5,718 research outputs found
Profile of multiboson signals
We investigate the visibility of signals characterised by wide bumps over a
smoothly falling background that cannot be accurately predicted by Monte Carlo
calculations. Examples of such are the wide bumps that triboson and quadriboson
resonance cascade decays would yield in diboson resonance searches in fully
hadronic final states. We find that the sensitivity to triboson bumps is rather
small: signals of a moderate size could be present in current data and yet
remain unnoticed. For quadriboson cascade decays the signals can hardly be
distinguished from the background in the current searches.Comment: LaTeX 17 pages. v2: fixed typos and comments added; journal versio
Ultraboosted and production at the HL-LHC and FCC-hh
Searches for anomalous and production provide an excellent
probe of flavour-changing top interactions when the energies considered are
very large. In this note we estimate the sensitivity to these interactions at
the high luminosity phase of the LHC and a future 100 TeV collider
(FCC-hh). For the LHC, the expected limits on branching
ratios from and production will reach the level, one
order of magnitude better than the existing projections for from production. For the FCC-hh, the limits on could
reach an impressive sensitivity at the level, with limits on at the level.Comment: LaTeX 11 pages. Plots fixed, journal versio
Running bumps from stealth bosons
For the "stealth bosons" , light boosted particles with a decay into four quarks and reconstructed as a single fat jet,
the groomed jet mass has a strong correlation with groomed jet substructure
variables. Consequently, the jet mass distribution is strongly affected by the
jet substructure selection cuts when applied on the groomed jet. We illustrate
this fact by recasting a CMS search for low-mass dijet resonances and show a
few representative examples. The mass distributions exhibit narrow and wide
bumps at several locations in the 100 - 300 GeV range, between the masses of
the daughter particles and the parent particle , depending on the jet
substructure selection. This striking observation introduces several caveats
when interpreting and comparing experimental results, for the case of
non-standard signatures. The possibility that a single boosted particle
decaying hadronically produces multiple bumps, at quite different jet masses,
and depending on the event selection, brings the game of anomaly chasing to the
next level.Comment: LaTeX 21 pages. Added one appendix and some plots. Journal versio
Zt, gamma t and t production at hadron colliders via strong flavour-changing neutral couplings
We consider gq -> Zt, gq -> gamma t and gq -> t production (q=u,c) mediated
by strong flavour-changing neutral interactions within an effective operator
framework. We provide total cross sections for Tevatron and LHC, showing
explicitly that the six processes can be described in full generality in terms
of only two parameters (anomalous couplings) for q=u plus two for q=c. In our
work we take into account and study in detail the effects of top quark decay.
For gamma t, the inclusion of the top quark decay in the matrix element reveals
an striking result: the largest contribution to the final state, e.g. gamma l
nu b, with l = e, mu, tau, does not result from gq -> gamma t -> gamma l nu b
but from on-shell gq -> t production with t -> gamma l nu b, being the photon
radiated off the top decay products. This contribution, missed in previous
literature, increases the signal cross sections by factors ranging between 3
and 6.5.Comment: LaTeX 19 pages, 23 PS figures. Typos corrected in text and equations.
Final version to appear in NPB
Pair production of heavy Q=2/3 singlets at LHC
We examine the LHC discovery potential for new Q=2/3 quark singlets T in the
process gg,qq -> T Tbar -> W+ b W- bbar, with one W boson decaying hadronically
and the other one leptonically. A particle-level simulation of this signal and
its main backgrounds is performed, showing that heavy quarks with masses of 500
GeV or lighter can be discovered at the 5 sigma level after a few months of
running, when an integrated luminosity of 3 fb^-1 is collected. With a
luminosity of 100 fb^-1, this process can signal the presence of heavy quarks
with masses up to approximately 1 TeV. Finally, we discuss the complementarity
among T Tbar, Tj production and indirect constraints from precise electroweak
data in order to discover a new quark or set bounds on its mass.Comment: LaTeX 18 pages, 15 figures. Comments and a reference added. To be
published in PL
Portrait of a colour octet
New colour octets stand out among the new physics proposals to explain the
anomalous forward-backward asymmetry measured in production by the
CDF experiment at the Tevatron. We perform a fit to observables at
the Tevatron and the LHC, including total cross sections, various asymmetries
and the top polarisation and spin correlations, to find the most likely
parameters of a light colour octet to be consistent with data. In particular,
an octet coupling only to right-handed quarks gives a good fit to all
measurements. The implications from the general fit are drawn in terms of
predictions for top polarisation observables whose measurements are yet not
very precise, and observables which simply have not been measured.Comment: LATeX 17 pages. Added a fit for a heavy octet. Final version to
appear in JHE
- …