31 research outputs found
Higgs portal to dark matter and decays
We consider a Higgs portal model in which the 125-GeV Higgs boson mixes with a light singlet mediator h coupling to particles of a Dark Sector and study potential b→sh decays in the Belle II experiment. Multiplying the gauge-dependent off-shell Standard-Model b-s-Higgs vertex with the sine of the Higgs mixing angle does not give the correct b-s-h vertex. We clarify this issue by calculating the b-s-h vertex in an arbitrary R gauge and demonstrate how the ξ dependence cancels from physical decay rates involving an on-shell or off-shell h. Then we revisit the b→sh phenomenology and point out that a simultaneous study of B→K∗h and B→Kh helps to discriminate between the Higgs portal and alternative models of the Dark Sector. We further advocate for the use of the h lifetime information contained in displaced-vertex data with h decaying back to Standard-Model particles to better constrain the h mass or to reveal additional h decay modes into long-lived particles
Higgs portal to dark matter and decays
We consider a Higgs portal model in which the 125-GeV Higgs boson mixes with
a light singlet mediator coupling to particles of a Dark Sector and study
potential decays in the Belle II experiment. Multiplying the
gauge-dependent off-shell Standard-Model --Higgs vertex with the sine of
the Higgs mixing angle does not give the correct -- vertex. We
clarify this issue by calculating the -- vertex in an arbitrary
gauge and demonstrate how the dependence cancels from physical
decay rates involving an on-shell or off-shell . Then we revisit the phenomenology and point out that a simultaneous study of
and helps to discriminate between the Higgs portal and alternative
models of the Dark Sector. We further advocate for the use of the
lifetime information contained in displaced-vertex data with decaying
back to Standard-Model particles to better constrain the mass or to
reveal additional decay modes into long-lived particles.Comment: 9 pages, 4 figures. v.2: minor clarifications, added Table 1, added
references, acknowledgements extende
Flavorful leptoquarks at the LHC and beyond: Spin 1
Evidence for electron-muon universality violation that has been revealed in
transitions in the observables by the LHCb
Collaboration can be explained with spin-1 leptoquarks in singlet
or triplet representations in the TeV range. We
explore the sensitivity of the high luminosity LHC (HL-LHC) and future
proton-proton colliders to and in the parameter space connected to
-data. We consider pair production and single production in
association with muons in different flavor benchmarks. Reinterpreting a recent
ATLAS search for scalar leptoquarks decaying to and , we extract
improved limits for the leptoquark masses: For gauge boson-type leptoquarks
() we obtain TeV, TeV, and TeV for leptoquarks decaying predominantly according to hierarchical,
flipped and democratic quark flavor structure, respectively. Future sensitivity
projections based on extrapolations of existing ATLAS and CMS searches are
worked out. We find that for the mass reach for pair (single)
production of can be up to 3 TeV (2.1 TeV) at the HL-LHC and up to 15 TeV
(19.9 TeV) at the FCC-hh with TeV and 20 \, \mbox{ab}^{-1}.
The mass limits and reach for the triplet are similar or higher,
depending on flavor. While there is the exciting possibility that leptoquarks
addressing the -anomalies are observed at the LHC, to fully cover
the parameter space -collisions beyond the LHC-energies are needed.Comment: 16 pages, 8 figures; v2: Clarifying comments, four plots and few
references added. Few typos corrected. Conclusions unchange
Higgs boson decay into a lepton pair and a photon: A roadmap to the discovery of H →zγ and probes of new physics
The decay H→ℓℓγ, ℓ=e, μ receives contributions from H→Z[→ℓℓ]γ and a nonresonant contribution, both of which are loop induced. We describe how one can separate these subprocesses in a gauge-independent way, define the decay rate Γ(H→Zγ), and extract the latter from differential H→ℓℓγ branching ratios. For ℓ=μ, also the tree decay rate, which is driven by the muon Yukawa coupling, is important. We propose kinematic cuts optimized to separate the three contributions, paving the way to the milestone (i) discovery of H→Zγ, (ii) discovery of H→μμγ| , and (iii) quantification of new physics in both the effective H−Z−γ and nonresonant H−ℓℓ−γ couplings
Addendum to "Impact of polarization observables and on new physics explanations of the anomaly"
In this addendum to arXiv:1811.09603 we update our results including the
recent measurement of and by the Belle
collaboration: and , resulting in the new HFLAV fit
result , , exhibiting a tension with the
Standard Model. We present the new fit results and update all figures,
including the relevant new collider constraints. The updated prediction for
from our sum rule reads . We also comment on theoretical predictions for the fragmentation
function of and their implication on the constraint from
data.Comment: 9 pages, 7 figures. v2: references added, matches PRD versio
Revisiting lifetimes of doubly charmed baryons
We present updated predictions for lifetimes of doubly charmed baryons,
within the heavy quark expansion, including available NLO
contributions and newly-computed terms in the series. Our improved
results confirm the expected hierarchy while the predicted lifetime
is
consistent with the recent LHCb determination. We provide predictions for the
lifetime ratios of the and baryons relative to
the baryon, namely
and
.Comment: 25 pages, 2 figures; v2: few clarifications added, one reference
added, matches version accepted for publicatio
Impact of polarization observables and on new physics explanations of the anomaly
The combined analysis of the BaBar, Belle, and LHCb data on ,
and decay observables shows evidence
of physics beyond the Standard Model (SM). In this article, we study all the
one- and two-dimensional scenarios which can be generated by adding a single
new particle to the SM. We put special emphasis on the model-discriminating
power of and of the polarizations, and especially on the
constraint from the branching fraction . We critically
review this constraint and do not support the aggressive limit of used in some analyses. While the impact of
is currently still limited, the constraint has a
significant impact: depending on whether one uses a limit of , or
, the pull for new physics (NP) in scalar operators changes drastically.
More specifically, for a conservative limit a scenario with scalar
operators gives the best fit to data, while for an aggressive limit this
scenario is strongly disfavored and the best fit is obtained in a scenario in
which only a left-handed vector operator is generated. We find a sum rule for
the branching ratios of , and which holds for any NP contribution to the Wilson
coefficients. This sum rule entails an enhancement of over its SM prediction by for the current
data.Comment: 16 pages, 6 figures; v2: clarifying comments and few references
added, matches version published in PRD; v3: typo corrected in eq. (28).
Updated results based on the HFLAV average for spring 2019 are available in
arXiv:1905.0825