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Rinaldi, M., Scopetta, S., Traini, M., & Vento, V. (2016). Correlations in double parton distributions: perturbative and non-perturbative effects. J. High Energy Phys., 10(10), 063–36pp.
Abstract: The correct description of Double Parton Scattering (DPS), which represents a background in several channels for the search of new Physics at the LHC, requires the knowledge of double parton distribution functions (dPDFs). These quantities represent also a novel tool for the study of the three-dimensional nucleon structure, complementary to the possibilities offered by electromagnetic probes. In this paper we analyze dPDFs using Poincare covariant predictions obtained by using a Light-Front constituent quark model proposed in a recent paper, and QCD evolution. We study to what extent factorized expressions for dPDFs, which neglect, at least in part, two-parton correlations, can be used. We show that they fail in reproducing the calculated dPDFs, in particular in the valence region. Actually measurable processes at existing facilities occur at low longitudinal momenta of the interacting partons; to have contact with these processes we have analyzed correlations between pairs of partons of different kind, finding that, in some cases, they are strongly suppressed at low longitudinal momenta, while for other distributions they can be sizeable. For example, the effect of gluon-gluon correlations can be as large as 20 %. We have shown that these behaviors can be understood in terms of a delicate interference of non-perturbative correlations, generated by the dynamics of the model, and perturbative ones, generated by the model independent evolution procedure. Our analysis shows that at LHC kinematics two-parton correlations can be relevant in DPS, and therefore we address the possibility to study them experimentally.
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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. (2016). Search for dark matter produced in association with a hadronically decaying vector boson in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 763, 251–268.
Abstract: A search is presented for dark matter produced in association with a hadronically decaying W or Z boson using 3.2 fb(-1) of ppcollisions at root s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with a hadronic jet compatible with a Wor Z boson and with large missing transverse momentum are analysed. The data are consistent with the Standard Model predictions and are interpreted in terms of both an effective field theory and a simplified model containing dark matter.
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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. (2016). Study of hard double-parton scattering in four-jet events in pp collisions root s=7 TeV with the ATLAS experiment. J. High Energy Phys., 11(11), 110–52pp.
Abstract: Inclusive four-jet events produced in proton-proton collisions at a centre-of mass energy of root s = 7 TeV are analysed for the presence of hard double-parton scattering using data corresponding to an integrated luminosity of 37.3 pb(-1), collected with the ATLAS detector at the LHC. The contribution of hard double-parton scattering to the production of four -jet events is extracted using an artificial neural network, assuming that hard double-parton scattering can be approximated by an uncorrelated overlaying of dijet events. For events containing at least four jets with transverse momentum PT >= 20 GeV and pseudorapidity vertical bar eta vertical bar <= 4.4, and at least one having pT >= 42.5 GeV, the contribution of hard double-parton scattering is estimated to be fDps = 0.092(-0.011)(+0.0005) (stat.) (+0.03337)(-0.011) (syst.). After combining this measurement with those of the inclusive dijet and four -jet cross -sections in the appropriate phase space regions, the effective cross-section, sigma(eff,) was determined to be sigma(eff) = 14.9(-1.0)(+1.2) (stat.) (+5.1)(-3.8) (syst.) mb. This result is consistent within the quoted uncertainties with previous measurements of sigma(eff), performed at centre-of-mass energies between 63 GeV and 8 TeV using various final states, and it corresponds to 21(-6%)(+7) of the total inelastic cross-section measured at root s = 7 TeV. The distributions of the observables sensitive to the contribution of hard double-parton scattering, corrected for detector effects, are also provided.
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Sborlini, G. F. R., Driencourt-Mangin, F., & Rodrigo, G. (2016). Four-dimensional unsubtraction with massive particles. J. High Energy Phys., 10(10), 162–34pp.
Abstract: We extend the four-dimensional unsubtraction method, which is based on the loop-tree duality (LTD), to deal with processes involving heavy particles. The method allows to perform the summation over degenerate IR configurations directly at integrand level in such a way that NLO corrections can be implemented directly in four space-time dimensions. We define a general momentum mapping between the real and virtual kinematics that accounts properly for the quasi-collinear configurations, and leads to an smooth massless limit. We illustrate the method first with a scalar toy example, and then analyse the case of the decay of a scalar or vector boson into a pair of massive quarks. The results presented in this paper are suitable for the application of the method to any multipartonic process.
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Boucenna, S. M., Celis, A., Fuentes-Martin, J., Vicente, A., & Virto, J. (2016). Phenomenology of an SU(2) x SU(2) x U(1) model with lepton-flavour non-universality. J. High Energy Phys., 12(12), 059–43pp.
Abstract: We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in b -> clv and b -> sl(+) l(-) decays at BaBar, Belle and LHCb. The model consists of an extended gauge group SU(2)(1) x SU(2)(2) x U(l)(Y) which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector -like fermions give rise to potentially large new physics contributions in flavour transitions mediated by WI and Z' bosons. This model can ease tensions in B -physics data while satisfying stringent bounds from flavour physics, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the ratios RM =Gamma(B -> M mu(+)mu(-))/Gamma(B -> Me(+)e(-)), with M = K*, phi, are found to be reduced with respect to the Standard Model expectation R-M similar or equal to 1.
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