Charge Parity Research Articles

Observation of the 4\u03c0-periodic Josephson effect in indium arsenide nanowires

Quantum computation by non-Abelian Majorana zero modes (MZMs) offers an approach to achieve fault tolerance by encoding quantum information in the non-local charge parity states of semiconductor nanowire networks in the topological superconductor regime. Thus far, experimental studies of MZMs chiefly relied on single electron tunneling measurements, which lead to the decoherence of the quantum information stored in the MZM. As a next step towards topological quantum computation, charge parity conserving experiments based on the Josephson effect are required, which can also help exclude suggested non-topological origins of the zero bias conductance anomaly. Here we report the direct measurement of the Josephson radiation frequency in indium arsenide nanowires with epitaxial aluminium shells. We observe the 4π-periodic Josephson effect above a magnetic field of ≈200 mT, consistent with the estimated and measured topological phase transition of similar devices.

Novel method for measuring charm-mixing parameters using multibody decays

We propose a novel method to measure flavor-oscillations and charge-parity (CP) violation in charm mixing. The approach uses multibody charm decays, such as $D^0\to K_S^0\pi^+\pi^-$, and avoids the need for a fit of the decay amplitudes while suppressing biases due to nonuniform signal-reconstruction efficiencies as functions of phase space and decay time. Data are partitioned in decay-time and Dalitz-plot regions (bins). The Dalitz-plot bins are symmetric with respect to the principal bisector and chosen to ensure nearly constant values of the strong-interaction phases in each. The ratios of signal yields observed in each symmetric bin pair are fit as functions of decay time, using independent auxiliary measurements of the strong-interaction phases as constraints, to determine the relevant physics parameters. Simulation shows that this approach improves the sensitivity to the normalized charm-eigenstate mass difference by 35% with respect to existing model-independent methods. In addition, we introduce a parametrization of oscillation and CP-violation effects in charm mixing that has attractive statistical properties and may find wider applicability.

Constraints on axionic dark matter in the 3‐3‐1 model

Dark matter in the form of axions can be included in models with SU(3)C ⊗ SU(3)L ⊗ U(1)X symmetry with right‐handed neutrinos, where the strong charge‐parity (CP) problem can be solved. Different versions of the model have the appealing characteristic of giving the observed dark matter abundance, measured by the Planck collaboration, for suitable values of the parameters. We studied the constraints on the parameter space of the model obtained when the axion mass is calculated taking into account both quantum chromodynamics (QCD) effects and gravitationally induced operators, making a comparison of three different models.

Measurement of the angular distribution of prompt gamma-rays emitted in the 117Sn(n, γ) reaction for a T-violation search

It is theoretically suggested that the violation of charge conjugation and parity symmetry (CP-violation) could be enhanced in several compound nuclear reactions. According to the CPT theorem the violation of time-reversal symmetry (T-violation) would be enhanced too. The experimental sensitivity to find a T-violating effect in neutron-induced compound nuclear reactions depends on the value of a spin factor κ(J), which is a parameter specific for each nuclide. It can be determined from the angular dependence of γ-ray emission in (n,γ) reactions induced near a p-wave resonance. In this paper, the measurement result and the analysis status of experiments using the target nucleus 117Sn are reported.

Charge-parity-violating effects in Casimir-Polder potentials

We demonstrate under which conditions a violation of the charge-parity (CP) symmetry in molecules will manifest itself in the Casimir-Polder interaction of these with a magnetodielectric surface. Charge-parity violation induces a specific electric-magnetic cross-polarisability in a molecule that is not chiral, but time-reversal (T) symmetry violating. As we show, a detection of such an effect via the Casimir-Polder potential requires a material medium that is also sensitive to time-reversal, i.e., it must exhibit a non-reciprocal electromagnetic response. As simple examples of such media we consider a perfectly reflecting non-reciprocal mirror that is a special case of a perfect electromagnetic conductor as well as a Chern-Simons medium. In addition, we show that Chern-Simons and related media can induce unusual atom-surface interactions for anisotropic molecules with and without a chiral response.

Radiation Damage Effects and Operation of the LHCb Vertex Locator

Vertex locator (VELO) is a silicon microstrip detector situated around the interaction point in the large Hadron Collider beauty (LHCb) spectrometer at the Large Hadron Collider. The LHCb experiment is dedicated to studying charge conjugation and parity symmetry violation in the heavy flavor sector and rare decays of B mesons. The precise reconstruction of both the primary and secondary vertices, obtained by the VELO, is crucial in the selection of signal events containing b and c quarks and lifetime measurements. VELO consists of two retractable parts that operate at 8 mm from the interaction region. Its proximity to proton beams makes the LHCb VELO a place for studying radiation damage effects in silicon detectors in proton–proton and heavy-ion collisions. The latest results from radiation damage studies and their impact on the operation of the LHCb VELO after the first data-taking period (Run I) and the ongoing Run II are presented in this paper. The main macroscopic parameters, influenced by particle fluence, are described along with selected methods of their monitoring. All the results show that VELO sustains the impact of high fluence of radiation, and its performance will not change significantly until the end of Run II.

Characterization of the 1S\u20132S transition in antihydrogen

In 1928, Dirac published an equation1 that combined quantum mechanics and special relativity. Negative-energy solutions to this equation, rather than being unphysical as initially thought, represented a class of hitherto unobserved and unimagined particles—antimatter. The existence of particles of antimatter was confirmed with the discovery of the positron2 (or anti-electron) by Anderson in 1932, but it is still unknown why matter, rather than antimatter, survived after the Big Bang. As a result, experimental studies of antimatter3–7, including tests of fundamental symmetries such as charge–parity and charge–parity–time, and searches for evidence of primordial antimatter, such as antihelium nuclei, have high priority in contemporary physics research. The fundamental role of the hydrogen atom in the evolution of the Universe and in the historical development of our understanding of quantum physics makes its antimatter counterpart—the antihydrogen atom—of particular interest. Current standard-model physics requires that hydrogen and antihydrogen have the same energy levels and spectral lines. The laser-driven 1S–2S transition was recently observed8 in antihydrogen. Here we characterize one of the hyperfine components of this transition using magnetically trapped atoms of antihydrogen and compare it to model calculations for hydrogen in our apparatus. We find that the shape of the spectral line agrees very well with that expected for hydrogen and that the resonance frequency agrees with that in hydrogen to about 5 kilohertz out of 2.5 × 1015 hertz. This is consistent with charge–parity–time invariance at a relative precision of 2 × 10−12—two orders of magnitude more precise than the previous determination8—corresponding to an absolute energy sensitivity of 2 × 10−20 GeV.

Neutrinos, DUNE and the world best bound on CPT invariance

CPT symmetry, the combination of Charge Conjugation, Parity and Time reversal, is a cornerstone of our model building strategy and therefore the repercussions of its potential violation will severely threaten the most extended tool we currently use to describe physics, i.e. local relativistic quantum fields. However, limits on its conservation from the Kaon system look indeed imposing. In this work we will show that neutrino oscillation experiments can improve this limit by several orders of magnitude and therefore are an ideal tool to explore the foundations of our approach to Nature.Strictly speaking testing CPT violation would require an explicit model for how CPT is broken and its effects on physics. Instead, what is presented in this paper is a test of one of the predictions of CPT conservation, i.e., the same mass and mixing parameters in neutrinos and antineutrinos. In order to do that we calculate the current CPT bound on all the neutrino mixing parameters and study the sensitivity of the DUNE experiment to such an observable. After deriving the most updated bound on CPT from neutrino oscillation data, we show that, if the recent T2K results turn out to be the true values of neutrino and antineutrino oscillations, DUNE would measure the fallout of CPT conservation at more than 3σ. Then, we study the sensitivity of the experiment to measure CPT invariance in general, finding that DUNE will be able to improve the current bounds on Δ(Δm312) by at least one order of magnitude. We also study the sensitivity to the other oscillation parameters. Finally we show that, if CPT is violated in nature, combining neutrino with antineutrino data in oscillation analysis will produce imposter solutions.

Updated determination of D0–D¯0 mixing and CP violation parameters with D0→K+π− decays

We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0\to K^+\pi^-$ to $D^0\to K^-\pi^+$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0$ fb$^{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be $x'^2=(3.9 \pm 2.7) \times10^{-5}$, $y'=(5.28 \pm 0.52) \times 10^{-3}$, and $R_D=(3.454 \pm 0.031)\times10^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and $\overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D =(-0.1\pm9.1)\times10^{-3}$, and magnitude of the ratio of mixing parameters $1.00< |q/p| <1.35$ at the $68.3\%$ confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.

Challenging the standard model by high-precision comparisons of the fundamental properties of protons and antiprotons.

The BASE collaboration investigates the fundamental properties of protons and antiprotons, such as charge-to-mass ratios and magnetic moments, using advanced cryogenic Penning trap systems. In recent years, we performed the most precise measurement of the magnetic moments of both the proton and the antiproton, and conducted the most precise comparison of the proton-to-antiproton charge-to-mass ratio. In addition, we have set the most stringent constraint on directly measured antiproton lifetime, based on a unique reservoir trap technique. Our matter/antimatter comparison experiments provide stringent tests of the fundamental charge–parity–time invariance, which is one of the fundamental symmetries of the standard model of particle physics. This article reviews the recent achievements of BASE and gives an outlook to our physics programme in the ELENA era.This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.

Recent Developments from ASACUSA on Antihydrogen Detection

The ASACUSA Collaboration at CERNs Antiproton Decelerator aims to measure the ground state hyperfine splitting of antihydrogen with high precision to test the fundamental symmetry of CPT (combination of charge conjugation, parity transformation, and time reversal). For this purpose an antihydrogen detector has been developed. Its task is to count the arriving antihydrogen atoms and therefore distinguish backgroundevents (mainly cosmics) from antiproton annihilations originating from antihydrogen atoms which are produced only in small amounts. A central BGO crystal disk with position sensitive read-out detects the annihilation and a surrounding two-layered hodoscope is used for tracking charged secondaries. The hodoscope has been recently upgraded to allow precise vertex reconstruction. A machine learning analysis based on measured antiproton annihilations and cosmic rays has been developed to identify antihydrogen events.

International Workshop on CPT and Lorentz Symmetry in Field Theory

PrefaceOn 6 and 7 July 2017 the International Workshop on ‘CPT and Lorentz Symmetry in Field Theory’ took place in Faro, Portugal (indico.cern.ch/event/596580). In this workshop we gathered theoretical physicists who are working on or are interested in issues related to CPT and Lorentz symmetry in field theory and gravity. Invariance of the laws of nature under both CPT and Lorentz symmetry is usually taken for granted, and there are profound theoretical reasons behind this idea. Lorentz invariance is generally considered as a basic building block for constructing consistent relativistic quantum field theories. Under the further assumptions of locality and unitarity, the CPT theorem then assures additional invariance of the action under the combined symmetries of charge conjugation, parity inversion, and time reversal. On the other hand, various approaches to quantum gravity allow for departures from CPT and Lorentz symmetry, either spontaneously or otherwise. While at low energies the ensuing effects can be expected to be extremely small due to Planck-scale suppression, they might be detectable in ultra-high precision tests. For these reasons, CPT and Lorentz violation constitute an attractive possibility to look for physics beyond the Standard Model and General Relativity possibly arising from quantum effects in gravity.Topics of the workshop included theoretical and phenomenological aspects of departures from CPT and Lorentz symmetry, involving field theory, gravitation, and particle physics. The contributions covered a wide range of issues, at the level of fundamental aspects and consistency of field theories such as causality, renormalization and renormalization group, anomalies, stability, effective field theory, (non)commutativity and (non)metricity, as well as more phenomenological issues, including the observed matter-antimatter asymmetry in the Universe, the Casimir effect, and hadronic physics. There were also two presentations about Hořava gravity, including a review talk. The common theme in all of these contributions was always CPT and/or Lorentz symmetry. Taken together, these presentations give a good overview of the state of the art of the field.List of Scientific and Organizing Committee, Workshop secretariat, Workshop sponsors, Group photo and the Conference poster are available in this pdf.

Searching for the Dark.

The article discusses the Axion Dark Matter Experiment (ADMX) as researchers entered its most sensitive phase yet in its searchfor invisible particles to explain the universe's hidden mass. Topics include weakly interacting massive particle (WIMP), concepts of quantum chromodynamics (QCD), and problems related to charge parity (CP). Also discussed is use of superconducting quantum-interference devices (SQUIDs).

Baryogenesis in nonminimally coupled f(R) theories

We generalize the mechanism for gravitational baryogensis in the context of $f(R)$ theories of gravity, including a nonminimal coupling between curvature and matter. In these models, the baryon asymmetry is generated through an effective coupling between the Ricci scalar curvature and the net baryon current that dynamically breaks Charge Conjugation, Parity and Time Reversal (CPT) invariance. We study the combinations of characteristic mass scales and exponents for both non-trivial functions present in the modified action functional and establish the allowed region for these parameters: we find that very small deviations from General Relativity are consistent with the observed baryon asymmetry and lead to temperatures compatible with the subsequent formation of the primordial abundances of light elements. In particular, we show the viability of a power-law nonminimal coupling function $f_2(R) \sim R^n$ with $ 0 < n \lesssim 0.078 $ and determine its characteristic curvature scale.

Andreev molecules in semiconductor nanowire double quantum dots

Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum dots are defined by gate voltages in indium antimonide nanowires. High transparency superconducting niobium titanium nitride contacts are made to each of the dots in order to induce superconductivity, as well as probe electron transport. Andreev bound states induced on each of dots hybridize to define Andreev molecular states. The evolution of these states is studied as a function of charge parity on the dots, and in magnetic field. The experiments are found in agreement with a numerical model.

CP as a Symmetry of Symmetries

It is explained that the Standard Model combined charge conjugation and parity transformation (CP) is a simultaneous complex conjugation outer automorphism transformation of gauge and space-time symmetries. Simple examples are given for the general concept of outer automorphisms (“symmetries of symmetries”), as well as for their possible actions on physical theories. It is highlighted that complex conjugation outer automorphisms do not, in general, exist for all symmetries. Examples are given for cases in which the physical CP transformation is violated as a consequence of requiring another symmetry. A toy model is illustrated in which CP is spontaneously violated in the broken phase of a continuous gauge symmetry, while an unbroken outer automorphism protects the topological vacuum angle at θ = 0.

Nature’s little linchpins

From the hunt for the violation of charge–parity symmetry to the quest to find Majorana particles, neutrinos may hold the key to moving physics beyond the Standard Model, as Ben Still explains

Particle asymmetries from quantum statistics

We consider a class of baryogenesis models where the Lagrangian in the visible sector is Charge-Parity (CP) invariant and a baryon asymmetry is produced only when quantum statistics is taken into account. The CP symmetry is broken by matter effects, namely the assumption that the primordial plasma contains another asymmetric species, such as dark matter. Out-of-equilibrium baryon number violating decays can then generate an asymmetry through Bose enhancement and/or Pauli blocking of certain decay channels.

Assessing safety and protein interactions of surface-modified iron oxide nanoparticles for potential use in biomedical areas

We have investigated the electrostatic interaction between bare iron oxide nanoparticles (IONPs) or low molecular weight chitosan coated iron oxide nanoparticles (LMWC-IONPs) and hen egg white lysozyme (HEWL) at different pH values using protein-nanoparticle reverse charge parity model. Physicochemical characterization of both IONPs and LMWC-IONPs were carried out using DLS, TEM, FE-SEM, XRD, TGA, XPS and VSM analysis. DLS, TEM and FE-SEM results indicated that both IONPs were monodispersed, with size ranging from 8 to 20nm. The coating of LMWC on IONPs was confirmed using zeta potential, TGA, XRD and XPS measurements. The cytotoxicity of both IONPs and LMWC-IONPs was studied in vitro in A549 human lung alveolar epithelial cells to assess their use in biomedical applications. Furthermore, the interactions between protein-nanoparticles were investigated by UV-visible, fluorescence and circular dichroism spectroscopic techniques. The present study suggests that water soluble LMWC surface modified IONPs are the promising nanomaterials. The safety and biocompatibility of these nanoparticles render them suitable for biomedical applications.

Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation

The current status of electric dipole moments of diamagnetic atoms which involves the synergy between atomic experiments and three different theoretical areas -- particle, nuclear and atomic is reviewed. Various models of particle physics that predict CP violation, which is necessary for the existence of such electric dipole moments, are presented. These include the standard model of particle physics and various extensions of it. Effective hadron level combined charge conjugation (C) and parity (P) symmetry violating interactions are derived taking into consideration different ways in which a nucleon interacts with other nucleons as well as with electrons. Nuclear structure calculations of the CP-odd nuclear Schiff moment are discussed using the shell model and other theoretical approaches. Results of the calculations of atomic electric dipole moments due to the interaction of the nuclear Schiff moment with the electrons and the P and time-reversal (T) symmetry violating tensor-pseudotensor electron-nucleus are elucidated using different relativistic many-body theories. The principles of the measurement of the electric dipole moments of diamagnetic atoms are outlined. Upper limits for the nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained combining the results of atomic experiments and relativistic many-body theories. The coefficients for the different sources of CP violation have been estimated at the elementary particle level for all the diamagnetic atoms of current experimental interest and their implications for physics beyond the standard model is discussed. Possible improvements of the current results of the measurements as well as quantum chromodynamics, nuclear and atomic calculations are suggested.