Violation Of CP Symmetry Research Articles

CP Violation in the Quark Sector: Mixing Matrix Unitarity

Since its discovery in the 1960s, the violation of CP symmetry has intrigued scientists and stimulated the advancement of knowledge in particle physics. Numerous experiments were designed and built to study it in increasingly deeper detail. Nowadays, the phenomenon is well framed within the Standard Model of Particle Physics. Nevertheless, new results are being produced by modern experiments at colliders that challenge the current understanding of the model. In this article, the current status of CP violation studies and the role of CP violation in the search for effects beyond the Standard Model are described together with the prospects for ongoing and future experiments.

Symmetry in Σ Hyperon Decay

CP symmetry violation is one of the fundamental requirements for having more matter than antimatter in our universe. However, the observed CP violation is not enough to explain the matter dominance. Searching for the new CP violation in the hyperon sector is therefore attracting people’s interests. In this article, we review the theoretical description of the spin one-half hyperon nonleptonic decay. In order to test the CP conservation, the asymmetry decay parameters might be compared between hyperon and antihyperon. The fixed-target experiments achieved the relevant measurements of the hyperon parameters but in the absence of the antihyperon results. The BESIII experiment with e+e− collision provided an entanglement environment to measure Σ+ and Σ¯− simultaneously. The important role of experimental inputs in CP violation evaluation is discussed in this paper, underlying the great potential of the future collider, which may allow us to reach the precision of the Standard Model predictions.

Hadronic currents and form factors in three-body semileptonic tau decays

Three-body semileptonic tau -decays offer a path to understand the properties of light hadronic systems and CP symmetry violations through searches for electric dipole moments. In studies of electro-weak physics, the hadronic part of the final states has traditionally been described using the language of form factors. Spectroscopic information, resolved in terms of orbital angular momentum quantum-numbers, is best being derived from an explicit decomposition of the hadronic current in the orbital angular momentum basis. Motivated by the upcoming large data samples from mathrm {B} factories, we present the full description of the hadronic currents decomposed into quantum numbers of the hadronic final state using the isobar picture. We present formulas for orbital angular momenta up to three and apply the rules derived from hadron spectroscopy to formulate the decay chain of hadronic three-body systems of arbitrary mass. We also translate this formalism to the language of form factors and thereby correct insufficiencies found in previous analyses of three-body hadronic final states.

A New Generation of Neutrino Cross Section Experiments: Challenges and Opportunities

Our knowledge of neutrino cross sections at the GeV scale, instrumental to test CP symmetry violation in the leptonic sector, has grown substantially in the last two decades. Still, their precision and understanding are far from the standard needed in contemporary neutrino physics. Nowadays, the knowledge of the neutrino cross section at O(10%) causes the main systematic uncertainty in oscillation experiments and jeopardizes their physics reach. In this paper, we envision the opportunities for a new generation of cross section experiments to be run in parallel with DUNE and HyperKamiokande. We identify the most prominent physics goals by looking at the theory and experimental limitations of the previous generation of experiments. We highlight the priorities in the theoretical understanding of GeV cross sections and the experimental challenges of this new generation of facilities.

New physics and the tau polarization vector in b \u2192 mathrm{c}tau {overline{nu}}_{tau } decays

For a general Hb → {H}_ctau {overline{nu}}_{tau } decay we analyze the role of the τ polarization vector {mathcal{P}}^{mu } in the context of lepton flavor universality violation studies. We use a general phenomenological approach that includes, in addition to the Standard Model (SM) contribution, vector, axial, scalar, pseudoscalar and tensor new physics (NP) terms which strength is governed by, complex in general, Wilson coefficients. We show that both in the laboratory frame, where the initial hadron is at rest, and in the center of mass of the two final leptons, a overrightarrow{mathcal{P}} component perpendicular to the plane defined by the three-momenta of the final hadron and the τ lepton is only possible for complex Wilson coefficients, being a clear signal for physics beyond the SM as well as time reversal (or CP-symmetry) violation. We make specific evaluations of the different polarization vector components for the Λb → Λc, {overline{B}}_c → ηc, J/ψ and overline{B} → D(*) semileptonic decays, and describe NP effects in the complete two-dimensional space associated with the independent kinematic variables on which the polarization vector depends. We find that the detailed study of {mathcal{P}}^{mu } has great potential to discriminate between different NP scenarios for 0− → 0− decays, but also for Λb → Λc transitions. For this latter reaction, we pay special attention to corrections to the SM predictions derived from complex Wilson coefficients contributions.

A new bound on CP violation in the \u03c4 lepton Yukawa coupling and electroweak baryogenesis

The origin of the matter-antimatter asymmetry in the Universe is a fundamental question of physics. Electroweak baryogenesis is a compelling scenario for explaining it but it requires beyond the Standard Model sources of the CP symmetry violation. The simplest possibility is CP violation in the third generation fermion Higgs couplings, widely investigated theoretically and searched for experimentally. It has been found that the experimental bounds on the CP violation in the quark Yukawa couplings exclude their significant role in the electroweak baryogenesis, but it can be still played by the τ lepton Yukawa coupling. It is shown in this paper that, within the context of the Standard Model Effective Field Theory and assuming an underlying flavour symmetry of the Wilson coefficients, the electron dipole moment bound on the τ lepton Yukawa coupling is two orders of magnitude stronger than previously reported. This sheds strong doubts on its role in the electroweak baryogenesis, further stimulates the interest in its experimental verification and makes electroweak baryogenesis even more difficult to explain.

Constraint on the matter-antimatter symmetry-violating phase in neutrino oscillations.

The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter-antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model's charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7-9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experimentthat shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [-3.41, -0.03] for the so-called normal mass ordering and [-2.54, -0.32] for the inverted mass ordering. Our results indicate CP violation in leptonsand our method enables sensitive searches for matter-antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.

An Improved Standard Model Comes with Explicit CPV and Productive of BAU

In this manuscript, we present an explicit way to describe the violation of CP symmetry in the standard model (SM) of electroweak interactions. In such a way, complex Cabbibo-Kobayashi-Maskawa (CKM) matrices are achieved which stand for the violation of CP symmetry. At the beginning, two necessary but not sufficient conditions for yielding a complex CKM matrix are stated as criteria. Then we found an interesting condition between the real and imaginary parts of a Hermitian $3\times 3$ matrix may provide extra relations among its parameters and reduce the number of them from eighteen down to five. In previous investigations, this can be done only down to nine. With another assumption among some of those parameters, the mass-matrix pattern is further simplified so as to be diagonalized analytically and in consequence four matrices which reveal $S_N$ symmetries among or between quark generations are obtained. In some of such $S_N$-symmetric cases, the derived CKM matrices are complex which indicate that CP symmetry is violated accordingly. Taking the Jarlskog invariant as an estimate of the CPV strength, the value predicted by this model is orders stronger than the empirical value detected experimentally. However, that happens to fill partly the gap between the cosmologically observed amount of Baryon Asymmetry of the Universe (BAU) and that current Standard Model of particle physics predicts. It also proves the long suspected existence of BAU-productive eras in early universe if some fermions were indistinguishable, i.e., $S_N$-symmetric, under circumstances of extremely high temperatures.

Experimental review of τ lepton studies at the B factories

Recent results of a high-statistics τ lepton studies at B factories are reported. Reviewed are the measurements of Michel parameters in leptonic and radiative leptonic τ decays at Belle, as well as the measurement of the branching fractions of the radiative leptonic τ decays at BABAR. Searches for CP symmetry violation in hadronic decays with $ \mathop K\nolimits_S^0 $ are also briefly discussed.

The Feasibility Study of the Long-baseline Neutrino Oscillation Experiment at the SUNLAB Laboratory in Poland

The feasibility study of an underground laboratory in the Polkowice -Sieroszowice mine in Poland (SUNLAB) as a host of a far detector in a long-baseline neutrino oscillation experiment was performed. The SUNLAB location was previously studied under the LAGUNA FP7 project as a location for the underground multipurpose laboratory. The complementary study of the long-baseline neutrino experiment presented in this paper was performed as a continuation of this idea. A neutrino beam produced at CERN and a far LAr-TPC detector hosted in the SUNLAB laboratory were simulated. The sensitivity of such an experiment for the determination of the CP symmetry violation in the neutrino sector was calculated. The experiment at SUNLAB equipped with the 100 kton LAr TPC detector after 10 years of data taking can give the coverage of {\delta}CP parameter space of 58% (60%) for the normal (inverted) neutrino mass hierarchy at 3{\sigma} level in both cases reaches 5{\sigma} level in case of the maximal violation.

Wave-function model for the CP violation in mesons.

In this paper, we propose a simple quantum model of the kaons decay providing an estimate of the CP symmetry violation parameter. We use the two-level Friedrich's Hamiltonian model to obtain a good quantitative agreement with the experimental estimate of the violation parameter for neutral kaons. A temporal wave-function approach, based on an analogy with spatial wave-functions, plays a crucial role in our model.

Casimir effect at finite temperature for pure-photon sector of the minimal Standard Model Extension

Dynamics between particles is governed by Lorentz and CPT symmetry. There is a violation of Parity (P) and CP symmetry at low levels. The unified theory, that includes particle physics and quantum gravity, may be expected to be covariant with Lorentz and CPT symmetry. At high enough energies, will the unified theory display violation of any symmetry? The Standard Model Extension (SME), with Lorentz and CPT violating terms, has been suggested to include particle dynamics. The minimal SME in the pure photon sector is considered in order to calculate the Casimir effect at finite temperature.

English

The leading theories suggest that in the first fractions of the second following the Big Bang, equal amounts of matter and antimatter were formed, and annihilated. Therefore, the asymmetry of matter and antimatter, and formation of the visible universe is one of the major unsolved problems in physics. Surprisingly, when the major characteristics of the cosmic matter- antimatter interactions, were compared to the biologic body- antibody system, unexpected similarities were observed. They relate to the outcomes of weak and strong interactions, their specificities, annihilation of most of the antimatter, excess of matter over antimatter, difficulty in producing antimatter, early deletion of antimatter, and the material nature of the antimatter. Based on these similarities, it is suggested that a mechanism, different from the charge- parity symmetry (CP) violation, allowed the formation and preservation of the visible universe. This hypothesis could have far reaching consequences on basic concepts in cosmology. Key words: Visible universe, CP symmetry violation, matter, antimatter, cosmology.

Decays of a neutral particle with zero spin and arbitrary CP parity into two off-mass-shell Z bosons

Effects are investigated of CP symmetry violation in the decay of a scalar particle X (the Higgs boson) into two off-mass-shell Z bosons both decaying into a fermion-antifermion pair, $X \to Z_1^* \, Z_2^* \to f_1 \bar{f_1} \, f_2 \bar{f_2}$. The most general form of the amplitude of the transition $X \to Z_1^* Z_2^*$, wherein the boson X may not have definite CP parity, is considered. Limits of applicability of the narrow-Z-width approximation used when obtaining differential widths of the decay under consideration are determined. Various observables connected with the structure of the amplitude of the decay $X \to Z_1^* Z_2^*$ are studied. These observables are analyzed in the Standard Model, as well as in models conceding indefinite CP parity of the Higgs boson. An experimental measurement at the LHC of angular and invariant mass distributions of the decay $X \to Z_1^* Z_2^* \to f_1 \bar{f_1} f_2 \bar{f_2}$ can give information about the CP properties of the Higgs boson and its interaction with the Z boson.

Time-Reversal Violation

The violation of CP symmetry between matter and antimatter in the neutral K and B meson systems is well established, with a high degree of consistency between all available experimental measurements and with the Standard Model of particle physics. On the basis of the up-to-now-unbroken CPT symmetry, the violation of CP symmetry strongly suggests that the behavior of these particles under weak interactions must also be asymmetric under time reversal T. Many searches for T violation have been performed and proposed using different observables and experimental approaches. These include T-odd observables, such as triple products in weak decays, and genuine observables, such as permanent electric dipole moments of nondegenerate stationary states and the breaking of the reciprocity relation. We discuss the conceptual basis of the required exchange of initial and final states with unstable particles, using quantum entanglement and the decay as a filtering measurement, for the case of neutral B and K mesons. Using this method, the BaBar experiment at SLAC has clearly observed T violation in B mesons.

Record-energy collisions coming soon at the LHC

The machine that discovered the Higgs boson is flexing its muscles again. The results could be stunning new findings or striking new mysteries.

$D\bar{D}$ mixing and CP-symmetry violation in the charm sector, and rare D-meson decays

An overview of selected recent results on [Formula: see text] mixing and CP-symmetry violation in the charm sector, and D meson rare decays, was presented at the Physics In Collision conference 2013 in Beijing.

A NEW ERA OF FLAVOR PHYSICS: BELLE II AND THE SuperKEKB PROJECT

The physics of heavy flavors, including the search for new sources of CP symmetry violation and for rare decays of B mesons and τ leptons, is one of the pillars of modern particle physics in the quest for finding the inevitable extensions or modifications of the Standard Model. In this paper we first summarize the present status of CP violation as measured using the two pioneering B-Factories PEP II in the US and KEKB in Japan. Both machines have stopped operation (PEP II in 2008, KEKB end of June 2010), and full data samples from the BaBar and Belle experiments are now being analyzed for the "final word." The Standard Model of CP violation, based on the quark flavor mixing matrix as formulated by Kobayashi and Maskawa, shows overall consistency with the measurements. Still there are some tantalizing hints of possible deviations from the conventional wisdom. Strong arguments therefore exist to push for a new round of high-precision experiments, which will become available with the next generation of ultrahigh luminosity machines ("Super B-Factories"). We discuss the physics potential of such machines, aiming at integrated luminosities about two orders of magnitude larger than the present samples. We then report on the concrete plans at KEK in Japan to upgrade the KEKB machine ("SuperKEKB") with the goal of achieving an instantaneous luminosity exceeding 8 × 1035 cm -2 s -1, which is a factor of 40 larger than KEKB's world record. Together with the machine, the Belle detector will be upgraded as well ("Belle II"), with significant improvements to increase its background tolerance as well as improving its physics performance. The Belle II experiment is scheduled to see first collisions in 2015.

REVIEW OF RECENT NEUTRINO PHYSICS RESEARCH

We review recent research in neutrino physics, including neutrino oscillations to test time reversal and CP symmetry violations, the measurement of parameters in the U matrix, sterile neutrino emission causing pulsar kicks, and neutrino energies in the neutrinosphere.

Searching for electric dipole moments

AbstractSearches for a permanent Electric Dipole Moment (EDM) of a fundamental particle provide a wide window for the discovery of potential New Physics. Within todays Standard Model in particle physics the well established violation of CP symmetry gives rise to EDMs which are several orders of magnitude below the present experimentally established upper bounds. On the other hand, EDMs appear quite naturally within many modern speculative theories, which have been suggested to improve the known shortcomings of the present Standard Model, e.g., the lack of giving reasons for certain established facts such as the mass hierarchy of the fundamental fermions or the number of three particle generations. They could be almost as large as the present experimental bounds. The speculative models provide for EDMs of different fundamental particles in specific ways. As there is no convincing indication, yet, which of the various extensions to the present standard theory may be more successful, a larger number of EDM searches is very well motivated. Still, even with the discovery of an EDM in one system several experiments will be required to pin down the precise nature and the underlying processes. Therefore searches are going on presently in a variety of systems, ranging from free leptons to complex condensed matter samples. These experiments utilize typically state of the art precision measurements which are often based on forefront technological developments. The experimental efforts are complemented and guided by the further development and refinement of particle theory. Here a few aspects of recent developments in this exciting field are summarized.