CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2010). Search for new color-octet vector particle decaying to t(t)over-bar in p(p)over-bar collisions at root s=1.96 TeV. Phys. Lett. B, 691(4), 183–190.
Abstract: We present the result of a search for a massive color-octet vector particle, (e.g. a massive gluon) decaying to a pair of top quarks in proton-antiproton collisions with a center-of-mass energy of 1.96 TeV. This search is based on 1.9 fb(-1) of data collected using the CDF detector during Run II of the Tevatron at Fermilab. We study t (t) over bar events in the lepton + jets channel with at least one b-tagged jet. A massive gluon is characterized by its mass, decay width, and the strength of its coupling to quarks. These parameters are determined according to the observed invariant mass distribution of top quark pairs. We set limits on the massive gluon coupling strength for masses between 400 and 800 GeV/c(2) and width-to-mass ratios between 0.05 and 0.50. The coupling strength of the hypothetical massive gluon to quarks is consistent with zero within the explored parameter space.
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Hernandez, E., Vijande, J., Valcarce, A., & Richard, J. M. (2020). Spectroscopy, lifetime and decay modes of the T-bb(-) tetraquark. Phys. Lett. B, 800, 135073–9pp.
Abstract: We present the first full-fledged study of the flavor-exotic isoscalar T-bb(-) equivalent to bb (u) over bar(d) over bar tetraquark with spin and parity J(P) = 1(+). We report accurate solutions of the four-body problem in a quark model, characterizing the structure of the state as a function of the ratio M-Q/m(q) of the heavy to light quark masses. For such a standard constituent model, T-bb(-) lies approximately 150 MeV below the strong decay threshold B- (B) over bar*(0) and 105 MeV below the electromagnetic decay threshold B- (B) over bar (0)gamma. We evaluate the lifetime of T-bb(-), identifying the promising decay modes where the tetraquark might be looked for in future experiments. Its total decay width is Gamma approximate to 87 x 10(-15) GeV and therefore its lifetime tau approximate to 7.6 ps. The promising final states are B*(-) D*(+) l (v) over bar (l) and (B) over bar*(0) l (v) over bar (l) among the semileptonic decays, and B*(-) D*(+) D-s*(-), (B) over bar*(0) D*(0) D-s*(-), and B*(-) D*(+) rho(-) among the nonleptonic ones. The semileptonic decay to the isoscalar J(P) = 0(+) tetraquark T-bc(0) is also relevant but it is not found to be dominant. There is a broad consensus about the existence of this tetraquark, and its detection will validate our understanding of the low-energy realizations of Quantum Chromodynamics (QCD) in the multiquark sector.
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Pinto-Gomez, F., De Soto, F., Ferreira, M. N., Papavassiliou, J., & Rodriguez-Quintero, J. (2023). Lattice three-gluon vertex in extended kinematics: Planar degeneracy. Phys. Lett. B, 838, 137737–8pp.
Abstract: We present novel results for the three-gluon vertex, obtained from an extensive quenched lattice simulation in the Landau gauge. The simulation evaluates the transversely projected vertex, spanned on a special tensorial basis, whose form factors are naturally parametrized in terms of individually Bosesymmetric variables. Quite interestingly, when evaluated in these kinematics, the corresponding form factors depend almost exclusively on a single kinematic variable, formed by the sum of the squares of the three incoming four-momenta, q, r, and p. Thus, all configurations lying on a given plane in the coordinate system (q2, r2, p2) share, to a high degree of accuracy, the same form factors, a property that we denominate planar degeneracy. We have confirmed the validity of this property through an exhaustive study of the set of configurations satisfying the condition q2 = r2, within the range [0, 5 GeV]. This drastic simplification allows for a remarkably compact description of the main bulk of the data, which is particularly suitable for future numerical applications. A semi-perturbative analysis reproduces the lattice findings rather accurately, once the inclusion of a gluon mass has cured all spurious divergences.
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Aguilar, A. C., De Soto, F., Ferreira, M. N., Papavassiliou, J., & Rodriguez-Quintero, J. (2021). Infrared facets of the three-gluon vertex. Phys. Lett. B, 818, 136352–7pp.
Abstract: We present novel lattice results for the form factors of the quenched three-gluon vertex of QCD, in two special kinematic configurations that depend on a single momentum scale. We consider three form factors, two associated with a classical tensor structure and one without tree-level counterpart, exhibiting markedly different infrared behaviors. Specifically, while the former display the typical suppression driven by a negative logarithmic singularity at the origin, the latter saturates at a small negative constant. These exceptional features are analyzed within the Schwinger-Dyson framework, with the aid of special relations obtained from the Slavnov-Taylor identities of the theory. The emerging picture of the underlying dynamics is thoroughly corroborated by the lattice results, both qualitatively as well as quantitatively.
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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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