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At least 73 records · Page 4Linked to original sources
arXiv2008

Taming Deeply Virtual Compton Scattering

We study recent Deeply Virtual Compton scattering (DVCS) data within a dual parameterization of the Generalized Parton Distributions (GPDs). This parameterization allows to quantify the maximum amount of information, that can be extracted from DVCS data, in a ``quintessence'' function. We present a ``zero step'' model for the latter solely based on the forward quark density, providing a parameter free prediction for the imaginary part of the DVCS amplitude. It is shown that the bulk effect of the $e p \to e p γ$ beam helicity asymmetry can be understood within such a model.

hep-ph↗
arXiv2008

Projected shell model description for nuclear isomers

Nuclear isomer is a current research focus. To describe isomers, we present a method based on the Projected Shell Model. Two kinds of isomers, K-isomers and shape isomers, are discussed. For the K-isomer treatment, K-mixing is properly implemented in the model. It is found however that in order to describe the strong K-violation more efficiently, it may be necessary to further introduce triaxiality into the shell model basis. To treat shape isomers, a scheme is outlined which allows mixing those configurations belonging to different shapes.

nucl-th↗
arXiv2008

Multimeson production in pp interactions as a background for eta and eta' decays

Multimeson production in pp interactions comprises important background for eta, omega and eta' mesons production experiments and for the studies of their decays planned with WASA detector at COSY. The available information about the reactions is summarized and the need for efforts to describe the processes is stressed.

nucl-ex↗
arXiv2008

Glauber Monte-Carlo predictions for LHC

In the framework of various Glauber-like models we compute several correlation observables in nuclear collisions at the SPS, RHIC, and LHC energies. We analyze fluctuations of the eccentricity of the fireball created in the collision, in particular the {variable-axes} harmonic moments $ε^\ast$, as well as the fluctuations of multiplicity of charged particles. We find moderate model dependence of the scaled standard deviation $σ(ε^\ast)/ε^\ast$ on the choice of the particular Glauber model. For all considered models the values of $σ(ε^\ast)/ε^\ast$ range from $\sim$~0.5 for central collisions to $\sim$~0.3-0.4 for peripheral collisions. The results are confronted to the recent measurement of the elliptic-flow fluctuations at RHIC. We also find that the dependence of multiplicity fluctuations on the centrality of the collision is too weak to explain the measurements at the SPS energies. The magnitude of the Glauber multiplicity fluctuations increases by about 20% from the RHIC to LHC energies.

nucl-th↗
arXiv2009

Neutrino masses from the GSI anomaly

We investigate the influence of the strong Coulomb field of a heavy nucleus on massive neutrinos, produced in the K-shell electron capture (EC) decays of the H-like 140Pr58+ and 142Pm60+ ions. The corrections to the neutrino masses due to virtually produced charged lepton W-boson pairs in the strong Coulomb field of a nucleus with charge Ze are calculated and discussed with respect to their influence on the period of the time-modulation of the number of daughter ions, observed recently in the EC-decays of the H-like 140Pr58+ and 142Pm60+ ions at GSI in Darmstadt. These corrections explain the 2.9 times higher difference of the squared neutrino masses obtained from the time-modulation of the EC-decays with respect to the value deduced from the antineutrino-oscillation experiments of KamLAND.

nucl-th↗
arXiv2008

Transverse Energy Measurement and Fluctuation Studies in Ultra-Relativistic Heavy Ion Collisions

Transverse energy ($E_T$) has been measured with both of it's components, namely hadronic ($E_T^{had}$) and electromagnetic ($E_T^{em}$) at mid-rapidity, for 62.4 GeV Au+Au collisions by the STAR experiment. In the common phase space of TPC and BEMC ($0 < η< 1$ and full $ϕ$), we have obtained $E_T^{had}$ from the TPC reconstructed tracks and $E_T^{em}$ from the BEMC tower hits after correcting for the hadronic contaminations in the calorimeter. The centrality behavior of $ /(0.5 N_{part})$ and the excitation function of $ /(0.5 N_{part})$ has been compared with the final state gluon saturation model (EKRT) along with similar measurements from SPS to RHIC. The most striking feature is the observation of a nearly constant value of $E_T/N_{ch} \sim 0.8$ GeV from AGS, SPS to RHIC. The $E_T$ and $N_{ch}$ production has been observed to follow a logarithmic behavior. The initial energy density estimated by the boost-invariant Bjorken hydrodynamic model, is well above the lattice QCD value for a deconfined matter of Quarks and Gluons. Taking similar colliding species i.e. Au+Au, the $ε_{Bj} .τ$ has been predicted for LHC, based on the measurements at RHIC. We have also made predictions for $(dE_T/dη)/(0.5 N_{part})$ and $(dN_{ch}/dη)/(0.5 N_{part})$ for the LHC energy. Furthermore, we have studied the event-by event fluctuations in $E_T$ and in the ratio of it's components using $σ/μ$ as the fluctuation observable.

nucl-ex↗
arXiv2008

Separating Signals from Non-Interfering Backgrounds using Probabilistic Event Weightings

A common situation in experimental physics is to have a signal which can not be separated from a non-interfering background through the use of any cut. In this paper, we describe a procedure for determining, on an event-by-event basis, a quality factor (Q-factor) that a given event originated from the signal distribution. This Q-factor can then be used as an event weight in subsequent analysis procedures, allowing one to more directly access the true spectrum of the signal.

physics.data-an↗
arXiv2014

Charmed hadron production at low transverse momentum in Au+Au collisions at RHIC

We report measurements of charmed hadron production from hadronic ($D^{0}\rightarrow Kπ$) and semileptonic ($μ$ and $e$) decays in 200 GeV Au+Au collisions at RHIC. Analysis of the spectra indicates that charmed hadrons have a different radial flow pattern from light or multi-strange hadrons. Charm cross sections at mid-rapidity are extracted by combining the three independent measurements, covering the transverse momentum range that contributes to $\sim$90% of the integrated cross section. The cross sections scale with number of binary collisions of the initial nucleons, a signature of charm production exclusively at the initial impact of colliding heavy ions. The implications for charm quark interaction and thermalization in the strongly interacting matter are discussed.

nucl-ex↗
arXiv2008

Systematics of Identified Particle Production in pp, dAu and Au-Au Collisions at RHIC Energies

(Abstract is abridged for arXiv.) Identified mid-rapidity particle spectra and freeze-out properties are presented for 200 GeV pp, 200 GeV dAu and 62.4 GeV Au-Au collisions, measured in the STAR-TPC. Evolution of the identified particle spectra ($π^{\pm}$, $K^{\pm}$, p and $\overline{p}$) with charged particle multiplicity and event centrality is investigated in detail. Thermal model fits to the measured particle ratios yield a chemical freeze-out temperature $\sim$ 155 MeV in 200 GeV pp, 200 GeV dAu and 62.4 GeV Au-Au collisions. The extracted chemical freeze-out temperature is close to the critical phase transition temperature predicted by lattice QCD calculations. The kinetic freeze-out temperature extracted from hydrodynamically motivated blast-wave models shows a continuous drop from pp, dAu and peripheral to central Au-Au collisions, while the transverse flow velocity increases from $\sim$ 0.2 in pp to $\sim$ 0.6 in central 200 GeV Au-Au collisions. The kinetic freeze-out parameters in 62.4 GeV and 200 GeV Au-Au collisions seem to be governed only by event multiplicity/centrality. In order to study the effect of resonance decays on the kinetic freeze-out parameters, the data are fitted with the blast-wave model including resonances. It is found that the thus extracted parameters are consistent with those obtained without including resonances, the resonance decays do not modify the spectral shapes significantly in the measured $p_{T}$ region in STAR.

nucl-ex↗
arXiv2008

Prototype Performance of Novel Muon Telescope Detector at STAR

Research on a large-area, cost-effective Muon Telescope Detector has been carried out for RHIC and for next generation detectors at future QCD Lab. We utilize state-of-the-art multi-gap resistive plate chambers with large modules and long readout strips in detector design \cite{MTDLDRD}. The results from cosmic ray and beam test will be presented to address intrinsic timing and spatial resolution for a Long-MRPC. The prototype performance of a novel muon telescope detector at STAR will be reported, including muon identification capability, timing and spatial resolution.

nucl-ex↗
arXiv2008

High $p_T$ Identified Particle Spectra

I will present an overview of identified particle spectra at high $p_T$ ($p_T{}^{>}_{\sim}$ 5 GeV/$c$) in both p+p collisions and AA collisions at RHIC. In p+p collisions, summary of particle ratios of K, $η$, $ω$, $ρ$, $ϕ$, $p$, $\bar{p}$, $Λ$ and heavy-flavor (open charm, $J/Ψ$) to $π$ at high-pt will be compiled and compared to the ratios of integrated yields. The spectra are used in $x_t$ scaling study and compared to pQCD calculations. These will help us establish particle composition in jets and the quark and gluon contributions to hadron production at high $p_T$. Similar jet chemistry has been extracted in Au+Au data in search for a quantitative measure of color charge dependence of jet energy loss.

nucl-ex↗
arXiv2008

Thermal Dimuon Emission in In-In at the CERN SPS

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. A significant excess of pairs is observed above the yield expected from neutral meson decays, consistent with a dominant contribution from $ππ\toρ\toμμ$. This paper presents precision results on the mass and transverse momentum spectra of the excess pairs. The space-time averaged rho spectral function associated to the measured mass distribution shows a significant broadening, but essentially no mass shift. The slope parameter $T_{eff}$ extracted from the spectra rises with dimuon mass up to the $ρ$, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline indicates a transition to an emission source with much smaller flow, possibly of partonic origin.

nucl-ex↗
arXiv2008

Probing gluon shadowing with forward photons at RHIC

There is a major need to better constrain nuclear parton densities in order to provide reliable perturbative QCD predictions at the LHC as well as to probe possible non-linear evolution at small values of x. In these proceedings, we discuss how the production of prompt photons at large rapidity in p-p and d-Au collisions at RHIC (sqrt(s_NN)=200 GeV) is sensitive to the nuclear modifications of gluon distributions at x~0.001 and at rather low scales, Q^2~10 GeV^2. The nuclear production ratio, R_dAu=sigma(d+A->gamma+X)/(2A sigma(p+p->gamma X), is computed for isolated prompt photons at NLO using the nDSg nuclear parton densities, in order to assess the visibility of the signal. We also emphasise that the expected counting rates in a year of running at RHIC are large, indicating that R_dAu could be measured with a high statistical accuracy.

hep-ph↗
arXiv2009

Absolute Total np and pp Cross Section Determinations

Absolute total cross sections for np and pp scattering below 1000 MeV are determined based on partial-wave analyses of NN scattering data. These cross sections are compared with most recent ENDF/B and JENDL data files, and the Nijmegen partial-wave analysis. Systematic deviations from the ENDF/B and JENDL evaluations are found to exist in the low-energy region.

nucl-ex↗
arXiv2008

Medium properties and jet-medium interaction from STAR

We report recent STAR results on medium modification of 2- and 3-particle correlations in heavy-ion collisions at RHIC. In particular properties of an additional extended correlation in pseudo-rapidity (``the ridge''), not present in p+p or d+Au collisions, are discussed. Next, the shape modification of the away-side correlation peak at low- and intermediate-$p_T$ is investigated to look for signals of Mach cone shock waves or Čerenkov gluon emission.

nucl-ex↗
arXiv2008

Constraining the density dependence of nuclear symmetry energy with heavy-ion reactions and its astrophysical impact

Recent analyses of several isospin effects in heavy-ion reactions have allowed us to constrain the density dependence of nuclear symmetry energy at sub-saturation densities within a narrow range. Combined with constraints on the Equation of State (EOS) of symmetric nuclear matter obtained previously from analyzing the elliptic flow in relativistic heavy-ion collisions, the EOS of neutron-rich nuclear matter is thus partially constrained. Here we report effects of the partially constrained EOS of neutron-rich nuclear matter on the mass-radius correlation, moment of inertia, elliptical deformation and gravitational radiation of (rapidly) rotating neutron stars.

nucl-th↗
arXiv2009

Microscopic approaches for nuclear Many-Body dynamics: applications to nuclear reactions

These lecture notes are addressed to PhD student and/or researchers who want a general overview of microscopic approaches based on mean-field and applied to nuclear dynamics. Our goal is to provide a good description of low energy heavy-ion collisions. We present both formal aspects and practical applications of the time-dependent Hartree-Fock (TDHF) theory. The TDHF approach gives a mean field dynamics of the system under the assumption that particles evolve independently in their self-consistent average field. As an example, we study the fusion of both spherical and deformed nuclei with TDHF. We also focus on nucleon transfer which may occur between nuclei below the barrier. These studies allow us to specify the range of applications of TDHF in one hand, and, on the other hand, its intrinsic limitations: absence of tunneling below the Coulomb barrier, missing dissipative effects and/or quantum fluctuations. Time-dependent mean-field theories should be improved to properly account for these effects. Several approaches, generically named "beyond TDHF" are presented which account for instance for pairing and/or direct nucleon-nucleon collisions. Finally we discuss recent progresses in exact ab-initio methods based on the stochastic mean-field concept.

nucl-th↗