Parity Violation In Weak Interactions Research Articles

A Relationship between the Molecular Parity-Violation Energy and the Electronic Chirality Measure.

When the weak forces producing parity-violating effects are taken into account, there is a tiny energy difference between the total electronic energies of two enantiomers (ΔEPV), which might be the key to understanding the evolution of the biological homochirality. We focus on the electronic chirality measure (ECM), a powerful descriptor based on the electronic charge density, for quantifying the chirality degree of a molecule, in a representative set of chiral molecules, together with their EPV energies. Our results show a novel, strong, and positive correlation between ΔEPV and ECM, supporting a subtle interplay between the weak forces acting within the nuclei of a given molecule and its chirality. These findings suggest that experimental investigations for molecular parity violation detection should consider molecules with ECM values as large as possible and may support that a chiral signature is imprinted on life by fundamental physics via the parity-violating weak interactions.

Chirality and the Origin of Life

The origin of life, based on the homochirality of biomolecules, is a persistent mystery. Did life begin by using both forms of chirality, and then one of the forms disappeared? Or did the choice of homochirality precede the formation of biomolecules that could ensure replication and information transfer? Is the natural choice of L-amino acids and D-sugars on which life is based deterministic or random? Is the handedness present in/of the Universe from its beginning? The whole biosystem on the Earth, all living creatures are chiral. Many theories try to explain the origin of life and chirality on the Earth: e.g., the panspermia hypothesis, the primordial soup hypothesis, theory of parity violation in weak interactions. Additionally, heavy neutrinos and the impact of the fact that only left-handed particles decay, and even dark matter, all have to be considered.

Enantiomer Superpositions from Matter-Wave Interference of Chiral Molecules

Molecular matter-wave interferometry enables novel strategies for manipulating the internal mechanical motion of complex molecules. Here, we show how chiral molecules can be prepared in a quantum superposition of two enantiomers by far-field matter-wave diffraction and how the resulting tunneling dynamics can be observed. We determine the impact of rovibrational phase averaging and propose a setup for sensing enantiomer-dependent forces, parity-violating weak interactions, and environment-induced superselection of handedness, as suggested to resolve Hund’s paradox. Using ab initio tunneling calculations, we identify [4]-helicene derivatives as promising candidates to implement the proposal with state-of-the-art techniques. This work opens the door for quantum sensing with chiral molecules.Received 20 January 2021Revised 4 June 2021Accepted 14 July 2021DOI:https://doi.org/10.1103/PhysRevX.11.031056Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasChiralityCold atoms & matter wavesQuantum opticsQuantum sensingPhysical SystemsAtomic & molecular beamsMoleculesTechniquesAb initio calculationsDensity functional theoryInterferometryQuantum chemistry methodsQuantum master equationAtomic, Molecular & OpticalQuantum InformationCondensed Matter, Materials & Applied Physics

Observing the polarization of cosmic-ray muons in student physics laboratory

An undergraduate-level student experiment has been designed and implemented to measure the forward–backward asymmetry of the decay of the cosmic-ray muons, offering a pedagogical view to the parity violation in weak interactions. The detector system consists of six plastic scintillators installed vertically in row. The backward–forward asymmetry of the decay e− and e+ with respect to the muon motion direction is correlated with the incident depth of the muon stopped in the scintillator. MC simulations have been carried out in order to better interpret the data and optimize the data analysis. The forward–backward asymmetry of 0.051 ± 0.027 is deduced for the decay of cosmic-ray muons in the energy range being studied. The results are consistent with the picture of parity violation in weak interactions. The experiment can be constructed by the senior undergraduate students under the guidance of the course teacher.

Axial and pseudoscalar form factors from charged current quasielastic neutrino-nucleon scattering

We study the scattering of neutrinos on polarized and unpolarized free nucleons, and also the polarization of recoil particles in these scatters. In contrast to electromagnetic processes, the parity-violating weak interaction gives rise to large spin asymmetries at leading order. Future polarization measurements could provide independent access to the proton axial structure and allow the first extraction of the pseudoscalar form factor from neutrino data without the conventional partially conserved axial current (PCAC) ansatz and assumptions about the pion-pole dominance. The pseudoscalar form factor can be accessed with precise measurements with muon (anti)neutrinos of a few hundreds $\mathrm{MeV}$ of energy or with tau (anti)neutrinos. The axial form factor can be extracted from scattering measurements using accelerator neutrinos of all energies.

Symmetries and Their Breaking in the Fundamental Laws of Physics

Symmetries in the Physical Laws of Nature lead to observable effects. Beyond the regularities and conserved magnitudes, the last few decades in particle physics have seen the identification of symmetries, and their well-defined breaking, as the guiding principle for the elementary constituents of matter and their interactions. Flavour SU(3) symmetry of hadrons led to the Quark Model and the antisymmetric requirement under exchange of identical fermions led to the colour degree of freedom. Colour became the generating charge for flavour-independent strong interactions of quarks and gluons in the exact colour SU(3) local gauge symmetry. Parity Violation in weak interactions led us to consider the chiral fields of fermions as the objects with definite transformation properties under the weak isospin SU(2) gauge group of the Unifying Electro-Weak SU(2) × U(1) symmetry, which predicted novel weak neutral current interactions. CP-Violation led to three families of quarks opening the field of Flavour Physics. Time-reversal violation has recently been observed with entangled neutral mesons, compatible with CPT-invariance. The cancellation of gauge anomalies, which would invalidate the gauge symmetry of the quantum field theory, led to Quark–Lepton Symmetry. Neutrinos were postulated in order to save the conservation laws of energy and angular momentum in nuclear beta decay. After the ups and downs of their mass, neutrino oscillations were discovered in 1998, opening a new era about their origin of mass, mixing, discrete symmetries and the possibility of global lepton-number violation through Majorana mass terms and Leptogenesis as the source of the matter–antimatter asymmetry in the universe. The experimental discovery of quarks and leptons and the mediators of their interactions, with physical observables in spectacular agreement with this Standard Theory, is the triumph of Symmetries. The gauge symmetry is exact only when the particles are massless. One needs a subtle breaking of the symmetry, providing the origin of mass without affecting the excellent description of the interactions. This is the Brout–Englert–Higgs Mechanism, which produces the Higgs Boson as a remnant, discovered at CERN in 2012. Open present problems are addressed with by searching the New Physics Beyond-the-Standard-Model.

Parity violation in weak interactions: How experiment can shape a theoretical framework

In this paper I will focus on the case of the discovery of parity nonconservation in weak interactions from the period spanning 1947–1957, and the lessons this episode provides for successful theory construction in HEP. I aim to (a) summarize the history into a coherent story for philosophers of science, and (b) use the history as a case study for the epistemological evolution of the understanding of weak interactions in HEP. Iconclude with some philosophical lessons regarding theory construction in physics.

Rethinking antiparticles. Hermann Weyl’s contribution to neutrino physics

This paper focuses on Hermann Weyl’s two-component theory and frames it within the early development of different theories of spinors and the history of the discovery of parity violation in weak interactions. In order to show the implications of Weyl’s theory, the paper discusses the case study of Ettore Majorana’s symmetric theory of electron and positron (1937), as well as its role in inspiring Case’s formulation of parity violation for massive neutrinos in 1957. In doing so, this paper clarifies the relevance of Weyl’s and Majorana’s theories for the foundations of neutrino physics and emphasizes which conceptual aspects of Weyl’s approach led to Lee’s and Yang’s works on neutrino physics and to the solution of the theta-tau puzzle in 1957. This contribution thus sheds a light on the alleged “re-discovery” of Weyl’s and Majorana’s theories in 1957, by showing that this did not happen all of a sudden. On the contrary, the scientific community was well versed in applying these theories in the 1950s on the ground of previous studies that involved important actors in both Europe and United States.

Muon decay: an old, yet alive experiment in the university physics curriculum

The classic experiment on muon decay is proposed in the undergraduate or master physics curriculum, making use of a single scintillation detector and observing in coincidence the delayed signal due to the electron following muon decay. Two experimental setups, with different geometries and scintillation materials, were considered, making use of standard equipment available in most undergraduate labs. The results obtained in the two cases were compared and discussed. For a better understanding of the results, and to also evaluate the possible effect of material surrounding the detector, detailed GEANT simulations were carried out for both experimental setups. Such simulations are also intended as an additional student activity to virtually exploit in a short time the effect of modifying detector and material configuration, which cannot be achieved during a single student session. The results of this experiment and its interpretation also proved to be a useful way to discuss with students many topics of interest in modern physics, such as—among others—the time dilation, the dependence of muon lifetime in matter, the Fermi weak interaction coupling constant and the parity violation in weak interactions.

LHC accessible second Higgs boson in the left-right model

A second Higgs doublet arises naturally as a parity partner of the standard model (SM) Higgs, once the SM is extended to its left-right symmetric version (LRSM) to understand the origin of parity violation in weak interactions, as well as to accommodate small neutrino masses via the seesaw mechanism. The flavor-changing neutral Higgs (FCNH) effects in the minimal version of this model (LRSM), however, push the second Higgs mass to more than 15 TeV, making it inaccessible at the LHC. Furthermore, since the second Higgs mass is directly linked to the ${W}_{R}$ mass, discovery of a ``low'' mass ${W}_{R}$ (${M}_{{W}_{R}}\ensuremath{\le}5--6\text{ }\text{ }\mathrm{TeV}$) at the LHC would require values for some Higgs self-couplings larger than 1. In this paper we present an extension of LRSM by adding a vectorlike $SU(2{)}_{R}$ quark doublet which weakens the FCNH constraints, allowing the second Higgs mass to be near or below the TeV range and a third neutral Higgs below 3 TeV for a ${W}_{R}$ mass below 5 TeV. It is then possible to search for these heavier Higgs bosons at the LHC without conflicting with FCNH constraints. A right-handed ${W}_{R}$ mass in the few TeV range is quite natural in this class of models without having to resort to large scalar coupling parameters. The CKM mixings are intimately linked to the vectorlike quark mixings with the known quarks, which is the main reason why the constraints on the second Higgs mass are relaxed. We present a detailed theoretical and phenomenological analysis of this extended left-right model and point out some tests as well as its potential for discovery of a second Higgs at the LHC. Two additional features of the model are a $5/3$-charged quark and a fermionic top partner with masses in the TeV range.

Neutrino masses, dominant neutrinoless double beta decay, and observable lepton flavor violation in left-right models and SO(10) grand unification with low mass W R , Z R bosons

While the detection of $W_R$-boson at the Large Hadron Collider is likely to resolve the mystery of parity violation in weak interaction, observation of neutrinoless double beta decay ($0\nu\beta\beta$) is expected to determine whether neutrinos are Majorana fermions. In this work we consider a class of LR models with TeV scale $W_R, Z_R$ bosons but having parity restoration at high scales where they originate from well known Pati-Salam symmetry or $SO(10)$ grand unified theory minimally extended to accommodate inverse seesaw frame work for neutrino masses. Most dominant new contribution to neutrinoless double beta decay is noted to occur via $W_L^{-}W_L^{-}$ mediation involving lighter sterile neutrino exchanges. The next dominant contribution is found to be through $W_L^{-}W_R^{-}$ mediation involving both light and heavy right-handed neutrino or sterile neutrino exchanges. The quark-lepton symmetric origin of the computed value of the Dirac neutrino mass matrix is also found to play a crucial role in determining these and other results on lepton flavor violating branching ratios for $\tau \rightarrow e + \gamma$, $\tau \rightarrow \mu + \gamma$, and $\mu \rightarrow e + \gamma$ accessible to ongoing search experiments. The underlying non-unitarity matrix is found to manifest in substantial CP-violating effects even when the leptonic Dirac phase $\delta_{\rm CP} \simeq 0, \pi, 2 \pi$. Finally we explore a possible origin of the model in non-supersymmetric SO(10) grand unified theory where, in addition to low mass $W_R^\pm$ and $Z_R$ bosons accessible to Large Hadron Collider, the model is found to predict observable neutron-antineutron oscillation and lepto-quark gauge boson mediated rare kaon decay with $\mbox{Br} \left(K_{\rm L} \rightarrow \mu\, \bar{e}\right) \simeq \left(10^{-9}- 10^{-11} \right)$.

Can we explain why leptonic electroweak interactions are chiral?

One of the fundamental ingredients in the standard model of electroweak interactions between fundamental particles is chirality. Currently there are no hints about why nature has chosen the chiral way. The answer to such a fundamental question could be the extension of the whole theory to the superluminal sector of the Lorentz-Poincaré group. Restricting ourselves to leptons, we postulate that the neutrinos are a priori described by a tachyonic Dirac Lagrangian. It could provide a simple explanation for the parity violation in weak interactions and why electroweak theory has a chiral aspect, leading to invariance under a SUL(2) × UY(1) gauge group. Right-handed neutrino becomes sterile and decoupled from the other particles quite naturally.

The first dozen years of the history of ITEP Theoretical Physics Laboratory

The theoretical investigations at ITEP in the years 1945-1958 are reviewed. There are exposed the most important theoretical results, obtained in the following branches of physics: 1) the theory of nuclear reactors on thermal neutrons; 2) the hydrogen bomb project ("Tube" in USSR and "Classical Super" in USA); 3) radiation theory; ~4) low temperature physics; 5) quantum electrodynamics and quantum field theories; 6) parity violation in weak interactions, the theory of $\beta$-decay and other weak processes; 7) strong interaction and nuclear physics. To the review are added the English translations of few papers, originally published in Russian, but unknown (or almost unknown) to Western readers.

Spontaneous mirror parity violation, common origin of matter and dark matter, and the LHC signatures

Existence of a mirror world in the Universe is a fundamental way to restore the observed parity violation in weak interactions and provides the lightest mirror nucleon as a unique GeV-scale dark matter particle candidate. The visible and mirror worlds share the same spacetime of the Universe and are connected by a unique space-inversion symmetry---the mirror parity ($P$). We conjecture that the mirror parity is respected by the fundamental interaction Lagrangian, and study its spontaneous breaking from minimizing the Higgs vacuum potential. The domain-wall problem is resolved by a unique soft-breaking linear term from the $P$-odd weak-singlet Higgs field. We also derive a constraint from big-bang nucleosynthesis. We then analyze the neutrino seesaw for both visible and mirror worlds, and demonstrate that the desired amounts of visible matter and mirror dark matter in the Universe arise from a common origin of $CP$ violation in the neutrino sector via leptogenesis. We derive the Higgs mass spectrum and Higgs couplings with gauge bosons and fermions. We show their consistency with the direct Higgs searches and the indirect precision constraints. We further study the distinctive signatures of the predicted nonstandard Higgs bosons at the LHC. Finally, we analyze the direct detections of GeV-scale mirror dark matter by the TEXONO and CDEX experiments.

Positronium portal into hidden sector: a new experiment to search for mirror dark matter

The understanding of the origin of dark matter has great importance for cosmology and particle physics. Several interesting extensions of the standard model dealing with solution of this problem motivate the concept of hidden sectors consisting of SU(3)C × SU(2)L × U(1)Y singlet fields. Among these models, the mirror matter model is certainly one of the most interesting. The model explains the origin of parity violation in weak interactions, it could also explain the baryon asymmetry of the Universe and provide a natural ground for the explanation of dark matter. The mirror matter could have a portal to our world through photon-mirror photon mixing (ϵ). This mixing would lead to orthopositronium (o−Ps) to mirror orthopositronium oscillations, the experimental signature of which is the apparently invisible decay of o−Ps. In this paper, we describe an experiment to search for the decay o−Ps→invisible in vacuum by using a pulsed slow positron beam and a massive 4π BGO crystal calorimeter. The developed high efficiency positron tagging system, the low calorimeter energy threshold and high hermiticity allow the expected sensitivity in mixing strength to be ϵ ≃ 10−9, which is more than one order of magnitude below the current Big Bang Nucleosynthesis limit and in a region of parameter space of great theoretical and phenomenological interest. The vacuum experiment with such sensitivity is particularly timely in light of the recent DAMA/LIBRA observations of the annual modulation signal consistent with a mirror type dark matter interpretation.

Detection of heavy Majorana neutrinos and right-handed bosons

The SU c (3) ⊗ SU L (2) ⊗ SU R (2) ⊗ U(1) left-right (LR) symmetric model explains the origin of the parity violation in weak interactions and predicts the existence of additional gauge bosons W R and Z′. In addition, heavy right-handed Majorana neutrino states N arise naturally within the LR symmetric model. The states N could be partners of light neutrino states, related to their nonzero masses through the seesaw mechanism. This makes the searches for W R , Z′, and N interesting and important. In the framework of the minimal LR model, we study the possibility to observe signals from N and W R production in pp collisions after three years of running at low LHC luminosity. We show that their decay signals can be identified with a small background, especially in the case of same-sign leptons in the final state. For the integral LHC luminosity of L t = 30 fb−1, the 5σ discovery of W R boson and heavy Majorana neutrinos N e with masses \(M_{W_R } \) up to 4 TeV and \(M_{N_e } \) up to 2.4 TeV, respectively, is found to be possible.

ON THE ROLE OF THE WEAK INTERACTION IN THE PROCESS OF NUCLEAR FISSION

We investigate the effect of the parity-violating weak interaction in the process of n-induced low-energy fission within a time-dependent microscopic description. We display two different mechanisms of enhancement: a) the well-known enhancement due to the chaotic complexity of compound nuclear states and the concomitant high density of levels, b) an additional dynamical enhancement which arises whenever the substates of a parity doublet cross as a function of the intrinsic octupole moment Q30 on the way to fission. In the last section we discuss other examples of this additional enhancement mechanism which is due to a spontaneous symmetry breaking.

The polarized electron target as a new solar-neutrino detector

In this paper, we analyze the scattering of solar neutrinos on the polarized electron target, and predict how the effect of parity violation in weak interactions may help to distinguish neutrino signal from detector background. We indicate that the knowledge of the Sun motion across the sky is sufficient to predict the day/night asymmetry in the (νee−) scattering on the polarized electron target. To make this detection feasible, the polarized electron target for solar neutrinos needs to be build from magnetic materials, e.g., from ferromagnetic iron foils, paramagnetic scintillator crystals or scintillating ferrofluids.

Feature Article: Neutrino Physics

It was a desperate attempt to rescue energy and angular momentum conservation in beta decays when Wolfgang Pauli postulated the neutrino in 1930. In his famous letter addressed to a meeting in Tübingen, Germany, Pauli expressed his apprehension that this new neutral and almost massless particle may never get detected experimentally. Indeed it took 26 years until F. Reines (Nobel prize 1995) and C. Cowan observed neutrinos via the inverse beta decay reaction which are emitted from the fission products in a nuclear power reactor. Neutrinos only interact with matter via weak forces and the cross section was measured to be σ = (1.1 ± 0.3) 10−43 cm2, which corresponds to an enormous absorption length of about 29 light years! In 1957 parity violation in weak interaction was detected by C. Wu and only one year later the helicity of neutrinos by a famous experiment performed by M. Goldhaber. He found the neutrino to be left handed, whereas the anti-neutrino is right handed. Since the right handed partner of the neutrino is missing, neutrinos are massless in the standard model. If the anti-neutrino is identical to the neutrino it is called Majorana particle.

Generation of primordial magnetic fields by α-effect driven by collective neutrino-plasma interaction

We suggest a new mechanism for generation of large-scale magnetic fields in the hot plasma of early universe which is based on the parity violation in weak interactions. The mechanism can result in a self-excitation of an (almost) uniform cosmological magnetic field.