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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2015). Search for anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with root s=8 TeV pp collisions using the ATLAS detector. J. High Energy Phys., 03(3), 041–48pp.
Abstract: A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb(-1) of integrated luminosity taken in 2012 at a centre-of-mass energy of 8TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type e(+/-) e(+/-), e(+/-) mu(+/-), and mu(+/-) mu(+/-) are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the exclusive gamma production cross-section in pp collisions at root s=7 TeV and 8 TeV. J. High Energy Phys., 09(9), 084–20pp.
Abstract: A study is presented of central exclusive production of gamma(n S) states, where the gamma (n S) resonances decay to the mu(+) mu(-) final state, using p p collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range 2 < y (gamma) < 4.5 where the muons are reconstructed in the pseudorapidity range 2 < eta (mu(+/-)) < 4.5. The data sample corresponds to an integrated luminosity of 2.9 fb(-1) and was collected at centreof- mass energies of 7TeV and 8TeV. The measured gamma(1 S) and gamma(2 S) production crosssections are sigma(pp -> p gamma(1S)p) = 9.0 +/- 1.7 pb and sigma(pp -> p gamma(2S)p) = 1.3 +/- 0.3 pb, where the first uncertainties are statistical and the second are systematic. The gamma (1S) cross-section is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95% confidence level for the exclusive gamma(3 S) production cross-section, including possible contamination from chi b (3P) -> gamma (3S)gamma decays.
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HADES Collaboration(Agakishiev, G. et al), Diaz, J., & Gil, A. (2015). Study of the quasi-free np -> np pi(+)pi(-) reaction with a deuterium beam at 1.25 GeV/nucleon. Phys. Lett. B, 750, 184–193.
Abstract: The tagged quasi-free np -> np pi(+)pi(-) reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon (root S similar to 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions of solid statistics for pi(+)pi(-) production in np collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the np -> np pi(+)pi(-) reaction are compared with different models. This comparison confirms the dominance of the t-channel with Delta Delta contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the pi(+)pi(-) invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M similar to 2.38 GeV and with width Gamma similar to 70 MeV. (C) 2015 The Authors. Published by Elsevier B.V.
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Oset, E. et al, Albaladejo, M., Nieves, J., Fernandez-Soler, P., & Sun, Z. F. (2016). Weak decays of heavy hadrons into dynamically generated resonances. Int. J. Mod. Phys. E, 25(1), 1630001–105pp.
Abstract: In this paper, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allow for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.
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Lutz, M. F. M. et al, & Nieves, J. (2016). Resonances in QCD. Nucl. Phys. A, 948, 93–105.
Abstract: We report on the EMMI Rapid Reaction Task Force meeting 'Resonances in QCD', which took place at GSI October 12-14,2015. A group of 26 people met to discuss the physics of resonances in QCD. The aim of the meeting was defined by the following three key questions: What is needed to understand the physics of resonances in QCD? Where does QCD lead us to expect resonances with exotic quantum numbers? What experimental efforts are required to arrive at a coherent picture? For light mesons and baryons only those with up, down and strange quark content were considered. For heavy-light and heavy-heavy meson systems, those with charm quarks were the focus. This document summarizes the discussions by the participants, which in turn led to the coherent conclusions we present here.
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