Download this PDF book: Particle Polarization in High Energy Physics: An Introduction and Case Studies on Vector Particle Production at the LHC 2022 English Edition by Pietro Faccioli, Carlos Lourenço
The subject of this book can be briefly summarised: it addresses studies of angular distributions of the decay products of a particle, discussing methodological aspects that should be taken into account to ensure accurate measurements, as well as reliable and unambiguous physical interpretations.
The angular decay distribution is directly determined by the physical properties of the decaying particle and by how it interacts with the other particles involved in the process. Above all, it reflects the particle’s polarization, i.e., the angular momentum state in which it was created, as defined by the production mechanism in the specific physical conditions of the experiment (the colliding particles, the collision energy, the covered phase space window, etc.).
By directly probing the nature of the studied particles, polarization measurements offer detailed insights into the mechanisms behind particle production, providing a window into the underlying fundamental interactions.
On the other hand, it is more challenging to measure polarizations than, for example, cross sections. To start with, we need larger event samples because the analyses are performed as a function of additional variables: the decay angles. Precise measurements of the kinematics of the decay particles are also needed, as they have a direct impact on the quality of the polarization results.
These are not major limiting factors in the case of the LHC experiments, which operate with record breaking integrated luminosities and relatively large cross sections (given the high energy of the collisions), associated with very efficient triggers, state-of-the-art data acquisition systems, high-performance offline computing infrastructures, and more powerful detector technologies and reconstruction techniques than those used in any previously-operating high-energy physics experiment.
We are left with the most delicate step of the polarization measurements: the definition of the data-analysis method. There are many potential hurdles in the path between the high-precision data and the high-accuracy physics results, and care must be taken to avoid the use of approximate or biased analysis methods, which can lead to ambiguous and puzzling results.
Indeed, precision does not mean accuracy: a precise result (small uncertainties) can be wrong, if it is obtained through the use of biased analysis techniques.
This open-access book addresses the following questions: how does the polarization of a particle, i.e., the angular momentum state in which it is produced, manifest itself in nature? What are the concepts and tools needed to perform rigorous measurements providing complete and unambiguous physical information?
Polarization measurements are important because they reflect the nature and coupling properties of a particle and provide unique insights into the underlying fundamental interactions, playing a central role in the study and understanding of the mechanisms of particle production.
Besides gradually reviewing many fundamental notions, the book presents several case studies relevant to physics analyses underway at the LHC, including the lepton-antilepton decays of vector states (Drell–Yan, Z and W bosons, quarkonia, etc.).
The book also offers a detailed discussion of cascade decays, where the vector particle is a daughter of another particle, as well as a survey of typical angular distributions of particles of any integer or half-integer spin.
With a visual approach to the presentation of the concepts and frequent use of pedagogical examples, taken from real measurements, gedankenexperiments, or detailed simulations, the book focuses on aspects of polarization measurements that are sometimes underestimated or left unexplored in experimental analyses, such as the importance of the choice of the reference frame, the existence of frame-independent relations, and the shapes of the physically allowed parameter domains.
Several examples are provided of pitfalls introduced when the intrinsic multidimensionality of the problem is neglected in exchange for a simplified analysis.
Targeting an audience of graduate students, post-docs, and other researchers involved in analyses of LHC data, this book helps to establish a solid bridge between high precision data, existing or soon to be collected, and accurate measurements, including high-sensitivity tests of the Standard Model.
Contents:
1 Dilepton decays of vector particles
2 Reference frames and transformations
3 A frame-independent study of the angular distribution
4 Meaning and interpretation of the frame-independent polarization
5 Smearing effects in non-planar processes
6 Polarization in cascade decays
7 Two-body decay distributions beyond the dilepton case
About the book:
Publisher : Springer; 1st ed. 2023 edition
Publication date : December 17, 2022
Language : English
Pages : 317
File : PDF, 10MB
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