Search results for "Nuclear physic"
showing 10 items of 5307 documents
Enhancement of charm quark production due to nonlinear corrections to the DGLAP equations
2004
We have studied how parton distributions based on the inclusion of nonlinear scale evolution and constraints from HERA data affect charm production in $pp$ collisions at center-of-mass energies of 5.5, 8.8 and 14 TeV. We find that, while the resulting enhancement can be substantial, it is very sensitive to the charm quark mass and the scale entering the parton densities and the strong coupling constant.
Pentaquark decay width in QCD sum rules
2005
In a diquark-diquark-antiquark picture of the pentaquark we study the decay $\Theta \rightarrow K^{+} n$ within the framework of QCD sum rules. After evaluation of the relevant three-point function, we extract the coupling $g_{\Theta nK}$ which is directly related to the pentaquark width. Restricting the decay diagrams to those with color exchange between the meson-like and baryon-like clusters reduces the coupling constant by a factor of four. Whereas a small decay width might be possible for a positive parity pentaquark, it seems difficult to explain the measured width for a pentaquark with negative parity.
Photo- and Electroproduction of Eta Mesons on Nucleons and Nuclei
1995
Eta photo- and electroproduction off the nucleon is investigated in an approach that contains Born terms, vector meson and nucleon resonance contributions. In a comparison with the new Mainz data we find a large sensitivity on the elementary ηN N coupling. Our analysis results in a pseudoscalar ηN N coupling with a coupling constant of g ηN N 2 /4π=0.4. Furthermore, we also study coincidence cross sections for eta electroproduction and present calculations for structure functions and kinematical conditions that are most sensitive to the S 11(1535) and the D 13(1520) resonances. Finally, we show results on the inclusive eta photoproduction off complex nuclei with a very good agreement with r…
Levels of 186Re populated in thermal neutron capture reaction
2015
Levels of 186 Re have been studied in the thermal neutron capture reaction with an enriched 185 Re target. Evaluation of spectrum measured with GAMS5 allowed to obtain energies and intensities of more than 500 γ -lines assigned to 186 Re. Most of the obtained transitions have been placed in the model-independent level scheme of the doubly odd 186 Re nucleus, taking into account the available data of earlier experiments as well as the results of recent 187 Re(p, d )186 Re reaction measurements. Structure of the 186 Re low-lying levels has been analysed in terms of the particle-plus-rotor coupling model.
Coherent Pions From Neutrino Scattering Off Nuclei
2010
We describe a model for pion production off nucleons and coherent pions from nuclei induced by neutrinos in the 1 GeV energy regime. Besides the dominant Delta pole contribution, it takes into account the effect of background terms required by chiral symmetry. Moreover, the model uses a reduced nucleon-to-Delta resonance axial coupling, which leads to coherent pion production cross sections around a factor two smaller than most of the previous theoretical estimates. Nuclear effects like medium corrections on the Delta propagator and final pion distortion are included.
Limits on anomalous trilinear gauge boson couplings from WW, WZ and Wγ production in pp¯ collisions at s=1.96 TeV
2012
We present searches for the anomalous γWW and ZWW trilinear gauge boson couplings from WW and WZ production using lepton plus dijet final states and a combination with results from Wγ, WW, and WZ production with leptonic final states. The analyzed data correspond to up to 8.6fb -1 of integrated luminosity collected by the D0 detector in pp- collisions at s=1.96TeV. We set the most stringent limits at a hadron collider to date assuming two different relations between the anomalous coupling parameters δκ γ, λ, and δg1Z for a cutoff energy scale Λ=2TeV. The combined 68% C.L. limits are -0.057lδκ γl0.154, -0.015lλl0.028, and -0.008lδg1Zl0.054 for the LEP parameterization, and -0.007lδκl0.081 an…
φ meson mass and decay width in nuclear matter
2002
The $\phi$ meson spectrum, which in vacuum is dominated by its coupling to the $\bar{K} K$ system, is modified in nuclear matter. Following a model based on chiral SU(3) dynamics we calculate the $\phi$ meson selfenergy in nuclear matter considering the $K$ and $\bar{K}$ in-medium properties. For the latter we use the results of previous calculations which account for $S-$ and $P-$wave kaon-nucleon interactions based on the lowest order meson-baryon chiral effective Lagrangian, and this leads to a dressing of the kaon propagators in the medium. In addition, a set of vertex corrections is evaluated to fulfill gauge invariance, which involves contact couplings of the $\phi$ meson to $S-$wave …
Microscopic quasiparticle–phonon description of beta decays of 113Cd and 115In using proton–neutron phonons
2007
Abstract The fourth-forbidden non-unique ground-state-to-ground-state beta decays of 113 Cd and 115 In are calculated using a realistic microscopic two-body interaction and a realistic single-particle model space. To describe the involved initial and final nuclear states we introduce a proton–neutron variant of the microscopic quasiparticle–phonon model (MQPM), the proton–neutron MQPM (pnMQPM). The states of the pnMQPM are created by coupling quasiparticles with phonons of the proton–neutron quasiparticle random-phase approximation (pnQRPA). The computed half-lives and log f t values are found to be in excellent agreement with experimental data. Computed beta spectra of the decays are also …
Eta-eta' Photoproduction and the axial isoscalar neutral current coupling
1995
We show that coherentη andη′ photoproduction by means of the Primakoff Effect on the proton depends on the strange component of the neutral axial current coupling. We construct polarization asymmetries that are sensitive to this coupling through theγ−Z interference. Theη′ is not a Goldstone boson of a spontaneously broken chiral symmetry, but a phenomenological analysis of theη andη′ production through chiral perturbation theory allows to calculate the observables of interest. The polarized proton or polarized photon asymmetries are predicted to be close to 10−4 for −q 2∼0.1−0.5 GeV2.
Search for flavor changing neutral currents in decays of top quarks
2011
We present a search for flavor changing neutral currents in decays of top quarks. The analysis is based on a search for ttbar -> l'null + jets (l, l' = e, mu) final states using 4.1 fb^-1 of integrated luminosity of ppbar collisions at sqrt(s) = 1.96 TeV. We extract limits on the branching ratio B(t -> Zq) (q = u, c quarks), assuming anomalous tuZ or tcZ couplings. We do not observe any sign of such anomalous coupling and set a limit of B < 3.2% at 95% C.L.