First search for double- \beta decay of platinum by ultra-low background HP Ge \gamma spectrometry

A search for double- $ \beta$ processes in ¹⁹⁰Pt and ¹⁹⁸Pt was realized with the help of ultra-low background HP Ge 468cm^3 $ \gamma$ spectrometer in the underground Gran Sasso National Laboratories of the INFN (Italy). After 1815 h of data taking with 42.5g platinum sample, T _1/2 limits on 2 $ \beta$ processes in ¹⁹⁰Pt ( $ \varepsilon$ $ \beta^{+}_{}$ and 2 $ \varepsilon$ have been established on the level of 10¹⁴-10¹⁶y, 3 to 4 orders of magnitude higher than those known previously. In particular, a possible resonant double-electron capture in ¹⁹⁰Pt was restricted on the level of 2.9×10¹⁶ y at 90% C.L. In addition, T _1/2 limit on 2 $ \beta^{-}_{}$ decay of ¹⁹⁸Pt (2 $ \nu$ +0 $ \nu$ ) to the 2⁺ ₁ excited level of ¹⁹⁸Hg has been set at the first time: T _1/2 > 3.5×10¹⁸ y. The radiopurity level of the used platinum sample is reported.     

Geant4 Monte Carlo simulations for the LPCTrap setup

The LPCTrap setup at GANIL is fully operational since 2006. The first breakthrough was the detection of 100000 coincidences between the $ \beta$ particles and the recoil ions from the decay of ⁶He⁺ produced by the SPIRAL source. After preparation, the decaying nuclei are confined in a transparent Paul trap which is surrounded by a $ \beta$ -telescope made of a double-sided silicon strip detector followed by a scintillator, and by a micro-channel plate position-sensitive detector to record in coincidence the $ \beta$ particles and the recoil ions. Simulations of this system are needed in order to study possible systematic effects and extract with high accuracy the $ \beta$ - $ \nu$ angular-correlation coefficient. A code based on Geant4 is well suited for this purpose. In this contribution the results from the simulations compared with those from the experiment will be presented and discussed.     

Beta-decay study of Tz = - 2 proton-rich nucleus 24Si

$ \beta$ -decay spectroscopy on a T _z = - 2 proton-rich nucleus ²⁴Si was performed. The decay scheme of ²⁴Si was reconstructed by the $ \beta$ -delayed $ \gamma$ -ray and proton measurements. Two $ \beta$ branches to the bound 1₁ ⁺ and 1₂ ⁺ states in ²⁴Al were observed for the first time. The observation of the allowed transition firmly established the spin-parity assignment for the 1₂ ⁺ states. The branching ratios to the 1₁ ⁺ and 1₂ ⁺ states were determined to be 31(4)% and 23.9(15)%, respectively. The branching ratios to three unbound states in ²⁴Al including a new level at 6.735MeV were also determined for the first time. The level structure of ²⁴Al was compared with its mirror nucleus ²⁴Na . The Thomas-Ehrman shift on the 1₂ ⁺ state indicates s -wave dominance in the state as well as a characteristic behavior of the weakly bound s -wave proton in ²⁴Al .     

Charmonium rescattering effects in \psi(2S) \rightarrow \gamma \eta_{c}^{} decay

Charmonium rescattering effects in the M1 transition of $ \psi$ (2S) $ \rightarrow$ $ \gamma$ $ \eta_{c}^{}$ are investigated by modeling a $ \chi_{{cJ}}^{}$ or J/ $ \psi$ rescattering into a $ \eta_{c}^{}$ final state. The absorptive and dispersive part of the transition amplitudes for the rescattering loops of $ \eta$ $ \psi$ ( $ \gamma^{{\ast}}_{}$ ) and $ \gamma$ $ \chi$ ( $ \psi$ ) are separately evaluated. The numerical results show that the contribution from the $ \gamma$ $ \chi$ ( $ \psi$ ) rescattering process is negligible. Compared with the virtual D $ \bar{{D}}$ (D ^*) rescattering processes, the $ \eta$ $ \psi$ ( $ \gamma^{{\ast}}_{}$ ) process may be regarded as the next-leading order of the hadronic loop mechanism, which only offers the partial decay width of ～ 0.045 keV to the $ \psi$ (2S) $ \rightarrow$ $ \gamma$ $ \eta_{c}^{}$ .     

Analysis of the vertexes \Xi_{Q}^{*}′QV , \Sigma_{Q}^{*} \Sigma_{Q}^{}V and radiative decays \Xi_{Q}^{*} \rightarrow ′Q \gamma , \Sigma_{Q}^{*} \rightarrow \Sigma_{Q}^{} \gamma

In this article, we study the vertexes $ \Xi_{Q}^{*}$ ′_Q V and $ \Sigma_{Q}^{*}$ $ \Sigma_{Q}^{}$ V with the light-cone QCD sum rules, then assume the vector meson dominance of the intermediate $ \phi$ (1020) , $ \rho$ (770) and $ \omega$ (782) , and calculate the radiative decays $ \Xi_{Q}^{*}$ $ \rightarrow$ ′_Q $ \gamma$ and $ \Sigma_{Q}^{*}$ $ \rightarrow$ $ \Sigma_{Q}^{}$ $ \gamma$ .     

Radiative open charm decay of the Y(3940) , Z(3930) , X(4160) resonances

We determine the radiative decay amplitudes for the decay into D^* and $ \bar{{D}}$ $ \gamma$ , or D ^* _s and $ \bar{{D}}_{s}^{}$ $ \gamma$ of some of the charmonium-like states classified as X , Y , Z resonances, plus some other hidden charm states which are dynamically generated from the interaction of vector mesons with charm. The mass distributions as a function of the $ \bar{{D}}$ $ \gamma$ or $ \bar{{D}}_{s}^{}$ $ \gamma$ invariant mass show a peculiar behavior as a consequence of the D ^* $ \bar{{D}}^{*}_{}$ nature of these states. The experimental search of these magnitudes can shed light on the nature of these states.     

High-spin excitations of the odd-odd 88 37Rb51 and 86 35Br51 nuclei: \pip3/2 \nud5/2 and \pif5/2 \nud5/2 residual interactions

The odd-odd ⁸⁸ ₃₇Rb₅₁ and ⁸⁶ ₃₅Br₅₁ nuclei have been produced as fission fragments in the fusion reaction ¹⁸O$ + $²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Their high-spin level schemes have been built from the triple $ \gamma$ -ray coincidence data and $ \gamma$ - $ \gamma$ angular correlations have been analyzed in order to assign spin and parity values to many observed states. The proposed configurations involve proton excitations from three sub-shells located close to the Fermi levels, $ \pi$ p _3/2 , $ \pi$ f _5/2 , and $ \pi$ g _9/2 , the $ \nu$ d _5/2 neutron acting as a spectator. The residual $ \pi$ $ \nu$ interactions are extracted from the multiplets of states resulting from the $ \pi$ p _3/2 $ \nu$ d _5/2 and $ \pi$ f _5/2 $ \nu$ d _5/2 configurations. The empirical values of the latter are discussed and compared to those known in two similar configurations having j _p = j _n with l _p = l _n + 1 , where the role of the tensor force had been highlighted.     

A new analysis improving the evidence of a narrow peak in the invariant-mass distribution of the \Lambdap system observed in the \bar{{p}} annihilation at rest on 4He

The presence of a narrow peak in the $ \Lambda$ p invariant-mass distribution observed in the $ \bar{{p}}$ annihilation reaction at rest $\ensuremath \bar{p} {}^4\mathrm{He}\rightarrow p\pi^-p\pi^+\pi^-n X$ is discussed again through an analysis procedure which improves the ratio signal/background in comparison with the previous analysis. The peak is centred at 2223.2±3.2_stat±1.2_syst MeV and has a statistical significance of 4.7 $ \sigma$ , values compatible with those published previously. If interpreted as the result of the decay into $ \Lambda$ p of a $\ensuremath { }_{\bar{K}}{}^2\mathrm{H}$ bound system, the corresponding binding energy should be B = - 151.0±3.2_stat±1.2_syst MeV and the width $ \Gamma_{{FWHM}}^{}$ < 33.9±6.2 MeV. The production rate has a lower limit of 1.2 10^-4. Data on the $ \bar{{p}}$ annihilation reaction at rest $ \bar{{p}}$ ⁴He $ \rightarrow$ p $ \pi^{-}_{}$ p $ \pi^{-}_{}$ p _s X , analyzed for the first time, lead to a result in qualitative agreement with the previous one.     

Exact solutions of relativistic perfect fluid hydrodynamics for a QCD Equation of State

The half-life of the mirror $\beta$ decay of ³¹S has been measured at the IGISOL facility at the University of Jyv?skyl?. The value obtained is $T_{1/2}(^{31}S)=(2553.4\pm 1.8)$ ms, in agreement with previous measurements, but with a precision that is better by a factor of ten than the literature value previously adopted. When the new result is combined with the Q_EC value measured recently at JYFLTRAP, a precision of better than $10^{-3}$ is obtained for the ft value.     

Identification of \mathrm{\ensuremath J^{\pi} = 19/2^+} and \mathrm{\ensuremath 23/2^+} isomeric states in 127Sb

The nucleus $\ensuremath {\rm ^{127}Sb}$ , which is on the neutron-rich periphery of the $\ensuremath \beta$ -stability region, has been populated in complex nuclear reactions involving deep-inelastic and fusion-fission processes with $\ensuremath {\rm {}^{136}Xe}$ beams incident on thick targets. The previously known isomer at 2325 keV in $\ensuremath {\rm {}^{127}Sb}$ has been assigned spin and parity $\ensuremath 23/2^+$ , based on the measured $\ensuremath \gamma$ - $\ensuremath \gamma$ angular correlations and total internal conversion coefficients. The half-life has been determined to be 234(12) ns, somewhat longer than the value reported previously. The 2194 keV state has been assigned $\ensuremath J^{\pi} = 19/2^+$ and identified as an isomer with $\ensuremath T_{1/2} = 14(1) {\rm ns}$ , decaying by two $\ensuremath E2$ branches. The observed level energies and transition strengths are compared with the predictions of a shell model calculation. Two $\ensuremath 15/2^+$ states have been identified close in energy, and their properties are discussed in terms of mixing between vibrational and three-quasiparticle configurations.     

Magnetic moment of proton halo nucleus 28 P

The magnetic moment of ²⁸P (I _π = 3^?+?, T_1/2 = 270.3 ms) in the ground state has been measured by the $\upbeta $ -nuclear magnetic resonance method for the first time. The measured magnetic moment of $\vert \upmu (^{28}$ P)∣ = 0.309(9)  $\upmu _{{\rm N}}$ is well reproduced by the shell model value of +0.306  $\upmu _{{\rm N} }$ . The shell model calculation also yields a proton density distribution with a long tail. The present results provide a strong confirmation of the configuration of the 2s _1/2 proton which should lead to the proton halo.     

Physics beyond the Standard Model through b → s μ ?+? μ ? transition

A comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b ?? s ?? ^?+? ?? ^? transition is performed. The effects of new vector?Caxial vector (VA), scalar?Cpseudoscalar (SP) and tensor (T) interactions on the differential branching ratios, forward?Cbackward asymmetries (A _FB??s), and direct CP asymmetries of ${\bar B}_{\rm s}^0 \to \mu^+ \mu^-$ , ${\bar B}_{\rm d}^0 \to$ $ X_{\rm s} \mu^+ \mu^-$ , ${\bar B}_{\rm s}^0 \to \mu^+ \mu^- \gamma$ , ${\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-$ , and ${\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-$ are examined. In ${\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-$ , we also explore the longitudinal polarization fraction f _L and the angular asymmetries $A_{\rm T}^{(2)}$ and A _LT, the direct CP asymmetries in them, as well as the triple-product CP asymmetries $A_{\rm T}^{\rm (im)}$ and $A^{\rm (im)}_{\rm LT}$ . While the new VA operators can significantly enhance most of the observables beyond the Standard Model predictions, the SP and T operators can do this only for A _FB in ${\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-$ .     

Reaction pp \rightarrow pp \pi \pi \pi as a background for hadronic decays of the \eta^{{\prime}}_{} meson

Isospin violating hadronic decays of the $ \eta$ and $ \eta{^\prime}$ mesons into 3 $ \pi$ mesons are driven by a term in the QCD Lagrangian proportional to the mass difference of the d and u quarks. The source giving large yield of the mesons for such decay studies are pp interactions close to the respective kinematical thresholds. The most important physics background for $ \eta$ , $ \eta{^\prime}$ $ \rightarrow$ $ \pi$ $ \pi$ $ \pi$ is coming from direct three-pion production reactions. In case of the $ \eta$ meson the background for the decays is relatively low ( $ \approx$ 10% . The purpose of this article is to provide an estimate of the direct pion production background for the $ \eta{^\prime}$ $ \rightarrow$ 3 $ \pi$ decays. Using the inclusive data from the COSY-11 experiment we have extracted the differential cross-section for the pp $ \rightarrow$ pp -multipion production reactions with the invariant mass of the pions equal to the $ \eta{^\prime}$ meson mass and estimated an upper limit for the signal to background ratio for studies of the $ \eta{^\prime}$ $ \rightarrow$ $ \pi^{+}_{}$ $ \pi^{-}_{}$ $ \pi^{0}_{}$ decay.     

Determination of the Dalitz plot parameter \alpha for the decay \eta → 3 \pi^{0}_{} with the Crystal Ball at MAMI-B

A precise measurement of the Dalitz plot parameter, $ \alpha$ , for the $ \eta$ → 3 $ \pi^{0}_{}$ decay is presented. The experiment was performed with the Crystal Ball and TAPS large-acceptance photon detectors at the tagged photon beam facility of the MAMI-B electron accelerator in Mainz. High statistics of 1.8 · 10⁶ $ \eta$ → 3 $ \pi^{0}_{}$ events were obtained, giving the result $ \alpha$ = - 0.032±0.002_stat±0.002_syst .     

Skyrme-QRPA calculations for low-lying excitation modes in deformed neutron-rich nuclei

Low-frequency modes of excitation in deformed neutron-rich nuclei are studied by means of the quasiparticle random-phase approximation on the Skyrme-Hartree-Fock-Bogoliubov mean field. We investigate the microscopic structure of the soft $\ensuremath K^{\pi} = 0^{+}$ modes systematically in neutron-rich magnesium isotopes with N = 22, 24, 26 and 28 close to the drip line, and it is found that the strong collectivity in ³⁴Mg and ⁴⁰Mg is acquired due to the coherent coupling between the $ \beta$ vibration and the pairing vibration of neutrons. Microscopic structure of the $\ensuremath K^{\pi} = 2^{+}$ modes changes gradually associated with the location of the Fermi level of neutrons, and it is found that the proton particle-hole excitation generating the $ \gamma$ -vibrational mode in ²⁴Mg continues to play a key role in the near-drip-line nucleus ⁴⁰Mg . The low-frequency octupole excitations are also investigated and the microscopic mechanism for the enhancement of transition strengths is discussed.     

Evolution under thermal annealing of Mn-doped iron disilicides obtained by ball milling

Phase formation in the Mn doped $\upbeta $ -FeSi₂ system (Fe_1???x Mn _x Si₂, with 0.00 ≤?x?≤ 0.24) was studied using X-ray diffraction and Mössbauer spectroscopy. Samples were prepared by the simultaneous mill of pure Si, Mn and Fe under Ar atmosphere followed by an annealing at 1,123 K during 4 h at 1 × 10^???7 Torr. After milling, an admixture of $\upbeta $ -FeSi₂, $\upalpha $ -FeSi₂ and $\upvarepsilon $ -FeSi phases was present while $\upalpha $ -FeSi₂ disappeared after annealing, resulting $\upbeta $ -FeSi₂ the main phase. Depending on Mn concentration, small amounts of $\upvarepsilon $ -FeSi and Si segregation were also observed. A preferential substitution of Fe atoms by Mn ones in the Fe_II site of the $\upbeta $ -FeSi₂ regular lattice was inferred from the Mössbauer results.     

Energy dependence of {\bar{K}N} interaction in nuclear medium

When the $\bar{K}N$ system is submerged in nuclear medium the $\bar{K}N$ scattering amplitude and the final state branching ratios exhibit a strong energy dependence when going to energies below the $\bar{K}N$ threshold. A sharp increase of $\bar{K}N$ attraction below the $\bar{K}N$ threshold provides a link between shallow $\bar{K}$ -nuclear potentials based on the chiral $\bar{K}N$ amplitude evaluated at threshold and the deep phenomenological optical potentials obtained in fits to kaonic atoms data. We show the energy dependence of the in-medium K ^??? p amplitude and demonstrate the impact of energy dependent branching ratios on the Λ-hypernuclear production rates.     

Extreme \alpha -clustering in the 18O nucleus

The structure of the ¹⁸O nucleus at excitation energies above the $ \alpha$ decay threshold was studied using ¹⁴C + $ \alpha$ resonance elastic scattering. A number of states with large $ \alpha$ reduced widths have been observed, indicating that the $ \alpha$ -cluster degree of freedom plays an important role in this N $ \ne$ Z nucleus. A 0⁺ state with an $ \alpha$ reduced width exceeding the single-particle limit was identified at an excitation energy of 9.9±0.3 MeV. We discuss evidence that states of this kind are common in light nuclei and give possible explanations of this feature.     

On the production of \pi^{+}_{} \pi^{+}_{} pairs in pp collisions at 0.8 GeV

Data accumulated recently for the exclusive measurement of the pp $ \rightarrow$ pp $ \pi^{+}_{}$ $ \pi^{-}_{}$ reaction at a beam energy of 0.793GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the pp $ \rightarrow$ nn $ \pi^{+}_{}$ $ \pi^{+}_{}$ reaction channel. The latter is expected to be the only $ \pi$ $ \pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $ \pi$ $ \pi$ production process. No single event has been found, which meets all conditions for being a candidate for the pp $ \rightarrow$ nn $ \pi^{+}_{}$ $ \pi^{+}_{}$ reaction. This gives an upper limit for the cross-section of 0.16μb (90% C.L.), which is more than an order of magnitude smaller than the cross-sections of the other two-pion production channels at the same incident energy.