Correlation search for coherent pion emission in heavy ion collisions

The methods allowing to extract the coherent component of pion emission conditioned by the formation of a quasi-classical pion source in heavy ion collisions are suggested. They exploit a nontrivial modification of the quantum statistical and final state interaction effects on the correlation functions of like and unlike pions in the presence of the coherent radiation. The extraction of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation functions and single--pion spectra is discussed in detail for large expanding systems produced in ultra-relativistic heavy ion collisions.Comment: 21 pages, 3 eps figures, ReVTeX, corrected submission abstract. Version published in PRC 65 (2002) 064904. Added is a detailed explanation of the differences between pure coherent states and charge constrained coherent states in the case of a simple example model. The expressions for two-particle spectra taking into account both the final state interaction and the coherent component of pion emission are derived in a more general and transparent wa

Relativistic instant-form approach to the structure of two-body composite systems

A new approach to the electroweak properties of two-particle composite systems is developed. The approach is based on the use of the instant form of relativistic Hamiltonian dynamics. The main novel feature of this approach is the new method of construction of the matrix element of the electroweak current operator. The electroweak current matrix element satisfies the relativistic covariance conditions and in the case of the electromagnetic current also the conservation law automatically. The properties of the system as well as the approximations are formulated in terms of form factors. The approach makes it possible to formulate relativistic impulse approximation in such a way that the Lorentz-covariance of the current is ensured. In the electromagnetic case the current conservation law is ensured, too. The results of the calculations are unambiguous: they do not depend on the choice of the coordinate frame and on the choice of "good" components of the current as it takes place in the standard form of light--front dynamics. Our approach gives good results for the pion electromagnetic form factor in the whole range of momentum transfers available for experiments at present time, as well as for lepton decay constant of pion.Comment: 26 pages, Revtex, 5 figure

Hard pomeron enhancement of ultrahigh-energy neutrino-nucleon cross-sections

An unknown small-x behavior of nucleon structure functions gives appreciable uncertainties to high-energy neutrino-nucleon cross-sections. We construct structure functions using at small x Regge inspired description by A. Donnachie and P. V. Landshoff with soft and hard pomerons, and employing at larger x the perturbative QCD expressions. The smooth interpolation between two regimes for each Q^2 is provided with the help of simple polynomial functions. To obtain low-x neutrino-nucleon structure functions $F_2^{\nu N, \bar \nu N}(x,Q^2)$ and singlet part of $F_{3}^{\nu N,\bar \nu N}(x,Q^2)$ from Donnachie-Landshoff function $F_2^{ep}(x,Q^2)$, we use the Q^2-dependent ratios R_2(Q^2) and R_3(Q^2) derived from perturbative QCD calculations. Non-singlet part of F_3 at low x, which is very small, is taken as power-law extrapolation of perturbative function at larger x. This procedure gives a full set of smooth neutrino-nucleon structure functions in the whole range of x and Q^2 at interest. Using these structure functions, we have calculated the neutrino-nucleon cross-sections and compared them with some other cross-sections known in literature. Our cross-sections turn out to be the highest among them at the highest energies, which is explained by contribution of the hard pomeron.Comment: Final revised version, accepted by Phys. Rev. D; 18 pages, 7 figure

Using the e±μ∓+ETmisse^{\pm}\mu^{\mp} + E_{T}^{miss} Signature in the Search for Supersymmetry and Lepton Flavour Violation in Neutralino Decays

The LHC (CMS) discovery potential of the $e^{\pm}\mu^{\mp} + E^{miss}_T$ signature in the search for supersymmetry and lepton flavour violation in neutralino decays is studied. A detailed study is done for the CMS test points LM1-LM9. It is shown that for the point LM1 it is possible to detect lepton flavour violation in neutralino decays with lepton flavour violating branching $Br(\tilde{\chi}^0_2 \to \mu^{\pm}e^{\mp}\tilde{\chi}^0_1) \geq 0.04 Br(\tilde{\chi}^0_2 \to e^{+}e^{-}\tilde{\chi}^0_1, \mu^{+}\mu^{-} \tilde{\chi}^0_1)$ for an integral luminosity $10 fb^{-1}$. A discovery potential in the mSUGRA-SUSY scenario with $\tan \beta = 10, ~sign(\mu) = +$ in the $(m_0, m_{1/2})$ plane using the $e^{\pm}\mu^{\mp} + E^{miss}_T$ signature is determined.The LHC (CMS) discovery potential of the $e^{\pm}\mu^{\mp} + E^{miss}_T$ signature in the search for supersymmetry and lepton flavour violation in neutralino decays is studied. A detailed study is done for the CMS test points LM1-LM9. It is shown that for the point LM1 it is possible to detect lepton flavour violation in neutralino decays with lepton flavour violating branching $Br(\tilde{\chi}^0_2 \to \mu^{\pm}e^{\mp}\tilde{\chi}^0_1) \geq 0.04 Br(\tilde{\chi}^0_2 \to e^{+}e^{-}\tilde{\chi}^0_1, \mu^{+}\mu^{-} \tilde{\chi}^0_1)$ for an integral luminosity $10 fb^{-1}$. A discovery potential in the mSUGRA-SUSY scenario with $\tan \beta = 10, ~sign(\mu) = +$ in the $(m_0, m_{1/2})$ plane using the $e^{\pm}\mu^{\mp} + E^{miss}_T$ signature is determined

BaGa₂GeS₆ and BaGa₂GeSe₆ crystals for nonlinear optical frequency conversion

Abstract We analyse the functional capabilities of new crystals, BaGa2GeS6 (BGGS) and BaGa2GeSe6 (BGGSe), which are used for nonlinear optical frequency conversion in their transparency range. The wavelengths at which maximum conversion efficiencies can be obtained and the tuning range for difference-frequency generation are found. It is shown that there are wavelength combinations at which the effective nonlinearity coefficient varies only slightly in a wide frequency band.</jats:p