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NEXT Collaboration(Azevedo, C. D. R. et al), Gomez-Cadenas, J. J., Alvarez, V., Benlloch-Rodriguez, J. M., Botas, A., Carcel, S., et al. (2018). Microscopic simulation of xenon-based optical TPCs in the presence of molecular additives. Nucl. Instrum. Methods Phys. Res. A, 877, 157–172.
Abstract: We introduce a simulation framework for the transport of high and low energy electrons in xenon-based optical time projection chambers (OTPCs). The simulation relies on elementary cross sections (electron-atom and electron-molecule) and incorporates, in order to compute the gas scintillation, the reaction/quenching rates (atom-atom and atom-molecule) of the first 41 excited states of xenon and the relevant associated excimers, together with their radiative cascade. The results compare positively with observations made in pure xenon and its mixtures with CO2 and CF4 in a range of pressures from 0.1 to 10 bar. This work sheds some light on the elementary processes responsible for the primary and secondary xenon-scintillation mechanisms in the presence of additives, that are of interest to the OTPC technology.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Measurement of jet fragmentation in 5.02 TeV proton-lead and proton-proton collisions with the ATLAS detector. Nucl. Phys. A, 978, 65–106.
Abstract: A measurement of the fragmentation functions of jets into charged particles in p Pb collisions and pp collisions is presented. The analysis utilizes 28 nb(-1) of p Pb data and 26 pb(-1) of pp data, both at root(TN)-T-s= 5.02 TeV, collected in 2013 and 2015, respectively, with the ATLAS detector at the LHC. The measurement is reported in the centre-of-mass frame of the nucleon-nucleon system for jets in the rapidity range vertical bar y*vertical bar <1.6 and with transverse momentum 45 < p(T) < 260 GeV. Results are presented both as a function of the charged-particle transverse momentum and as a function of the longitudinal momentum fraction of the particle with respect to the jet. The pp fragmentation functions are compared with results from Monte Carlo event generators and two theoretical models. The ratios of the p +Pb to pp fragmentation functions are found to be consistent with unity. (C) 2018 CERN for the benefit of the ATLAS Collaboration.
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Alvarez-Ruso, L. et al, & Nieves, J. (2018). NuSTEC White Paper: Status and challenges of neutrino-nucleus scattering. Prog. Part. Nucl. Phys., 100, 1–68.
Abstract: The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments require a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result. In this White Paper we discuss in detail the impact of neutrino-nucleus interactions, especially the nuclear effects, on the measurement of neutrino properties using the determination of oscillation parameters as a central example. After an Executive Summary and a concise Overview of the issues, we explain how the neutrino event generators work, what can be learned from electron-nucleus interactions and how each underlying physics process – from quasi-elastic to deep inelastic scattering – is understood today. We then emphasize how our understanding must improve to meet the demands of future experiments. With every topic we find that the challenges can be met only with the active support and collaboration among specialists in strong interactions and electroweak physics that include theorists and experimentalists from both the nuclear and high energy physics communities.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Search for a new heavy gauge-boson resonance decaying into a lepton and missing transverse momentum in 36 fb(-1) of pp collisions root s=13 TeV with the ATLAS experiment. Eur. Phys. J. C, 78(5), 401–23pp.
Abstract: The results of a search for new heavy W' bosons decaying to an electron or muon and a neutrino using proton-proton collision data at a centre-of-mass energy of root s = 13 TeV are presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb(-1). As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the W' boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the W' mass. Assuming a W' boson with the same couplings as the Standard Model W boson, W' masses below 5.1 TeV are excluded at the 95% confidence level.
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Bernabeu, J., & Segarra, A. (2018). Stimulated transitions in resonant atom Majorana mixing. J. High Energy Phys., 02(2), 017–16pp.
Abstract: Massive neutrinos demand to ask whether they are Dirac or Majorana particles. Majorana neutrinos are an irrefutable proof of physics beyond the Standard Model. Neutrinoless double electron capture is not a process but a virtual Delta L = 2 mixing between a parent (A)Z atom and a daughter (A)(Z – 2) excited atom with two electron holes. As a mixing between two neutral atoms and the observable signal in terms of emitted two-hole X-rays, the strategy, experimental signature and background are different from neutrinoless double beta decay. The mixing is resonantly enhanced for almost degeneracy and, under these conditions, there is no irreducible background from the standard two-neutrino channel. We reconstruct the natural time history of a nominally stable parent atom since its production either by nature or in the laboratory. After the time periods of atom oscillations and the decay of the short-lived daughter atom, at observable times the relevant 'stationary" states are the mixed metastable long-lived state and the non-orthogonal short-lived excited state, as well as the ground state of the daughter atom. We find that they have a natural population inversion which is most appropriate for exploiting the bosonic nature of the observed atomic transitions radiation. Among different observables of the atom Majorana mixing, we include the enhanced rate of stimulated X-ray emission from the long-lived metastable state by a high-intensity X-ray beam: a gain factor of 100 can be envisaged at current XFEL facilities. On the other hand, the historical population of the daughter atom ground state can be probed by exciting it with a current pulsed optical laser, showing the characteristic absorption lines: the whole population can be excited in a shorter time than typical pulse duration.
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Ghosh, P., Lara, I., Lopez-Fogliani, D. E., Muñoz, C., & Ruiz de Austri, R. (2018). Searching for left sneutrino LSP at the LHC. Int. J. Mod. Phys. A, 33(18-19), 1850110–62pp.
Abstract: We analyze relevant signals expected at the LHC for a left sneutrino as the lightest supersymmetric particle (LSP). The discussion is carried out in the “mu from nu” supersymmetric standard model (mu nu SSM), where the presence of R-parity breaking couplings involving right-handed neutrinos solves the μproblem and reproduces neutrino data. The sneutrinos are pair produced via a virtual W, Z or gamma in the s channel. From the prompt decay of a pair of left sneutrinos LSPs of any family, a significant diphoton signal plus missing transverse energy (MET) from neutrinos can be present in the mass range 118-132 GeV, with 13 TeV center-of-mass energy and an integrated luminosity of 100 fb(-1). In addition, in the case of a pair of tau left sneutrinos LSPs, given the large value of the tau Yukawa coupling diphoton plus leptons and/or multileptons can appear. We find that the number of expected events for the multilepton signal, together with properly adopted search strategies, is sufficient to give a significant evidence for a sneutrino of mass in the range 130-310 GeV, even with the integrated luminosity of 20 fb(-1). In the case of the signal producing diphoton plus leptons, an integrated luminosity of 100 fb(-1) is needed to give a significant evidence in the mass range 95-145 GeV. Finally, we discuss briefly the presence of displaced vertices and the associated range of masses.
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Cerdeño, D. G., De Romeri, V., Martin Lozano, V., Olive, K. A., & Seto, O. (2018). The Constrained NMSSM with right-handed neutrinos. Eur. Phys. J. C, 78(4), 290–12pp.
Abstract: In this article, we demonstrate that the inclusion of right-handed neutrino superfields in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) makes it possible to impose universality conditions on the soft supersymmetry-breaking parameters at the Grand Unification scale, alleviating many of the problems of the so-called Constrained NMSSM. We have studied the renormalization group equations of this model, showing that right-handed neutrinos greatly contribute to driving the singlet Higgs mass-squared parameter negative, which makes it considerably easier to satisfy the conditions for radiative electroweak symmetry breaking. The new fields also lead to larger values of the Standard Model Higgs mass, thus making it easier to reproduce the measured value. As a consequence, all bounds from colliders and low-energy observables can be fulfilled in wide areas of the parameter space. However, the relic density in these regions is generally too high requiring some form of late entropy production to dilute the density of the lightest supersymmetric particle.
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n_TOF Collaboration(Barbagallo, M. et al), Domingo-Pardo, C., & Tain, J. L. (2018). Experimental setup and procedure for the measurement of the Be-7(n,p)Li-7 reaction at n_TOF. Nucl. Instrum. Methods Phys. Res. A, 887, 27–33.
Abstract: Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron induced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the Be-7(n,alpha)alpha cross section, the Be-7(n,p)Li-7 reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.
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de Salas, P. F., Forero, D. V., Ternes, C. A., Tortola, M., & Valle, J. W. F. (2018). Status of neutrino oscillations 2018: 3 sigma hint for normal mass ordering and improved CP sensitivity. Phys. Lett. B, 782, 633–640.
Abstract: We present a new global fit of neutrino oscillation parameters within the simplest three-neutrino picture, including new data which appeared since our previous analysis[1]. In this update we include new long-baseline neutrino data involving the antineutrino channel in T2K, as well as new data in the neutrino channel, data from NO nu A, as well as new reactor data, such as the Daya Bay 1230 days electron antineutrino disappearance spectrum data and the 1500 live days prompt spectrum from RENO, as well as new Double Chooz data. We also include atmospheric neutrino data from the IceCube DeepCore and ANTARES neutrino telescopes and from Super-Kamiokande. Finally, we also update our solar oscillation analysis by including the 2055-day day/night spectrum from the fourth phase of the Super-Kamiokande experiment. With the new data we find a preference for the atmospheric angle in the upper octant for both neutrino mass orderings, with maximal mixing allowed at Delta chi(2)= 1.6 (3.2) for normal (inverted) ordering. We also obtain a strong preference for values of the CP phase delta in the range [pi, 2 pi], excluding values close to pi/2at more than 4 sigma. More remarkably, our global analysis shows a hint in favorof the normal mass ordering over the inverted one at more than 3 sigma. We discuss in detail the status of the mass ordering, CP violation and octant sensitivities, analyzing the interplay among the different neutrino data samples.
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Fileviez Perez, P., & Murgui, C. (2018). Sterile neutrinos and B-L symmetry. Phys. Lett. B, 777, 381–387.
Abstract: We revisit the relation between the neutrino masses and the spontaneous breaking of the B-L gauge symmetry. We discuss the main scenarios for Dirac and Majorana neutrinos and point out two simple mechanisms for neutrino masses. In this context the neutrino masses can be generated either at tree level or at quantum level and one predicts the existence of very light sterile neutrinos with masses below the eV scale. The predictions for lepton number violating processes such as μ-> e and μ-> e gamma are discussed in detail. The impact from the cosmological constraints on the effective number of relativistic degree of freedom is investigated.
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