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At least 109 records · Page 6Linked to original sources
arXiv2009

Progress Towards A Permanent Octupole Magnetic Ultra-Cold Neutron Trap for Lifetime Measurements

The current knowledge of the neutron $β$-decay lifetime has come under scrutiny as of late due to large disagreements between recent precise measurements. Measurements using magnetically trapped Ultra-Cold Neutrons (UCNs) offer the possibility of storage without spurious losses which can provide a reliable value for the neutron lifetime. The progress towards realizing a neutron lifetime measurement using a Ioffe-type trap made with a Halbach-type permanent octupole magnet is presented here. The experimental procedure extracts a gas of UCNs into vacuum, which reduces many known channels of neutron losses, and detects the neutron decays via in-situ detection of the produced protons.

nucl-ex↗
arXiv2008

Form Factors and Dyson-Schwinger Equations

A synopsis exemplifying the employment of Dyson-Schwinger equations in the calculation and explanation of hadron electromagnetic form factors and related phenomena. In particular the contribution: presents the pion form factor computed simultaneously at spacelike and timelike momenta; reports aspects of the evolution of the nucleon and Delta masses with current-quark mass and the correlation of their mass difference with that between scalar and axial-vector diquarks; describes an estimate of the s-quark content of a dressed u-quark and its impact on the nucleon's strangeness magnetic moment; and comments upon the domain within which a pseudoscalar meson cloud can materially contribute to hadron form factors.

nucl-th↗
arXiv2008

AGATA: Gamma-ray tracking in segmented HPGe detectors

The next generation of radioactive ion beam facilities, which will give experimental access to many exotic nuclei, are presently being developed. At the same time the next generation of high resolution gamma-ray spectrometers, based on gamma-ray tracking, for studying the structure of these exotic nuclei are being developed. One of the main differences in tracking of $γ$ rays versus charged particles is that the gamma rays do not deposit their energy "continuously" in the detector, but in a few discrete steps. Also, in the field of nuclear spectroscopy, the location of the source is mostly well known while the exact interaction position in the detector is the unknown quantity. This makes the challenges of gamma-ray tracking in germanium somewhat different compared to vertexing in silicon detectors. In these proceedings we present the methods for determining the 3D interaction positions in the detector and how these are used to reconstruct the gamma-ray tracks in the AGATA detector array. We also present preliminary simulation results of a proposed in-beam method to measure the interaction position resolution in the germanium detectors.

nucl-ex↗
arXiv2009

Overview of Kbar-N and Kbar-nucleus dynamics

The main features of coupled-channel Kbar-N dynamics near threshold and its repercussions in few-body Kbar-nuclear systems are briefly reviewed highlighting the I=1/2 Kbar-N-N system. For heavier nuclei, the extension of mean-field calculations to multi-Kbar nuclear quasibound states is discussed focusing on kaon condensation.

nucl-th↗
arXiv2008

Structure effects of the two protons - two neutrons correlations

The proton-neutron 2 particles - 2 holes correlations in superfluid nuclei, described by an effective, Josephson-type interaction ~[(P+N-)+(P-N+)], are studied within a boson approximation. The strength of this interaction is estimated using the symmetry energy for an even-even system of nucleons lying on the same degenerate level. The RPA vacuum is obtained explicitly, and the electroexcitation to isovector monopole states of oscillatory pair exchange between the proton and neutron superfluids is briefly discussed.

nucl-th↗
arXiv2009

Study of the Radiation Hardness of Vcsel and Pin Arrays

The silicon trackers of the ATLAS experiment at LHC (CERN) use optical links for data transmission. VCSEL arrays operating at 850 nm are used to transmit optical signals while PIN arrays are used to convert the optical signals into electrical signals. We investigate the feasibility of using the devices at the Super LHC (SLHC). We irradiated VCSEL and GaAs PIN arrays from three vendors and silicon PIN arrays from one vendor. All arrays can be operated up to the SLHC dosage except the GaAs PIN arrays which have very low responsivities after irradiation and hence are probably not suitable for the SLHC application.

physics.ins-det↗
arXiv2009

Kinetics vs hydrodynamics: generalization of Landau/Cooper-Frye prescription for freeze-out

The problem of spectra formation in hydrodynamic approach to A+A collisions is considered within the Boltzmann equations. It is shown analytically and illustrated by numerical calculations that the particle momentum spectra can be presented in the Cooper-Frye form despite freeze-out is not sharp and has the finite temporal width. The latter is equal to the inverse of the particle collision rate at points $(t_σ({\bf r},p),{\bf r})$ of the maximal emission at a fixed momentum $p$. The set of these points forms the hypersurfaces $t_σ({\bf r},p)$ which strongly depend on the values of $p$ and typically do not enclose completely the initially dense matter. This is an important difference from the standard Cooper-Frye prescription (CFp), with a common freeze-out hypersurface for all $p$, that affects significantly the predicted spectra. Also, the well known problem of CFp as for negative contributions to the spectra from non-space-like parts of the freeze-out hypersurface is naturally eliminated in this improved prescription.

nucl-th↗
arXiv2009

Beta decay studies of r-process nuclei at the National Superconducting Cyclotron Laboratory

The impact of nuclear physics on astrophysical r-process models is discussed, emphasizing the importance of beta-decay properties of neutron-rich nuclei. Several r-process motivated beta-decay experiments performed at the National Superconducting Cyclotron Laboratory are presented. The experiments include the measurement of beta-decay half-lives and neutron emission probabilities of nuclei in regions around Ni-78; Se-90; Zr-106 and Rh-120, as well as spectroscopic studies of Pd-120. A summary on the different experimental techniques employed, data analysis, results and impact on model calculations is presented.

nucl-ex↗
arXiv2009

Threshold Pion Production at Large Momentum Transfers

We consider threshold pion electroproduction on a proton target for photon virtualities in the region 1-10 GeV$^2$. The S-wave multipoles at threshold, $E_{0+}$ and $L_{0+}$, are calculated using light-cone sum rules.

hep-ph↗
arXiv2009

Ground State Magnetic Moments of Mirror Nuclei Studied at NSCL

Progress in the measurement of the ground state magnetic moments of mirror nuclei at NSCL is presented. The systematic trend of the spin expectation value $ $ and the linear behavior of $γ_p$ versus $γ_n$, both extracted from the magnetic moments of mirror partners, are updated to include all available data.

nucl-ex↗
arXiv2009

Femtoscopy in hadron and lepton collisions: RHIC results and world systematics

Femtoscopic measurements at a variety of facilities have established a clear dependence of spatial scales with event multiplicity and particle transverse mass ($m_T$) in heavy ion collisions from $\sqrt(s_{NN}) \sim 2-200 GeV$. The $m_T$-dependence is thought to arise from collective, explosive flow of the system, as probed by independent measurements, while the multiplicity dependence reflects the increased spatial extent of the final state with decreasing impact parameter. Qualitatively similar dependences have been reported from high energy hadron and lepton collisions, where the conceptual validity of an impact parameter or collective flow are less clear. We focus on results from elementary particle collisions, identify trends seen in the experimental data and compare them to those from heavy ion collisions.

nucl-ex↗
arXiv2009

$D\overline{D}$ momentum correlations versus relative azimuth as a sensitive probe for thermalization

In high-energy nuclear collisions at LHC, where a QGP might be created, the degree of thermalization at the partonic level is a key issue. Due to their large mass, heavy quarks are a powerful tool to probe thermalization. We propose to measure azimuthal correlations of heavy-quark hadrons and their decay products. Changes or even the complete absence of these initially existing azimuthal correlations in $Pb-Pb$ collisions might indicate thermalization at the partonic level. We present studies with PYTHIA for $p-p$ collisions at 14 TeV using the two-particle transverse momentum correlator ${<\overlineΔp_{t,1}\overlineΔp_{t,2}>}$ as a sensitive measure of potential changes in these azimuthal correlations. Contributions from transverse radial flow are estimated.

nucl-ex↗
arXiv2009

Symplectic dynamics of the nuclear mean-field

Elements of a restricted variational approach to the nuclear mean-field dynamics, providing the microscopic structure of the low energy collective modes, are summarized. The results are illustrated for the isovector states produced by the proton-neutron interactions in deformed and superfluid nuclei.

nucl-th↗
arXiv2009

The in-medium scale evolution in jet modification

The in-medium modification of the scale dependence of the fragmentation function in dense matter, brought about by higher twist corrections to the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations, is derived. A phenomenologically motivated resummation is outlined which incorporates the next-to-leading twist single gluon emission kernel along with the vacuum emission kernel and provides an in-medium virtuality evolution of the final fragmentation function of a hard jet propagating through dense matter. The concept of a fragmentation function is generalized to include a dependence on distance traveled in the medium. Following this, numerical implementations are carried out and compared to experimental results on the single inclusive suppression observed in Deep-Inelastic scattering (DIS) off a large nucleus.

nucl-th↗
arXiv2009

Overview of event-by-event fluctuations

Overview of event-by-event studies on relativistic heavy-ion collisions is given. I focus on fluctuation measurements and on theoretical ideas which appeared experimentally fruitful.

nucl-th↗