Abstract: The production of exclusive gamma gamma -> mu(+)mu(-) events in proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of 3.2 fb(-1). The measurement is performed for a dimuon invariant mass of 12 GeV < m(mu+mu-) < 70 GeV. The integrated cross-section is determined within a fiducial acceptance region of the ATLAS detector and differential cross-sections are measured as a function of the dimuon invariant mass. The results are compared to theoretical predictions both with and without corrections for absorptive effects.

Abstract: We have performed a study of the Lambda(0)(b) -> eta K-c(-) p and Lambda(0)(b) -> eta(c)pi Sigma reactions based on the dominant Cabibbo favored weak decay mechanism. We show that the K- p produced only couples to Lambda* states, not Sigma* and that the pi Sigma state is only generated from final state interaction of (K) over barN and eta Lambda channels which are produced in a primary stage. This guarantees that the pi Sigma state is generated in isospin I=0 and we see that the invariant mass produces a clean signal for the Lambda(1405) of higher mass at 1420 MeV. We also study the eta(c)p final state interaction, which is driven by the excitation of a hidden charm resonance predicted before. We relate the strength of the different invariant mass distributions and find similar strengths that should be clearly visible in an ongoing LHCb experiment. In particular we predict that a clean peak should be seen for a hidden charm resonance that couples to the eta(c)p channel in the invariant eta(c)p mass distribution.

Abstract: A measurement of the mass of the W boson is presented based on proton-proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb(-1) of integrated luminosity. The selected data sample consists of 7.8 x 10(6) candidates in the W -> μnu channel and 5.9 x 10(6) candidates in the W -> e nu channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding m(W) = 80370 +/- 7 (stat.) +/- 11(exp. syst.) +/- 14 (mod. syst.) MeV = 80370 +/- 19 MeV, where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the W+ and W- bosons yields m(W+) – m(W-) = -29 +/- 28 MeV.

Abstract: A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7 fb(-1) of proton-proton collisions at a centre-of-mass energy of root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed-Dimopoulos-Dvali (Randall-Sundrum) model with six (one) extra dimensions.

Abstract: We discuss leptogenesis in a model with heavy right-handed Majorana neutrinos propagating in a constant but otherwise generic CPT-violating axial time-like background (motivated by string theory). At temperatures much higher than the temperature of the electroweak phase transition, we solve approximately, but analytically (using Pade approximants), the corresponding Boltzmann equations, which describe the generation of lepton asymmetry from the tree-level decays of heavy neutrinos into Standard Model leptons. At such temperatures these leptons are effectively massless. The current work completes in a rigorous way a preliminary treatment of the same system, by some of the present authors. In this earlier work, lepton asymmetry was crudely estimated considering the decay of a righthanded neutrino at rest. Our present analysis includes thermal momentum modes for the heavy neutrino and this leads to a total lepton asymmetry which is bigger by a factor of two as compared to the previous estimate. Nevertheless, our current and preliminary results for the freezeout are found to be in agreement (within a similar to 12.5% uncertainty). Our analysis depends on a novel use of Pade approximants to solve the Boltzmann equations and may be more widely useful in cosmology.