Charge Conjugation And Parity Research Articles

Probing CP symmetry and weak phases with entangled double-strange baryons

Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matter–antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry1. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon–antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ− baryon and its antiparticle2{bar{{Xi }}}^{+}, has enabled a direct determination of the weak-phase difference, (ξP − ξS) = (1.2 ± 3.4 ± 0.8) × 10−2 rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods3. Finally, we provide an independent measurement of the recently debated Λ decay parameter αΛ (refs. 4,5). The {Lambda }bar{{Lambda }} asymmetry is in agreement with and compatible in precision to the most precise previous measurement4.

Methodologies to Measure the CP Structure of the Higgs Yukawa Coupling to Tau Leptons

One of the central goals of the Large Hadron Collider has been the search, and later the study, of the Higgs boson. Its coupling structure under charge conjugation and parity (CP) symmetries has been extensively investigated as a probe for new physics. This paper presents a review of the methods collected in the literature to access the CP structure of the Yukawa coupling of the Higgs boson to tau leptons at proton colliders. A new notation is introduced to classify already existing methods, highlighting their common features and favoring the investigation of new, more performing alternatives.

CP violation and beyond

Experiments around the world are looking for signs of the charge conjugation and parity (CP) symmetry violation. Some of these searches might also reveal physics beyond the standard model.

The Superconducting Toroid for the New International AXion Observatory (IAXO)

IAXO, the new International AXion Observatory, will feature the most ambitious detector for solar axions to date. Axions are hypothetical particles which were postulated to solve one of the puzzles arising in the standard model of particle physics, namely the strong CP (Charge conjugation and Parity) problem. This detector aims at achieving a sensitivity to the coupling between axions and photons of one order of magnitude beyond the limits of the current detector, the CERN Axion Solar Telescope (CAST). The IAXO detector relies on a high-magnetic field distributed over a very large volume to convert solar axions to detectable X-ray photons. Inspired by the ATLAS barrel and end-cap toroids, a large superconducting toroid is being designed. The toroid comprises eight, one meter wide and twenty one meters long racetrack coils. The assembled toroid is sized 5.2 m in diameter and 25 m in length and its mass is about 250 tons. The useful field in the bores is 2.5 T while the peak magnetic field in the windings is 5.4 T. At the operational current of 12 kA the stored energy is 500 MJ. The racetrack type of coils are wound with a reinforced Aluminum stabilized NbTi/Cu cable and are conduction cooled. The coils optimization is shortly described as well as new concepts for cryostat, cold mass, supporting structure and the sun tracking system. Materials selection and sizing, conductor, thermal loads, the cryogenics system and the electrical system are described. Lastly, quench simulations are reported to demonstrate the system's safe quench protection scheme.

Searching for physics beyond the Standard Model through the dipole interaction

The magnetic dipole interaction played a central role in the development of QED, and continued in that role for the Standard Model. The muon anomalous magnetic moment has served as a benchmark for models of new physics, and the present experimental value is larger than the standard-model value by more than three standard deviations. The electric dipole moment (EDM) violates parity (P) and time-reversal (T) symmetries, and in the context of the CPT theorem, the combination of charge conjugation and parity (CP). Since a new source of CP violation outside of that observed in the K and B meson systems is needed to help explain the baryon asymmetry of the universe, searches for EDMs are being carried out worldwide on a number of systems. The standard-model value of the EDM is immeasurably small, so any evidence for an EDM would signify the observation of new physics. Unique opportunities exist for EDM searches using polarized proton, deuteron or muon beams in storage rings. This talk will provide an overview of the theory of dipole moments, and the relevant experiments. The connection to the transition dipole moment that could produce lepton flavor violating interactions such as μ+ → e+γ is also mentioned.

Determining theCPProperties of the Higgs Boson

The search and the probe of the fundamental properties of Higgs boson(s) and, in particular, the determination of their charge conjugation and parity (CP) quantum numbers, are the main tasks of future high-energy colliders. We demonstrate that the CP properties of a standard model-like Higgs particle can be unambiguously assessed by measuring just the total cross section and the top polarization in associated Higgs boson production with top quark pairs in e(+)e(-) collisions.

Lattice QCD with chiral quarks: using symmetry to explore symmetry breaking

Over the last 15 years, lattice discretizations of quarks that preserve chiral symmetry have progressed from beautiful theoretical ideas to practical simulation tools. With control over chiral symmetry, lattice calculations of more of the matrix elements relevant to the violation of charge-conjugation and parity (CP) symmetry in the Standard Model can be done. The progression to practical simulation tool has been aided by the continued growth in computing power, as well as marked advances in algorithms. The status of simulations with chiral quarks will be reviewed, emphasizing the physics of CP violation that is currently being done. The prospects for future simulations with physical values for the light quarks will also be discussed.

Neutron sensitivity of the endcap RPC modules in Belle detector

The primary purpose in the Belle experiment at the asymmetric-energy e/sup =/e/sup -/ collider at the High-Energy Accelerator Research Organization (KEK B factory) is the measurement of charge conjugation and parity (CP) violation in B meson decays. The K/sub L/ mesons and muons (KLM) detector was designed to identify K/sub L/'s and muons in this experiment. Since October 2001, the luminosity in the KEK B accelerator has been remarkably improved. The data on B meson decay are successfully collected in the Belle detector. In contrast with the high luminosity operations of the accelerator, however, the high background rate leading to a lower detection efficiency has been observed in the endcap KLM detector. For present and future high luminosity operations, we have to identify the background source and consider the shielding. To identify the background source, the background data sampled from e/sup +/e/sup -//spl rarr//spl mu//sup +//spl mu//sup -/ events were investigated and the simulations of the sensitivity of the endcap KLM detector to neutrons and /spl gamma/'s as the background sources were performed using the Geant4 simulation toolkit. The comparisons of the simulations with the experimental data are presented.