Showing papers in "Journal of Physics G in 2008"

A precision constraint on multi-Higgs-doublet models

Abstract: We derive a general expression for Δρ (or, equivalently, for the oblique parameter T) in the SU(2) × U(1) electroweak model with an arbitrary number of scalar SU(2) doublets, with hypercharge ±1/2, and an arbitrary number of scalar SU(2) singlets. The experimental bound on Δρ constitutes a strong constraint on the masses and mixings of the scalar particles in that model.

Heavy-ion collisions at the LHC-Last call for predictions

Abstract: This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.

Top-quark physics at the LHC

Abstract: The physics perspectives of the production and decay of single top quarks and top-quark pairs at the CERN Large Hadron Collider (LHC) are reviewed from a phenomenological point of view.

A high-precision variational approach to three- and four-nucleon bound and zero-energy scattering states

Abstract: The hyperspherical harmonic (HH) method has been widely applied in recent times to the study of the bound states, using the Rayleigh–Ritz variational principle, and of low-energy scattering processes, using the Kohn variational principle, of A = 3 and 4 nuclear systems. When the wavefunction of the system is expanded over a sufficiently large set of HH basis functions, containing or not correlation factors, quite accurate results can be obtained for the observables of interest. In this review, the main aspects of the method are discussed together with its application to the A = 3 and 4 nuclear bound and zero-energy scattering states. Results for a variety of nucleon–nucleon (NN) and three-nucleon (3N) local or non-local interactions are reported. In particular, NN and 3N interactions derived in the framework of the chiral effective field theory and NN potentials from which the high-momentum components have been removed, as recently presented in the literature, are considered for the first time within the context of the HH method. The purpose of this review is twofold. The first is to present a complete description of the HH method for bound and scattering states, also including detailed formulae for the computation of the matrix elements of the NN and 3N interactions. The second is to report accurate results for bound and zero-energy scattering states obtained with the most commonly used interaction models. These results can be useful for comparison with those obtained by other techniques and are a significant test for different future approaches to such problems.

Low-scale B?L extension of the standard model

Abstract: The fact that neutrinos are massive indicates that the standard model (SM) requires extension. We propose a low-energy (TeV) B–L extension of the SM, which is based on the gauge group . We show that this model provides a natural explanation for the presence of three right-handed neutrinos in addition to an extra-gauge boson and a new scalar Higgs. Therefore, it can lead to very interesting phenomenological implications different from the SM results which can be tested at the LHC. Also we analyze the muon anomalous magnetic moment in this class of models. We show that one loop with exchange Z' may give dominant new contribution ~few × 10−11.

Tables of Hyperonic Matter Equation of State for Core-Collapse Supernovae

Abstract: We present sets of equation of state (EOS) of nuclear matter including hyperons using an SUf(3) extended relativistic mean field (RMF) model with a wide coverage of density, temperature and charge fraction for numerical simulations of core-collapse supernovae. Coupling constants of ? and ? hyperons with the ? meson are determined to fit the hyperon potential depths in nuclear matter, U?(?0) +30 MeV and U?(?0) ?15 MeV, which are suggested from recent analyses of hyperon production reactions. At low densities, the EOS of uniform matter is connected with the EOS by Shen et al, in which the formation of finite nuclei is included in the Thomas?Fermi approximation. In the present EOS, the maximum mass of neutron stars decreases from 2.17 M? (Ne?) to 1.63 M? (NYe?) when hyperons are included. In a spherical, adiabatic collapse of a 15 M? star by the hydrodynamics without neutrino transfer, hyperon effects are found to be small, since the temperature and density do not reach the region of hyperon mixture, where the hyperon fraction is above 1 % (T > 40 MeV or ?B > 0.4 fm?3).

Stability and Causality in relativistic dissipative hydrodynamics

Abstract: The stability and causality of the Landau–Lifshitz theory and the Israel–Stewart-type causal dissipative hydrodynamics are discussed. We show that the problems of acausality and instability are correlated in relativistic dissipative hydrodynamics and instability is induced by acausality. We further discuss the stability of the scaling solution. The scaling solution of the causal dissipative hydrodynamics can be unstable against inhomogeneous perturbations.

A semi-empirical model for alpha and cluster radioactivity

Abstract: A new semi-empirical model is proposed for determining the half lives of radioactive nuclei exhibiting cluster radioactivity. The parameters of the formula are obtained by making a least-square fit to the available experimental cluster decay data. The calculated half-life time for cluster decay is compared with the corresponding experimental values and with the values proposed by earlier scaling laws and with those predicted by the Coulomb and proximity potential model. The semi-empirical formula is applied to alpha decay of parents with Z = 85–102 and is compared with experimental data and with other semi-empirical formula predictions. The predicted alpha and cluster decay half-life time values are found to be in good agreement with the experimental data. The calculated alpha decay half-life time is also compared with the values predicted by Viola–Seaborg–Sobiczewski and Horoi systematics.

Masses and magnetic moments of heavy flavour baryons in the hyper central model

Abstract: Heavy flavour baryons containing one or two charm (beauty) quarks with light flavour combinations are studied using the hyper central description of the three-body system. The confinement potential is assumed as hyper central Coulomb plus power potential with a power index p. The ground state ( and ) masses of heavy flavour baryons are computed for different power indices, p starting from 0.5 to 2.0. The predicted masses are found to attain a saturated value with respect to the variation in p beyond the power index p > 1.0. Using the spin-flavour structure of the constituting quarks and by defining the effective mass of the confined quarks within the baryons, the magnetic moments are computed with no additional free parameters. The masses and magnetic moments of the single heavy and double heavy flavour baryons are found to be in accordance with other model predictions.

Ab initio symplectic no-core shell model

Abstract: The no-core shell model (NCSM) is a prominent ab initio method that yields a good description of the low-lying states in few-nucleon systems as well as in more complex p-shell nuclei. Nevertheless, its applicability is limited by the rapid growth of the many-body basis with larger model spaces and increasing number of nucleons. The symplectic no-core shell model (Sp-NCSM) aspires to extend the scope of the NCSM beyond the p-shell region by augmenting the conventional spherical harmonic oscillator basis with the physically relevant symplectic symmetry-adapted configurations of the symplectic shell model that describe naturally the monopole?quadrupole vibrational and rotational modes, and also partially incorporate ?-cluster correlations. In this review, the models underpinning the Sp-NCSM approach, namely, the NCSM, the Elliott SU(3) model and the symplectic shell model, are discussed. Following this, a prescription for constructing translationally invariant symplectic configurations in the spherical harmonic oscillator basis is given. This prescription is utilized to unveil the extent to which symplectic configurations enter into low-lying states in 12C and 16O nuclei calculated within the framework of the NCSM with the JISP16 realistic nucleon?nucleon interaction. The outcomes of this proof-of-principle study are presented in detail.

Charged current cross section for massive cosmological neutrinos impinging on radioactive nuclei

Abstract: We discuss the cross section formula for both massless and massive neutrinos on stable and radioactive nuclei. The latter could be of interest for the detection of cosmological neutrinos whose observation is one of the main challenges of modern cosmology. We analyse the signal-to-background ratio as a function of the ratio mν/Δ, i.e. the neutrino mass over the detector resolution and show that an energy resolution Δ ≤ 0.5 eV would be required for sub-eV neutrino masses, independently of the gravitational neutrino clustering. Finally, we mention the non-resonant character of neutrino capture on radioactive nuclei.

How resonances can synchronize with thresholds

Abstract: The mechanism by which a threshold may capture a resonance is examined. It involves a threshold cusp interfering constructively with either or both (i) a resonance produced via confinement, (ii) attractive t- and u-channel exchanges. The f0(980), X(3872) and Z(4430) are studied in detail. The f0(980) provides a valuable model of the locking mechanism. The X(3872) is too narrow to be fitted by a cusp and requires either a resonance or virtual state. The Z(4430) can be fitted as a resonance but also can be fitted successfully by a cusp with no nearby resonant pole.

Target mass corrections

Abstract: With recent advances in the precision of inclusive lepton–nuclear scattering experiments, it has become apparent that comparable improvements are needed in the accuracy of the theoretical analysis tools. In particular, when extracting parton distribution functions in the large-x region, it is crucial to correct the data for effects associated with the nonzero mass of the target. We present here a comprehensive review of these target mass corrections (TMC) to structure functions data, summarizing the relevant formulas for TMCs in electromagnetic and weak processes. We include a full analysis of both hadronic and partonic masses, and trace how these effects appear in the operator product expansion and the factorized parton model formalism, as well as their limitations when applied to data in the x → 1 limit. We evaluate the numerical effects of TMCs on various structure functions, and compare fits to data with and without these corrections.

Overconstrained estimates of neutrinoless double beta decay within the QRPA

Abstract: Estimates of nuclear matrix elements for neutrinoless double beta decay (0ν2β) based on the quasiparticle random phase approximations (QRPA) are affected by theoretical uncertainties, which can be substantially reduced by fixing the unknown strength parameter gpp of the residual particle–particle interaction through one experimental constraint—most notably through the two-neutrino double beta decay (2ν2β) lifetime. However, it has been noted that the gpp adjustment via 2ν2β data may bring QRPA models in disagreement with independent data on electron capture (EC) and single beta decay (β−) lifetimes. Actually, in two nuclei of interest for 0ν2β decay (100Mo and 116Cd), for which all such data are available, we show that the disagreement vanishes, provided that the axial vector coupling gA is treated as a free parameter, with allowance for gA 0) by the combination of all data. We discuss quantitatively, in each of the two nuclei, these phenomenological constraints and their consequences for QRPA estimates of the 0ν2β matrix elements and their uncertainties.

Anomalous centrality variation of minijet angular correlations in Au–Au collisions at 62 and 200 GeV from STAR

Abstract: We have measured 2D autocorrelations for all charged hadrons in STAR with p t > 0.15 GeV/c and |η| < 1 from Au+Au collisions at 62 and 200 GeV. The correlation structure is dominated by a peak centered at zero relative opening angles on η and Φ which we hypothesize is caused by minimum-bias jets (minijets). We observe a large excess of minijet correlations in more-central Au-Au collisions relative to binary-collision scaling (more correlated pairs than expected from surface emission or even volume emission). We also observe a sudden increase of the minijet peak amplitude and η width relative to binary-collision scaling of scattered partons which occurs at an energy-dependent centrality point. There is a possible scaling of the transition point with transverse particle density. The large minijet correlations bring into question the degree of thermalization in RHIC collisions.

An all-particle primary energy spectrum in the 3–200 PeV energy range

Abstract: We present an all-particle primary cosmic-ray energy spectrum in the 3 × 10 6 – 2 × 10 8 GeV energy range obtained by a multi-parametric event-by-event evaluation of the primary energy. The results are obtained on the basis of an expanded EAS data set detected at mountain level (700 g cm −2 )b y the GAMMA experiment. The energy evaluation method has been developed using the EAS simulation with the SIBYLL interaction model taking into account the response of GAMMA detectors and reconstruction uncertainties of EAS parameters. Nearly unbiased (<5%) energy estimations regardless of a primary nuclear mass with an accuracy of about 15–10% in the 3 × 10 6 –2 × 10 8 GeV energy range respectively are attained. An irregularity (‘bump’) in the spectrum is observed at primary energies of ∼7.4 × 10 7 GeV. This bump exceeds a smooth power-law fit to the data by about 4 standard deviations. By not rejecting the stochastic nature of the bump completely, we examined the systematic uncertainties of our methods and conclude that they cannot be responsible for the observed feature.

Strangeness production from SPS to LHC

Abstract: Global strangeness production in relativistic heavy ion collisions at SPS and RHIC is reviewed. Special emphasis is put on the comparison with the statistical model and the canonical suppression mechanism. It is shown that recent RHIC data on strange particle production as a function of centrality can be explained by a superposition of a fully equilibrated hadron gas and particle emission from single independent nucleon–nucleon collisions in the outer corona.

Dissipative effects from transport and viscous hydrodynamics

Abstract: We compare 2 → 2 covariant transport theory and causal Israel–Stewart hydrodynamics in a (2 + 1)-dimensional longitudinally boost-invariant geometry with RHIC-like initial conditions and a conformal e = 3p equation of state. The pressure evolution in the center of the collision zone and the final differential elliptic flow v2(pT) from the two theories agree remarkably well for a small shear viscosity to entropy density ratio η/s ≈ 1/(4π), and also for a large cross section σ ≈ 50 mb. A key to this agreement is keeping all terms in the Israel–Stewart equations of motion. Our results indicate promising prospects for the applicability of Israel–Stewart dissipative hydrodynamics at RHIC, provided the shear viscosity of hot and dense quark–gluon matter is indeed very small for the relevant temperatures T ~ 200–500 MeV.

Stellar matter with a strong magnetic field within density-dependent relativistic models

Abstract: The effect of strong magnetic fields on the equation of state (EoS) for compact stars described with density-dependent relativistic hadronic models is studied. A comparison with other mean-field relativistic models is done. It is shown that the largest differences between models occur for low densities, and that the magnetic field affects the crust properties of a star, namely its extension.

Trojan Horse as an indirect technique in nuclear astrophysics

Abstract: The Trojan Horse method is a powerful indirect technique that provides information to determine astrophysical factors for binary rearrangement processes x + A → b + B at astrophysically relevant energies by measuring the cross section for the Trojan Horse reaction a + A → y + b + B in quasi-free kinematics. We present the theory of the Trojan Horse method for resonant binary subreactions based on the half-off-energy-shell R matrix approach which takes into account the off-energy-shell effects and initial and final state interactions.

Contrasting solar and reactor neutrinos with a non-zero value of θ13

Abstract: When solar neutrino and KamLAND data are analyzed separately one finds that, even though allowed regions of neutrino parameters overlap, the values of δm2 and the mixing angle θ12 at the χ2 minima are different. We show that a non-zero, but small value of the angle θ13 can account for this behavior. From the joint analysis of solar neutrino and KamLAND data we find the best fit value of sin22θ13 = 0.01−0.01+0.09.

Decays of J/ psi and psi-prime into vector and pseudoscalar meson and the pseudoscalar glueball-q anti-q mixing.

Abstract: We introduce a parametrization scheme for $J/\psi(\psi^\prime)\to VP$ where the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation (DOZI) can be parametrized by certain parameters with explicit physical interpretations. This scheme can be used to clarify the glueball-$q\bar{q}$ mixing within the pseudoscalar mesons in a quark-flavor basis. We also include the contributions from the electromagnetic (EM) decays of $J/\psi$ and $\psi^\prime$ via $J/\psi(\psi^\prime)\to \gamma^*\to VP$. Via study of the isospin violated channels, such as $J/\psi(\psi^\prime)\to \rho\eta$, $\rho\eta^\prime$, $\omega\pi^0$, and $\phi\pi^0$, reasonable constraints on the EM decay contributions are obtained. With the up-to-date experimental data for $J/\psi(\psi^\prime)\to VP$, $J/\psi(\psi^\prime)\to \gamma P$, and $P\to \gamma\gamma$, etc, we arrive at a consistent description of those processes with a minimal set of parameters. As a consequence, we find that there exists an overall suppression of the $\psi^\prime\to 3g$ form factors, which sheds some light on the long-standing $\rho\pi$ puzzle. By determining the glueball components inside the pseudoscalar $\eta$ and $\eta^\prime$ in three different glueball-$q\bar{q}$ mixing schemes, we deduce that the lowest pseudoscalar glueball, if exists, has rather small $q\bar{q}$ component. This makes the $\eta(1405)$ a preferable candidate for $0^{-+}$ glueball.

A Uniform description of the states recently observed at B-factories

Abstract: The newly found states Y(4260), Y(4361), Y(4664) and Z±(4430) stir a broad interest in the study of spectroscopy in a typical charmonium scale. The Y(4260) which was observed earlier has been interpreted as hybrid, molecular state and baryonium, etc. In this paper we show for the first time that these new structures, which are hard to be interpreted as charmonium states, can be systematically embedded into an extended baryonium picture. According to this assignment, the, so far, known characters of these states are understandable. And, in the same framework, we make some predictions for measurement in future experiments.

New way for the production of heavy neutron-rich nuclei

Abstract: A new way is found to discover and examine unknown neutron-rich heavy nuclei at the ‘north-east’ part of the nuclear map. This ‘blank spot’ of the nuclear map can be reached neither in fusion–fission reactions nor in fragmentation processes widely used nowadays for the production of new nuclei. The present limits of the upper part of the nuclear map are very close to stability while the unexplored area of heavy neutron-rich nuclides along the neutron closed shell N = 126 (to the east of the stability line) is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. A novel idea is proposed for the production of these nuclei via low-energy multi-nucleon transfer reactions. The estimated yields of neutron-rich nuclei are found to be rather high in such reactions and several tens of new nuclides can be produced, for example, in the near-barrier collision of 136 Xe with 208 Pb. This finding may spur new studies at heavy-ion facilities and should have significant impact on future experiments. Communicated by Professor J Aichelin

Review of the Safety of LHC Collisions

Abstract: The safety of collisions at the Large Hadron Collider (LHC) was studied in 2003 by the LHC Safety Study Group, who concluded that they presented no danger. Here we review their 2003 analysis in light of additional experimental results and theoretical understanding, which enable us to confirm, update and extend the conclusions of the LHC Safety Study Group. The LHC reproduces in the laboratory, under controlled conditions, collisions at centre-of-mass energies, less than those reached in the atmosphere by some of the cosmic rays that have been bombarding the Earth for billions of years. We recall the rates for the collisions of cosmic rays with the Earth, Sun, neutron stars, white dwarfs and other astronomical bodies at energies higher than the LHC. The stability of astronomical bodies indicates that such collisions cannot be dangerous. Specifically, we study the possible production at the LHC of hypothetical objects such as vacuum bubbles, magnetic monopoles, microscopic black holes and strangelets, and find no associated risks. Any microscopic black holes produced at the LHC are expected to decay by Hawking radiation before they reach the detector walls. If some microscopic black holes were stable, those produced by cosmic rays would be stopped inside the Earth or other astronomical bodies. The stability of astronomical bodies strongly constrains the possible rate of accretion by any such microscopic black holes, so that they present no conceivable danger. In the case of strangelets, the good agreement of measurements of particle production at RHIC with simple thermodynamic models severely constrains the production of strangelets in heavy-ion collisions at the LHC, which also present no danger.

Dissipative hydrodynamics and heavy-ion collisions

Abstract: Space-time evolution and subsequent particle production from minimally viscous (η/s = 0.08) QGP fluid is studied using the second-order Israel–Stewart's theory of dissipative relativistic fluid. Compared to ideal fluid, energy density or temperature evolves slowly in viscous dynamics. Particle yield at high pT is increased. Elliptic flow on the other hand decreases in viscous dynamics. Minimally viscous QGP fluid is found to be consistent with a large number of experimental data.

Thermal dileptons at SPS energies

Abstract: Clear signs of excess dileptons above the known sources were found at the SPS over past years. However, a real clarification of these observations was only recently achieved by NA60, measuring dimuons with unprecedented precision in 158A GeV In–In collisions. The excess mass spectrum in the region M 1 GeV, the excess is found to be prompt, not due to enhanced charm production. The inverse slope parameter Teff associated with the transverse momentum spectra rises with mass up to ρ, followed by a sudden decline above. While the initial rise, coupled to a hierarchy in hadron freeze-out, points to the radial flow of a hadronic decay source, the decline above signals a transition to a low-flow source, presumably of partonic origin. The mass spectra show at low transverse momenta the steep rise toward low masses, characteristic for Planck-like radiation. The polarization of the excess referred to the Collins Soper frame is found to be isotropic. All observations are consistent with the interpretation of the excess as thermal radiation.

Experimental study of proton-induced nuclear reactions in 6,7 Li

Abstract: The 6Li(p,α)3He and 7Li(p,α)4He reaction cross sections were obtained for E = 90–580 keV and E = 90–1740 keV, respectively. R-matrix and polynomial fits to the bare astrophysical S-factor confirmed, with improved accuracy, previous work data, yielding Sb(0) = 3.52 ± 0.08 MeV b, and 55.6+0.8−1.7 keV b for the 6Li and 7Li reactions, respectively. Therefore, the astrophysical consequences related to these two isotopes remain essentially unchanged. With the present work Sb(E) data, a reanalysis of the low energy data for different environments—Li2WO4 insulator, Li metal, and PdLix alloys—confirms that the large electron screening effects can be explained by the plasma model of Debye applied to the quasi-free electrons in the metallic samples.

Measurements of enhanced electron screening in d+d reactions under UHV conditions

Abstract: Observation of the enhanced electron screening in metallic environments is of fundamental importance for the understanding of strongly coupled astrophysical plasmas. Experimental screening energies determined by different groups for many metals are much larger than the theoretical predictions. However, a comparison between experimental and theoretical data is rather ambiguous because of the contributions of systematic errors in the experiments. One of the most important problems is the uncertainty resulting from the oxidation of the target surface during the measurements. Here, we present results of the first ultra-high vacuum (UHV) experiments studying d+d nuclear reactions in a deuterized Zr target for which the experimental discrepancies are especially large. The total cross sections and angular distributions of the 2H(d,p)3H and 2H(d,n)3He reactions have been measured using a deuteron beam of energies between 8 and 30 keV provided by an electron cyclotron resonance ion source with excellent long-term stability. The cleanness of the target surface has been assured by combining Ar sputtering of the target and Auger spectroscopy. In an on-line analysis method, the homogeneity of the implanted deuteron densities could be monitored also. The resulting screening energy for Zr confirms the large value obtained in a previous experiment under poorer vacuum conditions.

Equation of state and more from lattice regularized QCD

Abstract: We present results from the calculation of the QCD equation of state with two light (up, down) and one heavier (strange) quark mass performed on lattices with three different values of the lattice cut-off. We show that also on the finest lattice analyzed by us observables sensitive to deconfinement and chiral symmetry restoration, respectively, vary most rapidly in the same temperature regime.