121359800
Measurement of beauty production in deep inelastic scattering at HERA
The beauty production cross section for deep inelastic scattering events with at least one hard jet in the Breit frame together with a muon has been measured, for photon virtualities Q2>2 GeV2, with the ZEUS detector at HERA using integrated luminosity of 72 pb-1. The total visible cross section is σbb(ep→e jet μX)=40.9±5.7(stat.)-4.4+6. 0(syst.) pb. The next-to-leading order QCD prediction lies about 2.5 standard deviations below the data. The differential cross sections are in general consistent with the NLO QCD predictions; however at low values of Q2, Bjorken x, and muon transverse momentum, and high values of jet transverse energy and muon pseudorapidity, the prediction is about two standard deviations below the data. © 2004 Published by Elsevier B.V.
53982386
Measurement of charged current deep inelastic scattering cross sections with a longitudinally polarised electron beam at HERA
Measurements of the cross sections for charged current deep inelastic scattering in e−p collisions with longitudinally polarised electron beams are presented. The measurements are based on a data sample with an integrated luminosity of 175 pb−1 collected with the ZEUS detector at HERA at a centre-of-mass energy of 318 GeV. The total cross section is given for positively and negatively polarised electron beams. The differential cross-sections dσ/dQ2, dσ/dx and dσ/dy are presented for Q2>200 GeV2. The double-differential cross-section d2σ/dxdQ2 is presented in the kinematic range 280<Q2<30 000 GeV2 and 0.015<x<0.65. The measured cross sections are compared with the predictions of the Standard Model.
16863612
The spectrometer system for measuring ZEUS luminosity at HERA
The upgrade of the HERA accelerator has provided much increased collider luminosity. In turn, the improvements have necessitated a new design for the ZEUS luminosity measurements. The intense synchrotron radiation field, as well as the high probability of a bremsstrahlung photon in each bunch crossing, posed new experimental constraints. In this report, we describe how these challenges were met with the ZEUS luminosity spectrometer system. The design, testing and commissioning of the device are described, and the results from the initial operational experience are reported.
62786869
Measurement of isolated photons accompanied by jets in deep inelastic ep scattering
The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326pb -1 . Measurements were made for exchanged photon virtualities, Q 2 , in the range 10 to 350GeV 2 . The photons were measured in the transverse-energy and pseudorapidity ranges 4 γ jet <1.8. Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20-30%. © 2012 Elsevier B.V.
125090919
Search for lepton-flavor violation at HERA
A search for lepton-flavor-violating interactions ep -> mu X and ep -> tau X has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of 130 pb(-1). The data were taken at center-of-mass energies, root s, of 300 and 318 GeV. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below root s, limits were set on lambda(eq1) root beta(lq), where lambda(eq1) is the coupling of the LQ to an electron and a first-generation quark q(1), and beta(eq) is the branching ratio of the LQ to the final-state lepton l (mu or tau) and a quark q. For LQ masses much larger than root s, limits were set on the four-fermion interaction term lambda(eq alpha)lambda(eq beta)/M(L)(2)Q for LQs that couple to an electron and a quark q(alpha) and to a lepton l and a quark q(beta), where alpha and beta are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process ep -> tau X, the ZEUS limits are the most stringent to date.
15474958
Measurement of prompt photons with associated jets in photoproduction at HERA
The photoproduction of prompt photons, together with an accompanying jet, has been studied in ep collisions at a centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 77 pb-1. Cross sections were measured for the transverse energy of the photon and the jet larger than 5 and 6 GeV, respectively. The differential γ+jet cross sections were reconstructed as functions of the transverse energy, pseudorapidity and xγobs, the fraction of the incoming photon momentum taken by the photon-jet system. Predictions based on leading-logarithm parton-shower Monte Carlo models and next-to-leading-order (NLO) QCD generally underestimate the cross sections for the transverse energies of prompt photons below 7 GeV, while the kT-factorisation QCD calculation agrees with the data better. When the minimum transverse energy of prompt photons is increased to 7 GeV, both NLO QCD and the kT-factorisation calculations are in good agreement with the data.
121943751
Theoretical study of nuclear charge densities with elastic electron scattering
The calculated cross sections for elastic Coulomb electron scattering from the phase-shift analysis method and the eikonal approximation are compared. It is shown that the phase-shift analysis method can reproduce the experimental data very well for both light and heavy nuclei. Then the phase-shift analysis is used to investigate elastic electron scattering along the O and S isotopic chains, where the charge densities are obtained from relativistic mean-field theory. Results show that the minima of the differential cross section shift inward and upward with the increase of the neutron number.
124573293
Unfavored alpha decay from ground state to ground state in the range 53 <= Z <= 91
Within the density-dependent cluster model, we have systematically investigated partial alpha-decay half-lives of ground-state (g.s.)-to-g.s. transitions. Emphasis is placed on the unfavored a transitions in the range 53 <= Z <= 91 of both odd-A and odd-odd nuclei. The alpha-preformation factor is estimated by means of the multiplication of the valence proton and neutron numbers NPNN, in addition to the constant formation factor for one kind of nuclei. By introducing a centrifugal term, the previous empirical relation for alpha-decay half-lives of our group is improved to reproduce a large number of experimental data including these unfavored transitions. Whatever concerns the theoretical calculation or the analytical expression, the agreement between theory and experiment is satisfied. This indicates that these studied unfavored g.s.-to-g.s. alpha decays can be reasonably described within the present approach extended from the treatment of favored ones.
123351519
Systematic studies of properties of nuclei by parity violating electron scattering
Two investigations by the parity violating electron scattering are performed theoretically: one is to investigate the properties of the surface for neutron-rich nuclei such as {sup 124}Sn and {sup 208}Pb, and the other is to predict the parity violating asymmetries for some isotopic chains, such as Ba and Pb, which have been proposed for the atomic parity nonconservation experiments. For the first topic, the neutron and proton densities are taken to be the 2pF distributions. Results show that the parity violating asymmetries are very sensitive to the type of neutron density. It means that the parity violating electron scattering can be used to verify the type of neutron distribution in neutron-rich stable nuclei. For the second topic, the neutron and proton densities are obtained from the relativistic mean-field (RMF) theory. By combining the results for these two topics, we find that for various proton and neutron densities the amplitudes of the parity violating asymmetries correspond to the distances between the minima of the proton and neutron form factors. Our results can provide useful references for future experiments.
121406531
New model of binding energies of heavy nuclei with Z >= 90
A new form of the binding energy formula of heavy nuclei with Z{>=}90 is proposed where new terms beyond the standard Bethe and Weizsaecker formula are introduced by analytical expressions. This can be considered an interesting development of the Bethe and Weizsaecker mass formula for heavy nuclei with Z{>=}90. Two versions of the formulae are presented. The first version of the formula can reproduce the 117 known binding energies of nuclei with Z{>=}90 and N{>=}140 with an average deviation 0.118 MeV. This is the first time that the binding energies of heavy nuclei with Z{>=}90 and N{>=}140 can be calculated very accurately by a formula with only seven parameters. The binding energies, {alpha}-decay energies, and {alpha}-decay half-lives of unknown superheavy nuclei are predicted. The second version of the formula is obtained by fitting the 181 data of nuclei with Z{>=}90 with nine parameters and good agreement with experimental binding energies is also reached for all nuclei with Z{>=}90.
122517028
Structure of 8Li from a reaction cross-section measurement
We have precisely measured reaction cross sections (sigma(R)) for Li-8 using Be-9, C-12, Al-27, and proton targets at intermediate energies by the transmission method. From the energy dependence of the sigma(R) including the high energy data, the density distribution of Li-8 was deduced through a modified Glauber model. It is shown that Li-8 has a shorter tail structure in the density as compared with that of B-8 and the matter radius of Li-8 is similar to those of the other nonhalo Li isotopes. The result is consistent with the previous experiments that there is a tendency for Li-8 to be a skin nucleus.