24,855 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
New signals in pair production of heavy Q=2/3 singlets at LHC
New quark singlets T can be produced in pairs at LHC through standard QCD
interactions, with a large cross section for masses of several hundreds of GeV.
Their charged current decays T Tbar T -> W+ b W- bbar, with semileptonic decay
of the W pair, give a final state l nu bb jj$, as in top pair production. The
mixed decay modes T Tbar -> W+ b H tbar, H t W- bbar -> W+ b W- bbar H, T Tbar
-> W+ b Z tbar, Z t W- bbar -> W+ b W- bbar Z, with H,Z -> jj, yield two more
jets, l nu bb jjjj, or the same state in the latter case for Z -> nu nubar. We
extend previous work examining in detail the extra H and Z contributions and
stressing one of the salient features of the T Tbar -> W+ b W- bbar signal: the
presence of a very energetic charged lepton. We finally compare with the
discovery potential in l nu bbbb jj final states, with four b tags.Comment: LaTeX, 10 pages, 11 PS figures, uses PoS.cls. Contribution to the
International Workshop on Top Quark Physics, January 12-15, 2006, Coimbra,
Portugal. To appear in the proceeding
Effective operators in top physics
Top interactions beyond the Standard Model can be conveniently described in
the framework of gauge-invariant effective operators. We briefly review the
general form of the fermion-fermion-gauge boson and fermion-fermion-Higgs
interactions arising from dimension-6 operators, focusing on the top quark. We
discuss in detail an expansion in powers of 1/Lambda^2, where Lambda is the new
physics scale, to consistently calculate observables in terms of top anomalous
couplings.Comment: LaTeX 4 pages, 2 PS figures. Presented at ICHEP 2010, Paris, France,
July 22-28, 2010, to appear in the proceeding
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
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