abstract

A precision luminosity measurement in the ZEUS experiment at the HERA electron–proton collider is described, based on the data collected by the ZEUS luminosity monitor in 1996. The method of the measurement relies on the detection of high-energy photons from the \(ep\) bremsstrahlung process. The large cross section of this process allows for the continuous and fast monitoring of the HERA luminosity as well as for the control of the electron beam steering and focusing. A 1 % precision of the luminosity determination has been achieved. The luminosity monitor has been also extensively used for studying quasi-real photoproduction, and radiative processes in deep inelastic scattering.

abstract

We use the perturbative QCD methods of Lepage and Brodsky to calculate the rate for \(\bar B_s\rightarrow \rho K_{\rm S} \), with an eye toward the \(CP\) violating unitarity triangle angle \(\gamma \). We show that, although the penguins are large, there are regions of the allowed parameter space of the Cabibbo–Kobayashi–Maskawa (CKM) mixing matrix wherein \(\gamma \) is measurable in the sense that penguins change of the value of \(\sin (2\gamma )\) one would extract from the attendant time dependent asymmetry measurement by less than \(29\%\), so that a 3\(\sigma \) measurement of \(\sin (2\gamma )\) as being different from \(0\) is allowed by the corresponding theoretical uncertainty. This would establish \(CP\) violation in \(B_s\) decays. The rates which we find tend to favour the type of luminosities now envisioned for hadron-based B-factories.

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We analyze the spectra of kaonic atoms using optical potentials with non-local (gradient) terms. The magnitude of the non-local terms follows from a self consistent many-body calculation of the kaon self energy in nuclear matter, which is based on \(s\)-wave kaon nucleon interactions. The optical potentials exhibit strong non-linearities in the nucleon density and sizeable non-local terms. We find that the non-local terms are quantitatively important in the analysis of the spectra and that a phenomenologically successful description can be obtained for \(p\)-wave like optical potentials. It is suggested that the microscopic form of the non-local interaction terms is obtained systematically by means of a semi-classical expansion of the nucleus structure. The resulting optical potential leads to less pronounced non-local effects.

abstract

We have updated our next to leading order QCD fit for polarised parton densities [S. Tatur, J. Bartelski, M. Kurzela, Acta Phys. Pol. B31, 647 (2000)] using recent experimental data on the deep inelastic spin asymmetries on nucleons. Our distributions have functional form inspired by the unpolarised ones given by MRST (Martin, Roberts, Stirling and Thorne) fit. In addition to usually used data sample (averaged over variable \(Q^2\) for the same value of \(x\) variable) we have also considered the points with the same \(x\) and different \(Q^2\). Our fits to both groups of data give very similar results with substantial antiquark contribution in the measured region of \(x\). In the first case we get rather small (\(\Delta G=0.31\)) gluon polarisation. For the non averaged data the best fit is obtained when gluon contribution vanishes at \( Q^{2}=1\, {\rm GeV^{2}}\). Our new parametrisation of parton densities and additional experimental data taken into account do not change much our previous results.

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Longitudinal polarization of the top quark, averaged over the production angle, is discussed for the top quark produced in \(e^+e^-\) annihilation near its production threshold. It is demonstrated that Coulomb type corrections and rescattering corrections are important. They change considerably measurable quantities and should be taken into account in phenomenological analysis.

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A form of mixing matrix for three active and three sterile, conventional Majorana neutrinos is proposed. Its Majorana lefthanded part arises from the popular bimaximal mixing matrix for three active neutrinos that works satisfactorily in solar and atmospheric experiments if the LSND effect is ignored. One of three sterile neutrinos, effective in the Majorana righthanded and Dirac parts of the proposed mixing matrix, is responsible perturbatively for the possible LSND effect by inducing one of three extra neutrino mass states to exist actively. The corresponding form of neutrino mass matrix is derived. If all three extra neutrino mass states get vanishing masses, the neutrino mass matrix is dominated by its specific Majorana lefthanded part. Then, the observed qualitative difference between mixings of neutrinos and down quarks may be connected with this Majorana lefthanded dominance realized for neutrinos. If \( m^2_1 \simeq m^2_2\) for two of three basic neutrino mass states, the sum rule \(\sin ^2 2\theta _{\rm sol} + \sin ^2 2 \theta _{\rm Chooz}/2 + \sin ^2 2\theta _{\rm LSND} = 1\) holds in the two-flavor approximation (for each of three cases). Thus, the solar neutrino oscillation amplitude, not fully maximal, leaves some room for the LSND effect, depending on the magnitude of Chooz effect (not observed so far).

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The Wilson discretization of the dimensionally reduced supersymmetric Yang–Mills theory is constructed. This gives a lattice version of the matrix model of M-theory. An SU(2) model is studied numerically in the quenched approximation for \(D=4\). The system shows canonical scaling in the continuum limit. A clear signal for a prototype of the “black hole to strings” phase transition is found. The pseudocritical temperature is determined and the temperature dependence of the total size of the system is measured in both phases. Further applications are outlined.

abstract

Long time ago Pagels and Tomboulis proposed a model for the nonperturbative gluodynamics which in the Abelian sector can be reduced to a strongly nonlinear electrodynamics. In the present paper we investigate Abelian, static solutions with external charges in that model. Nonzero total charge implies that the corresponding field has infinite energy due to slow fall off at large distances. For a pair of opposite charges the energy is finite — it grows like \(R^{\alpha }\), \(0\lt \alpha \lt 1\) with the distance \(R\) between the charges.

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Fermilab KTeV experiments have clearly established a direct \(CP\) violation in \(K_{\rm L} \rightarrow \pi \pi \) decays, observed a kinematical \(CP\) violating effect in \(K_{\rm L}\rightarrow \pi ^+\pi ^- e^+e^-\), set new upper limits on the branching ratios of \(CP\) violating \(K_{\rm L} \rightarrow \pi ^{0} \ell \overline {\ell }\) decays. It has also measured form factors and branching ratios of rare \(K_{\rm L}\) decays.

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It is shown that among four models of the Nijmegen baryon–baryon interaction, only model F is consistent both with the analysis of \({\mit \Sigma }^-\) atoms and \((K^-,\pi )\) reactions. Simple estimates of the strong-interaction shifts and widths of the lowest observed levels of \({\mit \Sigma }^-\) atoms are applied for model F with satisfying results. It is concluded that model F is favored as a realistic representation of the \({\mit \Sigma } N\) interaction.

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The effective mass concept was introduced for small non-local potentials. For Skyrme interactions the effective mass depends on the density of the system. We parameterised the density by a generalised Fermi distribution. The parameters of the distribution are fitted with the charge root mean square radii of spherical nuclei. To test the parameters of the velocity dependent term of the interaction at high density or temperature, we studied the behaviour of the effective mass with density and temperature. The behaviour of the Landau parameter \(F1\) was also discussed. We applied this study to most of the well known Skyrme forces. We recommended SKM* and SKS4 as good examples of Skyrme forces as they reveal small non-locality effects and well behaved functions at high density and temperature.

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We analyse inclusive scattering of the polarised electron on the polarised deuteron in the Plain Wave Impulse Approximation (PWIA). Assuming two kinds of functions for \(g_2(x)\), e.g. \(g_2=0\) and \(g_2=g_2^{WW}\), the longitudinal and transverse asymmetries are calculated versus the electron energy loss for the different initial electron energy and the scattering angle.

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A technique to calculate the rate of change of the nucleon–nucleon amplitude phase is given. The results for the nucleon–nucleon potential in the Gaussian form are consistent with the previous values of phase variation parameter \(\gamma \).

abstract

The parity and isospin forbidden \(p_0\)-decay from \(^{14}\)N\(^{*}(J^\pi \!\!=\!\!2^{+}; T\!\!=\!\!1;\) \(E_x=9.17225\) MeV) to \(^{13}\)C (g.s.) has been theoretically investigated via \(^{13}\)C\((\,\vec {p},\,p)^{13}\)C resonance scattering of polarized protons. Considering various strong and weak interaction models, the longitudinal (\(A_{L}\)) and the irregular transverse (\( A_b\)) analyzing powers have been calculated in the energy range around the \(2^{+}, E_x\!=\!9.17225\) MeV-resonance in \(^{14}\)N\(^{*}\). Energy anomalies for the expected interference effects, relevant for the experiments, have been found to be \(A_{L}\!=\!\left ( 0.19\!\div \! 1.82\right )\!\times \! 10^{-5}\) and \(A_b\!=\!\left ( 0.6\!\div \! 5.6\right )\!\times \!10^{-5}\). In addition, the circular polarizations of the \(2.36018\) and \(9.3893\) MeV \(\gamma \)-rays, populating the \(2^{+}0\), \( E_x=7.02912\,\)MeV and the ground state in \(^{14}\)N-nucleus, have been found to be \((0.22\!\div \! 2.07)\!\times \! 10^{-3}\) and \((0.20\!\div \! 1.89)\!\times \! 10^{-3}\), respectively.

abstract

Parity and time reversal are obvious and plausible candidates for fundamental symmetries of nature. Hypothesising that these symmetries exist implies the existence of a new form of matter, called mirror matter. The mirror matter theory (or exact parity model) makes four main predictions: (1) Dark matter in the form of mirror matter should exist in the Universe (i.e. mirror galaxies, stars, planets, meteoroids \(\dots \)), (2) Maximal ordinary neutrino–mirror neutrino oscillations if neutrinos have mass, (3) Ortho- positronium should have a shorter effective lifetime than predicted by QED (in “vacuum” experiments) because of the effects of photon–mirror photon mixing and (4) Higgs production and decay rate should be \(50\%\) lower than in the standard model due to Higgs mirror–Higgs mixing (assuming that the separation of the Higgs masses is larger than their decay widths). At the present time there is strong experimental/observational evidence supporting the first three of these predictions, while the fourth one is not tested yet because the Higgs boson, predicted in the standard model of particle physics, is yet to be found. This experimental/observational evidence is rich and varied ranging from the atmospheric and solar neutrino deficits, MACHO gravitational micro-lensing events, strange properties of extra-solar planets, the existence of “isolated” planets, orthopositronium lifetime anomaly, Tunguska and other strange “meteor” events including perhaps, the origin of the moon. The purpose of this article is to provide a not too technical review of these ideas along with some new results.

abstract

Mirror matter is predicted to exist if parity is an unbroken symmetry of nature. Currently, there is a large amount of evidence that mirror matter actually exists coming from astrophysics and particle physics. One of the most fascinating (but speculative) possibilities is that there is a significant abundance of mirror matter within our solar system. If the mirror matter condensed to form a large body of planetary or stellar mass then there could be interesting observable effects. Indeed studies of long period comets suggest the existence of a solar companion which has escaped direct detection and is, therefore, a candidate for a mirror body. Nemesis, hypothetical “death star” companion of the Sun, proposed to explain biological mass extinctions, may potentially be a mirror star. We examine the prospects for detecting these objects if they do indeed exist and are made of mirror matter.