Four Pion Final States with Tagged Photons at Electron Positron Colliders

A Monte Carlo generator has been constructed to simulate the reaction e^+e^- \to \gamma + 4 \pi, where the photon is assumed to be observed in the detector. Only initial state radiation is considered. Additional collinear photon radiation has been incorporated with the technique of structure functions. Predictions are presented for cms energies of 1GeV, 3GeV and 10GeV, corresponding to the energies of DAPHNE, BEBC and of B-meson factories. The event rates are sufficiently high to allow for a precise measurement of R(Q^2) in the region of Q between approximately 1GeV and 2.5GeV. For the construction of the program we employ isospin relations between the amplitudes governing tau decays into four pions and electron positron annihilation into four pions. Estimates of the kinematic breaking of these isospin relations as a consequence of the \pi^- -- \pi^0 mass difference are given.Comment: LATEX, 27 pages, 9 figures, discussion of the kinematic breaking of isospin relations extended, typos corrected, some formulations change

Radiative return at NLO and the measurement of the hadronic cross-section in electron-positron annihilation

Electron-positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for e^+ e^- annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process e^+ e^- \to \gamma +\gamma^* and the emission of two real hard photons: e^+ e^- \to \gamma + \gamma + \gamma^*. A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DAPHNE, CLEO-C and B-meson factories.Comment: 13 pages, 15 figure

Perspectives for the radiative return at meson factories

The measurement of the pion form factor and, more generally, of the cross section for electron-positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the Phi- or B-meson factories. This quantity is crucial for predictions of the hadronic contributions to the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling. But the radiative return opens the possibility of many other physical applications. The physics potential of this method at high luminosity meson factories is discussed, the last upgraded version of the event generator PHOKHARA is presented, and future developments are highlighted.Comment: Presented at SIGHAD03: Worskhop on Hadronic Cross Section at Low Energy, Pisa,Italy, October 8th-10th, 200

Measuring an entropy in heavy ion collisions

We propose to use the coincidence method of Ma to measure an entropy of the system created in heavy ion collisions. Moreover we estimate, in a simple model, the values of parameters for which the thermodynamical behaviour sets in.Comment: LATTICE98(hightemp), 3 pages, LaTeX with two eps figure

Effects of physics beyond the standard model on the neutrino charge radius: an effective Lagrangian approach

In this work, we look for possible new physics effects on the electromagnetic charge and anapole form factors, $f_Q(q^2)$ and $f_A(q^2)$, for a massless Dirac neutrino, when these quantities are calculated in the context of an effective electroweak Yang-Mills theory, which induces the most general $SU_L(2)$--invariant Lorentz tensor structure of nonrenormalizable type for the $WW\gamma$ vertex. It is found that in this context, besides the standard model contribution, the additional contribution to $f_{Q}(q^2)$ and $f_{A}(q^2)$ ($f_{Q}^{O_W}(q^2)$ and $f_{A}^{O_W}(q^2)$, respectively) are gauge independent and finite functions of $q^2$ after adopting a renormalization scheme. These form factors, $f_{Q}^{O_W}(q^2)$ and $f_{A}^{O_W}(q^2)$, get contribution at the one loop level only from the proper neutrino electromagnetic vertex. Besides, the relation $f_{Q}^{eff}(q^2)=q^2f_{A}^{eff}(q^2)$ ($f_{Q}^{eff}(q^2)=f_{Q}^{SM}(q^2)+f_{Q}^{O_W}(q^2)$, $f_{A}^{eff}(q^2)=f_{A}^{SM}(q^2)+f_{A}^{O_W}(q^2)$) is still fulfilled and hence the relation $a_{\nu}^{eff} = ^{eff} /6$ ($a_{\nu}^{eff} = a_{\nu}^{SM}+ a_{\nu}^{O_W}$, $^{eff} = ^{SM}+< r^2_{\nu} > ^{O_W}$)is gotten, just as in the SM. Using the experimental constraint on the anomalous $WW\gamma$ vertex, a value for the additional contribution to the charge radius of |^{O_W}| \lsim 10^{-34} cm^2 is obtained, which is one order of magnitude lower than the SM value.Comment: 9 pages, 3 figure

Studying thermodynamics in heavy ion collisions

We discuss the possibility to measure entropy of the system created in heavy ion collisions using the Ma coincidence method

Discovering the IPv6 Network Periphery

We consider the problem of discovering the IPv6 network periphery, i.e., the last hop router connecting endhosts in the IPv6 Internet. Finding the IPv6 periphery using active probing is challenging due to the IPv6 address space size, wide variety of provider addressing and subnetting schemes, and incomplete topology traces. As such, existing topology mapping systems can miss the large footprint of the IPv6 periphery, disadvantaging applications ranging from IPv6 census studies to geolocation and network resilience. We introduce "edgy," an approach to explicitly discover the IPv6 network periphery, and use it to find >~64M IPv6 periphery router addresses and >~87M links to these last hops -- several orders of magnitude more than in currently available IPv6 topologies. Further, only 0.2% of edgy's discovered addresses are known to existing IPv6 hitlists

Symmetry group analysis of an ideal plastic flow

In this paper, we study the Lie point symmetry group of a system describing an ideal plastic plane flow in two dimensions in order to find analytical solutions. The infinitesimal generators that span the Lie algebra for this system are obtained. We completely classify the subalgebras of up to codimension two in conjugacy classes under the action of the symmetry group. Based on invariant forms, we use Ansatzes to compute symmetry reductions in such a way that the obtained solutions cover simultaneously many invariant and partially invariant solutions. We calculate solutions of the algebraic, trigonometric, inverse trigonometric and elliptic type. Some solutions depending on one or two arbitrary functions of one variable have also been found. In some cases, the shape of a potentially feasible extrusion die corresponding to the solution is deduced. These tools could be used to thin, curve, undulate or shape a ring in an ideal plastic material

NNLO massive corrections to Bhabha scattering and theoretical precision of BabaYaga@NLO

We provide an exact calculation of next-to-next-to-leading order (NNLO) massive corrections to Bhabha scattering in QED, relevant for precision luminosity monitoring at meson factories. Using realistic reference event selections, exact numerical results for leptonic and hadronic corrections are given and compared with the corresponding approximate predictions of the event generator BabaYaga@NLO. It is shown that the NNLO massive corrections are necessary for luminosity measurements with per mille precision. At the same time they are found to be well accounted for in the generator at an accuracy level below the one per mille. An update of the total theoretical precision of BabaYaga@NLO is presented and possible directions for a further error reduction are sketched.Comment: 5 pages, 3 tables, contrib. to proceedings of International Workshop on e+e- collisions: from Phi to Psi, PHIPSI11, BINP, Novosibirsk, Russia, September 19-22, 201

Whitening of the Quark-Gluon Plasma

Parton-parton collisions do not neutralize local color charges in the quark-gluon plasma as they only redistribute the charges among momentum modes. We discuss color diffusion and color conductivity as the processes responsible for the neutralization of the plasma. For this purpose, we first compute the conductivity and diffusion coefficients in the plasma that is significantly colorful. Then, the time evolution of the color density due to the conductivity and diffusion is studied. The conductivity is shown to be much more efficient than the diffusion in neutralizing the plasma at the scale longer than the screening length. Estimates of the characteristic time scales, which are based on close to global equilibrium computations, suggest that first the plasma becomes white and then the momentum degrees of freedom thermalize.Comment: 9 pages, revised, to appear in Phys. Rev.