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Nuclear seminar

Electroweak Baryogenesis, ACME II, and Dark Sector CP Violation

The origin of the matter-anti-matter asymmetry in the universe is a big puzzle for particle physics and cosmology. Baryogenesis mechanisms at the electroweak scale are attractive for their testability at high-energy colliders and low-energy experiments. The recent measurement of electron electric dipole moment by ACME II sets stringent limit on weak scale CP violations and challenges the viable parameter space for successful electroweak baryogenesis in traditional models, such as two-Higgs doublet models and supersymmetry. In this talk, I present our recent proposal of triggering electroweak baryogenesis with dark sector CP violation, which evades the above problem and leads to a number of new predictions for experimental tests. In particular, I will discuss a simple extension of the standard model with gauged U(1) lepton number to realize the idea. This novel mechanism makes new experimental predictions for it to be distinguished.

Date:
-
Location:
CP 179
Event Series:

Particle Physics with Ultracold Neutrons

Since their discovery in 1932 by Chadwick, neutrons have been a critical probe in physics and sciences in general. It was Fermi who first realized that neutrons which are traveling slow enough would be totally reflected by a material surface. These slow moving neutrons can be trapped in material bottles and are called ultracold neutrons (UCN). Experiments performed with UCN take advantage of their slow velocities and long trapping time. Currently, UCN hold the world leading sensitivity of the neutron lifetime, a parameter critical to our understanding of the Weak force and Big Bang Nucleosynthesis. UCN are competitive in measuring decay correlations of the neutron and constraining tensor interactions. They are also used to search for Dark Matter and other exotic particles and interactions. Furthermore, UCN are responsible for the world limit on the sensitivity of the permanent neutron electric dipole moment (nEDM), a T and P symmetry violating observable. By the CPT theorem EDMs also violate CP. The Sakharov conditions require a new CP violating interaction for the observed dominance of matter over anti-matter. Thus, a new source of CP violation is expected, and is perhaps mediated by particles beyond the Standard Model. The present limit, 3×10−26 e cm, already has a reach for new CP violating physics generically at the TeV, and up to the PeV scale in some specific supersymmetric models. Future experiments plan to increase the sensitivity by up to two orders of magnitude. The goal sensitivities of these experiments are challenging targets, and require fascinating technological achievements for their success.


Date:
-
Location:
CP 179
Event Series:

Novel Experimental Probes of QCD in SIDIS and e+e− Annihilation

A new generation of experiments taking advantage of the upgraded electron beam facility at Jefferson Laboratory aims to explore the three-dimensional partonic structure of the proton with unprecedented precision. One of those is the CEBAF Large Acceptance Spectrometer (CLAS12), where semi-inclusive deep-inelastic scattering (SIDIS) events can be detected over a wide kinematic range. In SIDIS events, the incoming electron scatters off a quark in the proton which subsequently hadronizes into a detected final state. The quantum numbers of the hadronic final state are correlated to the quantum numbers of the parent quark and can therefore be used to extract information about the partonic content of the nucleon. Arguably, most information about parton distribution functions has been extracted from final states, where a single, spinless hadron such as a pion or kaon has been detected. Using more complex final states that can carry angular momentum quantum numbers, such as hadron-pairs or polarized hyperons, allows access to spin orbit correlations the hadronization process and a more targeted access to complex dynamics inside the proton. This talk will discuss di-hadron channels to extract parton distributions from SIDIS data taken at CLAS12 as well as the measurement of the corresponding fragmentation functions (FFs). Fragmentation functions describe the formation of hadrons from quarks and can be measured in e+e- annihilation. Here measurements of di-hadron and polarized lambda FFs at the B-factory Belle will be discussed

Date:
-
Location:
CP 179
Event Series: