Bounds on the width, mass difference and other properties of Χ(3872) →π + π - J/φ decays
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Choi, S.-K.↗
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Theoretical support for the {pi}(1300) and the recently claimed f{sub 0}(1790) as molecular resonances
A study of three-pseudoscalar {pi}KK and {pi}{pi}{eta} coupled system is made by solving the Faddeev equations within an approach based on unitary chiral dynamics. A resonance with total isospin one and spin-parity J{sup {pi}=}0{sup -} is found with mass {approx}1400 MeV when the KK system gets reorganized as the f{sub 0}(980). This resonance is identified with the {pi}(1300) listed by the Particle Data Group. Further, the two-body amplitude which describes the interaction between a {pi} and the f{sub 0}(980) is extracted from the study of the {pi}KK and {pi}{pi}{eta} system and is then employed to study the f{sub 0}(980){pi}{pi} system. As a result, a scalar resonance is found near 1790 MeV which drives the two f{sub 0}(980){pi} systems to resonate as the {pi}(1300) while the invariant mass of the two pions falls in the mass region of the scalar {sigma}(600). These findings support the existence of a new f{sub 0} resonance near 1790 MeV, as found by the BES and Crystal Barrel collaborations. Our results show that this f{sub 0}(1790) is definitely distinct to f{sub 0}(1710), the latter of which seems to possess a glueball structure dominantly.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
{rho} meson decay in 2+1 flavor lattice QCD
We perform a lattice QCD study of the {rho} meson decay from the N{sub f}=2+1 full QCD configurations generated with a renormalization group improved gauge action and a nonperturbatively O(a)-improved Wilson fermion action. The resonance parameters, the effective {rho}{yields}{pi}{pi} coupling constant and the resonance mass, are estimated from the P-wave scattering phase shift for the isospin I=1 two-pion system. The finite size formulas are employed to calculate the phase shift from the energy on the lattice. Our calculations are carried out at two quark masses, m{sub {pi}=}410 MeV (m{sub {pi}/}m{sub {rho}=}0.46) and m{sub {pi}=}300 MeV (m{sub {pi}/}m{sub {rho}=}0.35), on a 32{sup 3}x64 (La=2.9 fm) lattice at the lattice spacing a=0.091 fm. We compare our results at these two quark masses with those given in the previous works using N{sub f}=2 full QCD configurations and the experiment.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
LHC bounds on interactions of dark matter
We derive limits on the interactions of dark matter with quarks from ATLAS null searches for jets+missing energy based on {approx}1 fb{sup -1} of integrated luminosity, using a model-insensitive effective theory framework. We find that the new limits from the LHC significantly extend limits previously derived from CDF data at the Tevatron. Translated into the parameter space of direct searches, these limits are particularly effective for {approx} GeV mass weakly interacting massive particles. Our limits indicate tension with isospin-violating models satisfying minimal flavor violation which attempt to reconcile the purported CoGeNT excess with Xenon-100, indicating that either a light mediator or nontrivial flavor structure for the dark sector is necessary for a viable reconciliation of CoGeNT with Xenon.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
High-Precision Half-Life Measurement for the Superallowed {beta}{sup +} Emitter {sup 26}Al{sup m}
A high-precision half-life measurement for the superallowed {beta}{sup +} emitter {sup 26}Al{sup m} was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T{sub 1/2}=6346.54{+-}0.46{sub stat{+-}}0.60{sub syst} ms, consistent with, but 2.5 times more precise than, the previous world average. The {sup 26}Al{sup m} half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed {beta} decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for {sup 26}Al{sup m}, 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi {beta}-decay studies used to test the conserved vector current hypothesis and determine the V{sub ud} element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Mixed-Spin Pairing Condensates in Heavy Nuclei
We show that the Bogoliubov-de Gennes equations for nuclear ground-state wave functions support solutions in which the condensate has a mixture of spin-singlet and spin-triplet pairing. We find that such mixed-spin condensates do not occur when there are equal numbers of neutrons and protons, but only when there is an isospin imbalance. Using a phenomenological Hamiltonian, we predict that such nuclei may occur in the physical region within the proton dripline. We also solve the Bogoliubov-de Gennes equations with variable constraints on the spin-singlet and spin-triplet pairing amplitudes. For nuclei that exhibit this new pairing behavior, the resulting energy surface can be rather soft, suggesting that there may be low-lying excitations associated with the spin mixing.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Double Higgs production at LHC, see-saw type-II and Georgi-Machacek model
The double Higgs production in the models with isospin-triplet scalars is studied. It is shown that in the see-saw type-II model, the mode with an intermediate heavy scalar, pp → H + X → 2h + X, may have the cross section that is comparable with that in the Standard Model. In the Georgi-Machacek model, this cross section could be much larger than in the Standard Model because the vacuum expectation value of the triplet can be large.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
'Coulomb' description of basic relaxation parameters of isobar analog and charge-exchange giant monopole resonances
Within a semimicroscopic approach, basic relaxation parameters of the isobaric analog resonance and of the charge-exchange giant monopole resonance, which is an overtone of the isobaric analog resonance, are interpreted in terms of the mean Coulomb field of a nucleus. The continuum version of the random-phase approximation, allowance for an approximate isospin conservation in nuclei in an explicit form, and a phenomenological description of the fragmentation effect are basic ingredients of the approach used. The aforementioned parameters were calculated for a number of magic and near-magic nuclei by using a partly self-consistent phenomenological nuclear mean field and the isovector part of the Landau-Migdal interaction in the particle-hole channel. The results of the calculations are compared with corresponding experimental data.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Astrophysical S factors for radiative proton capture by {sup 3}H and {sup 7}Li nuclei
Within the potential cluster model where orbital states are classified according to Young diagrams and isospin, astrophysical S factors are considered for radiative proton capture by {sup 3}H and {sup 7}Li nuclei at energies of up to 1 and 10 keV, respectively. It is shown that the approach used, which takes into account only the E1 transition for the p{sup 3}H capture process, makes it possible to describe well the most recent experimental data at c.m. energies in the range from 50 keV to 5MeV. In the case of proton capture by {sup 7}Li nuclei, an M1 processwas taken into account in addition to the E1 transition, and a general behavior and the magnitude of the experimental S factor could be correctly reproduced owing to this at astrophysical energies, including the region around the resonance at 0.441 MeV (in the laboratory frame).
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Mechanism of pion production in {alpha}p scattering at 1 GeV/nucleon
An analysis of the experimental data on one-pion and two-pion production in the p({alpha}, {alpha} Prime )X reaction studied in a semi-exclusive experiment at an energy of E{sub {alpha}} = 4.2 GeV has been performed. The obtained results demonstrate that the inelastic {alpha}-particle scattering on the proton at the energy of the experiment proceeds either through excitation and decay of the {Delta} resonance in the projectile {alpha} particle, or through excitation in the target proton of the Roper resonance, which decays into a nucleon and a pion, or a nucleon and a {sigma} meson-a system of two pions in the isospin I = 0, S-wave state.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
On a microscopic representation of space-time
We start from a noncompact Lie algebra isomorphic to the Dirac algebra and relate this Lie algebra in a brief review to low-energy hadron physics described by the compact group SU(4). This step permits an overall physical identification of the operator actions. Then we discuss the geometrical origin of this noncompact Lie algebra and 'reduce' the geometry in order to introduce in each of these steps coordinate definitions which can be related to an algebraic representation in terms of the spontaneous symmetry breakdown along the Lie algebra chain su*(4) {yields} usp(4) {yields} su(2) Multiplication-Sign u(1). Standard techniques of Lie algebra decomposition(s) as well as the (physical) operator identification give rise to interesting physical aspects and lead to a rank-1 Riemannian space which provides an analytic representation and leads to a 5-dimensional hyperbolic space H{sub 5} with SO(5, 1) isometries. The action of the (compact) symplectic group decomposes this (globally) hyperbolic space into H{sub 2} Circled-Plus H{sub 3} with SO(2, 1) and SO(3, 1) isometries, respectively, which we relate to electromagnetic (dynamically broken SU(2) isospin) and Lorentz transformations. Last not least, we attribute this symmetry pattern to the algebraic representation of a projective geometry over the division algebra H and subsequent coordinate restrictions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Emergence of a nonuniform pion condensate in the (1 + 1)-dimensional Nambu-Jona-Lasinio model
The (1 + 1)-dimensional Nambu-Jona-Lasinio model describing the system of two-flavor quarks is studied in the limit of a large number of colors in the presence of a baryon chemical potential Micro-Sign and an isospin chemical potential Micro-Sign {sub I}. The possible formation of a nonuniform pion condensate in dense quark matter is considered for the cases of both the massive and the massless model.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Model-independent analysis of B → πℓ{sup +}ℓ{sup −} decays
The results obtained by calculating, on the basis of the Standard Model, the branching fractions for the decays B → πℓ{sup +}ℓ{sup −} (ℓ{sup ±} = e{sup ±}, µ{sup ±}) and the invariant-mass spectrum of dileptons for the process B{sup +} → π{sup +}ℓ{sup +}ℓ{sup −} are presented. The resulting theoretical estimates depend on the choice of model for the B → π transition form factors f{sub +}(q{sup 2}), f{sub 0}(q{sup 2}), and f{sub T} (q{sup 2}). However, one can get rid of this arbitrariness by employing experimental data or the results of QCD lattice calculations to determine the parameter dependence of the form factors. Data from B-meson factories were used to determine the dependence of the form factor f{sub +}(q{sup 2}) on the transfer momentum squared. Yet another required form factor, f{sub T} (q{sup 2}), was extracted from available lattice data on B → π and B → K transitions with allowance for nearly identical effects of the breakdown of flavor SU(3){sub F} symmetry in the respective form factors. The resulting value of the decay branching fraction, B(B{sup +} → π{sup +}µ{sup +}µ{sup −}) = (1.88{sub −0.21}{sup +0.32}) × 10{sup −8}, is in good agreement with the results of measurements of the LHCb Collaboration. The branching fraction for the isospin analog of the decay under consideration is B(B{sup +} → π{sup +}µ{sup +}µ{sup −}) = (0.94{sub −0.11}{sup +0.16}) × 10{sup −8}. Therefore, this decay can be measured at the Super-B factory under construction.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Photonuclear reactions on titanium isotopes
The photodisintegration of titanium isotopes in the giant-dipole-resonance energy region is studied by the photon-activation method. Bremsstrahlung photons whose spectrum has the endpoint energy of 55 MeV is used. The yields and integrated cross sections are determined for photoproton reactions on the titanium isotopes {sup 47,48,49,50}Ti. The respective experimental results are compared with their counterparts calculated on the basis of the TALYS code and a combined photonucleon-reaction model. The TALYS code disregards the isospin structure of the giant dipole resonance and is therefore unable to describe the yield of photoproton reactions on the heavy titanium isotopes {sup 49,50}Ti.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Modified version of the combined model of photonucleon reactions
A refined version of the combined photonucleon-reaction model is described. This version makes it possible to take into account the effect of structural features of the doorway dipole state on photonucleon reactions in the energy range of E{sub γ} ≤ 30 MeV. In relation to the previous version of the model, the treatment of isospin effects at the preequilibrium and evaporation reaction stages is refined; in addition, the description of the semidirect effect caused by nucleon emission from the doorway dipole state is improved. The model in question is used to study photonucleon reactions on the isotopes {sup 35-56}Ca and {sup 102-134}Sn in the energy range indicated above.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Nuclear symmetry energy in terms of single-nucleon potential and its effect on the proton fraction of β-stable npeμ matter
Momentum and density dependence of single-nucleon potential u{sub τ} (k, ρ, β) is analyzed using a density dependent finite range effective interaction of the Yukawa form. Depending on the choice of the strength parameters of exchange interaction, two different trends of the momentum dependence of nuclear symmetry potential are noticed which lead to two opposite types of neutron and proton effective mass splitting. The 2nd-order and 4th-order symmetry energy of isospin asymmetric nuclear matter are expressed analytically in terms of the single-nucleon potential. Two distinct behavior of the density dependence of 2nd-order and 4th-order symmetry energy are observed depending on neutron and proton effective mass splitting. It is also found that the 4th-order symmetry energy has a significant contribution towards the proton fraction of β-stable npeμ matter at high densities.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
On the extraction of cross sections for π{sup 0} and η photoproduction off neutrons from deuteron data
We discuss the procedure of extracting the photoproduction cross section for neutral pseudoscalar mesons off neutrons from deuteron data. The main statement is that the final-state-interaction corrections for the proton and neutron target are in general not equal, but for π{sup 0} production there are special cases where they have to be identical and there are large regions in the parameter space of incident photon energy and pion polar angle, Θ*, where they happen to be quite similar. The corrections for both target nucleons are practically identical for π0 production in the energy range of the Δ(1232)3/2+ resonance due to the specific isospin structure of this excitation. Also above the Δ-isobar range large differences between proton and neutron correction factors are only predicted for extreme forward angles (Θ* *lt; 20°), but the results are similar for larger angles. The case of η photoproduction is also briefly considered. Numerical results for the γp → π{sup 0}p and γn → π{sup 0}n correction factors are discussed. Also the model description for the available data on the differential γd → π{sup 0}pn cross sections are given.
74 ATOMIC AND MOLECULAR PHYSICS↗
Analyzing fragment production in mass-asymmetric reactions as a function of density dependent part of symmetry energy
We performed a theoretical investigation of different mass-asymmetric reactions to access the direct impact of the density-dependent part of symmetry energy on multifragmentation. The simulations are performed for a specific set of reactions having same system mass and N/Z content, using isospin-dependent quantum molecular dynamics model to estimate the quantitative dependence of fragment production on themass-asymmetry factor (τ) for various symmetry energy forms. The dynamics associated with different mass-asymmetric reactions is explored and the direct role of symmetry energy is checked. Also a comparison with the experimental data (asymmetric reaction) is presented for a different equation of states (symmetry energy forms).
74 ATOMIC AND MOLECULAR PHYSICS↗