Search For High Mass Z Gamma Resonances At Sqrts

A search for massive resonances decaying to a Z boson and a photon is performed in events with a hadronically decaying Z boson candidate, separately in light-quark and b quark decay modes, identified using jet substructure and advanced b tagging techniques. Results are based on samples of proton-proton collisions collected with the CMS detector at the LHC at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 2.7 inverse femtobarns, respectively. The results of the search are combined with those of a similar search in the leptonic decay modes of the Z boson, based on the same data sets. Spin-0 resonances with various widths and with masses in a range between 0.2 and 3.0 TeV are considered. No significant excess is observed either in the individual analyses or the combination. The results are presented in terms of upper limits on the production cross section of such resonances and constitute the most stringent limits to date for a wide range of masses.

A search for dark matter is performed using events with large missing transverse momentum and a Higgs boson decaying either to a pair of bottom quarks or to a pair of photons. The data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 2.3 inverse-femtobarns. Results are interpreted in the context of a Z'-two-Higgs-doublet model, where a high-mass resonance Z' decays into a pseudoscalar boson A and a CP-even scalar Higgs boson, and the A decays to a pair of dark matter particles. No significant excesses are observed over the background prediction. Combining results from the two decay channels yields exclusion limits in the signal cross section in the m[Z']-m[A] phase space. The observed data exclude, for Z' coupling strength g[Z'] = 0.8 and m[A] = 300 GeV for example, the Z' mass range of 600 to 1860 GeV. This is the first result on a search for dark matter produced in association with a Higgs boson that includes constraints on h to gamma-gamma obtained at sqrt(s) = 13 TeV.

Understanding the universe, its birth and its future is one of the biggest motivations in physics. In order to understand the cosmos, the fundamental particles forming the universe, the components our matter is built of need to be known and understood. Over time physicists have built a theory which describes the physics of the known fundamental particles very well: the Standard Model (SM) of particle physics. The SM describes the particles, their interactions and phenomena with high precision. So far no proven deviations from the SM have been found, though recently evidence for possible physics beyond the SM has been observed. The SM is not describing the mass of the elementary particles however and even with the addition of the Higgs mechanism giving mass to the particles, we have no full theory for all four fundamental forces. We know the model needs to be extended or replaced by another one, as gravitation is not included in the SM. Having a theory which describes all fundamental particles found so far and all but one fundamental interaction is a great success. However, all this describes about 4% of the universe we live in. 23% is dark matter and 73% is dark energy. Dark matter is believed to interact only through gravity and maybe the weak force, which makes it hardly observable. Dark energy is even more elusive. Among other theories the cosmologic constant and scalar fields are discussed to describe it. One should also note that other models exist which for example modify the Newtonian law of gravity. The Higgs mechanism has become the most popular model for mass generation. Alternative theories like Super Symmetry (SUSY), large Extra Dimensions, Technicolor, String Theory, to name just a few, have spread to describe the necessary mass generation or new particles. As proof for new physics beyond the SM has not been found yet, one assumes that new physics will manifest itself at a larger energy scale and therefore a higher particle mass. Particles with high masses are therefore presumed to be a window to test the SM for deviations caused by new physics. The heaviest fundamental particle which is in our reach is the top quark. Its mass is almost as large as that of a complete tungsten atom. It is so heavy, that it decays faster than it can hadronize. It seems the perfect probe to study new physics at the moment. In this analysis the top quark is used as a probe to search for a new resonance, whose properties are similar to a SM Z boson but is much more massive. This analysis will study t{bar t} decays to search for an excess in the invariant mass distribution of the t{bar t} pairs. Resonant states are suggested for massive Z-like bosons in extended gauge theories, Kaluza Klein states of the gluon or Z, axigluons, topcolor, and other beyond the Standard Model theories. Independent of the exact model a resonant production mechanism should be visible in the t{bar t} invariant mass distribution. In this thesis a model-independent search for a narrow-width heavy resonance X decaying into t{bar t} is performed. In the SM, the top quark decays into a W boson and a b quark nearly 100% of the time, which has been proven experimentally, too. The t{bar t} event signature is fully determined by the W boson decay modes. In this analysis, only the lepton+jets final state, which results from the leptonic decay of one of the W bosons and the hadronic decay of the other, is considered. The event signature is an isolated electron or muon with high transverse momentum, large transverse energy imbalance due to the undetected neutrino, and at least three jets, two of which result from the hadronization of b quarks.

Exploring the phenomenology of the Large Hadron Collider (LHC) at CERN, LHC Physics focuses on the first years of data collected at the LHC as well as the experimental and theoretical tools involved. It discusses a broad spectrum of experimental and theoretical activity in particle physics, from the searches for the Higgs boson and physics beyond the Standard Model to studies of quantum chromodynamics, the B-physics sector, and the properties of dense hadronic matter in heavy-ion collisions. Covering the topics in a pedagogical manner, the book introduces the theoretical and phenomenological framework of hadron collisions and presents the current theoretical models of frontier physics. It offers overviews of the main detector components, the initial calibration procedures, and search strategies. The authors also provide explicit examples of physics analyses drawn from the recently shut down Tevatron. In the coming years, or perhaps even sooner, the LHC experiments may reveal the Higgs boson and offer insight beyond the Standard Model. Written by some of the most prominent and active researchers in particle physics, this volume equips new physicists with the theory and tools needed to understand the various LHC experiments and prepares them to make future contributions to the field.

Prepare to learn everything we still don’t know about our strange and mysterious universe Humanity's understanding of the physical world is full of gaps. Not tiny little gaps you can safely ignore —there are huge yawning voids in our basic notions of how the world works. PHD Comics creator Jorge Cham and particle physicist Daniel Whiteson have teamed up to explore everything we don't know about the universe: the enormous holes in our knowledge of the cosmos. Armed with their popular infographics, cartoons, and unusually entertaining and lucid explanations of science, they give us the best answers currently available for a lot of questions that are still perplexing scientists, including: * Why does the universe have a speed limit? * Why aren't we all made of antimatter? * What (or who) is attacking Earth with tiny, superfast particles? * What is dark matter, and why does it keep ignoring us? It turns out the universe is full of weird things that don't make any sense. But Cham and Whiteson make a compelling case that the questions we can't answer are as interesting as the ones we can. This fully illustrated introduction to the biggest mysteries in physics also helpfully demystifies many complicated things we do know about, from quarks and neutrinos to gravitational waves and exploding black holes. With equal doses of humor and delight, Cham and Whiteson invite us to see the universe as a possibly boundless expanse of uncharted territory that's still ours to explore.