359 research outputs found
Measuring spin and CP from semi-hadronic ZZ decays using jet substructure
We apply novel jet techniques to investigate the spin and CP quantum numbers
of a heavy resonance X, singly produced in pp -> X -> ZZ -> l(+)l(-)jj at the
LHC. We take into account all dominant background processes to show that this
channel, which has been considered unobservable until now, can qualify under
realistic conditions to supplement measurements of the purely leptonic decay
channels X -> ZZ -> 4l. We perform a detailed investigation of spin- and
CP-sensitive angular observables on the fully-simulated final state for various
spin and CP quantum numbers of the state X, tracing how potential sensitivity
communicates through all the steps of a subjet analysis. This allows us to
elaborate on the prospects and limitations of performing such measurements with
the semihadronic final state. We find our analysis particularly sensitive to a
CP-even or CP-odd scalar resonance, while, for tensorial and vectorial
resonances, discriminative features are diminished in the boosted kinematical
regime.Comment: 12 pages, 7 figures, 2 tables, published versio
Getting Stuck: Using Monosignatures to Test Highly Ionizing Particles
In this paper we argue that monojet and monophoton searches can be a
sensitive test of very highly ionizing particles such as particles with charges
and more generally particles that do not reach the outer parts
of the detector. 8 TeV monojet data from the CMS experiment excludes such
objects with masses in the range and charges
. This nicely complements searches for highly ionizing objects at
ALICE, ATLAS, CMS and LHCb. Expected improvements in these channels will extend
the sensitivity range to . This search strategy can
directly be generalized to other particles that strongly interact with the
detector material, such as e.g. magnetic monopoles.Comment: 15 pages, 8 figures, version published in PL
Modified Higgs Sectors and NLO Associated Production
Many beyond the Standard Model (BSM) scenarios involve Higgs couplings to
additional electroweak fields. It is well established that these new fields may
modify Higgs gamma-gamma and gamma-Z decays at one-loop. However, one
unexplored aspect of such scenarios is that by electroweak symmetry one should
also expect modifications to the Higgs Z-Z coupling at one-loop and, more
generally, modifications to Higgs production and decay channels beyond
tree-level. In this paper we investigate the full BSM modified electroweak
corrections to associated Higgs production at both the LHC and a future lepton
collider in two simple SM extensions. From both inclusive and differential NLO
associated production cross sections we find BSM-NLO corrections can be as
large as O(>10%) when compared to the SM expectation, consistent with other
precision electroweak measurements, even in scenarios where modifications to
the Higgs diphoton rate are not significant. At the LHC such corrections are
comparable to the involved QCD uncertainties. At a lepton collider the Higgs
associated production cross section can be measured to high accuracy (O(1%)
independent of uncertainties in total width and other couplings), and such a
deviation could be easily observed even if the new states remain beyond
kinematic reach. This should be compared to the expected accuracy for a
model-independent determination of the Higgs diphoton coupling at a lepton
collider, which is O(15%). This work demonstrates that precision measurements
of the Higgs associated production cross section constitute a powerful probe of
modified Higgs sectors and will be valuable for indirectly exploring BSM
scenarios.Comment: 22 pages, 8 figure
Top quark electroweak couplings at future lepton colliders
We perform a comparative study of the reach of future collider
options for the scale of non-resonant new physics effects in the top quark
sector, phrased in the language of higher-dimensional operators. Our focus is
on the electroweak top quark pair production process , and we study benchmark scenarios at the ILC and CLIC. We find that
both are able to constrain mass scales up to the few TeV range in the most
sensitive cases, improving by orders of magnitude on the forecasted
capabilities of the LHC. We discuss the role played by observables such as
forward-backward asymmetries, and making use of different beam polarisation
settings, and highlight the possibility of lifting a degeneracy in the allowed
parameter space by combining top observables with precision -pole
measurements from LEP1.Comment: v1: 11 pages, 11 figures. v2: References added, Fig. 11 updated.
Matches version published in EPJ
Constraining new resonant physics with top spin polarisation information
We provide a comprehensive analysis of the power of including top
quark-polarisation information to kinematically challenging resonance
searches, for which ATLAS and CMS start losing sensitivity. Following the
general modeling and analysis strategies pursued by the experiments, we analyse
the semi-leptonic and the di-lepton channels and show that including
polarisation information can lead to large improvements in the limit setting
procedures with large data sets. This will allow us to set limits for parameter
choices where sensitivity from is not sufficient. This highlights
the importance of spin observables as part of a more comprehensive set of
observables to gain sensitivity to BSM resonance searches.Comment: 13 pages, 11 figure
Precise predictions for (non-standard) W+photon+jet production
We report on a detailed investigation of the next-to-leading order (NLO) QCD
corrections to +jet production at the Tevatron and the LHC using a
fully-flexible parton-level Monte Carlo program. We include the full leptonic
decay of the , taking into account all off-shell and finite width effects,
as well as non-standard couplings. We find particularly sizable
corrections for the currently allowed parameter range of anomalous couplings
imposed by LEP data. In total the NLO differential distributions reveal a
substantial phase space dependence of the corrections, leaving considerable
sensitivity to anomalous couplings beyond scale uncertainty at large momentum
transfers in the anomalous vertex.Comment: 22 pages, 14 figures, 2 tables, published versio
Ditau jets in Higgs searches
Understanding and identifying ditau jets -- jets consisting of pairs of tau
particles, can be of crucial importance and may even turn out to be a necessity
if the Higgs boson decays dominantly to new light scalars which, on the other
hand, decay to tau pairs. As often seen in various models of BSM such as in the
NMSSM, Higgs portals etc., the lightness of these new states ensures their
large transverse momenta and, as a consequence, the collinearity of their decay
products. We show that the non-standard signatures of these objects, which can
easily be missed by standard analysis techniques, can be superbly exploited in
an analysis based on subjet observables. When combined with additional
selection strategies, this analysis can even facilitate an early discovery of
the Higgs boson. To be specific, a light Higgs can be found with from of data. We combine all these
observables into a single discriminating likelihood that can be employed toward
the construction of a realistic and standalone ditau tagger.Comment: 9 pages, 9 figures. References added, typos corrected, published
versio
A UV Complete Compositeness Scenario: LHC Constraints Meet The Lattice
We investigate a recently proposed UV-complete composite Higgs scenario in
the light of the first LHC runs. The model is based on a gauge group
with global flavour symmetry breaking , giving rise to pseudo
Nambu-Goldstone bosons in addition to the Higgs doublet. This includes a real
and a complex electroweak triplet with exotic electric charges. Including
these, as well as constraints on other exotic states, we show that LHC
measurements are not yet sensitive enough to significantly constrain the
model's low energy constants. The Higgs potential is described by two
parameters which are on the one hand constrained by the LHC measurement of the
Higgs mass and Higgs decay channels and on the other hand can be computed from
correlation functions in the UV-complete theory. Hence to exclude the model at
least one constant needs to be determined and to validate the Higgs potential
both constants need to be reproduced by the UV-theory. Due to its
UV-formulation, a certain number of low energy constants can be computed from
first principle numerical simulations of the theory formulated on a lattice,
which can help in establishing the validity of this model. We assess the
potential impact of lattice calculations for phenomenological studies, as a
preliminary step towards Monte Carlo simulations.Comment: 12 pages, 6 figure
Giving top quark effective operators a boost
We investigate the prospects to systematically improve generic effective
field theory-based searches for new physics in the top sector during LHC run 2
as well as the high luminosity phase. In particular, we assess the benefits of
high momentum transfer final states on top EFT-fit as a function of systematic
uncertainties in comparison with sensitivity expected from fully-resolved
analyses focusing on production. We find that constraints are
typically driven by fully-resolved selections, while boosted top quarks can
serve to break degeneracies in the global fit. This demystifies and clarifies
the importance of high momentum transfer final states for global fits to new
interactions in the top sector from direct measurements.Comment: Published versio
- …