Showing papers in "Journal of Physics G in 2005"

Can diffusive shock acceleration in supernova remnants account for high-energy galactic cosmic rays?

Abstract: Diffusive shock acceleration at the outer front of expanding supernova remnants has provided by far the most popular model for the origin of galactic cosmic rays, and has been the subject of intensive theoretical investigation. But several problems loomed at high energies?how to explain the smooth continuation of the cosmic-ray spectrum far beyond 1014 eV, the very low level of TeV gamma-ray emission from several supernova remnants, and the very low anisotropy of cosmic rays (seeming to conflict with the short trapping times needed to convert a E?2 source spectrum into the observed E?2.7 spectrum of cosmic rays). However, recent work on the cosmic ray spectrum (especially at KASCADE) strongly indicates that about half of the flux does turn down rather sharply near 3 ? 1015 V rigidity, with a distinct tail extending to just beyond 1017 V rigidity; whilst a plausible description (Bell and Lucek) of the level of self-generated magnetic fields at the shock fronts of young supernova remnants implies that many SNRs in varying environments might very well generate spectra extending smoothly to just this 'knee' position, and a portion of the exploding red supergiants could extend the spectrum approximately as needed. At low energies, recent progress in relating cosmic ray compositional details to modified shock structure also adds weight to the belief that the model is working on the right lines, converting energy into cosmic rays very efficiently where injection can occur. The low level of TeV gamma-ray flux from many young SNRs is a serious challenge, though it may relate to variations in particle injection efficiency with time. The clear detection of TeV gamma rays from SNRs has now just begun, and predictions of a characteristic curved particle spectrum give a target for new tests by TeV observations. However, the isotropy seriously challenges the assumed cosmic-ray trapping time and hence the shape of the spectrum of particles released from SNRs. There is otherwise enough convergence of model and observation to encourage belief that the outline of the model is right, but there remains the possibility that the spectral shape of particles actually released is not as previously predicted.

Constituent quark model study of the meson spectra

Abstract: The spectrum is studied in a generalized constituent quark model constrained in the study of the NN phenomenology and the baryon spectrum. An overall good fit to the available experimental data is obtained. A detailed analysis of all sectors from the light-pseudoscalar and vector mesons to bottomonium is performed paying special attention to the existence and nature of some non well-established states. These results should serve as a complementary tool in distinguishing conventional quark model mesons from glueballs, hybrids or multiquark states.

Optimum orientations of deformed nuclei for cold synthesis of superheavy elements and the role of higher multipole deformations

Abstract: For collisions between deformed and oriented nuclei, the fragmentation theory is extended for the generalized nuclear proximity potential, with deformations included up to the hexadecupole deformations. For co-planar nuclei, the orientations are shown to get optimized (uniquely fixed) by the signs of their quadrupole deformations alone, not affected by the signs of their hexadecupole deformations. The optimum orientations are obtained for both the 'hot compact', and 'cold elongated' configurations of any two colliding nuclei. The hexadecupole deformations are shown to help fusion (hot or cold), depending on the choice of the reaction partners. Calculations are made for the 208Pb- and 48Ca-induced reactions and the neighbouring deformed nuclei. The calculated fragmentation potentials for optimally oriented nuclei, compared with both nuclei taken spherical, show that the excitation energy of the potential energy minima is significantly lowered for cold (elongated) fusion of deformed nuclei, but it remains nearly the same for at least the asymmetric hot (compact) fusion reactions. A number of new minima (target–projectile combinations) arise due to the cold and nearly symmetric hot fusion of deformed, optimally oriented nuclei.

The standard model prediction of the muon anomalous magnetic moment

Abstract: This paper reviews and updates the standard model prediction of the muon g-2. QED, electroweak and hadronic contributions are presented, and open questions discussed. The theoretical prediction deviates from the present experimental value by 2–3 standard deviations, if e+e− annihilation data are used to evaluate the leading hadronic term.

Unified consideration of deep inelastic, quasi-fission and fusion fission phenomena

Abstract: A new approach is proposed for a unified description of strongly coupled deep inelastic (DI) scattering, fusion, fission and quasi-fission (QF) processes of heavy-ion collisions. The standard (most important) degrees of freedom of the nuclear system, unified driving potential, and a unified set of dynamic equations of motion are used in this approach. This makes it possible to perform a full (continuous) time analysis of the evolution of heavy nuclear systems, starting from the approaching stage, moving up to the formation of the compound nucleus and eventually emerging into two final fission fragments. The calculated mass, charge, energy and angular distributions of the reaction products agree well with the corresponding experimental data. It gives us hope to obtain rather accurate predictions for the probabilities of superheavy element formation in near-barrier fusion reactions.

Reconstruction of electrons with the Gaussian-sum filter in the CMS tracker at the LHC

Abstract: The bremsstrahlung energy loss distribution of electrons propagating in matter is highly non-Gaussian. Because the Kalman filter relies solely on Gaussian probability density functions, it is not necessarily the optimal reconstruction algorithm for electron tracks. A Gaussian-sum filter (GSF) algorithm for electron reconstruction in the CMS tracker has therefore been developed and implemented. The basic idea is to model the bremsstrahlung energy loss distribution by a Gaussian mixture rather than by a single Gaussian. It is shown that the GSF is able to improve the momentum resolution of electrons compared to the standard Kalman filter. The momentum resolution and the quality of the error estimate are studied both with a fast simulation, modelling the radiative energy loss in a simplified detector, and the full CMS tracker simulation.

Electroweak phase transition in an extension of the standard model with a real Higgs singlet

Abstract: The Higgs potential of the standard model with an additional real Higgs singlet is studied in order to examine if it may allow the strongly first-order electroweak phase transition. It is found that there are parameter values for which this model at the one-loop level with a finite-temperature effect may allow the desired phase transition. Those parameter values also predict that the masses of the neutral scalar Higgs bosons of the model are consistent with the present experimental bound, and that their production in e+e− collisions may be searched at the proposed ILC with in the near future.

Influence of strange quarks on the QCD phase diagram and chemical freeze-out

Abstract: We study the influence of strange quarks on the QCD phase diagram and the location of the chemical freeze-out. We compare the lattice results on the QCD phase diagram for two and three flavours with the hadron resonance gas model (HRGM) calculations. Taking into account the truncations in the Taylor- expansion of the expression of energy densityas done in lattice calculations, we find that HRGM under the condition of constantdescribes very well the lattice QCD phase diagram. We study the chemical freeze-out parameters according to the entropy density s .T hes value has been taken from the lattice QCD calculations for two and three flavours. We find that the condition s/T 3 = 5 is excellent in reproducing the experimentally estimated parameters of the chemical freeze-out for two flavours. For three flavours the condition is s/T 3 = 7. (Some figures in this article are in colour only in the electronic version)

Probing the density dependence of the symmetry potential in intermediate-energy heavy ion collisions

Abstract: Based on the ultrarelativistic quantum molecular dynamics model, the effects of the density-dependent symmetry potential for baryons and of the Coulomb potential for produced mesons are investigated for neutron-rich heavy ion collisions at intermediate energies. The calculated results of the Δ−/Δ++ and π−/π+ production ratios show a clear beam-energy dependence on the density-dependent symmetry potential, which is stronger for the π−/π+ ratio close to the pion production threshold. The Coulomb potential of the mesons changes the transverse momentum distribution of the π−/π+ ratio significantly, though it alters only slightly the π− and π+ total yields. The π− yields, especially at midrapidity or at low transverse momenta and the π−/π+ ratios at low transverse momenta are shown to be sensitive probes of the density-dependent symmetry potential in dense nuclear matter. The effect of the density-dependent symmetry potential on the production of both K0 and K+ mesons is also investigated.

Photons in gapless colour-flavour-locked quark matter

Abstract: We calculate the Debye and Meissner masses of a gauge boson in a material consisting of two species of massless fermions that form a condensate of Cooper pairs. We perform the calculation as a function of temperature, for the cases of neutral Cooper pairs and charged Cooper pairs, and for a range of parameters including gapped quasiparticles, and ungapped quasiparticles with both quadratic and linear dispersion relations at low energy. Our results are relevant to the behaviour of photons and gluons in the gapless colour–flavour-locked phase of quark matter. We find that the photon's Meissner mass vanishes, and the Debye mass shows a non-monotonic temperature dependence, and at temperatures of order the pairing gap it drops to a minimum value of order times the quark chemical potential. We confirm previous claims that at zero temperature an imaginary Meissner mass can arise from a charged gapless condensate, and we find that at finite temperature this can also occur for a gapped condensate.

Infrared enhanced analytic coupling and chiral symmetry breaking in QCD

Abstract: We study the impact on chiral symmetry breaking of a recently developed model for the QCD analytic invariant charge. This charge contains no adjustable parameters, other than the QCD mass scale Λ, and embodies asymptotic freedom and infrared enhancement into a single expression. Its incorporation into the standard form of the quark gap equation gives rise to solutions for the dynamically generated mass that display a singular confining behaviour at the origin. Using the Pagels–Stokar method we relate the obtained solutions to the pion decay constant fπ, and estimate the scale parameter Λ, in the presence of four active quarks, to be about 880 MeV.

Development of a laser ion source at IGISOL

Abstract: FURIOS, the Fast Universal laser IOn Source, is under development at the IGISOL (Ion Guide Isotope Separator On-Line) mass separator facility in Jyvaskyla, Finland. This new laser ion source will combine a state-of-the-art solid state laser system together with a dye laser system, for the selective and efficient production of exotic radioactive species without compromising the universality and fast release inherent in the IGISOL system. The motivation for, and development of, this ion source is discussed in relation to the programme of research ongoing at this mass separator facility.

At what particle energy do extragalactic cosmic rays start to predominate

Abstract: We have previously argued (e.g. Szabelski et al 2002 Astropart. Phys. 17 125) that the well-known 'ankle' in the cosmic ray energy spectrum, at log E (eV) ~ 18.7–19.0, marks the transition from mainly galactic sources at lower energies to mainly extragalactic above. Recently, however, there have been claims for lower transitional energies, specifically from log E (eV) ~ 17.0 (Thompson et al 2004 Proc. Catania Cosmic Ray Conf.) via 17.2–17.8 (Berezinsky et al 2004 Astropart. Phys. 21 617) to 18.0 (Hillas 2004 Proc. Leeds Cosmic Ray Conf.). In our model the ankle arises naturally from the sum of simple power law-spectra with slopes differing by Δγ ~ 1.8; from differential slope γ = −3.8 for galactic particles (near log E = 19) to γ ~ −2.0 for extragalactic sources. In the other models, on the other hand, the ankle is intrinsic to the extragalactic component alone, and arises from the shape of the rate of energy loss versus energy for the (assumed) protons interacting with the cosmic microwave background (CMB). Our detailed analysis of the world's data on the ultra-high energy spectrum shows that taken together, or separately, the resulting mean sharpness of the ankle (second derivative of the log(intensity × E3) with respect to log E) is consistent with our 'mixed' model. For explanation in terms of extragalactic particles alone, however, the ankle will be at the wrong energy—for reasonable production models and of insufficient magnitude if, as seems likely, there is still a significant fraction of heavy nuclei at the ankle energy.

Transport theories for heavy-ion collisions in the 1 A GeV regime

Abstract: We compare multiplicities as well as rapidity and transverse momentum distributions of protons, pions and kaons calculated within presently available transport approaches for heavy-ion collisions around 1 A GeV. For this purpose, three reactions have been selected: Au+Au at 1 and 1.48 A GeV and Ni+Ni at 1.93 A GeV.

Baryon masses and nucleon sigma terms in manifestly Lorentz-invariant baryon chiral perturbation theory

Abstract: We discuss the masses of the ground state baryon octet and the nucleon sigma terms in the framework of manifestly Lorentz-invariant baryon chiral perturbation theory. In order to obtain a consistent power counting for renormalized diagrams the extended on-mass-shell renormalization scheme is applied.

Softly broken lepton number Le - Lμ - Lτ with non-maximal solar neutrino mixing

Abstract: We consider the most general neutrino mass matrix which leads to �13 = 0, and present the formulae needed for obtaining the neutrino masses and mixing parameters in that case. We apply this formalism to a model based on the lepton number ¯ L = Le − Lµ − Land on the seesaw mechanism. This model needs only one Higgs doublet and has only two right-handed neutrino singlets. Soft ¯ L breaking is accomplished by the Majorana mass terms of the right-handed neutrinos; if the ¯ L-conserving and ¯ L-breaking mass terms are of the same order of magnitude, then it is possible to obtain a consistent ¯ L model with a solar mixing angle significantly smaller than 45 ◦ . We show that the predictions of this model, m3 = 0 and �13 = 0, are invariant under the renormalization-group running of the neutrino mass matrix.

Precision experiments with relativistic exotic nuclei at GSI

Abstract: Exotic nuclei generated via projectile fragmentation and fission are characterized by a large phase-space population. Thus precision experiments based on kinematical observables are difficult and require special methods. The experiments described in this contribution are based on special ion-optical spectrometer modes or on phase-space reduction via cooling of stored ions. The studies are performed with the projectile fragment separator FRS and the storage-cooler ring ESR at GSI.

Hydrodynamics at RHIC: how well does it work, where and how does it break down?

Abstract: I review the successes and limitations of the ideal fluid dynamic model in describing hadron emission spectra from Au+Au collisions at the relativistic heavy ion collider (RHIC).

TIGRESS: TRIUMF-ISAC gamma-ray escape-suppressed spectrometer

Abstract: The TRIUMF-ISAC gamma-ray escape-suppressed spectrometer (TIGRESS) is a new γ-ray detector array being developed for use at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. TIGRESS will comprise 12 32-fold segmented clover-type HPGe detectors coupled with 20-fold segmented modular Compton suppression shields and custom digital signal processing electronics. This paper provides an overview of the TIGRESS project and progress in its development to date.

Fusion, break-up and elastic scattering of weakly bound nuclei

Abstract: We describe the behaviour of the fusion, break-up, reaction cross sections and elastic scattering of weakly bound nuclei, at near and above barrier energies. The total fusion cross sections are not affected by the break-up process at this energy regime. The elastic break-up cross sections are important at energies close and above the Coulomb barrier, even in systems with light targets, and increase the reaction cross sections. We also show that the break-up process at near and sub-barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and gives rise to a new type of anomaly, named by us as break-up threshold anomaly.

Electron screening in d(d, p)t for deuterated metals : temperature effects

Abstract: The electron screening in the d(d, p)t reaction has been studied for the deuterated metal Pt at a sample temperature T = 20 °C–340 °C and for Co at T = 20 °C and 200 °C. The enhanced electron screening decreases with increasing temperature, where the data agree with the plasma model of Debye applied to the quasi-free metallic electrons. The data represent the first observation of a temperature dependence of a nuclear cross section. We also measured the screening effect for the deuterated metal Ti (an element of group 4 of the periodic table) at T = −10 °C–200 °C: above 50 °C, the hydrogen solubility dropped to values far below 1 and a large screening effect became observable. Similarly, all metals of groups 3 and 4 and the lanthanides showed a solubility of a few per cent at T = 200 °C (compared to T = 20 °C) and a large screening also became observable. Within the Debye model, the deduced number of valence electrons per metallic atom agrees with the corresponding number from the Hall coefficient, for all metals investigated.

On a model with two zeros in the neutrino mass matrix

Abstract: We consider a Majorana neutrino mass matrix with , in the basis where the charged-lepton mass matrix is diagonal. We show that this pattern for the lepton mass matrices can be enforced by extending the standard model with three scalar SU(2) triplets and by using a horizontal symmetry group . The type-II seesaw mechanism leads to very small vacuum expectation values for the triplets, thus explaining the smallness of the neutrino masses; at the same time that mechanism renders the physical scalars originating in the triplets very heavy. We show that the conditions allow both for a normal neutrino mass spectrum and for an inverted one. In the first case, the neutrino masses must be larger than 0.1 eV and the atmospheric mixing angle θ23 must be practically equal to 45°. In the second case, the product sin θ13|tan 2θ23| must be of order one or larger, thus correlating the large or maximal atmospheric neutrino mixing with the smallness of the mixing angle θ13.

The quark–gluon plasma liquid

Abstract: The estimate of the Coulomb coupling parameter Γ contains an error. In QCD, where the Heavyside--Lorentz units are used, the Coulomb potential has to be divided by a factor 4π compared to CGS units [1]. Hence the correct Coulomb coupling parameter reads Γ = Cg2/(4πdT). Taking into account the magnetic interaction which is of the same magnitude as the electric interaction in an ultrarelativistic plasma, the coupling parameter is reduced by about a factor of 6. Consequently we obtain Γ = 1.5–5 in a QGP at T 200 MeV. Such a value still indicates that the QGP is in the liquid phase. However, the phase transition to the gas phase, assumed to happen at Γc 1, takes place now at a few times of the transition temperature from the hadronic phase to the QGP. Hence it might be possible that the gas–liquid transition occurs during the expansion of the fireball in nucleus–nucleus collisions at LHC [2]. The phase transition from the QGP liquid to the QGP gas expands the phase diagram of strongly interacting matter to high temperatures. This phase transition ends at a critical point, above which a supercritical fluid exists. The estimate of the cross section enhancement is also affected by the above error. The Coulomb radius should also be divided by a factor of 6, leading to ρ = 0.2–1 fm. Then β = ρ/λD=1–5 which gives a maximum impact parameter of (1.4–3.3)λD, from which, using equation (2), a cross section enhancement of a factor of 2 to 9 results. Acknowledgments The author would like to thank C Greiner and A Peshier for pointing out the error in the original article. References [1] Jackson J D 1975 Classical Electrodynamics (New York: Wiley) [2] Peshier A 2005 private communication

Similarity of extensive air showers with respect to the shower age

Abstract: Using CORSIKA simulations of the highest energy extensive air showers we show that all showers are similar when described by the shower age parameter: the angular and energy spectra of electrons at a given level in the atmosphere depend only on the shower age at this level. Moreover, electrons with a given energy have the same angular distributions at any level (age) of the shower. We have calculated these distributions and found analytical functions describing them quite well. The total number of particles can also be described in a simple way as a function of age by two halves of a Gaussian function with the widths, however, fluctuating from one shower to another. The description of large showers in terms of age (instead of depth in the atmosphere) is very useful in interpreting data from experiments observing fluorescence light, with admixture of Cherenkov, induced by the showers in the air.

Alpha decay half-life of bismuth isotopes

Abstract: The observed alpha decay half-life values of favoured alpha transitions of l = 5 in bismuth isotopes have been analysed in the framework of a model based on quantum mechanical tunnelling through a potential barrier where the centrifugal and overlapping effects are taken into account. In particular, the very recently measured alpha decay half-life value of (1.9 ± 0.2) × 1019 y for the unique naturally occurring 209Bi isotope has been reproduced by the present approach as (1.0 ± 0.3) × 1019 y. Also, the partial alpha decay half-lives for a number of unmeasured alpha transitions of l = 5 in bismuth isotopes are predicted by the model, thus making it possible to demonstrate the influence of the 126 neutron shell closure on the alpha decay half-life. The present approach is shown to be successfully applicable to other isotopic sequences of alpha-emitter nuclides.

Phenomenological constraints on extra-dimensional scalars

Abstract: We examine whether the ATLAS detector has sensitivity to extra-dimensional scalars (as opposed to components of higher-dimensional tensors which look like 4D scalars), in scenarios having the extra-dimensional Planck scale in the TeV range and n ≥ 2 non-warped extra dimensions. Such scalars appear as partners of the graviton in virtually all higher dimensional supersymmetric theories. Using the scalar's lowest dimensional effective couplings to quarks and gluons, we compute the rate for the production of a hard jet together with missing energy. We find a non-trivial range of graviscalar couplings to which ATLAS could be sensitive, with experiments being more sensitive to couplings to gluons than to quarks. Graviscalar emission increases the missing-energy signal by adding to graviton production, and so complicates the inference of the extra-dimensional Planck scale from an observed rate. Because graviscalar differential cross-sections resemble those for gravitons, it is unlikely that these can be experimentally distinguished from one another should a missing-energy signal be observed.

Neutrino-nucleus interactions as a probe to constrain double-beta decay predictions

Abstract: We propose to use charged-current neutrino–nucleus interactions as a probe of the many virtual transitions involved in neutrinoless double-beta decay. By performing ν and interaction studies on the initial and final nucleus, respectively, one can get information on the two branches involved in the double-beta decay process. The measurement of such reactions could help to further constrain double-beta decay predictions on the half-lives. We discuss that such studies can be performed either with conventional beams or with low-energy beta-beams. The search for neutrinoless double-beta decay is a crucial issue for learning about neutrino properties, in particular about the Dirac or Majorana nature of neutrinos, important for various domains of physics.

Evidence for chiral structures in 130Cs

Abstract: Two low lying positive-parity bands in 130Cs have been examined for chiral signatures. Small energy differences between the two bands, which have been previously observed, have been confirmed and the bands, as well as the number of transitions within and between the bands, extended. The intraband B(M1)/B(E2) ratios and B(M1)intraband/B(M1)interband ratios and the energy staggering parameter, S(I), have been deduced for these partner bands. The results are found to be consistent with a chiral interpretation for the two structures. Core–quasiparticle coupling model calculations have been performed to study 130Cs assuming a triaxial core. The experimental level energies and electromagnetic properties of the bands, resulting from the configuration, are reasonably well reproduced by the model, providing further evidence in support of the chiral interpretation of the two structures.

Charm elliptic flow from quark coalescence dynamics

Abstract: From covariant transport theory, a significant ∼10% light quark elliptic flow at RHIC implies an elliptic flow of similar magnitude for charm quarks, at moderately large p T >2.5-3 GeV. At lower transverse momenta, charm quark elliptic flow reduces progressively, reminiscent of the mass ordering pattern in ideal hydrodynamics. From the quark flows we predict the elliptic flow of D mesons at RHIC via quark coalescence. The large parton opacities needed to generate the light quark flow also lead to substantial ∼40-50% secondary charm production.

The influence of the strength of hyperon-hyperon interactions on neutron star properties

Abstract: An equation of state of neutron star matter with strange baryons has been obtained. The effects of the strength of hyperon–hyperon interactions on the equations of state constructed for the chosen parameter sets have been analysed. Numerous neutron star models show that the appearance of hyperons is connected with the increasing density in neutron star interiors. The performed calculations have indicated that a change of the hyperon–hyperon coupling constants affects the chemical composition of a neutron star. The obtained numerical hyperon star models exclude a large population of strange baryons in the star interior.