Isospin Multiplets Research Articles

Breakdown of the Isobaric Multiplet Mass Equation for theA=20and 21 Multiplets

Using the Penning trap mass spectrometer TITAN, we performed the first direct mass measurements of (20,21)Mg, isotopes that are the most proton-rich members of the A = 20 and A = 21 isospin multiplets. These measurements were possible through the use of a unique ion-guide laser ion source, a development that suppressed isobaric contamination by 6 orders of magnitude. Compared to the latest atomic mass evaluation, we find that the mass of (21)Mg is in good agreement but that the mass of (20)Mg deviates by 3 σ. These measurements reduce the uncertainties in the masses of (20,21)Mg by 15 and 22 times, respectively, resulting in a significant departure from the expected behavior of the isobaric multiplet mass equation in both the A = 20 and A = 21 multiplets. This presents a challenge to shell model calculations using either the isospin nonconserving universal sd USDA and USDB Hamiltonians or isospin nonconserving interactions based on chiral two- and three-nucleon forces.

Z(4430)and a new paradigm for spin interactions in tetraquarks

Following the recent confirmation of the Z+(4430) resonance with J^{PG}=1^{++}, we have re-examined the model of S- and P-wave tetraquarks. We propose a `type-II' diquark-antidiquark model which shows to be very effective at producing a simple and comprehensive picture of the J^{PG}=1^{++} and 1^{--} sectors of the recently discovered charged tetraquarks and of the observed Y resonances. The model is still faced with the unresolved difficulty of explaining why some states seem to have incomplete isospin multiplets.

Survey of Evaluated Isobaric Analog States

Isobaric analog states (IAS) can be used to estimate the masses of members belonging to the same isospin multiplet. Experimental and estimated IAS have been used frequently within the Atomic Mass Evaluation (AME) in the past, but the associated set of evaluated masses have been published for the first time in AME2012 and NUBASE2012. In this paper the current trends of the isobaric multiplet mass equation (IMME) coefficients are shown. The T = 2 multiplet is used as a detailed illustration.

Evaluated experimental isobaric analogue states from T=1/2 to T=3 and associated IMME coefficients

Isobaric multiplets can be used to provide reliable mass predictions through the Isobaric Multiplet Mass Equation (IMME). Isobaric analogue states (IAS) for isospin multiplets from $T=1/2$ to $T=3$ have been studied within the 2012 Atomic Mass Evaluation (Ame2012). Each IAS established from published experimental reaction data has been expressed in the form of a primary reaction $Q$-value, and if necessary, has been recalibrated. The evaluated IAS masses are provided here along with the associated IMME coefficients. Quadratic and higher order forms of the IMME have been considered, and global trends have been extracted. Particular nuclides, requiring experimental investigation, have been identified and discussed. This dataset is the most precise and extensive set of evaluated IAS to date.

How theZc(3900)Reveals the Spectra of Charmonium Hybrids and Tetraquarks

Flavor-exotic tetraquark mesons have recently been observed in the heavy-quark pair sectors of QCD, including two isospin multiplets in the b b-bar sector, Z_b(10610) and Z_b(10650), and one isospin multiplet in the c c-bar sector, Z_c(3900). We identify Z_b and Z_c as tetraquark mesons that are analogs of quarkonium hybrids with the gluon field replaced by an isospin-1 excitation of the light-quark fields. Given the identification of Y(4260) and Z_c(3900) as a ground-state charmonium hybrid and tetraquark, respectively, lattice QCD calculations of the charmonium spectrum can be used to estimate the masses of the lowest four spin-symmetry multiplets of charmonium hybrids and tetraquarks. The Z_b(10610) and Z_b(10650) can be assigned to excited-state multiplets of bottomonium tetraquarks, resulting in estimates of the masses of the ground-state multiplets of bottomonium hybrids and tetraquarks.

Strong contribution to octet baryon mass splittings

We calculate the md−mu contribution to the mass splittings in baryonic isospin multiplets using SU(3) chiral perturbation theory and lattice QCD. Fitting isospin-averaged perturbation theory functions to PACS-CS and QCDSF-UKQCD Collaboration lattice simulations of octet baryon masses, and using the physical light-quark mass ratio mu/md as input, allows Mn−Mp, MΣ−−MΣ+ and MΞ−−MΞ0 to be evaluated from the full SU(3) theory. The resulting values for each mass splitting are consistent with the experimental values after allowing for electromagnetic corrections. In the case of the nucleon, we find Mn−Mp=2.9±0.4 MeV, with the dominant uncertainty arising from the error in mu/md.

Lipopeptides from the Banyan Endophyte, Bacillus subtilis K1: Mass Spectrometric Characterization of a Library of Fengycins

Mass spectrometric analysis of a banyan endophyte, Bacillus subtilis K1, extract showing broad spectrum antifungal activity revealed a complex mixture of lipopeptides, iturins, surfactins, and fengycins. Fractionation by reversed-phase high performance liquid chromatography (HPLC) facilitated a detailed analysis of fengycin microheterogeneity. Matrix assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometric studies permitted the identification of several new fengycin variants. Four major sites of heterogeneity are identified: (1) N-terminus β-hydroxy fatty acid moiety, where chain length variation and the presence of unsaturation occur, (2) position 6 (Ala/Val/Ile/Leu), (3) position 10 (Val/Ile) within the macrocyclic ring, and (4) Gln to Glu replacement at position 8, resulting in fengycin variants that differ in mass by 1 Da. Diagnostic fragment ions provide a quick method for localizing the sites of variation in the macrocycle or the linear segment. Subsequent establishment of the sequences is achieved by MS/MS analysis of linear fengycin species produced by hydrolysis of the macrocyclic lactone. Unsaturation in the fatty acid chain and the presence of linear precursors in the B. subtilis K1 extract are also established by mass spectrometry. The anomalous distribution of intensities within isotopic multiplets is a diagnostic for Gln/Glu replacements. High resolution mass spectrometry facilitates the identification of fengycin species differing by 1 Da by localizing the variable position (Gln(8)/Glu(8)) in the fengycin variants.

Phenomenology of excited doubly charged heavy leptons at the LHC

We consider the production at the LHC of exotic composite leptons of charge Q=+2e. Such states are allowed in composite models which contain extended isospin multiplets (Iw=1 and Iw=3/2). These doubly charged leptons couple with Standard Model [SM] fermions via gauge interactions, thereby delineating and restricting their possible decay channels. We discuss the production cross section at the LHC of L++ (p p --> L++, l-) and concentrate on the leptonic signature deriving from the cascade decays L++ --> W+, l+ --> l+, l+, \nu_l i.e. p p --> l-, l+, l+, \nu_l showing that the invariant mass distribution of the like-sign dilepton has a sharp end point corresponding to excited lepton mass m*. We find that the sqrt{s}=7 TeV run is sensitive at the 3-sigma (5-sigma) level to a mass of the order of 600 GeV if L=10 fb^-1 (L=20 fb^-1). The sqrt{s}=14 TeV run can reach a sensitivity at 3-sigma (5-sigma) level up to m*=1 TeV for L=20 fb^-1 (L=60 fb^-1).

Shape isomerism and shape coexistence effects on the Coulomb energy differences in theN=Znucleus66As and neighboringT=1multiplets

Excited states of the N=Z=33 nucleus 66As have been populated in a fusion-evaporation reaction and studied using γ-ray spectroscopic techniques. Special emphasis was put into the search for candidates for the T=1 states. A new 3+ isomer has been observed with a lifetime of 1.1(3) ns. This is believed to be the predicted oblate shape isomer. The excited levels are discussed in terms of the shell model and of the complex excited Vampir approaches. Coulomb energy differences are determined from the comparison of the T=1 states with their analog partners. The unusual behavior of the Coulomb energy differences in the A=70 mass region is explained through different shape components (oblate and prolate) within the members of the same isospin multiplets. This breaking of the isospin symmetry is attributed to the correlations induced by the Coulomb interaction.Received 10 February 2012DOI:https://doi.org/10.1103/PhysRevC.85.034320©2012 American Physical Society

Quaternion-Octonion SU(3) Flavor Symmetry

Starting with the quaternionic formulation of isospin SU(2) group, we have derived the relations for different components of isospin with quark states. Extending this formalism to the case of SU(3) group we have considered the theory of octonion variables. Accordingly, the octonion splitting of SU(3) group have been reconsidered and various commutation relations for SU(3) group and its shift operators are also derived and verified for different iso-spin multiplets i.e. I, U and V- spins. Keywords: SU(3), Quaternions, Octonions and Gell Mann matrices PACS NO: 11.30.Hv: Flavor symmetries; 12.10-Dm: Unified field theories and models of strong and electroweak interactions

Isospin symmetry breaking in the chiral quark model

We discuss the isospin symmetry breaking (ISB) of the valence- and sea-quark distributions between the proton and the neutron in the framework of the chiral quark model. We assume that isospin symmetry breaking is the result of mass differences between isospin multiplets and then analyze the effects of isospin symmetry breaking on the Gottfried sum rule and the NuTeV anomaly. We show that, although both flavor asymmetry in the nucleon sea and the ISB between the proton and the neutron can lead to the violation of the Gottfried sum rule, the main contribution is from the flavor asymmetry in the framework of the chiral quark model. We also find that the correction to the NuTeV anomaly is in an opposite direction, so the NuTeV anomaly cannot be removed by isospin symmetry breaking in the chiral quark model. It is remarkable that our results of ISB for both valence- and sea-quark distributions are consistent with the Martin-Roberts-Stirling-Thorne parametrization of quark distributions.

Tautomerism and isotopic multiplets in the 13C NMR spectra of partially deuterated 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones and their sulfur analogs—evidence for elucidation of the structure backbone and tautomeric forms

The tautomerism of the synthesized 3-arylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones (1a-d) and 3-aryl-7-thioxo-7,8-dihydro-6H-pyrimido[4,5-c]pyridazine-5-ones (2a-d) was studied in dimethyl sulfoxide (DMSO)-d(6). (1)H NMR spectra of 1a-d showed a clustered water molecule in the structure backbone that is attached by strong intermolecular H bonding. The relation between the temperature and H bonding of the clustered water molecule with 1a was also studied as representative. The relation between the electronegativity (chi) of the substituent on phenyl ring and the chemical shifts of clustered water protons in 1a-d was also studied. All of 1a-d and also 2d compounds existed in lactam (I) form, whereas 2a-c compounds have two distinguished tautomers in DMSO-d(6) [lactam (I) and lactim (II) forms]. The solvent-substrate proton exchange was examined in compounds 1a-d and 2a-d by adding one drop of D(2)O. All compounds (except 1d) showed proton/deuterium exchange of the clustered water protons in DMSO by adding one drop of D(2)O. Some compounds (but not all of them) that are easily soluble in DMSO-d(6) containing D(2)O showed isotopic splitting (beta-isotope effect) in their (13)C NMR spectra. Among them, compound 1a was the best evidence to help the spectral assignments and structure determination of predominant tautomer by carbon-13 splitting (beta-isotope effect).

Coulomb versus spin-orbit interaction in few-electron carbon-nanotube quantum dots

Few-electron states in carbon-nanotube quantum dots are studied by means of the configuration-interaction method. The peculiar noninteracting feature of the tunneling spectrum for two electrons, recently measured by F. Kuemmeth, S. Ilani, D. C. Ralph, and P. L. McEuen [Nature (London) 452, 448 (2008)], is explained by the splitting of a low-lying isospin multiplet due to spin-orbit interaction. Nevertheless, the strongly interacting ground state forms a ``Wigner molecule'' made of electrons localized in space. Signatures of the electron molecule may be seen in tunneling spectra by varying the tunable dot confinement potential.

Special features of the isospin splitting of the giant dipole resonance in the 90Zr nucleus

Data on the proton and neutron channels of the 90Zr photodisintegration were analyzed in detail, basic parameters of the isospin splitting of the giant dipole resonance in 90Zr being determined by the properties of these channels. New data concerning the cross sections for the partial photoneutron reactions 90Zr(γ, n)89Zr and 90Zr(γ, 2n)88Zr and resulting from a simultaneous correction of data from experiments performed in Livermore (USA) and Saclay (France) by using beams of quasimonoenergetic annihilation photons were invoked. Use was made of information about the positions on the energy scale of states characterized by different isospin values in the 90Zr nucleus and nuclei neighboring it, which are members of the respective isospin multiplet. New data on the parameters of the isospin splitting of the giant dipole resonance in the 90Zr nucleus were obtained on the basis of a global analysis of data on the giant-dipole-resonance states of the 90Zr nucleus, which are manifested in the respective photoneutron and photoproton cross sections and in their decay channels involving states of different isospin in neighboring nuclei.

Isotopic Perturbation of the Conformational Equilibrium in Methylene-Functionalized Calixarenes

The 400 MHz 1H NMR spectrum of the tetramethoxycalixarene 2 (possessing hydroxyl groups at the bridges) in commercial acetone-d6 displays five signals (an isotopic multiplet) for a pair of methoxy groups. Inspection of the X-ray structures of 2 and its isomer 3 indicates that in the adopted 1,3-alternate conformation, the methoxy groups intramolecularly hydrogen bonded to neighboring OH groups are oriented "in" (pointing toward the cavity). Upon dissolution of 2 in acetone-d6, none, some, or all of the OH protons exchange with the deuterium atoms present in the residual water of the solvent. Several species (mutually relating as isotopomers and isotopologues) differing in the number and positions of the deuterated hydroxyl groups are possible for 2. In three of these species, the "in"-"out"/"out"-"in" conformational equilibrium of a pair of methoxy groups is nondegenerate. The four external lines of the apparent multiplet are ascribed to a single- and double-isotopic perturbation of the "in"-"out" conformational equilibrium of a pair of methoxy groups. On the basis of the assignment of the signals to the individual species and their statistical distribution, the intensities of the components of the isotopic multiplet obtained at different isotopic enrichments of the hydroxyl groups could be simulated. A sample of 2 55% deuterated at the hydroxyl groups in CDCl3 displayed an isotopic multiplet consisting of nine signals. The isotopic multiplet observed for the OH groups of 2 in acetone-d6 was simulated at different deuteration enrichments.

Mass splittings within heavy baryon isospin multiplets in chiral perturbation theory

We calculate the mass splittings within the heavy baryon isospin multiplets Σc(b) and Ξc(b)' in chiral perturbation theory to leading one-loop order. The pattern of the mass splittings in the Σc iso-triplet, which is different from that of any other known isospin multiplet, can be explained. We predict mΞc'+−mΞc'0 = −0.2±0.6 MeV, mΞb'0−mΞb'− = −4.0±1.9 MeV and the mass of the Σb0 to be 5810.3±1.9 MeV.

Automated Intensity Descent Algorithm for Interpretation of Complex High-Resolution Mass Spectra

This paper describes a new automated intensity descent algorithm for analysis of complex high-resolution mass spectra. The algorithm has been successfully applied to interpret Fourier transform mass spectra of proteins; however, it should be generally applicable to complex high-resolution mass spectra of large molecules recorded by other instruments. The algorithm locates all possible isotopic clusters by a novel peak selection method and a robust cluster subtraction technique according to the order of descending peak intensity after global noise level estimation and baseline correction. The peak selection method speeds up charge state determination and isotopic cluster identification. A Lorentzian-based peak subtraction technique resolves overlapping clusters in high peak density regions. A noise flag value is introduced to minimize false positive isotopic clusters. Moreover, correlation coefficients and matching errors between the identified isotopic multiplets and the averagine isotopic abundance distribution are the criteria for real isotopic clusters. The best fitted averagine isotopic abundance distribution of each isotopic cluster determines the charge state and the monoisotopic mass. Three high-resolution mass spectra were interpreted by the program. The results show that the algorithm is fast in computational speed, robust in identification of overlapping clusters, and efficient in minimization of false positives. In approximately 2 min, the program identified 611 isotopic clusters for a plasma ECD spectrum of carbonic anhydrase. Among them, 50 new identified isotopic clusters, which were missed previously by other methods, have been discovered in the high peak density regions or as weak clusters by this algorithm. As a result, 18 additional new bond cleavages have been identified from the 50 new clusters of carbonic anhydrase.

Gamow-Teller transitions toP32studied through theS32(d,He2)reaction atEd=170MeV

The S-32(d,He-2)P-32 charge-exchange reaction has been studied at forward angles and at an incident energy of E-d=170 MeV. The two protons in the S-1(0)(pp) state (indicated as He-2) were both momentum analyzed and detected by the same spectrometer and detector. High resolution He-2 spectra have been obtained allowing identification of many levels in the residual nucleus with high precision. The (d,He-2) reaction selectively excites spin-isospin-flip transitions, and at vanishing momentum transfer these are largely governed by the Gamow-Teller transition operator for the beta(+) direction. In the case of the self-conjugate nucleus S-32, the (d,He-2) probe is calibrated against the elementary (p,n) probe going into the mirror beta(-) direction. The deduced results are compared with those obtained from (p,p(')) and (e,e(')) reactions, which excite the same levels in the isospin multiplet. Angular distributions of cross sections for the (d,He-2) reaction are presented and compared with DWBA calculations. A level-by-level comparison with shell-model calculations using the USD interaction has been performed, and the structure of the l-forbidden ground state transition is discussed. From the comparison with (p,p(')), (e,e(')), and (p,n) data the isospin-analog J(pi)=1(+) levels in the triplet of the A=32 nuclei are deduced.

A method for calculating 16o/ 18o peptide ion ratios for the relative quantification of proteomes

A method is described for the identification and relative quantification of proteomes using accurate mass tags (AMT) generated by nLC-dual ESI-FT-ICR-MS on a 7T instrument in conjunction with stable isotope labeling using 16O/ 18O ratios. AMTs were used for putative peptide identification, followed by confirmation of peptide identity by tandem mass spectrometry. For a combined set of 58 tryptic peptides from bovine serum albumin (BSA) and human transferrin, a mean mass measurement accuracy of 1.9 ppm ±0.94 ppm (CIM 99%) was obtained. This subset of tryptic peptides was used to measure 16O/ 18O ratios of 0.36 ± 0.09 (CIM 99%) for BSA (μ = 0.33) and 1.48 ± 0.47 (CIM 99%) for transferrin (μ = 1.0) using a method for calculating 16O/ 18O ratios from overlapping isotopic multiplets arising from mixtures of 16O, 18O 1, and 18O 2 labeled C-termini. The model amino acid averagine was used to calculate a representative molecular formula for estimating and subtracting the contributions of naturally occurring isotopes solely as a function of peptide molecular weight. The method was tested against simulated composite 16O/ 18O spectra where peptide molecular weight, 16O/ 18O ratio, 18O 1/ 18O 2 ratios, and number of sulfur atoms were varied. Relative errors of 20% or less were incurred when the 16O/ 18O ratios were less than three, even for peptides where the number of sulfur atoms was over- or under-estimated. These data demonstrate that for biomarker discovery, it is advantageous to label the proteome representing the disease state with 18O; and the method is not sensitive to variations in 18O 1/ 18O 2 ratio. This approach allows a comprehensive differentiation of expression levels and tentative identification via AMTs, followed by targeted analysis of over- and under-expressed peptides using tandem mass spectrometry, for applications such as the discovery of disease biomarkers.

Main channels of the decay of the giant dipole resonance in the 20,22Ne nuclei and isospin splitting of the giant dipole resonance in the 22Ne nucleus

Data published in the literature on various photonuclear reactions for the 20,22Ne isotopes and for their natural mixture are analyzed with the aim of exploring special features of the decay of giant-dipole-resonance states in these two isotopes. With the aid of data on the abundances of the isotopes and on the energy reaction thresholds, the cross sections for the reactions 20,22Ne[(γ, n)+(γ, np)] and 20,22Ne[(γ, p)+(γ, np)] are broken down into the contributions from the one-nucleon reactions (γ, n) and (γ, p) and the contributions from the reactions (γ, np). The cross sections for the reactions 20,22Ne(γ, n)19,21Ne and 20,22Ne(γ, p)19,21F in the energy range Eγ=16.0–28.0 MeV and the cross sections for the reactions 20,22Ne(γ, np)18,20F in the energy range Eγ=23.3–28.0 MeV are estimated. The behavior of the cross-section ratio r=σ(γ, p)/σ(γ, n) for the 22Ne nucleus as a function of energy is analyzed, and the isospin components of the giant dipole resonance in the 22Ne nucleus are identified. The contributions of the isospin components of the giant dipole resonance in the 22Ne nucleus to the cross sections for various photonuclear reactions are determined on the basis of an analysis of the diagram of the excitation and decay of pure isospin states in the 22Ne nucleus and in nuclei neighboring it, which are members of the corresponding isospin multiplets. The isospin splitting of the giant dipole resonance and the ratio of the intensities of the isospin components are determined to be ΔE=4.57±0.69 MeV and R=0.24±0.04, respectively.