Mandal, R., Murgui, C., Peñuelas, A., & Pich, A. (2020). The role of right-handed neutrinos in b -> c tau nubar anomalies. J. High Energy Phys., 08(8), 022–46pp.
Abstract: Motivated by the persistent anomalies reported in the b -> c tau v<overbar></mml:mover> data, we perform a general model-independent analysis of these transitions, in the presence of light right-handed neutrinos. We adopt an effective field theory approach and write a low-energy effective Hamiltonian, including all possible dimension-six operators. The corresponding Wilson coefficients are determined through a numerical fit to all available experimental data. In order to work with a manageable set of free parameters, we define eleven well- motivated scenarios, characterized by the different types of new physics that could mediate these transitions, and analyse which options seem to be preferred by the current measurements. The data exhibit a clear preference for new-physics contributions, and good fits to the data are obtained in several cases. However, the current measurement of the longitudinal D<SUP></SUP> polarization in B -> D tau v<overbar></mml:mover> cannot be easily accommodated within its experimental 1 sigma range. A general analysis of the three-body B -> D tau v<overbar></mml:mover> and four-body B -> D<mml:mo><mml:mfenced close=“)” open=“(”><mml:mo>-> D pi</mml:mfenced>tau <mml:mover accent=“true”>v<mml:mo stretchy=“true”><overbar></mml:mover> angular distributions is also presented. The accessible angular observables are studied in order to assess their sensitivity to the different new physics scenarios. Experimental information on these distributions would help to disentangle the dynamical origin of the current anomalies.
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Delhom, A. (2020). Minimal coupling in presence of non-metricity and torsion. Eur. Phys. J. C, 80(8), 728–17pp.
Abstract: We deal with the question of what it means to define a minimal coupling prescription in presence of torsion and/or non-metricity, carefully explaining while the naive substitution partial derivative -> del introduces extra couplings between the matter fields and the connection that can be regarded as non-minimal in presence of torsion and/or non-metricity. We will also investigate whether minimal coupling prescriptions at the level of the action (MCPL) or at the level of field equations (MCPF) lead to different dynamics. To that end, we will first write the Euler-Lagrange equations for matter fields in terms of the covariant derivatives of a general non-Riemannian space, and derivate the form of the associated Noether currents and charges. Then we will see that if the minimal coupling prescriptions is applied as we discuss, for spin 0 and 1 fields the results of MCPL and MCPF are equivalent, while for spin 1/2 fields there is a difference if one applies the MCPF or the MCPL, since the former leads to charge violation.
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ATLAS and CMS Collaborations(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at root s=8 TeV. J. High Energy Phys., 08(8), 051–67pp.
Abstract: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb(-1)for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F-0), left-handed (F-L), or right-handed (F-R) polarizations. The resulting combined measurements of the polarization fractions are F-0= 0.693 +/- 0.014 and F-L= 0.315 +/- 0.011. The fractionF(R)is calculated from the unitarity constraint to be F-R=-0.008 +/- 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F-0(F-L) with respect to the most precise single measurement. A limit on anomalous right-handed vector (V-R), and left- and right-handed tensor (g(L), g(R)) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [-0.11,0.16] for V-R, [-0.08,0.05] for g(L), and [-0.04,0.02] for g(R), at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.
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Creminelli, P., Loayza, N., Serra, F., Trincherini, E., & Trombetta, L. G. (2020). Hairy black-holes in shift-symmetric theories. J. High Energy Phys., 08(8), 045–24pp.
Abstract: Scalar hair of black holes in theories with a shift symmetry are constrained by the no-hair theorem of Hui and Nicolis, assuming spherical symmetry, time-independence of the scalar field and asymptotic flatness. The most studied counterexample is a linear coupling of the scalar with the Gauss-Bonnet invariant. However, in this case the norm of the shift-symmetry current J(2) diverges at the horizon casting doubts on whether the solution is physically sound. We show that this is not an issue since J(2) is not a scalar quantity, since J(mu) is not a diffinvariant current in the presence of Gauss-Bonnet. The same theory can be written in Horndeski form with a non-analytic function G(5)similar to log X . In this case the shift-symmetry current is diff-invariant, but contains powers of X in the denominator, so that its divergence at the horizon is again immaterial. We confirm that other hairy solutions in the presence of non-analytic Horndeski functions are pathological, featuring divergences of physical quantities as soon as one departs from time-independence and spherical symmetry. We generalise the no-hair theorem to Beyond Horndeski and DHOST theories, showing that the coupling with Gauss-Bonnet is necessary to have hair.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Study of the psi(2)(3823) and chi(c1)(3872) states in B+->(J/psi pi(+)pi(-))K(+)decays. J. High Energy Phys., 08(8), 123–29pp.
Abstract: The decays B+-> J/psi pi(+)pi(-)K(+)are studied using a data set corresponding to an integrated luminosity of 9 fb(-1)collected with the LHCb detector in proton-proton collisions between 2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate psi(2)(3823), chi(c1)(3872) and psi(2S) states are reported. The values areBB+->psi 2(“>3823K+xB psi 2(”>3823 -> J/psi pi+pi-BB+->chi c1>3872K+xB chi c1>3872 -> J/psi pi+pi-=>3.56 +/- 0.67 +/- 0.11x10-2,BB+->psi 2>3823K+xB psi 2>3823 -> J/psi pi+pi-BB+->psi>2SK+xB psi>2S -> J/psi pi+pi-=>1.31 +/- 0.25 +/- 0.04x10-3,BB+->chi c1>3872K+xB chi c1>3872 -> J/psi pi+pi-BB+->psi>2SK+xB psi>2S -> J/psi pi+pi-= where the first uncertainty is statistical and the second is systematic. The decay of B+->psi(2)(3823)K(+)with psi(2)(3823)-> J/psi pi(+)pi(-)is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the psi(2)(3823), chi(c1)(3872) and psi(2S) states are measured to be m chi c1>3872-m psi 2>3823=47. 50 +/- 0.53 +/- 0.13MeV/c2,m psi 2 2S=185.49 +/- 0.06 +/- 0.03MeV/c2, resulting in the most precise determination of the chi(c1)(3872) mass. The width of the psi(2)(3823) state is found to be below 5.2 MeV at 90% confidence level. The Breit-Wigner width of the chi(c1)(3872) state is measured to be Gamma chi c13872BW=0.96-0.18+0.19 +/- 0.21MeV={0.96}_{-0.18}<^>{+0.19}\pm 0.21\;\mathrm{MeV} which is inconsistent with zero by 5.5 standard deviations.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking. J. High Energy Phys., 08(8), 080–53pp.
Abstract: The factor of four increase in the LHC luminosity, from 0.5x10(34)cm(-2)s(-1) to 2.0x10(34)cm(-2)s(-1), and the corresponding increase in pile-up collisions during the 2015-2018 data-taking period, presented a challenge for the ATLAS trigger, particularly for those algorithms that select events with missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achieved in earlier operations. A study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of >98% for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2020). Measurements of top-quark pair spin correlations in the e mu channel at root s=13 TeV using pp collisions in the ATLAS detector. Eur. Phys. J. C, 80(8), 754–43pp.
Abstract: A measurement of observables sensitive to spin correlations in tt<overbar></mml:mover> production is presented, using 36.1 fb-1 of pp collision data at <mml:msqrt>s</mml:msqrt>=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the t<mml:mover accent=“true”>t<mml:mo stretchy=“false”><overbar></mml:mover> system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.
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Cepedello, R., Hirsch, M., Rocha-Moran, P., & Vicente, A. (2020). Minimal 3-loop neutrino mass models and charged lepton flavor violation. J. High Energy Phys., 08(8), 067–37pp.
Abstract: We study charged lepton flavor violation for the three most popular 3-loop Majorana neutrino mass models. We call these models “minimal” since their particle content correspond to the minimal sets for which genuine 3-loop models can be constructed. In all the three minimal models the neutrino mass matrix is proportional to some powers of Standard Model lepton masses, providing additional suppression factors on top of the expected loop suppression. To correctly explain neutrino masses, therefore large Yukawa couplings are needed in these models. We calculate charged lepton flavor violating observables and find that the three minimal models survive the current constraints only in very narrow regions of their parameter spaces.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Observation of the associated production of a top quark and a Z boson in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 124–46pp.
Abstract: Single top-quark production in association with a Z boson, where the Z boson decays to a pair of charged leptons, is measured in the trilepton channel. The proton-proton collision data collected by the ATLAS experiment from 2015 to 2018 at a centre-of-mass energy of 13 TeV are used, corresponding to an integrated luminosity of 139 fb(-1). Events containing three isolated charged leptons (electrons or muons) and two or three jets, one of which is identified as containing a b-hadron, are selected. The main backgrounds are from t (t) over barZ and diboson production. Neural networks are used to improve the background rejection and extract the signal. The measured cross-section for tl(+)l(-) q production, including non-resonant dilepton pairs with m(l+l-) > 30 GeV, is 97 +/- 13 (stat.) +/- 7 (syst.) fb, consistent with the Standard Model prediction.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Measurements of the production cross-section for a Z boson in association with b-jets in proton-proton collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 044–58pp.
Abstract: This paper presents a measurement of the production cross-section of aZboson in association withb-jets, in proton-proton collisions at root s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb(-1). Inclusive and differential cross-sections are measured for events containing aZboson decaying into electrons or muons and produced in association with at least one or at least two b-jets with transverse momentum p(T)>20 GeV and rapidity vertical bar y vertical bar <2.5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet.
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