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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Measurements of Z gamma and Z gamma gamma production in pp collisions at root s=8 TeV with the ATLAS detector. Phys. Rev. D, 93(11), 112002–41pp.
Abstract: The production of Z bosons with one or two isolated high-energy photons is studied using pp collisions at root s = 8 TeV. The analyses use a data sample with an integrated luminosity of 20.3 fb(-1) collected by the ATLAS detector during the 2012 LHC data taking. The Z gamma and Z gamma gamma production cross sections are measured with leptonic (e(+) e(-), mu(+) mu(-), nu(nu) over bar) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z-boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy E-T > 250 GeV from l(+) l(-) gamma events and with E-T > 400 GeV from nu(nu) over bar gamma events are used to search for anomalous triple gauge-boson couplings ZZ gamma and Z gamma gamma. The yields of events with diphoton invariant mass m(gamma gamma) > 200 GeV from l(+) l(-) gamma gamma events and with m(gamma gamma) > 300 GeV from nu(nu) over bar gamma gamma events are used to search for anomalous quartic gauge-boson couplings ZZ gamma gamma and Z gamma gamma gamma. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.
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ANTARES, I. C., LIGO and Virgo Collaborations(Adrian-Martinez, S. et al), Barrios-Marti, J., Hernandez-Rey, J. J., Sanchez-Losa, A., Tönnis, C., Zornoza, J. D., et al. (2016). High-energy neutrino follow-up search of gravitational wave event GW150914 with ANTARES and IceCube. Phys. Rev. D, 93(12), 122010–15pp.
Abstract: We present the high-energy-neutrino follow-up observations of the first gravitational wave transient GW150914 observed by the Advanced LIGO detectors on September 14, 2015. We search for coincident neutrino candidates within the data recorded by the IceCube and ANTARES neutrino detectors. A possible joint detection could be used in targeted electromagnetic follow-up observations, given the significantly better angular resolution of neutrino events compared to gravitational waves. We find no neutrino candidates in both temporal and spatial coincidence with the gravitational wave event. Within +/- 500 s of the gravitational wave event, the number of neutrino candidates detected by IceCube and ANTARES were three and zero, respectively. This is consistent with the expected atmospheric background, and none of the neutrino candidates were directionally coincident with GW150914. We use this nondetection to constrain neutrino emission from the gravitational-wave event.
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Das, D., & Santamaria, A. (2016). Updated scalar sector constraints in the Higgs triplet model. Phys. Rev. D, 94(1), 015015–10pp.
Abstract: We show that in the Higgs triplet model, after the Higgs discovery, the mixing angle in the CP-even sector can be strongly constrained from unitarity. We also discuss how large quantum effects in h -> gamma gamma may arise in a Standard-Model-like scenario and a certain part of the parameter space can be ruled out from the diphoton signal strength. Using T-parameter and diphoton signal strength measurements, we update the bounds on the nonstandard scalar masses.
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Hiller Blin, A. N., Fernandez-Ramirez, C., Jackura, A., Mathieu, V., Mokeev, V. I., Pilloni, A., et al. (2016). Studying the P-c(4450) resonance in J/psi photoproduction off protons. Phys. Rev. D, 94(3), 034002–8pp.
Abstract: A resonancelike structure, the P-c(4450), has recently been observed in the J/psi p spectrum by the LHCb Collaboration. We discuss the feasibility of detecting this structure in J/psi photoproduction in the CLAS12 experiment at JLab. We present a first estimate of the upper limit for the branching ratio of the P-c (4450) to J/psi p. Our estimates, which take into account the experimental resolution effects, predict that it will be possible to observe a sizable cross section close to the J/psi production threshold and shed light on the P-c(4450) resonance in the future photoproduction measurements.
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Pagura, V. P., Gomez Dumm, D., Noguera, S., & Scoccola, N. N. (2017). Magnetic catalysis and inverse magnetic catalysis in nonlocal chiral quark models. Phys. Rev. D, 95(3), 034013–7pp.
Abstract: We study the behavior of strongly interacting matter under an external constant magnetic field in the context of nonlocal chiral quark models within the mean field approximation. We find that at zero temperature the behavior of the quark condensates shows the expected magnetic catalysis effect, our predictions being in good quantitative agreement with lattice QCD results. On the other hand, in contrast to what happens in the standard local Nambu-Jona-Lasinio model, when the analysis is extended to the case of finite temperature, our results show that nonlocal models naturally lead to the inverse magnetic catalysis effect.
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Ortega, P. G., Segovia, J., Entem, D. R., & Fernandez, F. (2016). Molecular components in P-wave charmed-strange mesons. Phys. Rev. D, 94(7), 074037–11pp.
Abstract: Results obtained by various experiments show that the D-s0(*)(2317) and D-s1(2460) mesons are very narrow states located below the DK and D*K thresholds, respectively. This is markedly in contrast with the expectations of naive quark models and heavy quark symmetry. Motivated by a recent lattice study which addresses the mass shifts of the c _ s ground states with quantum numbers J(P) = 1+ [D-s1 (2317)] and JP = 1(+) [D-s1(2460)] due to their coupling with S-wave D-(*) K thresholds, we perform a similar analysis within a nonrelativistic constituent quark model in which quark-antiquark and meson-meson degrees of freedom are incorporated. The quark model has been applied to a wide range of hadronic observables, and thus the model parameters are completely constrained. The coupling between quark- antiquark and mesonmeson Fock components is done using a P-3(0) model in which its only free parameter gamma has been elucidated, performing a global fit to the decay widths of mesons that belong to different quark sectors, from light to heavy. We observe that the coupling of the 0(+)(1(+)) meson sector to the DK (D*K) threshold is the key feature to simultaneously lower the masses of the corresponding D-s0(*)(2317) and D-s1(2460) states predicted by the naive quark model and describe the D-s1(2536) meson as the 1(+)state of the j(q)(p) =3/2(+) doublet predicted by heavy quark symmetry, reproducing its strong decay properties. Our calculation allows us to introduce the coupling with the D- wave D*K channel and the computation of the probabilities associated with the different Fock components of the physical state.
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Aguilar, A. C., Binosi, D., & Papavassiliou, J. (2017). Schwinger mechanism in linear covariant gauges. Phys. Rev. D, 95(3), 034017–16pp.
Abstract: In this work we explore the applicability of a special gluon mass generating mechanism in the context of the linear covariant gauges. In particular, the implementation of the Schwinger mechanism in pure Yang-Mills theories hinges crucially on the inclusion of massless bound-state excitations in the fundamental nonperturbative vertices of the theory. The dynamical formation of such excitations is controlled by a homogeneous linear Bethe-Salpeter equation, whose nontrivial solutions have been studied only in the Landau gauge. Here, the form of this integral equation is derived for general values of the gauge-fixing parameter, under a number of simplifying assumptions that reduce the degree of technical complexity. The kernel of this equation consists of fully dressed gluon propagators, for which recent lattice data are used as input, and of three-gluon vertices dressed by a single form factor, which is modeled by means of certain physically motivated Ansatze. The gauge-dependent terms contributing to this kernel impose considerable restrictions on the infrared behavior of the vertex form factor; specifically, only infrared finite Ansatze are compatible with the existence of nontrivial solutions. When such Ansatze are employed, the numerical study of the integral equation reveals a continuity in the type of solutions as one varies the gauge-fixing parameter, indicating a smooth departure from the Landau gauge. Instead, the logarithmically divergent form factor displaying the characteristic “zero crossing,” while perfectly consistent in the Landau gauge, has to undergo a dramatic qualitative transformation away from it, in order to yield acceptable solutions. The possible implications of these results are briefly discussed.
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Ge, S. F., Pasquini, P., Tortola, M., & Valle, J. W. F. (2017). Measuring the leptonic CP phase in neutrino oscillations with nonunitary mixing. Phys. Rev. D, 95(3), 033005–14pp.
Abstract: Non-unitary neutrino mixing implies an extra CP violating phase that can fake the leptonic Dirac CP phase delta(CP) of the simplest three-neutrino mixing benchmark scheme. This would hinder the possibility of probing for CP violation in accelerator-type experiments. We take T2K and T2HK as examples to demonstrate the degeneracy between the “standard” (or “unitary”) and “nonunitary” CP phases. We find, under the assumption of nonunitary mixing, that their CP sensitivities severely deteriorate. Fortunately, the TNT2K proposal of supplementing T2(H)K with a μDAR source for better measurement of delta(CP) can partially break the CP degeneracy by probing both cos delta(CP) and sin delta(CP) dependences in the wide spectrum of the μDAR flux. We also show that the further addition of a near detector to the μDAR setup can eliminate the degeneracy completely.
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Ortega, P. G., Segovia, J., Entem, D. R., & Fernandez, F. (2017). Threshold effects in P-wave bottom-strange mesons. Phys. Rev. D, 95(3), 034010–7pp.
Abstract: Using a nonrelativistic constituent quark model in which the degrees of freedom are quarkantiquark and meson- meson components, we have recently shown that the Dd((*))K thresholds play an important role in lowering the mass of the c (S) over bar states associated with the physical D-s0(*)(2317) and D-s1(2460) mesons. This observation is also supported by other theoretical approaches such as latticeregularized QCD or chiral unitary theory in coupled channels. Herein, we extend our computation to the lowest P- wave Bs mesons, taking into account the corresponding J(P) = 0(+), 1(-) and 2(+) bottomstrange states predicted by the naive quark model and the BK and B* K thresholds. We assume that mixing with B-s((*))eta and isospin-violating decays to B-s((*))pi are negligible. This computation is important because there is no experimental data in the b (S) over bar sector for the equivalent j(q)(p) = 1/2(+) (D-s0(*)(2317), D-s1 (2460)) heavy-quark multiplet and, as it has been seen in the c (s) over bar sector, the naive theoretical result can be wrong by more than 100 MeV. Our calculation allows us to introduce the coupling with the D-wave B*K channel and to compute the probabilities associated with the different Fock components of the physical state.
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PANDA Collaboration(Singh, B. et al), & Diaz, J. (2017). Feasibility study for the measurement of pi N transition distribution amplitudes at PANDA in bar(p) p -> J/psi pi(0). Phys. Rev. D, 95(3), 032003–25pp.
Abstract: The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is shown that the measurement can be done at (P) over bar ANDA with significant constraining power under the assumption of an integrated luminosity attainable in four to five months of data taking at the maximum design luminosity.
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