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Stephan Lammel
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The present status of searches for the Higgs boson(s) and new phenomena is reviewed. The focus is on analyses and results from the current runs of the HERA and Tevatron experiments. The LEP experiments have released their final combined MSSM Higgs results for this conference. Also included are results from sensitivity studies of the LHC experiments and lepton flavour violating searches from the B factories, KEKB and PEP-II.
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A model-independent search for deviations from the Standard Model prediction is performed in $e^+ p$ and $e^- p$ collisions at HERA II using all high energy data recorded by the H1 experiment. This corresponds to a total integrated luminosity of 337 pb$^{-1}$. All event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is used to search for deviations from the Standard Model in distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. The most siginificant deviation is found in the mujnp channel in $e^+p$ collisions.
SHiP is a newly proposed fixed-target experiment at the CERN SPS with the aim of searching for hidden particles that interact very weakly with SM particles. The work presented in this document investigates SHiPs physics reach in the parameter space of the Neutrino Minimal Standard Model ($ u$MSM), which is a theory that could solve most problems left open by the Standard Model with sterile neutrinos. A model introducing an extra $U(1)$ symmetry in the hidden sector, providing a natural candidate for dark matter, is also explored. This work shows that the SHiP experiment can improve by several orders of magnitude the sensitivity to Heavy Neutral Leptons below 2 GeV, scanning a large part of the parameter space below the $B$ meson mass. The remainder of the $ u$MSM parameter space, dominated by right-handed neutrinos with masses above 2 GeV, can be explored at a future $e^+e^-$ collider. Similarly, SHiP can greatly improve present constraints on $U(1)$ dark photons.
Multiple astrophysical and cosmological observations show that the majority of the matter in the universe is non-luminous. It is not made of known particles, and it is called dark matter. This is one of the few pieces of concrete experimental evidence of new physics beyond the Standard Model. Despite decades of effort, we still know very little about the identity of dark matter; it remains one of the biggest outstanding mysteries facing particle physics. Among the numerous proposals to explain its nature, the Weakly Interacting Massive Particle (WIMP) scenario stands out. The WIMP scenario is based on a simple assumption that dark matter is in thermal equilibrium in the early hot universe, and that the dark matter particles have mass and interactions not too different from the massive particles in the Standard Model. Testing the WIMP hypothesis is a focus for many experimental searches. A variety of techniques are employed including the observation of WIMP annihilation, the measurement of WIMP-nucleon scattering in terrestrial detectors, and the inference of WIMP production at high energy colliders. In this article, we will focus on the last approach, and in particular on WIMP dark matter searches at the Large Hadron Collider. Authors note: this paper (and references therein) correspond to the version that was submitted to the joint issue of Nature Physics and Nature Astronomy in January 2017.
Dark Matter (DM) detection prospects at future e+e- colliders are reviewed under the assumption that DM particles are fermions of the Majorana or Dirac type. Although the discussion is quite general, one will keep in mind the recently proposed candidate based on an excess of energetic photons observed in the center of our Galaxy with the Fermi-LAT satellite. If one assume that DM couples to a Zprime, using radiative return events e+e-->XX+photon, one could observe a spectacular signal at a TeV e+e- collider. This result relies on the ability of using highly polarized beams to eliminate a large part of the W exchange background. Prospects of discovery at LHC using mono-jets are also discussed and appear promising. In the second part, one assumes that DM particles annihilate through Higgs particles, either the SM boson h or MSSM type bosons called H, A. A promising scenario emerges, where one has e+e-->HA, with H decaying into hh, while A decays invisibly in most of the cases.
Results of recent Higgs boson and beyond standard model searches in CMS performed with datasets of 1.0 - 1.7 fb-1 will be summarized in this proceeding contributed to the 41st International Symposium on Multiparticle Dynamics (ISMD2011).
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