Table of contents

A strangeness and isospin asymmetry including statistical bootstrap model analysis of the multiparticle system produced in the Pb + Pb collision at 158 A GeV at CERN is presented. It is concluded that this interaction process has not crossed the deconfinement line. Direct comparisons with the results of similar analyses pertaining to nucleus–nucleus and p– collisions at CERN are made. The overall picture points to the S + S collision at 200 A GeV as a prime candidate of a process which has crossed the border separating the hadronic from the deconfined phase of matter.

We show that two nonets and a glueball provide a consistent description of data on scalar mesons below 1.7 GeV. Above 1 GeV the states form a conventional q nonet mixed with the glueball of lattice QCD. Below 1 GeV the states also form a nonet, as implied by the attractive forces of QCD, but of a more complicated nature. Near the centre they are (qq)()₃ in S-wave, with some q in P-wave, but further out they rearrange as (q)₁(q)₁ and finally as meson–meson states. A simple effective chiral model for such a system with two scalar nonets can be made involving two coupled linear sigma models. One of these could be looked upon as the Higgs sector of nonpertubative QCD.

In this paper we study quasi-radial oscillations of slowly rotating strange stars in strong magnetic fields in the density-dependent quark mass (DDQM) model. We see that the difference in frequency of rotating and non-rotating stars is more for higher magnetic fields. The change is small for low-mass stars but it increases with the mass of the star. This change of frequency is significant for maximum mass whereas it is marginal for a 1.4M_⊙ star.

The correlation between the neutral electromagnetic pion decay, the Sutherland–Veltman paradox and the AVV triangle anomaly phenomenon is discussed within the framework of an alternative strategy to handle the divergences involved in the perturbative evaluation of the associated physical amplitudes. We show that the general characteristic of the adopted strategy allows us to recover the traditional treatment for the problem as well as allowing us to construct an alternative way to look at the problem where the ambiguities play no relevant role.

The elastic scattering angular distributions for the ¹²C + ¹²C system at ten incident energies between 70 and 1016 MeV have been analysed by using the folding model based on an alpha particle model for the nucleus ¹²C. This folding model can well reproduce the strong dependence of the total reaction cross section on the incident energy.

We compute the contribution to charged Higgs boson pair production at the large hadron collider (LHC) due to the scattering of two electroweak (EW) gauge bosons, these being in turn generated via bremsstrahlung of incoming quarks: qq → qqV*V* → qqH⁺H⁻ (V = γ, Z, W^±). We verify that the production cross section of this mode is tan β independent and show that it is smaller than that of H⁺H⁻ production via qq-initiated processes, but generally larger than that of the loop-induced channel gg → H⁺H⁻. Pair production of charged Higgs bosons is crucial in order to test EW symmetry breaking scenarios beyond the standard model. We show that the detection of these kinds of processes at the standard LHC is, however, problematic, because of their poor production rates and large backgrounds.

The radiative decay B*_q → B_qγ, (q = u, d or s) is re-examined using a modified light-cone quantum chromodynamics (QCD) sum rule method. In this method, adequate chiral operators are chosen as the interpolating fields in the correlators used for a sum rule estimate of the relevant coupling g_B*qBqγ. Besides showing the physical picture consistent with the underlying physics in B*_q → B_qγ, the resulting sum rule can effectively avoid the pollution by the nonlocal matrix element ⟨γ(q)|(x)γ_μγ₅q(0)|0⟩ starting with twist-3, about which little is known. Also, a comparison is made with the previous results from light-cone QCD sum rules and chiral perturbation theory.

The QCD improved parton model is a very successful concept to treat processes in hadronic interactions, whenever large partonic transverse momenta p_⊥ are involved. However, cross sections diverge in the limit p_⊥ → 0, and the usual treatment is the definition of a lower cutoff p_⊥min, such that processes with a smaller p_⊥—the so-called soft processes—are simply ignored, which is certainly not correct, for example, at RHIC energies. A more consistent procedure amounts to introducing a technical parameter Q²₀, referred to as the soft virtuality scale, which is nothing but an artificial borderline between soft and hard physics. We will discuss such a formalism, which coincides with the improved parton model for high p_⊥ processes and with the phenomenological treatment of soft scattering, when only small virtualities are involved. The most important aspect of our approach is that it allows a smooth transition between soft and hard scattering to be obtained, and therefore no artificial dependence on a cutoff parameter should appear.

The nucleus ⁷⁰Se was studied using the ⁴⁰Ca(⁴⁰Ca, 2α2p) reaction at a beam energy of 185 MeV. Gamma rays were measured with the EUROBALL III spectrometer. The known positive-parity bands have been extended and one new band of positive parity and two of negative parity have been identified. These bands are interpreted in terms of the cranked Nilsson–Strutinsky approach. Calculations suggest that the two negative-parity bands, which have the same signature, are both based on a configuration with two protons and three neutrons lifted from the fp shell to the g_9/2 orbital, but at different nuclear shapes. This represents a shape coexistence at high spin.

We propose to perform the first measurement of the neutron–neutron scattering cross section in the through-channel of the pulsed aperiodic reactor YAGUAR (Snezhinsk, Russia). Such a measurement directly determines the neutron–neutron scattering length, and by comparison with the proton–proton scattering length bears upon the issue of charge symmetry of the nuclear force. The proposed experimental set-up, as well as modelling of the neutron density and of the frequency of neutron–neutron collisions is described. Experimental results are reported on the formation and optimization of the thermal neutron field inside the through-channel of the reactor YAGUAR. The instantaneous value of 1.1 × 10¹⁸ cm⁻² s⁻¹ obtained for the thermal neutron flux density is large enough to perform the first direct neutron–neutron scattering length measurement.

We consider the evolution of a parton system which is formed at the central rapidity region just after an ultrarelativistic heavy-ion collision. The evolution of the system, which is composed of gluons, quarks and antiquarks, is described by relativistic Boltzmann equations with collision terms including radiation and retardation effects. The equations are solved by the test particle method using Monte Carlo sampling. Our simulations do not show any evidence of kinetic equilibration, unless the cross sections are artificially increased to unrealistically large values.

The production of single top quarks via the electroweak interaction promises to provide new opportunities to both test the standard model and search for new physics. In particular, electroweak top production provides the only means to directly measure the CKM matrix element V_tb at ATLAS. The s-channel has the lowest rate, but is the best theoretically understood mechanism of electroweak top production. An evaluation of the potential for background suppression and V_tb measurement in this channel is presented. It is found that significant background suppression can be achieved and V_tb can be measured in the s-channel to a statistical precision of 2.8% after taking three years of low luminosity data (3 × 10⁴ pb⁻¹) at the large hadron collider.

An NLO QCD analysis of the ZEUS data on e⁺p deep inelastic scattering together with fixed-target data has been performed from which the gluon and quark densities of the proton and the value of the strong coupling parameter, α_s(M²_Z), have been extracted. The study includes a full treatment of the experimental systematic uncertainties, including point-to-point correlations. Different ways of incorporating correlated systematic uncertainties into the fit are discussed and compared.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

We examine what blind analysis is and what motivates its use in particle physics experiments. We explore the methods of blind analysis and give examples of its application in real experiments.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

I describe a framework for the presentation of search results which is motivated by frequentist statistics. The most well-known use of this framework is for the combined search for the Higgs boson at LEP. A toy neutrino oscillations experiment is used to illustrate the rich information available in the framework for exclusion and discovery. I argue that the so-called CL_s technique for setting limits is appropriate for determining exclusion intervals while the determination of confidence intervals advocated by Feldman and Cousins' method is more appropriate for treating established signals, i.e. going beyond discovery to measurement.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

I discuss the issue of uncertainties in parton distributions and in the physical quantities which are determined in terms of them. While there has been significant progress on the uncertainties associated with errors on the experimental data, there are still outstanding questions. Also, I demonstrate that in many circumstances this source of errors may be less important than errors due to underlying assumptions in the fitting procedure and due to the incomplete nature of the theoretical calculations.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

A discussion is presented of the manner in which uncertainties in parton distributions and related quantities are determined. One of the central problems is the criteria used to judge what variation of the parameters describing a set of partons is acceptable within the context of a global fit. Various ways of addressing this question are outlined.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

Statistical techniques used to analyse data from direct detection dark matter experiments are reviewed with an emphasis on general issues which could benefit from further study. In order to illustrate these issues three case studies are presented of detectors operating in different statistical regimes which require novel approaches to data analysis.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)

The Belle collaboration operates a general-purpose detector at the KEKB asymmetric energy e⁺e⁻ collider, performing a wide range of measurements in beauty, charm, tau and 2-photon physics. In this paper, the treatment of statistical problems in past and present Belle measurements is reviewed. Some open questions, such as the preferred method for quoting rare decay results, and the statistical treatment of the new B⁰/⁰ → π⁺π⁻ analysis, are discussed.

(From the workshop 'Advanced Statistical Techniques in Particle Physics', 18–22 March 2002)