15 research outputs found

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### Jet sampling: improving event reconstruction through multiple interpretations

The classification of events involving jets as signal-like or background-like can depend strongly on the jet algorithm used and its parameters. This is partly due to the fact that standard jet algorithms yield a single partition of the particles in an event into jets, even if no particular choice stands out from the others. As an alternative, we propose that one should consider multiple interpretations of each event, generalizing the Qjets procedure to event-level analysis. With multiple interpretations, an event is no longer restricted to either satisfy cuts or not satisfy them – it can be assigned a weight between 0 and 1 based on how well it satisfies the cuts. These cut-weights can then be used to improve the discrimination power of an analysis or reduce the uncertainty on mass or cross-section measurements. For example, using this approach on a Higgs plus Z boson sample, with H → b ¯b we find an 28% improvement in significance can be realized at the 8 TeV LHC. Through a number of other examples, we show various ways in which having multiple interpretations can be useful on the event level.Physic

### Probing Colored Particles with Photons, Leptons, and Jets

If pairs of new colored particles are produced at the Large Hadron Collider,
determining their quantum numbers, and even discovering them, can be
non-trivial. We suggest that valuable information can be obtained by measuring
the resonant signals of their near-threshold QCD bound states. If the particles
are charged, the resulting signatures include photons and leptons and are
sufficiently rich for unambiguously determining their various quantum numbers,
including the charge, color representation and spin, and obtaining a precise
mass measurement. These signals provide well-motivated benchmark models for
resonance searches in the dijet, photon+jet, diphoton and dilepton channels.
While these measurements require that the lifetime of the new particles be not
too short, the resulting limits, unlike those from direct searches for pair
production above threshold, do not depend on the particles' decay modes. These
limits may be competitive with more direct searches if the particles decay in
an obscure way.Comment: 39 pages, 9 figures; v2: more recent searches include

### LHC Coverage of RPV MSSM with Light Stops

We examine the sensitivity of recent LHC searches to signatures of
supersymmetry with R-parity violation (RPV). Motivated by naturalness of the
Higgs potential, which would favor light third-generation squarks, and the
stringent LHC bounds on spectra in which the gluino or first and second
generation squarks are light, we focus on scenarios dominated by the pair
production of light stops. We consider the various possible direct and cascade
decays of the stop that involve the trilinear RPV operators. We find that in
many cases, the existing searches exclude stops in the natural mass range and
beyond. However, typically there is little or no sensitivity to cases dominated
by UDD operators or LQD operators involving taus. We propose several ideas for
searches which could address the existing gaps in experimental coverage of
these signals.Comment: 41 pages, 12 figures; v2: included new searches (see footnote 10),
minor corrections and improvement

### Interpreting a 750 GeV diphoton resonance

We discuss the implications of the significant excesses in the diphoton final
state observed by the LHC experiments ATLAS and CMS around a diphoton invariant
mass of 750 GeV. The interpretation of the excess as a spin-zero s-channel resonance implies
model-independent lower bounds on both its branching ratio and its coupling to photons,
which stringently constrain dynamical models. We consider both the case where the
excess is described by a narrow and a broad resonance. We also obtain model-independent
constraints on the allowed couplings and branching fractions to final states other than
diphotons, by including the interplay with 8 TeV searches. These results can guide attempts
to construct viable dynamical models of the resonance. Turning to specific models,
our findings suggest that the anomaly cannot be accounted for by the presence of only an
additional singlet or doublet spin-zero field and the Standard Model degrees of freedom; this
includes all two-Higgs-doublet models. Likewise, heavy scalars in the MSSM cannot explain
the excess if stability of the electroweak vacuum is required, at least in a leading-order analysis.
If we assume that the resonance is broad we find that it is challenging to find a weakly
coupled explanation. However, we provide an existence proof in the form of a model with
vectorlike quarks with large electric charge that is perturbative up to the 100 TeV scale.
For the narrow-resonance case a similar model can be perturbative up to high scales also
with smaller charges. We also find that, in their simplest form, dilaton models cannot
explain the size of the excess. Some implications for flavor physics are briefly discussed

### Gluino-Squark Production at the LHC: The Threshold

An analysis of the cross section for hadronic production of gluino-squark
pairs close to threshold is presented. Within the framework of non-relativistic
QCD a significant enhancement compared to fixed order perturbation theory is
observed which originates from the characteristic remnants of the gluino-squark
resonances below the nominal pair threshold. The analysis includes all colour
configurations of S-wave gluino-squark pairs, i.e. triplet, sextet and 15
representation. Matching coefficients at leading order are separately evaluated
for all colour configurations. The dominant QCD corrections, arising from
initial- and final-state radiation are included. The non-relativistic dynamics
of the gluino pair is solved by calculating the Green's function in
Next-to-Leading Order (NLO). The results are applied to benchmark scenarios,
based on Snowmass Points and Slopes (SPS). As a consequence of the large decay
rate of at least one of the constituents squark or gluino annihilation decays
of the bound state (\tilde{g}\tilde{q})\rightarrow gq, q\gamma, qZ or q'W^{\pm}
are irrelevant. Thus the signatures of gluino-quark production below and above
the nominal threshold are identical. Numerical results for the cross section at
the Large Hadron Collider (LHC) at \sqrt{s}=7 TeV and 14 TeV are presented. The
enhancement of the total cross section through final state interaction amounts
to roughly 3%.Comment: 25 pages, 9 figures, Eq. 10 modified. Reference [30] added.
Discussion of the expected quality of the approximation added before eq. 23.
Some changes in notation. Typos correcte