Search for pairs of scalar leptoquarks decaying into quarks and electrons or muons in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector

Precision measurements of the Higgs couplings are, for the first time, directly probing the mechanism of fermion mass generation. The purpose of this work is to determine to what extent these measurements can distinguish between the tree-level mechanism of the Standard Model and the theoretically motivated alternative of radiative mass generation. Focusing on the third-family, we classify the minimal one-loop models and find that they fall into two general classes. By exploring several benchmark models in detail, we demonstrate that a radiative origin for the tau-lepton and bottom-quark masses is consistent with current observations. While future colliders will not be able to rule out a radiative origin, they can probe interesting regions of parameter space.

Section: Jhep04(2021)151mentioning

confidence: 99%

Has the origin of the third-family fermion masses been determined?

Baker

Cox

Volkas

2021

“…[29,72]), whereas our charged leptoquark decays only to second-family leptons. The most up-to-date constraints in muonic decay channels come from searches by ATLAS [70] for pair-produced scalar leptoquarks decaying into two muons plus two or more jets, which we use here.…”

Section: Leptoquark Pair Production At the Lhcmentioning

confidence: 99%

“…In ref. [70], limits on the S 3 mass are computed for each channel, in each case assuming that the leptoquark decays exclusively into one specific combination of quark flavour and lepton flavour. For our model this is not generically the case, but in the region of parameter space where α 3 α 1,2 , the S .…”

Section: Leptoquark Pair Production At the Lhcmentioning

confidence: 99%

“…Constraints on the ratio α 2 /α 3 vs. the leptoquark mass, with ∆C µ 9 = −∆C µ 10 everywhere fixed to the central value of the global fit[12] to B anomaly data. The brown hatched region (M S3 ≤ 1.7 TeV) is excluded by ATLAS direct searches[70]. The constraint from B s meson mixing is not visible on the plot, since at the best fit point for the anomalies it only imposes an upper bound of M S3 ≤ 55 TeV.…”

mentioning

confidence: 99%

“…to bµ + , and the ATLAS limit is M S 4qµ + , where q is a light quark (d or s), for which the limit is again M S 4/TeV[70]…”

mentioning

confidence: 99%

See 2 more Smart Citations

Anomalies and accidental symmetries: charging the scalar leptoquark under Lμ − Lτ

Davighi

Kirk

Nardecchia

2020

While the S3 scalar leptoquark presents a possible tree-level explanation of the b → sℓℓ flavour anomalies, it suffers from two conceptual problems which are often disregarded by model-builders. Firstly, the quantum numbers of the S3 allow for a renormalisable diquark operator that would trigger rapid proton decay unless its coupling were tuned away. Secondly, one expects the leptoquark to have generic couplings to leptons, which require tuning to avoid stringent experimental bounds on lepton flavour violation. By gauging a U(1) current that acts as Lμ− Lτ on the Standard Model (SM) fermions, and under which the leptoquark has charge −1, one can remedy both these problems. The additional U(1), which is spontaneously broken at some high scale, is associated with a massive Z′ gauge boson and a scalar SM singlet Φ, which play no direct role in mediating the anomalous B meson decays. By computing one- and two-loop mass corrections, we show that this pair of particles can be hidden away at much higher mass scales without destabilising either the Higgs or the leptoquark masses. The only low-energy relic of gauging Lμ− Lτ is thus the accidental global symmetry structure of the lagrangian. On the other hand, we find quite generally that an S3 leptoquark that mediates the b → sℓℓ anomalies cannot be much heavier than a few TeV without itself inducing large Higgs mass corrections.

Long-lived heavy neutral leptons at the LHC: four-fermion single-NR operators

Beltrán

Cottin

Helo

et al. 2022

Interest in searches for heavy neutral leptons (HNLs) at the LHC has increased considerably in the past few years. In the minimal scenario, HNLs are produced and decay via their mixing with active neutrinos in the Standard Model (SM) spectrum. However, many SM extensions with HNLs have been discussed in the literature, which sometimes change expectations for LHC sensitivities drastically. In the NRSMEFT, one extends the SM effective field theory with operators including SM singlet fermions, which allows to study HNL phenomenology in a “model independent” way. In this paper, we study the sensitivity of ATLAS to HNLs in the NRSMEFT for four-fermion operators with a single HNL. These operators might dominate both production and decay of HNLs, and we find that new physics scales in excess of 20 TeV could be probed at the high-luminosity LHC.