PRC Editor Selections

Global Calculation of Nuclear Shape Isomers

2009-11-20T00:00:00-05:00

Author(s): Peter Möller, Arnold J. Sierk, Ragnar Bengtsson, Hiroyuki Sagawa, and Takatoshi Ichikawa
To determine which nuclei may exhibit shape isomerism, we use a well-benchmarked macroscopic-microscopic model to calculate potential-energy surfaces as functions of spheroidal (ϵ_{2} ), hexadecapole (ϵ_{4} ), and axial-asymmetry (γ) shape coordinates for 7206 nuclei from A=31 to A=290. We analyze these and identify the deformations and energies of all minima deeper than 0.2 MeV. These minima may correspond to characteristic experimentally observable shape-isomeric states. Shape isomers mainly occur in the A=80 region, the A=100 region, and in an extended region centered around ^{208} Pb. We compare our model to experimental results for Kr isotopes. Moreover, in a plot versus N and Z we show for each of the 7206 nuclei the calculated number of minima. The results reveal one fairly unexplored region of shape isomerism, which is experimentally accessible, namely the region northeast of _{82} ^{208} Pb.
[Phys. Rev. Lett. 103, 212501] Published Fri Nov 20, 2009

Baryon magnetic moments in large-N_{c} chiral perturbation theory

Rubén Flores-Mendieta — 2009-11-20T00:00:00-05:00

Author(s): Rubén Flores-Mendieta
The baryon magnetic and transition magnetic moments are computed in heavy baryon chiral perturbation theory in the large-N_{c} limit, where N_{c} is the number of colors. One-loop nonanalytic corrections of orders m_{q}^{1/2} and m_{q} ln⁡m_{q} are incorporated into the analysis, where contributions of both intermediate octet and decuplet baryon states are explicitly included. Expressions are obtained in the limit of vanishing baryon mass differences and compared with the current experimental data. Furthermore, a comparison with conventional heavy baryon chiral perturbation theory is carried out for three light quarks flavors and at the physical value N_{c} =3.
[Phys. Rev. D 80, 094014] Published Fri Nov 20, 2009

Quark Structure of the Nucleon and Angular Asymmetry of Proton-Neutron Hard Elastic Scattering

Carlos G. Granados and Misak M. Sargsian — 2009-11-17T00:00:00-05:00

Author(s): Carlos G. Granados and Misak M. Sargsian
We investigate an asymmetry in the angular distribution of hard elastic proton-neutron scattering with respect to the 90° center of mass scattering angle and demonstrate that it’s magnitude is related to the helicity-isospin symmetry of the quark wave function of the nucleon. Our estimate of the asymmetry within the quark-interchange model of hard scattering demonstrates that the quark wave function of a nucleon based on the exact SU(6) symmetry predicts an angular asymmetry opposite to that of experimental observations. We found that the quark wave function based on the diquark picture of the nucleon produces a correct asymmetry. Comparison with the data allowed us to show that the vector diquarks contribute around 10% in the nucleon wave function and they are in negative phase relative to the scalar diquarks. These observations are essential in constraining QCD models of a nucleon.
[Phys. Rev. Lett. 103, 212001] Published Tue Nov 17, 2009

Supersoft Symmetry Energy Encountering Non-Newtonian Gravity in Neutron Stars

De-Hua Wen, Bao-An Li, and Lie-Wen Chen — 2009-11-16T00:00:00-05:00

Author(s): De-Hua Wen, Bao-An Li, and Lie-Wen Chen
Considering the non-Newtonian gravity proposed in grand unification theories, we show that the stability and observed global properties of neutron stars cannot rule out the supersoft nuclear symmetry energies at suprasaturation densities. The degree of possible violation of the inverse-square law of gravity in neutron stars is estimated using an equation of state of neutron-rich nuclear matter consistent with the available terrestrial laboratory data.
[Phys. Rev. Lett. 103, 211102] Published Mon Nov 16, 2009

New Measurements of the European Muon Collaboration Effect in Very Light Nuclei

J. Seely et al. — 2009-11-13T00:00:00-05:00

Author(s): J. Seely et al.
New Jefferson Lab data are presented on the nuclear dependence of the inclusive cross section from ^{2} H, ^{3} He, ^{4} He, ^{9} Be and ^{12} C for 0.3[Phys. Rev. Lett. 103, 202301] Published Fri Nov 13, 2009

Dark Matter, Constrained Minimal Supersymmetric Standard Model, and Lattice QCD

Joel Giedt, Anthony W. Thomas, and Ross D. Young — 2009-11-12T00:00:00-05:00

Author(s): Joel Giedt, Anthony W. Thomas, and Ross D. Young
Recent lattice measurements have given accurate estimates of the quark condensates in the proton. We use these results to significantly improve the dark matter predictions in benchmark models within the constrained minimal supersymmetric standard model. The predicted spin-independent cross sections are at least an order of magnitude smaller than previously suggested and our results have significant consequences for dark matter searches.
[Phys. Rev. Lett. 103, 201802] Published Thu Nov 12, 2009

Signature of Smooth Transition from Sudden to Adiabatic States in Heavy-Ion Fusion Reactions at Deep Sub-Barrier Energies

Takatoshi Ichikawa, Kouichi Hagino, and Akira Iwamoto — 2009-11-11T00:00:00-05:00

Author(s): Takatoshi Ichikawa, Kouichi Hagino, and Akira Iwamoto
We propose a novel extension of the standard coupled-channels framework for heavy-ion reactions in order to analyze fusion reactions at deep-sub-barrier incident energies. This extension simulates a smooth transition between the two-body and the adiabatic one-body states. To this end, we damp gradually the off-diagonal part of the coupling potential, for which the position of the onset of the damping varies for each eigenchannel. We show that this model accounts well for the steep falloff of the fusion cross sections for the ^{16} O+ ^{208} Pb, ^{64} Ni+ ^{64} Ni, and ^{58} Ni+ ^{58} Ni reactions.
[Phys. Rev. Lett. 103, 202701] Published Wed Nov 11, 2009

Nucleon strangeness form factors from N_{f} =2+1 clover fermion lattice QCD

2009-11-10T00:00:00-05:00

Author(s): Takumi Doi, Mridupawan Deka, Shao-Jing Dong, Terrence Draper, Keh-Fei Liu, Devdatta Mankame, Nilmani Mathur, and Thomas Streuer
We present the N_{f} =2+1 clover fermion lattice QCD calculation of the nucleon strangeness form factors. We evaluate disconnected insertions using the Z(4) stochastic method, along with unbiased subtractions from the hopping parameter expansion. We find that increasing the number of nucleon sources for each configuration improves the signal significantly. We obtain G_{M}^{s} (0)=-0.017(25)(07), where the first error is statistical, and the second is the uncertainties in Q^{2} and chiral extrapolations. This is consistent with experimental values, and has an order of magnitude smaller error.
[Phys. Rev. D 80, 094503] Published Tue Nov 10, 2009

High-Resolution Spectroscopy of _{Λ} ^{16} N by Electroproduction

F. Cusanno et al. — 2009-11-09T00:00:00-05:00

Author(s): F. Cusanno et al.
An experimental study of the ^{16} O(e,e^{′} K^{+} ) _{Λ} ^{16} N reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e,e^{′} K^{+} )Λ,Σ^{0} exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76±0.16 MeV was obtained for _{Λ} ^{16} N with better precision than previous measurements on the mirror hypernucleus _{Λ} ^{16} O. Precise energies have been determined for peaks arising from a Λ in s and p orbits coupled to the p_{1/2} and p_{3/2} hole states of the ^{15} N core nucleus.
[Phys. Rev. Lett. 103, 202501] Published Mon Nov 09, 2009

Role of Long-Range Correlations in the Quenching of Spectroscopic Factors

C. Barbieri — 2009-11-09T00:00:00-05:00

Author(s): C. Barbieri
We consider the proton and neutron quasiparticle orbits around the closed-shell ^{56} Ni and ^{48} Ca isotopes. It is found that large model spaces (beyond the capability of shell model applications) are necessary for predicting the quenching of spectroscopic factors. The particle-vibration coupling is identified as the principal mechanism. Additional correlations—due to configuration with several particle-hole excitations—are estimated using shell model calculations and generate an extra reduction which is ≲4% for most quasiparticle states. The theoretical calculations nicely agree with (e, e^{′} p) and inverse kinematics knockout experiments. These results open a new path for a microscopic understanding of the shell model.
[Phys. Rev. Lett. 103, 202502] Published Mon Nov 09, 2009

X(3872) as a molecular DD^{*} state in a potential model

Ian Woo Lee, Amand Faessler, Thomas Gutsche, and Valery E. Lyubovitskij — 2009-11-09T00:00:00-05:00

Author(s): Ian Woo Lee, Amand Faessler, Thomas Gutsche, and Valery E. Lyubovitskij
We discuss the possibility that the X(3872) can be a hadronic DD^{*} bound state in the framework of a potential model. The potential is generated by the exchange of pseudoscalar, scalar, and vector mesons resulting from the Lagrangian of heavy hadron chiral perturbation theory. The hadronic bound state configuration contains charged and neutral DD^{*} components, while orbital S and D waves are included. Isospin symmetry breaking effects are fully taken into account. We show that binding in the DD^{*} system with J^{PC} =1^{++} already exists for a reasonable value of the meson-exchange regularization parameter of Λ∼1.2 GeV. We also explore the possibility of hadronic BB^{*} bound states and show that binding can be achieved in the isoscalar limit for J^{PC} =1^{++} or 1^{+-} .
[Phys. Rev. D 80, 094005] Published Mon Nov 09, 2009

Aspects of meson-baryon scattering in three- and two-flavor chiral perturbation theory

Maxim Mai, Peter C. Bruns, Bastian Kubis, and Ulf-G. Meißner — 2009-11-09T00:00:00-05:00

Author(s): Maxim Mai, Peter C. Bruns, Bastian Kubis, and Ulf-G. Meißner
We analyze meson-baryon scattering lengths in the framework of covariant baryon chiral perturbation theory at leading one-loop order. We compute the complete set of matching relations between the dimension-two low-energy constants in the two- and three-flavor formulations of the theory. We derive new two-flavor low-energy theorems for pion-hyperon scattering that can be tested in lattice simulations.
[Phys. Rev. D 80, 094006] Published Mon Nov 09, 2009

Publisher’s Note: Ground-State and Single-Particle Energies of Nuclei around ^{16} O, ^{40} Ca, and ^{56} Ni from Realistic Nucleon-Nucleon Forces [Phys. Rev. Lett. 103, 182501 (2009)]

S. Fujii, R. Okamoto, and K. Suzuki — 2009-11-06T00:00:00-05:00

Author(s): S. Fujii, R. Okamoto, and K. Suzuki
[Phys. Rev. Lett. 103, 199903] Published Fri Nov 06, 2009

Parton distribution function nuclear corrections for charged lepton and neutrino deep inelastic scattering processes

2009-11-05T00:00:00-05:00

Author(s): I. Schienbein, J. Y. Yu, K. Kovařík, C. Keppel, J. G. Morfín, F. I. Olness, and J. F. Owens
We perform a χ^{2} analysis of nuclear parton distribution functions (NPDFs) using neutral current charged-lepton (ℓ^{±} A) deeply inelastic scattering (DIS), and Drell-Yan data for several nuclear targets. The nuclear A dependence of the NPDFs is extracted in a next-to-leading order fit. We compare the nuclear corrections factors (F_{2}^{Fe} /F_{2}^{D} ) for this charged-lepton data with other results from the literature. In particular, we compare and contrast fits based upon the charged-lepton DIS data with those using neutrino-nucleon DIS data.
[Phys. Rev. D 80, 094004] Published Thu Nov 05, 2009

N_{f}^{3} g^{6} term in the pressure of hot QCD

A. Gynther, A. Kurkela, and A. Vuorinen — 2009-11-05T00:00:00-05:00

Author(s): A. Gynther, A. Kurkela, and A. Vuorinen
We determine the first independent part of the g^{6} coefficient in the weak coupling expansion of the QCD pressure at high temperatures, the one proportional to the maximal power of the number of quark flavors N_{f} . In addition to introducing and developing computational methods that can be used in evaluating other parts of the expansion, our calculation provides a result that becomes dominant in the limit of large N_{f} and a fixed effective coupling g_{eff}^{2} ≡g^{2} N_{f} /2.
[Phys. Rev. D 80, 096002] Published Thu Nov 05, 2009

Reconstructing the neutron-star equation of state from astrophysical measurements

Feryal Özel and Dimitrios Psaltis — 2009-11-05T00:00:00-05:00

Author(s): Feryal Özel and Dimitrios Psaltis
The properties of matter at ultrahigh densities, low temperatures, and with a significant asymmetry between protons and neutrons can be studied exclusively through astrophysical observations of neutron stars. We show that measurements of the masses and radii of neutron stars can lead to tight constraints on the pressure of matter at three fiducial densities, from 1.85 to 7.4 times the density of nuclear saturation, in a manner that is largely model independent and that captures the key characteristics of the equation of state. We demonstrate that observations with 10% uncertainties of at least three neutron stars can lead to measurements of the pressure at these fiducial densities with an accuracy of 0.11 dex or ≃30%. Observations of three neutron stars with 5% uncertainties are sufficient to distinguish at a better than 3σ confidence level between currently proposed equations of state. In the electromagnetic spectrum, such accurate measurements will become possible for weakly magnetic neutron stars during thermonuclear flashes and in quiescence with future missions such as the International X-ray Observatory.
[Phys. Rev. D 80, 103003] Published Thu Nov 05, 2009

Precise Electromagnetic Tests of Ab Initio Calculations of Light Nuclei: States in ^{10} Be

2009-11-04T00:00:00-05:00

Author(s): E. A. McCutchan, C. J. Lister, R. B. Wiringa, Steven C. Pieper, D. Seweryniak, J. P. Greene, M. P. Carpenter, C. J. Chiara, R. V. F. Janssens, T. L. Khoo, T. Lauritsen, I. Stefanescu, and S. Zhu
In order to test ab initio calculations of light nuclei, we have remeasured lifetimes in ^{10} Be using the Doppler shift attenuation method (DSAM) following the ^{7} Li( ^{7} Li,α) ^{10} Be reaction at 8 and 10 MeV. The new experiments significantly reduce systematic uncertainties in the DSAM technique. The J^{π} =2_{1}^{+} state at 3.37 MeV has τ=205±(5)_{stat} ±(7)_{sys} fs corresponding to a B(E2↓) of 9.2(3)e^{2} fm^{4} in broad agreement with many calculations. The J^{π} =2_{2}^{+} state at 5.96 MeV was found to have a B(E2↓) of 0.11(2)e^{2} fm^{4} and provides a more discriminating test of nuclear models. New Green’s function Monte Carlo calculations for these states and transitions with a number of Hamiltonians are also reported and compared to experiment.
[Phys. Rev. Lett. 103, 192501] Published Wed Nov 04, 2009

Three-Body Nonmesonic Weak Decay of the _{Λ} ^{12} C Hypernucleus

M. Kim et al. — 2009-10-30T00:00:00-04:00

Author(s): M. Kim et al.
We have measured the branching ratio of the three-body process in the nonmesonic weak decay of _{Λ} ^{12} C to be 0.29±0.13. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, Γ_{n} and Γ_{p} , along with Γ_{2N} , whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.
[Phys. Rev. Lett. 103, 182502] Published Fri Oct 30, 2009

From scale properties of physical amplitudes to a predictive formulation of the Nambu–Jona-Lasinio model

O. A. Battistel and G. Dallabona — 2009-10-30T00:00:00-04:00

Author(s): O. A. Battistel and G. Dallabona
The predictive power of the Nambu–Jona-Lasinio model is considered in the light of a novel strategy to handle the divergences typical of perturbative calculations. The referred calculational strategy eliminates unphysical dependencies on the arbitrary choices for the routing of internal momenta and symmetry violating terms. In the present work we extend a previous one on the same issue by including vector interactions and performing the discussion in a more general context: the role of scale arbitrariness for the consistency of the calculations is considered. We show that the imposition of arbitrary scale independence for the consistent regularized amplitudes lead to additional properties for the irreducible divergent objects. These properties allow us to parametrize the remaining freedom in terms of a unique constant where resides all the arbitrariness involved. By searching for the best value for the arbitrary parameter we find a critical condition for the existence of an acceptable physical value for the dynamically generated quark mass. Such critical condition fixes the remaining arbitrariness turning the Nambu–Jona-Lasinio into a predictive model in the sense that its phenomenological consequences do not depend on possible choices made in intermediary steps. Numerical results are obtained for physical quantities like the vector and axial-vector masses and their coupling constants as genuine predictions.
[Phys. Rev. D 80, 085028] Published Fri Oct 30, 2009

Ground-State and Single-Particle Energies of Nuclei around ^{16} O, ^{40} Ca, and ^{56} Ni from Realistic Nucleon-Nucleon Forces

S. Fujii, R. Okamoto, and K. Suzuki — 2009-10-28T00:00:00-04:00

Author(s): S. Fujii, R. Okamoto, and K. Suzuki
We perform ab initio calculations for nuclei around ^{16} O, ^{40} Ca, and ^{56} Ni using realistic nucleon-nucleon forces. In particular, ^{56} Ni is computed as the heaviest nucleus in this kind of ab initio calculation. Ground-state and single-particle energies including three-body-cluster effects are obtained within the framework of the unitary-model-operator approach. It is shown that the CD-Bonn nucleon-nucleon potential gives quite good results close to the experimental values for all nuclei in the present work.
[Phys. Rev. Lett. 103, 182501] Published Wed Oct 28, 2009

Phase diagram evolution at finite coupling in strong coupling lattice QCD

Kohtaroh Miura, Takashi Z. Nakano, Akira Ohnishi, and Noboru Kawamoto — 2009-10-28T00:00:00-04:00

Author(s): Kohtaroh Miura, Takashi Z. Nakano, Akira Ohnishi, and Noboru Kawamoto
We investigate the chiral phase transition in the strong coupling lattice QCD at finite temperature and density with finite coupling effects. We adopt one species of staggered fermion, and develop an analytic formulation based on strong coupling and cluster expansions. We derive the effective potential as a function of two order parameters, the chiral condensate σ and the quark number density ρ_{q} , in a self-consistent treatment of the next-to-leading order (NLO) effective action terms. NLO contributions lead to modifications of quark mass, chemical potential, and the quark wave function renormalization factor. While the ratio μ_{c} (T=0)/T_{c} (μ=0) is too small in the strong coupling limit, it is found to increase as β=2N_{c} /g^{2} increases. The critical point is found to move in the lower T direction as β increases. Since the vector interaction induced by ρ_{q} is shown to grow as β, the present trend is consistent with the results in Nambu-Jona-Lasinio models. The interplay between two order parameters leads to the existence of partially chiral restored matter, where effective chemical potential is automatically adjusted to the quark excitation energy.
[Phys. Rev. D 80, 074034] Published Wed Oct 28, 2009

Sivers asymmetries for inclusive pion and kaon production in deep-inelastic scattering

John Ellis, Dae Sung Hwang, and Aram Kotzinian — 2009-10-27T00:00:00-04:00

Author(s): John Ellis, Dae Sung Hwang, and Aram Kotzinian
We calculate the Sivers distribution functions induced by the final-state interaction due to one-gluon exchange in diquark models of a nucleon structure, treating the cases of scalar and axial-vector diquarks with both dipole and Gaussian form factors. We use these distribution functions to calculate the Sivers single-spin asymmetries for inclusive pion and kaon production in deep-inelastic scattering. We compare our calculations with the results of HERMES and COMPASS, finding good agreement for π^{+} production at HERMES, and qualitative agreement for π^{0} and K^{+} production. Our predictions for pion and kaon production at COMPASS could be probed with increased statistics. The successful comparison of our calculations with the HERMES data constitutes prima facie evidence that the quarks in the nucleon have some orbital angular momentum in the infinite-momentum frame.
[Phys. Rev. D 80, 074033] Published Tue Oct 27, 2009

Constraints on Neutron Star Crusts from Oscillations in Giant Flares

Andrew W. Steiner and Anna L. Watts — 2009-10-26T00:00:00-04:00

Author(s): Andrew W. Steiner and Anna L. Watts
We show that the fundamental seismic shear mode, observed as a quasiperiodic oscillation in giant flares emitted by highly magnetized neutron stars, is particularly sensitive to the nuclear physics of the crust. The identification of an oscillation at ≈30 Hz as the fundamental crustal shear mode requires a nuclear symmetry energy that depends very weakly on density near saturation. If the nuclear symmetry energy varies more strongly with density, then lower frequency oscillations, previously identified as torsional Alfvén modes of the fluid core, could instead be associated with the crust. If this is the case, then future observations of giant flares should detect oscillations at around 18 Hz. An accurate measurement of the neutron-skin thickness of lead will also constrain the frequencies predicted by the model.
[Phys. Rev. Lett. 103, 181101] Published Mon Oct 26, 2009

New Possible Quark-Hadron Mixed Phase in Protoneutron Stars

G. Pagliara, M. Hempel, and J. Schaffner-Bielich — 2009-10-23T00:00:00-04:00

Author(s): G. Pagliara, M. Hempel, and J. Schaffner-Bielich
The transition from hadronic to quark matter at high density is a strong first order phase transition if the surface tension between the two phases is large. While this implies a constant-pressure mixed phase in cold neutron star matter this is not the case for the hot and lepton rich matter of protoneutron stars. By considering the global conservation of lepton number during the stage of neutrino trapping, we show that a new mixed phase with non-constant pressure could appear in protoneutron stars and it would gradually disappear during deleptonization. We discuss the peculiar properties of this mixed phase and its possible significant effects on the evolution of protoneutron stars and their neutrino emission.
[Phys. Rev. Lett. 103, 171102] Published Fri Oct 23, 2009

Transport Coefficients of Hadronic Matter Near T_{c}

Jacquelyn Noronha-Hostler, Jorge Noronha, and Carsten Greiner — 2009-10-22T00:00:00-04:00

Author(s): Jacquelyn Noronha-Hostler, Jorge Noronha, and Carsten Greiner
A hadron resonance gas model including all known particles and resonances with masses m<2 GeV and an exponentially rising density of Hagedorn states for m>2 GeV is used to obtain an upper bound on the shear viscosity to entropy density ratio, η/s≈1/(4π), of hadronic matter near T_{c} . We found a large trace anomaly and small speed of sound near T_{c} , which agree well with recent lattice calculations. We comment on the bulk viscosity to entropy density ratio close to T_{c} .
[Phys. Rev. Lett. 103, 172302] Published Thu Oct 22, 2009

Inhomogeneous phases in the Nambu–Jona-Lasinio and quark-meson model

Dominik Nickel — 2009-10-22T00:00:00-04:00

Author(s): Dominik Nickel
We discuss inhomogeneous ground states of the Nambu–Jona-Lasinio and quark-meson model within mean-field approximation and their possible existence in the respective phase diagrams. For this purpose we focus on lower-dimensional modulations and point out that known solutions in the 2+1 and 1+1 dimensional (chiral) Gross-Neveu model can be lifted to the to the 3+1 dimensional Nambu–Jona-Lasinio model. This is worked out in detail for one-dimensional modulations and numerical results for the phase diagrams are presented. Focus is put on the critical point and on vanishing temperatures. As an interesting result the first order transition line in the phase diagram of homogeneous phases gets replaced by an inhomogeneous phase which is bordered by two second order transition lines.
[Phys. Rev. D 80, 074025] Published Thu Oct 22, 2009

Pion electroproduction amplitude relations in the 1/N_{c} expansion

Richard F. Lebed and Lang Yu — 2009-10-16T00:00:00-04:00

Author(s): Richard F. Lebed and Lang Yu
We derive expressions for pion electroproduction amplitudes in the 1/N_{c} expansion of QCD, and obtain from them linear relations between the electromagnetic multipole amplitudes that hold at all energies. The leading-order relations in 1/N_{c} compare favorably with available data (especially away from resonances), but the next-to-leading-order relations tend to provide only small or no improvement.
[Phys. Rev. D 80, 076006] Published Fri Oct 16, 2009

Reinvestigation of the Direct Two-Proton Decay of the Long-Lived Isomer ^{94} Ag ^{m} [0.4 s, 6.7 MeV, (21+)]

2009-10-09T00:00:00-04:00

Author(s): J. Cerny, D. M. Moltz, D. W. Lee, K. Peräjärvi, B. R. Barquest, L. E. Grossman, W. Jeong, and C. C. Jewett
An attempt to confirm the reported direct one-proton and two-proton decays of the (21+) isomer at 6.7(5) MeV in ^{94} Ag has been made. The 0.39(4) s half-life of the isomer permitted use of a helium-jet system to transport reaction products from the ^{40} Ca+ ^{nat} Ni reaction at 197 MeV to a low-background area; 24 gas ΔE-(Si)E detector telescopes were used to identify emitted protons down to 0.4 MeV. No evidence was obtained for two-proton radioactivity with a summed energy of 1.9(1) MeV and a branching ratio of 0.5(3)%. Two groups of one-proton radioactivity from this isomer had also been reported; our data confirm the lower energy group at 0.79(3) MeV with its branching ratio of 1.9(5)%.
[Phys. Rev. Lett. 103, 152502] Published Fri Oct 09, 2009

Local Monte Carlo Implementation of the Non-Abelian Landau-Pomeranchuk-Migdal Effect

Korinna Zapp, Johanna Stachel, and Urs Achim Wiedemann — 2009-10-08T00:00:00-04:00

Author(s): Korinna Zapp, Johanna Stachel, and Urs Achim Wiedemann
The non-Abelian Landau-Pomeranschuk-Migdal (LPM) effect arises from the quantum interference between spatially separated, inelastic radiation processes in matter. A consistent probabilistic implementation of this LPM effect is a prerequisite for extending the use of Monte Carlo (MC) event generators to the simulation of jetlike multiparticle final states in nuclear collisions. Here, we propose a local MC algorithm, which is based solely on relating the LPM effect to the probabilistic concept of formation time for virtual quanta. This accounts probabilistically for the characteristic L^{2} dependence of average parton energy loss and the characteristic 1/ sqrt[ω] modification of the non-Abelian LPM effect. Additional kinematic constraints are found to modify these L^{2} and ω dependencies characteristically in accordance with analytical estimates.
[Phys. Rev. Lett. 103, 152302] Published Thu Oct 08, 2009

Energy and Momentum Deposited into a QCD Medium by a Jet Shower

G.-Y. Qin, A. Majumder, H. Song, and U. Heinz — 2009-10-08T00:00:00-04:00

Author(s): G.-Y. Qin, A. Majumder, H. Song, and U. Heinz
For a hard parton moving through a dense QCD medium, we compute self-consistently the energy loss and the fraction deposited into the medium due to showering and rescattering of the shower, assuming weak coupling between probe and medium. The same transport coefficients thus determine both the energy loss and its deposition into the medium. This allows a parameter free calculation of the latter once the former are computed or measured. We compute them for a weakly interacting medium. Assuming a short thermalization time for the deposited energy, we determine the medium’s hydrodynamical response and obtain a conical pattern that is strongly enhanced by showering.
[Phys. Rev. Lett. 103, 152303] Published Thu Oct 08, 2009