Gluino masses up to 1340 GeV are excluded, depending on the model, significantly extending the previous ATLAS limits.

Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using √s=8 TeV proton--proton collision data

A search for squarks and gluinos in final states containing high-pT jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2012 by the ATLAS experiment in √s = 8TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 20.3 fb−1. Results are interpreted in a variety of simplified and specific supersymmetry-breaking models assuming that R-parity is conserved and that the lightest neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1330GeV for a simplified model incorporating only a gluino and the lightest neutralino. For a simplified model involving the strong production of first- and second-generation squarks, squark masses below 850GeV (440GeV) are excluded for a massless lightest neutralino, assuming mass degenerate (single light-flavour) squarks. In mSUGRA/CMSSM models with tan β = 30, A0 = −2m0 and μ > 0, squarks and gluinos of equal mass are excluded for masses below 1700GeV. Additional limits are set for non-universal Higgs mass models with gaugino mediation and for simplified models involving the pair production of gluinos, each decaying to a top squark and a top quark, with the top squark decaying to a charm quark and a neutralino. These limits extend the region of supersymmetric parameter space excluded by previous searches with the ATLAS detector.

Measurement of chi_c1 and chi_c2 production with sqrts = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χc1 and χc2 charmonium states are measured in pp collisions at √s = 7TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χc states are reconstructed through the radiative decay χc → J/ψγ (with J/ψ → μ+μ−) where photons are reconstructed from γ → e+e− conversions. The production rate of the χc2 state relative to the χc1 state is measured for prompt and non-prompt χc as a function of J/ψ transverse momentum. The prompt χc cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χc decays. The fractions of χc1 and χc2 produced in b-hadron decays are also measured.

Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at √s = 7 TeV in 2010

This paper presents a study of the performance of the muon reconstruction in the analysis of proton–proton collisions at √s = 7TeV at theLHC, recorded by the ATLAS detector in 2010. This performance is described in terms of reconstruction and isolation efficiencies and momentum resolutions for different classes of reconstructed muons. The results are obtained from an analysis of J/ψ meson and Z boson decays to dimuons, reconstructed from a data sample corresponding to an integrated luminosity of 40 pb−1. The measured performance is compared to Monte Carlo predictions and deviations from the predicted performance are discussed.

Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton-proton collision data

Many of the interesting physics processes to be measured at the LHC have a signature involving one or more isolated electrons. The electron reconstruction and identification efficiencies of the ATLAS detector at the LHC have been evaluated using proton–proton collision data collected in 2011 at √s = 7 TeV and corresponding to an integrated luminosity of 4.7 fb−1. Tag-and-probe methods using events with leptonic decays of W and Z bosons and J/ψ mesons are employed to benchmark these performance parameters. The combination of all measurements results in identification efficiencies determined with an accuracy at the few per mil level for electron transverse energy greater than 30 GeV.

Search for direct top squark pair production in events with a Z boson, b-jets and missing transverse momentum in √s=8 TeV pp collisions with the ATLAS detector

A search is presented for direct top squark pair production using events with at least two leptons including a same-flavour opposite-sign pair with invariant mass consistent with the Z boson mass, jets tagged as originating from b-quarks and missing transverse momentum. The analysis is performed with proton–proton collision data at √ s = 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20.3 fb−1. No excess beyond the Standard Model expectation is observed. Interpretations of the results are provided in models based on the direct pair production of the heavier top squark state (˜t2) followed by the decay to the lighter top squark state (˜t1) via ˜t2 → Z ˜t1, and for ˜t1 pair production in natural gaugemediated supersymmetry breaking scenarios where the neutralino (˜χ 01 ) is the next-to-lightest supersymmetric particle and decays producing a Z boson and a gravitino ( ˜G ) via the ˜χ 01→ Z ˜G process.

Search for direct top-squark pair production in final states with two leptons in pp collisions at sqrts = 8TeV with the ATLAS detector

A search is presented for direct top-squark pair production in final states with two leptons (electrons or muons) of opposite charge using 20.3 fb−1 of pp collision data at ps = 8TeV, collected by the ATLAS experiment at the Large Hadron Collider in 2012. No excess over the Standard Model expectation is found. The results are interpreted under the separate assumptions (i) that the top squark decays to a b-quark in addition to an on-shell chargino whose decay occurs via a real or virtual W boson, or (ii) that the top squark decays to a t-quark and the lightest neutralino. A top squark with a mass between 150 GeV and 445 GeV decaying to a b-quark and an on-shell chargino is excluded at 95% confidence level for a top squark mass equal to the chargino mass plus 10 GeV, in the case of a 1 GeV lightest neutralino. Top squarks with masses between 215 (90) GeV and 530 (170) GeV decaying to an on-shell (off-shell) t-quark and a neutralino are excluded at 95% confidence level for a 1 GeV neutralino.