Measurement of the ttbar production cross section in the tau+jets channel using the ATLAS detector

A measurement of the top quark pair production cross section in the final state with a hadronically decaying tau lepton and jets is presented. The analysis is based on proton-proton collision data recorded by the ATLAS experiment at the LHC, with a centre-of-mass energy of 7 TeV. The data sample corresponds to an integrated luminosity of 1.67 fb(-1). The cross section is measured to be sigma(t (t) over bar) = 194 +/- 18 (stat.) +/- 46 (syst.) pb and is in agreement with other measurements and with the Standard Model prediction.

Measurement of the production cross section of jets in association with a Z boson in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

Measurements of the production of jets of particles in association with a Z boson in pp collisions at root s = 7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb(-1) collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p(T) > 30 GeV and rapidity vertical bar y vertical bar < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton showers.

Measurement of the production cross-section of ψ → J/ψ ( o μ+ μ) π π in pp collisions at √s = 7 TeV at ATLAS

The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb−1 of pp collision data at a centre-of-mass energy of 7TeV recorded by the ATLAS experiment at the LHC. The measurement exploits the ψ(2S) → J/ψ (→μ+μ−)π+π− decay mode, and probes ψ(2S) mesons with transverse momenta in the range10 ≤ pT < 100 GeV and rapidity |y| < 2.0. The results are compared to other measurements of ψ(2S) production at the LHC and to various theoretical models for prompt and non-prompt quarkonium production.

The differential production cross section of the phi (1020) meson in sqrts = 7 TeV pp collisions measured with the ATLAS detector

Ameasurement is presented of the φ×BR(φ → K+K−) production cross section at √s = 7 TeV using pp collision data corresponding to an integrated luminosity of 383 μb−1, collected with theATLAS experiment at the LHC. Selection of φ(1020) mesons is based on the identification of charged kaons by their energy loss in the pixel detector. The differential cross section ismeasured as a function of the transverse momentum, pT,φ , and rapidity, yφ, of the φ(1020) meson in the fiducial region 500< pT,φ <1200MeV, |yφ| < 0.8, kaon pT,K > 230 MeV and kaon momentum pK < 800 MeV. The integrated φ(1020)-meson production cross section in this fiducial range is measured to be σφ×BR(φ → K+K−) = 570 ± 8 (stat) ± 66 (syst) ± 20 (lumi) μb.

Measurement of the production cross section of prompt J/ψ mesons in association with a W± boson in pp collisions at √8 = 7 TeV with the ATLAS detector

The process pp ! W±J/ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb−1 of p s =7TeV pp collisions at the LHC, the first observation is made of the production of W± +prompt J/ events in hadronic collisions, using W± → μѵμ and Jψ → μ+μ−. A yield of 27.4+7.5−6.5 W± + prompt J/ψ events is observed, with a statistical significance of 5.1ơ. The production rate as a ratio to the inclusive W± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated.

Next-to-Next-to-Next-to-Leading Order QCD Prediction for the Top Antitop S-Wave Pair Production Cross Section Near Threshold in e + e − Annihilation

We present the third-order QCD prediction for the production of top antitop quark pairs in electron-positron collisions close to the threshold in the dominant S-wave state. We observe a significant reduction of the theoretical uncertainty and discuss the sensitivity to the top quark mass and width.

Measurement of the Z and W production cross section in pp collisions at LHC using a bayesian approach

L’obiettivo di tutto il mio lavoro è stato quello di misurare le sezioni d’urto di produzione dei bosoni deboli W ± e Z nei loro decadimenti leptonici (e, μ) coi dati raccolti dal rivelatore ATLAS a LHC con un’energia del centro di massa di √s = 13 TeV relativi all’estate 2015. Gli eventi selezionati sono gli stessi di quelli del recente articolo della Collaborazione ATLAS sullo stesso argomento, in modo anche da poter operare un confronto tra i risultati ottenuti. Confronto peraltro necessario, poichè i risultati sono stati ottenuti con due metodologie differenti: tradizionale (classica) per l’articolo, bayesiana in questa tesi. L’approccio bayesiano permette di combinare i vari canali e di trattare gli effetti sistematici in modo del tutto naturale. I risultati ottenuti sono in ottimo accordo con le predizioni dello Standard Model e con quelli pubblicati da ATLAS.

Molecular effects on the cross section for pair production and their importance in the evaluation of the total photonuclear cross section of {^16}O in the {\delta-resonance} region

The screening correction to the coherent pair-production cross section on the oxygen molecule has been calculated using self-consistent relativistic wave functions for the one-center and two-center Coulomb potentials. It is shown that the modification of the wave function due to molecular binding and the interference between contributions from the two atoms have both sizeable effects on the screening correction. The so-obtained coherent pair-production cross section which makes up the largest part of the total atomic cross section was used to evaluate the total nuclear absorption cross section from photon attenuation measurements on liquid oxygen. The result agrees with cross sections for other nuclei if A-scaling is assumed. The molecular effect on the pair cross section amounts to 15 % of the nuclear cross section in the {\delta-resonance} region.

Measurement of the hadronic activity in events with a Z and two jets and extraction of the cross section for the electroweak production of a Z with two jets in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the differential cross-section of B⁺ meson production in pp collisions at sqrts = 7 TeV at ATLAS

The production cross-section of B+ mesons is measured as a function of transverse momentum p T and rapidity y in proton-proton collisions at centre-of-mass energy root s = 7 TeV, using 2.4 fb(-1) of data recorded with the ATLAS detector at the Large Hadron Collider. The differential production cross-sections, determined in the range 9 GeV < p(T) < 120 GeV and vertical bar y vertical bar < 2.25, are compared to next-to-leading-order theoretical predictions.

Measurement of the cross-section for W boson production in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of the W+b-jets (W+b+X and W+b (b) over bar +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb(-1), collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W+b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range. Combining the muon and electron channels, the fiducial cross-section for W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent with the next-to-leading order QCD prediction, corrected for non-perturbative and double-parton interactions (DPI) contributions, of 4.70 +/- 0.09 (stat) (+0.60)(-0.49) (scale) +/- 0.06 (PDF) +/- 0.16 (non-pert) (+0.52)(-0.38) (DPI) pb.

Measurement of the top quark mass and pp̅ →tt̅ cross section in the all-hadronic mode with the CDF II detector

We present a measurement of the top quark mass and of the top-antitop pair production cross section using p-pbar data collected with the CDFII detector at the Tevatron Collider at the Fermi National Accelerator Laboratory and corresponding to an integrated luminosity of 2.9 fb-1. We select events with six or more jets satisfying a number of kinematical requirements imposed by means of a neural network algorithm. At least one of these jets must originate from a b quark, as identified by the reconstruction of a secondary vertex inside the jet. The mass measurement is based on a likelihood fit incorporating reconstructed mass distributions representative of signal and background, where the absolute jet energy scale (JES) is measured simultaneously with the top quark mass. The measurement yields a value of 174.8 +- 2.4(stat+JES) ^{+1.2}_{-1.0}(syst) GeV/c^2, where the uncertainty from the absolute jet energy scale is evaluated together with the statistical uncertainty. The procedure measures also the amount of signal from which we derive a cross section, sigma_{ttbar} = 7.2 +- 0.5(stat) +- 1.0 (syst) +- 0.4 (lum) pb, for the measured values of top quark mass and JES.