Perspectives on LHC Physics

The following sections are included:

• Preface

• Contents

The following sections are included:

• A “Why” Machine

• A Superpartner Factory

• Our String Vacuum

• After the Champagne

The majority of the universe is composed of some exotic substance, presumably an unknown particle. There are strong indications that this new particle may be produced at the LHC. We review how we came to believe that the universe was mostly of unknown composition, and discuss a few candidates for the identity of the mysterious Dark Matter.

We describe the design of the ATLAS and CMS detectors as they are being prepared to commence data-taking at CERN's Large Hadron Collider. The very high energy proton-proton collisions are meant to dissect matter and space-time itself into its primary elements and generators. The detectors by synthesizing the information from the debris of the collisions are reconstituting the interactions that took place. LHC's ATLAS and CMS experiments (and not only these) are at the closest point of answering in the lab some of the most puzzling fundamental observations in nature today.

I discuss the basic elements of the process that will lead to the discovery of possible new phenomena at the LHC. We review the status of the tools available to model the Standard Model backgrounds, and the role that such tools can play in the discovery phase, and in the exploration of the features and parameters of such new phenomena.

The following sections are included:

• The Landscape

• The Hierarchy

• Linkages
  • The strong CP problem

• Supersymmetry Breaking and the Landscape

• Black Holes at the LHC?

The LHC will be a top-quark factory. With 80 million pairs of top quarks and an additional 34 million single tops produced annually at the designed high luminosity, the properties of this particle will be studied to a great accuracy. The fact that the top quark is the heaviest elementary particle in the Standard Model with a mass right at the electroweak scale makes it tempting to contemplate its role in electroweak symmetry breaking, as well as its potential as a window to unknown new physics at the TeV scale. We summarize the expectations for top-quark physics at the LHC, and outline new physics scenarios in which the top quark is crucially involved.

With the LHC data arriving soon, carrying discoveries, we discuss a strategy for synthesizing a set of early measurements illuminating the dark matter of the universe.

Reflections on spontaneous symmetry breaking, and the connection between condensed matter physics and particle physics, as given in a talk at a symposium at the University of Illinois in Urbana, celebrating the 50th anniversary of the theory of superconductivity.

This chapter describes how to perform model-independent searches for new pair-produced color octet particles that each subsequently decay into two jets plus missing energy. The details of this analysis are focussed on the Tevatron, however, all of the lessons can be carried over to the LHC. Current searches are not sensitive to all regions of parameter space because they employ CMSSM-motivated cuts. Optimizing the H_T and E_T cuts expands the sensitivity of searches for all kinematically allowed decays.

The following sections are included:

• Naturalness in Scientific Thought

• Drowning by Numbers

• A Quantum Complication

• The Naturalness Criterion as a Principle

• An Account of Events

• The Paths Chosen by Nature

• Measuring Naturalness

• Anthropic Reasoning

• Naturalness versus Criticality

• Conclusions

• References

The investigation of the dynamics responsible for electroweak symmetry breaking is one of the prime tasks of experiments at the CERN Large Hadron Collider (LHC). The experiments ATLAS and CMS have been designed to be able to discover a Standard Model Higgs boson over the full mass range as well as Higgs bosons in extended models. In this chapter, the prospects for Higgs boson searches at the LHC are reviewed. In addition, the potential for the measurement of Higgs boson parameters is discussed.

Spin measurement is crucial in distinguishing major scenarios of TeV scale new physics once it is discovered at the LHC. We give a brief survey of methods of measuring the spin of new physics particles at the LHC. We focus on the case in which a long lived massive neutral particle is produced at the end of every cascade decay and escape detection. This is the case for R-parity preserving supersymmetry, Little Higgs models with T-parity, extra-dimensional models with KK-parity, and a large class of similar models and scenarios. After briefly commenting on measuring spin by combining mass and rate information, we concentrate on direct measurement by observing angular correlations among decay products of the new physics particles. We survey a wide range of possible channels, discuss the construction of possible correlation variables, and outline experimental challenges. We also briefly survey the Monte-Carlo tools which are useful in studying such correlations.

The standard model of fundamental interactions is remarkably successful, but it leaves an unfinished agenda. Several major questions seem ripe for exploration in the near future. I anticipate that the coming decade will be a Golden Age of discovery in fundamental physics.

Strongly interacting theories of electroweak (EW) symmetry breaking provide an elegant solution to the hierarchy problem. In these models the EW symmetry can either be broken without a Higgs or by means of a composite Higgs boson. These scenarios have been recently investigated in the framework of 5-dimensional warped models that, according to the AdS/CFT correspondence, have a 4-dimensional holographic interpretation in terms of strongly coupled field theories. We describe the minimal Higgsless and composite Higgs model and show how they can successfully pass all the electroweak precision tests and solve the flavor problems. We explore the implications of these models at the LHC.

I discuss how the Large Hadron Collider era should broaden our view of particle physics research, and apply this thinking to the case of Hidden Worlds. I focus on one of the simplest representative cases of a Hidden World, and detail the rich implications it has for LHC physics, including universal suppression of Higgs boson production, trans-TeV heavy Higgs boson signatures, heavy-to-light Higgs boson decays, weakly coupled exotic gauge bosons, and Higgs boson decays to four fermions via light exotic gauge bosons. Some signatures may be accessible in the very early stages of collider operation, whereas others motivate a later high-lumonosity upgrade.

LHCb is a dedicated detector for b physics at the LHC. In this article we present a concise review of the detector design and performance together with the main physics goals and their relevance for a precise test of the Standard Model and search of New Physics beyond it.

I discuss here some of the deeper connections between the physics studied at the LHC (electroweak phase transition, physics beyond the Standard Model, extra dimensions) and some of the most important issues in the field of particle astrophysics and cosmology (dark matter, primordial gravitational waves, black holes, …)