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At least 55 records · Page 3Linked to original sources
arXiv2007

Identified Particle Correlations at RHIC: Medium Interactions & Modified Fragmentation

Azimuthal angle two particle correlations have been shown to be a powerful probe for extracting novel features of jet induced correlations produced in Au+Au collisions at RHIC. At intermediate $p_T$, 2-5GeV/c, the jets have been shown to be significantly modified in both their particle composition and their angular distribution compared to p+p collisions. Two-particle angular correlations with identified particles provide sensitive probes of both the interactions between hard scattered partons and the medium. The systematics of these correlations are essential to understanding the physics of intermediate $p_T$ in heavy ion collisions.

nucl-ex↗
arXiv2008

Detection of fast neutrons and digital pulse-shape discrimination between neutrons and gamma rays

The basic principles of detection of fast neutrons with liquid scintillator detectors are reviewed, together with a real example in the form of the Neutron Wall array. Two of the challenges in neutron detection, discrimination of neutrons and gamma rays and identification of cross talk between detectors due to neutron scattering, are briefly discussed, as well as possible solutions to these problems. The possibilities of using digital techniques for pulse-shape discrimination are examined. Results from a digital and analog versions of the zero cross-over algorithm are presented. The digital pulse-shape discrimination is shown to give, at least, as good results as the corresponding analogue version.

nucl-ex↗
arXiv2007

Reconstructing Bottom mesons using displaced vertices from semi-leptonic decays

Precise determination of heavy flavor production cross-sections at LHC energies will be of primary importance. The produced heavy quarks are expected to be sensitive probes of parton energy loss in the medium formed in heavy-ion collisions. Through the measurement of charm and bottom suppression in Pb + Pb with respect to p + p, we hope to obtain insight into the color-charge and quark mass dependence of the energy loss mechanism. The ALICE experiment with its large acceptance is well suited to investigate the intermediate transverse momentum spectrum of heavy flavor mesons where these energy loss effects are expected to be visible. ALICE has very good electron PID capabilities over a large kinematic range using Time Projection Chamber (TPC), Transition Radiation Detector (TRD) and the Electromagnetic Calorimeter (EMCal). In addition the EMCal, to be installed for the Pb + Pb runs, is planned to allow efficient triggering on high-pT jets. We first introduce the EMCal project and an overview of detector specifications. Then we introduce a method developed to select preferentially electrons from heavy flavor decays by reconstructing displaced secondary vertices. The strategy is to reconstruct displaced vertices from semi-leptonic heavy flavor meson decays using the excellent spatial resolution of the Inner Tracking System (ITS). We show preliminary results of an efficiency study from charm vs. bottom vertices.

nucl-ex↗
arXiv2008

Mass measurements of neutron-rich nuclei at JYFLTRAP

The JYFLTRAP mass spectrometer was used to measure the masses of neutron-rich nuclei in the region between N = 28 to N = 82 with uncertainties better than 10 keV. The impacts on nuclear structure and the r-process paths are reviewed.

nucl-ex↗
arXiv2008

Bulk Properties of QCD-matter at Highest Collider Energies

The Large Hadron Collider at CERN will provide Pb-Pb collisions at energies up to $\sqrt{s_{NN}}$ = 5.5 TeV. We speculate on global observables, i.e. the charged particle density at mid-rapidity, chemical freeze-out conditions and collective parameters for transverse radial an elliptic flow. Finally, we present an idea how to address the important issue of thermalization by measuring the correlated production of heavy-quark hadrons.

nucl-ex↗
arXiv2008

Nuclear constraints on the momenta of inertia of neutron stars

Properties and structure of neutron stars are determined by the equation of state (EOS) of neutron-rich stellar matter. While the collective flow and particle production in relativistic heavy-ion collisions have constrained tightly the EOS of symmetric nuclear matter up to about five times the normal nuclear matter density, the more recent experimental data on isospin-diffusion and isoscaling in heavy-ion collisions at intermediate energies have constrained considerably the density dependence of the nuclear symmetry energy at subsaturation densities. Although there are still many uncertainties and challenges to pin down completely the EOS of neutron-rich nuclear matter, the heavy-ion reaction experiments in terrestrial laboratories have limited the EOS of neutron-rich nuclear matter in a range much narrower than that spanned by various EOSs currently used in astrophysical studies in the literature. These nuclear physics constraints could thus provide more reliable information about properties of neutron stars. Within well established formalisms using the nuclear constrained EOSs we study the momenta of inertia of neutron stars. We put the special emphasis on the component A of the extremely relativistic double neutron star system PSR J0737-3039. Its moment of inertia is found to be between 1.30 and 1.63 $(\times10^{45}g$ $cm^2)$. Moreover, the transition density at the crust-core boundary is shown to be in the narrow range of $ρ_t=[0.091-0.093](fm^{-3})$.

astro-ph↗
arXiv2008

On the time-modulation of the K-shell electron capture decay of H-like 140Pr58+ ions produced by neutrino-flavour mixing

According to recent experimental data at GSI, the rate of the number of daughter ions 140Ce58+, produced by the nuclear K-shell electron capture (EC) decay of the H-like ion 140Pr58+, is modulated in time with a period T_d = 7.06(8) sec and an amplitude a_(EC) = 0.20(2). We show that this phenomenon can be explained by neutrino-flavour mixing and derive a value for the difference of squared masses Delta m^2_(21) = m^2_2 - m^2_1 = 2.22(3)x10^(-4) eV^2.

nucl-th↗
arXiv2008

Direct Nuclear Reactions in Lithium-Lithium Systems: 7Li+7Li at Elab = 2 - 16 MeV

Angular distributions of 7Li(7Li,t), (7Li,alpha) and (7Li,6He) reactions were measured for laboratory energies from 2 - 16 MeV. Exact finite range DWBA analyses were performed with the aim to identify contributions of direct processes and to investigate the applicability of DWBA to such few nucleon systems. It turned out that DWBA can be successfully applied to estimate differential and total cross sections of direct transfer processes in 7Li+7Li interaction. The direct mechanism was found to play a dominant role in most of these reactions but significant contributions of other, strongly energy dependent processes were also established. It is suggested that these processes might be due to isolated resonances superimposed on the backround of statistical fluctuations arising from interference of compound nucleus and direct transfer contributions.

nucl-ex↗
arXiv2008

Observation of the n(3He,t)p Reaction by Detection of Far-Ultraviolet Radiation

We have detected Lyman alpha radiation as a product of the n(3He,t)p nuclear reaction occurring in a cell of 3He gas. The predominant source of this radiation appears to be decay of the 2p state of tritium produced by charge transfer and excitation collisions with the background 3He gas. Under the experimental conditions reported here we find yields of tens of Lyman alpha photons for every neutron reaction. These results suggest a method of cold neutron detection that is complementary to existing technologies that use proportional counters. In particular, this approach may provide single neutron sensitivity with wide dynamic range capability, and a class of neutron detectors that are compact and operate at relatively low voltages.

nucl-ex↗
arXiv2008

Prospects for identified leading particle correlation at LHC and in ALICE

Azimuthal di-hadron correlations play important role in the characterization of the medium created in heavy-ion collisions at RHIC. Moreover, as a novel phenomenon, strong modification of the away-side correlation is observed in Au+Au with respect to p+p collisions. Below the exclusive jet reconstruction threshold at LHC, leading particle correlations will provide access to the regime where hard scatterings and bulk medium properties can be simultaneously studied. Leading particle correlations can be extended to very low transverse momenta via the tracking and particle identification capabilities of ALICE, to the coalescence and hydrodynamic domains. In preparation for the first p+p and Pb+Pb collisions of LHC, we present prospects on leading particle correlations with identified particles in ALICE.

nucl-ex↗
arXiv2008

Two- and Three-Particle Jet-Like Correlations

We present results of 2-particle jet-like correlations, with high pT h+- triggers and identified pi+-, p, and pbar triggers in d+Au and Au+Au collisions and 3-particle jet-like azimuthal correlations in pp, d+Au, and Au+Au collisions at sqrt(s)=200 GeV. These results use data from the STAR TPC during RHIC runs II, III, and IV. Modifications in 2-particle correlations are observed in Au+Au collisions. These modifications are not seen in $pp$ or d+Au collisions. This demonstrates that the modifications are due to final state nuclear effects. High pT protons, anti-protons and charged pions are identified by the relativistic rise of dE/dx in the STAR TPC. Correlations of charged hadrons with high pT p, pbar, and pi+- show no discernible difference. The results post challenges to recombination and coalescence models which are otherwise very successful in explaining the large baryon/meson ratio and the splitting of the elliptic flow at intermediate pT. In central Au+Au collisions, the away-side 2-particle correlation is significantly broadened and even double humped in selective kinematic ranges. Three-particle correlations were employed to identify the underlying physics mechanism(s). Results in pp, d+Au and peripheral Au+Au collisions show dijet structure with away-side kT broadening. Results in mid-central and central Au+Au collisions are consistent with a near-side jet and on the away-side a combination of conical emission and large angle gluon radiation and deflected jets. The associated pT independent emission angle suggests Mach-cone shock waves being the underlying physics mechanism for the conical emission. The emission angle is measured to be 1.39+-0.01 (stat.)+-0.04(sys.) in ZDC triggered 0-12% Au+Au data.

nucl-ex↗
arXiv2008

Hadrons in Medium -- Theory meets Experiment

In this talk I give a short review of theoretical results on the properties of hadrons in cold, equilibrium nuclear matter. I then discuss the observable consequences of any changes of these properties inside the medium in actual experiments. I demonstrate that any experimental verification of in-medium effects requires a state-of-the-art treatment of the reaction dynamics and, in particular, also the final state interactions.

hep-ph↗
arXiv2008

Baryon Resonances Observed at BES

The $ψ$ decays provide a novel way to explore baryon spectroscopy and baryon structure. The baryon resonances observed from $ψ$ decays at BES are reviewed. The implications and prospects at upgraded BESIII/BEPCII are discussed.

nucl-ex↗
arXiv2008

Dilepton measurements with CERES

We report on dilepton measurements for central Pb on Au collisions at the top CERN SPS energy with the upgraded CERES experiment. The dilepton mass spectrum of 2000 data with improved mass resolution shows an enhancement over the expectation from hadron decays that is well described by a model including a strong broadening of the $ρ$ spectral function. The measured excess yield excludes the dropping mass scenario. We also report on the $ϕ$ meson measured simultaneously both in the $K^+K^-$ and in the dilepton decay channel for the first time in high energy heavy-ion collisions. An excellent agreement is found between the rapidity densities and the shape of the measured tranverse momentum spectrum. The data rule out a possible enhancement of the $ϕ$ yield in the leptonic over hadronic channel by a factor larger than 1.6 at 95% CL. CERES results are in agreement with NA49 results.

nucl-ex↗
arXiv2008

The Physics Program at MAMI-C

In February 2007, the fourth stage of the Mainz Microtron, MAMI-C, started operations with a first experiment. The new Harmonic Double-Sided Microtron delivers an electron beam with energies up to 1.5 GeV while preserving the excellent beam quality of the previous stages. The experimental program at MAMI is focused on studies of the hadron structure in the domain of non-perturbative QCD. In this paper, a few prominent selections of the extensive physics program at MAMI-C will be presented.

nucl-ex↗
arXiv2008

Heavy Quark Diffusion as a Probe of the Quark-Gluon Plasma

We report on recent research on the properties of elementary particle matter governed by the strong force at high temperatures, where QCD predicts hadrons to dissolve into the Quark-Gluon Plasma (QGP). After a short introduction to the basic elements of QCD in the vacuum, most notably quark confinement and mass generation, we discuss how these phenomena relate to phase changes in strongly interacting matter at high temperature. We briefly review the main experimental findings at the Relativistic Heavy Ion Collider (RHIC) which provide strong evidence that a QGP has been produced, with unprecedentedly small viscosity and large opacity. We discuss how heavy quarks (charm and bottom) can be utilized to quantitatively probe the transport properties of a strongly coupled QGP (sQGP). The large heavy-quark (HQ) mass allows to set up a Brownian motion approach, which can serve to evaluate different approaches for HQ interactions in the sQGP. The implementation of lattice QCD based HQ potentials generates pre-hadronic resonance structures in HQ scattering in the medium, leading to large interaction rates and small diffusion coefficients. The resonance correlations are strongest close to the critical temperature (T_c), suggesting an intimate connection to the hadronization of the QGP. The implementation of HQ transport into Langevin simulations of an expanding QGP fireball at RHIC enables quantitative comparisons with experiment. The extracted HQ diffusion coefficients are employed for schematic estimates of the shear viscosity, corroborating the notion of a strongly-coupled QGP in the vicinity of T_c.

hep-ph↗
arXiv2008

Isoscaling in Reactions on Enriched Tin Isotopes and Nuclear Symmetry Energy

Isospin effects in 12C ion induced reactions on enriched tin isotopes are investigated. The isoscaling parameter B is determined for different mass regions of product nuclei. It is shown that the isoscaling parameter is sensitive to the formation mechanism of products, and increases as the difference in the asymmetry is increasing. Using the exitatation energy obtained with the catcher technique temperatures, density ratio ro/ro0 for product nuclei in different mass regions and the values of symmetry energy coefficient for light mass regions of product nuclei for proton and deuteron induced reactions are determined.

nucl-ex↗