286 research outputs found

    MT2-reconstructed invisible momenta as spin analizers, and an application to top polarization

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    Full event reconstruction is known to be challenging in cases with more than one undetected final-state particle, such as pair production of two states each decaying semi-invisibly. On the other hand, full event reconstruction would allow to access angular distributions sensitive to the spin fractions of the decaying particles, thereby dissecting their production mechanism. We explore this possibility in the case of Standard-Model t-tbar production followed by a leptonic decay of both W bosons, implying two undetected final-state neutrinos. We estimate the t and tbar momentum vectors event by event using information extracted from the kinematic variable MT2. The faithfulness of the estimated momenta to the true momenta is then tested in observables sensitive to top polarization and t-tbar spin correlations. Our method thereby provides a novel approach towards the evaluation of these observables, and towards testing t-tbar production beyond the level of the total cross section. While our discussion is confined to t-tbar production as a benchmark, the method is applicable to any process whose decay topology allows to construct MT2.Comment: 28 pages, 14 figures, 3 tables. Changes in v2: new paragraph on ISR (end of sec. 2.2); new sec. 3.3 on the method's comparison with existing ones; typos fixed; reference added. Matches journal version (JHEP

    Supersymmetric Higgs-portal and X-ray lines

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    We consider a Dirac singlet fermion as thermal dark matter for explaining the X-ray line in the context of a supersymmetric Higgs-portal model or a generalized Dirac NMSSM. The Dirac singlet fermion gets a mass splitting due to their Yukawa couplings to two Higgs doublets and their superpartners, Higgsinos, after electroweak symmetry breaking. We show that a correct relic density can be obtained from thermal freeze-out, due to the co-annihilation with Higgsinos for the same Yukawa couplings. We discuss the phenomenology of the Higgsinos in this model such as displaced vertices at the LHC.Comment: 15 pages, 4 figures, references adde

    YAM2: Yet another library for the M2M_2 variables using sequential quadratic programming

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    The M2M_2 variables are devised to extend MT2M_{T2} by promoting transverse masses to Lorentz-invariant ones and making explicit use of on-shell mass relations. Unlike simple kinematic variables such as the invariant mass of visible particles, where the variable definitions directly provide how to calculate them, the calculation of the M2M_2 variables is undertaken by employing numerical algorithms. Essentially, the calculation of M2M_2 corresponds to solving a constrained minimization problem in mathematical optimization, and various numerical methods exist for the task. We find that the sequential quadratic programming method performs very well for the calculation of M2M_2, and its numerical performance is even better than the method implemented in the existing software package for M2M_2. As a consequence of our study, we have developed and released yet another software library, YAM2, for calculating the M2M_2 variables using several numerical algorithms.Comment: 1+22 pages, 5 figures; matches published version; fixed title page for inspire record; The library is distributed via https://github.com/cbpark/YAM

    Collider probes of singlet fermionic dark matter scenarios for the Fermi gamma-ray excess

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    We investigate the collider signatures of the three benchmark points in the singlet fermionic dark matter model. The benchmark points, which were introduced previously to explain the Fermi gamma-ray excess by dark matter (DM) pair annihilation at the Galactic center, have definite predictions for future collider experiments such as the International Linear Collider and the High-Luminosity LHC. We consider four collider observables: (1) Higgs signal strength (essentially hZZhZZ coupling), (2) triple Higgs coupling, (3) exotic Higgs decay, and (4) direct production of a new scalar particle. The benchmark points are classified by the final states of the DM annihilation process: a pair of bb quarks, SM-like Higgs bosons, and new scalar particles. Each benchmark scenario has detectable new physics signals for the above collider observables that can be well tested in the future lepton and hadron colliders.Comment: 14 pages, 1 figure, 1 tabl

    BB-meson anomalies and Higgs physics in flavored U(1)U(1)' model

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    We consider a simple extension of the Standard Model with flavor-dependent U(1)U(1)', that has been proposed to explain some of BB-meson anomalies recently reported at LHCb. The U(1)U(1)' charge is chosen as a linear combination of anomaly-free B3L3B_3-L_3 and LμLτL_\mu-L_\tau. In this model, the flavor structure in the SM is restricted due to flavor-dependent U(1)U(1)' charges, in particular, quark mixings are induced by a small vacuum expectation value of the extra Higgs doublet. As a result, it is natural to get sizable flavor-violating Yukawa couplings of heavy Higgs bosons involving the bottom quark. In this article, we focus on the phenomenology of the Higgs sector of the model including extra Higgs doublet and singlet scalars. We impose various bounds on the extended Higgs sector from Higgs and electroweak precision data, BB-meson mixings and decays as well as unitarity and stability bounds, then discuss the productions and decays of heavy Higgs bosons at the LHC.Comment: 40 pages, 11 figures, 1 table; v2: references added; v3: accepted version for publication in EPJ

    Resonant Higgs boson pair production in the hhbbˉ  WWbbˉ+ννˉhh\rightarrow b\bar{b} \; WW \rightarrow b\bar{b} \ell^+ \nu \ell^- \bar\nu decay channel

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    Adding a scalar singlet provides one of the simplest extensions of the Standard Model. In this work we briefly review the latest constraints on the mass and mixing of the new Higgs boson and study its production and decay at the LHC. We mainly focus on double Higgs production in the hhbbˉWWbbˉ+ννˉhh \rightarrow b \bar{b} WW \rightarrow b \bar{b} \ell^+ \nu \ell^- \bar{\nu} decay channel. This decay is found to be efficient in a region of masses of the heavy Higgs boson of 260 - 500 GeV, so it is complementary to the 4bb channel, more efficient for Higgs bosons having masses greater than 500 GeV. We analyse this di-leptonic decay channel in detail using kinematic variables such as MT2M_{\rm T2} and the MT2M_{\rm T2}-assisted on-shell reconstruction of invisible momenta. Using proper cuts, a significance of \sim 3σ\sigma for 3000 fb1^{-1} can be achieved at the 14 TeV LHC for mHm_H = 260 - 400 GeV if the mixing is close to its present limit and BR(Hhh)1{\rm BR}(H \rightarrow hh) \approx 1. Smaller mixing values would require combining various decay channels in order to reach a similar significance. The complementarity among Hhh H \rightarrow hh, HZZ H \rightarrow ZZ and HWW H \rightarrow WW channels is studied for arbitrary BR(Hhh){\rm BR}(H \rightarrow hh) values.Comment: 36 pages, 13 figure

    Minimal Flavor Violation with Axion-like Particles

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    We revisit the flavor-changing processes involving an axion-like particle (ALP) in the context of generic ALP effective lagrangian with a discussion of possible UV completions providing the origin of the relevant bare ALP couplings. We focus on the minimal scenario that ALP has flavor-conserving couplings at tree level, and the leading flavor-changing couplings arise from the loops involving the Yukawa couplings of the Standard Model fermions. We note that such radiatively generated flavor-changing ALP couplings can be easily suppressed in field theoretic ALP models with sensible UV completion. We discuss also the implication of our result for string theoretic ALP originating from higher-dimensional pp-form gauge fields, for instance for ALP in large volume string compactification scenario.Comment: 41 pages, 3 figures; v3: a discussion on general extended Higgs sector added in sec. 2, version published in JHE
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