Search results for "nuclear physics"
showing 10 items of 5307 documents
Exclusive muoproduction on transversely polarised protons and deuterons
2012
The transverse target spin azimuthal asymmetry A(UT)(sin(phi-phi s)) in hard exclusive production of rho(0) mesons was measured at COMPASS by scattering 160 GeV/c muons off transversely polarised protons and deuterons. The measured asymmetry is sensitive to the nucleon helicity-flip generalised parton distributions E-q, which are related to the orbital angular momentum of quarks in the nucleon. The Q(2), x-B-j and p(T)(2) dependence of A(UT)(sin(phi-phi s)) is presented in a wide kinematic range: 1 (GeV/c)(2) < Q(2) < 10 (GeV/c)(2), 0.003 < xB(j) < 0.3 and 0.05 (GeV/c)(2) < p(T)(2) < 0.5 (GeV/c)(2) for protons or 0.10 (GeV/c)(2) < p(T)(2) < 0.5 (GeV/c)(2) for deuterons. Results for deuteron…
Proton-antiproton annihilation at rest into two mesons and the quark line rule
1988
Proton-antiproton annihilation at rest into two mesons is analysed in a model describing annihilation by quark lines. The model allows to fit existing data with two parameters. The parameters describe the amplitudes for diagrams with and without rearrangement of quark lines.
The neutrinoless double beta decay of 76Ge, 82Se, 86Kr, 114Cd, 128, 130Te and 134, 136Xe in the framework of a relativistic quark confinement model
1991
The half-life of the 0+ → 0+ neutrinoless double beta decay is calculated for 76Ge, 82Se, 86Kr, 114Cd, 128, 130Te and 134, 136Xe and the upper limit for the effective neutrino mass of 3.0 eV is deduced from available experimental data. In addition, the contribution of the right-handed charged weak currents to the effective weak hamiltonian is estimated. The relevant parameters attain the values |〈Λ〉| < 4.1 × 10−6 and |〈ν〉| < 6.6 × 10−8. The nucleonic weak current is treated starting from the current quark level and evaluating the quark current using relativistic quark wave functions obtained from a Dirac equation with a harmonic confinement potential. The nuclear matrix elements of the thus…
Quark exchange in deep inelastic scattering
1995
We use a model for baryons that links the constituent structure to the deep inelastic (current) properties. The approach consists in a laboratory partonic description (based on a model of hadron structure), to which a low momentum scaleQ 0 is adscribed, which is evolved to high momenta by means of the renormalization group. A generalization of the model by means of the hadronic quark cluster decomposition, provides a description of the structure functions of nuclei and is the starting point to study the effects that the antisymmetrization at the quark level has on the structure function of a model deuteron. The analysis contains conventional and high momentum partonic components. We next st…
Lepton flavor violation in the Higgs sector and the role of hadronic tau-lepton decays
2013
It has been pointed out recently that current low-energy constraints still allow for sizable flavor-changing decay rates of the 125 GeV boson into leptons, h -> tau ell (ell= e, mu). In this work we discuss the role of hadronic tau-lepton decays in probing lepton flavor violating couplings in the Higgs sector. At low energy, the effective Higgs coupling to gluons induced by heavy quarks contributes to hadronic tau decays, establishing a direct connection with the relevant process at the LHC, pp (gg)-> h -> tau ell. Semileptonic transitions like tau -> ell pi pi are sensitive to flavor-changing scalar couplings while decays such as tau -> ell eta(') probe pseudoscalar coupling…
Mesonic decay of 5ΛHe with quark-model-based hypernuclear wave function
1993
Abstract We have evaluated the mesonic decay of the 5 Λ He hypernucleus by using a Λ wave function generated from the quark cluster model. As a consequence of the Λ N repulsion at short distances we obtain a Λ wave function in the nucleus with a large radius. The smaller overlap with the 4 He core with respect to simpler wave functions and the effect of the pion renormalization increase the mesonic width considerably and one obtains a good reproduction of the experimental data.
Heavy-quark production and elliptic flow in Au + Au collisions atsNN=62.4GeV
2015
We present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity (|y|< 0.35) in Au+Au collisions at sNN−−−−√=62.4 GeV. The data were collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range 1<peT<5 GeV/c. The invariant yield per binary collision is slightly enhanced above the p+p reference in Au+Au 0%–20%, 20%–40%, and 40%–60% centralities at a comparable level. At this low beam energy this may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy …
New leptoquark mechanism of neutrinoless double beta decay
1996
A new mechanism for neutrinoless double beta ($\znbb$) decay based on leptoquark exchange is discussed. Due to the specific helicity structure of the effective four-fermion interaction this contribution is strongly enhanced compared to the well-known mass mechanism of $\znbb$ decay. As a result the corresponding leptoquark parameters are severely constrained from non-observation of $\znbb$-decay. These constraints are more stringent than those derived from other experiments.
Parton polarization and constituent quarks
1995
Abstract A systematic study of the polarized-parton distributions is presented and related to the properties of the constituent quarks. The effects of breaking SU(6) symmetry are emphasized and the Isgur-Karl constituent model is discussed in detail. The results on the proton, neutron and deuteron structure functions are compared with the recent experimental data, and the role of the gluon polarization is pointed out. The role of the D-state admixture in the nucleon ground state is also investigated.
Search for first generation scalar leptoquarks in pp collisions at s=7 TeV with the ATLAS detector
2012
We report a search for first generation scalar leptoquarks using 1.03 fb(-1) of proton-proton collisions data produced by the Large Hadron Collider at root s = 7 TeV and recorded by the ATLAS experiment. Leptoquarks are sought via their decay into an electron or neutrino and a quark, producing events with two oppositely charged electrons and at least two jets, or events with an electron, missing transverse momentum and at least two jets. Control data samples are used to validate background predictions from Monte Carlo simulation. In the signal region, the observed event yields are consistent with the background expectations. We exclude at 95% confidence level the production of first generat…