![]() High-granularity electromagnetic (|η| < 3.2) and hadronic (|η| < 4.9) sampling calorimeters provide precision energy and direction measurement of electrons, photons, isolated hadrons and jets. It is surrounded by the superconducting solenoid that provides a 2 T axial magnetic field. Closest to the beam pipe is the inner tracking detector covering the pseudorapidity 1 range |η| < 2.5. It consists of several sub-detectors that play different roles. The ATLAS DetectorĪTLAS is a multi-purpose particle detector at the LHC with a forward-backward symmetry and nearly 4π coverage in the solid angle. The ATLAS Detector and Object Selection 2.1. The latest ATLAS results on LFV decays of Z, Higgs bosons and searches for other bosons decaying via LFV processes are summarized in sections 3, 4, and 5, respectively. First, the ATLAS detector and object selection common to below analyses are briefly described (section 2). Despite the large number of aforementioned models predicting the existence of LFV processes, the ATLAS searches presented in this review are performed as much as possible in a model-independent way, in order to be sensitive to any type of new physics phenomena giving rise to LFV processes. This paper summarizes the searches for LFV decays performed with the ATLAS detector using pp collision data collected at the center-of-mass energy of 13 TeV. Recently, new models have proposed LFV decays of the Higgs or heavier bosons as a necessary ingredient to explain the flavor anomalies observed by LHCb. The addition of an extra U(1) gauge symmetry to the SM results in a massive neutral Z′ boson that could also decay through LFV processes. Other models with more than one Higgs doublet, composite Higgs or warped extra dimension models predict LFV decays of the Higgs boson, too. This feature opens the possibility of detecting indirectly scenarios with very high m SUSY via LFV Higgs boson decays. In particular Minimal Supersymmetric SM scenarios with very high energy scale of the SUSY particle masses m SUSY present a non-decoupling behavior of the Higgs boson partial widths in two leptons of different flavor, with respect to m SUSY. For instance, LFV decays of the Z boson are predicted by models with heavy neutrinos, extended gauge models and supersymmetry (SUSY), which also allows for LFV decays of the Higgs boson. ![]() A possible sign of such processes would be the lepton-flavor-violation (LFV) in decays of heavy bosons, such as well-established Z and Higgs bosons or even not-yet-discovered bosons ( Z′, additional Higgs bosons, etc).ĭirect LFV processes are forbidden in the SM but are allowed in its many extensions. This result achieves an unprecedented precision which is particularly promising coming from a hadron collider.The search for processes beyond the Standard Model (SM) is one of the goals of the physics programme at the Large Hadron Collider (LHC) at CERN. The measurement is performed with a novel technique using di-leptonic $t\bar ]$ which is in good agreement with the Standard Model expectation of unity. Such a test is summarised here, that compares the decay rates of $W$ bosons to either tau-leptons or muons, using $R(\tau/\mu)= B(W\to\tau\nu)/B(W\to\mu\nu)$. This fundamental assumption is known as Lepton Flavour Universality (LFU) and can be tested by comparing the measured decay rates, or branching fractions ($B$), of (semi-)leptonic processes that differ only by lepton flavour. It assumes that, in the massless limit, the weak interactions of leptons are identical. The Standard Model of particle physics is our current best understanding of physics at the smallest scales.
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