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ATLAS Collaboration(Adragna, P. et al), Castelo, J., Castillo Gimenez, V., Cuenca, C., Ferrer, A., Fullana, E., et al. (2010). Measurement of pion and proton response and longitudinal shower profiles up to 20 nuclear interaction lengths with the ATLAS Tile calorimeter. Nucl. Instrum. Methods Phys. Res. A, 615(2), 158–181.
Abstract: The response of pions and protons in the energy range of 20-180 GeV, produced at CERN's SPS H8 test-beam line in the ATLAS iron-scintillator Tile hadron calorimeter, has been measured. The test-beam configuration allowed the measurement of the longitudinal shower development for pions and protons up to 20 nuclear interaction lengths. It was found that pions penetrate deeper in the calorimeter than protons. However, protons induce showers that are wider laterally to the direction of the impinging particle. Including the measured total energy response, the pion-to-proton energy ratio and the resolution, all observations are consistent with a higher electromagnetic energy fraction in pion-induced showers. The data are compared with GEANT4 simulations using several hadronic physics lists. The measured longitudinal shower profiles are described by an analytical shower parametrization within an accuracy of 5-10%. The amount of energy leaking out behind the calorimeter is determined and parametrized as a function of the beam energy and the calorimeter depth. This allows for a leakage correction of test-beam results in the standard projective geometry.
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Gomez Dumm, D., Noguera, S., & Scoccola, N. N. (2011). Pion radiative weak decays in nonlocal chiral quark models. Phys. Lett. B, 698(3), 236–242.
Abstract: We analyze the radiative pion decay pi(+) -> e(+) nu(e)gamma within nonlocal chiral quark models that include wave function renormalization. In this framework we calculate the vector and axial-vector form factors F-V and F-A at q(2) = 0 – where q(2) is the e(+) nu(e) squared invariant mass – and the slope a of F-V (q(2)) at q(2) -> 0. The calculations are carried out considering different nonlocal form factors, in particular those taken from lattice QCD evaluations, showing a reasonable agreement with the corresponding experimental data. The comparison of our results with those obtained in the (local) NJL model and the relation of F-V and a with the form factor in pi(0) -> gamma*gamma decays are discussed.
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NOMAD Collaboration(Kullenberg, C. T. et al), Cervera-Villanueva, A., & Gomez-Cadenas, J. J. (2012). A search for single photon events in neutrino interactions. Phys. Lett. B, 706(4-5), 268–275.
Abstract: We present a search for neutrino induced events containing a single, exclusive photon using data from the NOMAD experiment at the CERN SPS where the average energy of the neutrino flux is similar or equal to 25 GeV. The search is motivated by an excess of electron-like events in the 200-475 MeV energy region as reported by the MiniBooNE experiment. In NOMAD, photons are identified via their conversion to e(+)e(-) in an active target embedded in a magnetic field. The background to the single photon signal is dominated by the asymmetric decay of neutral pions produced either in a coherent neutrino-nucleus interaction, or in a neutrino-nucleon neutral current deep inelastic scattering, or in an interaction occurring outside the fiducial volume. All three backgrounds are determined in situ using control data samples prior to opening the 'signal-box'. In the signal region, we observe 155 events with a predicted background of 129.2 +/- 8.5 +/- 3.3. We interpret this as null evidence for excess of single photon events, and set a limit. Assuming that the hypothetical single photon has a momentum distribution similar to that of a photon from the coherent pi(0) decay, the measurement yields an upper limit on single photon events, < 4.0 x 10(-4) per nu(mu) charged current event. Narrowing the search to events where the photon is approximately collinear with the incident neutrino, we observe 78 events with a predicted background of 76.6 +/- 4.9 +/- 1.9 yielding a more stringent upper limit, < 1.6 x 10(-4) per nu(mu) charged current event.
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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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Vento, V. (2017). Skyrmions at high density. Int. J. Mod. Phys. E, 26(1-2), 1740029–15pp.
Abstract: The phase diagram of quantum chromodynamics is conjectured to have a rich structure containing at least three forms of matter: hadronic nuclear matter, quarkyonic matter and quark-gluon plasma. We justify the origin of the quarkyonic phase transition in a chiral-quark model and describe its formulation in terms of Skyrme crystals.
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