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Dhani, P. K., Rodrigo, G., & Sborlini, G. F. R. (2023). Triple-collinear splittings with massive particles. J. High Energy Phys., 12(12), 188–20pp.
Abstract: We analyze in detail the most singular behaviour of processes involving triple-collinear splittings with massive particles in the quasi-collinear limit, and present compact expressions for the splitting amplitudes and the corresponding splitting kernels at the squared-amplitude level. Our expressions fully agree with well-known triple-collinear splittings in the massless limit, which are used as a guide to achieve the final expressions. These results are important to quantify dominant mass effects in many observables, and constitute an essential ingredient of current high-precision computational frameworks for collider phenomenology.
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Alonso-Gonzalez, D., Amaral, D. W. P., Bariego-Quintana, A., Cerdeño, D., & de los Rios, M. (2023). Measuring the sterile neutrino mass in spallation source and direct detection experiments. J. High Energy Phys., 12(12), 096–27pp.
Abstract: We explore the complementarity of direct detection (DD) and spallation source (SS) experiments for the study of sterile neutrino physics. We focus on the sterile baryonic neutrino model: an extension of the Standard Model that introduces a massive sterile neutrino with couplings to the quark sector via a new gauge boson. In this scenario, the inelastic scattering of an active neutrino with the target material in both DD and SS experiments gives rise to a characteristic nuclear recoil energy spectrum that can allow for the reconstruction of the neutrino mass in the event of a positive detection. We first derive new bounds on this model based on the data from the COHERENT collaboration on CsI and LAr targets, which we find do not yet probe new areas of the parameter space. We then assess how well future SS experiments will be able to measure the sterile neutrino mass and mixings, showing that masses in the range similar to 15 – 50 MeV can be reconstructed. We show that there is a degeneracy in the measurement of the sterile neutrino mixing that substantially affects the reconstruction of parameters for masses of the order of 40 MeV. Thanks to their lower energy threshold and sensitivity to the solar tau neutrino flux, DD experiments allow us to partially lift the degeneracy in the sterile neutrino mixings and considerably improve its mass reconstruction down to 9 MeV. Our results demonstrate the excellent complementarity between DD and SS experiments in measuring the sterile neutrino mass and highlight the power of DD experiments in searching for new physics in the neutrino sector.
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Karan, A., Sadhukhan, S., & Valle, J. W. F. (2023). Phenomenological profile of scotogenic fermionic dark matter. J. High Energy Phys., 12(12), 185–34pp.
Abstract: We consider the possibility that neutrino masses arise from the exchange of dark matter states. We examine in detail the phenomenology of fermionic dark matter in the singlet-triplet scotogenic model. We explore the case of singlet-like fermionic dark matter, taking into account all coannihilation effects relevant for determining its relic abundance, such as fermion-fermion and scalar-fermion coannihilation. Although this in principle allows for dark matter below 60 GeV, the latter is in conflict with charged lepton flavour violation (cLFV) and/or collider physics constraints. We examine the prospects for direct dark matter detection in upcoming experiments up to 10 TeV. Fermion-scalar coannihilation is needed to obtain viable fermionic dark matter in the 60-100 GeV mass range. Fermion-fermion and fermion-scalar coannihilation play complementary roles in different parameter regions above 100 GeV.
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ATLAS Collaboration(Aad, G. et al), Akiot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Search for vector-boson resonances decaying into a top quark and a bottom quark using pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 12(12), 073–63pp.
Abstract: A search for a new massive charged gauge boson, W ', is performed with the ATLAS detector at the LHC. The dataset used in this analysis was collected from proton-proton collisions at a centre-of-mass energy of root s = 13 TeV, and corresponds to an integrated luminosity of 139 fb(-1). The reconstructed tb invariant mass is used to search for a W ' boson decaying into a top quark and a bottom quark. The result is interpreted in terms of a W ' boson with purely right-handed or left-handed chirality in a mass range of 0.5-6 TeV. Different values for the coupling of the W ' boson to the top and bottom quarks are considered, taking into account interference with single-top-quark production in the s-channel. No significant deviation from the background prediction is observed. The results are expressed as upper limits on the W ' -> tb production cross-section times branching ratio as a function of the W '-boson mass and in the plane of the coupling vs the W '-boson mass.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). Measurement of the CKM angle γ using the B± → D*h± channels. J. High Energy Phys., 12(12), 013–32pp.
Abstract: A measurement of the CP-violating observables from B -> (DK +/-)-K-* and B-+/- -> D-*pi(+/-) decays is presented, where D-*(D) is an admixture of D-*0 and D-0 (D-0 and (0)) states and is reconstructed through the decay chains D-*-> D pi(0)/gamma and D -> KS0 pi+pi-/KS0K+K-. The measurement is performed by analysing the signal yield variation across the D decay phase space and is independent of any amplitude model. The data sample used was collected by the LHCb experiment in proton-proton collisions and corresponds to a total integrated luminosity of 9 fb(-1) at centre-of-mass energies of 7, 8 and 13 TeV. The CKM angle gamma is determined to be (69(-14)(+13))degrees using the measured CP-violating observables. The hadronic parameters r(B)(D)*(K +/-),r(B)(D)*(pi +/-),delta(D)(B)*(K +/-),delta(D)(B)*(pi +/-), which are the ratios and strong phase differences between favoured and suppressed B-+/- decays, are also reported.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4l events with the ATLAS detector at √s=13 TeV. J. High Energy Phys., 12(12), 107–48pp.
Abstract: A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 +/- 0.60 fb, consistent with the next-to-leadingorder Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Search for heavy Higgs bosons with flavour-violating couplings in multi-lepton plus b-jets final states in pp collisions at 13 TeV with the ATLAS detector. J. High Energy Phys., 12(12), 081–68pp.
Abstract: A search for new heavy scalars with flavour-violating decays in final states with multiple leptons and b-tagged jets is presented. The results are interpreted in terms of a general two-Higgs-doublet model involving an additional scalar with couplings to the top-quark and the three up-type quarks (rho(tt),rho(tc), and rho(tu)). The targeted signals lead to final states with either a same-sign top-quark pair, three top-quarks, or four top-quarks. The search is based on a data sample of proton-proton collisions at root s = 13TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). Events are categorised depending on the multiplicity of light charged leptons (electrons or muons), total lepton charge, and a deep-neural-network output to enhance the purity of each of the signals. Masses of an additional scalar boson mH between 200- 630 GeV with couplings rho(tt) = 0.4, rho(tc) = 0.2, and rho(tu) = 0.2 are excluded at 95% confidence level. Additional interpretations are provided in models of R-parity violating supersymmetry, motivated by the recent flavour and ( g – 2) (mu) anomalies.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 12(12), 167–63pp.
Abstract: Searches for electroweak production of wino-like chargino pairs, (chi) over tilde (+)(1)(chi) over tilde (-), 1, and of wino-like chargino and next-to-lightest neutralino, (chi) over tilde (+/-)(1)(chi) over tilde (0)(2), are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, (chi) over tilde chi(+/-)(1) -> W-+/- (chi) over tilde (0)(1) The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to (chi) over tilde (0)(1) and either a Z or a Higgs boson, (chi) over tilde (0)(2) -> Z (chi) over tildeX(1)(0) or h (chi) over tilde (0)(1). The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb(-1) of root s = 13TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless (chi) over tilde (1)(0) in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless (chi) over tilde (1)(0) for (chi) over tilde (0)(2) -> Z (chi) over tilde (0)(1). For decays through an on-shell Higgs boson and for mass-splitting between (chi) over tilde (+/-)(1)/(chi) over tilde (0)(2) and (chi) over tilde (0)(1) as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200-260 GeV and 280-470 GeV compared to previous ATLAS constraints.
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ATLAS Collaboration(Aad, G. et al), Akiot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Search for flavour-changing neutral tqH interactions with H → γγ in pp collisions at √s=13 TeV using the ATLAS detector. J. High Energy Phys., 12(12), 195–53pp.
Abstract: A search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q ( q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb(-1), was collected at root s = 13TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t -> qH in tt production and the production process pp. tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t. cH and the t. uH branching ratios of 4.3x10(-4) and 3.8x10(-4), respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7x10(-4) and 3.9x10(-4). Combining this search with ATLAS searches in the H. t+ t- and H. b <overline> b final states yields observed (expected) upper limits on the t -> cH branching ratio of 5.8 x 10(-4) (3.0 x 10(-4)) at the 95% confidence level. The corresponding observed (expected) upper limit on the t -> uH branching ratio is 4.0 x 10(-4) (2.4 x 10(-4)).
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Jung, M., Pich, A., & Tuzon, P. (2010). Charged-Higgs phenomenology in the aligned two-Higgs-doublet model. J. High Energy Phys., 11(11), 003–45pp.
Abstract: The alignment in flavour space of the Yukawa matrices of a general two-Higgs-doublet model results in the absence of tree-level flavour-changing neutral currents. In addition to the usual fermion masses and mixings, the aligned Yukawa structure only contains three complex parameters zeta(f), which are potential new sources of CP violation [1]. For particular values of these three parameters all known specific implementations of the model based on discrete Z(2) symmetries are recovered. One of the most distinctive features of the two-Higgs-doublet model is the presence of a charged scalar H-+/-. In this work, we discuss its main phenomenological consequences in flavour-changing processes at low energies and derive the corresponding constraints on the parameters of the aligned two-Higgs-doublet model.
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