69 research outputs found

### Mass Measurement in Boosted Decay Chains with Missing Energy

We explore a novel method of mass reconstruction in events with missing
transverse momentum at hadron colliders. In events with sizeable boost factors
in the final steps of dual multi-stage decay chains, the missing energy
particles may each be approximately collinear with a visible standard model
particle, spanning a narrow "MET-cone." We exploit this collinear
approximation, when applicable, to reconstruct the masses of exotica.Comment: 5 pages, 5 figures, v2: typos fixed, references added, figures
aesthetically improve

### A Perturbative RS I Cosmological Phase Transition

We identify a class of Randall-Sundrum type models with a successful first
order cosmological phase transition during which a 5D dual of approximate
conformal symmetry is spontaneously broken. Our focus is on soft-wall models
that naturally realize a light radion/dilaton and suppressed dynamical
contribution to the cosmological constant. We discuss phenomenology of the
phase transition after developing a theoretical and numerical analysis of these
models both at zero and finite temperature. We demonstrate a model with a
TeV-Planck hierarchy and with a successful cosmological phase transition where
the UV value of the curvature corresponds, via AdS/CFT, to an $N$ of $20$,
where 5D gravity is expected to be firmly in the perturbative regime.Comment: 34pp, 12 figure

### The Minimal Model of a Diphoton Resonance: Production without Gluon Couplings

We consider the phenomenology of a resonance that couples to photons but not
gluons, and estimate its production rate at the LHC from photon-photon fusion
in elastic pp scattering using the effective photon and narrow width
approximations. The rate is sensitive only to the mass, the spin, the total
width of the resonance, and its branching fraction to photons. Production cross
sections of 5-10 fb at 13 TeV can be easily accommodated for a 750 GeV
resonance with partial photon width of 15 GeV. This provides the minimal
explanation of the reported diphoton anomaly in the early LHC Run II data.Comment: 8 pages, 3 figures, missing figure supplied, typos corrected,
references added, conclusions essentially unchange

### Radion Phenomenology in Realistic Warped Space Models

We investigate the phenomenology of the Randall-Sundrum radion in realistic
models of electroweak symmetry breaking with bulk gauge and fermion fields,
since the radion may turn out to be the lightest particle in such models. We
calculate the coupling of the radion in such scenarios to bulk fermion and
gauge modes. Special attention needs to be devoted to the coupling to massless
gauge fields (photon, gluon), since it is well known that loop effects may be
important for these fields. We also present a detailed explanation of these
couplings from the CFT interpretation. We then use these couplings to determine
the radion branching fractions and discuss some of the discovery potential of
the LHC for the radion. We find that the gamma-gamma signal is enhanced over
most of the range of the radion mass over the gamma-gamma signal of a SM Higgs,
as long as the RS scale is sufficiently low. However, the signal significance
depends strongly on free parameters that characterize the magnitude of bare
brane-localized kinetic terms for the massless gauge fields. In the absence of
such terms, the signal can be be enhanced over the traditional RS1 models
(where all standard model fields are localized on the IR brane), but the signal
can also be reduced compared to RS1 if the brane localized terms are sizeable.
We also show that for larger radion masses, where the gamma-gamma signal is no
longer significant, one can use the usual 4 lepton signal to discover the
radion.Comment: 28 pages, 7 figure

### Gluon vs. Photon Production of a 750 GeV Diphoton Resonance

The production mechanism of a 750 GeV diphoton resonance, either via gluon or
photon fusion, can be probed by studying kinematic observables in the diphoton
events. We perform a detector study of the two production modes of a
hypothetical scalar or tensor diphoton resonance in order to characterize the
features of the two scenarios. The nature of the resonance production can be
determined from the jet multiplicity, the jet and diphoton rapidities, the rate
of central pseudorapidity gaps, or the possible detection of forward protons
from elastic photoproduction for events in the signal region. Kinematic
distributions for both signals and expected irreducible diphoton background
events are provided for comparison along with a study of observables useful for
distinguishing the two scenarios at an integrated luminosity of 20 fb$^{-1}$.
We find that decay photons from a 750 GeV scalar resonance have a preference
for acceptance in the central detector barrel, while background events are more
likely to give accepted photons in the detector end caps. This disfavors the
interpretation of the large number of excess events found by the the Run-2 CMS
diphoton search with one photon detected in the end cap as a wide spin-0
resonance signal. However, one expects more end cap photons in the case of
spin-2 resonance.Comment: 14 pages, 15 figure

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