Sigma Hyperons Research Articles

A novel partition function for elementary particles

Three different partition functions are well-known and described in statistical physics. Here, a novel partition function for the description of intra-particular interactions and with this for the mass of particles is presented below. In statistical physics, three different partition functions are already well-established. These are the microcanonical, the canonical, and the macro-canonical partition functions. Here a fourth, novel partition function is added to these already well-established three. Thereby due to the properties of quantum mechanics and superposition, this novel partition function is of fundamental different nature. According to this concept, the new partition function for particles is first defined. The masses and energies of the elementary particles are then calculated using this novel partition function. The energy of an elementary particle is proportional to the mass on the one hand and to the novel partition function on the other. The constant of proportionality with respect to the new partition function is found to be identical with Rydberg constant and Rydberg energy. The relationships found for the proton, the electron, and the sigma particle are then generalized to all elementary particles.

Instanton induced spin–spin correlations

The QCD instanton can be observed at relatively low energies at Nica collider by studying the spin-spin correlations between the incoming proton and the produced Lambda or Sigma hyperons (or the Lambda and bar{Lambda } hyperons). Low Nica energy will allow to better record and to measure the polarization of the hyperon originated by the polarized valence quark(s) in the proton fragmentation region.

Advancing strength and counteracting embrittlement by displacive transformation in heterogeneous high-entropy alloys containing sigma phase

Metallic alloy design for room temperature applications typically aims at avoiding undesired brittle intermetallic phases. In transition metal alloys, the sigma phase is particularly known as a harmful phase leading to serious embrittlement. Here, we develop a novel strategy that utilizes displacive transformation and heterogeneous structures to mitigate the embrittlement of sigma phase particles in high-entropy alloys (HEAs). A careful study of the deformation behavior reveals that the displacive transformation from face-centered cubic (FCC) to hexagonal close packed (HCP) phase can effectively suppress the propagation of microcracks originated in these brittle sigma particles (310±52 nm) and contributes to high work hardening behavior during tensile deformation. This is achieved by tuning the stacking fault energy of the FCC matrix by reducing the Ni content to promote transformation induce plasticity (TRIP) around the sigma phase in a non-equiatomic Fe34Mn20Co20Cr20Ni6 (at. %) HEA. Such TRIP effect can be optimized in various heterogeneous structures with bimodal grain sizes via simple cold-rolling (∼60%) and subsequent annealing (30 min at 700 or 800 °C). The heterogeneously structured HEAs containing brittle sigma particles exhibit ultimate tensile strengths as high as ∼1.2 GPa while maintaining a ductility up to ∼50%. This is mainly attributed to the transformation induced stress-relaxation around the regions containing brittle sigma particles. The insights provide a new design strategy of combining TRIP effect and heterogeneous structures for developing strong and ductile alloys.

Displaced vertex and disappearing track signatures in type-III seesaw

We investigate a prospect of probing the type-III seesaw neutrino mass generation mechanism at various collider experiments by searching for a disappearing track and a displaced vertex signature originating from the decay of SU(2)_L triplet fermion (Sigma ). Since Sigma is primarily produced at colliders through the electroweak gauge interactions, its production rate is uniquely determined by its mass. We find that a Sigma particle produces a disappearing track signature from the decay of its charged component, which can be searched at the HL-LHC. Furthermore, we show that if the lightest observed neutrino has a mass of around 10^{-9} eV, the neutral component of {Sigma } can be discovered at the proposed MATHUSLA detector. We also show that the charged component of {Sigma } can be potentially be observed at FCC-he as a displaced vertex signature.

Influence of N on precipitation behavior and transformation kinetics of super austenitic stainless steels after isothermal ageing at 900 °C

The precipitation behavior and transformation kinetics of secondary phases of super austenitic stainless steels 654SMO containing 0.4wt.% N and 0.5wt.% N were investigated following ageing at 900 °C for varied time. It was revealed that the increase of N did not lead to the refinement of sigma precipitates. Super austenitic stainless steel with 0.4wt.% N presented more uniform and homogeneous precipitation. This unexpected event was caused by a higher sigma nucleation rate than the growth rate of the 0.4wt.% N alloy. The area fraction of precipitates of 0.5wt.% N alloy was lower than that of 0.4wt.% N alloy, which was most likely due to the lesser number of particles nucleated overcompensating the fast growth of sigma particles caused by rising N concentration. Furthermore, increasing the N content did not speed up but slowed down the precipitation of the Cr2N phase. The Cr2N phases were found nucleated at the σ/γ interface, implying that the higher sigma transformation fraction of the 0.4wt.% N alloy promoted the precipitation of nitrides. The modified Johnson-Mehl-Avrami model was used to describe the transformation kinetics of precipitates in both alloys. There was a good agreement between experimental data and model.

Structural Stability of Sandvik 3R60™ After 240 131 Hours Ageing and Creep Test at 700 °C

Sandvik 3R60™ is an AISI 316/316L type of stainless steel. In this paper, the structural stability of the material under long-term ageing or creep test has been studied. The material had been creep tested with a stress of 45 MPa at 700 °C. The predicted rupture time for the creep specimen was about 100,000 h; however, the specimen broke first after 240,131 h. The oxidation behavior and structural stability in both aged and creep-tested samples were studied using SEM/EDS, EBSD and ECCI techniques. Thin oxide layers near the sample surface are mainly spinel oxides and eskolaite (Cr2O3). Sigma phase, χ-phase, Eta phase, M23C6 and Cr2N have been observed in the matrix of the samples. In the crept sample, the amount of sigma phase has increased, so has Eta phase and χ-phase as well. Thermo-Calc evaluation can reasonably predict precipitation of sigma phase, Eta phase and M23C6, but not χ-phase and Cr2N phases. Creep crack initiation behavior has been studied. It is mainly noticed to start at surface oxide layer or coarse sigma particles at grain boundary or triple point. Additionally, it is also observed that the presence of a thin Cr2O3 layer between the oxide and matrix along with discontinuous sigma phase distribution at grain boundary that will reduce the risk for creep crack initiation. Further, the crack propagation behavior has also been discussed.

Microstructure and Failure Processes of Reactor Pressure Vessel Austenitic Cladding

This paper is dedicated to an experimental program focused on the evaluation of microstructure and failure mechanisms of WWER 440 type nuclear reactor pressure vessel cladding made from Sv 08Kh19N10G2B stainless steel. Static fracture toughness tests performed on standard precracked single edge bend specimens revealed extreme variations in fracture toughness values, J0.2. Fractured halves of test specimens were subject to detailed fractographic and metallographic analyses in order to identify the causes of this behavior and to determine the relationship between local microstructure, failure mode and fracture toughness. Results indicated that fracture toughness of the cladding was adversely affected by the brittle cracking of sigma particles which caused a considerable decrease in local ductile tearing resistance. Extreme variations in relative amounts of sigma phase, as well as the extreme overall structural heterogeneity of the cladding determined in individual specimens, provided a reasonable explanation for variations in fracture toughness values.

Pythagorean numbers and the calculation of the masses of the elementary particles

We attempt here to calculate the particle masses for all known elementary particles starting from the Rydberg equation and from the Sommerfeld fine structure constant. Remarkably, this is possible. Next, we try to explain why this is possible and what the meaning of the approach seems to be. Thereby, we find some interesting connections. In addition, we realize that there are two different kinds of mass-charge binding energies in an elementary particle: The internal mass-charge binding energy and the external mass-charge binding energy. These two kinds of mass-charge binding energies can explain the higher masses of the highly charged brother particles in some of the heavier particle triplets (such as the charmed sigma particles).

Development of Precipitation-Strengthened Al0.8NbTiVM (M = Co, Ni) Light-Weight Refractory High-Entropy Alloys.

Single-phase solid-solution refractory high-entropy alloys (RHEAs) have been receiving significant attention due to their excellent mechanical properties and phase stability at elevated temperatures. Recently, many studies have been reported regarding the precipitation-enhanced alloy design strategy to further improve the mechanical properties of RHEAs at elevated temperatures. In this study, we attempted to develop precipitation-hardened light-weight RHEAs via addition of Ni or Co into Al0.8NbTiV HEA. The added elements were selected due to their smaller atomic radius and larger mixing enthalpy, which is known to stimulate the formation of precipitates. The addition of the Ni or Co leads to the formation of the sigma precipitates with homogeneous distribution. The formation and homogeneous distribution of sigma particles plays a critical role in improvement of yield strength. Furthermore, the Al0.8NbTiVM0.2 (M = Co, Ni) HEAs show excellent specific yield strength compared to single-phase AlNbTiV and NbTiVZr RHEA alloys and conventional Ni-based superalloy (Inconel 718) at elevated temperatures.

Constraining CP violation in the main decay of the neutral Sigma hyperon

The Σ0 and Λ hyperons are close relatives of the neutron, being related by flavour SU(3) symmetry. This allows to estimate an upper limit for the electric dipole transition moment (EDTM) of the Σ0-Λ transition, based on the experimental knowledge of the upper limit of the neutron electric dipole moment. The three-body decay could show an angular asymmetry due to the interference of parity violating and conserving amplitudes in both the first and second step of the decay chain . This angular asymmetry, which will be measured at e.g. PANDA for both particle and antiparticle decays, is determined in this work from the Σ0-Λ EDTM, where a CP violating QCD theta-vacuum-angle term has been included. It turns out to be below any experimental resolution that one can expect in the foreseeable future. Any experimental significance would therefore point to physics beyond the Standard Model.

Λ(1405) as a K¯N Feshbach resonance in the Skyrme model

We describe the Lambda(1405) hyperon as a Feshbach resonance of a bar-KN quasi-bound state coupled by a decaying channel of pi Sigma in the Skyrme model. A weakly bound bar-KN state is generated in the laboratory frame, while the Sigma hyperon as a strongly bound state of bar-KN in the intrinsic frame. We obtain a coupling of bar-KN and pi Sigma channels by computing a baryon matrix element of the axial current. This coupling enables the decay of the bar-KN bound state to pi-Sigma . It is shown that the Skyrme model supports the Lambda(1405) as a narrow Feshbach resonance.

Radiative corrections for the decay varSigma ^0rightarrow varLambda e^+e^-

Electromagnetic form factors serve to explore the intrinsic structure of nucleons and their strangeness partners. With electron scattering at low energies the electromagnetic moments and radii of nucleons can be deduced. The corresponding experiments for hyperons are limited because of the unstable nature of the hyperons. Only for one process this turns to an advantage: the decay of the neutral Sigma hyperon to a Lambda hyperon and a real or virtual photon. Due to limited phase space the effects caused by the Sigma-to-Lambda transition form factors compete with the QED radiative corrections for the decay varSigma ^0rightarrow varLambda e^+e^-. These QED corrections are addressed in the present work, evaluated beyond the soft-photon approximation, i.e., over the whole range of the Dalitz plot and with no restrictions on the energy of the radiative photon.

Constraining P and CP violation in the main decay of the neutral Sigma hyperon

On general grounds based on quantum field theory the decay amplitude for Σ0→Λγ consists of a parity conserving magnetic and a parity violating electric dipole transition moment. Because of the subsequent self-analyzing weak decay of the Λ hyperon the interference between magnetic and electric dipole transition moment leads to an asymmetry in the angular distribution. Comparing the decay distributions for the Σ0 hyperon and its antiparticle gives access to possible C and CP violation. Based on flavor SU(3) symmetry the present upper limit on the neutron electric dipole moment can be translated to an upper limit for the angular asymmetry. It turns out to be far below any experimental resolution that one can expect in the foreseeable future. Thus any true observation of a CP violating angular asymmetry would constitute physics beyond the standard model, even if extended by a CP violating QCD theta-vacuum-angle term.

Hyperons in nuclear matter from SU(3) chiral effective field theory

Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Lambda and Sigma hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Sigma-nuclear potential and a weak Lambda-nuclear spin-orbit force.

A study of hyperons in nuclear matter based on chiral effective field theory

The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field theory and fitted to Lambda-N and Sigma-N scattering data, are investigated. Results for the single-particle potentials of the Lambda and Sigma hyperons in nuclear matter are reported, based on a conventional first-order Brueckner calculation. The Sigma-nucleus potential is found to be repulsive, in agreement with phenomenological information. A weak Lambda-nucleus spin-orbit interaction can be achieved by an appropriate adjustment of a low-energy constant corresponding to an antisymmetric Lambda-N -- Sigma-N spin-orbit interaction that arises at next-to-leading order in the effective field theory approach.

Baryonic resonances close to theK¯Nthreshold: The case ofΣ(1385)+inppcollisions

We present results of an exclusive measurement of the first excited state of the Sigma hyperon, Sigma(1385)^+, produced in p+p -> Sigma^+ + K^+ + n at 3.5 GeV beam energy. The extracted data allow to study in detail the invariant mass distribution of the Sigma(1385)^+. The mass distribution is well described by a relativistic Breit-Wigner function with a maximum at m_0 = 1383.2 +- 0.9 MeV/c^2 and a width of 40.2 +- 2.1 MeV/c^2. The exclusive production cross-section comes out to be 22.27 +- 0.89 +- 1.56 +3.07 -2.10 mu b. Angular distributions of the Sigma(1385)^+ in different reference frames are found to be compatible with the hypothesis that 33 % of Sigma(1385)^+ result from the decay of an intermediate Delta^{++} resonance.

Hyperon production in Ar + KCl collisions at 1.76A GeV

We present transverse momentum spectra, rapidity distribution and multiplicity of Lambda-hyperons measured with the HADES spectrometer in the reaction Ar(1.76A GeV)+KCl. The yield of Xi- is calculated from our previously reported Xi-/(Lambda+Sigma0) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities of the yet unmeasured charged Sigma hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of pi-, K+, K0s, K-, phi, Lambda and Xi-. The resulting chemical freeze-out temperature of T=(76+-2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the particles.

Producing nanostructured super-austenitic steels by friction stir processing

In the present work, friction stir processing (FSP) was used to produce the nanostructured super-austenitic steel. After preheating, the specimens were subjected to FSP using the rotation and traverse speed of 2600rpm and 30mmmin−1, respectively. The specimen temperature during FSP was about 950±2°C. The results show that a nanostructured layer of about 91μm thick was produced on the specimen surface. The formed nanograins ranged from 50 to 90nm. Besides, the hot severe deformation applied during FSP led to significant fragmentation of the coarse sigma particles to nanosize ones.The produced nanostructured layer was then characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The formed nanostructure led to a twofold increase in the hardness. The formation of nanostructure resulted in an increase in hardness up to 350Hv, comparing to 185Hv pertaining to base structure of super austenitic steel.

Unconventional Rotational Responses of Hadronic Superfluids in a Neutron Star Caused by Strong Entrainment and aΣ−Hyperon Gap

I show that the usual model of the rotational response of a neutron star, which predicts rotation-induced neutronic vortices and no rotation-induced protonic vortices, does not hold (i) beyond a certain threshold of entrainment interaction strength nor (ii) in the case of nonzero Sigma(-) hyperon gap. I show that in both of these cases the rotational response involves the creation of phase windings in an electrically charged condensate. Lattices of bound states of vortices which result from these phase windings can (for a range of parameters) strongly reduce the interaction between rotation-induced vortices with magnetic-field carrying superconducting components.

QuasifreeΛ,Σ0, andΣ−electroproduction fromH1,2,He3,4, and carbon

Kaon electroproduction from light nuclei and hydrogen, using 1H, 2H, 3He, 4He, and Carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Lambda and Sigma hyperons were determined at Q^2= 0.35(GeV/c)^2 and W= 1.91GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.