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Details of Grant 

EPSRC Reference: EP/T01623X/1
Title: Flavor and CP Violation as Probes of QCD and New Physics
Principal Investigator: Schacht, Dr S
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Researcher Co-Investigators:
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Department: Physics and Astronomy
Organisation: University of Manchester, The
Scheme: EPSRC Fellowship
Starts: 01 October 2020 Ends: 30 September 2024 Value (£): 437,772
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Panel History:
Panel DatePanel NameOutcome
03 Dec 2019 Stephen Hawking Fellowship Announced
21 Jan 2020 Stephen Hawking Fellowship Interview Panel 1 Announced
Summary on Grant Application Form
In High Energy Physics, we ask what are the fundamental laws of nature? That means, what are the smallest building blocks of matter and what fundamental forces act between them? Our methodology to answer these questions is to bring particles into collision at very large facilities in a controlled way and to study the scattering process. Due to the laws of relativity and quantum mechanics this process is very nontrivial. Especially, the outgoing particles are in most cases different particles than the incoming ones.

Today, we are already quite advanced in our answer to the question for the fundamental laws of nature, and it is based on axioms and symmetries for the interactions of elementary particles. The state of the art theory is called Standard Model, which includes electromagnetism as well as the so-called weak and strong forces. The strong force lets quarks build bound states like baryons, e.g. the proton and neutron, as well as mesons. An example for a process governed by the weak force is the radioactive beta decay.

The weak force is also an example for quark flavor physics, which is the subfield within particle physics that is concerned with the transformation of one type of quark into another. It turns out that matter comes in a generational structure, i.e. there exist not only the light up and down quarks which are present in the proton, but also much heavier copies of these particles that have the same electric charge as the ones in the proton. The transformation probabilities between these different "flavors" of quarks is encoded in the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The CKM matrix also contains a complex phase, which induces a difference in the behavior of matter and antimatter, the so-called CP violation.

In the decay of strange and beauty quarks, which are two of the different quark flavors, CP violation has been first observed a long time ago, with both discoveries leading to Noble Prizes. In the decays of charm quarks, which is another type of quark flavor, the first discovery of CP violation was very challenging and successful only very recently in March 2019.

This is a unique opportunity to study the difference between matter and antimatter in a region where we could not do it before. Actually, the new discovery opens up a whole new field. In the near future we anticipate many more measurements of charm CP violation in a multitude of different decays of bound states containing a charm quark. We plan to extract the underlying theory parameters governing charm CP violation and predict further observables that could be measured at the large experiments at CERN, Geneva, Switzerland and KEK, Tsukuba, Japan. The University of Manchester is the ideal place to carry out this theoretical research program because of its LHCb group that has made leading experimental contributions to the discovery of CP violation in charm.

From our studies we can learn a lot on possible physics beyond the Standard Model. As a matter of fact, we know for very solid reasons that the Standard Model is not the end of the story. For example it does not include gravity nor dark matter and leaves many questions unanswered, e.g. why are there three generations of matter? And why is the CP violation yet observed in terrestrial experiments so much smaller than the one we see on a cosmic level?

Additionally, we can also use the new measurements to learn more about the properties of the strong force and its approximate symmetries. Our studies will be an important step in order to find out if the amount of CP violation that we see in the experimental results forms a consistent picture as described in the Standard Model or if we need something fundamental new in order to account for it.

In that way we come one step closer to answering our big questions about the fundamental laws of nature.

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Organisation Website: http://www.man.ac.uk