We show that ultra-peripheral heavy-ion collisions at the LHC can be used to search for axionlike particles with mass below 100 GeV. The Z 4 enhanced photon-photon luminosity from the ions provides a large exclusive production rate, with a signature of a resonant pair of back-to-back photons and no other activity in the detector. In addition, we present both new and updated limits from recasting multi-photon searches at LEP II and the LHC, which are more stringent than those currently in the literature for the mass range 100 MeV to 100 GeV.

The discovery of the Higgs boson opens the door to new physics interacting via the Higgs Portal, including motivated scenarios relating to baryogenesis, dark matter, and electroweak naturalness. We systematically explore the collider signatures of singlet scalars produced via the Higgs Portal at the 14 TeV LHC and a prospective 100 TeV hadron collider. We focus on the challenging regime where the scalars are too heavy to be produced in the decays of an on-shell Higgs boson, and instead are produced primarily via an off-shell Higgs. Assuming these scalars escape the detector, promising channels include missing energy in association with vector boson fusion, monojets, and top pairs. We forecast the sensitivity of searches in these channels at √ s = 14 & 100 TeV and compare collider reach to the motivated parameter space of singlet-assisted electroweak baryogenesis, Higgs Portal dark matter, and neutral naturalness.ArXiv ePrint: 14xx.xxxx

Over the past decade, a large number of jet substructure observables have been proposed in the literature, and explored at the LHC experiments. Such observables attempt to utilize the internal structure of jets in order to distinguish those initiated by quarks, gluons, or by boosted heavy objects, such as top quarks and W bosons. This report, originating from and motivated by the BOOST2013 workshop, presents original particle-level studies that aim to improve our understanding of the relationships between jet substructure observables, their complementarity, and their dependence on the underlying jet properties, particularly the jet radius and jet transverse momentum. This is explored in the context of quark/gluon discrimination, boosted W boson tagging and boosted top quark tagging.

The dark matter may be a composite particle that is accessible via a weakly coupled portal. If these hidden-sector states are produced at the Large Hadron Collider (LHC), they would undergo a QCD-like shower. This would result in a spray of stable invisible dark matter along with unstable states that decay back to the Standard Model. Such "semi-visible" jets arise, for example, when their production and decay are driven by a leptophobic Z resonance; the resulting signature is characterized by significant missing energy aligned along the direction of one of the jets. These events are vetoed by the current suite of searches employed by the LHC, resulting in low acceptance. This Letter will demonstrate that the transverse mass-computed using the final-state jets and the missing energy-provides a powerful discriminator between the signal and the QCD background. Assuming that the Z couples to the Standard Model quarks with the same strength as the Z 0 , the proposed search can discover (exclude) Z masses up to 2.5 TeV (3.5 TeV) with 100 fb −1 of 14 TeV data at the LHC.The existence of dark matter provides one of the strongest motivations for physics beyond the Standard Model, and its discovery is one of the core missions for the Large Hadron Collider (LHC) program. Under the assumption that the dark-matter particle is neutral and stable, it escapes the detector and manifests as missing transverse energy ( E T ). The LHC collaborations have developed a comprehensive search strategy to look for signals with significant E T , accompanied by jets and/or leptons (see, e.g.[1] for a review). These searches are typically cast in terms of a Simplified Model [2] for supersymmetry or an effective theory of dark-matter interactions [3,4]. Yet if one relaxes the assumption that the dark sector is weakly coupled, a new class of dark-matter signatures emerge that evade this entire suite of analyses. Namely, it is possible that the dark matter has been lurking undercover within hadronic jets. The purpose of this Letter is to propose a straightforward discovery strategy for these "semi-visible" jets.Semi-visible jets may occur if the dark matter is the stable (or meta-stable) remnant of a more complicated dark sector. The dynamics of non-trivial dark sectors have been explored in many contexts, e.g. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In these models, the dark sector contains a dark-matter candidate(s) and possibly new force carriers and/or matter fields. Note that we are agnostic about how much of the cosmological relic density is accounted for by this dark-matter candidate. Messenger states that couple the dark sector to the Standard Model (SM) can exist. If the messenger is accessible at colliders, dark-sector states can be produced, leading to unique signatures such as large particle multiplicities, displaced vertices, multiple resonances, and lepton or photon jets [20][21][22][23][24][25][26][27][28][29][30][31][32][33].Another possibility is that the final state resulting from strongly coupled hidden secto...