Measurement of the cross section of high transverse momentum Z→bb̄ production in proton–proton collisions at √s = 8 TeV with the ATLAS detector

This Letter reports the observation of a high transverse momentum Z→bb̄ signal in proton–proton collisions at √s=8 TeV and the measurement of its production cross section. The data analysed were collected in 2012 with the ATLAS detector at the LHC and correspond to an integrated luminosity of 19.5 fb−¹. The Z→bb̄ decay is reconstructed from a pair of b -tagged jets, clustered with the anti-ktkt jet algorithm with R=0.4R=0.4, that have low angular separation and form a dijet with pT>200 GeVpT>200 GeV. The signal yield is extracted from a fit to the dijet invariant mass distribution, with the dominant, multi-jet background mass shape estimated by employing a fully data-driven technique that reduces the dependence of the analysis on simulation. The fiducial cross section is determined to be σZ→bb¯fid=2.02±0.20 (stat.) ±0.25 (syst.)±0.06 (lumi.) pb=2.02±0.33 pb, in good agreement with next-to-leading-order theoretical predictions

Dijet production in √s = 7 TeV pp collisions with large rapidity gaps at the ATLAS experiment

A 6.8 nb−¹ sample of pp collision data collected under low-luminosity conditions at √s = 7 TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with pT > 20 GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in ΔηF, the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, ξ˜, of the fractional momentum loss of the proton assuming single diffractive dissociation (pp → p X). Model comparisons indicate a dominant non-diffractive contribution up to moderately large ηF and small ξ˜, with a diffractive contribution which is significant at the highest ΔηF and the lowest ξ˜. The rapidity-gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton distribution functions

Search for the production of single vector-like and excited quarks in the Wt final state in pp collisions at √s=8 TeV with the ATLAS detector

A search for vector-like quarks and excited quarks in events containing a top quark and a W boson in the final state is reported here. The search is based on 20.3 fb−1 of proton-proton collision data taken at the LHC at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector. Events with one or two leptons, and one, two or three jets are selected with the additional requirement that at least one jet contains a b-quark. Single-lepton events are also required to contain at least one large-radius jet from the hadronic decay of a high-pTW boson or a top quark. No significant excess over the expected background is observed and upper limits on the cross-section times branching ratio for different vector-like quark and excited-quark model masses are derived. For the excited-quark production and decay to Wt with unit couplings, quarks with masses below 1500 GeV are excluded and coupling-dependent limits are set

Combination of searches for WW, WZ, and ZZ resonances in pp collisions at s=8 TeV with the ATLAS detector

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb-1 of pp collision data at s=8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the ℓνℓ'ℓ' (ℓ=μ, e), ℓℓqq-, ℓνqq- and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WZ bosons are compared with predictions of an extended gauge model with a heavy W' boson. In addition, direct searches for a neutral diboson resonance decaying to WW and ZZ in the ℓℓqq-, ℓνqq-, and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WW and ZZ bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall-Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension

Comparing body condition score and FAMACHA© to identify hair-sheep ewes with high faecal egg counts of gastrointestinal nematodes in farms under hot tropical conditions

Data from a targeted selective treatment (TST) survey in three sheep farms was used to compare body condition scores (BCS) ≤ 2 and FAMACHA© scores ≥4 or ≥3 as criteria to identify ewes with ≥ 750 eggs per gram of faeces (EPG), and to confirm whether that EPG threshold allowed maintaining a large proportion of animals with no anthelmintic (AH) treatment. The survey included monthly data from all grazing adult ewes in three commercial farms. Farms 1 and 3 were surveyed for 11 months, and Farm 2 for 6 months, with a total of 7342 events recorded. Mean monthly population consisted of 330 ewes (Farm 1), 129 ewes (Farm 2) and 265 ewes (Farm 3). The FAMACHA© scores and BCS of adult ewes were recorded monthly. Ewes with FAMACHA© ≥ 4 or BCS ≤ 2 were faecal sampled to determine faecal egg counts (FEC) (2788 events). Ewes with ≥ 750 EPG were treated with an AH (658 events). The TST survey showed that BCS ≤ 2 was the best criteria to find ewes with FEC ≥ 750 EPG, with 1.1% false negatives. Meanwhile, FAMACHA© ≥4 or ≥3 failed to identify half of the events with ≥ 750 EPG (50–55% false negatives). Thus, the TST scheme could focus on screening ewes with BCS ≤ 2, and the FEC of those animals can avoid unnecessary AH treatments. The TST scheme was easier to implement at the farm with largest ratio of ewes with BCS > 2, as fewer ewes were sampled and treated, compared to farms where many ewes had BCS ≤ 2. In the surveyed farms a threshold of ≥ 750 EPG resulted in 63.5% of all ewes maintained with no AH treatment for the duration of the survey.Los datos de una encuesta de tratamiento selectivo dirigido (TST) en tres granjas de ovejas se usaron para comparar puntajes de condición corporal (BCS) ≤ 2 y puntajes de FAMACHA © ≥4 o ≥3 como criterios para identificar ovejas con ≥ 750 huevos por gramo de heces (EPG) ), y para confirmar si ese umbral de EPG permitió mantener una gran proporción de animales sin tratamiento antihelmíntico (AH). La encuesta incluyó datos mensuales de todas las ovejas adultas que pastan en tres granjas comerciales. Las granjas 1 y 3 fueron encuestadas durante 11 meses, y la granja 2 durante 6 meses, con un total de 7342 eventos registrados. La población mensual promedio consistió en 330 ovejas (Granja 1), 129 ovejas (Granja 2) y 265 ovejas (Granja 3). Los puntajes FAMACHA © y BCS de ovejas adultas se registraron mensualmente. Las ovejas con FAMACHA © ≥ 4 o BCS ≤ 2 se tomaron muestras fecales para determinar el recuento de huevos fecales (FEC) (2788 eventos). Las ovejas con ≥ 750 EPG fueron tratadas con un AH (658 eventos). La encuesta TST mostró que BCS ≤ 2 fue el mejor criterio para encontrar ovejas con FEC ≥ 750 EPG, con 1.1% de falsos negativos. Mientras tanto, FAMACHA © ≥4 o ≥3 no pudieron identificar la mitad de los eventos con ≥ 750 EPG (50-55% de falsos negativos). Por lo tanto, el esquema TST podría centrarse en la detección de ovejas con BCS ≤ 2, y la FEC de esos animales puede evitar tratamientos innecesarios de AH. El esquema TST fue más fácil de implementar en la granja con la mayor proporción de ovejas con BCS> 2, ya que se muestrearon y trataron menos ovejas, en comparación con las granjas donde muchas ovejas tenían BCS ≤ 2. En las granjas encuestadas resultó un umbral de ≥ 750 EPG en el 63.5% de todas las ovejas mantenidas sin tratamiento AH durante la duración de la encuesta