119969482
β-decay rates of r-process waiting-point nuclei in the extended quasiparticle random-phase approximation
The beta(-) decays of the r-process waiting-point nuclei at the neutron magic numbers N = 50 and N = 82 are investigated within the extended quasiparticle random-phase approximation (QRPA), where neutron-neutron, proton-proton and neutron-proton (np) pairing correlations are considered in the specialized Hartree-Fock-Bogoliubov (HFB) calculation. The Bruckner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interaction in addition to the pairing interaction. It is found that the np pairing interaction plays an important role in reducing the calculated beta(-)-decay half-lives. The calculations with np pairing show good agreement with the available experimental data including the decay half-lives of Ni isotopes, which are usually overestimated in the self-consistent proton-neutron QRPA calculations.
119699060
β-decay half-lives including first-forbidden contributions for neutron-rich Zn isotopes in the extended QRPA with neutron-proton pairing
The β decays of neutron-rich Zn isotopes are investigated within the extended quasiparticle random-phase approximation, where neutron-neutron, proton-proton, and neutron-proton pairing correlations are considered in the similar manner. The Bruckner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions in addition to the pairing interactions. Contributions from both allowed Gamow-Teller and first-forbidden transitions are considered, and β-decay half-lives together with β-delayed neutron emission probabilities are calculated. The calculated results are found to agree well with the available experimental data.
121588345
Coupled-channels study of fine structure in the {alpha} decay of well deformed nuclei
We formulate a theoretical model for the {alpha} decay of well-deformed even-even nuclei based on the coupled-channel Schroedinger equation. The {alpha}-decay half-lives and fine structures observed in {alpha} decay are well described by the five-channel microscopic calculations. Since the branching ratios to high-spin states are hard to understand in the traditional {alpha}-decay theories, this success could be important to interpret future observations of heavier nuclei. It is also found that the {alpha} transition to high-spin states is a powerful tool to probe the energy spectrum and deformation of daughter nuclei.
122795101
Relativistic eikonal approaches to parity violating electron-nucleus scattering
The Coulomb electron scattering on even-even nuclei and the magnetic electron scattering on odd-$A$ nuclei have been investigated in the relativistic eikonal approximation and in the plane wave Born approximation, respectively. In this article, we generalize the relativistic eikonal approximation to the parity violating electron scattering on even-even nuclei. The parity violating asymmetries at electron energy of 850 MeV are calculated for three typical cases: Ca isotopes, $N=50$ isotones, and $N=Z$ doubly magic nuclei. In calculations the proton and neutron densities are obtained from the relativistic mean-field theory. The parity violating asymmetries are analyzed by comparing both the form factors and the densities of neutrons and protons. It is found that the parity violating asymmetries are sensitive to the differences between neutron and proton densities. Our results provide useful references for the parity violating electron-nucleus scattering experiments in the future.
126298012
New Geiger-Nuttall law for alpha decay of heavy nuclei
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.
118189949
Inclusive jet cross sections and dijet correlations in D photoproduction at HERA
Inclusive jet cross sections in photoproduction for events containing a D ∗ D ∗ meson have been measured with the ZEUS detector at HERA using an integrated luminosity of 78.6 pb −1 78.6 pb −1 . The events were required to have a virtuality of the incoming photon, Q 2 Q 2 , of less than 1 GeV 2 , and a photon–proton centre-of-mass energy in the range 130 γp 130 W γ p 280 GeV . The measurements are compared with next-to-leading-order (NLO) QCD calculations. Good agreement is found with the NLO calculations over most of the measured kinematic region. Requiring a second jet in the event allowed a more detailed comparison with QCD calculations. The measured dijet cross sections are also compared to Monte Carlo (MC) models which incorporate leading-order matrix elements followed by parton showers and hadronisation. The NLO QCD predictions are in general agreement with the data although differences have been isolated to regions where contributions from higher orders are expected to be significant. The MC models give a better description than the NLO predictions of the shape of the measured cross sections.
21554167
Measurement of the muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton–proton collision data
This paper presents the performance of the ATLAS muon reconstruction during the LHC run with $$pp$$pp collisions at $$\sqrt{s}=7$$s=7–8 TeV in 2011–2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of $${J/\psi \rightarrow \mu \mu }$$J/ψ→μμ, $$Z \rightarrow \mu \mu $$Z→μμ and $${\Upsilon \rightarrow \mu \mu }$$Υ→μμ decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon $$|\eta |<2.7$$|η|<2.7 and $$5 \lesssim p_{\mathrm{T}}\lesssim 100$$5≲pT≲100 GeV) the efficiency is above $$99\,\%$$99% and is measured with per-mille precision. The momentum resolution ranges from $$1.7\,\%$$1.7% at central rapidity and for transverse momentum $$p_{\mathrm{T}}\simeq 10$$pT≃10 GeV, to $$4\,\%$$4% at large rapidity and $$p_{\mathrm{T}}\simeq 100$$pT≃100 GeV. The momentum scale is known with an uncertainty of $$0.05\,\%$$0.05% to $$0.2\,\%$$0.2% depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.
123102281
Characterisation and mitigation of beam-induced backgrounds observed in the ATLAS detector during the 2011 proton-proton run
This paper presents a summary of beam-induced backgrounds observed in the ATLAS detector and discusses methods to tag and remove background contaminated events in data. Trigger-rate based monitoring of beam-related backgrounds is presented. The correlations of backgrounds with machine conditions, such as residual pressure in the beam-pipe, are discussed. Results from dedicated beam-background simulations are shown, and their qualitative agreement with data is evaluated. Data taken during the passage of unpaired, i.e. non-colliding, proton bunches is used to obtain background-enriched data samples. These are used to identify characteristic features of beam-induced backgrounds, which then are exploited to develop dedicated background tagging tools. These tools, based on observables in the Pixel detector, the muon spectrometer and the calorimeters, are described in detail and their efficiencies are evaluated. Finally an example of an application of these techniques to a monojet analysis is given, which demonstrates the importance of such event cleaning techniques for some new physics searches.
123014224
A neural network clustering algorithm for the ATLAS silicon pixel detector
A novel technique to identify and split clusters created by multiple charged particles in the ATLAS pixel detector using a set of artificial neural networks is presented. Such merged clusters are a common feature of tracks originating from highly energetic objects, such as jets. Neural networks are trained using Monte Carlo samples produced with a detailed detector simulation. This technique replaces the former clustering approach based on a connected component analysis and charge interpolation. The performance of the neural network splitting technique is quantified using data from proton-proton collisions at the LHC collected by the ATLAS detector in 2011 and from Monte Carlo simulations. This technique reduces the number of clusters shared between tracks in highly energetic jets by up to a factor of three. It also provides more precise position and error estimates of the clusters in both the transverse and longitudinal impact parameter resolution.
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.